Fix typechecking of kind signatures
[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, tcImplicitTKBndrsX,
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, kcLHsTyVarBndrs,
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 ( tcInstBinders, tcInstBinder )
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 <- tcWildCardBindersX newWildTyVar Nothing sig_wcs $ \ _ ->
360 tcCheckLHsType hs_ty kind
361 ; ty <- zonkPromoteType ty
362 ; checkValidType TypeAppCtxt ty
363 ; return ty }
364 -- NB: we don't call emitWildcardHoleConstraints here, because
365 -- we want any holes in visible type applications to be used
366 -- without fuss. No errors, warnings, extensions, etc.
367 tcHsTypeApp (XHsWildCardBndrs _) _ = panic "tcHsTypeApp"
368
369 {-
370 ************************************************************************
371 * *
372 The main kind checker: no validity checks here
373 * *
374 ************************************************************************
375
376 First a couple of simple wrappers for kcHsType
377 -}
378
379 ---------------------------
380 tcHsOpenType, tcHsLiftedType,
381 tcHsOpenTypeNC, tcHsLiftedTypeNC :: LHsType GhcRn -> TcM TcType
382 -- Used for type signatures
383 -- Do not do validity checking
384 tcHsOpenType ty = addTypeCtxt ty $ tcHsOpenTypeNC ty
385 tcHsLiftedType ty = addTypeCtxt ty $ tcHsLiftedTypeNC ty
386
387 tcHsOpenTypeNC ty = do { ek <- newOpenTypeKind
388 ; tc_lhs_type typeLevelMode ty ek }
389 tcHsLiftedTypeNC ty = tc_lhs_type typeLevelMode ty liftedTypeKind
390
391 -- Like tcHsType, but takes an expected kind
392 tcCheckLHsType :: LHsType GhcRn -> Kind -> TcM TcType
393 tcCheckLHsType hs_ty exp_kind
394 = addTypeCtxt hs_ty $
395 tc_lhs_type typeLevelMode hs_ty exp_kind
396
397 tcLHsType :: LHsType GhcRn -> TcM (TcType, TcKind)
398 -- Called from outside: set the context
399 tcLHsType ty = addTypeCtxt ty (tc_infer_lhs_type typeLevelMode ty)
400
401 -- Like tcLHsType, but use it in a context where type synonyms and type families
402 -- do not need to be saturated, like in a GHCi :kind call
403 tcLHsTypeUnsaturated :: LHsType GhcRn -> TcM (TcType, TcKind)
404 tcLHsTypeUnsaturated ty = addTypeCtxt ty (tc_infer_lhs_type mode ty)
405 where
406 mode = allowUnsaturated typeLevelMode
407
408 ---------------------------
409 -- | Should we generalise the kind of this type signature?
410 -- We *should* generalise if the type is closed
411 -- or if NoMonoLocalBinds is set. Otherwise, nope.
412 -- See Note [Kind generalisation plan]
413 decideKindGeneralisationPlan :: LHsSigType GhcRn -> TcM Bool
414 decideKindGeneralisationPlan sig_ty@(HsIB { hsib_ext
415 = HsIBRn { hsib_closed = closed } })
416 = do { mono_locals <- xoptM LangExt.MonoLocalBinds
417 ; let should_gen = not mono_locals || closed
418 ; traceTc "decideKindGeneralisationPlan"
419 (ppr sig_ty $$ text "should gen?" <+> ppr should_gen)
420 ; return should_gen }
421 decideKindGeneralisationPlan(XHsImplicitBndrs _)
422 = panic "decideKindGeneralisationPlan"
423
424 {- Note [Kind generalisation plan]
425 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
426 When should we do kind-generalisation for user-written type signature?
427 Answer: we use the same rule as for value bindings:
428
429 * We always kind-generalise if the type signature is closed
430 * Additionally, we attempt to generalise if we have NoMonoLocalBinds
431
432 Trac #13337 shows the problem if we kind-generalise an open type (i.e.
433 one that mentions in-scope type variable
434 foo :: forall k (a :: k) proxy. (Typeable k, Typeable a)
435 => proxy a -> String
436 foo _ = case eqT :: Maybe (k :~: Type) of
437 Nothing -> ...
438 Just Refl -> case eqT :: Maybe (a :~: Int) of ...
439
440 In the expression type sig on the last line, we have (a :: k)
441 but (Int :: Type). Since (:~:) is kind-homogeneous, this requires
442 k ~ *, which is true in the Refl branch of the outer case.
443
444 That equality will be solved if we allow it to float out to the
445 implication constraint for the Refl match, but not not if we aggressively
446 attempt to solve all equalities the moment they occur; that is, when
447 checking (Maybe (a :~: Int)). (NB: solveEqualities fails unless it
448 solves all the kind equalities, which is the right thing at top level.)
449
450 So here the right thing is simply not to do kind generalisation!
451
452 ************************************************************************
453 * *
454 Type-checking modes
455 * *
456 ************************************************************************
457
458 The kind-checker is parameterised by a TcTyMode, which contains some
459 information about where we're checking a type.
460
461 The renamer issues errors about what it can. All errors issued here must
462 concern things that the renamer can't handle.
463
464 -}
465
466 -- | Info about the context in which we're checking a type. Currently,
467 -- differentiates only between types and kinds, but this will likely
468 -- grow, at least to include the distinction between patterns and
469 -- not-patterns.
470 data TcTyMode
471 = TcTyMode { mode_level :: TypeOrKind
472 , mode_unsat :: Bool -- True <=> allow unsaturated type families
473 }
474 -- The mode_unsat field is solely so that type families/synonyms can be unsaturated
475 -- in GHCi :kind calls
476
477 typeLevelMode :: TcTyMode
478 typeLevelMode = TcTyMode { mode_level = TypeLevel, mode_unsat = False }
479
480 kindLevelMode :: TcTyMode
481 kindLevelMode = TcTyMode { mode_level = KindLevel, mode_unsat = False }
482
483 allowUnsaturated :: TcTyMode -> TcTyMode
484 allowUnsaturated mode = mode { mode_unsat = True }
485
486 -- switch to kind level
487 kindLevel :: TcTyMode -> TcTyMode
488 kindLevel mode = mode { mode_level = KindLevel }
489
490 instance Outputable TcTyMode where
491 ppr = ppr . mode_level
492
493 {-
494 Note [Bidirectional type checking]
495 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
496 In expressions, whenever we see a polymorphic identifier, say `id`, we are
497 free to instantiate it with metavariables, knowing that we can always
498 re-generalize with type-lambdas when necessary. For example:
499
500 rank2 :: (forall a. a -> a) -> ()
501 x = rank2 id
502
503 When checking the body of `x`, we can instantiate `id` with a metavariable.
504 Then, when we're checking the application of `rank2`, we notice that we really
505 need a polymorphic `id`, and then re-generalize over the unconstrained
506 metavariable.
507
508 In types, however, we're not so lucky, because *we cannot re-generalize*!
509 There is no lambda. So, we must be careful only to instantiate at the last
510 possible moment, when we're sure we're never going to want the lost polymorphism
511 again. This is done in calls to tcInstBinders.
512
513 To implement this behavior, we use bidirectional type checking, where we
514 explicitly think about whether we know the kind of the type we're checking
515 or not. Note that there is a difference between not knowing a kind and
516 knowing a metavariable kind: the metavariables are TauTvs, and cannot become
517 forall-quantified kinds. Previously (before dependent types), there were
518 no higher-rank kinds, and so we could instantiate early and be sure that
519 no types would have polymorphic kinds, and so we could always assume that
520 the kind of a type was a fresh metavariable. Not so anymore, thus the
521 need for two algorithms.
522
523 For HsType forms that can never be kind-polymorphic, we implement only the
524 "down" direction, where we safely assume a metavariable kind. For HsType forms
525 that *can* be kind-polymorphic, we implement just the "up" (functions with
526 "infer" in their name) version, as we gain nothing by also implementing the
527 "down" version.
528
529 Note [Future-proofing the type checker]
530 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
531 As discussed in Note [Bidirectional type checking], each HsType form is
532 handled in *either* tc_infer_hs_type *or* tc_hs_type. These functions
533 are mutually recursive, so that either one can work for any type former.
534 But, we want to make sure that our pattern-matches are complete. So,
535 we have a bunch of repetitive code just so that we get warnings if we're
536 missing any patterns.
537
538 Note [The tcType invariant]
539 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
540 If tc_ty = tc_hs_type hs_ty exp_kind
541 then
542 typeKind tc_ty = exp_kind
543 without any zonking needed. The reason for this is that in
544 tcInferApps we see (F ty), and we kind-check 'ty' with an
545 expected-kind coming from F. Then, to make the resulting application
546 well kinded --- see Note [Ensure well-kinded types] in TcType --- we
547 need the kind-checked 'ty' to have exactly the kind that F expects,
548 with no funny zonking nonsense in between.
549
550 The tcType invariant also applies to checkExpectedKind: if
551 (tc_ty, _, _) = checkExpectedKind ty act_ki exp_ki
552 then
553 typeKind tc_ty = exp_ki
554 -}
555
556 ------------------------------------------
557 -- | Check and desugar a type, returning the core type and its
558 -- possibly-polymorphic kind. Much like 'tcInferRho' at the expression
559 -- level.
560 tc_infer_lhs_type :: TcTyMode -> LHsType GhcRn -> TcM (TcType, TcKind)
561 tc_infer_lhs_type mode (L span ty)
562 = setSrcSpan span $
563 do { (ty', kind) <- tc_infer_hs_type mode ty
564 ; return (ty', kind) }
565
566 -- | Infer the kind of a type and desugar. This is the "up" type-checker,
567 -- as described in Note [Bidirectional type checking]
568 tc_infer_hs_type :: TcTyMode -> HsType GhcRn -> TcM (TcType, TcKind)
569 tc_infer_hs_type mode (HsParTy _ t) = tc_infer_lhs_type mode t
570 tc_infer_hs_type mode (HsTyVar _ _ (L _ tv)) = tcTyVar mode tv
571
572 tc_infer_hs_type mode (HsAppTy _ ty1 ty2)
573 = do { let (hs_fun_ty, hs_arg_tys) = splitHsAppTys ty1 [ty2]
574 ; (fun_ty, fun_kind) <- tc_infer_lhs_type mode hs_fun_ty
575 -- A worry: what if fun_kind needs zoonking?
576 -- We used to zonk it here, but that got fun_ty and fun_kind
577 -- out of sync (see the precondition to tcTyApps), which caused
578 -- Trac #14873. So I'm now zonking in tcTyVar, and not here.
579 -- Is that enough? Seems so, but I can't see how to be certain.
580 ; tcTyApps mode hs_fun_ty fun_ty fun_kind hs_arg_tys }
581
582 tc_infer_hs_type mode (HsOpTy _ lhs lhs_op@(L _ hs_op) rhs)
583 | not (hs_op `hasKey` funTyConKey)
584 = do { (op, op_kind) <- tcTyVar mode hs_op
585 -- See "A worry" in the HsApp case
586 ; tcTyApps mode (noLoc $ HsTyVar noExt NotPromoted lhs_op) op op_kind
587 [lhs, rhs] }
588
589 tc_infer_hs_type mode (HsKindSig _ ty sig)
590 = do { sig' <- tcLHsKindSig KindSigCtxt sig
591 -- We must typeckeck the kind signature, and solve all
592 -- its equalities etc; from this point on we may do
593 -- things like instantiate its foralls, so it needs
594 -- to be fully determined (Trac #149904)
595 ; traceTc "tc_infer_hs_type:sig" (ppr ty $$ ppr sig')
596 ; ty' <- tc_lhs_type mode ty sig'
597 ; return (ty', sig') }
598
599 -- HsSpliced is an annotation produced by 'RnSplice.rnSpliceType' to communicate
600 -- the splice location to the typechecker. Here we skip over it in order to have
601 -- the same kind inferred for a given expression whether it was produced from
602 -- splices or not.
603 --
604 -- See Note [Delaying modFinalizers in untyped splices].
605 tc_infer_hs_type mode (HsSpliceTy _ (HsSpliced _ _ (HsSplicedTy ty)))
606 = tc_infer_hs_type mode ty
607
608 tc_infer_hs_type mode (HsDocTy _ ty _) = tc_infer_lhs_type mode ty
609 tc_infer_hs_type _ (XHsType (NHsCoreTy ty)) = return (ty, typeKind ty)
610 tc_infer_hs_type mode other_ty
611 = do { kv <- newMetaKindVar
612 ; ty' <- tc_hs_type mode other_ty kv
613 ; return (ty', kv) }
614
615 ------------------------------------------
616 tc_lhs_type :: TcTyMode -> LHsType GhcRn -> TcKind -> TcM TcType
617 tc_lhs_type mode (L span ty) exp_kind
618 = setSrcSpan span $
619 tc_hs_type mode ty exp_kind
620
621 ------------------------------------------
622 tc_fun_type :: TcTyMode -> LHsType GhcRn -> LHsType GhcRn -> TcKind
623 -> TcM TcType
624 tc_fun_type mode ty1 ty2 exp_kind = case mode_level mode of
625 TypeLevel ->
626 do { arg_k <- newOpenTypeKind
627 ; res_k <- newOpenTypeKind
628 ; ty1' <- tc_lhs_type mode ty1 arg_k
629 ; ty2' <- tc_lhs_type mode ty2 res_k
630 ; checkExpectedKind (HsFunTy noExt ty1 ty2) (mkFunTy ty1' ty2')
631 liftedTypeKind exp_kind }
632 KindLevel -> -- no representation polymorphism in kinds. yet.
633 do { ty1' <- tc_lhs_type mode ty1 liftedTypeKind
634 ; ty2' <- tc_lhs_type mode ty2 liftedTypeKind
635 ; checkExpectedKind (HsFunTy noExt ty1 ty2) (mkFunTy ty1' ty2')
636 liftedTypeKind exp_kind }
637
638 ------------------------------------------
639 tc_hs_type :: TcTyMode -> HsType GhcRn -> TcKind -> TcM TcType
640 -- See Note [The tcType invariant]
641 -- See Note [Bidirectional type checking]
642
643 tc_hs_type mode (HsParTy _ ty) exp_kind = tc_lhs_type mode ty exp_kind
644 tc_hs_type mode (HsDocTy _ ty _) exp_kind = tc_lhs_type mode ty exp_kind
645 tc_hs_type _ ty@(HsBangTy _ bang _) _
646 -- While top-level bangs at this point are eliminated (eg !(Maybe Int)),
647 -- other kinds of bangs are not (eg ((!Maybe) Int)). These kinds of
648 -- bangs are invalid, so fail. (#7210, #14761)
649 = do { let bangError err = failWith $
650 text "Unexpected" <+> text err <+> text "annotation:" <+> ppr ty $$
651 text err <+> text "annotation cannot appear nested inside a type"
652 ; case bang of
653 HsSrcBang _ SrcUnpack _ -> bangError "UNPACK"
654 HsSrcBang _ SrcNoUnpack _ -> bangError "NOUNPACK"
655 HsSrcBang _ NoSrcUnpack SrcLazy -> bangError "laziness"
656 HsSrcBang _ _ _ -> bangError "strictness" }
657 tc_hs_type _ ty@(HsRecTy {}) _
658 -- Record types (which only show up temporarily in constructor
659 -- signatures) should have been removed by now
660 = failWithTc (text "Record syntax is illegal here:" <+> ppr ty)
661
662 -- HsSpliced is an annotation produced by 'RnSplice.rnSpliceType'.
