463c7e0672b391e1be90f7fb588477aff5e39d6b
[ghc.git] / compiler / typecheck / TcHsType.hs
1 {-
2 (c) The University of Glasgow 2006
3 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4
5 \section[TcMonoType]{Typechecking user-specified @MonoTypes@}
6 -}
7
8 {-# LANGUAGE CPP, TupleSections, MultiWayIf, RankNTypes #-}
9 {-# LANGUAGE ScopedTypeVariables #-}
10
11 module TcHsType (
12 -- Type signatures
13 kcHsSigType, tcClassSigType,
14 tcHsSigType, tcHsSigWcType,
15 tcHsPartialSigType,
16 funsSigCtxt, addSigCtxt, pprSigCtxt,
17
18 tcHsClsInstType,
19 tcHsDeriv, tcDerivStrategy,
20 tcHsTypeApp,
21 UserTypeCtxt(..),
22 tcImplicitTKBndrs, tcImplicitQTKBndrs,
23 tcExplicitTKBndrs,
24 kcExplicitTKBndrs, kcImplicitTKBndrs,
25
26 -- Type checking type and class decls
27 kcLookupTcTyCon, kcTyClTyVars, tcTyClTyVars,
28 tcDataKindSig,
29
30 -- tyvars
31 scopeTyVars, scopeTyVars2,
32
33 -- Kind-checking types
34 -- No kind generalisation, no checkValidType
35 kcLHsQTyVars,
36 tcWildCardBinders,
37 tcHsLiftedType, tcHsOpenType,
38 tcHsLiftedTypeNC, tcHsOpenTypeNC,
39 tcLHsType, tcLHsTypeUnsaturated, tcCheckLHsType,
40 tcHsMbContext, tcHsContext, tcLHsPredType, tcInferApps,
41 solveEqualities, -- useful re-export
42
43 typeLevelMode, kindLevelMode,
44
45 kindGeneralize, checkExpectedKindX, instantiateTyUntilN,
46 reportFloatingKvs,
47
48 -- Sort-checking kinds
49 tcLHsKindSig, badKindSig,
50
51 -- Zonking and promoting
52 zonkPromoteType,
53
54 -- Pattern type signatures
55 tcHsPatSigType, tcPatSig, funAppCtxt
56 ) where
57
58 #include "HsVersions.h"
59
60 import GhcPrelude
61
62 import HsSyn
63 import TcRnMonad
64 import TcEvidence
65 import TcEnv
66 import TcMType
67 import TcValidity
68 import TcUnify
69 import TcIface
70 import TcSimplify
71 import TcType
72 import TcHsSyn( zonkSigType )
73 import Inst ( tcInstTyBinders, tcInstTyBinder )
74 import TyCoRep( TyBinder(..) ) -- Used in tcDataKindSig
75 import Type
76 import Coercion
77 import Kind
78 import RdrName( lookupLocalRdrOcc )
79 import Var
80 import VarSet
81 import TyCon
82 import ConLike
83 import DataCon
84 import Class
85 import Name
86 import NameEnv
87 import NameSet
88 import VarEnv
89 import TysWiredIn
90 import BasicTypes
91 import SrcLoc
92 import Constants ( mAX_CTUPLE_SIZE )
93 import ErrUtils( MsgDoc )
94 import Unique
95 import Util
96 import UniqSupply
97 import Outputable
98 import FastString
99 import PrelNames hiding ( wildCardName )
100 import qualified GHC.LanguageExtensions as LangExt
101
102 import Maybes
103 import Data.List ( find, mapAccumR )
104 import Control.Monad
105
106 {-
107 ----------------------------
108 General notes
109 ----------------------------
110
111 Unlike with expressions, type-checking types both does some checking and
112 desugars at the same time. This is necessary because we often want to perform
113 equality checks on the types right away, and it would be incredibly painful
114 to do this on un-desugared types. Luckily, desugared types are close enough
115 to HsTypes to make the error messages sane.
116
117 During type-checking, we perform as little validity checking as possible.
118 This is because some type-checking is done in a mutually-recursive knot, and
119 if we look too closely at the tycons, we'll loop. This is why we always must
120 use mkNakedTyConApp and mkNakedAppTys, etc., which never look at a tycon.
121 The mkNamed... functions don't uphold Type invariants, but zonkTcTypeToType
122 will repair this for us. Note that zonkTcType *is* safe within a knot, and
123 can be done repeatedly with no ill effect: it just squeezes out metavariables.
124
125 Generally, after type-checking, you will want to do validity checking, say
126 with TcValidity.checkValidType.
127
128 Validity checking
129 ~~~~~~~~~~~~~~~~~
130 Some of the validity check could in principle be done by the kind checker,
131 but not all:
132
133 - During desugaring, we normalise by expanding type synonyms. Only
134 after this step can we check things like type-synonym saturation
135 e.g. type T k = k Int
136 type S a = a
137 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
138 and then S is saturated. This is a GHC extension.
139
140 - Similarly, also a GHC extension, we look through synonyms before complaining
141 about the form of a class or instance declaration
142
143 - Ambiguity checks involve functional dependencies, and it's easier to wait
144 until knots have been resolved before poking into them
145
146 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
147 finished building the loop. So to keep things simple, we postpone most validity
148 checking until step (3).
149
150 Knot tying
151 ~~~~~~~~~~
152 During step (1) we might fault in a TyCon defined in another module, and it might
153 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
154 knot around type declarations with ARecThing, so that the fault-in code can get
155 the TyCon being defined.
156
157 %************************************************************************
158 %* *
159 Check types AND do validity checking
160 * *
161 ************************************************************************
162 -}
163
164 funsSigCtxt :: [Located Name] -> UserTypeCtxt
165 -- Returns FunSigCtxt, with no redundant-context-reporting,
166 -- form a list of located names
167 funsSigCtxt (L _ name1 : _) = FunSigCtxt name1 False
168 funsSigCtxt [] = panic "funSigCtxt"
169
170 addSigCtxt :: UserTypeCtxt -> LHsType GhcRn -> TcM a -> TcM a
171 addSigCtxt ctxt hs_ty thing_inside
172 = setSrcSpan (getLoc hs_ty) $
173 addErrCtxt (pprSigCtxt ctxt hs_ty) $
174 thing_inside
175
176 pprSigCtxt :: UserTypeCtxt -> LHsType GhcRn -> SDoc
177 -- (pprSigCtxt ctxt <extra> <type>)
178 -- prints In the type signature for 'f':
179 -- f :: <type>
180 -- The <extra> is either empty or "the ambiguity check for"
181 pprSigCtxt ctxt hs_ty
182 | Just n <- isSigMaybe ctxt
183 = hang (text "In the type signature:")
184 2 (pprPrefixOcc n <+> dcolon <+> ppr hs_ty)
185
186 | otherwise
187 = hang (text "In" <+> pprUserTypeCtxt ctxt <> colon)
188 2 (ppr hs_ty)
189
190 tcHsSigWcType :: UserTypeCtxt -> LHsSigWcType GhcRn -> TcM Type
191 -- This one is used when we have a LHsSigWcType, but in
192 -- a place where wildards aren't allowed. The renamer has
193 -- already checked this, so we can simply ignore it.
194 tcHsSigWcType ctxt sig_ty = tcHsSigType ctxt (dropWildCards sig_ty)
195
196 kcHsSigType :: SkolemInfo -> [Located Name] -> LHsSigType GhcRn -> TcM ()
197 kcHsSigType skol_info names (HsIB { hsib_body = hs_ty
198 , hsib_ext = HsIBRn { hsib_vars = sig_vars }})
199 = addSigCtxt (funsSigCtxt names) hs_ty $
200 discardResult $
201 tcImplicitTKBndrs skol_info sig_vars $
202 tc_lhs_type typeLevelMode hs_ty liftedTypeKind
203 kcHsSigType _ _ (XHsImplicitBndrs _) = panic "kcHsSigType"
204
205 tcClassSigType :: SkolemInfo -> [Located Name] -> LHsSigType GhcRn -> TcM Type
206 -- Does not do validity checking; this must be done outside
207 -- the recursive class declaration "knot"
208 tcClassSigType skol_info names sig_ty
209 = addSigCtxt (funsSigCtxt names) (hsSigType sig_ty) $
210 tc_hs_sig_type_and_gen skol_info sig_ty liftedTypeKind
211
212 tcHsSigType :: UserTypeCtxt -> LHsSigType GhcRn -> TcM Type
213 -- Does validity checking
214 -- See Note [Recipe for checking a signature]
215 tcHsSigType ctxt sig_ty
216 = addSigCtxt ctxt (hsSigType sig_ty) $
217 do { traceTc "tcHsSigType {" (ppr sig_ty)
218 ; kind <- case expectedKindInCtxt ctxt of
219 AnythingKind -> newMetaKindVar
220 TheKind k -> return k
221 OpenKind -> newOpenTypeKind
222 -- The kind is checked by checkValidType, and isn't necessarily
223 -- of kind * in a Template Haskell quote eg [t| Maybe |]
224
225 -- Generalise here: see Note [Kind generalisation]
226 ; do_kind_gen <- decideKindGeneralisationPlan sig_ty
227 ; ty <- if do_kind_gen
228 then tc_hs_sig_type_and_gen skol_info sig_ty kind
229 else tc_hs_sig_type skol_info sig_ty kind
230
231 ; checkValidType ctxt ty
232 ; traceTc "end tcHsSigType }" (ppr ty)
233 ; return ty }
234 where
235 skol_info = SigTypeSkol ctxt
236
237 tc_hs_sig_type_and_gen :: SkolemInfo -> LHsSigType GhcRn -> Kind -> TcM Type
238 -- Kind-checks/desugars an 'LHsSigType',
239 -- solve equalities,
240 -- and then kind-generalizes.
241 -- This will never emit constraints, as it uses solveEqualities interally.
242 -- No validity checking, but it does zonk en route to generalization
243 tc_hs_sig_type_and_gen skol_info (HsIB { hsib_ext
244 = HsIBRn { hsib_vars = sig_vars }
245 , hsib_body = hs_ty }) kind
246 = do { (tkvs, ty) <- solveEqualities $
247 tcImplicitTKBndrs skol_info sig_vars $
248 tc_lhs_type typeLevelMode hs_ty kind
249 -- NB the call to solveEqualities, which unifies all those
250 -- kind variables floating about, immediately prior to
251 -- kind generalisation
252
253 -- We use the "InKnot" zonker, because this is called
254 -- on class method sigs in the knot
255 ; ty1 <- zonkPromoteTypeInKnot $ mkSpecForAllTys tkvs ty
256 ; kvs <- kindGeneralize ty1
257 ; zonkSigType (mkInvForAllTys kvs ty1) }
258
259 tc_hs_sig_type_and_gen _ (XHsImplicitBndrs _) _ = panic "tc_hs_sig_type_and_gen"
260
261 tc_hs_sig_type :: SkolemInfo -> LHsSigType GhcRn -> Kind -> TcM Type
262 -- Kind-check/desugar a 'LHsSigType', but does not solve
263 -- the equalities that arise from doing so; instead it may
264 -- emit kind-equality constraints into the monad
265 -- Zonking, but no validity checking
266 tc_hs_sig_type skol_info (HsIB { hsib_ext = HsIBRn { hsib_vars = sig_vars }
267 , hsib_body = hs_ty }) kind
268 = do { (tkvs, ty) <- tcImplicitTKBndrs skol_info sig_vars $
269 tc_lhs_type typeLevelMode hs_ty kind
270
271 -- need to promote any remaining metavariables; test case:
272 -- dependent/should_fail/T14066e.
273 ; zonkPromoteType (mkSpecForAllTys tkvs ty) }
274
275 tc_hs_sig_type _ (XHsImplicitBndrs _) _ = panic "tc_hs_sig_type"
276
277 -----------------
278 tcHsDeriv :: LHsSigType GhcRn -> TcM ([TyVar], (Class, [Type], [Kind]))
279 -- Like tcHsSigType, but for the ...deriving( C t1 ty2 ) clause
280 -- Returns the C, [ty1, ty2, and the kinds of C's remaining arguments
281 -- E.g. class C (a::*) (b::k->k)
282 -- data T a b = ... deriving( C Int )
283 -- returns ([k], C, [k, Int], [k->k])
284 tcHsDeriv hs_ty
285 = do { cls_kind <- newMetaKindVar
286 -- always safe to kind-generalize, because there
287 -- can be no covars in an outer scope
288 ; ty <- checkNoErrs $
289 -- avoid redundant error report with "illegal deriving", below
290 tc_hs_sig_type_and_gen (SigTypeSkol DerivClauseCtxt) hs_ty cls_kind
291 ; cls_kind <- zonkTcType cls_kind
292 ; let (tvs, pred) = splitForAllTys ty
293 ; let (args, _) = splitFunTys cls_kind
294 ; case getClassPredTys_maybe pred of
295 Just (cls, tys) -> return (tvs, (cls, tys, args))
296 Nothing -> failWithTc (text "Illegal deriving item" <+> quotes (ppr hs_ty)) }
297
298 -- | Typecheck something within the context of a deriving strategy.
299 -- This is of particular importance when the deriving strategy is @via@.
300 -- For instance:
301 --
302 -- @
303 -- deriving via (S a) instance C (T a)
304 -- @
305 --
306 -- We need to typecheck @S a@, and moreover, we need to extend the tyvar
307 -- environment with @a@ before typechecking @C (T a)@, since @S a@ quantified
308 -- the type variable @a@.
309 tcDerivStrategy
310 :: forall a.
311 UserTypeCtxt
312 -> Maybe (DerivStrategy GhcRn) -- ^ The deriving strategy
313 -> TcM ([TyVar], a) -- ^ The thing to typecheck within the context of the
314 -- deriving strategy, which might quantify some type
315 -- variables of its own.
316 -> TcM (Maybe (DerivStrategy GhcTc), [TyVar], a)
317 -- ^ The typechecked deriving strategy, all quantified tyvars, and
318 -- the payload of the typechecked thing.
319 tcDerivStrategy user_ctxt mds thing_inside
320 = case mds of
321 Nothing -> boring_case Nothing
322 Just ds -> do (ds', tvs, thing) <- tc_deriv_strategy ds
323 pure (Just ds', tvs, thing)
324 where
325 tc_deriv_strategy :: DerivStrategy GhcRn
326 -> TcM (DerivStrategy GhcTc, [TyVar], a)
327 tc_deriv_strategy StockStrategy = boring_case StockStrategy
328 tc_deriv_strategy AnyclassStrategy = boring_case AnyclassStrategy
329 tc_deriv_strategy NewtypeStrategy = boring_case NewtypeStrategy
330 tc_deriv_strategy (ViaStrategy ty) = do
331 cls_kind <- newMetaKindVar
332 ty' <- checkNoErrs $
333 tc_hs_sig_type_and_gen (SigTypeSkol user_ctxt) ty cls_kind
334 let (via_tvs, via_pred) = splitForAllTys ty'
335 tcExtendTyVarEnv via_tvs $ do
336 (thing_tvs, thing) <- thing_inside
337 pure (ViaStrategy via_pred, via_tvs ++ thing_tvs, thing)
338
339 boring_case :: mds -> TcM (mds, [TyVar], a)
340 boring_case mds = do
341 (thing_tvs, thing) <- thing_inside
342 pure (mds, thing_tvs, thing)
343
344 tcHsClsInstType :: UserTypeCtxt -- InstDeclCtxt or SpecInstCtxt
345 -> LHsSigType GhcRn
346 -> TcM ([TyVar], ThetaType, Class, [Type])
347 -- Like tcHsSigType, but for a class instance declaration
348 tcHsClsInstType user_ctxt hs_inst_ty
349 = setSrcSpan (getLoc (hsSigType hs_inst_ty)) $
350 do { inst_ty <- tc_hs_sig_type_and_gen (SigTypeSkol user_ctxt) hs_inst_ty constraintKind
351 ; checkValidInstance user_ctxt hs_inst_ty inst_ty }
352
353 ----------------------------------------------
354 -- | Type-check a visible type application
355 tcHsTypeApp :: LHsWcType GhcRn -> Kind -> TcM Type
356 -- See Note [Recipe for checking a signature] in TcHsType
357 tcHsTypeApp wc_ty kind
358 | HsWC { hswc_ext = sig_wcs, hswc_body = hs_ty } <- wc_ty
359 = do { ty <- solveLocalEqualities $
360 -- We are looking at a user-written type, very like a
361 -- signature so we want to solve its equalities right now
362 tcWildCardBindersX newWildTyVar Nothing sig_wcs $ \ _ ->
363 tcCheckLHsType hs_ty kind
364 ; ty <- zonkPromoteType ty
365 ; checkValidType TypeAppCtxt ty
366 ; return ty }
367 -- NB: we don't call emitWildcardHoleConstraints here, because
368 -- we want any holes in visible type applications to be used
369 -- without fuss. No errors, warnings, extensions, etc.
