3e691c1100059dca93eb4eb61c6a4eaa6996d6e0
[ghc.git] / compiler / typecheck / TcRnTypes.hs
1 {-
2 (c) The University of Glasgow 2006-2012
3 (c) The GRASP Project, Glasgow University, 1992-2002
4
5
6 Various types used during typechecking, please see TcRnMonad as well for
7 operations on these types. You probably want to import it, instead of this
8 module.
9
10 All the monads exported here are built on top of the same IOEnv monad. The
11 monad functions like a Reader monad in the way it passes the environment
12 around. This is done to allow the environment to be manipulated in a stack
13 like fashion when entering expressions... ect.
14
15 For state that is global and should be returned at the end (e.g not part
16 of the stack mechanism), you should use an TcRef (= IORef) to store them.
17 -}
18
19 {-# LANGUAGE CPP, ExistentialQuantification, GeneralizedNewtypeDeriving,
20 ViewPatterns #-}
21
22 module TcRnTypes(
23 TcRnIf, TcRn, TcM, RnM, IfM, IfL, IfG, -- The monad is opaque outside this module
24 TcRef,
25
26 -- The environment types
27 Env(..),
28 TcGblEnv(..), TcLclEnv(..),
29 IfGblEnv(..), IfLclEnv(..),
30 tcVisibleOrphanMods,
31
32 -- Frontend types (shouldn't really be here)
33 FrontendResult(..),
34
35 -- Renamer types
36 ErrCtxt, RecFieldEnv,
37 ImportAvails(..), emptyImportAvails, plusImportAvails,
38 WhereFrom(..), mkModDeps, modDepsElts,
39
40 -- Typechecker types
41 TcTypeEnv, TcIdBinderStack, TcIdBinder(..),
42 TcTyThing(..), PromotionErr(..),
43 IdBindingInfo(..), ClosedTypeId, RhsNames,
44 IsGroupClosed(..),
45 SelfBootInfo(..),
46 pprTcTyThingCategory, pprPECategory, CompleteMatch(..),
47
48 -- Desugaring types
49 DsM, DsLclEnv(..), DsGblEnv(..), PArrBuiltin(..),
50 DsMetaEnv, DsMetaVal(..), CompleteMatchMap,
51 mkCompleteMatchMap, extendCompleteMatchMap,
52
53 -- Template Haskell
54 ThStage(..), SpliceType(..), PendingStuff(..),
55 topStage, topAnnStage, topSpliceStage,
56 ThLevel, impLevel, outerLevel, thLevel,
57 ForeignSrcLang(..),
58
59 -- Arrows
60 ArrowCtxt(..),
61
62 -- TcSigInfo
63 TcSigFun, TcSigInfo(..), TcIdSigInfo(..),
64 TcIdSigInst(..), TcPatSynInfo(..),
65 isPartialSig, hasCompleteSig,
66
67 -- Canonical constraints
68 Xi, Ct(..), Cts, emptyCts, andCts, andManyCts, pprCts,
69 singleCt, listToCts, ctsElts, consCts, snocCts, extendCtsList,
70 isEmptyCts, isCTyEqCan, isCFunEqCan,
71 isPendingScDict, superClassesMightHelp,
72 isCDictCan_Maybe, isCFunEqCan_maybe,
73 isCIrredEvCan, isCNonCanonical, isWantedCt, isDerivedCt,
74 isGivenCt, isHoleCt, isOutOfScopeCt, isExprHoleCt, isTypeHoleCt,
75 isUserTypeErrorCt, getUserTypeErrorMsg,
76 ctEvidence, ctLoc, setCtLoc, ctPred, ctFlavour, ctEqRel, ctOrigin,
77 mkTcEqPredLikeEv,
78 mkNonCanonical, mkNonCanonicalCt, mkGivens,
79 ctEvPred, ctEvLoc, ctEvOrigin, ctEvEqRel,
80 ctEvTerm, ctEvCoercion, ctEvId,
81 tyCoVarsOfCt, tyCoVarsOfCts,
82 tyCoVarsOfCtList, tyCoVarsOfCtsList,
83
84 WantedConstraints(..), insolubleWC, emptyWC, isEmptyWC,
85 andWC, unionsWC, mkSimpleWC, mkImplicWC,
86 addInsols, getInsolubles, insolublesOnly, addSimples, addImplics,
87 tyCoVarsOfWC, dropDerivedWC, dropDerivedSimples, dropDerivedInsols,
88 tyCoVarsOfWCList, trulyInsoluble,
89 isDroppableDerivedLoc, isDroppableDerivedCt, insolubleImplic,
90 arisesFromGivens,
91
92 Implication(..), ImplicStatus(..), isInsolubleStatus, isSolvedStatus,
93 SubGoalDepth, initialSubGoalDepth, maxSubGoalDepth,
94 bumpSubGoalDepth, subGoalDepthExceeded,
95 CtLoc(..), ctLocSpan, ctLocEnv, ctLocLevel, ctLocOrigin,
96 ctLocTypeOrKind_maybe,
97 ctLocDepth, bumpCtLocDepth,
98 setCtLocOrigin, setCtLocEnv, setCtLocSpan,
99 CtOrigin(..), exprCtOrigin, lexprCtOrigin, matchesCtOrigin, grhssCtOrigin,
100 ErrorThing(..), mkErrorThing, errorThingNumArgs_maybe,
101 TypeOrKind(..), isTypeLevel, isKindLevel,
102 pprCtOrigin, pprCtLoc,
103 pushErrCtxt, pushErrCtxtSameOrigin,
104
105 SkolemInfo(..), pprSigSkolInfo, pprSkolInfo,
106 termEvidenceAllowed,
107
108 CtEvidence(..), TcEvDest(..),
109 mkGivenLoc, mkKindLoc, toKindLoc,
110 isWanted, isGiven, isDerived, isGivenOrWDeriv,
111 ctEvRole,
112
113 -- Constraint solver plugins
114 TcPlugin(..), TcPluginResult(..), TcPluginSolver,
115 TcPluginM, runTcPluginM, unsafeTcPluginTcM,
116 getEvBindsTcPluginM,
117
118 CtFlavour(..), ShadowInfo(..), ctEvFlavour,
119 CtFlavourRole, ctEvFlavourRole, ctFlavourRole,
120 eqCanRewriteFR, eqMayRewriteFR,
121 eqCanDischarge,
122 funEqCanDischarge, funEqCanDischargeF,
123
124 -- Pretty printing
125 pprEvVarTheta,
126 pprEvVars, pprEvVarWithType,
127
128 -- Misc other types
129 TcId, TcIdSet,
130 Hole(..), holeOcc,
131 NameShape(..),
132
133 -- Role annotations
134 RoleAnnotEnv, emptyRoleAnnotEnv, mkRoleAnnotEnv,
135 lookupRoleAnnot, getRoleAnnots,
136
137 ) where
138
139 #include "HsVersions.h"
140
141 import HsSyn
142 import CoreSyn
143 import HscTypes
144 import TcEvidence
145 import Type
146 import Class ( Class )
147 import TyCon ( TyCon, tyConKind )
148 import Coercion ( Coercion, mkHoleCo )
149 import ConLike ( ConLike(..) )
150 import DataCon ( DataCon, dataConUserType, dataConOrigArgTys )
151 import PatSyn ( PatSyn, pprPatSynType )
152 import Id ( idType, idName )
153 import FieldLabel ( FieldLabel )
154 import TcType
155 import Annotations
156 import InstEnv
157 import FamInstEnv
158 import PmExpr
159 import IOEnv
160 import RdrName
161 import Name
162 import NameEnv
163 import NameSet
164 import Avail
165 import Var
166 import FV
167 import VarEnv
168 import Module
169 import SrcLoc
170 import VarSet
171 import ErrUtils
172 import UniqFM
173 import UniqSupply
174 import BasicTypes
175 import Bag
176 import DynFlags
177 import Outputable
178 import ListSetOps
179 import FastString
180 import qualified GHC.LanguageExtensions as LangExt
181 import Fingerprint
182 import Util
183 import PrelNames ( isUnboundName )
184
185 import Control.Monad (ap, liftM, msum)
186 #if __GLASGOW_HASKELL__ > 710
187 import qualified Control.Monad.Fail as MonadFail
188 #endif
189 import Data.Set ( Set )
190 import qualified Data.Set as S
191
192 import Data.List ( sort )
193 import Data.Map ( Map )
194 import Data.Dynamic ( Dynamic )
195 import Data.Typeable ( TypeRep )
196 import Data.Maybe ( mapMaybe )
197 import GHCi.Message
198 import GHCi.RemoteTypes
199
200 import qualified Language.Haskell.TH as TH
201
202 -- | A 'NameShape' is a substitution on 'Name's that can be used
203 -- to refine the identities of a hole while we are renaming interfaces
204 -- (see 'RnModIface'). Specifically, a 'NameShape' for
205 -- 'ns_module_name' @A@, defines a mapping from @{A.T}@
206 -- (for some 'OccName' @T@) to some arbitrary other 'Name'.
207 --
208 -- The most intruiging thing about a 'NameShape', however, is
209 -- how it's constructed. A 'NameShape' is *implied* by the
210 -- exported 'AvailInfo's of the implementor of an interface:
211 -- if an implementor of signature @<H>@ exports @M.T@, you implicitly
212 -- define a substitution from @{H.T}@ to @M.T@. So a 'NameShape'
213 -- is computed from the list of 'AvailInfo's that are exported
214 -- by the implementation of a module, or successively merged
215 -- together by the export lists of signatures which are joining
216 -- together.
217 --
218 -- It's not the most obvious way to go about doing this, but it
219 -- does seem to work!
220 --
221 -- NB: Can't boot this and put it in NameShape because then we
222 -- start pulling in too many DynFlags things.
223 data NameShape = NameShape {
224 ns_mod_name :: ModuleName,
225 ns_exports :: [AvailInfo],
226 ns_map :: OccEnv Name
227 }
228
229
230 {-
231 ************************************************************************
232 * *
233 Standard monad definition for TcRn
234 All the combinators for the monad can be found in TcRnMonad
235 * *
236 ************************************************************************
237
238 The monad itself has to be defined here, because it is mentioned by ErrCtxt
239 -}
240
241 type TcRnIf a b = IOEnv (Env a b)
242 type TcRn = TcRnIf TcGblEnv TcLclEnv -- Type inference
243 type IfM lcl = TcRnIf IfGblEnv lcl -- Iface stuff
244 type IfG = IfM () -- Top level
245 type IfL = IfM IfLclEnv -- Nested
246 type DsM = TcRnIf DsGblEnv DsLclEnv -- Desugaring
247
248 -- TcRn is the type-checking and renaming monad: the main monad that
249 -- most type-checking takes place in. The global environment is
250 -- 'TcGblEnv', which tracks all of the top-level type-checking
251 -- information we've accumulated while checking a module, while the
252 -- local environment is 'TcLclEnv', which tracks local information as
253 -- we move inside expressions.
254
255 -- | Historical "renaming monad" (now it's just 'TcRn').
256 type RnM = TcRn
257
258 -- | Historical "type-checking monad" (now it's just 'TcRn').
259 type TcM = TcRn
260
261 -- We 'stack' these envs through the Reader like monad infrastructure
262 -- as we move into an expression (although the change is focused in
263 -- the lcl type).
264 data Env gbl lcl
265 = Env {
266 env_top :: HscEnv, -- Top-level stuff that never changes
267 -- Includes all info about imported things
268
269 env_us :: {-# UNPACK #-} !(IORef UniqSupply),
270 -- Unique supply for local variables
271
272 env_gbl :: gbl, -- Info about things defined at the top level
273 -- of the module being compiled
274
275 env_lcl :: lcl -- Nested stuff; changes as we go into
276 }
277
278 instance ContainsDynFlags (Env gbl lcl) where
279 extractDynFlags env = hsc_dflags (env_top env)
280
281 instance ContainsModule gbl => ContainsModule (Env gbl lcl) where
282 extractModule env = extractModule (env_gbl env)
283
284
285 {-
286 ************************************************************************
287 * *
288 The interface environments
289 Used when dealing with IfaceDecls
290 * *
291 ************************************************************************
292 -}
293
294 data IfGblEnv
295 = IfGblEnv {
296 -- Some information about where this environment came from;
297 -- useful for debugging.
298 if_doc :: SDoc,
299 -- The type environment for the module being compiled,
300 -- in case the interface refers back to it via a reference that
301 -- was originally a hi-boot file.
302 -- We need the module name so we can test when it's appropriate
303 -- to look in this env.
304 -- See Note [Tying the knot] in TcIface
305 if_rec_types :: Maybe (Module, IfG TypeEnv)
306 -- Allows a read effect, so it can be in a mutable
307 -- variable; c.f. handling the external package type env
308 -- Nothing => interactive stuff, no loops possible
309 }
310
311 data IfLclEnv
312 = IfLclEnv {
313 -- The module for the current IfaceDecl
314 -- So if we see f = \x -> x
315 -- it means M.f = \x -> x, where M is the if_mod
316 -- NB: This is a semantic module, see
317 -- Note [Identity versus semantic module]
318 if_mod :: Module,
319
320 -- Whether or not the IfaceDecl came from a boot
321 -- file or not; we'll use this to choose between
322 -- NoUnfolding and BootUnfolding
323 if_boot :: Bool,
324
325 -- The field is used only for error reporting
326 -- if (say) there's a Lint error in it
327 if_loc :: SDoc,
328 -- Where the interface came from:
329 -- .hi file, or GHCi state, or ext core
330 -- plus which bit is currently being examined
331
332 if_nsubst :: Maybe NameShape,
333
334 -- This field is used to make sure "implicit" declarations
335 -- (anything that cannot be exported in mi_exports) get
336 -- wired up correctly in typecheckIfacesForMerging. Most
337 -- of the time it's @Nothing@. See Note [Resolving never-exported Names in TcIface]
338 -- in TcIface.
339 if_implicits_env :: Maybe TypeEnv,
340
341 if_tv_env :: FastStringEnv TyVar, -- Nested tyvar bindings
342 if_id_env :: FastStringEnv Id -- Nested id binding
343 }
344
345 {-
346 ************************************************************************
347 * *
348 Desugarer monad
349 * *
350 ************************************************************************
351
352 Now the mondo monad magic (yes, @DsM@ is a silly name)---carry around
353 a @UniqueSupply@ and some annotations, which
354 presumably include source-file location information:
355 -}
356
357 -- If '-XParallelArrays' is given, the desugarer populates this table with the corresponding
358 -- variables found in 'Data.Array.Parallel'.
359 --
360 data PArrBuiltin
361 = PArrBuiltin
362 { lengthPVar :: Var -- ^ lengthP
363 , replicatePVar :: Var -- ^ replicateP
364 , singletonPVar :: Var -- ^ singletonP
365 , mapPVar :: Var -- ^ mapP
366 , filterPVar :: Var -- ^ filterP
367 , zipPVar :: Var -- ^ zipP
368 , crossMapPVar :: Var -- ^ crossMapP
369 , indexPVar :: Var -- ^ (!:)
370 , emptyPVar :: Var -- ^ emptyP
371 , appPVar :: Var -- ^ (+:+)
372 , enumFromToPVar :: Var -- ^ enumFromToP
373 , enumFromThenToPVar :: Var -- ^ enumFromThenToP
374 }
375
376 data DsGblEnv
377 = DsGblEnv
378 { ds_mod :: Module -- For SCC profiling
379 , ds_fam_inst_env :: FamInstEnv -- Like tcg_fam_inst_env
380 , ds_unqual :: PrintUnqualified
381 , ds_msgs :: IORef Messages -- Warning messages
382 , ds_if_env :: (IfGblEnv, IfLclEnv) -- Used for looking up global,
383 -- possibly-imported things
384 , ds_dph_env :: GlobalRdrEnv -- exported entities of 'Data.Array.Parallel.Prim'
385 -- iff '-fvectorise' flag was given as well as
386 -- exported entities of 'Data.Array.Parallel' iff
387 -- '-XParallelArrays' was given; otherwise, empty
388 , ds_parr_bi :: PArrBuiltin -- desugarer names for '-XParallelArrays'
389 , ds_complete_matches :: CompleteMatchMap
390 -- Additional complete pattern matches
391 }
392
393 instance ContainsModule DsGblEnv where
394 extractModule = ds_mod
395
396 data DsLclEnv = DsLclEnv {
397 dsl_meta :: DsMetaEnv, -- Template Haskell bindings
398 dsl_loc :: RealSrcSpan, -- To put in pattern-matching error msgs
399 dsl_dicts :: Bag EvVar, -- Constraints from GADT pattern-matching
400 dsl_tm_cs :: Bag SimpleEq,
401 dsl_pm_iter :: IORef Int -- no iterations for pmcheck
402 }
403
404 -- Inside [| |] brackets, the desugarer looks
405 -- up variables in the DsMetaEnv
406 type DsMetaEnv = NameEnv DsMetaVal
407
408 data DsMetaVal
409 = DsBound Id -- Bound by a pattern inside the [| |].
410 -- Will be dynamically alpha renamed.
411 -- The Id has type THSyntax.Var
412
413 | DsSplice (HsExpr GhcTc) -- These bindings are introduced by
414 -- the PendingSplices on a HsBracketOut
415
416
417 {-
418 ************************************************************************
419 * *
420 Global typechecker environment
421 * *
422 ************************************************************************
423 -}
424
425 -- | 'FrontendResult' describes the result of running the
426 -- frontend of a Haskell module. Usually, you'll get
427 -- a 'FrontendTypecheck', since running the frontend involves
428 -- typechecking a program, but for an hs-boot merge you'll
429 -- just get a ModIface, since no actual typechecking occurred.
430 --
431 -- This data type really should be in HscTypes, but it needs
432 -- to have a TcGblEnv which is only defined here.
433 data FrontendResult
434 = FrontendTypecheck TcGblEnv
435
436 -- Note [Identity versus semantic module]
437 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
438 -- When typechecking an hsig file, it is convenient to keep track
439 -- of two different "this module" identifiers:
440 --
441 -- - The IDENTITY module is simply thisPackage + the module
442 -- name; i.e. it uniquely *identifies* the interface file
443 -- we're compiling. For example, p[A=<A>]:A is an
444 -- identity module identifying the requirement named A
445 -- from library p.
446 --
447 -- - The SEMANTIC module, which is the actual module that
448 -- this signature is intended to represent (e.g. if
449 -- we have a identity module p[A=base:Data.IORef]:A,
450 -- then the semantic module is base:Data.IORef)
451 --
452 -- Which one should you use?
453 --
454 -- - In the desugarer and later phases of compilation,
455 -- identity and semantic modules coincide, since we never compile
456 -- signatures (we just generate blank object files for
457 -- hsig files.)
458 --
459 -- A corrolary of this is that the following invariant holds at any point
460 -- past desugaring,
461 --
462 -- if I have a Module, this_mod, in hand representing the module
463 -- currently being compiled,
464 -- then moduleUnitId this_mod == thisPackage dflags
465 --
466 -- - For any code involving Names, we want semantic modules.
467 -- See lookupIfaceTop in IfaceEnv, mkIface and addFingerprints
468 -- in MkIface, and tcLookupGlobal in TcEnv
469 --
470 -- - When reading interfaces, we want the identity module to
471 -- identify the specific interface we want (such interfaces
472 -- should never be loaded into the EPS). However, if a
473 -- hole module <A> is requested, we look for A.hi
474 -- in the home library we are compiling. (See LoadIface.)
475 -- Similarly, in RnNames we check for self-imports using
476 -- identity modules, to allow signatures to import their implementor.
477 --
478 -- - For recompilation avoidance, you want the identity module,
479 -- since that will actually say the specific interface you
480 -- want to track (and recompile if it changes)
481
482 -- | 'TcGblEnv' describes the top-level of the module at the
483 -- point at which the typechecker is finished work.
484 -- It is this structure that is handed on to the desugarer
485 -- For state that needs to be updated during the typechecking
486 -- phase and returned at end, use a 'TcRef' (= 'IORef').
487 data TcGblEnv
488 = TcGblEnv {
489 tcg_mod :: Module, -- ^ Module being compiled
490 tcg_semantic_mod :: Module, -- ^ If a signature, the backing module
491 -- See also Note [Identity versus semantic module]
492 tcg_src :: HscSource,
493 -- ^ What kind of module (regular Haskell, hs-boot, hsig)
494
495 tcg_rdr_env :: GlobalRdrEnv, -- ^ Top level envt; used during renaming
496 tcg_default :: Maybe [Type],
497 -- ^ Types used for defaulting. @Nothing@ => no @default@ decl
498
499 tcg_fix_env :: FixityEnv, -- ^ Just for things in this module
500 tcg_field_env :: RecFieldEnv, -- ^ Just for things in this module
501 -- See Note [The interactive package] in HscTypes
502
503 tcg_type_env :: TypeEnv,
504 -- ^ Global type env for the module we are compiling now. All
505 -- TyCons and Classes (for this module) end up in here right away,
506 -- along with their derived constructors, selectors.
