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* Add a warning for GADT match + NoMonoLocalBinds (#20485)Krzysztof Gogolewski2021-11-234-0/+41
| | | | | | | | | Previously, it was an error to pattern match on a GADT without GADTs or TypeFamilies. This is now allowed. Instead, we check the flag MonoLocalBinds; if it is not enabled, we issue a warning, controlled by -Wgadt-mono-local-binds. Also fixes #20485: pattern synonyms are now checked too.
* Desugarer: Bring existentials in scope when substituting into record GADTsRyan Scott2021-08-252-0/+20
| | | | | | | | | | This fixes an outright bug in which the desugarer did not bring the existentially quantified type variables of a record GADT into `in_subst`'s in-scope set, leading to #20278. It also addresses a minor inefficiency in which `out_subst` was made into a substitution when a simpler `TvSubstEnv` would suffice. Fixes #20278.
* Driver Rework PatchMatthew Pickering2021-06-032-5/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | This patch comprises of four different but closely related ideas. The net result is fixing a large number of open issues with the driver whilst making it simpler to understand. 1. Use the hash of the source file to determine whether the source file has changed or not. This makes the recompilation checking more robust to modern build systems which are liable to copy files around changing their modification times. 2. Remove the concept of a "stable module", a stable module was one where the object file was older than the source file, and all transitive dependencies were also stable. Now we don't rely on the modification time of the source file, the notion of stability is moot. 3. Fix TH/plugin recompilation after the removal of stable modules. The TH recompilation check used to rely on stable modules. Now there is a uniform and simple way, we directly track the linkables which were loaded into the interpreter whilst compiling a module. This is an over-approximation but more robust wrt package dependencies changing. 4. Fix recompilation checking for dynamic object files. Now we actually check if the dynamic object file exists when compiling with -dynamic-too Fixes #19774 #19771 #19758 #17434 #11556 #9121 #8211 #16495 #7277 #16093
* GHC Exactprint main commitAlan Zimmerman2021-03-203-4/+4
| | | | | | | | Metric Increase: T10370 parsing001 Updates haddock submodule
* Use GHC2021 as default languageJoachim Breitner2021-03-109-4/+9
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* Unify result type earlier to improve error messagesSimon Peyton Jones2021-03-012-13/+10
| | | | | | | | | | | | | | | | | | | | | | Ticket #19364 helpfully points out that we do not currently take advantage of pushing the result type of an application into the arguments. This makes error messages notably less good. The fix is rather easy: move the result-type unification step earlier. It's even a bit more efficient; in the the checking case we now do one less zonk. See Note [Unify with expected type before typechecking arguments] in GHC.Tc.Gen.App This change generally improves error messages, but it made one worse: typecheck/should_fail/T16204c. That led me to the realisation that a good error can be replaced by a less-good one, which provoked me to change GHC.Tc.Solver.Interact.inertsCanDischarge. It's explained in the new Note [Combining equalities] One other refactoring: I discovered that KindEqOrigin didn't need a Maybe in its type -- a nice simplification.
* Fix typosBrian Wignall2021-02-061-1/+1
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* Arrows: correctly query arrow methods (#17423)Sylvain Henry2020-12-112-38/+0
| | | | | | | | | | | | | | | | | | | | | | | | | Consider the following code: proc (C x y) -> ... Before this patch, the evidence binding for the Arrow dictionary was attached to the C pattern: proc (C x y) { $dArrow = ... } -> ... But then when we desugar this, we use arrow operations ("arr", ">>>"...) specialised for this arrow: let arr_xy = arr $dArrow -- <-- Not in scope! ... in arr_xy (\(C x y) { $dArrow = ... } -> ...) This patch allows arrow operations to be type-checked before the proc itself, avoiding this issue. Fix #17423
* Fix kind inference for data types. Again.Simon Peyton Jones2020-12-082-0/+17
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch fixes several aspects of kind inference for data type declarations, especially data /instance/ declarations Specifically 1. In kcConDecls/kcConDecl make it clear that the tc_res_kind argument is only used in the H98 case; and in that case there is no result kind signature; and hence no need for the disgusting splitPiTys in kcConDecls (now thankfully gone). The GADT case is a bit different to before, and much nicer. This is what fixes #18891. See Note [kcConDecls: kind-checking data type decls] 2. Do not look at the constructor decls of a data/newtype instance in tcDataFamInstanceHeader. See GHC.Tc.TyCl.Instance Note [Kind inference for data family instances]. This was a new realisation that arose when doing (1) This causes a few knock-on effects in the tests suite, because we require more information than before in the instance /header/. New user-manual material about this in "Kind inference in data type declarations" and "Kind inference for data/newtype instance declarations". 3. Minor improvement in kcTyClDecl, combining GADT and H98 cases 4. Fix #14111 and #8707 by allowing the header of a data instance to affect kind inferece for the the data constructor signatures; as described at length in Note [GADT return types] in GHC.Tc.TyCl This led to a modest refactoring of the arguments (and argument order) of tcConDecl/tcConDecls. 5. Fix #19000 by inverting the sense of the test in new_locs in GHC.Tc.Solver.Canonical.canDecomposableTyConAppOK.