370 tcHsTypeApp (XHsWildCardBndrs _) _ = panic "tcHsTypeApp"
371
372 {-
373 ************************************************************************
374 * *
375 The main kind checker: no validity checks here
376 * *
377 ************************************************************************
378
379 First a couple of simple wrappers for kcHsType
380 -}
381
382 ---------------------------
383 tcHsOpenType, tcHsLiftedType,
384 tcHsOpenTypeNC, tcHsLiftedTypeNC :: LHsType GhcRn -> TcM TcType
385 -- Used for type signatures
386 -- Do not do validity checking
387 tcHsOpenType ty = addTypeCtxt ty $ tcHsOpenTypeNC ty
388 tcHsLiftedType ty = addTypeCtxt ty $ tcHsLiftedTypeNC ty
389
390 tcHsOpenTypeNC ty = do { ek <- newOpenTypeKind
391 ; tc_lhs_type typeLevelMode ty ek }
392 tcHsLiftedTypeNC ty = tc_lhs_type typeLevelMode ty liftedTypeKind
393
394 -- Like tcHsType, but takes an expected kind
395 tcCheckLHsType :: LHsType GhcRn -> Kind -> TcM TcType
396 tcCheckLHsType hs_ty exp_kind
397 = addTypeCtxt hs_ty $
398 tc_lhs_type typeLevelMode hs_ty exp_kind
399
400 tcLHsType :: LHsType GhcRn -> TcM (TcType, TcKind)
401 -- Called from outside: set the context
402 tcLHsType ty = addTypeCtxt ty (tc_infer_lhs_type typeLevelMode ty)
403
404 -- Like tcLHsType, but use it in a context where type synonyms and type families
405 -- do not need to be saturated, like in a GHCi :kind call
406 tcLHsTypeUnsaturated :: LHsType GhcRn -> TcM (TcType, TcKind)
407 tcLHsTypeUnsaturated ty = addTypeCtxt ty (tc_infer_lhs_type mode ty)
408 where
409 mode = allowUnsaturated typeLevelMode
410
411 ---------------------------
412 -- | Should we generalise the kind of this type signature?
413 -- We *should* generalise if the type is closed
414 -- or if NoMonoLocalBinds is set. Otherwise, nope.
415 -- See Note [Kind generalisation plan]
416 decideKindGeneralisationPlan :: LHsSigType GhcRn -> TcM Bool
417 decideKindGeneralisationPlan sig_ty@(HsIB { hsib_ext
418 = HsIBRn { hsib_closed = closed } })
419 = do { mono_locals <- xoptM LangExt.MonoLocalBinds
420 ; let should_gen = not mono_locals || closed
421 ; traceTc "decideKindGeneralisationPlan"
422 (ppr sig_ty $$ text "should gen?" <+> ppr should_gen)
423 ; return should_gen }
424 decideKindGeneralisationPlan(XHsImplicitBndrs _)
425 = panic "decideKindGeneralisationPlan"
426
427 {- Note [Kind generalisation plan]
428 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
429 When should we do kind-generalisation for user-written type signature?
430 Answer: we use the same rule as for value bindings:
431
432 * We always kind-generalise if the type signature is closed
433 * Additionally, we attempt to generalise if we have NoMonoLocalBinds
434
435 Trac #13337 shows the problem if we kind-generalise an open type (i.e.
436 one that mentions in-scope type variable
437 foo :: forall k (a :: k) proxy. (Typeable k, Typeable a)
438 => proxy a -> String
439 foo _ = case eqT :: Maybe (k :~: Type) of
440 Nothing -> ...
441 Just Refl -> case eqT :: Maybe (a :~: Int) of ...
442
443 In the expression type sig on the last line, we have (a :: k)
444 but (Int :: Type). Since (:~:) is kind-homogeneous, this requires
445 k ~ *, which is true in the Refl branch of the outer case.
446
447 That equality will be solved if we allow it to float out to the
448 implication constraint for the Refl match, but not not if we aggressively
449 attempt to solve all equalities the moment they occur; that is, when
450 checking (Maybe (a :~: Int)). (NB: solveEqualities fails unless it
451 solves all the kind equalities, which is the right thing at top level.)
452
453 So here the right thing is simply not to do kind generalisation!
454
455 ************************************************************************
456 * *
457 Type-checking modes
458 * *
459 ************************************************************************
460
461 The kind-checker is parameterised by a TcTyMode, which contains some
462 information about where we're checking a type.
463
464 The renamer issues errors about what it can. All errors issued here must
465 concern things that the renamer can't handle.
466
467 -}
468
469 -- | Info about the context in which we're checking a type. Currently,
470 -- differentiates only between types and kinds, but this will likely
471 -- grow, at least to include the distinction between patterns and
472 -- not-patterns.
473 data TcTyMode
474 = TcTyMode { mode_level :: TypeOrKind
475 , mode_unsat :: Bool -- True <=> allow unsaturated type families
476 }
477 -- The mode_unsat field is solely so that type families/synonyms can be unsaturated
478 -- in GHCi :kind calls
479
480 typeLevelMode :: TcTyMode
481 typeLevelMode = TcTyMode { mode_level = TypeLevel, mode_unsat = False }
482
483 kindLevelMode :: TcTyMode
484 kindLevelMode = TcTyMode { mode_level = KindLevel, mode_unsat = False }
485
486 allowUnsaturated :: TcTyMode -> TcTyMode
487 allowUnsaturated mode = mode { mode_unsat = True }
488
489 -- switch to kind level
490 kindLevel :: TcTyMode -> TcTyMode
491 kindLevel mode = mode { mode_level = KindLevel }
492
493 instance Outputable TcTyMode where
494 ppr = ppr . mode_level
495
496 {-
497 Note [Bidirectional type checking]
498 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
499 In expressions, whenever we see a polymorphic identifier, say `id`, we are
500 free to instantiate it with metavariables, knowing that we can always
501 re-generalize with type-lambdas when necessary. For example:
502
503 rank2 :: (forall a. a -> a) -> ()
504 x = rank2 id
505
506 When checking the body of `x`, we can instantiate `id` with a metavariable.
507 Then, when we're checking the application of `rank2`, we notice that we really
508 need a polymorphic `id`, and then re-generalize over the unconstrained
509 metavariable.
510
511 In types, however, we're not so lucky, because *we cannot re-generalize*!
512 There is no lambda. So, we must be careful only to instantiate at the last
513 possible moment, when we're sure we're never going to want the lost polymorphism
514 again. This is done in calls to tcInstTyBinders.
515
516 To implement this behavior, we use bidirectional type checking, where we
517 explicitly think about whether we know the kind of the type we're checking
518 or not. Note that there is a difference between not knowing a kind and
519 knowing a metavariable kind: the metavariables are TauTvs, and cannot become
520 forall-quantified kinds. Previously (before dependent types), there were
521 no higher-rank kinds, and so we could instantiate early and be sure that
522 no types would have polymorphic kinds, and so we could always assume that
523 the kind of a type was a fresh metavariable. Not so anymore, thus the
524 need for two algorithms.
525
526 For HsType forms that can never be kind-polymorphic, we implement only the
527 "down" direction, where we safely assume a metavariable kind. For HsType forms
528 that *can* be kind-polymorphic, we implement just the "up" (functions with
529 "infer" in their name) version, as we gain nothing by also implementing the
530 "down" version.
531
532 Note [Future-proofing the type checker]
533 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
534 As discussed in Note [Bidirectional type checking], each HsType form is
535 handled in *either* tc_infer_hs_type *or* tc_hs_type. These functions
536 are mutually recursive, so that either one can work for any type former.
537 But, we want to make sure that our pattern-matches are complete. So,
538 we have a bunch of repetitive code just so that we get warnings if we're
539 missing any patterns.
540
541 Note [The tcType invariant]
542 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
543 If tc_ty = tc_hs_type hs_ty exp_kind
544 then
545 typeKind tc_ty = exp_kind
546 without any zonking needed. The reason for this is that in
547 tcInferApps we see (F ty), and we kind-check 'ty' with an
548 expected-kind coming from F. Then, to make the resulting application
549 well kinded --- see Note [Ensure well-kinded types] in TcType --- we
550 need the kind-checked 'ty' to have exactly the kind that F expects,
551 with no funny zonking nonsense in between.
552
553 The tcType invariant also applies to checkExpectedKind: if
554 (tc_ty, _, _) = checkExpectedKind ty act_ki exp_ki
555 then
556 typeKind tc_ty = exp_ki
557 -}
558
559 ------------------------------------------
560 -- | Check and desugar a type, returning the core type and its
561 -- possibly-polymorphic kind. Much like 'tcInferRho' at the expression
562 -- level.
563 tc_infer_lhs_type :: TcTyMode -> LHsType GhcRn -> TcM (TcType, TcKind)
564 tc_infer_lhs_type mode (L span ty)
565 = setSrcSpan span $
566 do { (ty', kind) <- tc_infer_hs_type mode ty
567 ; return (ty', kind) }
568
569 -- | Infer the kind of a type and desugar. This is the "up" type-checker,
570 -- as described in Note [Bidirectional type checking]
571 tc_infer_hs_type :: TcTyMode -> HsType GhcRn -> TcM (TcType, TcKind)
572 tc_infer_hs_type mode (HsParTy _ t) = tc_infer_lhs_type mode t
573 tc_infer_hs_type mode (HsTyVar _ _ (L _ tv)) = tcTyVar mode tv
574
575 tc_infer_hs_type mode (HsAppTy _ ty1 ty2)
576 = do { let (hs_fun_ty, hs_arg_tys) = splitHsAppTys ty1 [ty2]
577 ; (fun_ty, fun_kind) <- tc_infer_lhs_type mode hs_fun_ty
578 -- A worry: what if fun_kind needs zoonking?
579 -- We used to zonk it here, but that got fun_ty and fun_kind
580 -- out of sync (see the precondition to tcTyApps), which caused
581 -- Trac #14873. So I'm now zonking in tcTyVar, and not here.
582 -- Is that enough? Seems so, but I can't see how to be certain.
583 ; tcTyApps mode hs_fun_ty fun_ty fun_kind hs_arg_tys }
584
585 tc_infer_hs_type mode (HsOpTy _ lhs lhs_op@(L _ hs_op) rhs)
586 | not (hs_op `hasKey` funTyConKey)
587 = do { (op, op_kind) <- tcTyVar mode hs_op
588 -- See "A worry" in the HsApp case
589 ; tcTyApps mode (noLoc $ HsTyVar noExt NotPromoted lhs_op) op op_kind
590 [lhs, rhs] }
591
592 tc_infer_hs_type mode (HsKindSig _ ty sig)
593 = do { sig' <- tcLHsKindSig KindSigCtxt sig
594 -- We must typecheck the kind signature, and solve all
595 -- its equalities etc; from this point on we may do
596 -- things like instantiate its foralls, so it needs
597 -- to be fully determined (Trac #14904)
598 ; traceTc "tc_infer_hs_type:sig" (ppr ty $$ ppr sig')
599 ; ty' <- tc_lhs_type mode ty sig'
600 ; return (ty', sig') }
601
602 -- HsSpliced is an annotation produced by 'RnSplice.rnSpliceType' to communicate
603 -- the splice location to the typechecker. Here we skip over it in order to have
604 -- the same kind inferred for a given expression whether it was produced from
605 -- splices or not.
606 --
607 -- See Note [Delaying modFinalizers in untyped splices].
608 tc_infer_hs_type mode (HsSpliceTy _ (HsSpliced _ _ (HsSplicedTy ty)))
609 = tc_infer_hs_type mode ty
610
611 tc_infer_hs_type mode (HsDocTy _ ty _) = tc_infer_lhs_type mode ty
612 tc_infer_hs_type _ (XHsType (NHsCoreTy ty)) = return (ty, typeKind ty)
613 tc_infer_hs_type mode other_ty
614 = do { kv <- newMetaKindVar
615 ; ty' <- tc_hs_type mode other_ty kv
616 ; return (ty', kv) }
617
618 ------------------------------------------
619 tc_lhs_type :: TcTyMode -> LHsType GhcRn -> TcKind -> TcM TcType
620 tc_lhs_type mode (L span ty) exp_kind
621 = setSrcSpan span $
622 tc_hs_type mode ty exp_kind
623
624 ------------------------------------------
625 tc_fun_type :: TcTyMode -> LHsType GhcRn -> LHsType GhcRn -> TcKind
626 -> TcM TcType
627 tc_fun_type mode ty1 ty2 exp_kind = case mode_level mode of
628 TypeLevel ->
629 do { arg_k <- newOpenTypeKind
630 ; res_k <- newOpenTypeKind
631 ; ty1' <- tc_lhs_type mode ty1 arg_k
632 ; ty2' <- tc_lhs_type mode ty2 res_k
633 ; checkExpectedKind (HsFunTy noExt ty1 ty2) (mkFunTy ty1' ty2')
634 liftedTypeKind exp_kind }
635 KindLevel -> -- no representation polymorphism in kinds. yet.
636 do { ty1' <- tc_lhs_type mode ty1 liftedTypeKind
637 ; ty2' <- tc_lhs_type mode ty2 liftedTypeKind
638 ; checkExpectedKind (HsFunTy noExt ty1 ty2) (mkFunTy ty1' ty2')
639 liftedTypeKind exp_kind }
640
641 ------------------------------------------
642 tc_hs_type :: TcTyMode -> HsType GhcRn -> TcKind -> TcM TcType
643 -- See Note [The tcType invariant]
644 -- See Note [Bidirectional type checking]
645
646 tc_hs_type mode (HsParTy _ ty) exp_kind = tc_lhs_type mode ty exp_kind
647 tc_hs_type mode (HsDocTy _ ty _) exp_kind = tc_lhs_type mode ty exp_kind
648 tc_hs_type _ ty@(HsBangTy _ bang _) _
649 -- While top-level bangs at this point are eliminated (eg !(Maybe Int)),
650 -- other kinds of bangs are not (eg ((!Maybe) Int)). These kinds of
651 -- bangs are invalid, so fail. (#7210, #14761)
652 = do { let bangError err = failWith $
653 text "Unexpected" <+> text err <+> text "annotation:" <+> ppr ty $$
654 text err <+> text "annotation cannot appear nested inside a type"
655 ; case bang of
656 HsSrcBang _ SrcUnpack _ -> bangError "UNPACK"
657 HsSrcBang _ SrcNoUnpack _ -> bangError "NOUNPACK"
658 HsSrcBang _ NoSrcUnpack SrcLazy -> bangError "laziness"
659 HsSrcBang _ _ _ -> bangError "strictness" }
660 tc_hs_type _ ty@(HsRecTy {}) _
661 -- Record types (which only show up temporarily in constructor
662 -- signatures) should have been removed by now
663 = failWithTc (text "Record syntax is illegal here:" <+> ppr ty)
664
665 -- HsSpliced is an annotation produced by 'RnSplice.rnSpliceType'.
666 -- Here we get rid of it and add the finalizers to the global environment
667 -- while capturing the local environment.
668 --
669 -- See Note [Delaying modFinalizers in untyped splices].