507 --
508 -- (Ids defined in this module start in the local envt, though they
509 -- move to the global envt during zonking)
510 --
511 -- NB: for what "things in this module" means, see
512 -- Note [The interactive package] in HscTypes
513
514 tcg_type_env_var :: TcRef TypeEnv,
515 -- Used only to initialise the interface-file
516 -- typechecker in initIfaceTcRn, so that it can see stuff
517 -- bound in this module when dealing with hi-boot recursions
518 -- Updated at intervals (e.g. after dealing with types and classes)
519
520 tcg_inst_env :: InstEnv,
521 -- ^ Instance envt for all /home-package/ modules;
522 -- Includes the dfuns in tcg_insts
523 tcg_fam_inst_env :: FamInstEnv, -- ^ Ditto for family instances
524 tcg_ann_env :: AnnEnv, -- ^ And for annotations
525
526 -- | Family instances we have to check for consistency.
527 -- Invariant: each FamInst in the list's fi_fam matches the
528 -- key of the entry in the 'NameEnv'. This gets consumed
529 -- by 'checkRecFamInstConsistency'.
530 -- See Note [Don't check hs-boot type family instances too early]
531 tcg_pending_fam_checks :: NameEnv [([FamInst], FamInstEnv)],
532
533 -- Now a bunch of things about this module that are simply
534 -- accumulated, but never consulted until the end.
535 -- Nevertheless, it's convenient to accumulate them along
536 -- with the rest of the info from this module.
537 tcg_exports :: [AvailInfo], -- ^ What is exported
538 tcg_imports :: ImportAvails,
539 -- ^ Information about what was imported from where, including
540 -- things bound in this module. Also store Safe Haskell info
541 -- here about transitive trusted package requirements.
542 --
543 -- There are not many uses of this field, so you can grep for
544 -- all them.
545 --
546 -- The ImportAvails records information about the following
547 -- things:
548 --
549 -- 1. All of the modules you directly imported (tcRnImports)
550 -- 2. The orphans (only!) of all imported modules in a GHCi
551 -- session (runTcInteractive)
552 -- 3. The module that instantiated a signature
553 -- 4. Each of the signatures that merged in
554 --
555 -- It is used in the following ways:
556 -- - imp_orphs is used to determine what orphan modules should be
557 -- visible in the context (tcVisibleOrphanMods)
558 -- - imp_finsts is used to determine what family instances should
559 -- be visible (tcExtendLocalFamInstEnv)
560 -- - To resolve the meaning of the export list of a module
561 -- (tcRnExports)
562 -- - imp_mods is used to compute usage info (mkIfaceTc, deSugar)
563 -- - imp_trust_own_pkg is used for Safe Haskell in interfaces
564 -- (mkIfaceTc, as well as in HscMain)
565 -- - To create the Dependencies field in interface (mkDependencies)
566
567 tcg_dus :: DefUses, -- ^ What is defined in this module and what is used.
568 tcg_used_gres :: TcRef [GlobalRdrElt], -- ^ Records occurrences of imported entities
569 -- See Note [Tracking unused binding and imports]
570
571 tcg_keep :: TcRef NameSet,
572 -- ^ Locally-defined top-level names to keep alive.
573 --
574 -- "Keep alive" means give them an Exported flag, so that the
575 -- simplifier does not discard them as dead code, and so that they
576 -- are exposed in the interface file (but not to export to the
577 -- user).
578 --
579 -- Some things, like dict-fun Ids and default-method Ids are "born"
580 -- with the Exported flag on, for exactly the above reason, but some
581 -- we only discover as we go. Specifically:
582 --
583 -- * The to/from functions for generic data types
584 --
585 -- * Top-level variables appearing free in the RHS of an orphan
586 -- rule
587 --
588 -- * Top-level variables appearing free in a TH bracket
589
590 tcg_th_used :: TcRef Bool,
591 -- ^ @True@ <=> Template Haskell syntax used.
592 --
593 -- We need this so that we can generate a dependency on the
594 -- Template Haskell package, because the desugarer is going
595 -- to emit loads of references to TH symbols. The reference
596 -- is implicit rather than explicit, so we have to zap a
597 -- mutable variable.
598
599 tcg_th_splice_used :: TcRef Bool,
600 -- ^ @True@ <=> A Template Haskell splice was used.
601 --
602 -- Splices disable recompilation avoidance (see #481)
603
604 tcg_th_top_level_locs :: TcRef (Set RealSrcSpan),
605 -- ^ Locations of the top-level splices; used for providing details on
606 -- scope in error messages for out-of-scope variables
607
608 tcg_dfun_n :: TcRef OccSet,
609 -- ^ Allows us to choose unique DFun names.
610
611 tcg_merged :: [(Module, Fingerprint)],
612 -- ^ The requirements we merged with; we always have to recompile
613 -- if any of these changed.
614
615 -- The next fields accumulate the payload of the module
616 -- The binds, rules and foreign-decl fields are collected
617 -- initially in un-zonked form and are finally zonked in tcRnSrcDecls
618
619 tcg_rn_exports :: Maybe [Located (IE GhcRn)],
620 -- Nothing <=> no explicit export list
621 -- Is always Nothing if we don't want to retain renamed
622 -- exports
623
624 tcg_rn_imports :: [LImportDecl GhcRn],
625 -- Keep the renamed imports regardless. They are not
626 -- voluminous and are needed if you want to report unused imports
627
628 tcg_rn_decls :: Maybe (HsGroup GhcRn),
629 -- ^ Renamed decls, maybe. @Nothing@ <=> Don't retain renamed
630 -- decls.
631
632 tcg_dependent_files :: TcRef [FilePath], -- ^ dependencies from addDependentFile
633
634 tcg_th_topdecls :: TcRef [LHsDecl GhcPs],
635 -- ^ Top-level declarations from addTopDecls
636
637 tcg_th_foreign_files :: TcRef [(ForeignSrcLang, String)],
638 -- ^ Foreign files emitted from TH.
639
640 tcg_th_topnames :: TcRef NameSet,
641 -- ^ Exact names bound in top-level declarations in tcg_th_topdecls
642
643 tcg_th_modfinalizers :: TcRef [TcM ()],
644 -- ^ Template Haskell module finalizers.
645 --
646 -- They are computations in the @TcM@ monad rather than @Q@ because we
647 -- set them to use particular local environments.
648
649 tcg_th_state :: TcRef (Map TypeRep Dynamic),
650 tcg_th_remote_state :: TcRef (Maybe (ForeignRef (IORef QState))),
651 -- ^ Template Haskell state
652
653 tcg_ev_binds :: Bag EvBind, -- Top-level evidence bindings
654
655 -- Things defined in this module, or (in GHCi)
656 -- in the declarations for a single GHCi command.
657 -- For the latter, see Note [The interactive package] in HscTypes
658 tcg_tr_module :: Maybe Id, -- Id for $trModule :: GHC.Types.Module
659 -- for which every module has a top-level defn
660 -- except in GHCi in which case we have Nothing
661 tcg_binds :: LHsBinds GhcTc, -- Value bindings in this module
662 tcg_sigs :: NameSet, -- ...Top-level names that *lack* a signature
663 tcg_imp_specs :: [LTcSpecPrag], -- ...SPECIALISE prags for imported Ids
664 tcg_warns :: Warnings, -- ...Warnings and deprecations
665 tcg_anns :: [Annotation], -- ...Annotations
666 tcg_tcs :: [TyCon], -- ...TyCons and Classes
667 tcg_insts :: [ClsInst], -- ...Instances
668 tcg_fam_insts :: [FamInst], -- ...Family instances
669 tcg_rules :: [LRuleDecl GhcTc], -- ...Rules
670 tcg_fords :: [LForeignDecl GhcTc], -- ...Foreign import & exports
671 tcg_vects :: [LVectDecl GhcTc], -- ...Vectorisation declarations
672 tcg_patsyns :: [PatSyn], -- ...Pattern synonyms
673
674 tcg_doc_hdr :: Maybe LHsDocString, -- ^ Maybe Haddock header docs
675 tcg_hpc :: AnyHpcUsage, -- ^ @True@ if any part of the
676 -- prog uses hpc instrumentation.
677
678 tcg_self_boot :: SelfBootInfo, -- ^ Whether this module has a
679 -- corresponding hi-boot file
680
681 tcg_main :: Maybe Name, -- ^ The Name of the main
682 -- function, if this module is
683 -- the main module.
684
685 tcg_safeInfer :: TcRef (Bool, WarningMessages),
686 -- ^ Has the typechecker inferred this module as -XSafe (Safe Haskell)
687 -- See Note [Safe Haskell Overlapping Instances Implementation],
688 -- although this is used for more than just that failure case.
689
690 tcg_tc_plugins :: [TcPluginSolver],
691 -- ^ A list of user-defined plugins for the constraint solver.
692
693 tcg_top_loc :: RealSrcSpan,
694 -- ^ The RealSrcSpan this module came from
695
696 tcg_static_wc :: TcRef WantedConstraints,
697 -- ^ Wanted constraints of static forms.
698 -- See Note [Constraints in static forms].
699 tcg_complete_matches :: [CompleteMatch]
700 }
701
702 -- NB: topModIdentity, not topModSemantic!
703 -- Definition sites of orphan identities will be identity modules, not semantic
704 -- modules.
705
706 -- Note [Constraints in static forms]
707 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
708 --
709 -- When a static form produces constraints like
710 --
711 -- f :: StaticPtr (Bool -> String)
712 -- f = static show
713 --
714 -- we collect them in tcg_static_wc and resolve them at the end
715 -- of type checking. They need to be resolved separately because
716 -- we don't want to resolve them in the context of the enclosing
717 -- expression. Consider
718 --
719 -- g :: Show a => StaticPtr (a -> String)
720 -- g = static show
721 --
722 -- If the @Show a0@ constraint that the body of the static form produces was
723 -- resolved in the context of the enclosing expression, then the body of the
724 -- static form wouldn't be closed because the Show dictionary would come from
725 -- g's context instead of coming from the top level.
726
727 tcVisibleOrphanMods :: TcGblEnv -> ModuleSet
728 tcVisibleOrphanMods tcg_env
729 = mkModuleSet (tcg_mod tcg_env : imp_orphs (tcg_imports tcg_env))
730
731 instance ContainsModule TcGblEnv where
732 extractModule env = tcg_semantic_mod env
733
734 type RecFieldEnv = NameEnv [FieldLabel]
735 -- Maps a constructor name *in this module*
736 -- to the fields for that constructor.
737 -- This is used when dealing with ".." notation in record
738 -- construction and pattern matching.
739 -- The FieldEnv deals *only* with constructors defined in *this*
740 -- module. For imported modules, we get the same info from the
741 -- TypeEnv
742
743 data SelfBootInfo
744 = NoSelfBoot -- No corresponding hi-boot file
745 | SelfBoot
746 { sb_mds :: ModDetails -- There was a hi-boot file,
747 , sb_tcs :: NameSet } -- defining these TyCons,
748 -- What is sb_tcs used for? See Note [Extra dependencies from .hs-boot files]
749 -- in RnSource
750
751
752 {- Note [Tracking unused binding and imports]
753 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
754 We gather two sorts of usage information
755
756 * tcg_dus (defs/uses)
757 Records *defined* Names (local, top-level)
758 and *used* Names (local or imported)
759
760 Used (a) to report "defined but not used"
761 (see RnNames.reportUnusedNames)
762 (b) to generate version-tracking usage info in interface
763 files (see MkIface.mkUsedNames)
764 This usage info is mainly gathered by the renamer's
765 gathering of free-variables
766
767 * tcg_used_gres
768 Used only to report unused import declarations
769
770 Records each *occurrence* an *imported* (not locally-defined) entity.
771 The occurrence is recorded by keeping a GlobalRdrElt for it.
772 These is not the GRE that is in the GlobalRdrEnv; rather it
773 is recorded *after* the filtering done by pickGREs. So it reflect
774 /how that occurrence is in scope/. See Note [GRE filtering] in
775 RdrName.
776
777
778 ************************************************************************
779 * *
780 The local typechecker environment
781 * *
782 ************************************************************************
783
784 Note [The Global-Env/Local-Env story]
785 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
786 During type checking, we keep in the tcg_type_env
787 * All types and classes
788 * All Ids derived from types and classes (constructors, selectors)
789
790 At the end of type checking, we zonk the local bindings,
791 and as we do so we add to the tcg_type_env
792 * Locally defined top-level Ids
793
794 Why? Because they are now Ids not TcIds. This final GlobalEnv is
795 a) fed back (via the knot) to typechecking the
796 unfoldings of interface signatures
797 b) used in the ModDetails of this module
798 -}
799
800 data TcLclEnv -- Changes as we move inside an expression
801 -- Discarded after typecheck/rename; not passed on to desugarer
802 = TcLclEnv {
803 tcl_loc :: RealSrcSpan, -- Source span
804 tcl_ctxt :: [ErrCtxt], -- Error context, innermost on top
805 tcl_tclvl :: TcLevel, -- Birthplace for new unification variables
806
807 tcl_th_ctxt :: ThStage, -- Template Haskell context
808 tcl_th_bndrs :: ThBindEnv, -- and binder info
809 -- The ThBindEnv records the TH binding level of in-scope Names
810 -- defined in this module (not imported)
811 -- We can't put this info in the TypeEnv because it's needed
812 -- (and extended) in the renamer, for untyed splices
813
814 tcl_arrow_ctxt :: ArrowCtxt, -- Arrow-notation context
815
816 tcl_rdr :: LocalRdrEnv, -- Local name envt
817 -- Maintained during renaming, of course, but also during
818 -- type checking, solely so that when renaming a Template-Haskell
819 -- splice we have the right environment for the renamer.
820 --
821 -- Does *not* include global name envt; may shadow it
822 -- Includes both ordinary variables and type variables;
823 -- they are kept distinct because tyvar have a different
824 -- occurrence constructor (Name.TvOcc)
825 -- We still need the unsullied global name env so that
826 -- we can look up record field names
827
828 tcl_env :: TcTypeEnv, -- The local type environment:
829 -- Ids and TyVars defined in this module
830
831 tcl_bndrs :: TcIdBinderStack, -- Used for reporting relevant bindings
832
833 tcl_tidy :: TidyEnv, -- Used for tidying types; contains all
834 -- in-scope type variables (but not term variables)
835
836 tcl_tyvars :: TcRef TcTyVarSet, -- The "global tyvars"
837 -- Namely, the in-scope TyVars bound in tcl_env,
838 -- plus the tyvars mentioned in the types of Ids bound
839 -- in tcl_lenv.
840 -- Why mutable? see notes with tcGetGlobalTyCoVars
841
842 tcl_lie :: TcRef WantedConstraints, -- Place to accumulate type constraints
843 tcl_errs :: TcRef Messages -- Place to accumulate errors
844 }
845
846 type ErrCtxt = (Bool, TidyEnv -> TcM (TidyEnv, MsgDoc))
847 -- Monadic so that we have a chance
848 -- to deal with bound type variables just before error
849 -- message construction
850
851 -- Bool: True <=> this is a landmark context; do not
852 -- discard it when trimming for display
853
854 type TcTypeEnv = NameEnv TcTyThing
855
856 type ThBindEnv = NameEnv (TopLevelFlag, ThLevel)
857 -- Domain = all Ids bound in this module (ie not imported)
858 -- The TopLevelFlag tells if the binding is syntactically top level.
859 -- We need to know this, because the cross-stage persistence story allows
860 -- cross-stage at arbitrary types if the Id is bound at top level.
861 --
862 -- Nota bene: a ThLevel of 'outerLevel' is *not* the same as being
863 -- bound at top level! See Note [Template Haskell levels] in TcSplice
864
865 {- Note [Given Insts]
866 ~~~~~~~~~~~~~~~~~~
867 Because of GADTs, we have to pass inwards the Insts provided by type signatures
868 and existential contexts. Consider
869 data T a where { T1 :: b -> b -> T [b] }
870 f :: Eq a => T a -> Bool
871 f (T1 x y) = [x]==[y]
872
873 The constructor T1 binds an existential variable 'b', and we need Eq [b].
874 Well, we have it, because Eq a refines to Eq [b], but we can only spot that if we
875 pass it inwards.
876
877 -}
878
879 -- | Type alias for 'IORef'; the convention is we'll use this for mutable
880 -- bits of data in 'TcGblEnv' which are updated during typechecking and
881 -- returned at the end.
882 type TcRef a = IORef a
883 -- ToDo: when should I refer to it as a 'TcId' instead of an 'Id'?
884 type TcId = Id
885 type TcIdSet = IdSet
886
887 ---------------------------
888 -- The TcIdBinderStack
889 ---------------------------
890
891 type TcIdBinderStack = [TcIdBinder]
892 -- This is a stack of locally-bound ids, innermost on top
893 -- Used only in error reporting (relevantBindings in TcError)
894 -- We can't use the tcl_env type environment, because it doesn't
895 -- keep track of the nesting order
896
897 data TcIdBinder
898 = TcIdBndr
899 TcId
900 TopLevelFlag -- Tells whether the binding is syntactically top-level
901 -- (The monomorphic Ids for a recursive group count
902 -- as not-top-level for this purpose.)
903 | TcIdBndr_ExpType -- Variant that allows the type to be specified as
904 -- an ExpType
905 Name
906 ExpType
907 TopLevelFlag
908
909 instance Outputable TcIdBinder where
910 ppr (TcIdBndr id top_lvl) = ppr id <> brackets (ppr top_lvl)
911 ppr (TcIdBndr_ExpType id _ top_lvl) = ppr id <> brackets (ppr top_lvl)
912
913 instance HasOccName TcIdBinder where
914 occName (TcIdBndr id _) = (occName (idName id))
915 occName (TcIdBndr_ExpType name _ _) = (occName name)
916
917 ---------------------------
918 -- Template Haskell stages and levels
919 ---------------------------
920
921 data SpliceType = Typed | Untyped
922
923 data ThStage -- See Note [Template Haskell state diagram] in TcSplice
924 = Splice SpliceType -- Inside a top-level splice
925 -- This code will be run *at compile time*;
926 -- the result replaces the splice
927 -- Binding level = 0
928
929 | RunSplice (TcRef [ForeignRef (TH.Q ())])
930 -- Set when running a splice, i.e. NOT when renaming or typechecking the
931 -- Haskell code for the splice. See Note [RunSplice ThLevel].
932 --
933 -- Contains a list of mod finalizers collected while executing the splice.
934 --
935 -- 'addModFinalizer' inserts finalizers here, and from here they are taken
936 -- to construct an @HsSpliced@ annotation for untyped splices. See Note
937 -- [Delaying modFinalizers in untyped splices] in "RnSplice".
938 --
939 -- For typed splices, the typechecker takes finalizers from here and
940 -- inserts them in the list of finalizers in the global environment.
941 --
942 -- See Note [Collecting modFinalizers in typed splices] in "TcSplice".
943
944 | Comp -- Ordinary Haskell code
945 -- Binding level = 1
946
947 | Brack -- Inside brackets
948 ThStage -- Enclosing stage
949 PendingStuff
950
951 data PendingStuff
952 = RnPendingUntyped -- Renaming the inside of an *untyped* bracket
953 (TcRef [PendingRnSplice]) -- Pending splices in here
954
955 | RnPendingTyped -- Renaming the inside of a *typed* bracket
956
957 | TcPending -- Typechecking the inside of a typed bracket
958 (TcRef [PendingTcSplice]) -- Accumulate pending splices here
959 (TcRef WantedConstraints) -- and type constraints here
960
961 topStage, topAnnStage, topSpliceStage :: ThStage
962 topStage = Comp
963 topAnnStage = Splice Untyped
964 topSpliceStage = Splice Untyped
965
966 instance Outputable ThStage where
967 ppr (Splice _) = text "Splice"
968 ppr (RunSplice _) = text "RunSplice"
969 ppr Comp = text "Comp"
970 ppr (Brack s _) = text "Brack" <> parens (ppr s)
971
972 type ThLevel = Int
973 -- NB: see Note [Template Haskell levels] in TcSplice
974 -- Incremented when going inside a bracket,
975 -- decremented when going inside a splice
976 -- NB: ThLevel is one greater than the 'n' in Fig 2 of the
977 -- original "Template meta-programming for Haskell" paper
978
979 impLevel, outerLevel :: ThLevel
980 impLevel = 0 -- Imported things; they can be used inside a top level splice
981 outerLevel = 1 -- Things defined outside brackets
982
983 thLevel :: ThStage -> ThLevel
984 thLevel (Splice _) = 0
985 thLevel (RunSplice _) =
986 -- See Note [RunSplice ThLevel].