663 -- Here we get rid of it and add the finalizers to the global environment
664 -- while capturing the local environment.
665 --
666 -- See Note [Delaying modFinalizers in untyped splices].
667 tc_hs_type mode (HsSpliceTy _ (HsSpliced _ mod_finalizers (HsSplicedTy ty)))
668 exp_kind
669 = do addModFinalizersWithLclEnv mod_finalizers
670 tc_hs_type mode ty exp_kind
671
672 -- This should never happen; type splices are expanded by the renamer
673 tc_hs_type _ ty@(HsSpliceTy {}) _exp_kind
674 = failWithTc (text "Unexpected type splice:" <+> ppr ty)
675
676 ---------- Functions and applications
677 tc_hs_type mode (HsFunTy _ ty1 ty2) exp_kind
678 = tc_fun_type mode ty1 ty2 exp_kind
679
680 tc_hs_type mode (HsOpTy _ ty1 (L _ op) ty2) exp_kind
681 | op `hasKey` funTyConKey
682 = tc_fun_type mode ty1 ty2 exp_kind
683
684 --------- Foralls
685 tc_hs_type mode forall@(HsForAllTy { hst_bndrs = hs_tvs, hst_body = ty }) exp_kind
686 = do { (tvs', ty') <- tcExplicitTKBndrs (ForAllSkol (ppr forall)) hs_tvs $
687 tc_lhs_type mode ty exp_kind
688 -- Do not kind-generalise here! See Note [Kind generalisation]
689 -- Why exp_kind? See Note [Body kind of HsForAllTy]
690 ; let bndrs = mkTyVarBinders Specified tvs'
691 ; return (mkForAllTys bndrs ty') }
692
693 tc_hs_type mode (HsQualTy { hst_ctxt = ctxt, hst_body = ty }) exp_kind
694 | null (unLoc ctxt)
695 = tc_lhs_type mode ty exp_kind
696
697 | otherwise
698 = do { ctxt' <- tc_hs_context mode ctxt
699
700 -- See Note [Body kind of a HsQualTy]
701 ; ty' <- if isConstraintKind exp_kind
702 then tc_lhs_type mode ty constraintKind
703 else do { ek <- newOpenTypeKind
704 -- The body kind (result of the function)
705 -- can be * or #, hence newOpenTypeKind
706 ; ty' <- tc_lhs_type mode ty ek
707 ; checkExpectedKind (unLoc ty) ty' liftedTypeKind exp_kind }
708
709 ; return (mkPhiTy ctxt' ty') }
710
711 --------- Lists, arrays, and tuples
712 tc_hs_type mode rn_ty@(HsListTy _ elt_ty) exp_kind
713 = do { tau_ty <- tc_lhs_type mode elt_ty liftedTypeKind
714 ; checkWiredInTyCon listTyCon
715 ; checkExpectedKind rn_ty (mkListTy tau_ty) liftedTypeKind exp_kind }
716
717 -- See Note [Distinguishing tuple kinds] in HsTypes
718 -- See Note [Inferring tuple kinds]
719 tc_hs_type mode rn_ty@(HsTupleTy _ HsBoxedOrConstraintTuple hs_tys) exp_kind
720 -- (NB: not zonking before looking at exp_k, to avoid left-right bias)
721 | Just tup_sort <- tupKindSort_maybe exp_kind
722 = traceTc "tc_hs_type tuple" (ppr hs_tys) >>
723 tc_tuple rn_ty mode tup_sort hs_tys exp_kind
724 | otherwise
725 = do { traceTc "tc_hs_type tuple 2" (ppr hs_tys)
726 ; (tys, kinds) <- mapAndUnzipM (tc_infer_lhs_type mode) hs_tys
727 ; kinds <- mapM zonkTcType kinds
728 -- Infer each arg type separately, because errors can be
729 -- confusing if we give them a shared kind. Eg Trac #7410
730 -- (Either Int, Int), we do not want to get an error saying
731 -- "the second argument of a tuple should have kind *->*"
732
733 ; let (arg_kind, tup_sort)
734 = case [ (k,s) | k <- kinds
735 , Just s <- [tupKindSort_maybe k] ] of
736 ((k,s) : _) -> (k,s)
737 [] -> (liftedTypeKind, BoxedTuple)
738 -- In the [] case, it's not clear what the kind is, so guess *
739
740 ; tys' <- sequence [ setSrcSpan loc $
741 checkExpectedKind hs_ty ty kind arg_kind
742 | ((L loc hs_ty),ty,kind) <- zip3 hs_tys tys kinds ]
743
744 ; finish_tuple rn_ty tup_sort tys' (map (const arg_kind) tys') exp_kind }
745
746
747 tc_hs_type mode rn_ty@(HsTupleTy _ hs_tup_sort tys) exp_kind
748 = tc_tuple rn_ty mode tup_sort tys exp_kind
749 where
750 tup_sort = case hs_tup_sort of -- Fourth case dealt with above
751 HsUnboxedTuple -> UnboxedTuple
752 HsBoxedTuple -> BoxedTuple
753 HsConstraintTuple -> ConstraintTuple
754 _ -> panic "tc_hs_type HsTupleTy"
755
756 tc_hs_type mode rn_ty@(HsSumTy _ hs_tys) exp_kind
757 = do { let arity = length hs_tys
758 ; arg_kinds <- mapM (\_ -> newOpenTypeKind) hs_tys
759 ; tau_tys <- zipWithM (tc_lhs_type mode) hs_tys arg_kinds
760 ; let arg_reps = map getRuntimeRepFromKind arg_kinds
761 arg_tys = arg_reps ++ tau_tys
762 ; checkExpectedKind rn_ty
763 (mkTyConApp (sumTyCon arity) arg_tys)
764 (unboxedSumKind arg_reps)
765 exp_kind
766 }
767
768 --------- Promoted lists and tuples
769 tc_hs_type mode rn_ty@(HsExplicitListTy _ _ tys) exp_kind
770 = do { tks <- mapM (tc_infer_lhs_type mode) tys
771 ; (taus', kind) <- unifyKinds tys tks
772 ; let ty = (foldr (mk_cons kind) (mk_nil kind) taus')
773 ; checkExpectedKind rn_ty ty (mkListTy kind) exp_kind }
774 where
775 mk_cons k a b = mkTyConApp (promoteDataCon consDataCon) [k, a, b]
776 mk_nil k = mkTyConApp (promoteDataCon nilDataCon) [k]
777
778 tc_hs_type mode rn_ty@(HsExplicitTupleTy _ tys) exp_kind
779 -- using newMetaKindVar means that we force instantiations of any polykinded
780 -- types. At first, I just used tc_infer_lhs_type, but that led to #11255.
781 = do { ks <- replicateM arity newMetaKindVar
782 ; taus <- zipWithM (tc_lhs_type mode) tys ks
783 ; let kind_con = tupleTyCon Boxed arity
784 ty_con = promotedTupleDataCon Boxed arity
785 tup_k = mkTyConApp kind_con ks
786 ; checkExpectedKind rn_ty (mkTyConApp ty_con (ks ++ taus)) tup_k exp_kind }
787 where
788 arity = length tys
789
790 --------- Constraint types
791 tc_hs_type mode rn_ty@(HsIParamTy _ (L _ n) ty) exp_kind
792 = do { MASSERT( isTypeLevel (mode_level mode) )
793 ; ty' <- tc_lhs_type mode ty liftedTypeKind
794 ; let n' = mkStrLitTy $ hsIPNameFS n
795 ; ipClass <- tcLookupClass ipClassName
796 ; checkExpectedKind rn_ty (mkClassPred ipClass [n',ty'])
797 constraintKind exp_kind }
798
799 tc_hs_type mode rn_ty@(HsEqTy _ ty1 ty2) exp_kind
800 = do { (ty1', kind1) <- tc_infer_lhs_type mode ty1
801 ; (ty2', kind2) <- tc_infer_lhs_type mode ty2
802 ; ty2'' <- checkExpectedKind (unLoc ty2) ty2' kind2 kind1
803 ; eq_tc <- tcLookupTyCon eqTyConName
804 ; let ty' = mkNakedTyConApp eq_tc [kind1, ty1', ty2'']
805 ; checkExpectedKind rn_ty ty' constraintKind exp_kind }
806
807 tc_hs_type _ rn_ty@(HsStarTy _ _) exp_kind
808 -- Desugaring 'HsStarTy' to 'Data.Kind.Type' here means that we don't have to
809 -- handle it in 'coreView' and 'tcView'.
810 = checkExpectedKind rn_ty liftedTypeKind liftedTypeKind exp_kind
811
812 --------- Literals
813 tc_hs_type _ rn_ty@(HsTyLit _ (HsNumTy _ n)) exp_kind
814 = do { checkWiredInTyCon typeNatKindCon
815 ; checkExpectedKind rn_ty (mkNumLitTy n) typeNatKind exp_kind }
816
817 tc_hs_type _ rn_ty@(HsTyLit _ (HsStrTy _ s)) exp_kind
818 = do { checkWiredInTyCon typeSymbolKindCon
819 ; checkExpectedKind rn_ty (mkStrLitTy s) typeSymbolKind exp_kind }
820
821 --------- Potentially kind-polymorphic types: call the "up" checker
822 -- See Note [Future-proofing the type checker]
823 tc_hs_type mode ty@(HsTyVar {}) ek = tc_infer_hs_type_ek mode ty ek
824 tc_hs_type mode ty@(HsAppTy {}) ek = tc_infer_hs_type_ek mode ty ek
825 tc_hs_type mode ty@(HsOpTy {}) ek = tc_infer_hs_type_ek mode ty ek
826 tc_hs_type mode ty@(HsKindSig {}) ek = tc_infer_hs_type_ek mode ty ek
827 tc_hs_type mode ty@(XHsType (NHsCoreTy{})) ek = tc_infer_hs_type_ek mode ty ek
828
829 tc_hs_type _ (HsWildCardTy wc) exp_kind
830 = do { wc_ty <- tcWildCardOcc wc exp_kind
831 ; return (mkNakedCastTy wc_ty (mkTcNomReflCo exp_kind))
832 -- Take care here! Even though the coercion is Refl,
833 -- we still need it to establish Note [The tcType invariant]
834 }
835
836 tcWildCardOcc :: HsWildCardInfo -> Kind -> TcM TcType
837 tcWildCardOcc wc_info exp_kind
838 = do { wc_tv <- tcLookupTyVar (wildCardName wc_info)
839 -- The wildcard's kind should be an un-filled-in meta tyvar
840 ; checkExpectedKind (HsWildCardTy wc_info) (mkTyVarTy wc_tv)
841 (tyVarKind wc_tv) exp_kind }
842
843 ---------------------------
844 -- | Call 'tc_infer_hs_type' and check its result against an expected kind.
845 tc_infer_hs_type_ek :: TcTyMode -> HsType GhcRn -> TcKind -> TcM TcType
846 tc_infer_hs_type_ek mode hs_ty ek
847 = do { (ty, k) <- tc_infer_hs_type mode hs_ty
848 ; checkExpectedKind hs_ty ty k ek }
849
850 ---------------------------
851 tupKindSort_maybe :: TcKind -> Maybe TupleSort
852 tupKindSort_maybe k
853 | Just (k', _) <- splitCastTy_maybe k = tupKindSort_maybe k'
854 | Just k' <- tcView k = tupKindSort_maybe k'
855 | isConstraintKind k = Just ConstraintTuple
856 | isLiftedTypeKind k = Just BoxedTuple
857 | otherwise = Nothing
858
859 tc_tuple :: HsType GhcRn -> TcTyMode -> TupleSort -> [LHsType GhcRn] -> TcKind -> TcM TcType
860 tc_tuple rn_ty mode tup_sort tys exp_kind
861 = do { arg_kinds <- case tup_sort of
862 BoxedTuple -> return (nOfThem arity liftedTypeKind)
863 UnboxedTuple -> mapM (\_ -> newOpenTypeKind) tys
864 ConstraintTuple -> return (nOfThem arity constraintKind)
865 ; tau_tys <- zipWithM (tc_lhs_type mode) tys arg_kinds
866 ; finish_tuple rn_ty tup_sort tau_tys arg_kinds exp_kind }
867 where
868 arity = length tys
869
870 finish_tuple :: HsType GhcRn
871 -> TupleSort
872 -> [TcType] -- ^ argument types
873 -> [TcKind] -- ^ of these kinds
874 -> TcKind -- ^ expected kind of the whole tuple
875 -> TcM TcType
876 finish_tuple rn_ty tup_sort tau_tys tau_kinds exp_kind
877 = do { traceTc "finish_tuple" (ppr res_kind $$ ppr tau_kinds $$ ppr exp_kind)
878 ; let arg_tys = case tup_sort of
879 -- See also Note [Unboxed tuple RuntimeRep vars] in TyCon
880 UnboxedTuple -> tau_reps ++ tau_tys
881 BoxedTuple -> tau_tys
882 ConstraintTuple -> tau_tys
883 ; tycon <- case tup_sort of
884 ConstraintTuple
885 | arity > mAX_CTUPLE_SIZE
886 -> failWith (bigConstraintTuple arity)
887 | otherwise -> tcLookupTyCon (cTupleTyConName arity)
888 BoxedTuple -> do { let tc = tupleTyCon Boxed arity
889 ; checkWiredInTyCon tc
890 ; return tc }
891 UnboxedTuple -> return (tupleTyCon Unboxed arity)
892 ; checkExpectedKind rn_ty (mkTyConApp tycon arg_tys) res_kind exp_kind }
893 where
894 arity = length tau_tys
895 tau_reps = map getRuntimeRepFromKind tau_kinds
896 res_kind = case tup_sort of
897 UnboxedTuple -> unboxedTupleKind tau_reps
898 BoxedTuple -> liftedTypeKind
899 ConstraintTuple -> constraintKind
900
901 bigConstraintTuple :: Arity -> MsgDoc
902 bigConstraintTuple arity
903 = hang (text "Constraint tuple arity too large:" <+> int arity
904 <+> parens (text "max arity =" <+> int mAX_CTUPLE_SIZE))
905 2 (text "Instead, use a nested tuple")
906
907 ---------------------------
908 -- | Apply a type of a given kind to a list of arguments. This instantiates
909 -- invisible parameters as necessary. Always consumes all the arguments,
910 -- using matchExpectedFunKind as necessary.
911 -- This takes an optional @VarEnv Kind@ which maps kind variables to kinds.
912 -- These kinds should be used to instantiate invisible kind variables;
913 -- they come from an enclosing class for an associated type/data family.
914 tcInferApps :: TcTyMode
915 -> Maybe (VarEnv Kind) -- ^ Possibly, kind info (see above)
916 -> LHsType GhcRn -- ^ Function (for printing only)
917 -> TcType -- ^ Function (could be knot-tied)
918 -> TcKind -- ^ Function kind (zonked)
919 -> [LHsType GhcRn] -- ^ Args
920 -> TcM (TcType, [TcType], TcKind) -- ^ (f args, args, result kind)
921 -- Precondition: typeKind fun_ty = fun_ki
922 -- Reason: we will return a type application like (fun_ty arg1 ... argn),
923 -- and that type must be well-kinded
924 -- See Note [The tcType invariant]
925 tcInferApps mode mb_kind_info orig_hs_ty fun_ty fun_ki orig_hs_args
926 = do { traceTc "tcInferApps {" (ppr orig_hs_ty $$ ppr orig_hs_args $$ ppr fun_ki)
927 ; stuff <- go 1 [] empty_subst fun_ty orig_ki_binders orig_inner_ki orig_hs_args
928 ; traceTc "tcInferApps }" empty
929 ; return stuff }
930 where
931 empty_subst = mkEmptyTCvSubst $ mkInScopeSet $
932 tyCoVarsOfType fun_ki
933 (orig_ki_binders, orig_inner_ki) = tcSplitPiTys fun_ki
934
935 go :: Int -- the # of the next argument
936 -> [TcType] -- already type-checked args, in reverse order
937 -> TCvSubst -- instantiating substitution
938 -> TcType -- function applied to some args, could be knot-tied
939 -> [TyBinder] -- binders in function kind (both vis. and invis.)