* Remove flattening variablesRichard Eisenberg2020-12-013-7/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch redesigns the flattener to simplify type family applications directly instead of using flattening meta-variables and skolems. The key new innovation is the CanEqLHS type and the new CEqCan constraint (Ct). A CanEqLHS is either a type variable or exactly-saturated type family application; either can now be rewritten using a CEqCan constraint in the inert set. Because the flattener no longer reduces all type family applications to variables, there was some performance degradation if a lengthy type family application is now flattened over and over (not making progress). To compensate, this patch contains some extra optimizations in the flattener, leading to a number of performance improvements. Close #18875. Close #18910. There are many extra parts of the compiler that had to be affected in writing this patch: * The family-application cache (formerly the flat-cache) sometimes stores coercions built from Given inerts. When these inerts get kicked out, we must kick out from the cache as well. (This was, I believe, true previously, but somehow never caused trouble.) Kicking out from the cache requires adding a filterTM function to TrieMap. * This patch obviates the need to distinguish "blocking" coercion holes from non-blocking ones (which, previously, arose from CFunEqCans). There is thus some simplification around coercion holes. * Extra commentary throughout parts of the code I read through, to preserve the knowledge I gained while working. * A change in the pure unifier around unifying skolems with other types. Unifying a skolem now leads to SurelyApart, not MaybeApart, as documented in Note [Binding when looking up instances] in GHC.Core.InstEnv. * Some more use of MCoercion where appropriate. * Previously, class-instance lookup automatically noticed that e.g. C Int was a "unifier" to a target [W] C (F Bool), because the F Bool was flattened to a variable. Now, a little more care must be taken around checking for unifying instances. * Previously, tcSplitTyConApp_maybe would split (Eq a => a). This is silly, because (=>) is not a tycon in Haskell. Fixed now, but there are some knock-on changes in e.g. TrieMap code and in the canonicaliser. * New function anyFreeVarsOf{Type,Co} to check whether a free variable satisfies a certain predicate. * Type synonyms now remember whether or not they are "forgetful"; a forgetful synonym drops at least one argument. This is useful when flattening; see flattenView. * The pattern-match completeness checker invokes the solver. This invocation might need to look through newtypes when checking representational equality. Thus, the desugarer needs to keep track of the in-scope variables to know what newtype constructors are in scope. I bet this bug was around before but never noticed. * Extra-constraints wildcards are no longer simplified before printing. See Note [Do not simplify ConstraintHoles] in GHC.Tc.Solver. * Whether or not there are Given equalities has become slightly subtler. See the new HasGivenEqs datatype. * Note [Type variable cycles in Givens] in GHC.Tc.Solver.Canonical explains a significant new wrinkle in the new approach. * See Note [What might match later?] in GHC.Tc.Solver.Interact, which explains the fix to #18910. * The inert_count field of InertCans wasn't actually used, so I removed it. Though I (Richard) did the implementation, Simon PJ was very involved in design and review. This updates the Haddock submodule to avoid #18932 by adding a type signature. ------------------------- Metric Decrease: T12227 T5030 T9872a T9872b T9872c Metric Increase: T9872d -------------------------
* Add -Wnoncanonical-{monad,monoid}-instances to standardWarningsFumiaki Kinoshita2020-10-142-12/+9
| | | | | | | | | ------------------------- Metric Decrease: T12425 Metric Increase: T17516 -------------------------
* Improve kind generalisation, error messagesSimon Peyton Jones2020-09-244-23/+20