987 panic "thLevel: called when running a splice"
988 thLevel Comp = 1
989 thLevel (Brack s _) = thLevel s + 1
990
991 {- Node [RunSplice ThLevel]
992 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
993 The 'RunSplice' stage is set when executing a splice, and only when running a
994 splice. In particular it is not set when the splice is renamed or typechecked.
995
996 'RunSplice' is needed to provide a reference where 'addModFinalizer' can insert
997 the finalizer (see Note [Delaying modFinalizers in untyped splices]), and
998 'addModFinalizer' runs when doing Q things. Therefore, It doesn't make sense to
999 set 'RunSplice' when renaming or typechecking the splice, where 'Splice', 'Brak'
1000 or 'Comp' are used instead.
1001
1002 -}
1003
1004 ---------------------------
1005 -- Arrow-notation context
1006 ---------------------------
1007
1008 {- Note [Escaping the arrow scope]
1009 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1010 In arrow notation, a variable bound by a proc (or enclosed let/kappa)
1011 is not in scope to the left of an arrow tail (-<) or the head of (|..|).
1012 For example
1013
1014 proc x -> (e1 -< e2)
1015
1016 Here, x is not in scope in e1, but it is in scope in e2. This can get
1017 a bit complicated:
1018
1019 let x = 3 in
1020 proc y -> (proc z -> e1) -< e2
1021
1022 Here, x and z are in scope in e1, but y is not.
1023
1024 We implement this by
1025 recording the environment when passing a proc (using newArrowScope),
1026 and returning to that (using escapeArrowScope) on the left of -< and the
1027 head of (|..|).
1028
1029 All this can be dealt with by the *renamer*. But the type checker needs
1030 to be involved too. Example (arrowfail001)
1031 class Foo a where foo :: a -> ()
1032 data Bar = forall a. Foo a => Bar a
1033 get :: Bar -> ()
1034 get = proc x -> case x of Bar a -> foo -< a
1035 Here the call of 'foo' gives rise to a (Foo a) constraint that should not
1036 be captured by the pattern match on 'Bar'. Rather it should join the
1037 constraints from further out. So we must capture the constraint bag
1038 from further out in the ArrowCtxt that we push inwards.
1039 -}
1040
1041 data ArrowCtxt -- Note [Escaping the arrow scope]
1042 = NoArrowCtxt
1043 | ArrowCtxt LocalRdrEnv (TcRef WantedConstraints)
1044
1045
1046 ---------------------------
1047 -- TcTyThing
1048 ---------------------------
1049
1050 -- | A typecheckable thing available in a local context. Could be
1051 -- 'AGlobal' 'TyThing', but also lexically scoped variables, etc.
1052 -- See 'TcEnv' for how to retrieve a 'TyThing' given a 'Name'.
1053 data TcTyThing
1054 = AGlobal TyThing -- Used only in the return type of a lookup
1055
1056 | ATcId -- Ids defined in this module; may not be fully zonked
1057 { tct_id :: TcId
1058 , tct_info :: IdBindingInfo -- See Note [Meaning of IdBindingInfo]
1059 }
1060
1061 | ATyVar Name TcTyVar -- The type variable to which the lexically scoped type
1062 -- variable is bound. We only need the Name
1063 -- for error-message purposes; it is the corresponding
1064 -- Name in the domain of the envt
1065
1066 | ATcTyCon TyCon -- Used temporarily, during kind checking, for the
1067 -- tycons and clases in this recursive group
1068 -- The TyCon is always a TcTyCon. Its kind
1069 -- can be a mono-kind or a poly-kind; in TcTyClsDcls see
1070 -- Note [Type checking recursive type and class declarations]
1071
1072 | APromotionErr PromotionErr
1073
1074 data PromotionErr
1075 = TyConPE -- TyCon used in a kind before we are ready
1076 -- data T :: T -> * where ...
1077 | ClassPE -- Ditto Class
1078
1079 | FamDataConPE -- Data constructor for a data family
1080 -- See Note [AFamDataCon: not promoting data family constructors]
1081 -- in TcEnv.
1082 | PatSynPE -- Pattern synonyms
1083 -- See Note [Don't promote pattern synonyms] in TcEnv
1084
1085 | RecDataConPE -- Data constructor in a recursive loop
1086 -- See Note [Recursion and promoting data constructors] in TcTyClsDecls
1087 | NoDataKindsTC -- -XDataKinds not enabled (for a tycon)
1088 | NoDataKindsDC -- -XDataKinds not enabled (for a datacon)
1089 | NoTypeInTypeTC -- -XTypeInType not enabled (for a tycon)
1090 | NoTypeInTypeDC -- -XTypeInType not enabled (for a datacon)
1091
1092 instance Outputable TcTyThing where -- Debugging only
1093 ppr (AGlobal g) = ppr g
1094 ppr elt@(ATcId {}) = text "Identifier" <>
1095 brackets (ppr (tct_id elt) <> dcolon
1096 <> ppr (varType (tct_id elt)) <> comma
1097 <+> ppr (tct_info elt))
1098 ppr (ATyVar n tv) = text "Type variable" <+> quotes (ppr n) <+> equals <+> ppr tv
1099 ppr (ATcTyCon tc) = text "ATcTyCon" <+> ppr tc <+> dcolon <+> ppr (tyConKind tc)
1100 ppr (APromotionErr err) = text "APromotionErr" <+> ppr err
1101
1102 -- | IdBindingInfo describes how an Id is bound.
1103 --
1104 -- It is used for the following purposes:
1105 -- a) for static forms in TcExpr.checkClosedInStaticForm and
1106 -- b) to figure out when a nested binding can be generalised,
1107 -- in TcBinds.decideGeneralisationPlan.
1108 --
1109 data IdBindingInfo -- See Note [Meaning of IdBindingInfo and ClosedTypeId]
1110 = NotLetBound
1111 | ClosedLet
1112 | NonClosedLet
1113 RhsNames -- Used for (static e) checks only
1114 ClosedTypeId -- Used for generalisation checks
1115 -- and for (static e) checks
1116
1117 -- | IsGroupClosed describes a group of mutually-recursive bindings
1118 data IsGroupClosed
1119 = IsGroupClosed
1120 (NameEnv RhsNames) -- Free var info for the RHS of each binding in the goup
1121 -- Used only for (static e) checks
1122
1123 ClosedTypeId -- True <=> all the free vars of the group are
1124 -- imported or ClosedLet or
1125 -- NonClosedLet with ClosedTypeId=True.
1126 -- In particular, no tyvars, no NotLetBound
1127
1128 type RhsNames = NameSet -- Names of variables, mentioned on the RHS of
1129 -- a definition, that are not Global or ClosedLet
1130
1131 type ClosedTypeId = Bool
1132 -- See Note [Meaning of IdBindingInfo and ClosedTypeId]
1133
1134 {- Note [Meaning of IdBindingInfo]
1135 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1136 NotLetBound means that
1137 the Id is not let-bound (e.g. it is bound in a
1138 lambda-abstraction or in a case pattern)
1139
1140 ClosedLet means that
1141 - The Id is let-bound,
1142 - Any free term variables are also Global or ClosedLet
1143 - Its type has no free variables (NB: a top-level binding subject
1144 to the MR might have free vars in its type)
1145 These ClosedLets can definitely be floated to top level; and we
1146 may need to do so for static forms.
1147
1148 Property: ClosedLet
1149 is equivalent to
1150 NonClosedLet emptyNameSet True
1151
1152 (NonClosedLet (fvs::RhsNames) (cl::ClosedTypeId)) means that
1153 - The Id is let-bound
1154
1155 - The fvs::RhsNames contains the free names of the RHS,
1156 excluding Global and ClosedLet ones.
1157
1158 - For the ClosedTypeId field see Note [Bindings with closed types]
1159
1160 For (static e) to be valid, we need for every 'x' free in 'e',
1161 x's binding must be floatable to top level. Specifically:
1162 * x's RhsNames must be non-empty
1163 * x's type has no free variables
1164 See Note [Grand plan for static forms] in StaticPtrTable.hs.
1165 This test is made in TcExpr.checkClosedInStaticForm.
1166 Actually knowing x's RhsNames (rather than just its emptiness
1167 or otherwise) is just so we can produce better error messages
1168
1169 Note [Bindings with closed types: ClosedTypeId]
1170 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1171 Consider
1172
1173 f x = let g ys = map not ys
1174 in ...
1175
1176 Can we generalise 'g' under the OutsideIn algorithm? Yes,
1177 because all g's free variables are top-level; that is they themselves
1178 have no free type variables, and it is the type variables in the
1179 environment that makes things tricky for OutsideIn generalisation.
1180
1181 Here's the invariant:
1182 If an Id has ClosedTypeId=True (in its IdBindingInfo), then
1183 the Id's type is /definitely/ closed (has no free type variables).
1184 Specifically,
1185 a) The Id's acutal type is closed (has no free tyvars)
1186 b) Either the Id has a (closed) user-supplied type signature
1187 or all its free varaibles are Global/ClosedLet
1188 or NonClosedLet with ClosedTypeId=True.
1189 In particular, none are NotLetBound.
1190
1191 Why is (b) needed? Consider
1192 \x. (x :: Int, let y = x+1 in ...)
1193 Initially x::alpha. If we happen to typecheck the 'let' before the
1194 (x::Int), y's type will have a free tyvar; but if the other way round
1195 it won't. So we treat any let-bound variable with a free
1196 non-let-bound variable as not ClosedTypeId, regardless of what the
1197 free vars of its type actually are.
1198
1199 But if it has a signature, all is well:
1200 \x. ...(let { y::Int; y = x+1 } in
1201 let { v = y+2 } in ...)...
1202 Here the signature on 'v' makes 'y' a ClosedTypeId, so we can
1203 generalise 'v'.
1204
1205 Note that:
1206
1207 * A top-level binding may not have ClosedTypeId=True, if it suffers
1208 from the MR
1209
1210 * A nested binding may be closed (eg 'g' in the example we started
1211 with). Indeed, that's the point; whether a function is defined at
1212 top level or nested is orthogonal to the question of whether or
1213 not it is closed.
1214
1215 * A binding may be non-closed because it mentions a lexically scoped
1216 *type variable* Eg
1217 f :: forall a. blah
1218 f x = let g y = ...(y::a)...
1219
1220 Under OutsideIn we are free to generalise an Id all of whose free
1221 variables have ClosedTypeId=True (or imported). This is an extension
1222 compared to the JFP paper on OutsideIn, which used "top-level" as a
1223 proxy for "closed". (It's not a good proxy anyway -- the MR can make
1224 a top-level binding with a free type variable.)
1225 -}
1226
1227 instance Outputable IdBindingInfo where
1228 ppr NotLetBound = text "NotLetBound"
1229 ppr ClosedLet = text "TopLevelLet"
1230 ppr (NonClosedLet fvs closed_type) =
1231 text "TopLevelLet" <+> ppr fvs <+> ppr closed_type
1232
1233 instance Outputable PromotionErr where
1234 ppr ClassPE = text "ClassPE"
1235 ppr TyConPE = text "TyConPE"
1236 ppr PatSynPE = text "PatSynPE"
1237 ppr FamDataConPE = text "FamDataConPE"
1238 ppr RecDataConPE = text "RecDataConPE"
1239 ppr NoDataKindsTC = text "NoDataKindsTC"
1240 ppr NoDataKindsDC = text "NoDataKindsDC"
1241 ppr NoTypeInTypeTC = text "NoTypeInTypeTC"
1242 ppr NoTypeInTypeDC = text "NoTypeInTypeDC"
1243
1244 pprTcTyThingCategory :: TcTyThing -> SDoc
1245 pprTcTyThingCategory (AGlobal thing) = pprTyThingCategory thing
1246 pprTcTyThingCategory (ATyVar {}) = text "Type variable"
1247 pprTcTyThingCategory (ATcId {}) = text "Local identifier"
1248 pprTcTyThingCategory (ATcTyCon {}) = text "Local tycon"
1249 pprTcTyThingCategory (APromotionErr pe) = pprPECategory pe
1250
1251 pprPECategory :: PromotionErr -> SDoc
1252 pprPECategory ClassPE = text "Class"
1253 pprPECategory TyConPE = text "Type constructor"
1254 pprPECategory PatSynPE = text "Pattern synonym"
1255 pprPECategory FamDataConPE = text "Data constructor"
1256 pprPECategory RecDataConPE = text "Data constructor"
1257 pprPECategory NoDataKindsTC = text "Type constructor"
1258 pprPECategory NoDataKindsDC = text "Data constructor"
1259 pprPECategory NoTypeInTypeTC = text "Type constructor"
1260 pprPECategory NoTypeInTypeDC = text "Data constructor"
1261
1262 {-
1263 ************************************************************************
1264 * *
1265 Operations over ImportAvails
1266 * *
1267 ************************************************************************
1268 -}
1269
1270 -- | 'ImportAvails' summarises what was imported from where, irrespective of
1271 -- whether the imported things are actually used or not. It is used:
1272 --
1273 -- * when processing the export list,
1274 --
1275 -- * when constructing usage info for the interface file,
1276 --
1277 -- * to identify the list of directly imported modules for initialisation
1278 -- purposes and for optimised overlap checking of family instances,
1279 --
1280 -- * when figuring out what things are really unused
1281 --
1282 data ImportAvails
1283 = ImportAvails {
1284 imp_mods :: ImportedMods,
1285 -- = ModuleEnv [ImportedModsVal],
1286 -- ^ Domain is all directly-imported modules
1287 --
1288 -- See the documentation on ImportedModsVal in HscTypes for the
1289 -- meaning of the fields.
1290 --
1291 -- We need a full ModuleEnv rather than a ModuleNameEnv here,
1292 -- because we might be importing modules of the same name from
1293 -- different packages. (currently not the case, but might be in the
1294 -- future).
1295
1296 imp_dep_mods :: ModuleNameEnv (ModuleName, IsBootInterface),
1297 -- ^ Home-package modules needed by the module being compiled
1298 --
1299 -- It doesn't matter whether any of these dependencies
1300 -- are actually /used/ when compiling the module; they
1301 -- are listed if they are below it at all. For
1302 -- example, suppose M imports A which imports X. Then
1303 -- compiling M might not need to consult X.hi, but X
1304 -- is still listed in M's dependencies.
1305
1306 imp_dep_pkgs :: Set InstalledUnitId,
1307 -- ^ Packages needed by the module being compiled, whether directly,
1308 -- or via other modules in this package, or via modules imported
1309 -- from other packages.
1310
1311 imp_trust_pkgs :: Set InstalledUnitId,
1312 -- ^ This is strictly a subset of imp_dep_pkgs and records the
1313 -- packages the current module needs to trust for Safe Haskell
1314 -- compilation to succeed. A package is required to be trusted if
1315 -- we are dependent on a trustworthy module in that package.
1316 -- While perhaps making imp_dep_pkgs a tuple of (UnitId, Bool)
1317 -- where True for the bool indicates the package is required to be
1318 -- trusted is the more logical design, doing so complicates a lot
1319 -- of code not concerned with Safe Haskell.
1320 -- See Note [RnNames . Tracking Trust Transitively]
1321
1322 imp_trust_own_pkg :: Bool,
1323 -- ^ Do we require that our own package is trusted?
1324 -- This is to handle efficiently the case where a Safe module imports
1325 -- a Trustworthy module that resides in the same package as it.
1326 -- See Note [RnNames . Trust Own Package]
1327
1328 imp_orphs :: [Module],
1329 -- ^ Orphan modules below us in the import tree (and maybe including
1330 -- us for imported modules)
1331
1332 imp_finsts :: [Module]
1333 -- ^ Family instance modules below us in the import tree (and maybe
1334 -- including us for imported modules)
1335 }
1336
1337 mkModDeps :: [(ModuleName, IsBootInterface)]
1338 -> ModuleNameEnv (ModuleName, IsBootInterface)
1339 mkModDeps deps = foldl add emptyUFM deps
1340 where
1341 add env elt@(m,_) = addToUFM env m elt
1342
1343 modDepsElts
1344 :: ModuleNameEnv (ModuleName, IsBootInterface)
1345 -> [(ModuleName, IsBootInterface)]
1346 modDepsElts = sort . nonDetEltsUFM
1347 -- It's OK to use nonDetEltsUFM here because sorting by module names
1348 -- restores determinism
1349
1350 emptyImportAvails :: ImportAvails
1351 emptyImportAvails = ImportAvails { imp_mods = emptyModuleEnv,
1352 imp_dep_mods = emptyUFM,
1353 imp_dep_pkgs = S.empty,
1354 imp_trust_pkgs = S.empty,
1355 imp_trust_own_pkg = False,
1356 imp_orphs = [],
1357 imp_finsts = [] }
1358
1359 -- | Union two ImportAvails
1360 --
1361 -- This function is a key part of Import handling, basically
1362 -- for each import we create a separate ImportAvails structure
1363 -- and then union them all together with this function.
1364 plusImportAvails :: ImportAvails -> ImportAvails -> ImportAvails
1365 plusImportAvails
1366 (ImportAvails { imp_mods = mods1,
1367 imp_dep_mods = dmods1, imp_dep_pkgs = dpkgs1,
1368 imp_trust_pkgs = tpkgs1, imp_trust_own_pkg = tself1,
1369 imp_orphs = orphs1, imp_finsts = finsts1 })
1370 (ImportAvails { imp_mods = mods2,
1371 imp_dep_mods = dmods2, imp_dep_pkgs = dpkgs2,
1372 imp_trust_pkgs = tpkgs2, imp_trust_own_pkg = tself2,
1373 imp_orphs = orphs2, imp_finsts = finsts2 })
1374 = ImportAvails { imp_mods = plusModuleEnv_C (++) mods1 mods2,
1375 imp_dep_mods = plusUFM_C plus_mod_dep dmods1 dmods2,
1376 imp_dep_pkgs = dpkgs1 `S.union` dpkgs2,
1377 imp_trust_pkgs = tpkgs1 `S.union` tpkgs2,
1378 imp_trust_own_pkg = tself1 || tself2,
1379 imp_orphs = orphs1 `unionLists` orphs2,
1380 imp_finsts = finsts1 `unionLists` finsts2 }
1381 where
1382 plus_mod_dep (m1, boot1) (m2, boot2)
1383 = WARN( not (m1 == m2), (ppr m1 <+> ppr m2) $$ (ppr boot1 <+> ppr boot2) )
1384 -- Check mod-names match
1385 (m1, boot1 && boot2) -- If either side can "see" a non-hi-boot interface, use that
1386
1387 {-
1388 ************************************************************************
1389 * *
1390 \subsection{Where from}
1391 * *
1392 ************************************************************************
1393
1394 The @WhereFrom@ type controls where the renamer looks for an interface file
1395 -}
1396
1397 data WhereFrom
1398 = ImportByUser IsBootInterface -- Ordinary user import (perhaps {-# SOURCE #-})
1399 | ImportBySystem -- Non user import.
1400 | ImportByPlugin -- Importing a plugin;
1401 -- See Note [Care with plugin imports] in LoadIface
1402
1403 instance Outputable WhereFrom where
1404 ppr (ImportByUser is_boot) | is_boot = text "{- SOURCE -}"
1405 | otherwise = empty
1406 ppr ImportBySystem = text "{- SYSTEM -}"
1407 ppr ImportByPlugin = text "{- PLUGIN -}"
1408
1409
1410 {- *********************************************************************
1411 * *
1412 Type signatures
1413 * *
1414 ********************************************************************* -}
1415
1416 -- These data types need to be here only because
1417 -- TcSimplify uses them, and TcSimplify is fairly
1418 -- low down in the module hierarchy
1419
1420 type TcSigFun = Name -> Maybe TcSigInfo
1421
1422 data TcSigInfo = TcIdSig TcIdSigInfo
1423 | TcPatSynSig TcPatSynInfo
1424
1425 data TcIdSigInfo -- See Note [Complete and partial type signatures]
1426 = CompleteSig -- A complete signature with no wildcards,
1427 -- so the complete polymorphic type is known.