670 tc_hs_type mode (HsSpliceTy _ (HsSpliced _ mod_finalizers (HsSplicedTy ty)))
671 exp_kind
672 = do addModFinalizersWithLclEnv mod_finalizers
673 tc_hs_type mode ty exp_kind
674
675 -- This should never happen; type splices are expanded by the renamer
676 tc_hs_type _ ty@(HsSpliceTy {}) _exp_kind
677 = failWithTc (text "Unexpected type splice:" <+> ppr ty)
678
679 ---------- Functions and applications
680 tc_hs_type mode (HsFunTy _ ty1 ty2) exp_kind
681 = tc_fun_type mode ty1 ty2 exp_kind
682
683 tc_hs_type mode (HsOpTy _ ty1 (L _ op) ty2) exp_kind
684 | op `hasKey` funTyConKey
685 = tc_fun_type mode ty1 ty2 exp_kind
686
687 --------- Foralls
688 tc_hs_type mode forall@(HsForAllTy { hst_bndrs = hs_tvs, hst_body = ty }) exp_kind
689 = do { (tvs', ty') <- tcExplicitTKBndrs (ForAllSkol (ppr forall)) hs_tvs $
690 tc_lhs_type mode ty exp_kind
691 -- Do not kind-generalise here! See Note [Kind generalisation]
692 -- Why exp_kind? See Note [Body kind of HsForAllTy]
693 ; let bndrs = mkTyVarBinders Specified tvs'
694 ; return (mkForAllTys bndrs ty') }
695
696 tc_hs_type mode (HsQualTy { hst_ctxt = ctxt, hst_body = ty }) exp_kind
697 | null (unLoc ctxt)
698 = tc_lhs_type mode ty exp_kind
699
700 | otherwise
701 = do { ctxt' <- tc_hs_context mode ctxt
702
703 -- See Note [Body kind of a HsQualTy]
704 ; ty' <- if isConstraintKind exp_kind
705 then tc_lhs_type mode ty constraintKind
706 else do { ek <- newOpenTypeKind
707 -- The body kind (result of the function)
708 -- can be * or #, hence newOpenTypeKind
709 ; ty' <- tc_lhs_type mode ty ek
710 ; checkExpectedKind (unLoc ty) ty' liftedTypeKind exp_kind }
711
712 ; return (mkPhiTy ctxt' ty') }
713
714 --------- Lists, arrays, and tuples
715 tc_hs_type mode rn_ty@(HsListTy _ elt_ty) exp_kind
716 = do { tau_ty <- tc_lhs_type mode elt_ty liftedTypeKind
717 ; checkWiredInTyCon listTyCon
718 ; checkExpectedKind rn_ty (mkListTy tau_ty) liftedTypeKind exp_kind }
719
720 -- See Note [Distinguishing tuple kinds] in HsTypes
721 -- See Note [Inferring tuple kinds]
722 tc_hs_type mode rn_ty@(HsTupleTy _ HsBoxedOrConstraintTuple hs_tys) exp_kind
723 -- (NB: not zonking before looking at exp_k, to avoid left-right bias)
724 | Just tup_sort <- tupKindSort_maybe exp_kind
725 = traceTc "tc_hs_type tuple" (ppr hs_tys) >>
726 tc_tuple rn_ty mode tup_sort hs_tys exp_kind
727 | otherwise
728 = do { traceTc "tc_hs_type tuple 2" (ppr hs_tys)
729 ; (tys, kinds) <- mapAndUnzipM (tc_infer_lhs_type mode) hs_tys
730 ; kinds <- mapM zonkTcType kinds
731 -- Infer each arg type separately, because errors can be
732 -- confusing if we give them a shared kind. Eg Trac #7410
733 -- (Either Int, Int), we do not want to get an error saying
734 -- "the second argument of a tuple should have kind *->*"
735
736 ; let (arg_kind, tup_sort)
737 = case [ (k,s) | k <- kinds
738 , Just s <- [tupKindSort_maybe k] ] of
739 ((k,s) : _) -> (k,s)
740 [] -> (liftedTypeKind, BoxedTuple)
741 -- In the [] case, it's not clear what the kind is, so guess *
742
743 ; tys' <- sequence [ setSrcSpan loc $
744 checkExpectedKind hs_ty ty kind arg_kind
745 | ((L loc hs_ty),ty,kind) <- zip3 hs_tys tys kinds ]
746
747 ; finish_tuple rn_ty tup_sort tys' (map (const arg_kind) tys') exp_kind }
748
749
750 tc_hs_type mode rn_ty@(HsTupleTy _ hs_tup_sort tys) exp_kind
751 = tc_tuple rn_ty mode tup_sort tys exp_kind
752 where
753 tup_sort = case hs_tup_sort of -- Fourth case dealt with above
754 HsUnboxedTuple -> UnboxedTuple
755 HsBoxedTuple -> BoxedTuple
756 HsConstraintTuple -> ConstraintTuple
757 _ -> panic "tc_hs_type HsTupleTy"
758
759 tc_hs_type mode rn_ty@(HsSumTy _ hs_tys) exp_kind
760 = do { let arity = length hs_tys
761 ; arg_kinds <- mapM (\_ -> newOpenTypeKind) hs_tys
762 ; tau_tys <- zipWithM (tc_lhs_type mode) hs_tys arg_kinds
763 ; let arg_reps = map getRuntimeRepFromKind arg_kinds
764 arg_tys = arg_reps ++ tau_tys
765 ; checkExpectedKind rn_ty
766 (mkTyConApp (sumTyCon arity) arg_tys)
767 (unboxedSumKind arg_reps)
768 exp_kind
769 }
770
771 --------- Promoted lists and tuples
772 tc_hs_type mode rn_ty@(HsExplicitListTy _ _ tys) exp_kind
773 = do { tks <- mapM (tc_infer_lhs_type mode) tys
774 ; (taus', kind) <- unifyKinds tys tks
775 ; let ty = (foldr (mk_cons kind) (mk_nil kind) taus')
776 ; checkExpectedKind rn_ty ty (mkListTy kind) exp_kind }
777 where
778 mk_cons k a b = mkTyConApp (promoteDataCon consDataCon) [k, a, b]
779 mk_nil k = mkTyConApp (promoteDataCon nilDataCon) [k]
780
781 tc_hs_type mode rn_ty@(HsExplicitTupleTy _ tys) exp_kind
782 -- using newMetaKindVar means that we force instantiations of any polykinded
783 -- types. At first, I just used tc_infer_lhs_type, but that led to #11255.
784 = do { ks <- replicateM arity newMetaKindVar
785 ; taus <- zipWithM (tc_lhs_type mode) tys ks
786 ; let kind_con = tupleTyCon Boxed arity
787 ty_con = promotedTupleDataCon Boxed arity
788 tup_k = mkTyConApp kind_con ks
789 ; checkExpectedKind rn_ty (mkTyConApp ty_con (ks ++ taus)) tup_k exp_kind }
790 where
791 arity = length tys
792
793 --------- Constraint types
794 tc_hs_type mode rn_ty@(HsIParamTy _ (L _ n) ty) exp_kind
795 = do { MASSERT( isTypeLevel (mode_level mode) )
796 ; ty' <- tc_lhs_type mode ty liftedTypeKind
797 ; let n' = mkStrLitTy $ hsIPNameFS n
798 ; ipClass <- tcLookupClass ipClassName
799 ; checkExpectedKind rn_ty (mkClassPred ipClass [n',ty'])
800 constraintKind exp_kind }
801
802 tc_hs_type _ rn_ty@(HsStarTy _ _) exp_kind
803 -- Desugaring 'HsStarTy' to 'Data.Kind.Type' here means that we don't have to
804 -- handle it in 'coreView' and 'tcView'.
805 = checkExpectedKind rn_ty liftedTypeKind liftedTypeKind exp_kind
806
807 --------- Literals
808 tc_hs_type _ rn_ty@(HsTyLit _ (HsNumTy _ n)) exp_kind
809 = do { checkWiredInTyCon typeNatKindCon
810 ; checkExpectedKind rn_ty (mkNumLitTy n) typeNatKind exp_kind }
811
812 tc_hs_type _ rn_ty@(HsTyLit _ (HsStrTy _ s)) exp_kind
813 = do { checkWiredInTyCon typeSymbolKindCon
814 ; checkExpectedKind rn_ty (mkStrLitTy s) typeSymbolKind exp_kind }
815
816 --------- Potentially kind-polymorphic types: call the "up" checker
817 -- See Note [Future-proofing the type checker]
818 tc_hs_type mode ty@(HsTyVar {}) ek = tc_infer_hs_type_ek mode ty ek
819 tc_hs_type mode ty@(HsAppTy {}) ek = tc_infer_hs_type_ek mode ty ek
820 tc_hs_type mode ty@(HsOpTy {}) ek = tc_infer_hs_type_ek mode ty ek
821 tc_hs_type mode ty@(HsKindSig {}) ek = tc_infer_hs_type_ek mode ty ek
822 tc_hs_type mode ty@(XHsType (NHsCoreTy{})) ek = tc_infer_hs_type_ek mode ty ek
823
824 tc_hs_type _ (HsWildCardTy wc) exp_kind
825 = do { wc_ty <- tcWildCardOcc wc exp_kind
826 ; return (mkNakedCastTy wc_ty (mkTcNomReflCo exp_kind))
827 -- Take care here! Even though the coercion is Refl,
828 -- we still need it to establish Note [The tcType invariant]
829 }
830
831 tcWildCardOcc :: HsWildCardInfo -> Kind -> TcM TcType
832 tcWildCardOcc wc_info exp_kind
833 = do { wc_tv <- tcLookupTyVar (wildCardName wc_info)
834 -- The wildcard's kind should be an un-filled-in meta tyvar
835 ; checkExpectedKind (HsWildCardTy wc_info) (mkTyVarTy wc_tv)
836 (tyVarKind wc_tv) exp_kind }
837
838 ---------------------------
839 -- | Call 'tc_infer_hs_type' and check its result against an expected kind.
840 tc_infer_hs_type_ek :: TcTyMode -> HsType GhcRn -> TcKind -> TcM TcType
841 tc_infer_hs_type_ek mode hs_ty ek
842 = do { (ty, k) <- tc_infer_hs_type mode hs_ty
843 ; checkExpectedKind hs_ty ty k ek }
844
845 ---------------------------
846 tupKindSort_maybe :: TcKind -> Maybe TupleSort
847 tupKindSort_maybe k
848 | Just (k', _) <- splitCastTy_maybe k = tupKindSort_maybe k'
849 | Just k' <- tcView k = tupKindSort_maybe k'
850 | isConstraintKind k = Just ConstraintTuple
851 | isLiftedTypeKind k = Just BoxedTuple
852 | otherwise = Nothing
853
854 tc_tuple :: HsType GhcRn -> TcTyMode -> TupleSort -> [LHsType GhcRn] -> TcKind -> TcM TcType
855 tc_tuple rn_ty mode tup_sort tys exp_kind
856 = do { arg_kinds <- case tup_sort of
857 BoxedTuple -> return (nOfThem arity liftedTypeKind)
858 UnboxedTuple -> mapM (\_ -> newOpenTypeKind) tys
859 ConstraintTuple -> return (nOfThem arity constraintKind)
860 ; tau_tys <- zipWithM (tc_lhs_type mode) tys arg_kinds
861 ; finish_tuple rn_ty tup_sort tau_tys arg_kinds exp_kind }
862 where
863 arity = length tys
864
865 finish_tuple :: HsType GhcRn
866 -> TupleSort
867 -> [TcType] -- ^ argument types
868 -> [TcKind] -- ^ of these kinds
869 -> TcKind -- ^ expected kind of the whole tuple
870 -> TcM TcType
871 finish_tuple rn_ty tup_sort tau_tys tau_kinds exp_kind
872 = do { traceTc "finish_tuple" (ppr res_kind $$ ppr tau_kinds $$ ppr exp_kind)
873 ; let arg_tys = case tup_sort of
874 -- See also Note [Unboxed tuple RuntimeRep vars] in TyCon
875 UnboxedTuple -> tau_reps ++ tau_tys
876 BoxedTuple -> tau_tys
877 ConstraintTuple -> tau_tys
878 ; tycon <- case tup_sort of
879 ConstraintTuple
880 | arity > mAX_CTUPLE_SIZE
881 -> failWith (bigConstraintTuple arity)
882 | otherwise -> tcLookupTyCon (cTupleTyConName arity)
883 BoxedTuple -> do { let tc = tupleTyCon Boxed arity
884 ; checkWiredInTyCon tc
885 ; return tc }
886 UnboxedTuple -> return (tupleTyCon Unboxed arity)
887 ; checkExpectedKind rn_ty (mkTyConApp tycon arg_tys) res_kind exp_kind }
888 where
889 arity = length tau_tys
890 tau_reps = map getRuntimeRepFromKind tau_kinds
891 res_kind = case tup_sort of
892 UnboxedTuple -> unboxedTupleKind tau_reps
893 BoxedTuple -> liftedTypeKind
894 ConstraintTuple -> constraintKind
895
896 bigConstraintTuple :: Arity -> MsgDoc
897 bigConstraintTuple arity
898 = hang (text "Constraint tuple arity too large:" <+> int arity
899 <+> parens (text "max arity =" <+> int mAX_CTUPLE_SIZE))
900 2 (text "Instead, use a nested tuple")
901
902 ---------------------------
903 -- | Apply a type of a given kind to a list of arguments. This instantiates
904 -- invisible parameters as necessary. Always consumes all the arguments,
905 -- using matchExpectedFunKind as necessary.
906 -- This takes an optional @VarEnv Kind@ which maps kind variables to kinds.
907 -- These kinds should be used to instantiate invisible kind variables;
908 -- they come from an enclosing class for an associated type/data family.
909 tcInferApps :: TcTyMode
910 -> Maybe (VarEnv Kind) -- ^ Possibly, kind info (see above)
911 -> LHsType GhcRn -- ^ Function (for printing only)
912 -> TcType -- ^ Function (could be knot-tied)
913 -> TcKind -- ^ Function kind (zonked)
914 -> [LHsType GhcRn] -- ^ Args
915 -> TcM (TcType, [TcType], TcKind) -- ^ (f args, args, result kind)
916 -- Precondition: typeKind fun_ty = fun_ki
917 -- Reason: we will return a type application like (fun_ty arg1 ... argn),
918 -- and that type must be well-kinded
919 -- See Note [The tcType invariant]
920 tcInferApps mode mb_kind_info orig_hs_ty fun_ty fun_ki orig_hs_args
921 = do { traceTc "tcInferApps {" (ppr orig_hs_ty $$ ppr orig_hs_args $$ ppr fun_ki)
922 ; stuff <- go 1 [] empty_subst fun_ty orig_ki_binders orig_inner_ki orig_hs_args
923 ; traceTc "tcInferApps }" empty
924 ; return stuff }
925 where
926 empty_subst = mkEmptyTCvSubst $ mkInScopeSet $
927 tyCoVarsOfType fun_ki
928 (orig_ki_binders, orig_inner_ki) = tcSplitPiTys fun_ki
929
930 go :: Int -- the # of the next argument
931 -> [TcType] -- already type-checked args, in reverse order
932 -> TCvSubst -- instantiating substitution
933 -> TcType -- function applied to some args, could be knot-tied
934 -> [TyBinder] -- binders in function kind (both vis. and invis.)
935 -> TcKind -- function kind body (not a Pi-type)
936 -> [LHsType GhcRn] -- un-type-checked args
937 -> TcM (TcType, [TcType], TcKind) -- same as overall return type
938
939 -- no user-written args left. We're done!
940 go _ acc_args subst fun ki_binders inner_ki []
941 = return (fun, reverse acc_args, substTy subst $ mkPiTys ki_binders inner_ki)
942
943 -- The function's kind has a binder. Is it visible or invisible?
944 go n acc_args subst fun (ki_binder:ki_binders) inner_ki
945 all_args@(arg:args)
946 | isInvisibleBinder ki_binder
947 -- It's invisible. Instantiate.
948 = do { traceTc "tcInferApps (invis)" (ppr ki_binder $$ ppr subst)
949 ; (subst', arg') <- tcInstTyBinder mb_kind_info subst ki_binder
950 ; go n (arg' : acc_args) subst' (mkNakedAppTy fun arg')
951 ki_binders inner_ki all_args }
952
953 | otherwise
954 -- It's visible. Check the next user-written argument
955 = do { traceTc "tcInferApps (vis)" (vcat [ ppr ki_binder, ppr arg
956 , ppr (tyBinderType ki_binder)
957 , ppr subst ])
958 ; arg' <- addErrCtxt (funAppCtxt orig_hs_ty arg n) $
959 tc_lhs_type mode arg (substTy subst $ tyBinderType ki_binder)
960 ; let subst' = extendTvSubstBinderAndInScope subst ki_binder arg'
961 ; go (n+1) (arg' : acc_args) subst'
962 (mkNakedAppTy fun arg')
963 ki_binders inner_ki args }
964
965 -- We've run out of known binders in the functions's kind.
966 go n acc_args subst fun [] inner_ki all_args
967 | not (null new_ki_binders)
968 -- But, after substituting, we have more binders.
969 = go n acc_args zapped_subst fun new_ki_binders new_inner_ki all_args
970
971 | otherwise
972 -- Even after substituting, still no binders. Use matchExpectedFunKind
973 = do { traceTc "tcInferApps (no binder)" (ppr new_inner_ki $$ ppr zapped_subst)
974 ; (co, arg_k, res_k) <- matchExpectedFunKind hs_ty substed_inner_ki
975 ; let new_in_scope = tyCoVarsOfTypes [arg_k, res_k]
976 subst' = zapped_subst `extendTCvInScopeSet` new_in_scope
977 ; go n acc_args subst'
978 (fun `mkNakedCastTy` co)
979 [mkAnonBinder arg_k]
980 res_k all_args }
981 where
982 substed_inner_ki = substTy subst inner_ki
983 (new_ki_binders, new_inner_ki) = tcSplitPiTys substed_inner_ki
984 zapped_subst = zapTCvSubst subst
985 hs_ty = mkHsAppTys orig_hs_ty (take (n-1) orig_hs_args)
986
987
988 -- | Applies a type to a list of arguments.
989 -- Always consumes all the arguments, using 'matchExpectedFunKind' as
990 -- necessary. If you wish to apply a type to a list of HsTypes, this is
991 -- your function.
992 -- Used for type-checking types only.
993 tcTyApps :: TcTyMode
994 -> LHsType GhcRn -- ^ Function (for printing only)
995 -> TcType -- ^ Function (could be knot-tied)
996 -> TcKind -- ^ Function kind (zonked)
997 -> [LHsType GhcRn] -- ^ Args
998 -> TcM (TcType, TcKind) -- ^ (f args, result kind)
999 -- Precondition: see precondition for tcInferApps
1000 tcTyApps mode orig_hs_ty fun_ty fun_ki args
1001 = do { (ty', _args, ki') <- tcInferApps mode Nothing orig_hs_ty fun_ty fun_ki args
1002 ; return (ty', ki') }
1003
1004 --------------------------
1005 -- Like checkExpectedKindX, but returns only the final type; convenient wrapper
1006 -- Obeys Note [The tcType invariant]
1007 checkExpectedKind :: HsType GhcRn -- type we're checking (for printing)
1008 -> TcType -- type we're checking (might be knot-tied)
1009 -> TcKind -- the known kind of that type
1010 -> TcKind -- the expected kind
1011 -> TcM TcType
1012 checkExpectedKind hs_ty ty act exp
1013 = fstOf3 <$> checkExpectedKindX Nothing (ppr hs_ty) ty act exp
1014
1015 checkExpectedKindX :: Maybe (VarEnv Kind) -- Possibly, instantiations for kind vars
1016 -> SDoc -- HsType whose kind we're checking
1017 -> TcType -- the type whose kind we're checking
1018 -> TcKind -- the known kind of that type, k
1019 -> TcKind -- the expected kind, exp_kind
1020 -> TcM (TcType, [TcType], TcCoercionN)
1021 -- (the new args, the coercion)
1022 -- Instantiate a kind (if necessary) and then call unifyType
1023 -- (checkExpectedKind ty act_kind exp_kind)
1024 -- checks that the actual kind act_kind is compatible
1025 -- with the expected kind exp_kind
1026 checkExpectedKindX mb_kind_env pp_hs_ty ty act_kind exp_kind
1027 = do { -- We need to make sure that both kinds have the same number of implicit
1028 -- foralls out front. If the actual kind has more, instantiate accordingly.