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch does two things: * It refactors GHC.Tc.Errors a bit. In debugging Quick Look I was forced to look in detail at error messages, and ended up doing a bit of refactoring, esp in mkTyVarEqErr'. It's still quite a mess, but a bit better, I think. * It makes a significant improvement to the kind checking of type and class declarations. Specifically, we now ensure that if kind checking fails with an unsolved constraint, all the skolems are in scope. That wasn't the case before, which led to some obscure error messages; and occasional failures with "no skolem info" (eg #16245). Both of these, and the main Quick Look patch itself, affect a /lot/ of error messages, as you can see from the number of files changed. I've checked them all; I think they are as good or better than before. Smaller things * I documented the various instances of VarBndr better. See Note [The VarBndr tyep and its uses] in GHC.Types.Var * Renamed GHC.Tc.Solver.simpl_top to simplifyTopWanteds * A bit of refactoring in bindExplicitTKTele, to avoid the footwork with Either. Simpler now. * Move promoteTyVar from GHC.Tc.Solver to GHC.Tc.Utils.TcMType Fixes #16245 (comment 211369), memorialised as typecheck/polykinds/T16245a Also fixes the three bugs in #18640
* Make GADT constructors adhere to the forall-or-nothing rule properlyRyan Scott2020-06-097-39/+62
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Issue #18191 revealed that the types of GADT constructors don't quite adhere to the `forall`-or-nothing rule. This patch serves to clean up this sad state of affairs somewhat. The main change is not in the code itself, but in the documentation, as this patch introduces two sections to the GHC User's Guide: * A "Formal syntax for GADTs" section that presents a BNF-style grammar for what is and isn't allowed in GADT constructor types. This mostly exists to codify GHC's existing behavior, but it also imposes a new restriction that addresses #18191: the outermost `forall` and/or context in a GADT constructor is not allowed to be surrounded by parentheses. Doing so would make these `forall`s/contexts nested, and GADTs do not support nested `forall`s/contexts at present. * A "`forall`-or-nothing rule" section that describes exactly what the `forall`-or-nothing rule is all about. Surprisingly, there was no mention of this anywhere in the User's Guide up until now! To adhere the new specification in the "Formal syntax for GADTs" section of the User's Guide, the following code changes were made: * A new function, `GHC.Hs.Type.splitLHsGADTPrefixTy`, was introduced. This is very much like `splitLHsSigmaTy`, except that it avoids splitting apart any parentheses, which can be syntactically significant for GADT types. See `Note [No nested foralls or contexts in GADT constructors]` in `GHC.Hs.Type`. * `ConDeclGADTPrefixPs`, an extension constructor for `XConDecl`, was introduced so that `GHC.Parser.PostProcess.mkGadtDecl` can return it when given a prefix GADT constructor. Unlike `ConDeclGADT`, `ConDeclGADTPrefixPs` does not split the GADT type into its argument and result types, as this cannot be done until after the type is renamed (see `Note [GADT abstract syntax]` in `GHC.Hs.Decls` for why this is the case). * `GHC.Renamer.Module.rnConDecl` now has an additional case for `ConDeclGADTPrefixPs` that (1) splits apart the full `LHsType` into its `forall`s, context, argument types, and result type, and (2) checks for nested `forall`s/contexts. Step (2) used to be performed the typechecker (in `GHC.Tc.TyCl.badDataConTyCon`) rather than the renamer, but now the relevant code from the typechecker can simply be deleted. One nice side effect of this change is that we are able to give a more accurate error message for GADT constructors that use visible dependent quantification (e.g., `MkFoo :: forall a -> a -> Foo a`), which improves the stderr in the `T16326_Fail6` test case. Fixes #18191. Bumps the Haddock submodule.