1428 { sig_bndr :: TcId -- The polymorphic Id with that type
1429
1430 , sig_ctxt :: UserTypeCtxt -- In the case of type-class default methods,
1431 -- the Name in the FunSigCtxt is not the same
1432 -- as the TcId; the former is 'op', while the
1433 -- latter is '$dmop' or some such
1434
1435 , sig_loc :: SrcSpan -- Location of the type signature
1436 }
1437
1438 | PartialSig -- A partial type signature (i.e. includes one or more
1439 -- wildcards). In this case it doesn't make sense to give
1440 -- the polymorphic Id, because we are going to /infer/ its
1441 -- type, so we can't make the polymorphic Id ab-initio
1442 { psig_name :: Name -- Name of the function; used when report wildcards
1443 , psig_hs_ty :: LHsSigWcType GhcRn -- The original partial signature in
1444 -- HsSyn form
1445 , sig_ctxt :: UserTypeCtxt
1446 , sig_loc :: SrcSpan -- Location of the type signature
1447 }
1448
1449
1450 {- Note [Complete and partial type signatures]
1451 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1452 A type signature is partial when it contains one or more wildcards
1453 (= type holes). The wildcard can either be:
1454 * A (type) wildcard occurring in sig_theta or sig_tau. These are
1455 stored in sig_wcs.
1456 f :: Bool -> _
1457 g :: Eq _a => _a -> _a -> Bool
1458 * Or an extra-constraints wildcard, stored in sig_cts:
1459 h :: (Num a, _) => a -> a
1460
1461 A type signature is a complete type signature when there are no
1462 wildcards in the type signature, i.e. iff sig_wcs is empty and
1463 sig_extra_cts is Nothing.
1464 -}
1465
1466 data TcIdSigInst
1467 = TISI { sig_inst_sig :: TcIdSigInfo
1468
1469 , sig_inst_skols :: [(Name, TcTyVar)]
1470 -- Instantiated type and kind variables, SigTvs
1471 -- The Name is the Name that the renamer chose;
1472 -- but the TcTyVar may come from instantiating
1473 -- the type and hence have a different unique.
1474 -- No need to keep track of whether they are truly lexically
1475 -- scoped because the renamer has named them uniquely
1476 -- See Note [Binding scoped type variables] in TcSigs
1477
1478 , sig_inst_theta :: TcThetaType
1479 -- Instantiated theta. In the case of a
1480 -- PartialSig, sig_theta does not include
1481 -- the extra-constraints wildcard
1482
1483 , sig_inst_tau :: TcSigmaType -- Instantiated tau
1484 -- See Note [sig_inst_tau may be polymorphic]
1485
1486 -- Relevant for partial signature only
1487 , sig_inst_wcs :: [(Name, TcTyVar)]
1488 -- Like sig_inst_skols, but for wildcards. The named
1489 -- wildcards scope over the binding, and hence their
1490 -- Names may appear in type signatures in the binding
1491
1492 , sig_inst_wcx :: Maybe TcTyVar
1493 -- Extra-constraints wildcard to fill in, if any
1494 }
1495
1496 {- Note [sig_inst_tau may be polymorphic]
1497 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1498 Note that "sig_inst_tau" might actually be a polymorphic type,
1499 if the original function had a signature like
1500 forall a. Eq a => forall b. Ord b => ....
1501 But that's ok: tcMatchesFun (called by tcRhs) can deal with that
1502 It happens, too! See Note [Polymorphic methods] in TcClassDcl.
1503
1504 Note [Wildcards in partial signatures]
1505 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1506 The wildcards in psig_wcs may stand for a type mentioning
1507 the universally-quantified tyvars of psig_ty
1508
1509 E.g. f :: forall a. _ -> a
1510 f x = x
1511 We get sig_inst_skols = [a]
1512 sig_inst_tau = _22 -> a
1513 sig_inst_wcs = [_22]
1514 and _22 in the end is unified with the type 'a'
1515
1516 Moreover the kind of a wildcard in sig_inst_wcs may mention
1517 the universally-quantified tyvars sig_inst_skols
1518 e.g. f :: t a -> t _
1519 Here we get
1520 sig_inst_skols = [k:*, (t::k ->*), (a::k)]
1521 sig_inst_tau = t a -> t _22
1522 sig_inst_wcs = [ _22::k ]
1523 -}
1524
1525 data TcPatSynInfo
1526 = TPSI {
1527 patsig_name :: Name,
1528 patsig_implicit_bndrs :: [TyVarBinder], -- Implicitly-bound kind vars (Inferred) and
1529 -- implicitly-bound type vars (Specified)
1530 -- See Note [The pattern-synonym signature splitting rule] in TcPatSyn
1531 patsig_univ_bndrs :: [TyVar], -- Bound by explicit user forall
1532 patsig_req :: TcThetaType,
1533 patsig_ex_bndrs :: [TyVar], -- Bound by explicit user forall
1534 patsig_prov :: TcThetaType,
1535 patsig_body_ty :: TcSigmaType
1536 }
1537
1538 instance Outputable TcSigInfo where
1539 ppr (TcIdSig idsi) = ppr idsi
1540 ppr (TcPatSynSig tpsi) = text "TcPatSynInfo" <+> ppr tpsi
1541
1542 instance Outputable TcIdSigInfo where
1543 ppr (CompleteSig { sig_bndr = bndr })
1544 = ppr bndr <+> dcolon <+> ppr (idType bndr)
1545 ppr (PartialSig { psig_name = name, psig_hs_ty = hs_ty })
1546 = text "psig" <+> ppr name <+> dcolon <+> ppr hs_ty
1547
1548 instance Outputable TcIdSigInst where
1549 ppr (TISI { sig_inst_sig = sig, sig_inst_skols = skols
1550 , sig_inst_theta = theta, sig_inst_tau = tau })
1551 = hang (ppr sig) 2 (vcat [ ppr skols, ppr theta <+> darrow <+> ppr tau ])
1552
1553 instance Outputable TcPatSynInfo where
1554 ppr (TPSI{ patsig_name = name}) = ppr name
1555
1556 isPartialSig :: TcIdSigInst -> Bool
1557 isPartialSig (TISI { sig_inst_sig = PartialSig {} }) = True
1558 isPartialSig _ = False
1559
1560 -- | No signature or a partial signature
1561 hasCompleteSig :: TcSigFun -> Name -> Bool
1562 hasCompleteSig sig_fn name
1563 = case sig_fn name of
1564 Just (TcIdSig (CompleteSig {})) -> True
1565 _ -> False
1566
1567
1568 {-
1569 ************************************************************************
1570 * *
1571 * Canonical constraints *
1572 * *
1573 * These are the constraints the low-level simplifier works with *
1574 * *
1575 ************************************************************************
1576 -}
1577
1578 -- The syntax of xi (ΞΎ) types:
1579 -- xi ::= a | T xis | xis -> xis | ... | forall a. tau
1580 -- Two important notes:
1581 -- (i) No type families, unless we are under a ForAll
1582 -- (ii) Note that xi types can contain unexpanded type synonyms;
1583 -- however, the (transitive) expansions of those type synonyms
1584 -- will not contain any type functions, unless we are under a ForAll.
1585 -- We enforce the structure of Xi types when we flatten (TcCanonical)
1586
1587 type Xi = Type -- In many comments, "xi" ranges over Xi
1588
1589 type Cts = Bag Ct
1590
1591 data Ct
1592 -- Atomic canonical constraints
1593 = CDictCan { -- e.g. Num xi
1594 cc_ev :: CtEvidence, -- See Note [Ct/evidence invariant]
1595
1596 cc_class :: Class,
1597 cc_tyargs :: [Xi], -- cc_tyargs are function-free, hence Xi
1598
1599 cc_pend_sc :: Bool -- See Note [The superclass story] in TcCanonical
1600 -- True <=> (a) cc_class has superclasses
1601 -- (b) we have not (yet) added those
1602 -- superclasses as Givens
1603 }
1604
1605 | CIrredEvCan { -- These stand for yet-unusable predicates
1606 cc_ev :: CtEvidence -- See Note [Ct/evidence invariant]
1607 -- The ctev_pred of the evidence is
1608 -- of form (tv xi1 xi2 ... xin)
1609 -- or (tv1 ~ ty2) where the CTyEqCan kind invariant fails
1610 -- or (F tys ~ ty) where the CFunEqCan kind invariant fails
1611 -- See Note [CIrredEvCan constraints]
1612 }
1613
1614 | CTyEqCan { -- tv ~ rhs
1615 -- Invariants:
1616 -- * See Note [Applying the inert substitution] in TcFlatten
1617 -- * tv not in tvs(rhs) (occurs check)
1618 -- * If tv is a TauTv, then rhs has no foralls
1619 -- (this avoids substituting a forall for the tyvar in other types)
1620 -- * typeKind ty `tcEqKind` typeKind tv
1621 -- * rhs may have at most one top-level cast
1622 -- * rhs (perhaps under the one cast) is not necessarily function-free,
1623 -- but it has no top-level function.
1624 -- E.g. a ~ [F b] is fine
1625 -- but a ~ F b is not
1626 -- * If the equality is representational, rhs has no top-level newtype
1627 -- See Note [No top-level newtypes on RHS of representational
1628 -- equalities] in TcCanonical
1629 -- * If rhs (perhaps under the cast) is also a tv, then it is oriented
1630 -- to give best chance of
1631 -- unification happening; eg if rhs is touchable then lhs is too
1632 cc_ev :: CtEvidence, -- See Note [Ct/evidence invariant]
1633 cc_tyvar :: TcTyVar,
1634 cc_rhs :: TcType, -- Not necessarily function-free (hence not Xi)
1635 -- See invariants above
1636
1637 cc_eq_rel :: EqRel -- INVARIANT: cc_eq_rel = ctEvEqRel cc_ev
1638 }
1639
1640 | CFunEqCan { -- F xis ~ fsk
1641 -- Invariants:
1642 -- * isTypeFamilyTyCon cc_fun
1643 -- * typeKind (F xis) = tyVarKind fsk
1644 -- * always Nominal role
1645 cc_ev :: CtEvidence, -- See Note [Ct/evidence invariant]
1646 cc_fun :: TyCon, -- A type function
1647
1648 cc_tyargs :: [Xi], -- cc_tyargs are function-free (hence Xi)
1649 -- Either under-saturated or exactly saturated
1650 -- *never* over-saturated (because if so
1651 -- we should have decomposed)
1652
1653 cc_fsk :: TcTyVar -- [Given] always a FlatSkolTv
1654 -- [Wanted] always a FlatMetaTv
1655 -- See Note [The flattening story] in TcFlatten
1656 }
1657
1658 | CNonCanonical { -- See Note [NonCanonical Semantics] in TcSMonad
1659 cc_ev :: CtEvidence
1660 }
1661
1662 | CHoleCan { -- See Note [Hole constraints]
1663 -- Treated as an "insoluble" constraint
1664 -- See Note [Insoluble constraints]
1665 cc_ev :: CtEvidence,
1666 cc_hole :: Hole
1667 }
1668
1669 -- | An expression or type hole
1670 data Hole = ExprHole UnboundVar
1671 -- ^ Either an out-of-scope variable or a "true" hole in an
1672 -- expression (TypedHoles)
1673 | TypeHole OccName
1674 -- ^ A hole in a type (PartialTypeSignatures)
1675
1676 holeOcc :: Hole -> OccName
1677 holeOcc (ExprHole uv) = unboundVarOcc uv
1678 holeOcc (TypeHole occ) = occ
1679
1680 {- Note [Hole constraints]
1681 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1682 CHoleCan constraints are used for two kinds of holes,
1683 distinguished by cc_hole:
1684
1685 * For holes in expressions (including variables not in scope)
1686 e.g. f x = g _ x
1687
1688 * For holes in type signatures
1689 e.g. f :: _ -> _
1690 f x = [x,True]
1691
1692 Note [CIrredEvCan constraints]
1693 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1694 CIrredEvCan constraints are used for constraints that are "stuck"
1695 - we can't solve them (yet)
1696 - we can't use them to solve other constraints
1697 - but they may become soluble if we substitute for some
1698 of the type variables in the constraint
1699
1700 Example 1: (c Int), where c :: * -> Constraint. We can't do anything
1701 with this yet, but if later c := Num, *then* we can solve it
1702
1703 Example 2: a ~ b, where a :: *, b :: k, where k is a kind variable
1704 We don't want to use this to substitute 'b' for 'a', in case
1705 'k' is subequently unifed with (say) *->*, because then
1706 we'd have ill-kinded types floating about. Rather we want
1707 to defer using the equality altogether until 'k' get resolved.
1708
1709 Note [Ct/evidence invariant]
1710 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1711 If ct :: Ct, then extra fields of 'ct' cache precisely the ctev_pred field
1712 of (cc_ev ct), and is fully rewritten wrt the substitution. Eg for CDictCan,
1713 ctev_pred (cc_ev ct) = (cc_class ct) (cc_tyargs ct)
1714 This holds by construction; look at the unique place where CDictCan is
1715 built (in TcCanonical).
1716
1717 In contrast, the type of the evidence *term* (ctev_dest / ctev_evar) in
1718 the evidence may *not* be fully zonked; we are careful not to look at it
1719 during constraint solving. See Note [Evidence field of CtEvidence].
1720 -}
1721
1722 mkNonCanonical :: CtEvidence -> Ct
1723 mkNonCanonical ev = CNonCanonical { cc_ev = ev }
1724
1725 mkNonCanonicalCt :: Ct -> Ct
1726 mkNonCanonicalCt ct = CNonCanonical { cc_ev = cc_ev ct }
1727
1728 mkGivens :: CtLoc -> [EvId] -> [Ct]
1729 mkGivens loc ev_ids
1730 = map mk ev_ids
1731 where
1732 mk ev_id = mkNonCanonical (CtGiven { ctev_evar = ev_id
1733 , ctev_pred = evVarPred ev_id
1734 , ctev_loc = loc })
1735
1736 ctEvidence :: Ct -> CtEvidence
1737 ctEvidence = cc_ev
1738
1739 ctLoc :: Ct -> CtLoc
1740 ctLoc = ctEvLoc . ctEvidence
1741
1742 setCtLoc :: Ct -> CtLoc -> Ct
1743 setCtLoc ct loc = ct { cc_ev = (cc_ev ct) { ctev_loc = loc } }
1744
1745 ctOrigin :: Ct -> CtOrigin
1746 ctOrigin = ctLocOrigin . ctLoc
1747
1748 ctPred :: Ct -> PredType
1749 -- See Note [Ct/evidence invariant]
1750 ctPred ct = ctEvPred (cc_ev ct)
1751
1752 -- | Makes a new equality predicate with the same role as the given
1753 -- evidence.
1754 mkTcEqPredLikeEv :: CtEvidence -> TcType -> TcType -> TcType
1755 mkTcEqPredLikeEv ev
1756 = case predTypeEqRel pred of
1757 NomEq -> mkPrimEqPred
1758 ReprEq -> mkReprPrimEqPred
1759 where
1760 pred = ctEvPred ev
1761
1762 -- | Get the flavour of the given 'Ct'
1763 ctFlavour :: Ct -> CtFlavour
1764 ctFlavour = ctEvFlavour . ctEvidence
1765
1766 -- | Get the equality relation for the given 'Ct'
1767 ctEqRel :: Ct -> EqRel
1768 ctEqRel = ctEvEqRel . ctEvidence
1769
1770 instance Outputable Ct where
1771 ppr ct = ppr (cc_ev ct) <+> parens pp_sort
1772 where
1773 pp_sort = case ct of
1774 CTyEqCan {} -> text "CTyEqCan"
1775 CFunEqCan {} -> text "CFunEqCan"
1776 CNonCanonical {} -> text "CNonCanonical"
1777 CDictCan { cc_pend_sc = pend_sc }
1778 | pend_sc -> text "CDictCan(psc)"
1779 | otherwise -> text "CDictCan"
1780 CIrredEvCan {} -> text "CIrredEvCan"
1781 CHoleCan { cc_hole = hole } -> text "CHoleCan:" <+> ppr (holeOcc hole)
1782
1783 {-
1784 ************************************************************************
1785 * *
1786 Simple functions over evidence variables
1787 * *
1788 ************************************************************************
1789 -}
1790
1791 ---------------- Getting free tyvars -------------------------
1792
1793 -- | Returns free variables of constraints as a non-deterministic set
1794 tyCoVarsOfCt :: Ct -> TcTyCoVarSet
1795 tyCoVarsOfCt = fvVarSet . tyCoFVsOfCt
1796
1797 -- | Returns free variables of constraints as a deterministically ordered.
1798 -- list. See Note [Deterministic FV] in FV.
1799 tyCoVarsOfCtList :: Ct -> [TcTyCoVar]
1800 tyCoVarsOfCtList = fvVarList . tyCoFVsOfCt
1801
1802 -- | Returns free variables of constraints as a composable FV computation.
1803 -- See Note [Deterministic FV] in FV.
1804 tyCoFVsOfCt :: Ct -> FV
1805 tyCoFVsOfCt (CTyEqCan { cc_tyvar = tv, cc_rhs = xi })
1806 = tyCoFVsOfType xi `unionFV` FV.unitFV tv
1807 `unionFV` tyCoFVsOfType (tyVarKind tv)
1808 tyCoFVsOfCt (CFunEqCan { cc_tyargs = tys, cc_fsk = fsk })
1809 = tyCoFVsOfTypes tys `unionFV` FV.unitFV fsk
1810 `unionFV` tyCoFVsOfType (tyVarKind fsk)
1811 tyCoFVsOfCt (CDictCan { cc_tyargs = tys }) = tyCoFVsOfTypes tys
1812 tyCoFVsOfCt (CIrredEvCan { cc_ev = ev }) = tyCoFVsOfType (ctEvPred ev)
1813 tyCoFVsOfCt (CHoleCan { cc_ev = ev }) = tyCoFVsOfType (ctEvPred ev)
1814 tyCoFVsOfCt (CNonCanonical { cc_ev = ev }) = tyCoFVsOfType (ctEvPred ev)
1815
1816 -- | Returns free variables of a bag of constraints as a non-deterministic
1817 -- set. See Note [Deterministic FV] in FV.
1818 tyCoVarsOfCts :: Cts -> TcTyCoVarSet
1819 tyCoVarsOfCts = fvVarSet . tyCoFVsOfCts
1820
1821 -- | Returns free variables of a bag of constraints as a deterministically
1822 -- odered list. See Note [Deterministic FV] in FV.
1823 tyCoVarsOfCtsList :: Cts -> [TcTyCoVar]
1824 tyCoVarsOfCtsList = fvVarList . tyCoFVsOfCts
1825
1826 -- | Returns free variables of a bag of constraints as a composable FV
1827 -- computation. See Note [Deterministic FV] in FV.
1828 tyCoFVsOfCts :: Cts -> FV
1829 tyCoFVsOfCts = foldrBag (unionFV . tyCoFVsOfCt) emptyFV
1830
1831 -- | Returns free variables of WantedConstraints as a non-deterministic
1832 -- set. See Note [Deterministic FV] in FV.
1833 tyCoVarsOfWC :: WantedConstraints -> TyCoVarSet
1834 -- Only called on *zonked* things, hence no need to worry about flatten-skolems
1835 tyCoVarsOfWC = fvVarSet . tyCoFVsOfWC
1836
1837 -- | Returns free variables of WantedConstraints as a deterministically
1838 -- ordered list. See Note [Deterministic FV] in FV.
1839 tyCoVarsOfWCList :: WantedConstraints -> [TyCoVar]
1840 -- Only called on *zonked* things, hence no need to worry about flatten-skolems
1841 tyCoVarsOfWCList = fvVarList . tyCoFVsOfWC
1842
1843 -- | Returns free variables of WantedConstraints as a composable FV
1844 -- computation. See Note [Deterministic FV] in FV.
1845 tyCoFVsOfWC :: WantedConstraints -> FV
1846 -- Only called on *zonked* things, hence no need to worry about flatten-skolems
1847 tyCoFVsOfWC (WC { wc_simple = simple, wc_impl = implic, wc_insol = insol })
1848 = tyCoFVsOfCts simple `unionFV`
1849 tyCoFVsOfBag tyCoFVsOfImplic implic `unionFV`
1850 tyCoFVsOfCts insol
1851
1852 -- | Returns free variables of Implication as a composable FV computation.
1853 -- See Note [Deterministic FV] in FV.