940 -> TcKind -- function kind body (not a Pi-type)
941 -> [LHsType GhcRn] -- un-type-checked args
942 -> TcM (TcType, [TcType], TcKind) -- same as overall return type
943
944 -- no user-written args left. We're done!
945 go _ acc_args subst fun ki_binders inner_ki []
946 = return (fun, reverse acc_args, substTy subst $ mkPiTys ki_binders inner_ki)
947
948 -- The function's kind has a binder. Is it visible or invisible?
949 go n acc_args subst fun (ki_binder:ki_binders) inner_ki
950 all_args@(arg:args)
951 | isInvisibleBinder ki_binder
952 -- It's invisible. Instantiate.
953 = do { traceTc "tcInferApps (invis)" (ppr ki_binder $$ ppr subst)
954 ; (subst', arg') <- tcInstBinder mb_kind_info subst ki_binder
955 ; go n (arg' : acc_args) subst' (mkNakedAppTy fun arg')
956 ki_binders inner_ki all_args }
957
958 | otherwise
959 -- It's visible. Check the next user-written argument
960 = do { traceTc "tcInferApps (vis)" (vcat [ ppr ki_binder, ppr arg
961 , ppr (tyBinderType ki_binder)
962 , ppr subst ])
963 ; arg' <- addErrCtxt (funAppCtxt orig_hs_ty arg n) $
964 tc_lhs_type mode arg (substTy subst $ tyBinderType ki_binder)
965 ; let subst' = extendTvSubstBinderAndInScope subst ki_binder arg'
966 ; go (n+1) (arg' : acc_args) subst'
967 (mkNakedAppTy fun arg')
968 ki_binders inner_ki args }
969
970 -- We've run out of known binders in the functions's kind.
971 go n acc_args subst fun [] inner_ki all_args
972 | not (null new_ki_binders)
973 -- But, after substituting, we have more binders.
974 = go n acc_args zapped_subst fun new_ki_binders new_inner_ki all_args
975
976 | otherwise
977 -- Even after substituting, still no binders. Use matchExpectedFunKind
978 = do { traceTc "tcInferApps (no binder)" (ppr new_inner_ki $$ ppr zapped_subst)
979 ; (co, arg_k, res_k) <- matchExpectedFunKind hs_ty substed_inner_ki
980 ; let new_in_scope = tyCoVarsOfTypes [arg_k, res_k]
981 subst' = zapped_subst `extendTCvInScopeSet` new_in_scope
982 ; go n acc_args subst'
983 (fun `mkNakedCastTy` co)
984 [mkAnonBinder arg_k]
985 res_k all_args }
986 where
987 substed_inner_ki = substTy subst inner_ki
988 (new_ki_binders, new_inner_ki) = tcSplitPiTys substed_inner_ki
989 zapped_subst = zapTCvSubst subst
990 hs_ty = mkHsAppTys orig_hs_ty (take (n-1) orig_hs_args)
991
992
993 -- | Applies a type to a list of arguments.
994 -- Always consumes all the arguments, using 'matchExpectedFunKind' as
995 -- necessary. If you wish to apply a type to a list of HsTypes, this is
996 -- your function.
997 -- Used for type-checking types only.
998 tcTyApps :: TcTyMode
999 -> LHsType GhcRn -- ^ Function (for printing only)
1000 -> TcType -- ^ Function (could be knot-tied)
1001 -> TcKind -- ^ Function kind (zonked)
1002 -> [LHsType GhcRn] -- ^ Args
1003 -> TcM (TcType, TcKind) -- ^ (f args, result kind)
1004 -- Precondition: see precondition for tcInferApps
1005 tcTyApps mode orig_hs_ty fun_ty fun_ki args
1006 = do { (ty', _args, ki') <- tcInferApps mode Nothing orig_hs_ty fun_ty fun_ki args
1007 ; return (ty', ki') }
1008
1009 --------------------------
1010 -- Like checkExpectedKindX, but returns only the final type; convenient wrapper
1011 -- Obeys Note [The tcType invariant]
1012 checkExpectedKind :: HsType GhcRn -- type we're checking (for printing)
1013 -> TcType -- type we're checking (might be knot-tied)
1014 -> TcKind -- the known kind of that type
1015 -> TcKind -- the expected kind
1016 -> TcM TcType
1017 checkExpectedKind hs_ty ty act exp
1018 = fstOf3 <$> checkExpectedKindX Nothing (ppr hs_ty) ty act exp
1019
1020 checkExpectedKindX :: Maybe (VarEnv Kind) -- Possibly, instantiations for kind vars
1021 -> SDoc -- HsType whose kind we're checking
1022 -> TcType -- the type whose kind we're checking
1023 -> TcKind -- the known kind of that type, k
1024 -> TcKind -- the expected kind, exp_kind
1025 -> TcM (TcType, [TcType], TcCoercionN)
1026 -- (the new args, the coercion)
1027 -- Instantiate a kind (if necessary) and then call unifyType
1028 -- (checkExpectedKind ty act_kind exp_kind)
1029 -- checks that the actual kind act_kind is compatible
1030 -- with the expected kind exp_kind
1031 checkExpectedKindX mb_kind_env pp_hs_ty ty act_kind exp_kind
1032 = do { -- We need to make sure that both kinds have the same number of implicit
1033 -- foralls out front. If the actual kind has more, instantiate accordingly.
1034 -- Otherwise, just pass the type & kind through: the errors are caught
1035 -- in unifyType.
1036 let (exp_bndrs, _) = splitPiTysInvisible exp_kind
1037 n_exp = length exp_bndrs
1038 ; (new_args, act_kind') <- instantiateTyUntilN mb_kind_env n_exp act_kind
1039
1040 ; let origin = TypeEqOrigin { uo_actual = act_kind'
1041 , uo_expected = exp_kind
1042 , uo_thing = Just pp_hs_ty
1043 , uo_visible = True } -- the hs_ty is visible
1044 ty' = mkNakedAppTys ty new_args
1045
1046 ; traceTc "checkExpectedKind" $
1047 vcat [ pp_hs_ty
1048 , text "act_kind:" <+> ppr act_kind
1049 , text "act_kind':" <+> ppr act_kind'
1050 , text "exp_kind:" <+> ppr exp_kind ]
1051
1052 ; if act_kind' `tcEqType` exp_kind
1053 then return (ty', new_args, mkTcNomReflCo exp_kind) -- This is very common
1054 else do { co_k <- uType KindLevel origin act_kind' exp_kind
1055 ; traceTc "checkExpectedKind" (vcat [ ppr act_kind
1056 , ppr exp_kind
1057 , ppr co_k ])
1058 ; let result_ty = ty' `mkNakedCastTy` co_k
1059 -- See Note [The tcType invariant]
1060 ; return (result_ty, new_args, co_k) } }
1061
1062 -- | Instantiate @n@ invisible arguments to a type. If @n <= 0@, no instantiation
1063 -- occurs. If @n@ is too big, then all available invisible arguments are instantiated.
1064 -- (In other words, this function is very forgiving about bad values of @n@.)
1065 instantiateTyN :: Maybe (VarEnv Kind) -- ^ Predetermined instantiations
1066 -- (for assoc. type patterns)
1067 -> Int -- ^ @n@
1068 -> [TyBinder] -> TcKind -- ^ its kind
1069 -> TcM ([TcType], TcKind) -- ^ The inst'ed type, new args, kind
1070 instantiateTyN mb_kind_env n bndrs inner_ki
1071 | n <= 0
1072 = return ([], ki)
1073
1074 | otherwise
1075 = do { (subst, inst_args) <- tcInstBinders empty_subst mb_kind_env inst_bndrs
1076 ; let rebuilt_ki = mkPiTys leftover_bndrs inner_ki
1077 ki' = substTy subst rebuilt_ki
1078 ; traceTc "instantiateTyN" (vcat [ ppr ki
1079 , ppr n
1080 , ppr subst
1081 , ppr rebuilt_ki
1082 , ppr ki' ])
1083 ; return (inst_args, ki') }
1084 where
1085 -- NB: splitAt is forgiving with invalid numbers
1086 (inst_bndrs, leftover_bndrs) = splitAt n bndrs
1087 ki = mkPiTys bndrs inner_ki
1088 empty_subst = mkEmptyTCvSubst (mkInScopeSet (tyCoVarsOfType ki))
1089
1090 -- | Instantiate a type to have at most @n@ invisible arguments.
1091 instantiateTyUntilN :: Maybe (VarEnv Kind) -- ^ Possibly, instantiations for vars
1092 -> Int -- ^ @n@
1093 -> TcKind -- ^ its kind
1094 -> TcM ([TcType], TcKind) -- ^ The new args, final kind
1095 instantiateTyUntilN mb_kind_env n ki
1096 = let (bndrs, inner_ki) = splitPiTysInvisible ki
1097 num_to_inst = length bndrs - n
1098 in
1099 instantiateTyN mb_kind_env num_to_inst bndrs inner_ki
1100
1101 ---------------------------
1102 tcHsMbContext :: Maybe (LHsContext GhcRn) -> TcM [PredType]
1103 tcHsMbContext Nothing = return []
1104 tcHsMbContext (Just cxt) = tcHsContext cxt
1105
1106 tcHsContext :: LHsContext GhcRn -> TcM [PredType]
1107 tcHsContext = tc_hs_context typeLevelMode
1108
1109 tcLHsPredType :: LHsType GhcRn -> TcM PredType
1110 tcLHsPredType = tc_lhs_pred typeLevelMode
1111
1112 tc_hs_context :: TcTyMode -> LHsContext GhcRn -> TcM [PredType]
1113 tc_hs_context mode ctxt = mapM (tc_lhs_pred mode) (unLoc ctxt)
1114
1115 tc_lhs_pred :: TcTyMode -> LHsType GhcRn -> TcM PredType
1116 tc_lhs_pred mode pred = tc_lhs_type mode pred constraintKind
1117
1118 ---------------------------
1119 tcTyVar :: TcTyMode -> Name -> TcM (TcType, TcKind)
1120 -- See Note [Type checking recursive type and class declarations]
1121 -- in TcTyClsDecls
1122 tcTyVar mode name -- Could be a tyvar, a tycon, or a datacon
1123 = do { traceTc "lk1" (ppr name)
1124 ; thing <- tcLookup name
1125 ; case thing of
1126 ATyVar _ tv -> -- Important: zonk before returning
1127 -- We may have the application ((a::kappa) b)
1128 -- where kappa is already unified to (k1 -> k2)
1129 -- Then we want to see that arrow. Best done
1130 -- here because we are also maintaining
1131 -- Note [The tcType invariant], so we don't just
1132 -- want to zonk the kind, leaving the TyVar
1133 -- un-zonked (Trac #114873)
1134 do { ty <- zonkTcTyVar tv
1135 ; return (ty, typeKind ty) }
1136
1137 ATcTyCon tc_tc -> do { -- See Note [GADT kind self-reference]
1138 unless
1139 (isTypeLevel (mode_level mode))
1140 (promotionErr name TyConPE)
1141 ; check_tc tc_tc
1142 ; tc <- get_loopy_tc name tc_tc
1143 ; handle_tyfams tc tc_tc }
1144 -- mkNakedTyConApp: see Note [Type-checking inside the knot]
1145
1146 AGlobal (ATyCon tc)
1147 -> do { check_tc tc
1148 ; handle_tyfams tc tc }
1149
1150 AGlobal (AConLike (RealDataCon dc))
1151 -> do { data_kinds <- xoptM LangExt.DataKinds
1152 ; unless (data_kinds || specialPromotedDc dc) $
1153 promotionErr name NoDataKindsDC
1154 ; when (isFamInstTyCon (dataConTyCon dc)) $
1155 -- see Trac #15245
1156 promotionErr name FamDataConPE
1157 ; let (_, _, _, theta, _, _) = dataConFullSig dc
1158 ; case dc_theta_illegal_constraint theta of
1159 Just pred -> promotionErr name $
1160 ConstrainedDataConPE pred
1161 Nothing -> pure ()
1162 ; let tc = promoteDataCon dc
1163 ; return (mkNakedTyConApp tc [], tyConKind tc) }
1164
1165 APromotionErr err -> promotionErr name err
1166
1167 _ -> wrongThingErr "type" thing name }
1168 where
1169 check_tc :: TyCon -> TcM ()
1170 check_tc tc = do { data_kinds <- xoptM LangExt.DataKinds
1171 ; unless (isTypeLevel (mode_level mode) ||
1172 data_kinds ||
1173 isKindTyCon tc) $
1174 promotionErr name NoDataKindsTC }
1175
1176 -- if we are type-checking a type family tycon, we must instantiate
1177 -- any invisible arguments right away. Otherwise, we get #11246
1178 handle_tyfams :: TyCon -- the tycon to instantiate (might be loopy)
1179 -> TcTyCon -- a non-loopy version of the tycon
1180 -> TcM (TcType, TcKind)
1181 handle_tyfams tc tc_tc
1182 | mightBeUnsaturatedTyCon tc_tc || mode_unsat mode
1183 -- This is where mode_unsat is used
1184 = do { traceTc "tcTyVar2a" (ppr tc_tc $$ ppr tc_kind)
1185 ; return (mkNakedTyConApp tc [], tc_kind) }
1186
1187 | otherwise
1188 = do { (tc_args, kind) <- instantiateTyN Nothing (length (tyConBinders tc_tc))
1189 tc_kind_bndrs tc_inner_ki
1190 ; let tc_ty = mkNakedTyConApp tc tc_args
1191 -- tc and tc_ty must not be traced here, because that would
1192 -- force the evaluation of a potentially knot-tied variable (tc),
1193 -- and the typechecker would hang, as per #11708
1194 ; traceTc "tcTyVar2b" (vcat [ ppr tc_tc <+> dcolon <+> ppr tc_kind
1195 , ppr kind ])
1196 ; return (tc_ty, kind) }
1197 where
1198 tc_kind = tyConKind tc_tc
1199 (tc_kind_bndrs, tc_inner_ki) = splitPiTysInvisible tc_kind
1200
1201 get_loopy_tc :: Name -> TyCon -> TcM TyCon
1202 -- Return the knot-tied global TyCon if there is one
1203 -- Otherwise the local TcTyCon; we must be doing kind checking
1204 -- but we still want to return a TyCon of some sort to use in
1205 -- error messages
1206 get_loopy_tc name tc_tc
1207 = do { env <- getGblEnv
1208 ; case lookupNameEnv (tcg_type_env env) name of
1209 Just (ATyCon tc) -> return tc
1210 _ -> do { traceTc "lk1 (loopy)" (ppr name)
1211 ; return tc_tc } }
1212
1213 -- We cannot promote a data constructor with a context that contains
1214 -- constraints other than equalities, so error if we find one.