* Simple subsumptionwip/T17775Simon Peyton Jones2020-06-055-13/+22
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch simplifies GHC to use simple subsumption. Ticket #17775 Implements GHC proposal #287 https://github.com/ghc-proposals/ghc-proposals/blob/master/ proposals/0287-simplify-subsumption.rst All the motivation is described there; I will not repeat it here. The implementation payload: * tcSubType and friends become noticably simpler, because it no longer uses eta-expansion when checking subsumption. * No deeplyInstantiate or deeplySkolemise That in turn means that some tests fail, by design; they can all be fixed by eta expansion. There is a list of such changes below. Implementing the patch led me into a variety of sticky corners, so the patch includes several othe changes, some quite significant: * I made String wired-in, so that "foo" :: String rather than "foo" :: [Char] This improves error messages, and fixes #15679 * The pattern match checker relies on knowing about in-scope equality constraints, andd adds them to the desugarer's environment using addTyCsDs. But the co_fn in a FunBind was missed, and for some reason simple-subsumption ends up with dictionaries there. So I added a call to addTyCsDs. This is really part of #18049. * I moved the ic_telescope field out of Implication and into ForAllSkol instead. This is a nice win; just expresses the code much better. * There was a bug in GHC.Tc.TyCl.Instance.tcDataFamInstHeader. We called checkDataKindSig inside tc_kind_sig, /before/ solveEqualities and zonking. Obviously wrong, easily fixed. * solveLocalEqualitiesX: there was a whole mess in here, around failing fast enough. I discovered a bad latent bug where we could successfully kind-check a type signature, and use it, but have unsolved constraints that could fill in coercion holes in that signature -- aargh. It's all explained in Note [Failure in local type signatures] in GHC.Tc.Solver. Much better now. * I fixed a serious bug in anonymous type holes. IN f :: Int -> (forall a. a -> _) -> Int that "_" should be a unification variable at the /outer/ level; it cannot be instantiated to 'a'. This was plain wrong. New fields mode_lvl and mode_holes in TcTyMode, and auxiliary data type GHC.Tc.Gen.HsType.HoleMode. This fixes #16292, but makes no progress towards the more ambitious #16082 * I got sucked into an enormous refactoring of the reporting of equality errors in GHC.Tc.Errors, especially in mkEqErr1 mkTyVarEqErr misMatchMsg misMatchMsgOrCND In particular, the very tricky mkExpectedActualMsg function is gone. It took me a full day. But the result is far easier to understand. (Still not easy!) This led to various minor improvements in error output, and an enormous number of test-case error wibbles. One particular point: for occurs-check errors I now just say Can't match 'a' against '[a]' rather than using the intimidating language of "occurs check". * Pretty-printing AbsBinds Tests review * Eta expansions T11305: one eta expansion T12082: one eta expansion (undefined) T13585a: one eta expansion T3102: one eta expansion T3692: two eta expansions (tricky) T2239: two eta expansions T16473: one eta determ004: two eta expansions (undefined) annfail06: two eta (undefined) T17923: four eta expansions (a strange program indeed!) tcrun035: one eta expansion * Ambiguity check at higher rank. Now that we have simple subsumption, a type like f :: (forall a. Eq a => Int) -> Int is no longer ambiguous, because we could write g :: (forall a. Eq a => Int) -> Int g = f and it'd typecheck just fine. But f's type is a bit suspicious, and we might want to consider making the ambiguity check do a check on each sub-term. Meanwhile, these tests are accepted, whereas they were previously rejected as ambiguous: T7220a T15438 T10503 T9222 * Some more interesting error message wibbles T13381: Fine: one error (Int ~ Exp Int) rather than two (Int ~ Exp Int, Exp Int ~ Int) T9834: Small change in error (improvement) T10619: Improved T2414: Small change, due to order of unification, fine T2534: A very simple case in which a change of unification order means we get tow unsolved constraints instead of one tc211: bizarre impredicative tests; just accept this for now Updates Cabal and haddock submodules. Metric Increase: T12150 T12234 T5837 haddock.base Metric Decrease: haddock.compiler haddock.Cabal haddock.base Merge note: This appears to break the `UnliftedNewtypesDifficultUnification` test. It has been marked as broken in the interest of merging. (cherry picked from commit 66b7b195cb3dce93ed5078b80bf568efae904cc5)
* Do eager instantation in termsSimon Peyton Jones2020-04-221-3/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch implements eager instantiation, a small but critical change to the type inference engine, #17173. The main change is this: When inferring types, always return an instantiated type (for now, deeply instantiated; in future shallowly instantiated) There is more discussion in https://www.tweag.io/posts/2020-04-02-lazy-eager-instantiation.html There is quite a bit of refactoring in this patch: * The ir_inst field of GHC.Tc.Utils.TcType.InferResultk has entirely gone. So tcInferInst and tcInferNoInst have collapsed into tcInfer. * Type inference of applications, via tcInferApp and tcInferAppHead, are substantially refactored, preparing the way for Quick Look impredicativity. * New pure function GHC.Tc.Gen.Expr.collectHsArgs and applyHsArgs are beatifully dual. We can see the zipper! * GHC.Tc.Gen.Expr.tcArgs is now much nicer; no longer needs to return a wrapper * In HsExpr, HsTypeApp now contains the the actual type argument, and is used in desugaring, rather than putting it in a mysterious wrapper. * I struggled a bit with good error reporting in Unify.matchActualFunTysPart. It's a little bit simpler than before, but still not great. Some smaller things * Rename tcPolyExpr --> tcCheckExpr tcMonoExpr --> tcLExpr * tcPatSig moves from GHC.Tc.Gen.HsType to GHC.Tc.Gen.Pat Metric Decrease: T9961 Reduction of 1.6% in comiler allocation on T9961, I think.