1854 tyCoFVsOfImplic :: Implication -> FV
1855 -- Only called on *zonked* things, hence no need to worry about flatten-skolems
1856 tyCoFVsOfImplic (Implic { ic_skols = skols
1857 , ic_given = givens
1858 , ic_wanted = wanted })
1859 = FV.delFVs (mkVarSet skols `unionVarSet` mkVarSet givens)
1860 (tyCoFVsOfWC wanted `unionFV` tyCoFVsOfTypes (map evVarPred givens))
1861
1862 tyCoFVsOfBag :: (a -> FV) -> Bag a -> FV
1863 tyCoFVsOfBag tvs_of = foldrBag (unionFV . tvs_of) emptyFV
1864
1865 --------------------------
1866 dropDerivedSimples :: Cts -> Cts
1867 -- Drop all Derived constraints, but make [W] back into [WD],
1868 -- so that if we re-simplify these constraints we will get all
1869 -- the right derived constraints re-generated. Forgetting this
1870 -- step led to #12936
1871 dropDerivedSimples simples = mapMaybeBag dropDerivedCt simples
1872
1873 dropDerivedCt :: Ct -> Maybe Ct
1874 dropDerivedCt ct
1875 = case ctEvFlavour ev of
1876 Wanted WOnly -> Just (ct' { cc_ev = ev_wd })
1877 Wanted _ -> Just ct'
1878 _ -> ASSERT( isDerivedCt ct ) Nothing
1879 -- simples are all Wanted or Derived
1880 where
1881 ev = ctEvidence ct
1882 ev_wd = ev { ctev_nosh = WDeriv }
1883 ct' = setPendingScDict ct -- See Note [Resetting cc_pend_sc]
1884
1885 {- Note [Resetting cc_pend_sc]
1886 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1887 When we discard Derived constraints, in dropDerivedSimples, we must
1888 set the cc_pend_sc flag to True, so that if we re-process this
1889 CDictCan we will re-generate its derived superclasses. Otherwise
1890 we might miss some fundeps. Trac #13662 showed this up.
1891
1892 See Note [The superclass story] in TcCanonical.
1893 -}
1894
1895
1896 dropDerivedInsols :: Cts -> Cts
1897 -- See Note [Dropping derived constraints]
1898 dropDerivedInsols insols
1899 = filterBag (not . isDroppableDerivedCt) insols
1900 -- insols can include Given
1901
1902 isDroppableDerivedCt :: Ct -> Bool
1903 isDroppableDerivedCt ct
1904 | isDerivedCt ct = isDroppableDerivedLoc (ctLoc ct)
1905 | otherwise = False
1906
1907 isDroppableDerivedLoc :: CtLoc -> Bool
1908 -- See Note [Dropping derived constraints]
1909 isDroppableDerivedLoc loc
1910 = case ctLocOrigin loc of
1911 HoleOrigin {} -> False
1912 KindEqOrigin {} -> False
1913 GivenOrigin {} -> False
1914
1915 -- See Note [Dropping derived constraints]
1916 -- For fundeps, drop wanted/wanted interactions
1917 FunDepOrigin2 {} -> False
1918 FunDepOrigin1 _ loc1 _ loc2
1919 | isGivenLoc loc1 || isGivenLoc loc2 -> False
1920 | otherwise -> True
1921 _ -> True
1922
1923 arisesFromGivens :: Ct -> Bool
1924 arisesFromGivens ct
1925 = case ctEvidence ct of
1926 CtGiven {} -> True
1927 CtWanted {} -> False
1928 CtDerived { ctev_loc = loc } -> isGivenLoc loc
1929
1930 isGivenLoc :: CtLoc -> Bool
1931 isGivenLoc loc = isGivenOrigin (ctLocOrigin loc)
1932
1933 isGivenOrigin :: CtOrigin -> Bool
1934 isGivenOrigin (GivenOrigin {}) = True
1935 isGivenOrigin (FunDepOrigin1 _ l1 _ l2) = isGivenLoc l1 && isGivenLoc l2
1936 isGivenOrigin (FunDepOrigin2 _ o1 _ _) = isGivenOrigin o1
1937 isGivenOrigin _ = False
1938
1939 {- Note [Dropping derived constraints]
1940 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1941 In general we discard derived constraints at the end of constraint solving;
1942 see dropDerivedWC. For example
1943
1944 * If we have an unsolved [W] (Ord a), we don't want to complain about
1945 an unsolved [D] (Eq a) as well.
1946
1947 * If we have [W] a ~ Int, [W] a ~ Bool, improvement will generate
1948 [D] Int ~ Bool, and we don't want to report that because it's incomprehensible.
1949 That is why we don't rewrite wanteds with wanteds!
1950
1951 But (tiresomely) we do keep *some* Derived insolubles:
1952
1953 * Type holes are derived constraints, because they have no evidence
1954 and we want to keep them, so we get the error report
1955
1956 * Insoluble derived equalities (e.g. [D] Int ~ Bool) may arise from
1957 functional dependency interactions:
1958 - Given or Wanted interacting with an instance declaration (FunDepOrigin2)
1959 - Given/Given interactions (FunDepOrigin1); this reflects unreachable code
1960 - Given/Wanted interactions (FunDepOrigin1); see Trac #9612
1961
1962 But for Wanted/Wanted interactions we do /not/ want to report an
1963 error (Trac #13506). Consider [W] C Int Int, [W] C Int Bool, with
1964 a fundep on class C. We don't want to report an insoluble Int~Bool;
1965 c.f. "wanteds do not rewrite wanteds".
1966
1967 Moreover, we keep *all* derived insolubles under some circumstances:
1968
1969 * They are looked at by simplifyInfer, to decide whether to
1970 generalise. Example: [W] a ~ Int, [W] a ~ Bool
1971 We get [D] Int ~ Bool, and indeed the constraints are insoluble,
1972 and we want simplifyInfer to see that, even though we don't
1973 ultimately want to generate an (inexplicable) error message from it
1974
1975 To distinguish these cases we use the CtOrigin.
1976
1977
1978 ************************************************************************
1979 * *
1980 CtEvidence
1981 The "flavor" of a canonical constraint
1982 * *
1983 ************************************************************************
1984 -}
1985
1986 isWantedCt :: Ct -> Bool
1987 isWantedCt = isWanted . cc_ev
1988
1989 isGivenCt :: Ct -> Bool
1990 isGivenCt = isGiven . cc_ev
1991
1992 isDerivedCt :: Ct -> Bool
1993 isDerivedCt = isDerived . cc_ev
1994
1995 isCTyEqCan :: Ct -> Bool
1996 isCTyEqCan (CTyEqCan {}) = True
1997 isCTyEqCan (CFunEqCan {}) = False
1998 isCTyEqCan _ = False
1999
2000 isCDictCan_Maybe :: Ct -> Maybe Class
2001 isCDictCan_Maybe (CDictCan {cc_class = cls }) = Just cls
2002 isCDictCan_Maybe _ = Nothing
2003
2004 isCIrredEvCan :: Ct -> Bool
2005 isCIrredEvCan (CIrredEvCan {}) = True
2006 isCIrredEvCan _ = False
2007
2008 isCFunEqCan_maybe :: Ct -> Maybe (TyCon, [Type])
2009 isCFunEqCan_maybe (CFunEqCan { cc_fun = tc, cc_tyargs = xis }) = Just (tc, xis)
2010 isCFunEqCan_maybe _ = Nothing
2011
2012 isCFunEqCan :: Ct -> Bool
2013 isCFunEqCan (CFunEqCan {}) = True
2014 isCFunEqCan _ = False
2015
2016 isCNonCanonical :: Ct -> Bool
2017 isCNonCanonical (CNonCanonical {}) = True
2018 isCNonCanonical _ = False
2019
2020 isHoleCt:: Ct -> Bool
2021 isHoleCt (CHoleCan {}) = True
2022 isHoleCt _ = False
2023
2024 isOutOfScopeCt :: Ct -> Bool
2025 -- We treat expression holes representing out-of-scope variables a bit
2026 -- differently when it comes to error reporting
2027 isOutOfScopeCt (CHoleCan { cc_hole = ExprHole (OutOfScope {}) }) = True
2028 isOutOfScopeCt _ = False
2029
2030 isExprHoleCt :: Ct -> Bool
2031 isExprHoleCt (CHoleCan { cc_hole = ExprHole {} }) = True
2032 isExprHoleCt _ = False
2033
2034 isTypeHoleCt :: Ct -> Bool
2035 isTypeHoleCt (CHoleCan { cc_hole = TypeHole {} }) = True
2036 isTypeHoleCt _ = False
2037
2038
2039 {- Note [Custom type errors in constraints]
2040 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2041
2042 When GHC reports a type-error about an unsolved-constraint, we check
2043 to see if the constraint contains any custom-type errors, and if so
2044 we report them. Here are some examples of constraints containing type
2045 errors:
2046
2047 TypeError msg -- The actual constraint is a type error
2048
2049 TypError msg ~ Int -- Some type was supposed to be Int, but ended up
2050 -- being a type error instead
2051
2052 Eq (TypeError msg) -- A class constraint is stuck due to a type error
2053
2054 F (TypeError msg) ~ a -- A type function failed to evaluate due to a type err
2055
2056 It is also possible to have constraints where the type error is nested deeper,
2057 for example see #11990, and also:
2058
2059 Eq (F (TypeError msg)) -- Here the type error is nested under a type-function
2060 -- call, which failed to evaluate because of it,
2061 -- and so the `Eq` constraint was unsolved.
2062 -- This may happen when one function calls another
2063 -- and the called function produced a custom type error.
2064 -}
2065
2066 -- | A constraint is considered to be a custom type error, if it contains
2067 -- custom type errors anywhere in it.
2068 -- See Note [Custom type errors in constraints]
2069 getUserTypeErrorMsg :: Ct -> Maybe Type
2070 getUserTypeErrorMsg ct = findUserTypeError (ctPred ct)
2071 where
2072 findUserTypeError t = msum ( userTypeError_maybe t
2073 : map findUserTypeError (subTys t)
2074 )
2075
2076 subTys t = case splitAppTys t of
2077 (t,[]) ->
2078 case splitTyConApp_maybe t of
2079 Nothing -> []
2080 Just (_,ts) -> ts
2081 (t,ts) -> t : ts
2082
2083
2084
2085
2086 isUserTypeErrorCt :: Ct -> Bool
2087 isUserTypeErrorCt ct = case getUserTypeErrorMsg ct of
2088 Just _ -> True
2089 _ -> False
2090
2091 isPendingScDict :: Ct -> Maybe Ct
2092 -- Says whether cc_pend_sc is True, AND if so flips the flag
2093 isPendingScDict ct@(CDictCan { cc_pend_sc = True })
2094 = Just (ct { cc_pend_sc = False })
2095 isPendingScDict _ = Nothing
2096
2097 setPendingScDict :: Ct -> Ct
2098 -- Set the cc_pend_sc flag to True
2099 setPendingScDict ct@(CDictCan { cc_pend_sc = False })
2100 = ct { cc_pend_sc = True }
2101 setPendingScDict ct = ct
2102
2103 superClassesMightHelp :: Ct -> Bool
2104 -- ^ True if taking superclasses of givens, or of wanteds (to perhaps
2105 -- expose more equalities or functional dependencies) might help to
2106 -- solve this constraint. See Note [When superclasses help]
2107 superClassesMightHelp ct
2108 = isWantedCt ct && not (is_ip ct)
2109 where
2110 is_ip (CDictCan { cc_class = cls }) = isIPClass cls
2111 is_ip _ = False
2112
2113 {- Note [When superclasses help]
2114 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2115 First read Note [The superclass story] in TcCanonical.
2116
2117 We expand superclasses and iterate only if there is at unsolved wanted
2118 for which expansion of superclasses (e.g. from given constraints)
2119 might actually help. The function superClassesMightHelp tells if
2120 doing this superclass expansion might help solve this constraint.
2121 Note that
2122
2123 * Superclasses help only for Wanted constraints. Derived constraints
2124 are not really "unsolved" and we certainly don't want them to
2125 trigger superclass expansion. This was a good part of the loop
2126 in Trac #11523
2127
2128 * Even for Wanted constraints, we say "no" for implicit parameters.
2129 we have [W] ?x::ty, expanding superclasses won't help:
2130 - Superclasses can't be implicit parameters
2131 - If we have a [G] ?x:ty2, then we'll have another unsolved
2132 [D] ty ~ ty2 (from the functional dependency)
2133 which will trigger superclass expansion.
2134
2135 It's a bit of a special case, but it's easy to do. The runtime cost
2136 is low because the unsolved set is usually empty anyway (errors
2137 aside), and the first non-imlicit-parameter will terminate the search.
2138
2139 The special case is worth it (Trac #11480, comment:2) because it
2140 applies to CallStack constraints, which aren't type errors. If we have
2141 f :: (C a) => blah
2142 f x = ...undefined...
2143 we'll get a CallStack constraint. If that's the only unsolved
2144 constraint it'll eventually be solved by defaulting. So we don't
2145 want to emit warnings about hitting the simplifier's iteration
2146 limit. A CallStack constraint really isn't an unsolved
2147 constraint; it can always be solved by defaulting.
2148 -}
2149
2150 singleCt :: Ct -> Cts
2151 singleCt = unitBag
2152
2153 andCts :: Cts -> Cts -> Cts
2154 andCts = unionBags
2155
2156 listToCts :: [Ct] -> Cts
2157 listToCts = listToBag
2158
2159 ctsElts :: Cts -> [Ct]
2160 ctsElts = bagToList
2161
2162 consCts :: Ct -> Cts -> Cts
2163 consCts = consBag
2164
2165 snocCts :: Cts -> Ct -> Cts
2166 snocCts = snocBag
2167
2168 extendCtsList :: Cts -> [Ct] -> Cts
2169 extendCtsList cts xs | null xs = cts
2170 | otherwise = cts `unionBags` listToBag xs
2171
2172 andManyCts :: [Cts] -> Cts
2173 andManyCts = unionManyBags
2174
2175 emptyCts :: Cts
2176 emptyCts = emptyBag
2177
2178 isEmptyCts :: Cts -> Bool
2179 isEmptyCts = isEmptyBag
2180
2181 pprCts :: Cts -> SDoc
2182 pprCts cts = vcat (map ppr (bagToList cts))
2183
2184 {-
2185 ************************************************************************
2186 * *
2187 Wanted constraints
2188 These are forced to be in TcRnTypes because
2189 TcLclEnv mentions WantedConstraints
2190 WantedConstraint mentions CtLoc
2191 CtLoc mentions ErrCtxt
2192 ErrCtxt mentions TcM
2193 * *
2194 v%************************************************************************
2195 -}
2196
2197 data WantedConstraints
2198 = WC { wc_simple :: Cts -- Unsolved constraints, all wanted
2199 , wc_impl :: Bag Implication
2200 , wc_insol :: Cts -- Insoluble constraints, can be
2201 -- wanted, given, or derived
2202 -- See Note [Insoluble constraints]
2203 }
2204
2205 emptyWC :: WantedConstraints
2206 emptyWC = WC { wc_simple = emptyBag, wc_impl = emptyBag, wc_insol = emptyBag }
2207
2208 mkSimpleWC :: [CtEvidence] -> WantedConstraints
2209 mkSimpleWC cts
2210 = WC { wc_simple = listToBag (map mkNonCanonical cts)
2211 , wc_impl = emptyBag
2212 , wc_insol = emptyBag }
2213
2214 mkImplicWC :: Bag Implication -> WantedConstraints
2215 mkImplicWC implic
2216 = WC { wc_simple = emptyBag, wc_impl = implic, wc_insol = emptyBag }
2217
2218 isEmptyWC :: WantedConstraints -> Bool
2219 isEmptyWC (WC { wc_simple = f, wc_impl = i, wc_insol = n })
2220 = isEmptyBag f && isEmptyBag i && isEmptyBag n
2221
2222 andWC :: WantedConstraints -> WantedConstraints -> WantedConstraints
2223 andWC (WC { wc_simple = f1, wc_impl = i1, wc_insol = n1 })
2224 (WC { wc_simple = f2, wc_impl = i2, wc_insol = n2 })
2225 = WC { wc_simple = f1 `unionBags` f2
2226 , wc_impl = i1 `unionBags` i2
2227 , wc_insol = n1 `unionBags` n2 }
2228
2229 unionsWC :: [WantedConstraints] -> WantedConstraints
2230 unionsWC = foldr andWC emptyWC
2231
2232 addSimples :: WantedConstraints -> Bag Ct -> WantedConstraints
2233 addSimples wc cts
2234 = wc { wc_simple = wc_simple wc `unionBags` cts }
2235 -- Consider: Put the new constraints at the front, so they get solved first
2236
2237 addImplics :: WantedConstraints -> Bag Implication -> WantedConstraints
2238 addImplics wc implic = wc { wc_impl = wc_impl wc `unionBags` implic }
2239
2240 addInsols :: WantedConstraints -> Bag Ct -> WantedConstraints
2241 addInsols wc cts
2242 = wc { wc_insol = wc_insol wc `unionBags` cts }
2243
2244 getInsolubles :: WantedConstraints -> Cts
2245 getInsolubles = wc_insol
2246
2247 insolublesOnly :: WantedConstraints -> WantedConstraints
2248 -- Keep only the insolubles
2249 insolublesOnly wc = wc { wc_simple = emptyBag, wc_impl = emptyBag }
2250
2251 dropDerivedWC :: WantedConstraints -> WantedConstraints
2252 -- See Note [Dropping derived constraints]
2253 dropDerivedWC wc@(WC { wc_simple = simples, wc_insol = insols })
2254 = wc { wc_simple = dropDerivedSimples simples
2255 , wc_insol = dropDerivedInsols insols }
2256 -- The wc_impl implications are already (recursively) filtered
2257
2258 isSolvedStatus :: ImplicStatus -> Bool
2259 isSolvedStatus (IC_Solved {}) = True
2260 isSolvedStatus _ = False
2261
2262 isInsolubleStatus :: ImplicStatus -> Bool
2263 isInsolubleStatus IC_Insoluble = True
2264 isInsolubleStatus _ = False
2265
2266 insolubleImplic :: Implication -> Bool
2267 insolubleImplic ic = isInsolubleStatus (ic_status ic)
2268
2269 insolubleWC :: WantedConstraints -> Bool
2270 insolubleWC (WC { wc_impl = implics, wc_insol = insols })
2271 = anyBag trulyInsoluble insols
2272 || anyBag insolubleImplic implics
2273
2274 trulyInsoluble :: Ct -> Bool
2275 -- Constraints in the wc_insol set which ARE NOT
2276 -- treated as truly insoluble:
2277 -- a) type holes, arising from PartialTypeSignatures,
2278 -- b) "true" expression holes arising from TypedHoles
2279 --
2280 -- An "expression hole" or "type hole" constraint isn't really an error
2281 -- at all; it's a report saying "_ :: Int" here. But an out-of-scope
2282 -- variable masquerading as expression holes IS treated as truly
2283 -- insoluble, so that it trumps other errors during error reporting.
2284 -- Yuk!
2285 trulyInsoluble insol
2286 | isHoleCt insol = isOutOfScopeCt insol
2287 | otherwise = True
2288
2289 instance Outputable WantedConstraints where
2290 ppr (WC {wc_simple = s, wc_impl = i, wc_insol = n})
2291 = text "WC" <+> braces (vcat
2292 [ ppr_bag (text "wc_simple") s
2293 , ppr_bag (text "wc_insol") n
2294 , ppr_bag (text "wc_impl") i ])
2295
2296 ppr_bag :: Outputable a => SDoc -> Bag a -> SDoc
2297 ppr_bag doc bag
2298 | isEmptyBag bag = empty
2299 | otherwise = hang (doc <+> equals)
2300 2 (foldrBag (($$) . ppr) empty bag)
2301
2302 {-
2303 ************************************************************************
2304 * *
2305 Implication constraints
2306 * *
2307 ************************************************************************
2308 -}
2309
2310 data Implication
2311 = Implic {
2312 ic_tclvl :: TcLevel, -- TcLevel of unification variables
2313 -- allocated /inside/ this implication
2314
2315 ic_skols :: [TcTyVar], -- Introduced skolems
2316 ic_info :: SkolemInfo, -- See Note [Skolems in an implication]
2317 -- See Note [Shadowing in a constraint]
2318
2319 ic_given :: [EvVar], -- Given evidence variables
2320 -- (order does not matter)
2321 -- See Invariant (GivenInv) in TcType
2322
2323 ic_no_eqs :: Bool, -- True <=> ic_givens have no equalities, for sure
2324 -- False <=> ic_givens might have equalities
2325
2326 ic_env :: TcLclEnv, -- Gives the source location and error context
2327 -- for the implication, and hence for all the
2328 -- given evidence variables
2329
2330 ic_wanted :: WantedConstraints, -- The wanted
2331
2332 ic_binds :: EvBindsVar, -- Points to the place to fill in the
2333 -- abstraction and bindings.