1029 -- Otherwise, just pass the type & kind through: the errors are caught
1030 -- in unifyType.
1031 let (exp_bndrs, _) = splitPiTysInvisible exp_kind
1032 n_exp = length exp_bndrs
1033 ; (new_args, act_kind') <- instantiateTyUntilN mb_kind_env n_exp act_kind
1034
1035 ; let origin = TypeEqOrigin { uo_actual = act_kind'
1036 , uo_expected = exp_kind
1037 , uo_thing = Just pp_hs_ty
1038 , uo_visible = True } -- the hs_ty is visible
1039 ty' = mkNakedAppTys ty new_args
1040
1041 ; traceTc "checkExpectedKind" $
1042 vcat [ pp_hs_ty
1043 , text "act_kind:" <+> ppr act_kind
1044 , text "act_kind':" <+> ppr act_kind'
1045 , text "exp_kind:" <+> ppr exp_kind ]
1046
1047 ; if act_kind' `tcEqType` exp_kind
1048 then return (ty', new_args, mkTcNomReflCo exp_kind) -- This is very common
1049 else do { co_k <- uType KindLevel origin act_kind' exp_kind
1050 ; traceTc "checkExpectedKind" (vcat [ ppr act_kind
1051 , ppr exp_kind
1052 , ppr co_k ])
1053 ; let result_ty = ty' `mkNakedCastTy` co_k
1054 -- See Note [The tcType invariant]
1055 ; return (result_ty, new_args, co_k) } }
1056
1057 -- | Instantiate @n@ invisible arguments to a type. If @n <= 0@, no instantiation
1058 -- occurs. If @n@ is too big, then all available invisible arguments are instantiated.
1059 -- (In other words, this function is very forgiving about bad values of @n@.)
1060 instantiateTyN :: Maybe (VarEnv Kind) -- ^ Predetermined instantiations
1061 -- (for assoc. type patterns)
1062 -> Int -- ^ @n@
1063 -> [TyBinder] -> TcKind -- ^ its kind
1064 -> TcM ([TcType], TcKind) -- ^ The inst'ed type, new args, kind
1065 instantiateTyN mb_kind_env n bndrs inner_ki
1066 | n <= 0
1067 = return ([], ki)
1068
1069 | otherwise
1070 = do { (subst, inst_args) <- tcInstTyBinders empty_subst mb_kind_env inst_bndrs
1071 ; let rebuilt_ki = mkPiTys leftover_bndrs inner_ki
1072 ki' = substTy subst rebuilt_ki
1073 ; traceTc "instantiateTyN" (vcat [ ppr ki
1074 , ppr n
1075 , ppr subst
1076 , ppr rebuilt_ki
1077 , ppr ki' ])
1078 ; return (inst_args, ki') }
1079 where
1080 -- NB: splitAt is forgiving with invalid numbers
1081 (inst_bndrs, leftover_bndrs) = splitAt n bndrs
1082 ki = mkPiTys bndrs inner_ki
1083 empty_subst = mkEmptyTCvSubst (mkInScopeSet (tyCoVarsOfType ki))
1084
1085 -- | Instantiate a type to have at most @n@ invisible arguments.
1086 instantiateTyUntilN :: Maybe (VarEnv Kind) -- ^ Possibly, instantiations for vars
1087 -> Int -- ^ @n@
1088 -> TcKind -- ^ its kind
1089 -> TcM ([TcType], TcKind) -- ^ The new args, final kind
1090 instantiateTyUntilN mb_kind_env n ki
1091 = let (bndrs, inner_ki) = splitPiTysInvisible ki
1092 num_to_inst = length bndrs - n
1093 in
1094 instantiateTyN mb_kind_env num_to_inst bndrs inner_ki
1095
1096 ---------------------------
1097 tcHsMbContext :: Maybe (LHsContext GhcRn) -> TcM [PredType]
1098 tcHsMbContext Nothing = return []
1099 tcHsMbContext (Just cxt) = tcHsContext cxt
1100
1101 tcHsContext :: LHsContext GhcRn -> TcM [PredType]
1102 tcHsContext = tc_hs_context typeLevelMode
1103
1104 tcLHsPredType :: LHsType GhcRn -> TcM PredType
1105 tcLHsPredType = tc_lhs_pred typeLevelMode
1106
1107 tc_hs_context :: TcTyMode -> LHsContext GhcRn -> TcM [PredType]
1108 tc_hs_context mode ctxt = mapM (tc_lhs_pred mode) (unLoc ctxt)
1109
1110 tc_lhs_pred :: TcTyMode -> LHsType GhcRn -> TcM PredType
1111 tc_lhs_pred mode pred = tc_lhs_type mode pred constraintKind
1112
1113 ---------------------------
1114 tcTyVar :: TcTyMode -> Name -> TcM (TcType, TcKind)
1115 -- See Note [Type checking recursive type and class declarations]
1116 -- in TcTyClsDecls
1117 tcTyVar mode name -- Could be a tyvar, a tycon, or a datacon
1118 = do { traceTc "lk1" (ppr name)
1119 ; thing <- tcLookup name
1120 ; case thing of
1121 ATyVar _ tv -> -- Important: zonk before returning
1122 -- We may have the application ((a::kappa) b)
1123 -- where kappa is already unified to (k1 -> k2)
1124 -- Then we want to see that arrow. Best done
1125 -- here because we are also maintaining
1126 -- Note [The tcType invariant], so we don't just
1127 -- want to zonk the kind, leaving the TyVar
1128 -- un-zonked (Trac #114873)
1129 do { ty <- zonkTcTyVar tv
1130 ; return (ty, typeKind ty) }
1131
1132 ATcTyCon tc_tc -> do { -- See Note [GADT kind self-reference]
1133 unless
1134 (isTypeLevel (mode_level mode))
1135 (promotionErr name TyConPE)
1136 ; check_tc tc_tc
1137 ; tc <- get_loopy_tc name tc_tc
1138 ; handle_tyfams tc tc_tc }
1139 -- mkNakedTyConApp: see Note [Type-checking inside the knot]
1140
1141 AGlobal (ATyCon tc)
1142 -> do { check_tc tc
1143 ; handle_tyfams tc tc }
1144
1145 AGlobal (AConLike (RealDataCon dc))
1146 -> do { data_kinds <- xoptM LangExt.DataKinds
1147 ; unless (data_kinds || specialPromotedDc dc) $
1148 promotionErr name NoDataKindsDC
1149 ; when (isFamInstTyCon (dataConTyCon dc)) $
1150 -- see Trac #15245
1151 promotionErr name FamDataConPE
1152 ; let (_, _, _, theta, _, _) = dataConFullSig dc
1153 ; case dc_theta_illegal_constraint theta of
1154 Just pred -> promotionErr name $
1155 ConstrainedDataConPE pred
1156 Nothing -> pure ()
1157 ; let tc = promoteDataCon dc
1158 ; return (mkNakedTyConApp tc [], tyConKind tc) }
1159
1160 APromotionErr err -> promotionErr name err
1161
1162 _ -> wrongThingErr "type" thing name }
1163 where
1164 check_tc :: TyCon -> TcM ()
1165 check_tc tc = do { data_kinds <- xoptM LangExt.DataKinds
1166 ; unless (isTypeLevel (mode_level mode) ||
1167 data_kinds ||
1168 isKindTyCon tc) $
1169 promotionErr name NoDataKindsTC }
1170
1171 -- if we are type-checking a type family tycon, we must instantiate
1172 -- any invisible arguments right away. Otherwise, we get #11246
1173 handle_tyfams :: TyCon -- the tycon to instantiate (might be loopy)
1174 -> TcTyCon -- a non-loopy version of the tycon
1175 -> TcM (TcType, TcKind)
1176 handle_tyfams tc tc_tc
1177 | mightBeUnsaturatedTyCon tc_tc || mode_unsat mode
1178 -- This is where mode_unsat is used
1179 = do { traceTc "tcTyVar2a" (ppr tc_tc $$ ppr tc_kind)
1180 ; return (mkNakedTyConApp tc [], tc_kind) }
1181
1182 | otherwise
1183 = do { (tc_args, kind) <- instantiateTyN Nothing (length (tyConBinders tc_tc))
1184 tc_kind_bndrs tc_inner_ki
1185 ; let tc_ty = mkNakedTyConApp tc tc_args
1186 -- tc and tc_ty must not be traced here, because that would
1187 -- force the evaluation of a potentially knot-tied variable (tc),
1188 -- and the typechecker would hang, as per #11708
1189 ; traceTc "tcTyVar2b" (vcat [ ppr tc_tc <+> dcolon <+> ppr tc_kind
1190 , ppr kind ])
1191 ; return (tc_ty, kind) }
1192 where
1193 tc_kind = tyConKind tc_tc
1194 (tc_kind_bndrs, tc_inner_ki) = splitPiTysInvisible tc_kind
1195
1196 get_loopy_tc :: Name -> TyCon -> TcM TyCon
1197 -- Return the knot-tied global TyCon if there is one
1198 -- Otherwise the local TcTyCon; we must be doing kind checking
1199 -- but we still want to return a TyCon of some sort to use in
1200 -- error messages
1201 get_loopy_tc name tc_tc
1202 = do { env <- getGblEnv
1203 ; case lookupNameEnv (tcg_type_env env) name of
1204 Just (ATyCon tc) -> return tc
1205 _ -> do { traceTc "lk1 (loopy)" (ppr name)
1206 ; return tc_tc } }
1207
1208 -- We cannot promote a data constructor with a context that contains
1209 -- constraints other than equalities, so error if we find one.
1210 -- See Note [Constraints handled in types] in Inst.
1211 dc_theta_illegal_constraint :: ThetaType -> Maybe PredType
1212 dc_theta_illegal_constraint = find go
1213 where
1214 go :: PredType -> Bool
1215 go pred | Just tc <- tyConAppTyCon_maybe pred
1216 = not $ tc `hasKey` eqTyConKey
1217 || tc `hasKey` heqTyConKey
1218 | otherwise = True
1219
1220 {-
1221 Note [Type-checking inside the knot]
1222 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1223 Suppose we are checking the argument types of a data constructor. We
1224 must zonk the types before making the DataCon, because once built we
1225 can't change it. So we must traverse the type.
1226
1227 BUT the parent TyCon is knot-tied, so we can't look at it yet.
1228
1229 So we must be careful not to use "smart constructors" for types that
1230 look at the TyCon or Class involved.
1231
1232 * Hence the use of mkNakedXXX functions. These do *not* enforce
1233 the invariants (for example that we use (FunTy s t) rather
1234 than (TyConApp (->) [s,t])).
1235
1236 * The zonking functions establish invariants (even zonkTcType, a change from
1237 previous behaviour). So we must never inspect the result of a
1238 zonk that might mention a knot-tied TyCon. This is generally OK
1239 because we zonk *kinds* while kind-checking types. And the TyCons
1240 in kinds shouldn't be knot-tied, because they come from a previous
1241 mutually recursive group.
1242
1243 * TcHsSyn.zonkTcTypeToType also can safely check/establish
1244 invariants.
1245
1246 This is horribly delicate. I hate it. A good example of how
1247 delicate it is can be seen in Trac #7903.
1248
1249 Note [GADT kind self-reference]
1250 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1251
1252 A promoted type cannot be used in the body of that type's declaration.
1253 Trac #11554 shows this example, which made GHC loop:
1254
1255 import Data.Kind
1256 data P (x :: k) = Q
1257 data A :: Type where
1258 B :: forall (a :: A). P a -> A
1259
1260 In order to check the constructor B, we need to have the promoted type A, but in
1261 order to get that promoted type, B must first be checked. To prevent looping, a
1262 TyConPE promotion error is given when tcTyVar checks an ATcTyCon in kind mode.
1263 Any ATcTyCon is a TyCon being defined in the current recursive group (see data
1264 type decl for TcTyThing), and all such TyCons are illegal in kinds.
1265
1266 Trac #11962 proposes checking the head of a data declaration separately from
1267 its constructors. This would allow the example above to pass.
1268
1269 Note [Body kind of a HsForAllTy]
1270 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1271 The body of a forall is usually a type, but in principle
1272 there's no reason to prohibit *unlifted* types.
1273 In fact, GHC can itself construct a function with an
1274 unboxed tuple inside a for-all (via CPR analysis; see
1275 typecheck/should_compile/tc170).
1276
1277 Moreover in instance heads we get forall-types with
1278 kind Constraint.
1279
1280 It's tempting to check that the body kind is either * or #. But this is
1281 wrong. For example:
1282
1283 class C a b
1284 newtype N = Mk Foo deriving (C a)
1285
1286 We're doing newtype-deriving for C. But notice how `a` isn't in scope in
1287 the predicate `C a`. So we quantify, yielding `forall a. C a` even though
1288 `C a` has kind `* -> Constraint`. The `forall a. C a` is a bit cheeky, but
1289 convenient. Bottom line: don't check for * or # here.
1290
1291 Note [Body kind of a HsQualTy]
1292 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1293 If ctxt is non-empty, the HsQualTy really is a /function/, so the
1294 kind of the result really is '*', and in that case the kind of the
1295 body-type can be lifted or unlifted.
1296
1297 However, consider
1298 instance Eq a => Eq [a] where ...
1299 or
1300 f :: (Eq a => Eq [a]) => blah
1301 Here both body-kind of the HsQualTy is Constraint rather than *.
1302 Rather crudely we tell the difference by looking at exp_kind. It's
1303 very convenient to typecheck instance types like any other HsSigType.
1304
1305 Admittedly the '(Eq a => Eq [a]) => blah' case is erroneous, but it's
1306 better to reject in checkValidType. If we say that the body kind
1307 should be '*' we risk getting TWO error messages, one saying that Eq
1308 [a] doens't have kind '*', and one saying that we need a Constraint to
1309 the left of the outer (=>).
1310
1311 How do we figure out the right body kind? Well, it's a bit of a
1312 kludge: I just look at the expected kind. If it's Constraint, we
1313 must be in this instance situation context. It's a kludge because it
1314 wouldn't work if any unification was involved to compute that result
1315 kind -- but it isn't. (The true way might be to use the 'mode'
1316 parameter, but that seemed like a sledgehammer to crack a nut.)
1317
1318 Note [Inferring tuple kinds]
1319 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1320 Give a tuple type (a,b,c), which the parser labels as HsBoxedOrConstraintTuple,
1321 we try to figure out whether it's a tuple of kind * or Constraint.
1322 Step 1: look at the expected kind
1323 Step 2: infer argument kinds
1324
1325 If after Step 2 it's not clear from the arguments that it's
1326 Constraint, then it must be *. Once having decided that we re-check
1327 the Check the arguments again to give good error messages
1328 in eg. `(Maybe, Maybe)`
1329
1330 Note that we will still fail to infer the correct kind in this case:
1331
1332 type T a = ((a,a), D a)
1333 type family D :: Constraint -> Constraint
1334
1335 While kind checking T, we do not yet know the kind of D, so we will default the
1336 kind of T to * -> *. It works if we annotate `a` with kind `Constraint`.
1337
1338 Note [Desugaring types]
1339 ~~~~~~~~~~~~~~~~~~~~~~~
1340 The type desugarer is phase 2 of dealing with HsTypes. Specifically:
1341
1342 * It transforms from HsType to Type
1343
1344 * It zonks any kinds. The returned type should have no mutable kind
1345 or type variables (hence returning Type not TcType):
1346 - any unconstrained kind variables are defaulted to (Any *) just
1347 as in TcHsSyn.
1348 - there are no mutable type variables because we are
1349 kind-checking a type
1350 Reason: the returned type may be put in a TyCon or DataCon where
1351 it will never subsequently be zonked.
1352
1353 You might worry about nested scopes:
1354 ..a:kappa in scope..
1355 let f :: forall b. T '[a,b] -> Int
1356 In this case, f's type could have a mutable kind variable kappa in it;
1357 and we might then default it to (Any *) when dealing with f's type
1358 signature. But we don't expect this to happen because we can't get a
1359 lexically scoped type variable with a mutable kind variable in it. A
1360 delicate point, this. If it becomes an issue we might need to
1361 distinguish top-level from nested uses.
1362
1363 Moreover
1364 * it cannot fail,
1365 * it does no unifications
1366 * it does no validity checking, except for structural matters, such as
1367 (a) spurious ! annotations.
1368 (b) a class used as a type
1369
1370 Note [Kind of a type splice]
1371 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1372 Consider these terms, each with TH type splice inside:
1373 [| e1 :: Maybe $(..blah..) |]
1374 [| e2 :: $(..blah..) |]
1375 When kind-checking the type signature, we'll kind-check the splice
1376 $(..blah..); we want to give it a kind that can fit in any context,
1377 as if $(..blah..) :: forall k. k.
1378
1379 In the e1 example, the context of the splice fixes kappa to *. But
1380 in the e2 example, we'll desugar the type, zonking the kind unification
1381 variables as we go. When we encounter the unconstrained kappa, we
1382 want to default it to '*', not to (Any *).
1383
1384 Help functions for type applications
1385 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1386 -}
1387
1388 addTypeCtxt :: LHsType GhcRn -> TcM a -> TcM a
1389 -- Wrap a context around only if we want to show that contexts.