1215 -- See Note [Don't promote data constructors with non-equality contexts]
1216 dc_theta_illegal_constraint :: ThetaType -> Maybe PredType
1217 dc_theta_illegal_constraint = find go
1218 where
1219 go :: PredType -> Bool
1220 go pred | Just tc <- tyConAppTyCon_maybe pred
1221 = not $ tc `hasKey` eqTyConKey
1222 || tc `hasKey` heqTyConKey
1223 | otherwise = True
1224
1225 {-
1226 Note [Type-checking inside the knot]
1227 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1228 Suppose we are checking the argument types of a data constructor. We
1229 must zonk the types before making the DataCon, because once built we
1230 can't change it. So we must traverse the type.
1231
1232 BUT the parent TyCon is knot-tied, so we can't look at it yet.
1233
1234 So we must be careful not to use "smart constructors" for types that
1235 look at the TyCon or Class involved.
1236
1237 * Hence the use of mkNakedXXX functions. These do *not* enforce
1238 the invariants (for example that we use (FunTy s t) rather
1239 than (TyConApp (->) [s,t])).
1240
1241 * The zonking functions establish invariants (even zonkTcType, a change from
1242 previous behaviour). So we must never inspect the result of a
1243 zonk that might mention a knot-tied TyCon. This is generally OK
1244 because we zonk *kinds* while kind-checking types. And the TyCons
1245 in kinds shouldn't be knot-tied, because they come from a previous
1246 mutually recursive group.
1247
1248 * TcHsSyn.zonkTcTypeToType also can safely check/establish
1249 invariants.
1250
1251 This is horribly delicate. I hate it. A good example of how
1252 delicate it is can be seen in Trac #7903.
1253
1254 Note [GADT kind self-reference]
1255 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1256
1257 A promoted type cannot be used in the body of that type's declaration.
1258 Trac #11554 shows this example, which made GHC loop:
1259
1260 import Data.Kind
1261 data P (x :: k) = Q
1262 data A :: Type where
1263 B :: forall (a :: A). P a -> A
1264
1265 In order to check the constructor B, we need to have the promoted type A, but in
1266 order to get that promoted type, B must first be checked. To prevent looping, a
1267 TyConPE promotion error is given when tcTyVar checks an ATcTyCon in kind mode.
1268 Any ATcTyCon is a TyCon being defined in the current recursive group (see data
1269 type decl for TcTyThing), and all such TyCons are illegal in kinds.
1270
1271 Trac #11962 proposes checking the head of a data declaration separately from
1272 its constructors. This would allow the example above to pass.
1273
1274 Note [Body kind of a HsForAllTy]
1275 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1276 The body of a forall is usually a type, but in principle
1277 there's no reason to prohibit *unlifted* types.
1278 In fact, GHC can itself construct a function with an
1279 unboxed tuple inside a for-all (via CPR analysis; see
1280 typecheck/should_compile/tc170).
1281
1282 Moreover in instance heads we get forall-types with
1283 kind Constraint.
1284
1285 It's tempting to check that the body kind is either * or #. But this is
1286 wrong. For example:
1287
1288 class C a b
1289 newtype N = Mk Foo deriving (C a)
1290
1291 We're doing newtype-deriving for C. But notice how `a` isn't in scope in
1292 the predicate `C a`. So we quantify, yielding `forall a. C a` even though
1293 `C a` has kind `* -> Constraint`. The `forall a. C a` is a bit cheeky, but
1294 convenient. Bottom line: don't check for * or # here.
1295
1296 Note [Body kind of a HsQualTy]
1297 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1298 If ctxt is non-empty, the HsQualTy really is a /function/, so the
1299 kind of the result really is '*', and in that case the kind of the
1300 body-type can be lifted or unlifted.
1301
1302 However, consider
1303 instance Eq a => Eq [a] where ...
1304 or
1305 f :: (Eq a => Eq [a]) => blah
1306 Here both body-kind of the HsQualTy is Constraint rather than *.
1307 Rather crudely we tell the difference by looking at exp_kind. It's
1308 very convenient to typecheck instance types like any other HsSigType.
1309
1310 Admittedly the '(Eq a => Eq [a]) => blah' case is erroneous, but it's
1311 better to reject in checkValidType. If we say that the body kind
1312 should be '*' we risk getting TWO error messages, one saying that Eq
1313 [a] doens't have kind '*', and one saying that we need a Constraint to
1314 the left of the outer (=>).
1315
1316 How do we figure out the right body kind? Well, it's a bit of a
1317 kludge: I just look at the expected kind. If it's Constraint, we
1318 must be in this instance situation context. It's a kludge because it
1319 wouldn't work if any unification was involved to compute that result
1320 kind -- but it isn't. (The true way might be to use the 'mode'
1321 parameter, but that seemed like a sledgehammer to crack a nut.)
1322
1323 Note [Inferring tuple kinds]
1324 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1325 Give a tuple type (a,b,c), which the parser labels as HsBoxedOrConstraintTuple,
1326 we try to figure out whether it's a tuple of kind * or Constraint.
1327 Step 1: look at the expected kind
1328 Step 2: infer argument kinds
1329
1330 If after Step 2 it's not clear from the arguments that it's
1331 Constraint, then it must be *. Once having decided that we re-check
1332 the Check the arguments again to give good error messages
1333 in eg. `(Maybe, Maybe)`
1334
1335 Note that we will still fail to infer the correct kind in this case:
1336
1337 type T a = ((a,a), D a)
1338 type family D :: Constraint -> Constraint
1339
1340 While kind checking T, we do not yet know the kind of D, so we will default the
1341 kind of T to * -> *. It works if we annotate `a` with kind `Constraint`.
1342
1343 Note [Desugaring types]
1344 ~~~~~~~~~~~~~~~~~~~~~~~
1345 The type desugarer is phase 2 of dealing with HsTypes. Specifically:
1346
1347 * It transforms from HsType to Type
1348
1349 * It zonks any kinds. The returned type should have no mutable kind
1350 or type variables (hence returning Type not TcType):
1351 - any unconstrained kind variables are defaulted to (Any *) just
1352 as in TcHsSyn.
1353 - there are no mutable type variables because we are
1354 kind-checking a type
1355 Reason: the returned type may be put in a TyCon or DataCon where
1356 it will never subsequently be zonked.
1357
1358 You might worry about nested scopes:
1359 ..a:kappa in scope..
1360 let f :: forall b. T '[a,b] -> Int
1361 In this case, f's type could have a mutable kind variable kappa in it;
1362 and we might then default it to (Any *) when dealing with f's type
1363 signature. But we don't expect this to happen because we can't get a
1364 lexically scoped type variable with a mutable kind variable in it. A
1365 delicate point, this. If it becomes an issue we might need to
1366 distinguish top-level from nested uses.
1367
1368 Moreover
1369 * it cannot fail,
1370 * it does no unifications
1371 * it does no validity checking, except for structural matters, such as
1372 (a) spurious ! annotations.
1373 (b) a class used as a type
1374
1375 Note [Kind of a type splice]
1376 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1377 Consider these terms, each with TH type splice inside:
1378 [| e1 :: Maybe $(..blah..) |]
1379 [| e2 :: $(..blah..) |]
1380 When kind-checking the type signature, we'll kind-check the splice
1381 $(..blah..); we want to give it a kind that can fit in any context,
1382 as if $(..blah..) :: forall k. k.
1383
1384 In the e1 example, the context of the splice fixes kappa to *. But
1385 in the e2 example, we'll desugar the type, zonking the kind unification
1386 variables as we go. When we encounter the unconstrained kappa, we
1387 want to default it to '*', not to (Any *).
1388
1389 Note [Don't promote data constructors with non-equality contexts]
1390 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1391 With -XTypeInType, one can promote almost any data constructor. There is a
1392 notable exception to this rule, however: data constructors that contain
1393 non-equality constraints, such as:
1394
1395 data Foo a where
1396 MkFoo :: Show a => Foo a
1397
1398 MkFoo cannot be promoted since GHC cannot produce evidence for (Show a) at the
1399 kind level. Therefore, we check the context of each data constructor before
1400 promotion, and give a sensible error message if the context contains an illegal
1401 constraint.
1402
1403 Note that equality constraints (i.e, (~) and (~~)) /are/
1404 permitted inside data constructor contexts. All other constraints are
1405 off-limits, however (and likely will remain off-limits until dependent types
1406 become a reality in GHC).
1407
1408 Help functions for type applications
1409 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1410 -}
1411
1412 addTypeCtxt :: LHsType GhcRn -> TcM a -> TcM a
1413 -- Wrap a context around only if we want to show that contexts.
1414 -- Omit invisible ones and ones user's won't grok
1415 addTypeCtxt (L _ ty) thing
1416 = addErrCtxt doc thing
1417 where
1418 doc = text "In the type" <+> quotes (ppr ty)
1419
1420 {-
1421 ************************************************************************
1422 * *
1423 Type-variable binders
1424 %* *
1425 %************************************************************************
1426
1427 Note [Dependent LHsQTyVars]
1428 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1429 We track (in the renamer) which explicitly bound variables in a
1430 LHsQTyVars are manifestly dependent; only precisely these variables
1431 may be used within the LHsQTyVars. We must do this so that kcLHsQTyVars
1432 can produce the right TyConBinders, and tell Anon vs. Required.
1433
1434 Example data T k1 (a:k1) (b:k2) c
1435 = MkT (Proxy a) (Proxy b) (Proxy c)
1436
1437 Here
1438 (a:k1),(b:k2),(c:k3)
1439 are Anon (explicitly specified as a binder, not used
1440 in the kind of any other binder
1441 k1 is Required (explicitly specifed as a binder, but used
1442 in the kind of another binder i.e. dependently)
1443 k2 is Specified (not explicitly bound, but used in the kind
1444 of another binder)
1445 k3 in Inferred (not lexically in scope at all, but inferred
1446 by kind inference)
1447 and
1448 T :: forall {k3} k1. forall k3 -> k1 -> k2 -> k3 -> *
1449
1450 See Note [TyVarBndrs, TyVarBinders, TyConBinders, and visibility]
1451 in TyCoRep.
1452
1453 kcLHsQTyVars uses the hsq_dependent field to decide whether
1454 k1, a, b, c should be Required or Anon.
1455
1456 Earlier, thought it would work simply to do a free-variable check
1457 during kcLHsQTyVars, but this is bogus, because there may be
1458 unsolved equalities about. And we don't want to eagerly solve the
1459 equalities, because we may get further information after
1460 kcLHsQTyVars is called. (Recall that kcLHsQTyVars is called
1461 only from getInitialKind.)
1462 This is what implements the rule that all variables intended to be
1463 dependent must be manifestly so.
1464
1465 Sidenote: It's quite possible that later, we'll consider (t -> s)
1466 as a degenerate case of some (pi (x :: t) -> s) and then this will
1467 all get more permissive.
1468
1469 Note [Kind generalisation and SigTvs]
1470 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1471 Consider
1472 data T (a :: k1) x = MkT (S a ())
1473 data S (b :: k2) y = MkS (T b ())
1474
1475 While we are doing kind inference for the mutually-recursive S,T,
1476 we will end up unifying k1 and k2 together. So they can't be skolems.
1477 We therefore make them SigTvs, which can unify with type variables,
1478 but not with general types. All this is very similar at the level
1479 of terms: see Note [Quantified variables in partial type signatures]
1480 in TcBinds.
1481
1482 There are some wrinkles
1483
1484 * We always want to kind-generalise over SigTvs, and /not/ default
1485 them to Type. Another way to say this is: a SigTV should /never/
1486 stand for a type, even via defaulting. Hence the check in
1487 TcSimplify.defaultTyVarTcS, and TcMType.defaultTyVar. Here's
1488 another example (Trac #14555):
1489 data Exp :: [TYPE rep] -> TYPE rep -> Type where
1490 Lam :: Exp (a:xs) b -> Exp xs (a -> b)
1491 We want to kind-generalise over the 'rep' variable.
1492 Trac #14563 is another example.
1493
1494 * Consider Trac #11203
1495 data SameKind :: k -> k -> *
1496 data Q (a :: k1) (b :: k2) c = MkQ (SameKind a b)
1497 Here we will unify k1 with k2, but this time doing so is an error,
1498 because k1 and k2 are bound in the same delcaration.
1499
1500 We sort this out using findDupSigTvs, in TcTyClTyVars; very much
1501 as we do with partial type signatures in mk_psig_qtvs in
1502 TcBinds.chooseInferredQuantifiers
1503
1504 Note [Keeping scoped variables in order: Explicit]
1505 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1506 When the user writes `forall a b c. blah`, we bring a, b, and c into
1507 scope and then check blah. In the process of checking blah, we might
1508 learn the kinds of a, b, and c, and these kinds might indicate that
1509 b depends on c, and thus that we should reject the user-written type.
1510
1511 One approach to doing this would be to bring each of a, b, and c into
1512 scope, one at a time, creating an implication constraint and
1513 bumping the TcLevel for each one. This would work, because the kind
1514 of, say, b would be untouchable when c is in scope (and the constraint
1515 couldn't float out because c blocks it). However, it leads to terrible
1516 error messages, complaining about skolem escape. While it is indeed
1517 a problem of skolem escape, we can do better.
1518
1519 Instead, our approach is to bring the block of variables into scope
1520 all at once, creating one implication constraint for the lot. The
1521 user-written variables are skolems in the implication constraint. In
1522 TcSimplify.setImplicationStatus, we check to make sure that the ordering
1523 is correct, choosing ImplicationStatus IC_BadTelescope if they aren't.
1524 Then, in TcErrors, we report if there is a bad telescope. This way,
1525 we can report a suggested ordering to the user if there is a problem.
1526
1527 Note [Keeping scoped variables in order: Implicit]
1528 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1529 When the user implicitly quantifies over variables (say, in a type
1530 signature), we need to come up with some ordering on these variables.
1531 This is done by bumping the TcLevel, bringing the tyvars into scope,
1532 and then type-checking the thing_inside. The constraints are all
1533 wrapped in an implication, which is then solved. Finally, we can
1534 zonk all the binders and then order them with toposortTyVars.
1535
1536 It's critical to solve before zonking and ordering in order to uncover
1537 any unifications. You might worry that this eager solving could cause
1538 trouble elsewhere. I don't think it will. Because it will solve only
1539 in an increased TcLevel, it can't unify anything that was mentioned
1540 elsewhere. Additionally, we require that the order of implicitly
1541 quantified variables is manifest by the scope of these variables, so
1542 we're not going to learn more information later that will help order
1543 these variables.
1544
1545 Note [Recipe for checking a signature]
1546 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1547 Checking a user-written signature requires several steps:
1548
1549 1. Generate constraints.
1550 2. Solve constraints.
1551 3. Zonk and promote tyvars.
1552 4. (Optional) Kind-generalize.
1553 5. Check validity.
1554
1555 There may be some surprises in here:
1556
1557 Step 2 is necessary for two reasons: most signatures also bring
1558 implicitly quantified variables into scope, and solving is necessary
1559 to get these in the right order (see Note [Keeping scoped variables in
1560 order: Implicit]). Additionally, solving is necessary in order to
1561 kind-generalize correctly.
1562
1563 Step 3 requires *promoting* type variables. If there are any foralls
1564 in a type, the TcLevel will be bumped within the forall. This might
1565 lead to the generation of matavars with a high level. If we don't promote,
1566 we violate MetaTvInv of Note [TcLevel and untouchable type variables]
1567 in TcType.