2334
2335 ic_needed :: VarSet, -- Union of the ics_need fields of any /discarded/
2336 -- solved implications in ic_wanted
2337
2338 ic_status :: ImplicStatus
2339 }
2340
2341 data ImplicStatus
2342 = IC_Solved -- All wanteds in the tree are solved, all the way down
2343 { ics_need :: VarSet -- Evidence variables bound further out,
2344 -- but needed by this solved implication
2345 , ics_dead :: [EvVar] } -- Subset of ic_given that are not needed
2346 -- See Note [Tracking redundant constraints] in TcSimplify
2347
2348 | IC_Insoluble -- At least one insoluble constraint in the tree
2349
2350 | IC_Unsolved -- Neither of the above; might go either way
2351
2352 instance Outputable Implication where
2353 ppr (Implic { ic_tclvl = tclvl, ic_skols = skols
2354 , ic_given = given, ic_no_eqs = no_eqs
2355 , ic_wanted = wanted, ic_status = status
2356 , ic_binds = binds, ic_needed = needed , ic_info = info })
2357 = hang (text "Implic" <+> lbrace)
2358 2 (sep [ text "TcLevel =" <+> ppr tclvl
2359 , text "Skolems =" <+> pprTyVars skols
2360 , text "No-eqs =" <+> ppr no_eqs
2361 , text "Status =" <+> ppr status
2362 , hang (text "Given =") 2 (pprEvVars given)
2363 , hang (text "Wanted =") 2 (ppr wanted)
2364 , text "Binds =" <+> ppr binds
2365 , text "Needed =" <+> ppr needed
2366 , pprSkolInfo info ] <+> rbrace)
2367
2368 instance Outputable ImplicStatus where
2369 ppr IC_Insoluble = text "Insoluble"
2370 ppr IC_Unsolved = text "Unsolved"
2371 ppr (IC_Solved { ics_need = vs, ics_dead = dead })
2372 = text "Solved"
2373 <+> (braces $ vcat [ text "Dead givens =" <+> ppr dead
2374 , text "Needed =" <+> ppr vs ])
2375
2376 {-
2377 Note [Needed evidence variables]
2378 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2379 Th ic_need_evs field holds the free vars of ic_binds, and all the
2380 ic_binds in nested implications.
2381
2382 * Main purpose: if one of the ic_givens is not mentioned in here, it
2383 is redundant.
2384
2385 * solveImplication may drop an implication altogether if it has no
2386 remaining 'wanteds'. But we still track the free vars of its
2387 evidence binds, even though it has now disappeared.
2388
2389 Note [Shadowing in a constraint]
2390 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2391 We assume NO SHADOWING in a constraint. Specifically
2392 * The unification variables are all implicitly quantified at top
2393 level, and are all unique
2394 * The skolem variables bound in ic_skols are all freah when the
2395 implication is created.
2396 So we can safely substitute. For example, if we have
2397 forall a. a~Int => ...(forall b. ...a...)...
2398 we can push the (a~Int) constraint inwards in the "givens" without
2399 worrying that 'b' might clash.
2400
2401 Note [Skolems in an implication]
2402 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2403 The skolems in an implication are not there to perform a skolem escape
2404 check. That happens because all the environment variables are in the
2405 untouchables, and therefore cannot be unified with anything at all,
2406 let alone the skolems.
2407
2408 Instead, ic_skols is used only when considering floating a constraint
2409 outside the implication in TcSimplify.floatEqualities or
2410 TcSimplify.approximateImplications
2411
2412 Note [Insoluble constraints]
2413 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2414 Some of the errors that we get during canonicalization are best
2415 reported when all constraints have been simplified as much as
2416 possible. For instance, assume that during simplification the
2417 following constraints arise:
2418
2419 [Wanted] F alpha ~ uf1
2420 [Wanted] beta ~ uf1 beta
2421
2422 When canonicalizing the wanted (beta ~ uf1 beta), if we eagerly fail
2423 we will simply see a message:
2424 'Can't construct the infinite type beta ~ uf1 beta'
2425 and the user has no idea what the uf1 variable is.
2426
2427 Instead our plan is that we will NOT fail immediately, but:
2428 (1) Record the "frozen" error in the ic_insols field
2429 (2) Isolate the offending constraint from the rest of the inerts
2430 (3) Keep on simplifying/canonicalizing
2431
2432 At the end, we will hopefully have substituted uf1 := F alpha, and we
2433 will be able to report a more informative error:
2434 'Can't construct the infinite type beta ~ F alpha beta'
2435
2436 Insoluble constraints *do* include Derived constraints. For example,
2437 a functional dependency might give rise to [D] Int ~ Bool, and we must
2438 report that. If insolubles did not contain Deriveds, reportErrors would
2439 never see it.
2440
2441
2442 ************************************************************************
2443 * *
2444 Pretty printing
2445 * *
2446 ************************************************************************
2447 -}
2448
2449 pprEvVars :: [EvVar] -> SDoc -- Print with their types
2450 pprEvVars ev_vars = vcat (map pprEvVarWithType ev_vars)
2451
2452 pprEvVarTheta :: [EvVar] -> SDoc
2453 pprEvVarTheta ev_vars = pprTheta (map evVarPred ev_vars)
2454
2455 pprEvVarWithType :: EvVar -> SDoc
2456 pprEvVarWithType v = ppr v <+> dcolon <+> pprType (evVarPred v)
2457
2458 {-
2459 ************************************************************************
2460 * *
2461 CtEvidence
2462 * *
2463 ************************************************************************
2464
2465 Note [Evidence field of CtEvidence]
2466 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2467 During constraint solving we never look at the type of ctev_evar/ctev_dest;
2468 instead we look at the ctev_pred field. The evtm/evar field
2469 may be un-zonked.
2470
2471 Note [Bind new Givens immediately]
2472 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2473 For Givens we make new EvVars and bind them immediately. Two main reasons:
2474 * Gain sharing. E.g. suppose we start with g :: C a b, where
2475 class D a => C a b
2476 class (E a, F a) => D a
2477 If we generate all g's superclasses as separate EvTerms we might
2478 get selD1 (selC1 g) :: E a
2479 selD2 (selC1 g) :: F a
2480 selC1 g :: D a
2481 which we could do more economically as:
2482 g1 :: D a = selC1 g
2483 g2 :: E a = selD1 g1
2484 g3 :: F a = selD2 g1
2485
2486 * For *coercion* evidence we *must* bind each given:
2487 class (a~b) => C a b where ....
2488 f :: C a b => ....
2489 Then in f's Givens we have g:(C a b) and the superclass sc(g,0):a~b.
2490 But that superclass selector can't (yet) appear in a coercion
2491 (see evTermCoercion), so the easy thing is to bind it to an Id.
2492
2493 So a Given has EvVar inside it rather than (as previously) an EvTerm.
2494
2495 Note [Given in ctEvCoercion]
2496 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2497 When retrieving the evidence from a Given equality, we update the type of the EvVar
2498 from the ctev_pred field. In Note [Evidence field of CtEvidence], we claim that
2499 the type of the evidence is never looked at -- but this isn't true in the case of
2500 a coercion that is used in a type. (See the comments in Note [Flattening] in TcFlatten
2501 about the FTRNotFollowed case of flattenTyVar.) So, right here where we are retrieving
2502 the coercion from a Given, we update the type to make sure it's zonked.
2503
2504 -}
2505
2506 -- | A place for type-checking evidence to go after it is generated.
2507 -- Wanted equalities are always HoleDest; other wanteds are always
2508 -- EvVarDest.
2509 data TcEvDest
2510 = EvVarDest EvVar -- ^ bind this var to the evidence
2511 -- EvVarDest is always used for non-type-equalities
2512 -- e.g. class constraints
2513
2514 | HoleDest CoercionHole -- ^ fill in this hole with the evidence
2515 -- HoleDest is always used for type-equalities
2516 -- See Note [Coercion holes] in TyCoRep
2517
2518 data CtEvidence
2519 = CtGiven -- Truly given, not depending on subgoals
2520 { ctev_pred :: TcPredType -- See Note [Ct/evidence invariant]
2521 , ctev_evar :: EvVar -- See Note [Evidence field of CtEvidence]
2522 , ctev_loc :: CtLoc }
2523
2524
2525 | CtWanted -- Wanted goal
2526 { ctev_pred :: TcPredType -- See Note [Ct/evidence invariant]
2527 , ctev_dest :: TcEvDest
2528 , ctev_nosh :: ShadowInfo -- See Note [Constraint flavours]
2529 , ctev_loc :: CtLoc }
2530
2531 | CtDerived -- A goal that we don't really have to solve and can't
2532 -- immediately rewrite anything other than a derived
2533 -- (there's no evidence!) but if we do manage to solve
2534 -- it may help in solving other goals.
2535 { ctev_pred :: TcPredType
2536 , ctev_loc :: CtLoc }
2537
2538 ctEvPred :: CtEvidence -> TcPredType
2539 -- The predicate of a flavor
2540 ctEvPred = ctev_pred
2541
2542 ctEvLoc :: CtEvidence -> CtLoc
2543 ctEvLoc = ctev_loc
2544
2545 ctEvOrigin :: CtEvidence -> CtOrigin
2546 ctEvOrigin = ctLocOrigin . ctEvLoc
2547
2548 -- | Get the equality relation relevant for a 'CtEvidence'
2549 ctEvEqRel :: CtEvidence -> EqRel
2550 ctEvEqRel = predTypeEqRel . ctEvPred
2551
2552 -- | Get the role relevant for a 'CtEvidence'
2553 ctEvRole :: CtEvidence -> Role
2554 ctEvRole = eqRelRole . ctEvEqRel
2555
2556 ctEvTerm :: CtEvidence -> EvTerm
2557 ctEvTerm ev@(CtWanted { ctev_dest = HoleDest _ }) = EvCoercion $ ctEvCoercion ev
2558 ctEvTerm ev = EvId (ctEvId ev)
2559
2560 -- Always returns a coercion whose type is precisely ctev_pred of the CtEvidence.
2561 -- See also Note [Given in ctEvCoercion]
2562 ctEvCoercion :: CtEvidence -> Coercion
2563 ctEvCoercion (CtGiven { ctev_pred = pred_ty, ctev_evar = ev_id })
2564 = mkTcCoVarCo (setVarType ev_id pred_ty) -- See Note [Given in ctEvCoercion]
2565 ctEvCoercion (CtWanted { ctev_dest = dest, ctev_pred = pred })
2566 | HoleDest hole <- dest
2567 , Just (role, ty1, ty2) <- getEqPredTys_maybe pred
2568 = -- ctEvCoercion is only called on type equalities
2569 -- and they always have HoleDests
2570 mkHoleCo hole role ty1 ty2
2571 ctEvCoercion ev
2572 = pprPanic "ctEvCoercion" (ppr ev)
2573
2574 ctEvId :: CtEvidence -> TcId
2575 ctEvId (CtWanted { ctev_dest = EvVarDest ev }) = ev
2576 ctEvId (CtGiven { ctev_evar = ev }) = ev
2577 ctEvId ctev = pprPanic "ctEvId:" (ppr ctev)
2578
2579 instance Outputable TcEvDest where
2580 ppr (HoleDest h) = text "hole" <> ppr h
2581 ppr (EvVarDest ev) = ppr ev
2582
2583 instance Outputable CtEvidence where
2584 ppr ev = ppr (ctEvFlavour ev)
2585 <+> pp_ev
2586 <+> braces (ppr (ctl_depth (ctEvLoc ev))) <> dcolon
2587 -- Show the sub-goal depth too
2588 <+> ppr (ctEvPred ev)
2589 where
2590 pp_ev = case ev of
2591 CtGiven { ctev_evar = v } -> ppr v
2592 CtWanted {ctev_dest = d } -> ppr d
2593 CtDerived {} -> text "_"
2594
2595 isWanted :: CtEvidence -> Bool
2596 isWanted (CtWanted {}) = True
2597 isWanted _ = False
2598
2599 isGiven :: CtEvidence -> Bool
2600 isGiven (CtGiven {}) = True
2601 isGiven _ = False
2602
2603 isDerived :: CtEvidence -> Bool
2604 isDerived (CtDerived {}) = True
2605 isDerived _ = False
2606
2607 {-
2608 %************************************************************************
2609 %* *
2610 CtFlavour
2611 %* *
2612 %************************************************************************
2613
2614 Note [Constraint flavours]
2615 ~~~~~~~~~~~~~~~~~~~~~~~~~~
2616 Constraints come in four flavours:
2617
2618 * [G] Given: we have evidence
2619
2620 * [W] Wanted WOnly: we want evidence
2621
2622 * [D] Derived: any solution must satisfy this constraint, but
2623 we don't need evidence for it. Examples include:
2624 - superclasses of [W] class constraints
2625 - equalities arising from functional dependencies
2626 or injectivity
2627
2628 * [WD] Wanted WDeriv: a single constraint that represents
2629 both [W] and [D]
2630 We keep them paired as one both for efficiency, and because
2631 when we have a finite map F tys -> CFunEqCan, it's inconvenient
2632 to have two CFunEqCans in the range
2633
2634 The ctev_nosh field of a Wanted distinguishes between [W] and [WD]
2635
2636 Wanted constraints are born as [WD], but are split into [W] and its
2637 "shadow" [D] in TcSMonad.maybeEmitShadow.
2638
2639 See Note [The improvement story and derived shadows] in TcSMonad
2640 -}
2641
2642 data CtFlavour -- See Note [Constraint flavours]
2643 = Given
2644 | Wanted ShadowInfo
2645 | Derived
2646 deriving Eq
2647
2648 data ShadowInfo
2649 = WDeriv -- [WD] This Wanted constraint has no Derived shadow,
2650 -- so it behaves like a pair of a Wanted and a Derived
2651 | WOnly -- [W] It has a separate derived shadow
2652 -- See Note [Derived shadows]
2653 deriving( Eq )
2654
2655 isGivenOrWDeriv :: CtFlavour -> Bool
2656 isGivenOrWDeriv Given = True
2657 isGivenOrWDeriv (Wanted WDeriv) = True
2658 isGivenOrWDeriv _ = False
2659
2660 instance Outputable CtFlavour where
2661 ppr Given = text "[G]"
2662 ppr (Wanted WDeriv) = text "[WD]"
2663 ppr (Wanted WOnly) = text "[W]"
2664 ppr Derived = text "[D]"
2665
2666 ctEvFlavour :: CtEvidence -> CtFlavour
2667 ctEvFlavour (CtWanted { ctev_nosh = nosh }) = Wanted nosh
2668 ctEvFlavour (CtGiven {}) = Given
2669 ctEvFlavour (CtDerived {}) = Derived
2670
2671 -- | Whether or not one 'Ct' can rewrite another is determined by its
2672 -- flavour and its equality relation. See also
2673 -- Note [Flavours with roles] in TcSMonad
2674 type CtFlavourRole = (CtFlavour, EqRel)
2675
2676 -- | Extract the flavour, role, and boxity from a 'CtEvidence'
2677 ctEvFlavourRole :: CtEvidence -> CtFlavourRole
2678 ctEvFlavourRole ev = (ctEvFlavour ev, ctEvEqRel ev)
2679
2680 -- | Extract the flavour, role, and boxity from a 'Ct'
2681 ctFlavourRole :: Ct -> CtFlavourRole
2682 ctFlavourRole = ctEvFlavourRole . cc_ev
2683
2684 {- Note [eqCanRewrite]
2685 ~~~~~~~~~~~~~~~~~~~~~~
2686 (eqCanRewrite ct1 ct2) holds if the constraint ct1 (a CTyEqCan of form
2687 tv ~ ty) can be used to rewrite ct2. It must satisfy the properties of
2688 a can-rewrite relation, see Definition [Can-rewrite relation] in
2689 TcSMonad.
2690
2691 With the solver handling Coercible constraints like equality constraints,
2692 the rewrite conditions must take role into account, never allowing
2693 a representational equality to rewrite a nominal one.
2694
2695 Note [Wanteds do not rewrite Wanteds]
2696 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2697 We don't allow Wanteds to rewrite Wanteds, because that can give rise
2698 to very confusing type error messages. A good example is Trac #8450.
2699 Here's another
2700 f :: a -> Bool
2701 f x = ( [x,'c'], [x,True] ) `seq` True
2702 Here we get
2703 [W] a ~ Char
2704 [W] a ~ Bool
2705 but we do not want to complain about Bool ~ Char!
2706
2707 Note [Deriveds do rewrite Deriveds]
2708 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2709 However we DO allow Deriveds to rewrite Deriveds, because that's how
2710 improvement works; see Note [The improvement story] in TcInteract.
2711
2712 However, for now at least I'm only letting (Derived,NomEq) rewrite
2713 (Derived,NomEq) and not doing anything for ReprEq. If we have
2714 eqCanRewriteFR (Derived, NomEq) (Derived, _) = True
2715 then we lose property R2 of Definition [Can-rewrite relation]
2716 in TcSMonad
2717 R2. If f1 >= f, and f2 >= f,
2718 then either f1 >= f2 or f2 >= f1
2719 Consider f1 = (Given, ReprEq)
2720 f2 = (Derived, NomEq)
2721 f = (Derived, ReprEq)
2722
2723 I thought maybe we could never get Derived ReprEq constraints, but
2724 we can; straight from the Wanteds during improvement. And from a Derived
2725 ReprEq we could conceivably get a Derived NomEq improvement (by decomposing
2726 a type constructor with Nomninal role), and hence unify.
2727 -}
2728
2729 eqCanRewriteFR :: CtFlavourRole -> CtFlavourRole -> Bool
2730 -- Can fr1 actually rewrite fr2?
2731 -- Very important function!
2732 -- See Note [eqCanRewrite]
2733 -- See Note [Wanteds do not rewrite Wanteds]
2734 -- See Note [Deriveds do rewrite Deriveds]
2735 eqCanRewriteFR (Given, NomEq) (_, _) = True
2736 eqCanRewriteFR (Given, ReprEq) (_, ReprEq) = True
2737 eqCanRewriteFR (Wanted WDeriv, NomEq) (Derived, NomEq) = True
2738 eqCanRewriteFR (Derived, NomEq) (Derived, NomEq) = True
2739 eqCanRewriteFR _ _ = False
2740
2741 eqMayRewriteFR :: CtFlavourRole -> CtFlavourRole -> Bool
2742 -- Is it /possible/ that fr1 can rewrite fr2?
2743 -- This is used when deciding which inerts to kick out,
2744 -- at which time a [WD] inert may be split into [W] and [D]
2745 eqMayRewriteFR (Wanted WDeriv, NomEq) (Wanted WDeriv, NomEq) = True
2746 eqMayRewriteFR (Derived, NomEq) (Wanted WDeriv, NomEq) = True
2747 eqMayRewriteFR fr1 fr2 = eqCanRewriteFR fr1 fr2
2748
2749 -----------------
2750 {- Note [funEqCanDischarge]
2751 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
2752 Suppose we have two CFunEqCans with the same LHS:
2753 (x1:F ts ~ f1) `funEqCanDischarge` (x2:F ts ~ f2)
2754 Can we drop x2 in favour of x1, either unifying
2755 f2 (if it's a flatten meta-var) or adding a new Given
2756 (f1 ~ f2), if x2 is a Given?
2757
2758 Answer: yes if funEqCanDischarge is true.
2759 -}
2760
2761 funEqCanDischarge
2762 :: CtEvidence -> CtEvidence
2763 -> ( SwapFlag -- NotSwapped => lhs can discharge rhs
2764 -- Swapped => rhs can discharge lhs
2765 , Bool) -- True <=> upgrade non-discharded one
2766 -- from [W] to [WD]
2767 -- See Note [funEqCanDischarge]
2768 funEqCanDischarge ev1 ev2
2769 = ASSERT2( ctEvEqRel ev1 == NomEq, ppr ev1 )
2770 ASSERT2( ctEvEqRel ev2 == NomEq, ppr ev2 )
2771 -- CFunEqCans are all Nominal, hence asserts
2772 funEqCanDischargeF (ctEvFlavour ev1) (ctEvFlavour ev2)
2773
2774 funEqCanDischargeF :: CtFlavour -> CtFlavour -> (SwapFlag, Bool)
2775 funEqCanDischargeF Given _ = (NotSwapped, False)
2776 funEqCanDischargeF _ Given = (IsSwapped, False)
2777 funEqCanDischargeF (Wanted WDeriv) _ = (NotSwapped, False)
2778 funEqCanDischargeF _ (Wanted WDeriv) = (IsSwapped, True)
2779 funEqCanDischargeF (Wanted WOnly) (Wanted WOnly) = (NotSwapped, False)
2780 funEqCanDischargeF (Wanted WOnly) Derived = (NotSwapped, True)
2781 funEqCanDischargeF Derived (Wanted WOnly) = (IsSwapped, True)
2782 funEqCanDischargeF Derived Derived = (NotSwapped, False)
2783
2784
2785 {- Note [eqCanDischarge]
2786 ~~~~~~~~~~~~~~~~~~~~~~~~
2787 Suppose we have two identical CTyEqCan equality constraints
2788 (i.e. both LHS and RHS are the same)
2789 (x1:a~t) `eqCanDischarge` (xs:a~t)
2790 Can we just drop x2 in favour of x1?
2791
2792 Answer: yes if eqCanDischarge is true.
2793
2794 Note that we do /not/ allow Wanted to discharge Derived.
2795 We must keep both. Why? Because the Derived may rewrite
2796 other Deriveds in the model whereas the Wanted cannot.