* Modules: type-checker (#13009)Sylvain Henry2020-04-071-1/+1
| | | | Update Haddock submodule
* Module hierarchy: Iface (cf #13009)Sylvain Henry2020-01-061-2/+2
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* Fix typos, via a Levenshtein-style correctorBrian Wignall2020-01-041-1/+1
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* Remove prefix arrow support for GADTs (#17211)Krzysztof Gogolewski2019-11-252-7/+0
| | | | | | | This reverts the change in #9096. The specialcasing done for prefix (->) is brittle and does not support VTA, type families, type synonyms etc.
* testsuite: Add test for #17423Ben Gamari2019-11-012-0/+38
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* Report better suggestion for GADT data constructorSimon Peyton Jones2019-03-154-4/+17
| | | | This addresses issue #16427. An easy fix.
* Update Trac ticket URLs to point to GitLabRyan Scott2019-03-1514-14/+14
| | | | | This moves all URL references to Trac tickets to their corresponding GitLab counterparts.
* testsuite: Use makefile_testBen Gamari2019-01-301-3/+3
| | | | | This eliminates most uses of run_command in the testsuite in favor of the more structured makefile_test.
* Revert "Batch merge"Ben Gamari2019-01-301-3/+3
| | | | This reverts commit 76c8fd674435a652c75a96c85abbf26f1f221876.
* Batch mergeBen Gamari2019-01-301-3/+3
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* Enable -Wcompat=error in the testsuiteVladislav Zavialov2018-10-1510-16/+34
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Enabling -Werror=compat in the testsuite allows us to easily see the impact that a new warning has on code. It also means that in the period between adding the warning and making the actual breaking change, all new test cases that are being added to the testsuite will be forwards-compatible. This is good because it will make the actual breaking change contain less irrelevant testsuite updates. Things that -Wcompat warns about are things that are going to break in the future, so we can be proactive and keep our testsuite forwards-compatible. This patch consists of two main changes: * Add `TEST_HC_OPTS += -Werror=compat` to the testsuite configuration. * Fix all broken test cases. Test Plan: Validate Reviewers: hvr, goldfire, bgamari, simonpj, RyanGlScott Reviewed By: goldfire, RyanGlScott Subscribers: rwbarton, carter GHC Trac Issues: #15278 Differential Revision: https://phabricator.haskell.org/D5200
* Better error reporting for inaccessible codeSimon Peyton Jones2018-08-243-0/+24
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch fixes Trac #15558. There turned out to be two distinct problems * In TcExpr.tc_poly_expr_nc we had tc_poly_expr_nc (L loc expr) res_ty = do { traceTc "tcPolyExprNC" (ppr res_ty) ; (wrap, expr') <- tcSkolemiseET GenSigCtxt res_ty $ \ res_ty -> setSrcSpan loc $ -- NB: setSrcSpan *after* skolemising, -- so we get better skolem locations tcExpr expr res_ty Putting the setSrcSpan inside the tcSkolemise means that the location on the Implication constraint is the /call/ to the function rather than the /argument/ to the call, and that is really quite wrong. I don't know what Richard's comment NB means -- I moved the setSrcSpan outside, and the "binding site" info in error messages actually improved. The reason I found this is that it affects the span reported for Trac #15558. * In TcErrors.mkGivenErrorReporter we carefully munge the location for an insoluble Given constraint (Note [Inaccessible code]). But the 'implic' passed in wasn't necesarily the immediately- enclosing implication -- but for location-munging purposes it jolly well should be. Solution: use the innermost implication. This actually simplifies the code -- no need to pass an implication in to mkGivenErrorReporter.