1568
1569 -}
1570
1571 tcWildCardBinders :: SkolemInfo
1572 -> [Name]
1573 -> ([(Name, TcTyVar)] -> TcM a)
1574 -> TcM a
1575 tcWildCardBinders info = tcWildCardBindersX new_tv (Just info)
1576 where
1577 new_tv name = do { kind <- newMetaKindVar
1578 ; newSkolemTyVar name kind }
1579
1580 tcWildCardBindersX :: (Name -> TcM TcTyVar)
1581 -> Maybe SkolemInfo -- Just <=> we're bringing fresh vars
1582 -- into scope; use scopeTyVars
1583 -> [Name]
1584 -> ([(Name, TcTyVar)] -> TcM a)
1585 -> TcM a
1586 tcWildCardBindersX new_wc maybe_skol_info wc_names thing_inside
1587 = do { wcs <- mapM new_wc wc_names
1588 ; let wc_prs = wc_names `zip` wcs
1589 ; scope_tvs wc_prs $
1590 thing_inside wc_prs }
1591 where
1592 scope_tvs
1593 | Just info <- maybe_skol_info = scopeTyVars2 info
1594 | otherwise = tcExtendNameTyVarEnv
1595
1596 -- | Kind-check a 'LHsQTyVars'. If the decl under consideration has a complete,
1597 -- user-supplied kind signature (CUSK), generalise the result.
1598 -- Used in 'getInitialKind' (for tycon kinds and other kinds)
1599 -- and in kind-checking (but not for tycon kinds, which are checked with
1600 -- tcTyClDecls). See also Note [Complete user-supplied kind signatures] in
1601 -- HsDecls.
1602 --
1603 -- This function does not do telescope checking.
1604 kcLHsQTyVars :: Name -- ^ of the thing being checked
1605 -> TyConFlavour -- ^ What sort of 'TyCon' is being checked
1606 -> Bool -- ^ True <=> the decl being checked has a CUSK
1607 -> LHsQTyVars GhcRn
1608 -> TcM (Kind, r) -- ^ The result kind, possibly with other info
1609 -> TcM (TcTyCon, r) -- ^ A suitably-kinded TcTyCon
1610 kcLHsQTyVars name flav cusk
1611 user_tyvars@(HsQTvs { hsq_ext = HsQTvsRn { hsq_implicit = kv_ns
1612 , hsq_dependent = dep_names }
1613 , hsq_explicit = hs_tvs }) thing_inside
1614 | cusk
1615 = do { (scoped_kvs, (tc_tvs, (res_kind, stuff)))
1616 <- solveEqualities $
1617 tcImplicitTKBndrsX newSkolemTyVar skol_info kv_ns $
1618 kcLHsTyVarBndrs cusk open_fam skol_info hs_tvs thing_inside
1619
1620 -- Now, because we're in a CUSK, quantify over the mentioned
1621 -- kind vars, in dependency order.
1622 ; let tc_binders_unzonked = zipWith mk_tc_binder hs_tvs tc_tvs
1623 ; dvs <- zonkTcTypeAndSplitDepVars (mkSpecForAllTys scoped_kvs $
1624 mkTyConKind tc_binders_unzonked res_kind)
1625 ; qkvs <- quantifyTyVars emptyVarSet dvs
1626 -- don't call tcGetGlobalTyCoVars. For associated types, it gets the
1627 -- tyvars from the enclosing class -- but that's wrong. We *do* want
1628 -- to quantify over those tyvars.
1629
1630 ; scoped_kvs <- mapM zonkTcTyVarToTyVar scoped_kvs
1631 ; tc_tvs <- mapM zonkTcTyVarToTyVar tc_tvs
1632 ; res_kind <- zonkTcType res_kind
1633 ; let tc_binders = zipWith mk_tc_binder hs_tvs tc_tvs
1634
1635 -- If any of the scoped_kvs aren't actually mentioned in a binder's
1636 -- kind (or the return kind), then we're in the CUSK case from
1637 -- Note [Free-floating kind vars]
1638 ; let all_tc_tvs = scoped_kvs ++ tc_tvs
1639 all_mentioned_tvs = mapUnionVarSet (tyCoVarsOfType . tyVarKind)
1640 all_tc_tvs
1641 `unionVarSet` tyCoVarsOfType res_kind
1642 unmentioned_kvs = filterOut (`elemVarSet` all_mentioned_tvs)
1643 scoped_kvs
1644 ; reportFloatingKvs name flav all_tc_tvs unmentioned_kvs
1645
1646 ; let final_binders = map (mkNamedTyConBinder Inferred) qkvs
1647 ++ map (mkNamedTyConBinder Specified) scoped_kvs
1648 ++ tc_binders
1649 tycon = mkTcTyCon name (ppr user_tyvars) final_binders res_kind
1650 (mkTyVarNamePairs (scoped_kvs ++ tc_tvs))
1651 flav
1652 -- the tvs contain the binders already
1653 -- in scope from an enclosing class, but
1654 -- re-adding tvs to the env't doesn't cause
1655 -- harm
1656
1657 ; traceTc "kcLHsQTyVars: cusk" $
1658 vcat [ ppr name, ppr kv_ns, ppr hs_tvs, ppr dep_names
1659 , ppr tc_tvs, ppr (mkTyConKind final_binders res_kind)
1660 , ppr qkvs, ppr final_binders ]
1661
1662 ; return (tycon, stuff) }
1663
1664 | otherwise
1665 = do { (scoped_kvs, (tc_tvs, (res_kind, stuff)))
1666 -- Why kcImplicitTKBndrs which uses newSigTyVar?
1667 -- See Note [Kind generalisation and sigTvs]
1668 <- kcImplicitTKBndrs kv_ns $
1669 kcLHsTyVarBndrs cusk open_fam skol_info hs_tvs thing_inside
1670
1671 ; let -- NB: Don't add scoped_kvs to tyConTyVars, because they
1672 -- must remain lined up with the binders
1673 tc_binders = zipWith mk_tc_binder hs_tvs tc_tvs
1674 tycon = mkTcTyCon name (ppr user_tyvars) tc_binders res_kind
1675 (mkTyVarNamePairs (scoped_kvs ++ tc_tvs))
1676 flav
1677
1678 ; traceTc "kcLHsQTyVars: not-cusk" $
1679 vcat [ ppr name, ppr kv_ns, ppr hs_tvs, ppr dep_names
1680 , ppr tc_tvs, ppr (mkTyConKind tc_binders res_kind) ]
1681 ; return (tycon, stuff) }
1682 where
1683 open_fam = tcFlavourIsOpen flav
1684 skol_info = TyConSkol flav name
1685
1686 mk_tc_binder :: LHsTyVarBndr GhcRn -> TyVar -> TyConBinder
1687 -- See Note [Dependent LHsQTyVars]
1688 mk_tc_binder hs_tv tv
1689 | hsLTyVarName hs_tv `elemNameSet` dep_names
1690 = mkNamedTyConBinder Required tv
1691 | otherwise
1692 = mkAnonTyConBinder tv
1693
1694 kcLHsQTyVars _ _ _ (XLHsQTyVars _) _ = panic "kcLHsQTyVars"
1695
1696 kcLHsTyVarBndrs :: Bool -- True <=> bump the TcLevel when bringing vars into scope
1697 -> Bool -- True <=> Default un-annotated tyvar
1698 -- binders to kind *
1699 -> SkolemInfo
1700 -> [LHsTyVarBndr GhcRn]
1701 -> TcM r
1702 -> TcM ([TyVar], r)
1703 -- There may be dependency between the explicit "ty" vars.
1704 -- So, we have to handle them one at a time.
1705 kcLHsTyVarBndrs _ _ _ [] thing
1706 = do { stuff <- thing; return ([], stuff) }
1707
1708 kcLHsTyVarBndrs cusk open_fam skol_info (L _ hs_tv : hs_tvs) thing
1709 = do { tv_pair@(tv, _) <- kc_hs_tv hs_tv
1710 -- NB: Bring all tvs into scope, even non-dependent ones,
1711 -- as they're needed in type synonyms, data constructors, etc.
1712
1713 ; (tvs, stuff) <- bind_unless_scoped tv_pair $
1714 kcLHsTyVarBndrs cusk open_fam skol_info hs_tvs $
1715 thing
1716
1717 ; return ( tv : tvs, stuff ) }
1718 where
1719 -- | Bind the tyvar in the env't unless the bool is True
1720 bind_unless_scoped :: (TcTyVar, Bool) -> TcM a -> TcM a
1721 bind_unless_scoped (_, True) thing_inside = thing_inside
1722 bind_unless_scoped (tv, False) thing_inside
1723 | cusk = scopeTyVars skol_info [tv] thing_inside
1724 | otherwise = tcExtendTyVarEnv [tv] thing_inside
1725 -- These variables haven't settled down yet, so we don't want to bump
1726 -- the TcLevel. If we do, then we'll have metavars of too high a level
1727 -- floating about. Changing this causes many, many failures in the
1728 -- `dependent` testsuite directory.
1729
1730 kc_hs_tv :: HsTyVarBndr GhcRn -> TcM (TcTyVar, Bool)
1731 kc_hs_tv (UserTyVar _ lname@(L _ name))
1732 = do { tv_pair@(tv, in_scope) <- tcHsTyVarName newSkolemTyVar Nothing name
1733
1734 -- Open type/data families default their variables to kind *.
1735 -- But don't default in-scope class tyvars, of course
1736 ; when (open_fam && not in_scope) $
1737 discardResult $ unifyKind (Just (HsTyVar noExt NotPromoted lname))
1738 liftedTypeKind (tyVarKind tv)
1739
1740 ; return tv_pair }
1741
1742 kc_hs_tv (KindedTyVar _ (L _ name) lhs_kind)
1743 = do { kind <- tcLHsKindSig (TyVarBndrKindCtxt name) lhs_kind
1744 ; tcHsTyVarName newSkolemTyVar (Just kind) name }
1745
1746 kc_hs_tv (XTyVarBndr{}) = panic "kc_hs_tv"
1747
1748 tcImplicitTKBndrs :: SkolemInfo
1749 -> [Name]
1750 -> TcM a
1751 -> TcM ([TcTyVar], a)
1752 tcImplicitTKBndrs = tcImplicitTKBndrsX newSkolemTyVar
1753
1754 -- | Like 'tcImplicitTKBndrs', but uses 'newSigTyVar' to create tyvars
1755 tcImplicitTKBndrsSig :: SkolemInfo
1756 -> [Name]
1757 -> TcM a
1758 -> TcM ([TcTyVar], a)
1759 tcImplicitTKBndrsSig = tcImplicitTKBndrsX newSigTyVar
1760
1761 tcImplicitTKBndrsX :: (Name -> Kind -> TcM TcTyVar) -- new_tv function
1762 -> SkolemInfo
1763 -> [Name]
1764 -> TcM a
1765 -> TcM ([TcTyVar], a) -- these tyvars are dependency-ordered
1766 -- * Guarantees to call solveLocalEqualities to unify
1767 -- all constraints from thing_inside.
1768 --
1769 -- * Returned TcTyVars have the supplied HsTyVarBndrs,
1770 -- but may be in different order to the original [Name]
1771 -- (because of sorting to respect dependency)
1772 --
1773 -- * Returned TcTyVars have zonked kinds
1774 -- See Note [Keeping scoped variables in order: Implicit]
1775 tcImplicitTKBndrsX new_tv skol_info tv_names thing_inside
1776 | null tv_names -- Short cut for the common case where there
1777 -- are no implicit type variables to bind
1778 = do { result <- solveLocalEqualities thing_inside
1779 ; return ([], result) }
1780
1781 | otherwise
1782 = do { (skol_tvs, result)
1783 <- solveLocalEqualities $
1784 checkTvConstraints skol_info Nothing $
1785 do { tv_pairs <- mapM (tcHsTyVarName new_tv Nothing) tv_names
1786 ; let must_scope_tvs = [ tv | (tv, False) <- tv_pairs ]
1787 ; result <- tcExtendTyVarEnv must_scope_tvs $
1788 thing_inside
1789 ; return (map fst tv_pairs, result) }
1790
1791
1792 ; skol_tvs <- mapM zonkTcTyCoVarBndr skol_tvs
1793 -- use zonkTcTyCoVarBndr because a skol_tv might be a SigTv
1794
1795 ; let final_tvs = toposortTyVars skol_tvs
1796 ; traceTc "tcImplicitTKBndrs" (ppr tv_names $$ ppr final_tvs)
1797 ; return (final_tvs, result) }
1798
1799 -- | Bring implicitly quantified type/kind variables into scope during
1800 -- kind checking. Uses SigTvs, as per Note [Use SigTvs in kind-checking pass]
1801 -- in TcTyClsDecls.
1802 kcImplicitTKBndrs :: [Name] -- of the vars
1803 -> TcM a
1804 -> TcM ([TcTyVar], a) -- returns the tyvars created
1805 -- these are *not* dependency ordered
1806 kcImplicitTKBndrs var_ns thing_inside
1807 = do { tkvs_pairs <- mapM (tcHsTyVarName newSigTyVar Nothing) var_ns
1808 ; let must_scope_tkvs = [ tkv | (tkv, False) <- tkvs_pairs ]
1809 ; result <- tcExtendTyVarEnv must_scope_tkvs $
1810 thing_inside
1811 ; return (map fst tkvs_pairs, result) }
1812
1813 tcExplicitTKBndrs :: SkolemInfo
1814 -> [LHsTyVarBndr GhcRn]
1815 -> TcM a
1816 -> TcM ([TcTyVar], a)
1817 -- See also Note [Associated type tyvar names] in Class
1818 tcExplicitTKBndrs skol_info hs_tvs thing_inside
1819 -- This function brings into scope a telescope of binders as written by
1820 -- the user. At first blush, it would then seem that we should bring
1821 -- them into scope one at a time, bumping the TcLevel each time.
1822 -- (Recall that we bump the level to prevent skolem escape from happening.)
1823 -- However, this leads to terrible error messages, because we end up
1824 -- failing to unify with some `k0`. Better would be to allow type inference
1825 -- to work, potentially creating a skolem-escape problem, and then to
1826 -- notice that the telescope is out of order. That's what we do here,
1827 -- following the logic of tcImplicitTKBndrsX.
1828 -- See also Note [Keeping scoped variables in order: Explicit]
1829 --
1830 -- No cloning: returned TyVars have the same Name as the incoming LHsTyVarBndrs
1831 | null hs_tvs -- Short cut that avoids creating an implication
1832 -- constraint in the common case where none is needed
1833 = do { result <- thing_inside
1834 ; return ([], result) }
1835
1836 | otherwise
1837 = do { (skol_tvs, result) <- checkTvConstraints skol_info (Just doc) $
1838 bind_tvbs hs_tvs
1839
1840 ; traceTc "tcExplicitTKBndrs" $
1841 vcat [ text "Hs vars:" <+> ppr hs_tvs
1842 , text "tvs:" <+> pprTyVars skol_tvs ]
1843
1844 ; return (skol_tvs, result) }
1845
1846 where
1847 bind_tvbs [] = do { result <- thing_inside
1848 ; return ([], result) }
1849 bind_tvbs (L _ tvb : tvbs)
1850 = do { (tv, in_scope) <- tcHsTyVarBndr newSkolemTyVar tvb
1851 ; (if in_scope then id else tcExtendTyVarEnv [tv]) $
1852 do { (tvs, result) <- bind_tvbs tvbs
1853 ; return (tv : tvs, result) }}
1854
1855 doc = sep (map ppr hs_tvs)
1856
1857 -- | Used during the "kind-checking" pass in TcTyClsDecls only.