1390 -- Omit invisible ones and ones user's won't grok
1391 addTypeCtxt (L _ ty) thing
1392 = addErrCtxt doc thing
1393 where
1394 doc = text "In the type" <+> quotes (ppr ty)
1395
1396 {-
1397 ************************************************************************
1398 * *
1399 Type-variable binders
1400 %* *
1401 %************************************************************************
1402
1403 Note [Dependent LHsQTyVars]
1404 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1405 We track (in the renamer) which explicitly bound variables in a
1406 LHsQTyVars are manifestly dependent; only precisely these variables
1407 may be used within the LHsQTyVars. We must do this so that kcLHsQTyVars
1408 can produce the right TyConBinders, and tell Anon vs. Required.
1409
1410 Example data T k1 (a:k1) (b:k2) c
1411 = MkT (Proxy a) (Proxy b) (Proxy c)
1412
1413 Here
1414 (a:k1),(b:k2),(c:k3)
1415 are Anon (explicitly specified as a binder, not used
1416 in the kind of any other binder
1417 k1 is Required (explicitly specifed as a binder, but used
1418 in the kind of another binder i.e. dependently)
1419 k2 is Specified (not explicitly bound, but used in the kind
1420 of another binder)
1421 k3 in Inferred (not lexically in scope at all, but inferred
1422 by kind inference)
1423 and
1424 T :: forall {k3} k1. forall k3 -> k1 -> k2 -> k3 -> *
1425
1426 See Note [TyVarBndrs, TyVarBinders, TyConBinders, and visibility]
1427 in TyCoRep.
1428
1429 kcLHsQTyVars uses the hsq_dependent field to decide whether
1430 k1, a, b, c should be Required or Anon.
1431
1432 Earlier, thought it would work simply to do a free-variable check
1433 during kcLHsQTyVars, but this is bogus, because there may be
1434 unsolved equalities about. And we don't want to eagerly solve the
1435 equalities, because we may get further information after
1436 kcLHsQTyVars is called. (Recall that kcLHsQTyVars is called
1437 only from getInitialKind.)
1438 This is what implements the rule that all variables intended to be
1439 dependent must be manifestly so.
1440
1441 Sidenote: It's quite possible that later, we'll consider (t -> s)
1442 as a degenerate case of some (pi (x :: t) -> s) and then this will
1443 all get more permissive.
1444
1445 Note [Kind generalisation and SigTvs]
1446 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1447 Consider
1448 data T (a :: k1) x = MkT (S a ())
1449 data S (b :: k2) y = MkS (T b ())
1450
1451 While we are doing kind inference for the mutually-recursive S,T,
1452 we will end up unifying k1 and k2 together. So they can't be skolems.
1453 We therefore make them SigTvs, which can unify with type variables,
1454 but not with general types. All this is very similar at the level
1455 of terms: see Note [Quantified variables in partial type signatures]
1456 in TcBinds.
1457
1458 There are some wrinkles
1459
1460 * We always want to kind-generalise over SigTvs, and /not/ default
1461 them to Type. Another way to say this is: a SigTV should /never/
1462 stand for a type, even via defaulting. Hence the check in
1463 TcSimplify.defaultTyVarTcS, and TcMType.defaultTyVar. Here's
1464 another example (Trac #14555):
1465 data Exp :: [TYPE rep] -> TYPE rep -> Type where
1466 Lam :: Exp (a:xs) b -> Exp xs (a -> b)
1467 We want to kind-generalise over the 'rep' variable.
1468 Trac #14563 is another example.
1469
1470 * Consider Trac #11203
1471 data SameKind :: k -> k -> *
1472 data Q (a :: k1) (b :: k2) c = MkQ (SameKind a b)
1473 Here we will unify k1 with k2, but this time doing so is an error,
1474 because k1 and k2 are bound in the same delcaration.
1475
1476 We sort this out using findDupSigTvs, in TcTyClTyVars; very much
1477 as we do with partial type signatures in mk_psig_qtvs in
1478 TcBinds.chooseInferredQuantifiers
1479
1480 Note [Keeping scoped variables in order: Explicit]
1481 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1482 When the user writes `forall a b c. blah`, we bring a, b, and c into
1483 scope and then check blah. In the process of checking blah, we might
1484 learn the kinds of a, b, and c, and these kinds might indicate that
1485 b depends on c, and thus that we should reject the user-written type.
1486
1487 One approach to doing this would be to bring each of a, b, and c into
1488 scope, one at a time, creating an implication constraint and
1489 bumping the TcLevel for each one. This would work, because the kind
1490 of, say, b would be untouchable when c is in scope (and the constraint
1491 couldn't float out because c blocks it). However, it leads to terrible
1492 error messages, complaining about skolem escape. While it is indeed
1493 a problem of skolem escape, we can do better.
1494
1495 Instead, our approach is to bring the block of variables into scope
1496 all at once, creating one implication constraint for the lot. The
1497 user-written variables are skolems in the implication constraint. In
1498 TcSimplify.setImplicationStatus, we check to make sure that the ordering
1499 is correct, choosing ImplicationStatus IC_BadTelescope if they aren't.
1500 Then, in TcErrors, we report if there is a bad telescope. This way,
1501 we can report a suggested ordering to the user if there is a problem.
1502
1503 Note [Keeping scoped variables in order: Implicit]
1504 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1505 When the user implicitly quantifies over variables (say, in a type
1506 signature), we need to come up with some ordering on these variables.
1507 This is done by bumping the TcLevel, bringing the tyvars into scope,
1508 and then type-checking the thing_inside. The constraints are all
1509 wrapped in an implication, which is then solved. Finally, we can
1510 zonk all the binders and then order them with toposortTyVars.
1511
1512 It's critical to solve before zonking and ordering in order to uncover
1513 any unifications. You might worry that this eager solving could cause
1514 trouble elsewhere. I don't think it will. Because it will solve only
1515 in an increased TcLevel, it can't unify anything that was mentioned
1516 elsewhere. Additionally, we require that the order of implicitly
1517 quantified variables is manifest by the scope of these variables, so
1518 we're not going to learn more information later that will help order
1519 these variables.
1520
1521 Note [Recipe for checking a signature]
1522 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1523 Checking a user-written signature requires several steps:
1524
1525 1. Generate constraints.
1526 2. Solve constraints.
1527 3. Zonk and promote tyvars.
1528 4. (Optional) Kind-generalize.
1529 5. Check validity.
1530
1531 There may be some surprises in here:
1532
1533 Step 2 is necessary for two reasons: most signatures also bring
1534 implicitly quantified variables into scope, and solving is necessary
1535 to get these in the right order (see Note [Keeping scoped variables in
1536 order: Implicit]). Additionally, solving is necessary in order to
1537 kind-generalize correctly.
1538
1539 Step 3 requires *promoting* type variables. If there are any foralls
1540 in a type, the TcLevel will be bumped within the forall. This might
1541 lead to the generation of matavars with a high level. If we don't promote,
1542 we violate MetaTvInv of Note [TcLevel and untouchable type variables]
1543 in TcType.
1544
1545 -}
1546
1547 tcWildCardBinders :: SkolemInfo
1548 -> [Name]
1549 -> ([(Name, TcTyVar)] -> TcM a)
1550 -> TcM a
1551 tcWildCardBinders info = tcWildCardBindersX new_tv (Just info)
1552 where
1553 new_tv name = do { kind <- newMetaKindVar
1554 ; newSkolemTyVar name kind }
1555
1556 tcWildCardBindersX :: (Name -> TcM TcTyVar)
1557 -> Maybe SkolemInfo -- Just <=> we're bringing fresh vars
1558 -- into scope; use scopeTyVars
1559 -> [Name]
1560 -> ([(Name, TcTyVar)] -> TcM a)
1561 -> TcM a
1562 tcWildCardBindersX new_wc maybe_skol_info wc_names thing_inside
1563 = do { wcs <- mapM new_wc wc_names
1564 ; let wc_prs = wc_names `zip` wcs
1565 ; scope_tvs wc_prs $
1566 thing_inside wc_prs }
1567 where
1568 scope_tvs
1569 | Just info <- maybe_skol_info = scopeTyVars2 info
1570 | otherwise = tcExtendNameTyVarEnv
1571
1572 -- | Kind-check a 'LHsQTyVars'. If the decl under consideration has a complete,
1573 -- user-supplied kind signature (CUSK), generalise the result.
1574 -- Used in 'getInitialKind' (for tycon kinds and other kinds)
1575 -- and in kind-checking (but not for tycon kinds, which are checked with
1576 -- tcTyClDecls). See also Note [Complete user-supplied kind signatures] in
1577 -- HsDecls.
1578 --
1579 -- This function does not do telescope checking.
1580 kcLHsQTyVars :: Name -- ^ of the thing being checked
1581 -> TyConFlavour -- ^ What sort of 'TyCon' is being checked
1582 -> Bool -- ^ True <=> the decl being checked has a CUSK
1583 -> LHsQTyVars GhcRn
1584 -> TcM (Kind, r) -- ^ The result kind, possibly with other info
1585 -> TcM (TcTyCon, r) -- ^ A suitably-kinded TcTyCon
1586 kcLHsQTyVars name flav cusk
1587 user_tyvars@(HsQTvs { hsq_ext = HsQTvsRn { hsq_implicit = kv_ns
1588 , hsq_dependent = dep_names }
1589 , hsq_explicit = hs_tvs }) thing_inside
1590 | cusk
1591 = do { (scoped_kvs, (tc_tvs, (res_kind, stuff)))
1592 <- solveEqualities $
1593 tcImplicitQTKBndrs skol_info kv_ns $
1594 kcLHsQTyVarBndrs cusk open_fam skol_info hs_tvs thing_inside
1595
1596 -- Now, because we're in a CUSK, quantify over the mentioned
1597 -- kind vars, in dependency order.
1598 ; let tc_binders_unzonked = zipWith mk_tc_binder hs_tvs tc_tvs
1599 ; dvs <- zonkTcTypeAndSplitDepVars (mkSpecForAllTys scoped_kvs $
1600 mkTyConKind tc_binders_unzonked res_kind)
1601 ; qkvs <- quantifyTyVars emptyVarSet dvs
1602 -- don't call tcGetGlobalTyCoVars. For associated types, it gets the
1603 -- tyvars from the enclosing class -- but that's wrong. We *do* want
1604 -- to quantify over those tyvars.
1605
1606 ; scoped_kvs <- mapM zonkTcTyVarToTyVar scoped_kvs
1607 ; tc_tvs <- mapM zonkTcTyVarToTyVar tc_tvs
1608 ; res_kind <- zonkTcType res_kind
1609 ; let tc_binders = zipWith mk_tc_binder hs_tvs tc_tvs
1610
1611 -- If any of the scoped_kvs aren't actually mentioned in a binder's
1612 -- kind (or the return kind), then we're in the CUSK case from
1613 -- Note [Free-floating kind vars]
1614 ; let all_tc_tvs = scoped_kvs ++ tc_tvs
1615 all_mentioned_tvs = mapUnionVarSet (tyCoVarsOfType . tyVarKind)
1616 all_tc_tvs
1617 `unionVarSet` tyCoVarsOfType res_kind
1618 unmentioned_kvs = filterOut (`elemVarSet` all_mentioned_tvs)
1619 scoped_kvs
1620 ; reportFloatingKvs name flav all_tc_tvs unmentioned_kvs
1621
1622 ; let final_binders = map (mkNamedTyConBinder Inferred) qkvs
1623 ++ map (mkNamedTyConBinder Specified) scoped_kvs
1624 ++ tc_binders
1625 tycon = mkTcTyCon name (ppr user_tyvars) final_binders res_kind
1626 (mkTyVarNamePairs (scoped_kvs ++ tc_tvs))
1627 flav
1628 -- the tvs contain the binders already
1629 -- in scope from an enclosing class, but
1630 -- re-adding tvs to the env't doesn't cause
1631 -- harm
1632
1633 ; traceTc "kcLHsQTyVars: cusk" $
1634 vcat [ ppr name, ppr kv_ns, ppr hs_tvs, ppr dep_names
1635 , ppr tc_tvs, ppr (mkTyConKind final_binders res_kind)
1636 , ppr qkvs, ppr final_binders ]
1637
1638 ; return (tycon, stuff) }
1639
1640 | otherwise
1641 = do { (scoped_kvs, (tc_tvs, (res_kind, stuff)))
1642 -- Why kcImplicitTKBndrs which uses newSigTyVar?
1643 -- See Note [Kind generalisation and sigTvs]
1644 <- kcImplicitTKBndrs kv_ns $
1645 kcLHsQTyVarBndrs cusk open_fam skol_info hs_tvs thing_inside
1646
1647 ; let -- NB: Don't add scoped_kvs to tyConTyVars, because they
1648 -- must remain lined up with the binders
1649 tc_binders = zipWith mk_tc_binder hs_tvs tc_tvs
1650 tycon = mkTcTyCon name (ppr user_tyvars) tc_binders res_kind
1651 (mkTyVarNamePairs (scoped_kvs ++ tc_tvs))
1652 flav
1653
1654 ; traceTc "kcLHsQTyVars: not-cusk" $
1655 vcat [ ppr name, ppr kv_ns, ppr hs_tvs, ppr dep_names
1656 , ppr tc_tvs, ppr (mkTyConKind tc_binders res_kind) ]
1657 ; return (tycon, stuff) }
1658 where
1659 open_fam = tcFlavourIsOpen flav
1660 skol_info = TyConSkol flav name
1661
1662 mk_tc_binder :: LHsTyVarBndr GhcRn -> TyVar -> TyConBinder
1663 -- See Note [Dependent LHsQTyVars]
1664 mk_tc_binder hs_tv tv
1665 | hsLTyVarName hs_tv `elemNameSet` dep_names
1666 = mkNamedTyConBinder Required tv
1667 | otherwise
1668 = mkAnonTyConBinder tv
1669
1670 kcLHsQTyVars _ _ _ (XLHsQTyVars _) _ = panic "kcLHsQTyVars"
1671
1672 kcLHsQTyVarBndrs :: Bool -- True <=> bump the TcLevel when bringing vars into scope
1673 -> Bool -- True <=> Default un-annotated tyvar
1674 -- binders to kind *
1675 -> SkolemInfo
1676 -> [LHsTyVarBndr GhcRn]
1677 -> TcM r
1678 -> TcM ([TyVar], r)
1679 -- There may be dependency between the explicit "ty" vars.
1680 -- So, we have to handle them one at a time.
1681 kcLHsQTyVarBndrs _ _ _ [] thing
1682 = do { stuff <- thing; return ([], stuff) }
1683
1684 kcLHsQTyVarBndrs cusk open_fam skol_info (L _ hs_tv : hs_tvs) thing
1685 = do { tv_pair@(tv, _) <- kc_hs_tv hs_tv
1686 -- NB: Bring all tvs into scope, even non-dependent ones,
1687 -- as they're needed in type synonyms, data constructors, etc.
1688
1689 ; (tvs, stuff) <- bind_unless_scoped tv_pair $
1690 kcLHsQTyVarBndrs cusk open_fam skol_info hs_tvs $
1691 thing
1692
1693 ; return ( tv : tvs, stuff ) }
1694 where
1695 -- | Bind the tyvar in the env't unless the bool is True
1696 bind_unless_scoped :: (TcTyVar, Bool) -> TcM a -> TcM a
1697 bind_unless_scoped (_, True) thing_inside = thing_inside
1698 bind_unless_scoped (tv, False) thing_inside
1699 | cusk = scopeTyVars skol_info [tv] thing_inside
1700 | otherwise = tcExtendTyVarEnv [tv] thing_inside
1701 -- These variables haven't settled down yet, so we don't want to bump
1702 -- the TcLevel. If we do, then we'll have metavars of too high a level
1703 -- floating about. Changing this causes many, many failures in the
1704 -- `dependent` testsuite directory.
1705
1706 kc_hs_tv :: HsTyVarBndr GhcRn -> TcM (TcTyVar, Bool)
1707 -- Special handling for the case where the binder is already in scope
1708 -- See Note [Associated type tyvar names] in Class and
1709 -- Note [TyVar binders for associated decls] in HsDecls
1710 kc_hs_tv (UserTyVar _ (L _ name))
1711 = do { mb_tv <- tcLookupLcl_maybe name
1712 ; case mb_tv of -- See Note [TyVar binders for associated decls]
1713 Just (ATyVar _ tv) -> return (tv, True)
1714 _ -> do { kind <- if open_fam
1715 then return liftedTypeKind
1716 else newMetaKindVar
1717 -- Open type/data families default their variables
1718 -- variables to kind *. But don't default in-scope
1719 -- class tyvars, of course
1720 ; tv <- newSkolemTyVar name kind
1721 ; return (tv, False) } }
1722
1723 kc_hs_tv (KindedTyVar _ lname@(L _ name) lhs_kind)
1724 = do { kind <- tcLHsKindSig (TyVarBndrKindCtxt name) lhs_kind
1725 ; mb_tv <- tcLookupLcl_maybe name
1726 ; case mb_tv of
1727 Just (ATyVar _ tv)
1728 -> do { discardResult $
1729 unifyKind (Just (HsTyVar noExt NotPromoted lname))
1730 kind (tyVarKind tv)
1731 ; return (tv, True) }
1732 _ -> do { tv <- newSkolemTyVar name kind
1733 ; return (tv, False) } }
1734
1735 kc_hs_tv (XTyVarBndr{}) = panic "kc_hs_tv"
1736
1737 {- Note [Kind-checking tyvar binders for associated types]
1738 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1739 When kind-checking the type-variable binders for associated
1740 data/newtype decls
1741 family decls
1742 we behave specially for type variables that are already in scope;
1743 that is, bound by the enclosing class decl. This is done in
1744 kcLHsQTyVarBndrs:
1745 * The use of tcImplicitQTKBndrs
1746 * The tcLookupLocal_maybe code in kc_hs_tv
1747
1748 See Note [Associated type tyvar names] in Class and
1749 Note [TyVar binders for associated decls] in HsDecls
1750
1751 We must do the same for family instance decls, where the in-scope
1752 variables may be bound by the enclosing class instance decl.