* Embrace -XTypeInType, add -XStarIsTypeVladislav Zavialov2018-06-144-8/+12
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Summary: Implement the "Embrace Type :: Type" GHC proposal, .../ghc-proposals/blob/master/proposals/0020-no-type-in-type.rst GHC 8.0 included a major change to GHC's type system: the Type :: Type axiom. Though casual users were protected from this by hiding its features behind the -XTypeInType extension, all programs written in GHC 8+ have the axiom behind the scenes. In order to preserve backward compatibility, various legacy features were left unchanged. For example, with -XDataKinds but not -XTypeInType, GADTs could not be used in types. Now these restrictions are lifted and -XTypeInType becomes a redundant flag that will be eventually deprecated. * Incorporate the features currently in -XTypeInType into the -XPolyKinds and -XDataKinds extensions. * Introduce a new extension -XStarIsType to control how to parse * in code and whether to print it in error messages. Test Plan: Validate Reviewers: goldfire, hvr, bgamari, alanz, simonpj Reviewed By: goldfire, simonpj Subscribers: rwbarton, thomie, mpickering, carter GHC Trac Issues: #15195 Differential Revision: https://phabricator.haskell.org/D4748
* Turn "inaccessible code" error into a warningTobias Dammers2018-06-025-27/+23
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | With GADTs, it is possible to write programs such that the type constraints make some code branches inaccessible. Take, for example, the following program :: {-# LANGUAGE GADTs #-} data Foo a where Foo1 :: Foo Char Foo2 :: Foo Int data TyEquality a b where Refl :: TyEquality a a checkTEQ :: Foo t -> Foo u -> Maybe (TyEquality t u) checkTEQ x y = error "unimportant" step2 :: Bool step2 = case checkTEQ Foo1 Foo2 of Just Refl -> True -- Inaccessible code Nothing -> False Clearly, the `Just Refl` case cannot ever be reached, because the `Foo1` and `Foo2` constructors say `t ~ Char` and `u ~ Int`, while the `Refl` constructor essentially mandates `t ~ u`, and thus `Char ~ Int`. Previously, GHC would reject such programs entirely; however, in practice this is too harsh. Accepting such code does little harm, since attempting to use the "impossible" code will still produce errors down the chain, while rejecting it means we cannot legally write or generate such code at all. Hence, we turn the error into a warning, and provide `-Winaccessible-code` to control GHC's behavior upon encountering this situation. Test Plan: ./validate Reviewers: bgamari Reviewed By: bgamari Subscribers: rwbarton, thomie, carter GHC Trac Issues: #11066 Differential Revision: https://phabricator.haskell.org/D4744
* Improved Valid Hole FitsMatthías Páll Gissurarson2018-05-301-4/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | I've changed the name from `Valid substitutions` to `Valid hole fits`, since "substitution" already has a well defined meaning within the theory. As part of this change, the flags and output is reanamed, with substitution turning into hole-fit in most cases. "hole fit" was already used internally in the code, it's clear and shouldn't cause any confusion. In this update, I've also reworked how we manage side-effects in the hole we are considering. This allows us to consider local bindings such as where clauses and arguments to functions, suggesting e.g. `a` for `head (x:xs) where head :: [a] -> a`. It also allows us to find suggestions such as `maximum` for holes of type `Ord a => a -> [a]`, and `max` when looking for a match for the hole in `g = foldl1 _`, where `g :: Ord a => [a] -> a`. We also show much improved output for refinement hole fits, and fixes #14990. We now show the correct type of the function, but we also now show what the arguments to the function should be e.g. `foldl1 (_ :: Integer -> Integer -> Integer)` when looking for `[Integer] -> Integer`. I've moved the bulk of the code from `TcErrors.hs` to a new file, `TcHoleErrors.hs`, since it was getting too big to not live on it's own. This addresses the considerations raised in #14969, and takes proper care to set the `tcLevel` of the variables to the right level before passing it to the simplifier. We now also zonk the suggestions properly, which improves the output of the refinement hole fits considerably. This also filters out suggestions from the `GHC.Err` module, since even though `error` and `undefined` are indeed valid hole fits, they are "trivial", and almost never useful to the user. We now find the hole fits using the proper manner, namely by solving nested implications. This entails that the givens are passed along using the implications the hole was nested in, which in turn should mean that there will be fewer weird bugs in the typed holes. I've also added a new sorting method (as suggested by SPJ) and sort by the size of the types needed to turn the hole fits into the type of the hole. This gives a reasonable approximation to relevance, and is much faster than the subsumption check. I've also added a flag to toggle whether to use this new sorting algorithm (as is done by default) or the subsumption algorithm. This fixes #14969 I've also added documentation for these new flags and update the documentation according to the new output. Reviewers: bgamari, goldfire Reviewed By: bgamari Subscribers: simonpj, rwbarton, thomie, carter GHC Trac Issues: #14969, #14990, #10946 Differential Revision: https://phabricator.haskell.org/D4444