1858 -- See Note [Use SigTvs in kind-checking pass] in TcTyClsDecls
1859 kcExplicitTKBndrs :: [LHsTyVarBndr GhcRn]
1860 -> TcM a
1861 -> TcM a
1862 kcExplicitTKBndrs [] thing_inside = thing_inside
1863 kcExplicitTKBndrs (L _ hs_tv : hs_tvs) thing_inside
1864 = do { (tv, _) <- tcHsTyVarBndr newSigTyVar hs_tv
1865 ; tcExtendTyVarEnv [tv] $
1866 kcExplicitTKBndrs hs_tvs thing_inside }
1867
1868 tcHsTyVarBndr :: (Name -> Kind -> TcM TyVar)
1869 -> HsTyVarBndr GhcRn -> TcM (TcTyVar, Bool)
1870 -- Return a TcTyVar, built using the provided function
1871 -- Typically the Kind inside the HsTyVarBndr will be a tyvar
1872 -- with a mutable kind in it.
1873 --
1874 -- These variables might be in scope already (with associated types, for example).
1875 -- This function then checks that the kind annotation (if any) matches the
1876 -- kind of the in-scope type variable.
1877 --
1878 -- Returned TcTyVar has the same name; no cloning
1879 --
1880 -- See also Note [Associated type tyvar names] in Class
1881 --
1882 -- Returns True iff the tyvar was already in scope
1883 tcHsTyVarBndr new_tv (UserTyVar _ (L _ tv_nm))
1884 = tcHsTyVarName new_tv Nothing tv_nm
1885 tcHsTyVarBndr new_tv (KindedTyVar _ (L _ tv_nm) lhs_kind)
1886 = do { kind <- tcLHsKindSig (TyVarBndrKindCtxt tv_nm) lhs_kind
1887 ; tcHsTyVarName new_tv (Just kind) tv_nm }
1888 tcHsTyVarBndr _ (XTyVarBndr _) = panic "tcHsTyVarBndr"
1889
1890 newWildTyVar :: Name -> TcM TcTyVar
1891 -- ^ New unification variable for a wildcard
1892 newWildTyVar _name
1893 = do { kind <- newMetaKindVar
1894 ; uniq <- newUnique
1895 ; details <- newMetaDetails TauTv
1896 ; let name = mkSysTvName uniq (fsLit "w")
1897 tyvar = (mkTcTyVar name kind details)
1898 ; traceTc "newWildTyVar" (ppr tyvar)
1899 ; return tyvar }
1900
1901 -- | Produce a tyvar of the given name (with the kind provided, or
1902 -- otherwise a meta-var kind). If
1903 -- the name is already in scope, return the scoped variable, checking
1904 -- to make sure the known kind matches any kind provided. The
1905 -- second return value says whether the variable is in scope (True)
1906 -- or not (False). (Use this for associated types, for example.)
1907 tcHsTyVarName :: (Name -> Kind -> TcM TcTyVar) -- new_tv function
1908 -> Maybe Kind -- Just k <=> use k as the variable's kind
1909 -- Nothing <=> use a meta-tyvar
1910 -> Name -> TcM (TcTyVar, Bool)
1911 tcHsTyVarName new_tv m_kind name
1912 = do { mb_tv <- tcLookupLcl_maybe name
1913 ; case mb_tv of
1914 Just (ATyVar _ tv)
1915 -> do { whenIsJust m_kind $ \ kind ->
1916 discardResult $
1917 unifyKind (Just (HsTyVar noExt NotPromoted (noLoc name)))
1918 kind (tyVarKind tv)
1919 ; return (tv, True) }
1920 _ -> do { kind <- case m_kind of
1921 Just kind -> return kind
1922 Nothing -> newMetaKindVar
1923 ; tv <- new_tv name kind
1924 ; return (tv, False) }}
1925
1926 --------------------------
1927 -- Bringing tyvars into scope
1928 --------------------------
1929
1930 -- | Bring tyvars into scope, wrapping the thing_inside in an implication
1931 -- constraint. The implication constraint is necessary to provide SkolemInfo
1932 -- for the tyvars and to ensure that no unification variables made outside
1933 -- the scope of these tyvars (i.e. lower TcLevel) unify with the locally-scoped
1934 -- tyvars (i.e. higher TcLevel).
1935 --
1936 -- INVARIANT: The thing_inside must check only types, never terms.
1937 --
1938 -- Use this (not tcExtendTyVarEnv) wherever you expect a Λ or ∀ in Core.
1939 -- Use tcExtendTyVarEnv otherwise.
1940 scopeTyVars :: SkolemInfo -> [TcTyVar] -> TcM a -> TcM a
1941 scopeTyVars skol_info tvs = scopeTyVars2 skol_info [(tyVarName tv, tv) | tv <- tvs]
1942
1943 -- | Like 'scopeTyVars', but allows you to specify different scoped names
1944 -- than the Names stored within the tyvars.
1945 scopeTyVars2 :: SkolemInfo -> [(Name, TcTyVar)] -> TcM a -> TcM a
1946 scopeTyVars2 skol_info prs thing_inside
1947 = fmap snd $ -- discard the TcEvBinds, which will always be empty
1948 checkConstraints skol_info (map snd prs) [{- no EvVars -}] $
1949 tcExtendNameTyVarEnv prs $
1950 thing_inside
1951
1952 ------------------
1953 kindGeneralize :: TcType -> TcM [KindVar]
1954 -- Quantify the free kind variables of a kind or type
1955 -- In the latter case the type is closed, so it has no free
1956 -- type variables. So in both cases, all the free vars are kind vars
1957 -- Input must be zonked.
1958 -- NB: You must call solveEqualities or solveLocalEqualities before
1959 -- kind generalization
1960 kindGeneralize kind_or_type
1961 = do { let kvs = tyCoVarsOfTypeDSet kind_or_type
1962 dvs = DV { dv_kvs = kvs, dv_tvs = emptyDVarSet }
1963 ; gbl_tvs <- tcGetGlobalTyCoVars -- Already zonked
1964 ; quantifyTyVars gbl_tvs dvs }
1965
1966 {-
1967 Note [Kind generalisation]
1968 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1969 We do kind generalisation only at the outer level of a type signature.
1970 For example, consider
1971 T :: forall k. k -> *
1972 f :: (forall a. T a -> Int) -> Int
1973 When kind-checking f's type signature we generalise the kind at
1974 the outermost level, thus:
1975 f1 :: forall k. (forall (a:k). T k a -> Int) -> Int -- YES!
1976 and *not* at the inner forall:
1977 f2 :: (forall k. forall (a:k). T k a -> Int) -> Int -- NO!
1978 Reason: same as for HM inference on value level declarations,
1979 we want to infer the most general type. The f2 type signature
1980 would be *less applicable* than f1, because it requires a more
1981 polymorphic argument.
1982
1983 NB: There are no explicit kind variables written in f's signature.
1984 When there are, the renamer adds these kind variables to the list of
1985 variables bound by the forall, so you can indeed have a type that's
1986 higher-rank in its kind. But only by explicit request.
1987
1988 Note [Kinds of quantified type variables]
1989 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1990 tcTyVarBndrsGen quantifies over a specified list of type variables,
1991 *and* over the kind variables mentioned in the kinds of those tyvars.
1992
1993 Note that we must zonk those kinds (obviously) but less obviously, we
1994 must return type variables whose kinds are zonked too. Example
1995 (a :: k7) where k7 := k9 -> k9
1996 We must return
1997 [k9, a:k9->k9]
1998 and NOT
1999 [k9, a:k7]
2000 Reason: we're going to turn this into a for-all type,
2001 forall k9. forall (a:k7). blah
2002 which the type checker will then instantiate, and instantiate does not
2003 look through unification variables!
2004
2005 Hence using zonked_kinds when forming tvs'.
2006
2007 Note [Free-floating kind vars]
2008 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2009 Consider
2010
2011 data T = MkT (forall (a :: k). Proxy a)
2012 -- from test ghci/scripts/T7873
2013
2014 This is not an existential datatype, but a higher-rank one (the forall
2015 to the right of MkT). Also consider
2016
2017 data S a = MkS (Proxy (a :: k))
2018
2019 According to the rules around implicitly-bound kind variables, in both
2020 cases those k's scope over the whole declaration. The renamer grabs
2021 it and adds it to the hsq_implicits field of the HsQTyVars of the
2022 tycon. So it must be in scope during type-checking, but we want to
2023 reject T while accepting S.
2024
2025 Why reject T? Because the kind variable isn't fixed by anything. For
2026 a variable like k to be implicit, it needs to be mentioned in the kind
2027 of a tycon tyvar. But it isn't.
2028
2029 Why accept S? Because kind inference tells us that a has kind k, so it's
2030 all OK.
2031
2032 Our approach depends on whether or not the datatype has a CUSK.
2033
2034 Non-CUSK: In the first pass (kcTyClTyVars) we just bring
2035 k into scope. In the second pass (tcTyClTyVars),
2036 we check to make sure that k has been unified with some other variable
2037 (or generalized over, making k into a skolem). If it hasn't been, then
2038 it must be a free-floating kind var. Error.
2039
2040 CUSK: When we determine the tycon's final, never-to-be-changed kind
2041 in kcLHsQTyVars, we check to make sure all implicitly-bound kind
2042 vars are indeed mentioned in a kind somewhere. If not, error.
2043
2044 We also perform free-floating kind var analysis for type family instances
2045 (see #13985). Here is an interesting example:
2046
2047 type family T :: k
2048 type instance T = (Nothing :: Maybe a)
2049
2050 Upon a cursory glance, it may appear that the kind variable `a` is
2051 free-floating above, since there are no (visible) LHS patterns in `T`. However,
2052 there is an *invisible* pattern due to the return kind, so inside of GHC, the
2053 instance looks closer to this:
2054
2055 type family T @k :: k
2056 type instance T @(Maybe a) = (Nothing :: Maybe a)
2057
2058 Here, we can see that `a` really is bound by a LHS type pattern, so `a` is in
2059 fact not free-floating. Contrast that with this example:
2060
2061 type instance T = Proxy (Nothing :: Maybe a)
2062
2063 This would looks like this inside of GHC:
2064
2065 type instance T @(*) = Proxy (Nothing :: Maybe a)
2066
2067 So this time, `a` is neither bound by a visible nor invisible type pattern on
2068 the LHS, so it would be reported as free-floating.
2069
2070 Finally, here's one more brain-teaser (from #9574). In the example below:
2071
2072 class Funct f where
2073 type Codomain f :: *
2074 instance Funct ('KProxy :: KProxy o) where
2075 type Codomain 'KProxy = NatTr (Proxy :: o -> *)
2076
2077 As it turns out, `o` is not free-floating in this example. That is because `o`
2078 bound by the kind signature of the LHS type pattern 'KProxy. To make this more
2079 obvious, one can also write the instance like so:
2080
2081 instance Funct ('KProxy :: KProxy o) where
2082 type Codomain ('KProxy :: KProxy o) = NatTr (Proxy :: o -> *)
2083
2084 -}
2085
2086 --------------------
2087 -- getInitialKind has made a suitably-shaped kind for the type or class
2088 -- Look it up in the local environment. This is used only for tycons
2089 -- that we're currently type-checking, so we're sure to find a TcTyCon.
2090 kcLookupTcTyCon :: Name -> TcM TcTyCon
2091 kcLookupTcTyCon nm
2092 = do { tc_ty_thing <- tcLookup nm
2093 ; return $ case tc_ty_thing of
2094 ATcTyCon tc -> tc
2095 _ -> pprPanic "kcLookupTcTyCon" (ppr tc_ty_thing) }
2096
2097 -----------------------
2098 -- | Bring tycon tyvars into scope. This is used during the "kind-checking"
2099 -- pass in TcTyClsDecls. (Never in getInitialKind, never in the
2100 -- "type-checking"/desugaring pass.)
2101 -- Never emits constraints, though the thing_inside might.
2102 kcTyClTyVars :: Name -> TcM a -> TcM a
2103 kcTyClTyVars tycon_name thing_inside
2104 -- See Note [Use SigTvs in kind-checking pass] in TcTyClsDecls
2105 = do { tycon <- kcLookupTcTyCon tycon_name
2106 ; tcExtendNameTyVarEnv (tcTyConScopedTyVars tycon) $ thing_inside }
2107
2108 tcTyClTyVars :: Name
2109 -> ([TyConBinder] -> Kind -> TcM a) -> TcM a
2110 -- ^ Used for the type variables of a type or class decl
2111 -- on the second full pass (type-checking/desugaring) in TcTyClDecls.
2112 -- This is *not* used in the initial-kind run, nor in the "kind-checking" pass.
2113 -- Accordingly, everything passed to the continuation is fully zonked.
2114 --
2115 -- (tcTyClTyVars T [a,b] thing_inside)
2116 -- where T : forall k1 k2 (a:k1 -> *) (b:k1). k2 -> *
2117 -- calls thing_inside with arguments
2118 -- [k1,k2,a,b] [k1:*, k2:*, Anon (k1 -> *), Anon k1] (k2 -> *)
2119 -- having also extended the type environment with bindings
2120 -- for k1,k2,a,b
2121 --
2122 -- Never emits constraints.
2123 --
2124 -- The LHsTyVarBndrs is always user-written, and the full, generalised
2125 -- kind of the tycon is available in the local env.
2126 tcTyClTyVars tycon_name thing_inside
2127 = do { tycon <- kcLookupTcTyCon tycon_name
2128
2129 -- Do checks on scoped tyvars
2130 -- See Note [Free-floating kind vars]
2131 ; let flav = tyConFlavour tycon
2132 scoped_prs = tcTyConScopedTyVars tycon
2133 scoped_tvs = map snd scoped_prs
2134 still_sig_tvs = filter isSigTyVar scoped_tvs
2135
2136 ; mapM_ report_sig_tv_err (findDupSigTvs scoped_prs)
2137
2138 ; checkNoErrs $ reportFloatingKvs tycon_name flav
2139 scoped_tvs still_sig_tvs
2140
2141 ; let res_kind = tyConResKind tycon
2142 binders = correct_binders (tyConBinders tycon) res_kind
2143 ; traceTc "tcTyClTyVars" (ppr tycon_name <+> ppr binders)
2144 ; scopeTyVars2 (TyConSkol flav tycon_name) scoped_prs $
2145 thing_inside binders res_kind }
2146 where
2147 report_sig_tv_err (n1, n2)
2148 = setSrcSpan (getSrcSpan n2) $
2149 addErrTc (text "Couldn't match" <+> quotes (ppr n1)
2150 <+> text "with" <+> quotes (ppr n2))
2151
2152 -- Given some TyConBinders and a TyCon's result kind, make sure that the
2153 -- correct any wrong Named/Anon choices. For example, consider
2154 -- type Syn k = forall (a :: k). Proxy a
2155 -- At first, it looks like k should be named -- after all, it appears on the RHS.
2156 -- However, the correct kind for Syn is (* -> *).
2157 -- (Why? Because k is the kind of a type, so k's kind is *. And the RHS also has
2158 -- kind *.) See also #13963.