1753 Hence the use of tcImplicitQTKBndrs in tcFamTyPats.
1754 -}
1755
1756
1757 --------------------------------------
1758 -- Implicit binders
1759 --------------------------------------
1760
1761 -- | Bring implicitly quantified type/kind variables into scope during
1762 -- kind checking. Uses SigTvs, as per Note [Use SigTvs in kind-checking pass]
1763 -- in TcTyClsDecls.
1764 kcImplicitTKBndrs :: [Name] -- of the vars
1765 -> TcM a
1766 -> TcM ([TcTyVar], a) -- returns the tyvars created
1767 -- these are *not* dependency ordered
1768 kcImplicitTKBndrs var_ns thing_inside
1769 = do { tkvs <- mapM newFlexiKindedSigTyVar var_ns
1770 ; result <- tcExtendTyVarEnv tkvs thing_inside
1771 ; return (tkvs, result) }
1772
1773
1774 tcImplicitTKBndrs, tcImplicitTKBndrsSig, tcImplicitQTKBndrs
1775 :: SkolemInfo
1776 -> [Name]
1777 -> TcM a
1778 -> TcM ([TcTyVar], a)
1779 tcImplicitTKBndrs = tcImplicitTKBndrsX newFlexiKindedSkolemTyVar
1780 tcImplicitTKBndrsSig = tcImplicitTKBndrsX newFlexiKindedSigTyVar
1781 tcImplicitQTKBndrs = tcImplicitTKBndrsX newFlexiKindedQTyVar
1782
1783 tcImplicitTKBndrsX :: (Name -> TcM TcTyVar) -- new_tv function
1784 -> SkolemInfo
1785 -> [Name]
1786 -> TcM a
1787 -> TcM ([TcTyVar], a) -- these tyvars are dependency-ordered
1788 -- * Guarantees to call solveLocalEqualities to unify
1789 -- all constraints from thing_inside.
1790 --
1791 -- * Returned TcTyVars have the supplied HsTyVarBndrs,
1792 -- but may be in different order to the original [Name]
1793 -- (because of sorting to respect dependency)
1794 --
1795 -- * Returned TcTyVars have zonked kinds
1796 -- See Note [Keeping scoped variables in order: Implicit]
1797 tcImplicitTKBndrsX new_tv skol_info tv_names thing_inside
1798 | null tv_names -- Short cut for the common case where there
1799 -- are no implicit type variables to bind
1800 = do { result <- solveLocalEqualities thing_inside
1801 ; return ([], result) }
1802
1803 | otherwise
1804 = do { (skol_tvs, result)
1805 <- solveLocalEqualities $
1806 checkTvConstraints skol_info Nothing $
1807 do { tkvs <- mapM new_tv tv_names
1808 ; result <- tcExtendTyVarEnv tkvs thing_inside
1809 ; return (tkvs, result) }
1810
1811 ; skol_tvs <- mapM zonkTcTyCoVarBndr skol_tvs
1812 -- use zonkTcTyCoVarBndr because a skol_tv might be a SigTv
1813
1814 ; let final_tvs = toposortTyVars skol_tvs
1815 ; traceTc "tcImplicitTKBndrs" (ppr tv_names $$ ppr final_tvs)
1816 ; return (final_tvs, result) }
1817
1818 newFlexiKindedQTyVar :: Name -> TcM TcTyVar
1819 -- Make a new skolem for an implicit binder in a type/class/type
1820 -- instance declaration, with a flexi-kind
1821 -- But check for in-scope-ness, and if so return that instead
1822 newFlexiKindedQTyVar name
1823 = do { mb_tv <- tcLookupLcl_maybe name
1824 ; case mb_tv of
1825 Just (ATyVar _ tv) -> return tv
1826 _ -> newFlexiKindedSkolemTyVar name }
1827
1828 newFlexiKindedTyVar :: (Name -> Kind -> TcM TyVar) -> Name -> TcM TyVar
1829 newFlexiKindedTyVar new_tv name
1830 = do { kind <- newMetaKindVar
1831 ; new_tv name kind }
1832
1833 newFlexiKindedSkolemTyVar :: Name -> TcM TyVar
1834 newFlexiKindedSkolemTyVar = newFlexiKindedTyVar newSkolemTyVar
1835
1836 newFlexiKindedSigTyVar :: Name -> TcM TyVar
1837 newFlexiKindedSigTyVar = newFlexiKindedTyVar newSigTyVar
1838
1839 --------------------------------------
1840 -- Explicit binders
1841 --------------------------------------
1842
1843 -- | Used during the "kind-checking" pass in TcTyClsDecls only,
1844 -- and even then only for data-con declarations.
1845 -- See Note [Use SigTvs in kind-checking pass] in TcTyClsDecls
1846 kcExplicitTKBndrs :: [LHsTyVarBndr GhcRn]
1847 -> TcM a
1848 -> TcM a
1849 kcExplicitTKBndrs [] thing_inside = thing_inside
1850 kcExplicitTKBndrs (L _ hs_tv : hs_tvs) thing_inside
1851 = do { tv <- tcHsTyVarBndr newSigTyVar hs_tv
1852 ; tcExtendTyVarEnv [tv] $
1853 kcExplicitTKBndrs hs_tvs thing_inside }
1854
1855 tcExplicitTKBndrs :: SkolemInfo
1856 -> [LHsTyVarBndr GhcRn]
1857 -> TcM a
1858 -> TcM ([TcTyVar], a)
1859 tcExplicitTKBndrs skol_info hs_tvs thing_inside
1860 -- Used for the forall'd binders in type signatures of various kinds:
1861 -- - function signatures
1862 -- - data con signatures in GADT-style decls
1863 -- - pattern synonym signatures
1864 -- - expression type signatures
1865 --
1866 -- Specifically NOT used for the binders of a data type
1867 -- or type family decl. So the forall'd variables always /shadow/
1868 -- anything already in scope, and the complications of
1869 -- tcHsQTyVarName to not apply.
1870 --
1871 -- This function brings into scope a telescope of binders as written by
1872 -- the user. At first blush, it would then seem that we should bring
1873 -- them into scope one at a time, bumping the TcLevel each time.
1874 -- (Recall that we bump the level to prevent skolem escape from happening.)
1875 -- However, this leads to terrible error messages, because we end up
1876 -- failing to unify with some `k0`. Better would be to allow type inference
1877 -- to work, potentially creating a skolem-escape problem, and then to
1878 -- notice that the telescope is out of order. That's what we do here,
1879 -- following the logic of tcImplicitTKBndrsX.
1880 -- See also Note [Keeping scoped variables in order: Explicit]
1881 --
1882 -- No cloning: returned TyVars have the same Name as the incoming LHsTyVarBndrs
1883 | null hs_tvs -- Short cut that avoids creating an implication
1884 -- constraint in the common case where none is needed
1885 = do { result <- thing_inside
1886 ; return ([], result) }
1887
1888 | otherwise
1889 = do { (skol_tvs, result) <- checkTvConstraints skol_info (Just doc) $
1890 bind_tvbs hs_tvs
1891
1892 ; traceTc "tcExplicitTKBndrs" $
1893 vcat [ text "Hs vars:" <+> ppr hs_tvs
1894 , text "tvs:" <+> pprTyVars skol_tvs ]
1895
1896 ; return (skol_tvs, result) }
1897
1898 where
1899 bind_tvbs [] = do { result <- thing_inside
1900 ; return ([], result) }
1901 bind_tvbs (L _ tvb : tvbs)
1902 = do { tv <- tcHsTyVarBndr newSkolemTyVar tvb
1903 ; tcExtendTyVarEnv [tv] $
1904 do { (tvs, result) <- bind_tvbs tvbs
1905 ; return (tv : tvs, result) }}
1906
1907 doc = sep (map ppr hs_tvs)
1908
1909 -----------------
1910 tcHsTyVarBndr :: (Name -> Kind -> TcM TyVar)
1911 -> HsTyVarBndr GhcRn -> TcM TcTyVar
1912 -- Return a TcTyVar, built using the provided function
1913 -- Typically the Kind inside the HsTyVarBndr will be a tyvar
1914 -- with a mutable kind in it.
1915 --
1916 -- Returned TcTyVar has the same name; no cloning
1917 tcHsTyVarBndr new_tv (UserTyVar _ (L _ tv_nm))
1918 = newFlexiKindedTyVar new_tv tv_nm
1919 tcHsTyVarBndr new_tv (KindedTyVar _ (L _ tv_nm) lhs_kind)
1920 = do { kind <- tcLHsKindSig (TyVarBndrKindCtxt tv_nm) lhs_kind
1921 ; new_tv tv_nm kind }
1922 tcHsTyVarBndr _ (XTyVarBndr _) = panic "tcHsTyVarBndr"
1923
1924 -----------------
1925 newWildTyVar :: Name -> TcM TcTyVar
1926 -- ^ New unification variable for a wildcard
1927 newWildTyVar _name
1928 = do { kind <- newMetaKindVar
1929 ; uniq <- newUnique
1930 ; details <- newMetaDetails TauTv
1931 ; let name = mkSysTvName uniq (fsLit "w")
1932 tyvar = (mkTcTyVar name kind details)
1933 ; traceTc "newWildTyVar" (ppr tyvar)
1934 ; return tyvar }
1935
1936 --------------------------
1937 -- Bringing tyvars into scope
1938 --------------------------
1939
1940 -- | Bring tyvars into scope, wrapping the thing_inside in an implication
1941 -- constraint. The implication constraint is necessary to provide SkolemInfo
1942 -- for the tyvars and to ensure that no unification variables made outside
1943 -- the scope of these tyvars (i.e. lower TcLevel) unify with the locally-scoped
1944 -- tyvars (i.e. higher TcLevel).
1945 --
1946 -- INVARIANT: The thing_inside must check only types, never terms.
1947 --
1948 -- Use this (not tcExtendTyVarEnv) wherever you expect a Λ or ∀ in Core.
1949 -- Use tcExtendTyVarEnv otherwise.
1950 scopeTyVars :: SkolemInfo -> [TcTyVar] -> TcM a -> TcM a
1951 scopeTyVars skol_info tvs = scopeTyVars2 skol_info [(tyVarName tv, tv) | tv <- tvs]
1952
1953 -- | Like 'scopeTyVars', but allows you to specify different scoped names
1954 -- than the Names stored within the tyvars.
1955 scopeTyVars2 :: SkolemInfo -> [(Name, TcTyVar)] -> TcM a -> TcM a
1956 scopeTyVars2 skol_info prs thing_inside
1957 = fmap snd $ -- discard the TcEvBinds, which will always be empty
1958 checkConstraints skol_info (map snd prs) [{- no EvVars -}] $
1959 tcExtendNameTyVarEnv prs $
1960 thing_inside
1961
1962 ------------------
1963 kindGeneralize :: TcType -> TcM [KindVar]
1964 -- Quantify the free kind variables of a kind or type
1965 -- In the latter case the type is closed, so it has no free
1966 -- type variables. So in both cases, all the free vars are kind vars
1967 -- Input must be zonked.
1968 -- NB: You must call solveEqualities or solveLocalEqualities before
1969 -- kind generalization
1970 kindGeneralize kind_or_type
1971 = do { let kvs = tyCoVarsOfTypeDSet kind_or_type
1972 dvs = DV { dv_kvs = kvs, dv_tvs = emptyDVarSet }
1973 ; gbl_tvs <- tcGetGlobalTyCoVars -- Already zonked
1974 ; quantifyTyVars gbl_tvs dvs }
1975
1976 {-
1977 Note [Kind generalisation]
1978 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1979 We do kind generalisation only at the outer level of a type signature.
1980 For example, consider
1981 T :: forall k. k -> *
1982 f :: (forall a. T a -> Int) -> Int
1983 When kind-checking f's type signature we generalise the kind at
1984 the outermost level, thus:
1985 f1 :: forall k. (forall (a:k). T k a -> Int) -> Int -- YES!
1986 and *not* at the inner forall:
1987 f2 :: (forall k. forall (a:k). T k a -> Int) -> Int -- NO!
1988 Reason: same as for HM inference on value level declarations,
1989 we want to infer the most general type. The f2 type signature
1990 would be *less applicable* than f1, because it requires a more
1991 polymorphic argument.
1992
1993 NB: There are no explicit kind variables written in f's signature.
1994 When there are, the renamer adds these kind variables to the list of
1995 variables bound by the forall, so you can indeed have a type that's
1996 higher-rank in its kind. But only by explicit request.
1997
1998 Note [Kinds of quantified type variables]
1999 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2000 tcTyVarBndrsGen quantifies over a specified list of type variables,
2001 *and* over the kind variables mentioned in the kinds of those tyvars.
2002
2003 Note that we must zonk those kinds (obviously) but less obviously, we
2004 must return type variables whose kinds are zonked too. Example
2005 (a :: k7) where k7 := k9 -> k9
2006 We must return
2007 [k9, a:k9->k9]
2008 and NOT
2009 [k9, a:k7]
2010 Reason: we're going to turn this into a for-all type,
2011 forall k9. forall (a:k7). blah
2012 which the type checker will then instantiate, and instantiate does not
2013 look through unification variables!
2014
2015 Hence using zonked_kinds when forming tvs'.
2016
2017 Note [Free-floating kind vars]
2018 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2019 Consider
2020
2021 data T = MkT (forall (a :: k). Proxy a)
2022 -- from test ghci/scripts/T7873
2023
2024 This is not an existential datatype, but a higher-rank one (the forall
2025 to the right of MkT). Also consider
2026
2027 data S a = MkS (Proxy (a :: k))
2028
2029 According to the rules around implicitly-bound kind variables, in both
2030 cases those k's scope over the whole declaration. The renamer grabs
2031 it and adds it to the hsq_implicits field of the HsQTyVars of the
2032 tycon. So it must be in scope during type-checking, but we want to
2033 reject T while accepting S.
2034
2035 Why reject T? Because the kind variable isn't fixed by anything. For
2036 a variable like k to be implicit, it needs to be mentioned in the kind
2037 of a tycon tyvar. But it isn't.
2038
2039 Why accept S? Because kind inference tells us that a has kind k, so it's
2040 all OK.
2041
2042 Our approach depends on whether or not the datatype has a CUSK.
2043
2044 Non-CUSK: In the first pass (kcTyClTyVars) we just bring
2045 k into scope. In the second pass (tcTyClTyVars),
2046 we check to make sure that k has been unified with some other variable
2047 (or generalized over, making k into a skolem). If it hasn't been, then
2048 it must be a free-floating kind var. Error.
2049
2050 CUSK: When we determine the tycon's final, never-to-be-changed kind
2051 in kcLHsQTyVars, we check to make sure all implicitly-bound kind
2052 vars are indeed mentioned in a kind somewhere. If not, error.
2053
2054 We also perform free-floating kind var analysis for type family instances
2055 (see #13985). Here is an interesting example:
2056
2057 type family T :: k
2058 type instance T = (Nothing :: Maybe a)
2059
2060 Upon a cursory glance, it may appear that the kind variable `a` is
2061 free-floating above, since there are no (visible) LHS patterns in `T`. However,
2062 there is an *invisible* pattern due to the return kind, so inside of GHC, the
2063 instance looks closer to this:
2064
2065 type family T @k :: k
2066 type instance T @(Maybe a) = (Nothing :: Maybe a)
2067
2068 Here, we can see that `a` really is bound by a LHS type pattern, so `a` is in
2069 fact not free-floating. Contrast that with this example:
2070
2071 type instance T = Proxy (Nothing :: Maybe a)
2072
2073 This would looks like this inside of GHC:
2074
2075 type instance T @(*) = Proxy (Nothing :: Maybe a)
2076
2077 So this time, `a` is neither bound by a visible nor invisible type pattern on
2078 the LHS, so it would be reported as free-floating.
2079
2080 Finally, here's one more brain-teaser (from #9574). In the example below:
2081
2082 class Funct f where
2083 type Codomain f :: *
2084 instance Funct ('KProxy :: KProxy o) where
2085 type Codomain 'KProxy = NatTr (Proxy :: o -> *)
2086
2087 As it turns out, `o` is not free-floating in this example. That is because `o`
2088 bound by the kind signature of the LHS type pattern 'KProxy. To make this more
2089 obvious, one can also write the instance like so:
2090
2091 instance Funct ('KProxy :: KProxy o) where
2092 type Codomain ('KProxy :: KProxy o) = NatTr (Proxy :: o -> *)
2093
2094 -}
2095
2096 --------------------
2097 -- getInitialKind has made a suitably-shaped kind for the type or class
2098 -- Look it up in the local environment. This is used only for tycons
2099 -- that we're currently type-checking, so we're sure to find a TcTyCon.