2797
2798 However a Wanted can certainly discharge an identical Wanted. So
2799 eqCanDischarge does /not/ define a can-rewrite relation in the
2800 sense of Definition [Can-rewrite relation] in TcSMonad.
2801
2802 We /do/ say that a [W] can discharge a [WD]. In evidence terms it
2803 certainly can, and the /caller/ arranges that the otherwise-lost [D]
2804 is spat out as a new Derived. -}
2805
2806 eqCanDischarge :: CtEvidence -> CtEvidence -> Bool
2807 -- See Note [eqCanDischarge]
2808 eqCanDischarge ev1 ev2 = eqCanDischargeFR (ctEvFlavourRole ev1)
2809 (ctEvFlavourRole ev2)
2810
2811 eqCanDischargeFR :: CtFlavourRole -> CtFlavourRole -> Bool
2812 eqCanDischargeFR (_, ReprEq) (_, NomEq) = False
2813 eqCanDischargeFR (f1,_) (f2, _) = eqCanDischargeF f1 f2
2814
2815 eqCanDischargeF :: CtFlavour -> CtFlavour -> Bool
2816 eqCanDischargeF Given _ = True
2817 eqCanDischargeF (Wanted _) (Wanted _) = True
2818 eqCanDischargeF (Wanted WDeriv) Derived = True
2819 eqCanDischargeF Derived Derived = True
2820 eqCanDischargeF _ _ = False
2821
2822
2823 {-
2824 ************************************************************************
2825 * *
2826 SubGoalDepth
2827 * *
2828 ************************************************************************
2829
2830 Note [SubGoalDepth]
2831 ~~~~~~~~~~~~~~~~~~~
2832 The 'SubGoalDepth' takes care of stopping the constraint solver from looping.
2833
2834 The counter starts at zero and increases. It includes dictionary constraints,
2835 equality simplification, and type family reduction. (Why combine these? Because
2836 it's actually quite easy to mistake one for another, in sufficiently involved
2837 scenarios, like ConstraintKinds.)
2838
2839 The flag -fcontext-stack=n (not very well named!) fixes the maximium
2840 level.
2841
2842 * The counter includes the depth of type class instance declarations. Example:
2843 [W] d{7} : Eq [Int]
2844 That is d's dictionary-constraint depth is 7. If we use the instance
2845 $dfEqList :: Eq a => Eq [a]
2846 to simplify it, we get
2847 d{7} = $dfEqList d'{8}
2848 where d'{8} : Eq Int, and d' has depth 8.
2849
2850 For civilised (decidable) instance declarations, each increase of
2851 depth removes a type constructor from the type, so the depth never
2852 gets big; i.e. is bounded by the structural depth of the type.
2853
2854 * The counter also increments when resolving
2855 equalities involving type functions. Example:
2856 Assume we have a wanted at depth 7:
2857 [W] d{7} : F () ~ a
2858 If there is an type function equation "F () = Int", this would be rewritten to
2859 [W] d{8} : Int ~ a
2860 and remembered as having depth 8.
2861
2862 Again, without UndecidableInstances, this counter is bounded, but without it
2863 can resolve things ad infinitum. Hence there is a maximum level.
2864
2865 * Lastly, every time an equality is rewritten, the counter increases. Again,
2866 rewriting an equality constraint normally makes progress, but it's possible
2867 the "progress" is just the reduction of an infinitely-reducing type family.
2868 Hence we need to track the rewrites.
2869
2870 When compiling a program requires a greater depth, then GHC recommends turning
2871 off this check entirely by setting -freduction-depth=0. This is because the
2872 exact number that works is highly variable, and is likely to change even between
2873 minor releases. Because this check is solely to prevent infinite compilation
2874 times, it seems safe to disable it when a user has ascertained that their program
2875 doesn't loop at the type level.
2876
2877 -}
2878
2879 -- | See Note [SubGoalDepth]
2880 newtype SubGoalDepth = SubGoalDepth Int
2881 deriving (Eq, Ord, Outputable)
2882
2883 initialSubGoalDepth :: SubGoalDepth
2884 initialSubGoalDepth = SubGoalDepth 0
2885
2886 bumpSubGoalDepth :: SubGoalDepth -> SubGoalDepth
2887 bumpSubGoalDepth (SubGoalDepth n) = SubGoalDepth (n + 1)
2888
2889 maxSubGoalDepth :: SubGoalDepth -> SubGoalDepth -> SubGoalDepth
2890 maxSubGoalDepth (SubGoalDepth n) (SubGoalDepth m) = SubGoalDepth (n `max` m)
2891
2892 subGoalDepthExceeded :: DynFlags -> SubGoalDepth -> Bool
2893 subGoalDepthExceeded dflags (SubGoalDepth d)
2894 = mkIntWithInf d > reductionDepth dflags
2895
2896 {-
2897 ************************************************************************
2898 * *
2899 CtLoc
2900 * *
2901 ************************************************************************
2902
2903 The 'CtLoc' gives information about where a constraint came from.
2904 This is important for decent error message reporting because
2905 dictionaries don't appear in the original source code.
2906 type will evolve...
2907 -}
2908
2909 data CtLoc = CtLoc { ctl_origin :: CtOrigin
2910 , ctl_env :: TcLclEnv
2911 , ctl_t_or_k :: Maybe TypeOrKind -- OK if we're not sure
2912 , ctl_depth :: !SubGoalDepth }
2913 -- The TcLclEnv includes particularly
2914 -- source location: tcl_loc :: RealSrcSpan
2915 -- context: tcl_ctxt :: [ErrCtxt]
2916 -- binder stack: tcl_bndrs :: TcIdBinderStack
2917 -- level: tcl_tclvl :: TcLevel
2918
2919 mkGivenLoc :: TcLevel -> SkolemInfo -> TcLclEnv -> CtLoc
2920 mkGivenLoc tclvl skol_info env
2921 = CtLoc { ctl_origin = GivenOrigin skol_info
2922 , ctl_env = env { tcl_tclvl = tclvl }
2923 , ctl_t_or_k = Nothing -- this only matters for error msgs
2924 , ctl_depth = initialSubGoalDepth }
2925
2926 mkKindLoc :: TcType -> TcType -- original *types* being compared
2927 -> CtLoc -> CtLoc
2928 mkKindLoc s1 s2 loc = setCtLocOrigin (toKindLoc loc)
2929 (KindEqOrigin s1 (Just s2) (ctLocOrigin loc)
2930 (ctLocTypeOrKind_maybe loc))
2931
2932 -- | Take a CtLoc and moves it to the kind level
2933 toKindLoc :: CtLoc -> CtLoc
2934 toKindLoc loc = loc { ctl_t_or_k = Just KindLevel }
2935
2936 ctLocEnv :: CtLoc -> TcLclEnv
2937 ctLocEnv = ctl_env
2938
2939 ctLocLevel :: CtLoc -> TcLevel
2940 ctLocLevel loc = tcl_tclvl (ctLocEnv loc)
2941
2942 ctLocDepth :: CtLoc -> SubGoalDepth
2943 ctLocDepth = ctl_depth
2944
2945 ctLocOrigin :: CtLoc -> CtOrigin
2946 ctLocOrigin = ctl_origin
2947
2948 ctLocSpan :: CtLoc -> RealSrcSpan
2949 ctLocSpan (CtLoc { ctl_env = lcl}) = tcl_loc lcl
2950
2951 ctLocTypeOrKind_maybe :: CtLoc -> Maybe TypeOrKind
2952 ctLocTypeOrKind_maybe = ctl_t_or_k
2953
2954 setCtLocSpan :: CtLoc -> RealSrcSpan -> CtLoc
2955 setCtLocSpan ctl@(CtLoc { ctl_env = lcl }) loc = setCtLocEnv ctl (lcl { tcl_loc = loc })
2956
2957 bumpCtLocDepth :: CtLoc -> CtLoc
2958 bumpCtLocDepth loc@(CtLoc { ctl_depth = d }) = loc { ctl_depth = bumpSubGoalDepth d }
2959
2960 setCtLocOrigin :: CtLoc -> CtOrigin -> CtLoc
2961 setCtLocOrigin ctl orig = ctl { ctl_origin = orig }
2962
2963 setCtLocEnv :: CtLoc -> TcLclEnv -> CtLoc
2964 setCtLocEnv ctl env = ctl { ctl_env = env }
2965
2966 pushErrCtxt :: CtOrigin -> ErrCtxt -> CtLoc -> CtLoc
2967 pushErrCtxt o err loc@(CtLoc { ctl_env = lcl })
2968 = loc { ctl_origin = o, ctl_env = lcl { tcl_ctxt = err : tcl_ctxt lcl } }
2969
2970 pushErrCtxtSameOrigin :: ErrCtxt -> CtLoc -> CtLoc
2971 -- Just add information w/o updating the origin!
2972 pushErrCtxtSameOrigin err loc@(CtLoc { ctl_env = lcl })
2973 = loc { ctl_env = lcl { tcl_ctxt = err : tcl_ctxt lcl } }
2974
2975 {-
2976 ************************************************************************
2977 * *
2978 SkolemInfo
2979 * *
2980 ************************************************************************
2981 -}
2982
2983 -- SkolemInfo gives the origin of *given* constraints
2984 -- a) type variables are skolemised
2985 -- b) an implication constraint is generated
2986 data SkolemInfo
2987 = SigSkol -- A skolem that is created by instantiating
2988 -- a programmer-supplied type signature
2989 -- Location of the binding site is on the TyVar
2990 -- See Note [SigSkol SkolemInfo]
2991 UserTypeCtxt -- What sort of signature
2992 TcType -- Original type signature (before skolemisation)
2993 [(Name,TcTyVar)] -- Maps the original name of the skolemised tyvar
2994 -- to its instantiated version
2995
2996 | ClsSkol Class -- Bound at a class decl
2997
2998 | DerivSkol Type -- Bound by a 'deriving' clause;
2999 -- the type is the instance we are trying to derive
3000
3001 | InstSkol -- Bound at an instance decl
3002 | InstSC TypeSize -- A "given" constraint obtained by superclass selection.
3003 -- If (C ty1 .. tyn) is the largest class from
3004 -- which we made a superclass selection in the chain,
3005 -- then TypeSize = sizeTypes [ty1, .., tyn]
3006 -- See Note [Solving superclass constraints] in TcInstDcls
3007
3008 | DataSkol -- Bound at a data type declaration
3009 | FamInstSkol -- Bound at a family instance decl
3010 | PatSkol -- An existential type variable bound by a pattern for
3011 ConLike -- a data constructor with an existential type.
3012 (HsMatchContext Name)
3013 -- e.g. data T = forall a. Eq a => MkT a
3014 -- f (MkT x) = ...
3015 -- The pattern MkT x will allocate an existential type
3016 -- variable for 'a'.
3017
3018 | ArrowSkol -- An arrow form (see TcArrows)
3019
3020 | IPSkol [HsIPName] -- Binding site of an implicit parameter
3021
3022 | RuleSkol RuleName -- The LHS of a RULE
3023
3024 | InferSkol [(Name,TcType)]
3025 -- We have inferred a type for these (mutually-recursivive)
3026 -- polymorphic Ids, and are now checking that their RHS
3027 -- constraints are satisfied.
3028
3029 | BracketSkol -- Template Haskell bracket
3030
3031 | UnifyForAllSkol -- We are unifying two for-all types
3032 TcType -- The instantiated type *inside* the forall
3033
3034 | UnkSkol -- Unhelpful info (until I improve it)
3035
3036 instance Outputable SkolemInfo where
3037 ppr = pprSkolInfo
3038
3039 termEvidenceAllowed :: SkolemInfo -> Bool
3040 -- Whether an implication constraint with this SkolemInfo
3041 -- is permitted to have term-level evidence. There is
3042 -- only one that is not, associated with unifiying
3043 -- forall-types
3044 termEvidenceAllowed (UnifyForAllSkol {}) = False
3045 termEvidenceAllowed _ = True
3046
3047 pprSkolInfo :: SkolemInfo -> SDoc
3048 -- Complete the sentence "is a rigid type variable bound by..."
3049 pprSkolInfo (SigSkol cx ty _) = pprSigSkolInfo cx ty
3050 pprSkolInfo (IPSkol ips) = text "the implicit-parameter binding" <> plural ips <+> text "for"
3051 <+> pprWithCommas ppr ips
3052 pprSkolInfo (ClsSkol cls) = text "the class declaration for" <+> quotes (ppr cls)
3053 pprSkolInfo (DerivSkol pred) = text "the deriving clause for" <+> quotes (ppr pred)
3054 pprSkolInfo InstSkol = text "the instance declaration"
3055 pprSkolInfo (InstSC n) = text "the instance declaration" <> ifPprDebug (parens (ppr n))
3056 pprSkolInfo DataSkol = text "a data type declaration"
3057 pprSkolInfo FamInstSkol = text "a family instance declaration"
3058 pprSkolInfo BracketSkol = text "a Template Haskell bracket"
3059 pprSkolInfo (RuleSkol name) = text "the RULE" <+> pprRuleName name
3060 pprSkolInfo ArrowSkol = text "an arrow form"
3061 pprSkolInfo (PatSkol cl mc) = sep [ pprPatSkolInfo cl
3062 , text "in" <+> pprMatchContext mc ]
3063 pprSkolInfo (InferSkol ids) = sep [ text "the inferred type of"
3064 , vcat [ ppr name <+> dcolon <+> ppr ty
3065 | (name,ty) <- ids ]]
3066 pprSkolInfo (UnifyForAllSkol ty) = text "the type" <+> ppr ty
3067
3068 -- UnkSkol
3069 -- For type variables the others are dealt with by pprSkolTvBinding.
3070 -- For Insts, these cases should not happen
3071 pprSkolInfo UnkSkol = WARN( True, text "pprSkolInfo: UnkSkol" ) text "UnkSkol"
3072
3073 pprSigSkolInfo :: UserTypeCtxt -> TcType -> SDoc
3074 -- The type is already tidied
3075 pprSigSkolInfo ctxt ty
3076 = case ctxt of
3077 FunSigCtxt f _ -> vcat [ text "the type signature for:"
3078 , nest 2 (pprPrefixOcc f <+> dcolon <+> ppr ty) ]
3079 PatSynCtxt {} -> pprUserTypeCtxt ctxt -- See Note [Skolem info for pattern synonyms]
3080 _ -> vcat [ pprUserTypeCtxt ctxt <> colon
3081 , nest 2 (ppr ty) ]
3082
3083 pprPatSkolInfo :: ConLike -> SDoc
3084 pprPatSkolInfo (RealDataCon dc)
3085 = sep [ text "a pattern with constructor:"
3086 , nest 2 $ ppr dc <+> dcolon
3087 <+> pprType (dataConUserType dc) <> comma ]
3088 -- pprType prints forall's regardless of -fprint-explicit-foralls
3089 -- which is what we want here, since we might be saying
3090 -- type variable 't' is bound by ...
3091
3092 pprPatSkolInfo (PatSynCon ps)
3093 = sep [ text "a pattern with pattern synonym:"
3094 , nest 2 $ ppr ps <+> dcolon
3095 <+> pprPatSynType ps <> comma ]
3096
3097 {- Note [Skolem info for pattern synonyms]
3098 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3099 For pattern synonym SkolemInfo we have
3100 SigSkol (PatSynCtxt p) ty _
3101 but the type 'ty' is not very helpful. The full pattern-synonym type
3102 has the provided and required pieces, which it is inconvenient to
3103 record and display here. So we simply don't display the type at all,
3104 contenting outselves with just the name of the pattern synonym, which
3105 is fine. We could do more, but it doesn't seem worth it.
3106
3107 Note [SigSkol SkolemInfo]
3108 ~~~~~~~~~~~~~~~~~~~~~~~~~
3109 Suppose we (deeply) skolemise a type
3110 f :: forall a. a -> forall b. b -> a
3111 Then we'll instantiate [a :-> a', b :-> b'], and with the instantiated
3112 a' -> b' -> a.
3113 But when, in an error message, we report that "b is a rigid type
3114 variable bound by the type signature for f", we want to show the foralls
3115 in the right place. So we proceed as follows:
3116
3117 * In SigSkol we record
3118 - the original signature forall a. a -> forall b. b -> a
3119 - the instantiation mapping [a :-> a', b :-> b']
3120
3121 * Then when tidying in TcMType.tidySkolemInfo, we first tidy a' to
3122 whatever it tidies to, say a''; and then we walk over the type
3123 replacing the binder a by the tidied version a'', to give
3124 forall a''. a'' -> forall b''. b'' -> a''
3125 We need to do this under function arrows, to match what deeplySkolemise
3126 does.
3127
3128 * Typically a'' will have a nice pretty name like "a", but the point is
3129 that the foral-bound variables of the signature we report line up with
3130 the instantiated skolems lying around in other types.
3131
3132
3133 ************************************************************************
3134 * *
3135 CtOrigin
3136 * *
3137 ************************************************************************
3138 -}
3139
3140 data CtOrigin
3141 = GivenOrigin SkolemInfo
3142
3143 -- All the others are for *wanted* constraints
3144 | OccurrenceOf Name -- Occurrence of an overloaded identifier
3145 | OccurrenceOfRecSel RdrName -- Occurrence of a record selector
3146 | AppOrigin -- An application of some kind
3147
3148 | SpecPragOrigin UserTypeCtxt -- Specialisation pragma for
3149 -- function or instance
3150
3151 | TypeEqOrigin { uo_actual :: TcType
3152 , uo_expected :: TcType
3153 , uo_thing :: Maybe ErrorThing
3154 -- ^ The thing that has type "actual"
3155 }
3156
3157 | KindEqOrigin
3158 TcType (Maybe TcType) -- A kind equality arising from unifying these two types
3159 CtOrigin -- originally arising from this
3160 (Maybe TypeOrKind) -- the level of the eq this arises from
3161
3162 | IPOccOrigin HsIPName -- Occurrence of an implicit parameter
3163 | OverLabelOrigin FastString -- Occurrence of an overloaded label
3164
3165 | LiteralOrigin (HsOverLit GhcRn) -- Occurrence of a literal
3166 | NegateOrigin -- Occurrence of syntactic negation
3167
3168 | ArithSeqOrigin (ArithSeqInfo GhcRn) -- [x..], [x..y] etc
3169 | PArrSeqOrigin (ArithSeqInfo GhcRn) -- [:x..y:] and [:x,y..z:]
3170 | SectionOrigin
3171 | TupleOrigin -- (..,..)
3172 | ExprSigOrigin -- e :: ty
3173 | PatSigOrigin -- p :: ty
3174 | PatOrigin -- Instantiating a polytyped pattern at a constructor
3175 | ProvCtxtOrigin -- The "provided" context of a pattern synonym signature
3176 (PatSynBind GhcRn GhcRn) -- Information about the pattern synonym, in
3177 -- particular the name and the right-hand side
3178 | RecordUpdOrigin
3179 | ViewPatOrigin
3180
3181 | ScOrigin TypeSize -- Typechecking superclasses of an instance declaration
3182 -- If the instance head is C ty1 .. tyn
3183 -- then TypeSize = sizeTypes [ty1, .., tyn]
3184 -- See Note [Solving superclass constraints] in TcInstDcls
3185
3186 | DerivOrigin -- Typechecking deriving
3187 | DerivOriginDC DataCon Int
3188 -- Checking constraints arising from this data con and field index
3189 | DerivOriginCoerce Id Type Type
3190 -- DerivOriginCoerce id ty1 ty2: Trying to coerce class method `id` from
3191 -- `ty1` to `ty2`.
3192 | StandAloneDerivOrigin -- Typechecking stand-alone deriving
3193 | DefaultOrigin -- Typechecking a default decl
3194 | DoOrigin -- Arising from a do expression
3195 | DoPatOrigin (LPat GhcRn) -- Arising from a failable pattern in
3196 -- a do expression
3197 | MCompOrigin -- Arising from a monad comprehension
3198 | MCompPatOrigin (LPat GhcRn) -- Arising from a failable pattern in a
3199 -- monad comprehension
3200 | IfOrigin -- Arising from an if statement
3201 | ProcOrigin -- Arising from a proc expression
3202 | AnnOrigin -- An annotation
3203
3204 | FunDepOrigin1 -- A functional dependency from combining
3205 PredType CtLoc -- This constraint arising from ...
3206 PredType CtLoc -- and this constraint arising from ...
3207
3208 | FunDepOrigin2 -- A functional dependency from combining
3209 PredType CtOrigin -- This constraint arising from ...
3210 PredType SrcSpan -- and this top-level instance
3211 -- We only need a CtOrigin on the first, because the location
3212 -- is pinned on the entire error message
3213
3214 | HoleOrigin
3215 | UnboundOccurrenceOf OccName
3216 | ListOrigin -- An overloaded list
3217 | StaticOrigin -- A static form
3218 | FailablePattern (LPat GhcTcId) -- A failable pattern in do-notation for the
3219 -- MonadFail Proposal (MFP). Obsolete when
3220 -- actual desugaring to MonadFail.fail is
3221 -- live.