2159 correct_binders :: [TyConBinder] -> Kind -> [TyConBinder]
2160 correct_binders binders kind
2161 = binders'
2162 where
2163 (_, binders') = mapAccumR go (tyCoVarsOfType kind) binders
2164
2165 go :: TyCoVarSet -> TyConBinder -> (TyCoVarSet, TyConBinder)
2166 go fvs binder
2167 | isNamedTyConBinder binder
2168 , not (tv `elemVarSet` fvs)
2169 = (new_fvs, mkAnonTyConBinder tv)
2170
2171 | not (isNamedTyConBinder binder)
2172 , tv `elemVarSet` fvs
2173 = (new_fvs, mkNamedTyConBinder Required tv)
2174 -- always Required, because it was anonymous (i.e. visible) previously
2175
2176 | otherwise
2177 = (new_fvs, binder)
2178
2179 where
2180 tv = binderVar binder
2181 new_fvs = fvs `delVarSet` tv `unionVarSet` tyCoVarsOfType (tyVarKind tv)
2182
2183 -----------------------------------
2184 tcDataKindSig :: [TyConBinder]
2185 -> Kind
2186 -> TcM ([TyConBinder], Kind)
2187 -- GADT decls can have a (perhaps partial) kind signature
2188 -- e.g. data T a :: * -> * -> * where ...
2189 -- This function makes up suitable (kinded) TyConBinders for the
2190 -- argument kinds. E.g. in this case it might return
2191 -- ([b::*, c::*], *)
2192 -- Never emits constraints.
2193 -- It's a little trickier than you might think: see
2194 -- Note [TyConBinders for the result kind signature of a data type]
2195 tcDataKindSig tc_bndrs kind
2196 = do { loc <- getSrcSpanM
2197 ; uniqs <- newUniqueSupply
2198 ; rdr_env <- getLocalRdrEnv
2199 ; let new_occs = [ occ
2200 | str <- allNameStrings
2201 , let occ = mkOccName tvName str
2202 , isNothing (lookupLocalRdrOcc rdr_env occ)
2203 -- Note [Avoid name clashes for associated data types]
2204 , not (occ `elem` lhs_occs) ]
2205 new_uniqs = uniqsFromSupply uniqs
2206 subst = mkEmptyTCvSubst (mkInScopeSet (mkVarSet lhs_tvs))
2207 ; return (go loc new_occs new_uniqs subst [] kind) }
2208 where
2209 lhs_tvs = map binderVar tc_bndrs
2210 lhs_occs = map getOccName lhs_tvs
2211
2212 go loc occs uniqs subst acc kind
2213 = case splitPiTy_maybe kind of
2214 Nothing -> (reverse acc, substTy subst kind)
2215
2216 Just (Anon arg, kind')
2217 -> go loc occs' uniqs' subst' (tcb : acc) kind'
2218 where
2219 arg' = substTy subst arg
2220 tv = mkTyVar (mkInternalName uniq occ loc) arg'
2221 subst' = extendTCvInScope subst tv
2222 tcb = TvBndr tv AnonTCB
2223 (uniq:uniqs') = uniqs
2224 (occ:occs') = occs
2225
2226 Just (Named (TvBndr tv vis), kind')
2227 -> go loc occs uniqs subst' (tcb : acc) kind'
2228 where
2229 (subst', tv') = substTyVarBndr subst tv
2230 tcb = TvBndr tv' (NamedTCB vis)
2231
2232 badKindSig :: Bool -> Kind -> SDoc
2233 badKindSig check_for_type kind
2234 = hang (sep [ text "Kind signature on data type declaration has non-*"
2235 , (if check_for_type then empty else text "and non-variable") <+>
2236 text "return kind" ])
2237 2 (ppr kind)
2238
2239 {- Note [TyConBinders for the result kind signature of a data type]
2240 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2241 Given
2242 data T (a::*) :: * -> forall k. k -> *
2243 we want to generate the extra TyConBinders for T, so we finally get
2244 (a::*) (b::*) (k::*) (c::k)
2245 The function tcDataKindSig generates these extra TyConBinders from
2246 the result kind signature.
2247
2248 We need to take care to give the TyConBinders
2249 (a) OccNames that are fresh (because the TyConBinders of a TyCon
2250 must have distinct OccNames
2251
2252 (b) Uniques that are fresh (obviously)
2253
2254 For (a) we need to avoid clashes with the tyvars declared by
2255 the user before the "::"; in the above example that is 'a'.
2256 And also see Note [Avoid name clashes for associated data types].
2257
2258 For (b) suppose we have
2259 data T :: forall k. k -> forall k. k -> *
2260 where the two k's are identical even up to their uniques. Surprisingly,
2261 this can happen: see Trac #14515.
2262
2263 It's reasonably easy to solve all this; just run down the list with a
2264 substitution; hence the recursive 'go' function. But it has to be
2265 done.
2266
2267 Note [Avoid name clashes for associated data types]
2268 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2269 Consider class C a b where
2270 data D b :: * -> *
2271 When typechecking the decl for D, we'll invent an extra type variable
2272 for D, to fill out its kind. Ideally we don't want this type variable
2273 to be 'a', because when pretty printing we'll get
2274 class C a b where
2275 data D b a0
2276 (NB: the tidying happens in the conversion to IfaceSyn, which happens
2277 as part of pretty-printing a TyThing.)
2278
2279 That's why we look in the LocalRdrEnv to see what's in scope. This is
2280 important only to get nice-looking output when doing ":info C" in GHCi.
2281 It isn't essential for correctness.
2282
2283
2284 ************************************************************************
2285 * *
2286 Partial signatures
2287 * *
2288 ************************************************************************
2289
2290 -}
2291
2292 tcHsPartialSigType
2293 :: UserTypeCtxt
2294 -> LHsSigWcType GhcRn -- The type signature
2295 -> TcM ( [(Name, TcTyVar)] -- Wildcards
2296 , Maybe TcType -- Extra-constraints wildcard
2297 , [Name] -- Original tyvar names, in correspondence with ...
2298 , [TcTyVar] -- ... Implicitly and explicitly bound type variables
2299 , TcThetaType -- Theta part
2300 , TcType ) -- Tau part
2301 -- See Note [Recipe for checking a signature]
2302 tcHsPartialSigType ctxt sig_ty
2303 | HsWC { hswc_ext = sig_wcs, hswc_body = ib_ty } <- sig_ty
2304 , HsIB { hsib_ext = HsIBRn { hsib_vars = implicit_hs_tvs }
2305 , hsib_body = hs_ty } <- ib_ty
2306 , (explicit_hs_tvs, L _ hs_ctxt, hs_tau) <- splitLHsSigmaTy hs_ty
2307 = addSigCtxt ctxt hs_ty $
2308 do { (implicit_tvs, (explicit_tvs, (wcs, wcx, theta, tau)))
2309 <- tcWildCardBindersX newWildTyVar Nothing sig_wcs $ \ wcs ->
2310 tcImplicitTKBndrsSig skol_info implicit_hs_tvs $
2311 tcExplicitTKBndrs skol_info explicit_hs_tvs $
2312 do { -- Instantiate the type-class context; but if there
2313 -- is an extra-constraints wildcard, just discard it here
2314 (theta, wcx) <- tcPartialContext hs_ctxt
2315
2316 ; tau <- tcHsOpenType hs_tau
2317
2318 ; return (wcs, wcx, theta, tau) }
2319
2320 -- We must return these separately, because all the zonking below
2321 -- might change the name of a SigTv. This, in turn, causes trouble
2322 -- in partial type signatures that bind scoped type variables, as
2323 -- we bring the wrong name into scope in the function body.
2324 -- Test case: partial-sigs/should_compile/LocalDefinitionBug
2325 ; let tv_names = map tyVarName (implicit_tvs ++ explicit_tvs)
2326
2327 -- Spit out the wildcards (including the extra-constraints one)
2328 -- as "hole" constraints, so that they'll be reported if necessary
2329 -- See Note [Extra-constraint holes in partial type signatures]
2330 ; emitWildCardHoleConstraints wcs
2331
2332 -- The SigTvs created above will sometimes have too high a TcLevel
2333 -- (note that they are generated *after* bumping the level in
2334 -- the tc{Im,Ex}plicitTKBndrsSig functions. Bumping the level
2335 -- is still important here, because the kinds of these variables
2336 -- do indeed need to have the higher level, so they can unify
2337 -- with other local type variables. But, now that we've type-checked
2338 -- everything (and solved equalities in the tcImplicit call)
2339 -- we need to promote the SigTvs so we don't violate the TcLevel
2340 -- invariant
2341 ; all_tvs <- mapM zonkPromoteTyCoVarBndr (implicit_tvs ++ explicit_tvs)
2342 -- zonkPromoteTyCoVarBndr deals well with SigTvs
2343
2344 ; theta <- mapM zonkPromoteType theta
2345 ; tau <- zonkPromoteType tau
2346
2347 ; checkValidType ctxt (mkSpecForAllTys all_tvs $ mkPhiTy theta tau)
2348
2349 ; traceTc "tcHsPartialSigType" (ppr all_tvs)
2350 ; return (wcs, wcx, tv_names, all_tvs, theta, tau) }
2351 where
2352 skol_info = SigTypeSkol ctxt
2353 tcHsPartialSigType _ (HsWC _ (XHsImplicitBndrs _)) = panic "tcHsPartialSigType"
2354 tcHsPartialSigType _ (XHsWildCardBndrs _) = panic "tcHsPartialSigType"
2355
2356 tcPartialContext :: HsContext GhcRn -> TcM (TcThetaType, Maybe TcType)
2357 tcPartialContext hs_theta
2358 | Just (hs_theta1, hs_ctxt_last) <- snocView hs_theta
2359 , L _ (HsWildCardTy wc) <- ignoreParens hs_ctxt_last
2360 = do { wc_tv_ty <- tcWildCardOcc wc constraintKind
2361 ; theta <- mapM tcLHsPredType hs_theta1
2362 ; return (theta, Just wc_tv_ty) }
2363 | otherwise
2364 = do { theta <- mapM tcLHsPredType hs_theta
2365 ; return (theta, Nothing) }
2366
2367 {- Note [Extra-constraint holes in partial type signatures]
2368 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2369 Consider
2370 f :: (_) => a -> a
2371 f x = ...
2372
2373 * The renamer makes a wildcard name for the "_", and puts it in
2374 the hswc_wcs field.
2375
2376 * Then, in tcHsPartialSigType, we make a new hole TcTyVar, in
2377 tcWildCardBindersX.
2378
2379 * TcBinds.chooseInferredQuantifiers fills in that hole TcTyVar
2380 with the inferred constraints, e.g. (Eq a, Show a)
2381
2382 * TcErrors.mkHoleError finally reports the error.
2383
2384 An annoying difficulty happens if there are more than 62 inferred
2385 constraints. Then we need to fill in the TcTyVar with (say) a 70-tuple.
2386 Where do we find the TyCon? For good reasons we only have constraint
2387 tuples up to 62 (see Note [How tuples work] in TysWiredIn). So how
2388 can we make a 70-tuple? This was the root cause of Trac #14217.
2389
2390 It's incredibly tiresome, because we only need this type to fill
2391 in the hole, to communicate to the error reporting machinery. Nothing
2392 more. So I use a HACK:
2393
2394 * I make an /ordinary/ tuple of the constraints, in
2395 TcBinds.chooseInferredQuantifiers. This is ill-kinded because
2396 ordinary tuples can't contain constraints, but it works fine. And for
2397 ordinary tuples we don't have the same limit as for constraint
2398 tuples (which need selectors and an assocated class).
2399
2400 * Because it is ill-kinded, it trips an assert in writeMetaTyVar,
2401 so now I disable the assertion if we are writing a type of
2402 kind Constraint. (That seldom/never normally happens so we aren't
2403 losing much.)
2404
2405 Result works fine, but it may eventually bite us.
2406
2407
2408 ************************************************************************
2409 * *
2410 Pattern signatures (i.e signatures that occur in patterns)
2411 * *
2412 ********************************************************************* -}
2413
2414 tcHsPatSigType :: UserTypeCtxt
2415 -> LHsSigWcType GhcRn -- The type signature
2416 -> TcM ( [(Name, TcTyVar)] -- Wildcards
2417 , [(Name, TcTyVar)] -- The new bit of type environment, binding
2418 -- the scoped type variables
2419 , TcType) -- The type
2420 -- Used for type-checking type signatures in
2421 -- (a) patterns e.g f (x::Int) = e
2422 -- (b) RULE forall bndrs e.g. forall (x::Int). f x = x
2423 --
2424 -- This may emit constraints
2425 -- See Note [Recipe for checking a signature]
2426 tcHsPatSigType ctxt sig_ty
2427 | HsWC { hswc_ext = sig_wcs, hswc_body = ib_ty } <- sig_ty
2428 , HsIB { hsib_ext = HsIBRn { hsib_vars = sig_vars}
2429 , hsib_body = hs_ty } <- ib_ty
2430 = addSigCtxt ctxt hs_ty $
2431 do { sig_tkvs <- mapM new_implicit_tv sig_vars
2432 ; (wcs, sig_ty)
2433 <- tcWildCardBindersX newWildTyVar Nothing sig_wcs $ \ wcs ->
2434 tcExtendTyVarEnv sig_tkvs $
2435 do { sig_ty <- tcHsOpenType hs_ty
2436 ; return (wcs, sig_ty) }
2437
2438 ; emitWildCardHoleConstraints wcs
2439
2440 -- sig_ty might have tyvars that are at a higher TcLevel (if hs_ty
2441 -- contains a forall). Promote these.
2442 ; sig_ty <- zonkPromoteType sig_ty
2443 ; checkValidType ctxt sig_ty
2444
2445 ; tv_pairs <- mapM mk_tv_pair sig_tkvs
2446
2447 ; traceTc "tcHsPatSigType" (ppr sig_vars)
2448 ; return (wcs, tv_pairs, sig_ty) }
2449 where
2450 new_implicit_tv name = do { kind <- newMetaKindVar
2451 ; new_tv name kind }
2452
2453 new_tv = case ctxt of
2454 RuleSigCtxt {} -> newSkolemTyVar
2455 _ -> newSigTyVar
2456 -- See Note [Pattern signature binders]
2457 -- See Note [Unifying SigTvs]
2458
2459 mk_tv_pair tv = do { tv' <- zonkTcTyVarToTyVar tv
2460 ; return (tyVarName tv, tv') }
2461 -- The Name is one of sig_vars, the lexically scoped name
2462 -- But if it's a SigTyVar, it might have been unified
2463 -- with an existing in-scope skolem, so we must zonk
2464 -- here. See Note [Pattern signature binders]
2465 tcHsPatSigType _ (HsWC _ (XHsImplicitBndrs _)) = panic "tcHsPatSigType"
2466 tcHsPatSigType _ (XHsWildCardBndrs _) = panic "tcHsPatSigType"
2467
2468 tcPatSig :: Bool -- True <=> pattern binding
2469 -> LHsSigWcType GhcRn
2470 -> ExpSigmaType
2471 -> TcM (TcType, -- The type to use for "inside" the signature
2472 [(Name,TcTyVar)], -- The new bit of type environment, binding
2473 -- the scoped type variables
2474 [(Name,TcTyVar)], -- The wildcards
2475 HsWrapper) -- Coercion due to unification with actual ty
2476 -- Of shape: res_ty ~ sig_ty
2477 tcPatSig in_pat_bind sig res_ty
2478 = do { (sig_wcs, sig_tvs, sig_ty) <- tcHsPatSigType PatSigCtxt sig
2479 -- sig_tvs are the type variables free in 'sig',
2480 -- and not already in scope. These are the ones
2481 -- that should be brought into scope
2482
2483 ; if null sig_tvs then do {
2484 -- Just do the subsumption check and return
2485 wrap <- addErrCtxtM (mk_msg sig_ty) $
2486 tcSubTypeET PatSigOrigin PatSigCtxt res_ty sig_ty
2487 ; return (sig_ty, [], sig_wcs, wrap)
2488 } else do
2489 -- Type signature binds at least one scoped type variable
2490
2491 -- A pattern binding cannot bind scoped type variables
2492 -- It is more convenient to make the test here
2493 -- than in the renamer
2494 { when in_pat_bind (addErr (patBindSigErr sig_tvs))
2495
2496 -- Check that all newly-in-scope tyvars are in fact
2497 -- constrained by the pattern. This catches tiresome
2498 -- cases like
2499 -- type T a = Int
2500 -- f :: Int -> Int
2501 -- f (x :: T a) = ...