* Orient TyVar/TyVar equalities with deepest on the leftSimon Peyton Jones2018-05-182-0/+21
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Trac #15009 showed that, for Given TyVar/TyVar equalities, we really want to orient them with the deepest-bound skolem on the left. As it happens, we also want to do the same for Wanteds, but for a different reason (more likely to be touchable). Either way, deepest wins: see TcUnify Note [Deeper level on the left]. This observation led me to some significant changes: * A SkolemTv already had a TcLevel, but the level wasn't really being used. Now it is! * I updated added invariant (SkolInf) to TcType Note [TcLevel and untouchable type variables], documenting that the level number of all the ic_skols should be the same as the ic_tclvl of the implication * FlatSkolTvs and FlatMetaTvs previously had a dummy level-number of zero, which messed the scheme up. Now they get a level number the same way as all other TcTyVars, instead of being a special case. * To make sure that FlatSkolTvs and FlatMetaTvs are untouchable (which was previously done via their magic zero level) isTouchableMetaTyVar just tests for those two cases. * TcUnify.swapOverTyVars is the crucial orientation function; see the new Note [TyVar/TyVar orientation]. I completely rewrote this function, and it's now much much easier to understand. I ended up doing some related refactoring, of course * I noticed that tcImplicitTKBndrsX and tcExplicitTKBndrsX were doing a lot of useless work in the case where there are no skolems; I added a fast-patch * Elminate the un-used tcExplicitTKBndrsSig; and thereby get rid of the higher-order parameter to tcExpliciTKBndrsX. * Replace TcHsType.emitTvImplication with TcUnify.checkTvConstraints, by analogy with TcUnify.checkConstraints. * Inline TcUnify.buildImplication into its only call-site in TcUnify.checkConstraints * TcS.buildImplication becomes TcS.CheckConstraintsTcS, with a simpler API * Now that we have NoEvBindsVar we have no need of termEvidenceAllowed; nuke the latter, adding Note [No evidence bindings] to TcEvidence.
* Track type variable scope more carefully.Richard Eisenberg2018-03-311-3/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The main job of this commit is to track more accurately the scope of tyvars introduced by user-written foralls. For example, it would be to have something like this: forall a. Int -> (forall k (b :: k). Proxy '[a, b]) -> Bool In that type, a's kind must be k, but k isn't in scope. We had a terrible way of doing this before (not worth repeating or describing here, but see the old tcImplicitTKBndrs and friends), but now we have a principled approach: make an Implication when kind-checking a forall. Doing so then hooks into the existing machinery for preventing skolem-escape, performing floating, etc. This also means that we bump the TcLevel whenever going into a forall. The new behavior is done in TcHsType.scopeTyVars, but see also TcHsType.tc{Im,Ex}plicitTKBndrs, which have undergone significant rewriting. There are several Notes near there to guide you. Of particular interest there is that Implication constraints can now have skolems that are out of order; this situation is reported in TcErrors. A major consequence of this is a slightly tweaked process for type- checking type declarations. The new Note [Use SigTvs in kind-checking pass] in TcTyClsDecls lays it out. The error message for dependent/should_fail/TypeSkolEscape has become noticeably worse. However, this is because the code in TcErrors goes to some length to preserve pre-8.0 error messages for kind errors. It's time to rip off that plaster and get rid of much of the kind-error-specific error messages. I tried this, and doing so led to a lovely error message for TypeSkolEscape. So: I'm accepting the error message quality regression for now, but will open up a new ticket to fix it, along with a larger error-message improvement I've been pondering. This applies also to dependent/should_fail/{BadTelescope2,T14066,T14066e}, polykinds/T11142. Other minor changes: - isUnliftedTypeKind didn't look for tuples and sums. It does now. - check_type used check_arg_type on both sides of an AppTy. But the left side of an AppTy isn't an arg, and this was causing a bad error message. I've changed it to use check_type on the left-hand side. - Some refactoring around when we print (TYPE blah) in error messages. The changes decrease the times when we do so, to good effect. Of course, this is still all controlled by -fprint-explicit-runtime-reps Fixes #14066 #14749 Test cases: dependent/should_compile/{T14066a,T14749}, dependent/should_fail/T14066{,c,d,e,f,g,h}