3222 | Shouldn'tHappenOrigin String
3223 -- the user should never see this one,
3224 -- unless ImpredicativeTypes is on, where all
3225 -- bets are off
3226 | InstProvidedOrigin Module ClsInst
3227 -- Skolem variable arose when we were testing if an instance
3228 -- is solvable or not.
3229
3230 -- | A thing that can be stored for error message generation only.
3231 -- It is stored with a function to zonk and tidy the thing.
3232 data ErrorThing
3233 = forall a. Outputable a => ErrorThing a
3234 (Maybe Arity) -- # of args, if known
3235 (TidyEnv -> a -> TcM (TidyEnv, a))
3236
3237 -- | Flag to see whether we're type-checking terms or kind-checking types
3238 data TypeOrKind = TypeLevel | KindLevel
3239 deriving Eq
3240
3241 instance Outputable TypeOrKind where
3242 ppr TypeLevel = text "TypeLevel"
3243 ppr KindLevel = text "KindLevel"
3244
3245 isTypeLevel :: TypeOrKind -> Bool
3246 isTypeLevel TypeLevel = True
3247 isTypeLevel KindLevel = False
3248
3249 isKindLevel :: TypeOrKind -> Bool
3250 isKindLevel TypeLevel = False
3251 isKindLevel KindLevel = True
3252
3253 -- | Make an 'ErrorThing' that doesn't need tidying or zonking
3254 mkErrorThing :: Outputable a => a -> ErrorThing
3255 mkErrorThing thing = ErrorThing thing Nothing (\env x -> return (env, x))
3256
3257 -- | Retrieve the # of arguments in the error thing, if known
3258 errorThingNumArgs_maybe :: ErrorThing -> Maybe Arity
3259 errorThingNumArgs_maybe (ErrorThing _ args _) = args
3260
3261 instance Outputable CtOrigin where
3262 ppr = pprCtOrigin
3263
3264 instance Outputable ErrorThing where
3265 ppr (ErrorThing thing _ _) = ppr thing
3266
3267 ctoHerald :: SDoc
3268 ctoHerald = text "arising from"
3269
3270 -- | Extract a suitable CtOrigin from a HsExpr
3271 lexprCtOrigin :: LHsExpr GhcRn -> CtOrigin
3272 lexprCtOrigin (L _ e) = exprCtOrigin e
3273
3274 exprCtOrigin :: HsExpr GhcRn -> CtOrigin
3275 exprCtOrigin (HsVar (L _ name)) = OccurrenceOf name
3276 exprCtOrigin (HsUnboundVar uv) = UnboundOccurrenceOf (unboundVarOcc uv)
3277 exprCtOrigin (HsConLikeOut {}) = panic "exprCtOrigin HsConLikeOut"
3278 exprCtOrigin (HsRecFld f) = OccurrenceOfRecSel (rdrNameAmbiguousFieldOcc f)
3279 exprCtOrigin (HsOverLabel _ l) = OverLabelOrigin l
3280 exprCtOrigin (HsIPVar ip) = IPOccOrigin ip
3281 exprCtOrigin (HsOverLit lit) = LiteralOrigin lit
3282 exprCtOrigin (HsLit {}) = Shouldn'tHappenOrigin "concrete literal"
3283 exprCtOrigin (HsLam matches) = matchesCtOrigin matches
3284 exprCtOrigin (HsLamCase ms) = matchesCtOrigin ms
3285 exprCtOrigin (HsApp e1 _) = lexprCtOrigin e1
3286 exprCtOrigin (HsAppType e1 _) = lexprCtOrigin e1
3287 exprCtOrigin (HsAppTypeOut {}) = panic "exprCtOrigin HsAppTypeOut"
3288 exprCtOrigin (OpApp _ op _ _) = lexprCtOrigin op
3289 exprCtOrigin (NegApp e _) = lexprCtOrigin e
3290 exprCtOrigin (HsPar e) = lexprCtOrigin e
3291 exprCtOrigin (SectionL _ _) = SectionOrigin
3292 exprCtOrigin (SectionR _ _) = SectionOrigin
3293 exprCtOrigin (ExplicitTuple {}) = Shouldn'tHappenOrigin "explicit tuple"
3294 exprCtOrigin ExplicitSum{} = Shouldn'tHappenOrigin "explicit sum"
3295 exprCtOrigin (HsCase _ matches) = matchesCtOrigin matches
3296 exprCtOrigin (HsIf (Just syn) _ _ _) = exprCtOrigin (syn_expr syn)
3297 exprCtOrigin (HsIf {}) = Shouldn'tHappenOrigin "if expression"
3298 exprCtOrigin (HsMultiIf _ rhs) = lGRHSCtOrigin rhs
3299 exprCtOrigin (HsLet _ e) = lexprCtOrigin e
3300 exprCtOrigin (HsDo _ _ _) = DoOrigin
3301 exprCtOrigin (ExplicitList {}) = Shouldn'tHappenOrigin "list"
3302 exprCtOrigin (ExplicitPArr {}) = Shouldn'tHappenOrigin "parallel array"
3303 exprCtOrigin (RecordCon {}) = Shouldn'tHappenOrigin "record construction"
3304 exprCtOrigin (RecordUpd {}) = Shouldn'tHappenOrigin "record update"
3305 exprCtOrigin (ExprWithTySig {}) = ExprSigOrigin
3306 exprCtOrigin (ExprWithTySigOut {}) = panic "exprCtOrigin ExprWithTySigOut"
3307 exprCtOrigin (ArithSeq {}) = Shouldn'tHappenOrigin "arithmetic sequence"
3308 exprCtOrigin (PArrSeq {}) = Shouldn'tHappenOrigin "parallel array sequence"
3309 exprCtOrigin (HsSCC _ _ e) = lexprCtOrigin e
3310 exprCtOrigin (HsCoreAnn _ _ e) = lexprCtOrigin e
3311 exprCtOrigin (HsBracket {}) = Shouldn'tHappenOrigin "TH bracket"
3312 exprCtOrigin (HsRnBracketOut {})= Shouldn'tHappenOrigin "HsRnBracketOut"
3313 exprCtOrigin (HsTcBracketOut {})= panic "exprCtOrigin HsTcBracketOut"
3314 exprCtOrigin (HsSpliceE {}) = Shouldn'tHappenOrigin "TH splice"
3315 exprCtOrigin (HsProc {}) = Shouldn'tHappenOrigin "proc"
3316 exprCtOrigin (HsStatic {}) = Shouldn'tHappenOrigin "static expression"
3317 exprCtOrigin (HsArrApp {}) = panic "exprCtOrigin HsArrApp"
3318 exprCtOrigin (HsArrForm {}) = panic "exprCtOrigin HsArrForm"
3319 exprCtOrigin (HsTick _ e) = lexprCtOrigin e
3320 exprCtOrigin (HsBinTick _ _ e) = lexprCtOrigin e
3321 exprCtOrigin (HsTickPragma _ _ _ e) = lexprCtOrigin e
3322 exprCtOrigin EWildPat = panic "exprCtOrigin EWildPat"
3323 exprCtOrigin (EAsPat {}) = panic "exprCtOrigin EAsPat"
3324 exprCtOrigin (EViewPat {}) = panic "exprCtOrigin EViewPat"
3325 exprCtOrigin (ELazyPat {}) = panic "exprCtOrigin ELazyPat"
3326 exprCtOrigin (HsWrap {}) = panic "exprCtOrigin HsWrap"
3327
3328 -- | Extract a suitable CtOrigin from a MatchGroup
3329 matchesCtOrigin :: MatchGroup GhcRn (LHsExpr GhcRn) -> CtOrigin
3330 matchesCtOrigin (MG { mg_alts = alts })
3331 | L _ [L _ match] <- alts
3332 , Match { m_grhss = grhss } <- match
3333 = grhssCtOrigin grhss
3334
3335 | otherwise
3336 = Shouldn'tHappenOrigin "multi-way match"
3337
3338 -- | Extract a suitable CtOrigin from guarded RHSs
3339 grhssCtOrigin :: GRHSs GhcRn (LHsExpr GhcRn) -> CtOrigin
3340 grhssCtOrigin (GRHSs { grhssGRHSs = lgrhss }) = lGRHSCtOrigin lgrhss
3341
3342 -- | Extract a suitable CtOrigin from a list of guarded RHSs
3343 lGRHSCtOrigin :: [LGRHS GhcRn (LHsExpr GhcRn)] -> CtOrigin
3344 lGRHSCtOrigin [L _ (GRHS _ (L _ e))] = exprCtOrigin e
3345 lGRHSCtOrigin _ = Shouldn'tHappenOrigin "multi-way GRHS"
3346
3347 pprCtLoc :: CtLoc -> SDoc
3348 -- "arising from ... at ..."
3349 -- Not an instance of Outputable because of the "arising from" prefix
3350 pprCtLoc (CtLoc { ctl_origin = o, ctl_env = lcl})
3351 = sep [ pprCtOrigin o
3352 , text "at" <+> ppr (tcl_loc lcl)]
3353
3354 pprCtOrigin :: CtOrigin -> SDoc
3355 -- "arising from ..."
3356 -- Not an instance of Outputable because of the "arising from" prefix
3357 pprCtOrigin (GivenOrigin sk) = ctoHerald <+> ppr sk
3358
3359 pprCtOrigin (SpecPragOrigin ctxt)
3360 = case ctxt of
3361 FunSigCtxt n _ -> text "a SPECIALISE pragma for" <+> quotes (ppr n)
3362 SpecInstCtxt -> text "a SPECIALISE INSTANCE pragma"
3363 _ -> text "a SPECIALISE pragma" -- Never happens I think
3364
3365 pprCtOrigin (FunDepOrigin1 pred1 loc1 pred2 loc2)
3366 = hang (ctoHerald <+> text "a functional dependency between constraints:")
3367 2 (vcat [ hang (quotes (ppr pred1)) 2 (pprCtLoc loc1)
3368 , hang (quotes (ppr pred2)) 2 (pprCtLoc loc2) ])
3369
3370 pprCtOrigin (FunDepOrigin2 pred1 orig1 pred2 loc2)
3371 = hang (ctoHerald <+> text "a functional dependency between:")
3372 2 (vcat [ hang (text "constraint" <+> quotes (ppr pred1))
3373 2 (pprCtOrigin orig1 )
3374 , hang (text "instance" <+> quotes (ppr pred2))
3375 2 (text "at" <+> ppr loc2) ])
3376
3377 pprCtOrigin (KindEqOrigin t1 (Just t2) _ _)
3378 = hang (ctoHerald <+> text "a kind equality arising from")
3379 2 (sep [ppr t1, char '~', ppr t2])
3380
3381 pprCtOrigin (KindEqOrigin t1 Nothing _ _)
3382 = hang (ctoHerald <+> text "a kind equality when matching")
3383 2 (ppr t1)
3384
3385 pprCtOrigin (UnboundOccurrenceOf name)
3386 = ctoHerald <+> text "an undeclared identifier" <+> quotes (ppr name)
3387
3388 pprCtOrigin (DerivOriginDC dc n)
3389 = hang (ctoHerald <+> text "the" <+> speakNth n
3390 <+> text "field of" <+> quotes (ppr dc))
3391 2 (parens (text "type" <+> quotes (ppr ty)))
3392 where
3393 ty = dataConOrigArgTys dc !! (n-1)
3394
3395 pprCtOrigin (DerivOriginCoerce meth ty1 ty2)
3396 = hang (ctoHerald <+> text "the coercion of the method" <+> quotes (ppr meth))
3397 2 (sep [ text "from type" <+> quotes (ppr ty1)
3398 , nest 2 $ text "to type" <+> quotes (ppr ty2) ])
3399
3400 pprCtOrigin (DoPatOrigin pat)
3401 = ctoHerald <+> text "a do statement"
3402 $$
3403 text "with the failable pattern" <+> quotes (ppr pat)
3404
3405 pprCtOrigin (MCompPatOrigin pat)
3406 = ctoHerald <+> hsep [ text "the failable pattern"
3407 , quotes (ppr pat)
3408 , text "in a statement in a monad comprehension" ]
3409 pprCtOrigin (FailablePattern pat)
3410 = ctoHerald <+> text "the failable pattern" <+> quotes (ppr pat)
3411 $$
3412 text "(this will become an error in a future GHC release)"
3413
3414 pprCtOrigin (Shouldn'tHappenOrigin note)
3415 = sdocWithDynFlags $ \dflags ->
3416 if xopt LangExt.ImpredicativeTypes dflags
3417 then text "a situation created by impredicative types"
3418 else
3419 vcat [ text "<< This should not appear in error messages. If you see this"
3420 , text "in an error message, please report a bug mentioning" <+> quotes (text note) <+> text "at"
3421 , text "https://ghc.haskell.org/trac/ghc/wiki/ReportABug >>" ]
3422
3423 pprCtOrigin (ProvCtxtOrigin PSB{ psb_id = (L _ name) })
3424 = hang (ctoHerald <+> text "the \"provided\" constraints claimed by")
3425 2 (text "the signature of" <+> quotes (ppr name))
3426
3427 pprCtOrigin (InstProvidedOrigin mod cls_inst)
3428 = vcat [ text "arising when attempting to show that"
3429 , ppr cls_inst
3430 , text "is provided by" <+> quotes (ppr mod)]
3431
3432 pprCtOrigin simple_origin
3433 = ctoHerald <+> pprCtO simple_origin
3434
3435 -- | Short one-liners
3436 pprCtO :: CtOrigin -> SDoc
3437 pprCtO (OccurrenceOf name) = hsep [text "a use of", quotes (ppr name)]
3438 pprCtO (OccurrenceOfRecSel name) = hsep [text "a use of", quotes (ppr name)]
3439 pprCtO AppOrigin = text "an application"
3440 pprCtO (IPOccOrigin name) = hsep [text "a use of implicit parameter", quotes (ppr name)]
3441 pprCtO (OverLabelOrigin l) = hsep [text "the overloaded label"
3442 ,quotes (char '#' <> ppr l)]
3443 pprCtO RecordUpdOrigin = text "a record update"
3444 pprCtO ExprSigOrigin = text "an expression type signature"
3445 pprCtO PatSigOrigin = text "a pattern type signature"
3446 pprCtO PatOrigin = text "a pattern"
3447 pprCtO ViewPatOrigin = text "a view pattern"
3448 pprCtO IfOrigin = text "an if expression"
3449 pprCtO (LiteralOrigin lit) = hsep [text "the literal", quotes (ppr lit)]
3450 pprCtO (ArithSeqOrigin seq) = hsep [text "the arithmetic sequence", quotes (ppr seq)]
3451 pprCtO (PArrSeqOrigin seq) = hsep [text "the parallel array sequence", quotes (ppr seq)]
3452 pprCtO SectionOrigin = text "an operator section"
3453 pprCtO TupleOrigin = text "a tuple"
3454 pprCtO NegateOrigin = text "a use of syntactic negation"
3455 pprCtO (ScOrigin n) = text "the superclasses of an instance declaration"
3456 <> ifPprDebug (parens (ppr n))
3457 pprCtO DerivOrigin = text "the 'deriving' clause of a data type declaration"
3458 pprCtO StandAloneDerivOrigin = text "a 'deriving' declaration"
3459 pprCtO DefaultOrigin = text "a 'default' declaration"
3460 pprCtO DoOrigin = text "a do statement"
3461 pprCtO MCompOrigin = text "a statement in a monad comprehension"
3462 pprCtO ProcOrigin = text "a proc expression"
3463 pprCtO (TypeEqOrigin t1 t2 _)= text "a type equality" <+> sep [ppr t1, char '~', ppr t2]
3464 pprCtO AnnOrigin = text "an annotation"
3465 pprCtO HoleOrigin = text "a use of" <+> quotes (text "_")
3466 pprCtO ListOrigin = text "an overloaded list"
3467 pprCtO StaticOrigin = text "a static form"
3468 pprCtO _ = panic "pprCtOrigin"
3469
3470 {-
3471 Constraint Solver Plugins
3472 -------------------------
3473 -}
3474
3475 type TcPluginSolver = [Ct] -- given
3476 -> [Ct] -- derived
3477 -> [Ct] -- wanted
3478 -> TcPluginM TcPluginResult
3479
3480 newtype TcPluginM a = TcPluginM (EvBindsVar -> TcM a)
3481
3482 instance Functor TcPluginM where
3483 fmap = liftM
3484
3485 instance Applicative TcPluginM where
3486 pure x = TcPluginM (const $ pure x)
3487 (<*>) = ap
3488
3489 instance Monad TcPluginM where
3490 fail x = TcPluginM (const $ fail x)
3491 TcPluginM m >>= k =
3492 TcPluginM (\ ev -> do a <- m ev
3493 runTcPluginM (k a) ev)
3494
3495 #if __GLASGOW_HASKELL__ > 710
3496 instance MonadFail.MonadFail TcPluginM where
3497 fail x = TcPluginM (const $ fail x)
3498 #endif
3499
3500 runTcPluginM :: TcPluginM a -> EvBindsVar -> TcM a
3501 runTcPluginM (TcPluginM m) = m
3502
3503 -- | This function provides an escape for direct access to
3504 -- the 'TcM` monad. It should not be used lightly, and
3505 -- the provided 'TcPluginM' API should be favoured instead.
3506 unsafeTcPluginTcM :: TcM a -> TcPluginM a
3507 unsafeTcPluginTcM = TcPluginM . const
3508
3509 -- | Access the 'EvBindsVar' carried by the 'TcPluginM' during
3510 -- constraint solving. Returns 'Nothing' if invoked during
3511 -- 'tcPluginInit' or 'tcPluginStop'.
3512 getEvBindsTcPluginM :: TcPluginM EvBindsVar
3513 getEvBindsTcPluginM = TcPluginM return
3514
3515
3516 data TcPlugin = forall s. TcPlugin
3517 { tcPluginInit :: TcPluginM s
3518 -- ^ Initialize plugin, when entering type-checker.
3519
3520 , tcPluginSolve :: s -> TcPluginSolver
3521 -- ^ Solve some constraints.
3522 -- TODO: WRITE MORE DETAILS ON HOW THIS WORKS.
3523
3524 , tcPluginStop :: s -> TcPluginM ()
3525 -- ^ Clean up after the plugin, when exiting the type-checker.
3526 }
3527
3528 data TcPluginResult
3529 = TcPluginContradiction [Ct]
3530 -- ^ The plugin found a contradiction.
3531 -- The returned constraints are removed from the inert set,
3532 -- and recorded as insoluble.
3533
3534 | TcPluginOk [(EvTerm,Ct)] [Ct]
3535 -- ^ The first field is for constraints that were solved.
3536 -- These are removed from the inert set,
3537 -- and the evidence for them is recorded.
3538 -- The second field contains new work, that should be processed by
3539 -- the constraint solver.
3540
3541 {- *********************************************************************
3542 * *
3543 Role annotations
3544 * *
3545 ********************************************************************* -}
3546
3547 type RoleAnnotEnv = NameEnv (LRoleAnnotDecl GhcRn)
3548
3549 mkRoleAnnotEnv :: [LRoleAnnotDecl GhcRn] -> RoleAnnotEnv
3550 mkRoleAnnotEnv role_annot_decls
3551 = mkNameEnv [ (name, ra_decl)
3552 | ra_decl <- role_annot_decls
3553 , let name = roleAnnotDeclName (unLoc ra_decl)
3554 , not (isUnboundName name) ]
3555 -- Some of the role annots will be unbound;
3556 -- we don't wish to include these
3557
3558 emptyRoleAnnotEnv :: RoleAnnotEnv
3559 emptyRoleAnnotEnv = emptyNameEnv
3560
3561 lookupRoleAnnot :: RoleAnnotEnv -> Name -> Maybe (LRoleAnnotDecl GhcRn)
3562 lookupRoleAnnot = lookupNameEnv
3563
3564 getRoleAnnots :: [Name] -> RoleAnnotEnv
3565 -> ([LRoleAnnotDecl GhcRn], RoleAnnotEnv)
3566 getRoleAnnots bndrs role_env
3567 = ( mapMaybe (lookupRoleAnnot role_env) bndrs
3568 , delListFromNameEnv role_env bndrs )