2502 -- Here 'a' doesn't get a binding. Sigh
2503 ; let bad_tvs = [ tv | (_,tv) <- sig_tvs
2504 , not (tv `elemVarSet` exactTyCoVarsOfType sig_ty) ]
2505 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
2506
2507 -- Now do a subsumption check of the pattern signature against res_ty
2508 ; wrap <- addErrCtxtM (mk_msg sig_ty) $
2509 tcSubTypeET PatSigOrigin PatSigCtxt res_ty sig_ty
2510
2511 -- Phew!
2512 ; return (sig_ty, sig_tvs, sig_wcs, wrap)
2513 } }
2514 where
2515 mk_msg sig_ty tidy_env
2516 = do { (tidy_env, sig_ty) <- zonkTidyTcType tidy_env sig_ty
2517 ; res_ty <- readExpType res_ty -- should be filled in by now
2518 ; (tidy_env, res_ty) <- zonkTidyTcType tidy_env res_ty
2519 ; let msg = vcat [ hang (text "When checking that the pattern signature:")
2520 4 (ppr sig_ty)
2521 , nest 2 (hang (text "fits the type of its context:")
2522 2 (ppr res_ty)) ]
2523 ; return (tidy_env, msg) }
2524
2525 patBindSigErr :: [(Name,TcTyVar)] -> SDoc
2526 patBindSigErr sig_tvs
2527 = hang (text "You cannot bind scoped type variable" <> plural sig_tvs
2528 <+> pprQuotedList (map fst sig_tvs))
2529 2 (text "in a pattern binding signature")
2530
2531 {- Note [Pattern signature binders]
2532 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2533 Consider
2534 data T = forall a. T a (a->Int)
2535 f (T x (f :: b->Int)) = blah
2536
2537 Here
2538 * The pattern (T p1 p2) creates a *skolem* type variable 'a_sk',
2539 It must be a skolem so that that it retains its identity, and
2540 TcErrors.getSkolemInfo can thereby find the binding site for the skolem.
2541
2542 * The type signature pattern (f :: b->Int) makes a fresh meta-tyvar b_sig
2543 (a SigTv), and binds "b" :-> b_sig in the envt
2544
2545 * Then unification makes b_sig := a_sk
2546 That's why we must make b_sig a MetaTv (albeit a SigTv),
2547 not a SkolemTv, so that it can unify to a_sk.
2548
2549 * Finally, in 'blah' we must have the envt "b" :-> a_sk. The pair
2550 ("b" :-> a_sk) is returned by tcHsPatSigType, constructed by
2551 mk_tv_pair in that function.
2552
2553 Another example (Trac #13881):
2554 fl :: forall (l :: [a]). Sing l -> Sing l
2555 fl (SNil :: Sing (l :: [y])) = SNil
2556 When we reach the pattern signature, 'l' is in scope from the
2557 outer 'forall':
2558 "a" :-> a_sk :: *
2559 "l" :-> l_sk :: [a_sk]
2560 We make up a fresh meta-SigTv, y_sig, for 'y', and kind-check
2561 the pattern signature
2562 Sing (l :: [y])
2563 That unifies y_sig := a_sk. We return from tcHsPatSigType with
2564 the pair ("y" :-> a_sk).
2565
2566 For RULE binders, though, things are a bit different (yuk).
2567 RULE "foo" forall (x::a) (y::[a]). f x y = ...
2568 Here this really is the binding site of the type variable so we'd like
2569 to use a skolem, so that we get a complaint if we unify two of them
2570 together.
2571
2572 Note [Unifying SigTvs]
2573 ~~~~~~~~~~~~~~~~~~~~~~
2574 ALAS we have no decent way of avoiding two SigTvs getting unified.
2575 Consider
2576 f (x::(a,b)) (y::c)) = [fst x, y]
2577 Here we'd really like to complain that 'a' and 'c' are unified. But
2578 for the reasons above we can't make a,b,c into skolems, so they
2579 are just SigTvs that can unify. And indeed, this would be ok,
2580 f x (y::c) = case x of
2581 (x1 :: a1, True) -> [x,y]
2582 (x1 :: a2, False) -> [x,y,y]
2583 Here the type of x's first component is called 'a1' in one branch and
2584 'a2' in the other. We could try insisting on the same OccName, but
2585 they definitely won't have the sane lexical Name.
2586
2587 I think we could solve this by recording in a SigTv a list of all the
2588 in-scope variables that it should not unify with, but it's fiddly.
2589
2590
2591 ************************************************************************
2592 * *
2593 Checking kinds
2594 * *
2595 ************************************************************************
2596
2597 -}
2598
2599 unifyKinds :: [LHsType GhcRn] -> [(TcType, TcKind)] -> TcM ([TcType], TcKind)
2600 unifyKinds rn_tys act_kinds
2601 = do { kind <- newMetaKindVar
2602 ; let check rn_ty (ty, act_kind) = checkExpectedKind (unLoc rn_ty) ty act_kind kind
2603 ; tys' <- zipWithM check rn_tys act_kinds
2604 ; return (tys', kind) }
2605
2606 {-
2607 ************************************************************************
2608 * *
2609 Promotion
2610 * *
2611 ************************************************************************
2612 -}
2613
2614 -- | Whenever a type is about to be added to the environment, it's necessary
2615 -- to make sure that any free meta-tyvars in the type are promoted to the
2616 -- current TcLevel. (They might be at a higher level due to the level-bumping
2617 -- in tcExplicitTKBndrs, for example.) This function both zonks *and*
2618 -- promotes.
2619 zonkPromoteType :: TcType -> TcM TcType
2620 zonkPromoteType = mapType zonkPromoteMapper ()
2621
2622 -- cf. TcMType.zonkTcTypeMapper
2623 zonkPromoteMapper :: TyCoMapper () TcM
2624 zonkPromoteMapper = TyCoMapper { tcm_smart = True
2625 , tcm_tyvar = const zonkPromoteTcTyVar
2626 , tcm_covar = const covar
2627 , tcm_hole = const hole
2628 , tcm_tybinder = const tybinder }
2629 where
2630 covar cv
2631 = mkCoVarCo <$> zonkPromoteTyCoVarKind cv
2632
2633 hole :: CoercionHole -> TcM Coercion
2634 hole h
2635 = do { contents <- unpackCoercionHole_maybe h
2636 ; case contents of
2637 Just co -> do { co <- zonkPromoteCoercion co
2638 ; checkCoercionHole cv co }
2639 Nothing -> do { cv' <- zonkPromoteTyCoVarKind cv
2640 ; return $ mkHoleCo (setCoHoleCoVar h cv') } }
2641 where
2642 cv = coHoleCoVar h
2643
2644 tybinder :: TyVar -> ArgFlag -> TcM ((), TyVar)
2645 tybinder tv _flag = ((), ) <$> zonkPromoteTyCoVarKind tv
2646
2647 zonkPromoteTcTyVar :: TyCoVar -> TcM TcType
2648 zonkPromoteTcTyVar tv
2649 | isMetaTyVar tv
2650 = do { let ref = metaTyVarRef tv
2651 ; contents <- readTcRef ref
2652 ; case contents of
2653 Flexi -> do { promoted <- promoteTyVar tv
2654 ; if promoted
2655 then zonkPromoteTcTyVar tv -- read it again
2656 else mkTyVarTy <$> zonkPromoteTyCoVarKind tv }
2657 Indirect ty -> zonkPromoteType ty }
2658
2659 | isTcTyVar tv && isSkolemTyVar tv -- NB: isSkolemTyVar says "True" to pure TyVars
2660 = do { tc_lvl <- getTcLevel
2661 ; mkTyVarTy <$> zonkPromoteTyCoVarKind (promoteSkolem tc_lvl tv) }
2662
2663 | otherwise
2664 = mkTyVarTy <$> zonkPromoteTyCoVarKind tv
2665
2666 zonkPromoteTyCoVarKind :: TyCoVar -> TcM TyCoVar
2667 zonkPromoteTyCoVarKind = updateTyVarKindM zonkPromoteType
2668
2669 zonkPromoteTyCoVarBndr :: TyCoVar -> TcM TyCoVar
2670 zonkPromoteTyCoVarBndr tv
2671 | isSigTyVar tv
2672 = tcGetTyVar "zonkPromoteTyCoVarBndr SigTv" <$> zonkPromoteTcTyVar tv
2673
2674 | isTcTyVar tv && isSkolemTyVar tv
2675 = do { tc_lvl <- getTcLevel
2676 ; zonkPromoteTyCoVarKind (promoteSkolem tc_lvl tv) }
2677
2678 | otherwise
2679 = zonkPromoteTyCoVarKind tv
2680
2681 zonkPromoteCoercion :: Coercion -> TcM Coercion
2682 zonkPromoteCoercion = mapCoercion zonkPromoteMapper ()
2683
2684 zonkPromoteTypeInKnot :: TcType -> TcM TcType
2685 zonkPromoteTypeInKnot = mapType (zonkPromoteMapper { tcm_smart = False }) ()
2686 -- NB: Just changing smart to False will still use the smart zonker (not suitable
2687 -- for in-the-knot) for kinds. But that's OK, because kinds aren't knot-tied.
2688
2689 {-
2690 ************************************************************************
2691 * *
2692 Sort checking kinds
2693 * *
2694 ************************************************************************
2695
2696 tcLHsKindSig converts a user-written kind to an internal, sort-checked kind.
2697 It does sort checking and desugaring at the same time, in one single pass.
2698 -}
2699
2700 tcLHsKindSig :: UserTypeCtxt -> LHsKind GhcRn -> TcM Kind
2701 tcLHsKindSig ctxt hs_kind
2702 -- See Note [Recipe for checking a signature] in TcHsType
2703 = do { kind <- solveLocalEqualities $
2704 tc_lhs_kind kindLevelMode hs_kind
2705 ; kind <- zonkPromoteType kind
2706 -- This zonk is very important in the case of higher rank kinds
2707 -- E.g. Trac #13879 f :: forall (p :: forall z (y::z). <blah>).
2708 -- <more blah>
2709 -- When instantiating p's kind at occurrences of p in <more blah>
2710 -- it's crucial that the kind we instantiate is fully zonked,
2711 -- else we may fail to substitute properly
2712
2713 ; checkValidType ctxt kind
2714 ; return kind }
2715
2716 tc_lhs_kind :: TcTyMode -> LHsKind GhcRn -> TcM Kind
2717 tc_lhs_kind mode k
2718 = addErrCtxt (text "In the kind" <+> quotes (ppr k)) $
2719 tc_lhs_type (kindLevel mode) k liftedTypeKind
2720
2721 promotionErr :: Name -> PromotionErr -> TcM a
2722 promotionErr name err
2723 = failWithTc (hang (pprPECategory err <+> quotes (ppr name) <+> text "cannot be used here")
2724 2 (parens reason))
2725 where
2726 reason = case err of
2727 ConstrainedDataConPE pred
2728 -> text "it has an unpromotable context"
2729 <+> quotes (ppr pred)
2730 FamDataConPE -> text "it comes from a data family instance"
2731 NoDataKindsTC -> text "perhaps you intended to use DataKinds"
2732 NoDataKindsDC -> text "perhaps you intended to use DataKinds"
2733 PatSynPE -> text "pattern synonyms cannot be promoted"
2734 PatSynExPE -> sep [ text "the existential variables of a pattern synonym"
2735 , text "signature do not scope over the pattern" ]
2736 _ -> text "it is defined and used in the same recursive group"
2737
2738 {-
2739 ************************************************************************
2740 * *
2741 Scoped type variables
2742 * *
2743 ************************************************************************
2744 -}
2745
2746 badPatSigTvs :: TcType -> [TyVar] -> SDoc
2747 badPatSigTvs sig_ty bad_tvs
2748 = vcat [ fsep [text "The type variable" <> plural bad_tvs,
2749 quotes (pprWithCommas ppr bad_tvs),
2750 text "should be bound by the pattern signature" <+> quotes (ppr sig_ty),
2751 text "but are actually discarded by a type synonym" ]
2752 , text "To fix this, expand the type synonym"
2753 , text "[Note: I hope to lift this restriction in due course]" ]
2754
2755 {-
2756 ************************************************************************
2757 * *
2758 Error messages and such
2759 * *
2760 ************************************************************************
2761 -}
2762
2763 -- | Make an appropriate message for an error in a function argument.
2764 -- Used for both expressions and types.
2765 funAppCtxt :: (Outputable fun, Outputable arg) => fun -> arg -> Int -> SDoc
2766 funAppCtxt fun arg arg_no
2767 = hang (hsep [ text "In the", speakNth arg_no, ptext (sLit "argument of"),
2768 quotes (ppr fun) <> text ", namely"])
2769 2 (quotes (ppr arg))
2770
2771 -- See Note [Free-floating kind vars]
2772 reportFloatingKvs :: Name -- of the tycon
2773 -> TyConFlavour -- What sort of TyCon it is
2774 -> [TcTyVar] -- all tyvars, not necessarily zonked
2775 -> [TcTyVar] -- floating tyvars
2776 -> TcM ()
2777 reportFloatingKvs tycon_name flav all_tvs bad_tvs
2778 = unless (null bad_tvs) $ -- don't bother zonking if there's no error
2779 do { all_tvs <- mapM zonkTcTyVarToTyVar all_tvs
2780 ; bad_tvs <- mapM zonkTcTyVarToTyVar bad_tvs
2781 ; let (tidy_env, tidy_all_tvs) = tidyOpenTyCoVars emptyTidyEnv all_tvs
2782 tidy_bad_tvs = map (tidyTyVarOcc tidy_env) bad_tvs
2783 ; mapM_ (report tidy_all_tvs) tidy_bad_tvs }
2784 where
2785 report tidy_all_tvs tidy_bad_tv
2786 = addErr $
2787 vcat [ text "Kind variable" <+> quotes (ppr tidy_bad_tv) <+>
2788 text "is implicitly bound in" <+> ppr flav
2789 , quotes (ppr tycon_name) <> comma <+>
2790 text "but does not appear as the kind of any"
2791 , text "of its type variables. Perhaps you meant"
2792 , text "to bind it explicitly somewhere?"
2793 , ppWhen (not (null tidy_all_tvs)) $
2794 hang (text "Type variables with inferred kinds:")
2795 2 (ppr_tv_bndrs tidy_all_tvs) ]
2796
2797 ppr_tv_bndrs tvs = sep (map pp_tv tvs)
2798 pp_tv tv = parens (ppr tv <+> dcolon <+> ppr (tyVarKind tv))