2100 kcLookupTcTyCon :: Name -> TcM TcTyCon
2101 kcLookupTcTyCon nm
2102 = do { tc_ty_thing <- tcLookup nm
2103 ; return $ case tc_ty_thing of
2104 ATcTyCon tc -> tc
2105 _ -> pprPanic "kcLookupTcTyCon" (ppr tc_ty_thing) }
2106
2107 -----------------------
2108 -- | Bring tycon tyvars into scope. This is used during the "kind-checking"
2109 -- pass in TcTyClsDecls. (Never in getInitialKind, never in the
2110 -- "type-checking"/desugaring pass.)
2111 -- Never emits constraints, though the thing_inside might.
2112 kcTyClTyVars :: Name -> TcM a -> TcM a
2113 kcTyClTyVars tycon_name thing_inside
2114 -- See Note [Use SigTvs in kind-checking pass] in TcTyClsDecls
2115 = do { tycon <- kcLookupTcTyCon tycon_name
2116 ; tcExtendNameTyVarEnv (tcTyConScopedTyVars tycon) $ thing_inside }
2117
2118 tcTyClTyVars :: Name
2119 -> ([TyConBinder] -> Kind -> TcM a) -> TcM a
2120 -- ^ Used for the type variables of a type or class decl
2121 -- on the second full pass (type-checking/desugaring) in TcTyClDecls.
2122 -- This is *not* used in the initial-kind run, nor in the "kind-checking" pass.
2123 -- Accordingly, everything passed to the continuation is fully zonked.
2124 --
2125 -- (tcTyClTyVars T [a,b] thing_inside)
2126 -- where T : forall k1 k2 (a:k1 -> *) (b:k1). k2 -> *
2127 -- calls thing_inside with arguments
2128 -- [k1,k2,a,b] [k1:*, k2:*, Anon (k1 -> *), Anon k1] (k2 -> *)
2129 -- having also extended the type environment with bindings
2130 -- for k1,k2,a,b
2131 --
2132 -- Never emits constraints.
2133 --
2134 -- The LHsTyVarBndrs is always user-written, and the full, generalised
2135 -- kind of the tycon is available in the local env.
2136 tcTyClTyVars tycon_name thing_inside
2137 = do { tycon <- kcLookupTcTyCon tycon_name
2138
2139 -- Do checks on scoped tyvars
2140 -- See Note [Free-floating kind vars]
2141 ; let flav = tyConFlavour tycon
2142 scoped_prs = tcTyConScopedTyVars tycon
2143 scoped_tvs = map snd scoped_prs
2144 still_sig_tvs = filter isSigTyVar scoped_tvs
2145
2146 ; mapM_ report_sig_tv_err (findDupSigTvs scoped_prs)
2147
2148 ; checkNoErrs $ reportFloatingKvs tycon_name flav
2149 scoped_tvs still_sig_tvs
2150
2151 ; let res_kind = tyConResKind tycon
2152 binders = correct_binders (tyConBinders tycon) res_kind
2153 ; traceTc "tcTyClTyVars" (ppr tycon_name <+> ppr binders)
2154 ; scopeTyVars2 (TyConSkol flav tycon_name) scoped_prs $
2155 thing_inside binders res_kind }
2156 where
2157 report_sig_tv_err (n1, n2)
2158 = setSrcSpan (getSrcSpan n2) $
2159 addErrTc (text "Couldn't match" <+> quotes (ppr n1)
2160 <+> text "with" <+> quotes (ppr n2))
2161
2162 -- Given some TyConBinders and a TyCon's result kind, make sure that the
2163 -- correct any wrong Named/Anon choices. For example, consider
2164 -- type Syn k = forall (a :: k). Proxy a
2165 -- At first, it looks like k should be named -- after all, it appears on the RHS.
2166 -- However, the correct kind for Syn is (* -> *).
2167 -- (Why? Because k is the kind of a type, so k's kind is *. And the RHS also has
2168 -- kind *.) See also #13963.
2169 correct_binders :: [TyConBinder] -> Kind -> [TyConBinder]
2170 correct_binders binders kind
2171 = binders'
2172 where
2173 (_, binders') = mapAccumR go (tyCoVarsOfType kind) binders
2174
2175 go :: TyCoVarSet -> TyConBinder -> (TyCoVarSet, TyConBinder)
2176 go fvs binder
2177 | isNamedTyConBinder binder
2178 , not (tv `elemVarSet` fvs)
2179 = (new_fvs, mkAnonTyConBinder tv)
2180
2181 | not (isNamedTyConBinder binder)
2182 , tv `elemVarSet` fvs
2183 = (new_fvs, mkNamedTyConBinder Required tv)
2184 -- always Required, because it was anonymous (i.e. visible) previously
2185
2186 | otherwise
2187 = (new_fvs, binder)
2188
2189 where
2190 tv = binderVar binder
2191 new_fvs = fvs `delVarSet` tv `unionVarSet` tyCoVarsOfType (tyVarKind tv)
2192
2193 -----------------------------------
2194 tcDataKindSig :: [TyConBinder]
2195 -> Kind
2196 -> TcM ([TyConBinder], Kind)
2197 -- GADT decls can have a (perhaps partial) kind signature
2198 -- e.g. data T a :: * -> * -> * where ...
2199 -- This function makes up suitable (kinded) TyConBinders for the
2200 -- argument kinds. E.g. in this case it might return
2201 -- ([b::*, c::*], *)
2202 -- Never emits constraints.
2203 -- It's a little trickier than you might think: see
2204 -- Note [TyConBinders for the result kind signature of a data type]
2205 tcDataKindSig tc_bndrs kind
2206 = do { loc <- getSrcSpanM
2207 ; uniqs <- newUniqueSupply
2208 ; rdr_env <- getLocalRdrEnv
2209 ; let new_occs = [ occ
2210 | str <- allNameStrings
2211 , let occ = mkOccName tvName str
2212 , isNothing (lookupLocalRdrOcc rdr_env occ)
2213 -- Note [Avoid name clashes for associated data types]
2214 , not (occ `elem` lhs_occs) ]
2215 new_uniqs = uniqsFromSupply uniqs
2216 subst = mkEmptyTCvSubst (mkInScopeSet (mkVarSet lhs_tvs))
2217 ; return (go loc new_occs new_uniqs subst [] kind) }
2218 where
2219 lhs_tvs = map binderVar tc_bndrs
2220 lhs_occs = map getOccName lhs_tvs
2221
2222 go loc occs uniqs subst acc kind
2223 = case splitPiTy_maybe kind of
2224 Nothing -> (reverse acc, substTy subst kind)
2225
2226 Just (Anon arg, kind')
2227 -> go loc occs' uniqs' subst' (tcb : acc) kind'
2228 where
2229 arg' = substTy subst arg
2230 tv = mkTyVar (mkInternalName uniq occ loc) arg'
2231 subst' = extendTCvInScope subst tv
2232 tcb = TvBndr tv AnonTCB
2233 (uniq:uniqs') = uniqs
2234 (occ:occs') = occs
2235
2236 Just (Named (TvBndr tv vis), kind')
2237 -> go loc occs uniqs subst' (tcb : acc) kind'
2238 where
2239 (subst', tv') = substTyVarBndr subst tv
2240 tcb = TvBndr tv' (NamedTCB vis)
2241
2242 badKindSig :: Bool -> Kind -> SDoc
2243 badKindSig check_for_type kind
2244 = hang (sep [ text "Kind signature on data type declaration has non-*"
2245 , (if check_for_type then empty else text "and non-variable") <+>
2246 text "return kind" ])
2247 2 (ppr kind)
2248
2249 {- Note [TyConBinders for the result kind signature of a data type]
2250 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2251 Given
2252 data T (a::*) :: * -> forall k. k -> *
2253 we want to generate the extra TyConBinders for T, so we finally get
2254 (a::*) (b::*) (k::*) (c::k)
2255 The function tcDataKindSig generates these extra TyConBinders from
2256 the result kind signature.
2257
2258 We need to take care to give the TyConBinders
2259 (a) OccNames that are fresh (because the TyConBinders of a TyCon
2260 must have distinct OccNames
2261
2262 (b) Uniques that are fresh (obviously)
2263
2264 For (a) we need to avoid clashes with the tyvars declared by
2265 the user before the "::"; in the above example that is 'a'.
2266 And also see Note [Avoid name clashes for associated data types].
2267
2268 For (b) suppose we have
2269 data T :: forall k. k -> forall k. k -> *
2270 where the two k's are identical even up to their uniques. Surprisingly,
2271 this can happen: see Trac #14515.
2272
2273 It's reasonably easy to solve all this; just run down the list with a
2274 substitution; hence the recursive 'go' function. But it has to be
2275 done.
2276
2277 Note [Avoid name clashes for associated data types]
2278 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2279 Consider class C a b where
2280 data D b :: * -> *
2281 When typechecking the decl for D, we'll invent an extra type variable
2282 for D, to fill out its kind. Ideally we don't want this type variable
2283 to be 'a', because when pretty printing we'll get
2284 class C a b where
2285 data D b a0
2286 (NB: the tidying happens in the conversion to IfaceSyn, which happens
2287 as part of pretty-printing a TyThing.)
2288
2289 That's why we look in the LocalRdrEnv to see what's in scope. This is
2290 important only to get nice-looking output when doing ":info C" in GHCi.
2291 It isn't essential for correctness.
2292
2293
2294 ************************************************************************
2295 * *
2296 Partial signatures
2297 * *
2298 ************************************************************************
2299
2300 -}
2301
2302 tcHsPartialSigType
2303 :: UserTypeCtxt
2304 -> LHsSigWcType GhcRn -- The type signature
2305 -> TcM ( [(Name, TcTyVar)] -- Wildcards
2306 , Maybe TcType -- Extra-constraints wildcard
2307 , [Name] -- Original tyvar names, in correspondence with ...
2308 , [TcTyVar] -- ... Implicitly and explicitly bound type variables
2309 , TcThetaType -- Theta part
2310 , TcType ) -- Tau part
2311 -- See Note [Recipe for checking a signature]
2312 tcHsPartialSigType ctxt sig_ty
2313 | HsWC { hswc_ext = sig_wcs, hswc_body = ib_ty } <- sig_ty
2314 , HsIB { hsib_ext = HsIBRn { hsib_vars = implicit_hs_tvs }
2315 , hsib_body = hs_ty } <- ib_ty
2316 , (explicit_hs_tvs, L _ hs_ctxt, hs_tau) <- splitLHsSigmaTy hs_ty
2317 = addSigCtxt ctxt hs_ty $
2318 do { (implicit_tvs, (explicit_tvs, (wcs, wcx, theta, tau)))
2319 <- tcWildCardBindersX newWildTyVar Nothing sig_wcs $ \ wcs ->
2320 tcImplicitTKBndrsSig skol_info implicit_hs_tvs $
2321 tcExplicitTKBndrs skol_info explicit_hs_tvs $
2322 do { -- Instantiate the type-class context; but if there
2323 -- is an extra-constraints wildcard, just discard it here
2324 (theta, wcx) <- tcPartialContext hs_ctxt
2325
2326 ; tau <- tcHsOpenType hs_tau
2327
2328 ; return (wcs, wcx, theta, tau) }
2329
2330 -- We must return these separately, because all the zonking below
2331 -- might change the name of a SigTv. This, in turn, causes trouble
2332 -- in partial type signatures that bind scoped type variables, as
2333 -- we bring the wrong name into scope in the function body.
2334 -- Test case: partial-sigs/should_compile/LocalDefinitionBug
2335 ; let tv_names = map tyVarName (implicit_tvs ++ explicit_tvs)
2336
2337 -- Spit out the wildcards (including the extra-constraints one)
2338 -- as "hole" constraints, so that they'll be reported if necessary
2339 -- See Note [Extra-constraint holes in partial type signatures]
2340 ; emitWildCardHoleConstraints wcs
2341
2342 -- The SigTvs created above will sometimes have too high a TcLevel
2343 -- (note that they are generated *after* bumping the level in
2344 -- the tc{Im,Ex}plicitTKBndrsSig functions. Bumping the level
2345 -- is still important here, because the kinds of these variables
2346 -- do indeed need to have the higher level, so they can unify
2347 -- with other local type variables. But, now that we've type-checked
2348 -- everything (and solved equalities in the tcImplicit call)
2349 -- we need to promote the SigTvs so we don't violate the TcLevel
2350 -- invariant
2351 ; all_tvs <- mapM zonkPromoteTyCoVarBndr (implicit_tvs ++ explicit_tvs)
2352 -- zonkPromoteTyCoVarBndr deals well with SigTvs
2353
2354 ; theta <- mapM zonkPromoteType theta
2355 ; tau <- zonkPromoteType tau
2356
2357 ; checkValidType ctxt (mkSpecForAllTys all_tvs $ mkPhiTy theta tau)
2358
2359 ; traceTc "tcHsPartialSigType" (ppr all_tvs)
2360 ; return (wcs, wcx, tv_names, all_tvs, theta, tau) }
2361 where
2362 skol_info = SigTypeSkol ctxt
2363 tcHsPartialSigType _ (HsWC _ (XHsImplicitBndrs _)) = panic "tcHsPartialSigType"
2364 tcHsPartialSigType _ (XHsWildCardBndrs _) = panic "tcHsPartialSigType"
2365
2366 tcPartialContext :: HsContext GhcRn -> TcM (TcThetaType, Maybe TcType)
2367 tcPartialContext hs_theta
2368 | Just (hs_theta1, hs_ctxt_last) <- snocView hs_theta
2369 , L _ (HsWildCardTy wc) <- ignoreParens hs_ctxt_last
2370 = do { wc_tv_ty <- tcWildCardOcc wc constraintKind
2371 ; theta <- mapM tcLHsPredType hs_theta1
2372 ; return (theta, Just wc_tv_ty) }
2373 | otherwise
2374 = do { theta <- mapM tcLHsPredType hs_theta
2375 ; return (theta, Nothing) }
2376
2377 {- Note [Extra-constraint holes in partial type signatures]
2378 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2379 Consider
2380 f :: (_) => a -> a
2381 f x = ...
2382
2383 * The renamer makes a wildcard name for the "_", and puts it in
2384 the hswc_wcs field.
2385
2386 * Then, in tcHsPartialSigType, we make a new hole TcTyVar, in
2387 tcWildCardBindersX.
2388
2389 * TcBinds.chooseInferredQuantifiers fills in that hole TcTyVar
2390 with the inferred constraints, e.g. (Eq a, Show a)
2391
2392 * TcErrors.mkHoleError finally reports the error.
2393
2394 An annoying difficulty happens if there are more than 62 inferred
2395 constraints. Then we need to fill in the TcTyVar with (say) a 70-tuple.
2396 Where do we find the TyCon? For good reasons we only have constraint
2397 tuples up to 62 (see Note [How tuples work] in TysWiredIn). So how
2398 can we make a 70-tuple? This was the root cause of Trac #14217.
2399
2400 It's incredibly tiresome, because we only need this type to fill
2401 in the hole, to communicate to the error reporting machinery. Nothing
2402 more. So I use a HACK:
2403
2404 * I make an /ordinary/ tuple of the constraints, in
2405 TcBinds.chooseInferredQuantifiers. This is ill-kinded because
2406 ordinary tuples can't contain constraints, but it works fine. And for
2407 ordinary tuples we don't have the same limit as for constraint
2408 tuples (which need selectors and an assocated class).
2409
2410 * Because it is ill-kinded, it trips an assert in writeMetaTyVar,
2411 so now I disable the assertion if we are writing a type of
2412 kind Constraint. (That seldom/never normally happens so we aren't
2413 losing much.)
2414
2415 Result works fine, but it may eventually bite us.
2416
2417
2418 ************************************************************************
2419 * *
2420 Pattern signatures (i.e signatures that occur in patterns)
2421 * *
2422 ********************************************************************* -}
2423
2424 tcHsPatSigType :: UserTypeCtxt
2425 -> LHsSigWcType GhcRn -- The type signature
2426 -> TcM ( [(Name, TcTyVar)] -- Wildcards
2427 , [(Name, TcTyVar)] -- The new bit of type environment, binding
2428 -- the scoped type variables
2429 , TcType) -- The type
2430 -- Used for type-checking type signatures in
2431 -- (a) patterns e.g f (x::Int) = e
2432 -- (b) RULE forall bndrs e.g. forall (x::Int). f x = x
2433 --
2434 -- This may emit constraints
2435 -- See Note [Recipe for checking a signature]
2436 tcHsPatSigType ctxt sig_ty
2437 | HsWC { hswc_ext = sig_wcs, hswc_body = ib_ty } <- sig_ty
2438 , HsIB { hsib_ext = HsIBRn { hsib_vars = sig_vars}
2439 , hsib_body = hs_ty } <- ib_ty
2440 = addSigCtxt ctxt hs_ty $
2441 do { sig_tkvs <- mapM new_implicit_tv sig_vars
2442 ; (wcs, sig_ty)
2443 <- tcWildCardBindersX newWildTyVar Nothing sig_wcs $ \ wcs ->
2444 tcExtendTyVarEnv sig_tkvs $
2445 do { sig_ty <- tcHsOpenType hs_ty
2446 ; return (wcs, sig_ty) }
2447
2448 ; emitWildCardHoleConstraints wcs
2449
2450 -- sig_ty might have tyvars that are at a higher TcLevel (if hs_ty
2451 -- contains a forall). Promote these.
2452 ; sig_ty <- zonkPromoteType sig_ty
2453 ; checkValidType ctxt sig_ty
2454
2455 ; tv_pairs <- mapM mk_tv_pair sig_tkvs
2456
2457 ; traceTc "tcHsPatSigType" (ppr sig_vars)
2458 ; return (wcs, tv_pairs, sig_ty) }
2459 where
2460 new_implicit_tv name = do { kind <- newMetaKindVar
2461 ; new_tv name kind }
2462
2463 new_tv = case ctxt of
2464 RuleSigCtxt {} -> newSkolemTyVar
2465 _ -> newSigTyVar
2466 -- See Note [Pattern signature binders]
2467 -- See Note [Unifying SigTvs]
2468
2469 mk_tv_pair tv = do { tv' <- zonkTcTyVarToTyVar tv
2470 ; return (tyVarName tv, tv') }
2471 -- The Name is one of sig_vars, the lexically scoped name
2472 -- But if it's a SigTyVar, it might have been unified
2473 -- with an existing in-scope skolem, so we must zonk
2474 -- here. See Note [Pattern signature binders]
2475 tcHsPatSigType _ (HsWC _ (XHsImplicitBndrs _)) = panic "tcHsPatSigType"
2476 tcHsPatSigType _ (XHsWildCardBndrs _) = panic "tcHsPatSigType"
2477
2478 tcPatSig :: Bool -- True <=> pattern binding
2479 -> LHsSigWcType GhcRn
2480 -> ExpSigmaType
2481 -> TcM (TcType, -- The type to use for "inside" the signature
2482 [(Name,TcTyVar)], -- The new bit of type environment, binding
2483 -- the scoped type variables
2484 [(Name,TcTyVar)], -- The wildcards
2485 HsWrapper) -- Coercion due to unification with actual ty
2486 -- Of shape: res_ty ~ sig_ty
2487 tcPatSig in_pat_bind sig res_ty
2488 = do { (sig_wcs, sig_tvs, sig_ty) <- tcHsPatSigType PatSigCtxt sig
2489 -- sig_tvs are the type variables free in 'sig',
2490 -- and not already in scope. These are the ones
2491 -- that should be brought into scope
2492
2493 ; if null sig_tvs then do {
2494 -- Just do the subsumption check and return
2495 wrap <- addErrCtxtM (mk_msg sig_ty) $
2496 tcSubTypeET PatSigOrigin PatSigCtxt res_ty sig_ty
2497 ; return (sig_ty, [], sig_wcs, wrap)
2498 } else do
2499 -- Type signature binds at least one scoped type variable
2500
2501 -- A pattern binding cannot bind scoped type variables
2502 -- It is more convenient to make the test here
2503 -- than in the renamer
2504 { when in_pat_bind (addErr (patBindSigErr sig_tvs))
2505
2506 -- Check that all newly-in-scope tyvars are in fact
2507 -- constrained by the pattern. This catches tiresome
2508 -- cases like
2509 -- type T a = Int
2510 -- f :: Int -> Int
2511 -- f (x :: T a) = ...
2512 -- Here 'a' doesn't get a binding. Sigh
2513 ; let bad_tvs = [ tv | (_,tv) <- sig_tvs
2514 , not (tv `elemVarSet` exactTyCoVarsOfType sig_ty) ]
2515 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
2516
2517 -- Now do a subsumption check of the pattern signature against res_ty
2518 ; wrap <- addErrCtxtM (mk_msg sig_ty) $
2519 tcSubTypeET PatSigOrigin PatSigCtxt res_ty sig_ty
2520
2521 -- Phew!
2522 ; return (sig_ty, sig_tvs, sig_wcs, wrap)
2523 } }
2524 where
2525 mk_msg sig_ty tidy_env
2526 = do { (tidy_env, sig_ty) <- zonkTidyTcType tidy_env sig_ty
2527 ; res_ty <- readExpType res_ty -- should be filled in by now
2528 ; (tidy_env, res_ty) <- zonkTidyTcType tidy_env res_ty
2529 ; let msg = vcat [ hang (text "When checking that the pattern signature:")
2530 4 (ppr sig_ty)
2531 , nest 2 (hang (text "fits the type of its context:")
2532 2 (ppr res_ty)) ]
2533 ; return (tidy_env, msg) }
2534
2535 patBindSigErr :: [(Name,TcTyVar)] -> SDoc
2536 patBindSigErr sig_tvs
2537 = hang (text "You cannot bind scoped type variable" <> plural sig_tvs
2538 <+> pprQuotedList (map fst sig_tvs))
2539 2 (text "in a pattern binding signature")
2540
2541 {- Note [Pattern signature binders]
2542 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2543 Consider
2544 data T = forall a. T a (a->Int)
2545 f (T x (f :: b->Int)) = blah
2546
2547 Here
2548 * The pattern (T p1 p2) creates a *skolem* type variable 'a_sk',
2549 It must be a skolem so that that it retains its identity, and
2550 TcErrors.getSkolemInfo can thereby find the binding site for the skolem.
2551
2552 * The type signature pattern (f :: b->Int) makes a fresh meta-tyvar b_sig
2553 (a SigTv), and binds "b" :-> b_sig in the envt
2554
2555 * Then unification makes b_sig := a_sk
2556 That's why we must make b_sig a MetaTv (albeit a SigTv),
2557 not a SkolemTv, so that it can unify to a_sk.
2558
2559 * Finally, in 'blah' we must have the envt "b" :-> a_sk. The pair
2560 ("b" :-> a_sk) is returned by tcHsPatSigType, constructed by
2561 mk_tv_pair in that function.
2562
2563 Another example (Trac #13881):
2564 fl :: forall (l :: [a]). Sing l -> Sing l
2565 fl (SNil :: Sing (l :: [y])) = SNil
2566 When we reach the pattern signature, 'l' is in scope from the
2567 outer 'forall':
2568 "a" :-> a_sk :: *
2569 "l" :-> l_sk :: [a_sk]
2570 We make up a fresh meta-SigTv, y_sig, for 'y', and kind-check
2571 the pattern signature
2572 Sing (l :: [y])
2573 That unifies y_sig := a_sk. We return from tcHsPatSigType with
2574 the pair ("y" :-> a_sk).
2575
2576 For RULE binders, though, things are a bit different (yuk).
2577 RULE "foo" forall (x::a) (y::[a]). f x y = ...
2578 Here this really is the binding site of the type variable so we'd like
2579 to use a skolem, so that we get a complaint if we unify two of them
2580 together.
2581
2582 Note [Unifying SigTvs]
2583 ~~~~~~~~~~~~~~~~~~~~~~
2584 ALAS we have no decent way of avoiding two SigTvs getting unified.
2585 Consider
2586 f (x::(a,b)) (y::c)) = [fst x, y]
2587 Here we'd really like to complain that 'a' and 'c' are unified. But
2588 for the reasons above we can't make a,b,c into skolems, so they
2589 are just SigTvs that can unify. And indeed, this would be ok,
2590 f x (y::c) = case x of
2591 (x1 :: a1, True) -> [x,y]
2592 (x1 :: a2, False) -> [x,y,y]
2593 Here the type of x's first component is called 'a1' in one branch and
2594 'a2' in the other. We could try insisting on the same OccName, but
2595 they definitely won't have the sane lexical Name.
2596
2597 I think we could solve this by recording in a SigTv a list of all the
2598 in-scope variables that it should not unify with, but it's fiddly.
2599
2600
2601 ************************************************************************
2602 * *
2603 Checking kinds
2604 * *
2605 ************************************************************************
2606
2607 -}
2608
2609 unifyKinds :: [LHsType GhcRn] -> [(TcType, TcKind)] -> TcM ([TcType], TcKind)
2610 unifyKinds rn_tys act_kinds
2611 = do { kind <- newMetaKindVar
2612 ; let check rn_ty (ty, act_kind) = checkExpectedKind (unLoc rn_ty) ty act_kind kind
2613 ; tys' <- zipWithM check rn_tys act_kinds
2614 ; return (tys', kind) }
2615
2616 {-
2617 ************************************************************************
2618 * *
2619 Promotion
2620 * *
2621 ************************************************************************
2622 -}
2623
2624 -- | Whenever a type is about to be added to the environment, it's necessary
2625 -- to make sure that any free meta-tyvars in the type are promoted to the
2626 -- current TcLevel. (They might be at a higher level due to the level-bumping
2627 -- in tcExplicitTKBndrs, for example.) This function both zonks *and*
2628 -- promotes.
2629 zonkPromoteType :: TcType -> TcM TcType
2630 zonkPromoteType = mapType zonkPromoteMapper ()
2631
2632 -- cf. TcMType.zonkTcTypeMapper
2633 zonkPromoteMapper :: TyCoMapper () TcM
2634 zonkPromoteMapper = TyCoMapper { tcm_smart = True
2635 , tcm_tyvar = const zonkPromoteTcTyVar
2636 , tcm_covar = const covar
2637 , tcm_hole = const hole
2638 , tcm_tybinder = const tybinder }
2639 where
2640 covar cv
2641 = mkCoVarCo <$> zonkPromoteTyCoVarKind cv
2642
2643 hole :: CoercionHole -> TcM Coercion
2644 hole h
2645 = do { contents <- unpackCoercionHole_maybe h
2646 ; case contents of
2647 Just co -> do { co <- zonkPromoteCoercion co
2648 ; checkCoercionHole cv co }
2649 Nothing -> do { cv' <- zonkPromoteTyCoVarKind cv
2650 ; return $ mkHoleCo (setCoHoleCoVar h cv') } }
2651 where
2652 cv = coHoleCoVar h
2653
2654 tybinder :: TyVar -> ArgFlag -> TcM ((), TyVar)
2655 tybinder tv _flag = ((), ) <$> zonkPromoteTyCoVarKind tv
2656
2657 zonkPromoteTcTyVar :: TyCoVar -> TcM TcType
2658 zonkPromoteTcTyVar tv
2659 | isMetaTyVar tv
2660 = do { let ref = metaTyVarRef tv
2661 ; contents <- readTcRef ref
2662 ; case contents of
2663 Flexi -> do { promoted <- promoteTyVar tv
2664 ; if promoted
2665 then zonkPromoteTcTyVar tv -- read it again
2666 else mkTyVarTy <$> zonkPromoteTyCoVarKind tv }
2667 Indirect ty -> zonkPromoteType ty }
2668
2669 | isTcTyVar tv && isSkolemTyVar tv -- NB: isSkolemTyVar says "True" to pure TyVars
2670 = do { tc_lvl <- getTcLevel
2671 ; mkTyVarTy <$> zonkPromoteTyCoVarKind (promoteSkolem tc_lvl tv) }
2672
2673 | otherwise
2674 = mkTyVarTy <$> zonkPromoteTyCoVarKind tv
2675
2676 zonkPromoteTyCoVarKind :: TyCoVar -> TcM TyCoVar
2677 zonkPromoteTyCoVarKind = updateTyVarKindM zonkPromoteType
2678
2679 zonkPromoteTyCoVarBndr :: TyCoVar -> TcM TyCoVar
2680 zonkPromoteTyCoVarBndr tv
2681 | isSigTyVar tv
2682 = tcGetTyVar "zonkPromoteTyCoVarBndr SigTv" <$> zonkPromoteTcTyVar tv
2683
2684 | isTcTyVar tv && isSkolemTyVar tv
2685 = do { tc_lvl <- getTcLevel
2686 ; zonkPromoteTyCoVarKind (promoteSkolem tc_lvl tv) }
2687
2688 | otherwise
2689 = zonkPromoteTyCoVarKind tv
2690
2691 zonkPromoteCoercion :: Coercion -> TcM Coercion
2692 zonkPromoteCoercion = mapCoercion zonkPromoteMapper ()
2693
2694 zonkPromoteTypeInKnot :: TcType -> TcM TcType
2695 zonkPromoteTypeInKnot = mapType (zonkPromoteMapper { tcm_smart = False }) ()
2696 -- NB: Just changing smart to False will still use the smart zonker (not suitable
2697 -- for in-the-knot) for kinds. But that's OK, because kinds aren't knot-tied.
2698
2699 {-
2700 ************************************************************************
2701 * *
2702 Sort checking kinds
2703 * *
2704 ************************************************************************
2705
2706 tcLHsKindSig converts a user-written kind to an internal, sort-checked kind.
2707 It does sort checking and desugaring at the same time, in one single pass.
2708 -}
2709
2710 tcLHsKindSig :: UserTypeCtxt -> LHsKind GhcRn -> TcM Kind
2711 tcLHsKindSig ctxt hs_kind
2712 -- See Note [Recipe for checking a signature] in TcHsType
2713 = do { kind <- solveLocalEqualities $
2714 tc_lhs_kind kindLevelMode hs_kind
2715 ; kind <- zonkPromoteType kind
2716 -- This zonk is very important in the case of higher rank kinds
2717 -- E.g. Trac #13879 f :: forall (p :: forall z (y::z). <blah>).
2718 -- <more blah>
2719 -- When instantiating p's kind at occurrences of p in <more blah>
2720 -- it's crucial that the kind we instantiate is fully zonked,
2721 -- else we may fail to substitute properly
2722
2723 ; checkValidType ctxt kind
2724 ; return kind }
2725
2726 tc_lhs_kind :: TcTyMode -> LHsKind GhcRn -> TcM Kind
2727 tc_lhs_kind mode k
2728 = addErrCtxt (text "In the kind" <+> quotes (ppr k)) $
2729 tc_lhs_type (kindLevel mode) k liftedTypeKind
2730
2731 promotionErr :: Name -> PromotionErr -> TcM a
2732 promotionErr name err
2733 = failWithTc (hang (pprPECategory err <+> quotes (ppr name) <+> text "cannot be used here")
2734 2 (parens reason))
2735 where
2736 reason = case err of
2737 ConstrainedDataConPE pred
2738 -> text "it has an unpromotable context"
2739 <+> quotes (ppr pred)
2740 FamDataConPE -> text "it comes from a data family instance"
2741 NoDataKindsTC -> text "perhaps you intended to use DataKinds"
2742 NoDataKindsDC -> text "perhaps you intended to use DataKinds"
2743 PatSynPE -> text "pattern synonyms cannot be promoted"
2744 PatSynExPE -> sep [ text "the existential variables of a pattern synonym"
2745 , text "signature do not scope over the pattern" ]
2746 _ -> text "it is defined and used in the same recursive group"
2747
2748 {-
2749 ************************************************************************
2750 * *
2751 Scoped type variables
2752 * *
2753 ************************************************************************
2754 -}
2755
2756 badPatSigTvs :: TcType -> [TyVar] -> SDoc
2757 badPatSigTvs sig_ty bad_tvs
2758 = vcat [ fsep [text "The type variable" <> plural bad_tvs,
2759 quotes (pprWithCommas ppr bad_tvs),
2760 text "should be bound by the pattern signature" <+> quotes (ppr sig_ty),
2761 text "but are actually discarded by a type synonym" ]
2762 , text "To fix this, expand the type synonym"
2763 , text "[Note: I hope to lift this restriction in due course]" ]
2764
2765 {-
2766 ************************************************************************
2767 * *
2768 Error messages and such
2769 * *
2770 ************************************************************************
2771 -}
2772
2773 -- | Make an appropriate message for an error in a function argument.
2774 -- Used for both expressions and types.
2775 funAppCtxt :: (Outputable fun, Outputable arg) => fun -> arg -> Int -> SDoc
2776 funAppCtxt fun arg arg_no
2777 = hang (hsep [ text "In the", speakNth arg_no, ptext (sLit "argument of"),
2778 quotes (ppr fun) <> text ", namely"])
2779 2 (quotes (ppr arg))
2780
2781 -- See Note [Free-floating kind vars]
2782 reportFloatingKvs :: Name -- of the tycon
2783 -> TyConFlavour -- What sort of TyCon it is
2784 -> [TcTyVar] -- all tyvars, not necessarily zonked
2785 -> [TcTyVar] -- floating tyvars
2786 -> TcM ()
2787 reportFloatingKvs tycon_name flav all_tvs bad_tvs
2788 = unless (null bad_tvs) $ -- don't bother zonking if there's no error
2789 do { all_tvs <- mapM zonkTcTyVarToTyVar all_tvs
2790 ; bad_tvs <- mapM zonkTcTyVarToTyVar bad_tvs
2791 ; let (tidy_env, tidy_all_tvs) = tidyOpenTyCoVars emptyTidyEnv all_tvs
2792 tidy_bad_tvs = map (tidyTyVarOcc tidy_env) bad_tvs
2793 ; mapM_ (report tidy_all_tvs) tidy_bad_tvs }
2794 where
2795 report tidy_all_tvs tidy_bad_tv
2796 = addErr $
2797 vcat [ text "Kind variable" <+> quotes (ppr tidy_bad_tv) <+>
2798 text "is implicitly bound in" <+> ppr flav
2799 , quotes (ppr tycon_name) <> comma <+>
2800 text "but does not appear as the kind of any"
2801 , text "of its type variables. Perhaps you meant"
2802 , text "to bind it explicitly somewhere?"
2803 , ppWhen (not (null tidy_all_tvs)) $
2804 hang (text "Type variables with inferred kinds:")
2805 2 (ppr_tv_bndrs tidy_all_tvs) ]
2806
2807 ppr_tv_bndrs tvs = sep (map pp_tv tvs)
2808 pp_tv tv = parens (ppr tv <+> dcolon <+> ppr (tyVarKind tv))