* Wombling around in Trac #14808Simon Peyton Jones2018-03-051-0/+6
| | | | | | | | | | | Comment:4 in Trac #14808 explains why I'm unhappy with the current state of affairs -- at least the lack of documentation. This smallpatch does nothing major: * adds comments * uses existing type synonyms more (notably FreeKiTyVarsWithDups) * adds another test case to T14808
* Rename the types in a GADT constructor in toposorted orderRyan Scott2018-02-182-0/+13
| | | | | | | | | | | | | | | | | | | | | | | | | | Previously, we were extracting the free variables from a GADT constructor in an incorrect order, which caused the type variables for the constructor's type signature to end up in non-toposorted order. Thankfully, rearranging the order of types during renaming makes swift work of this bug. This fixes a regression introduced in commit fa29df02a1b0b926afb2525a258172dcbf0ea460. For whatever reason, that commit also commented out a significant portion of the `T13123` test. This code appears to work, so I've opted to uncomment it. Test Plan: make test TEST=T14808 Reviewers: simonpj, bgamari Reviewed By: bgamari Subscribers: rwbarton, thomie, carter GHC Trac Issues: #14808 Differential Revision: https://phabricator.haskell.org/D4413
* Fix #14719 by using the setting the right SrcSpanRyan Scott2018-01-263-0/+27
| | | | | | | | | | | | | | | | | | | | Currently, error messages that germane to GADT constructors put the source span at only the first character in the constructor, leading to insufficient caret diagnostics. This can be easily fixed by using a source span that spans the entire constructor, instead of just the first character. Test Plan: make test TEST=T14719 Reviewers: alanz, bgamari, simonpj Reviewed By: alanz, simonpj Subscribers: simonpj, goldfire, rwbarton, thomie, carter GHC Trac Issues: #14719 Differential Revision: https://phabricator.haskell.org/D4344
* typecheck: Clarify errors mentioned in #14385Ben Gamari2017-10-253-3/+3
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* Fix #14320 by looking through HsParTy in more placesRyan Scott2017-10-072-0/+16
| | | | | | | | | | | | | | | | | | | | | | Summary: GHC was needlessly rejecting GADT constructors' type signatures that were surrounded in parentheses due to the fact that `splitLHsForAllTy` and `splitLHsQualTy` (which are used to check as part of checking if GADT constructor return types are correct) weren't looking through parentheses (i.e., `HsParTy`). This is easily fixed, though. Test Plan: make test TEST=T14320 Reviewers: austin, bgamari Reviewed By: bgamari Subscribers: rwbarton, thomie GHC Trac Issues: #14320 Differential Revision: https://phabricator.haskell.org/D4072
* Track the order of user-written tyvars in DataConRyan Scott2017-10-031-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | After typechecking a data constructor's type signature, its type variables are partitioned into two distinct groups: the universally quantified type variables and the existentially quantified type variables. Then, when prompted for the type of the data constructor, GHC gives this: ```lang=haskell MkT :: forall <univs> <exis>. (...) ``` For H98-style datatypes, this is a fine thing to do. But for GADTs, this can sometimes produce undesired results with respect to `TypeApplications`. For instance, consider this datatype: ```lang=haskell data T a where MkT :: forall b a. b -> T a ``` Here, the user clearly intended to have `b` be available for visible type application before `a`. That is, the user would expect `MkT @Int @Char` to be of type `Int -> T Char`, //not// `Char -> T Int`. But alas, up until now that was not how GHC operated—regardless of the order in which the user actually wrote the tyvars, GHC would give `MkT` the type: ```lang=haskell MkT :: forall a b. b -> T a ``` Since `a` is universal and `b` is existential. This makes predicting what order to use for `TypeApplications` quite annoying, as demonstrated in #11721 and #13848. This patch cures the problem by tracking more carefully the order in which a user writes type variables in data constructor type signatures, either explicitly (with a `forall`) or implicitly (without a `forall`, in which case the order is inferred). This is accomplished by adding a new field `dcUserTyVars` to `DataCon`, which is a subset of `dcUnivTyVars` and `dcExTyVars` that is permuted to the order in which the user wrote them. For more details, refer to `Note [DataCon user type variables]` in `DataCon.hs`. An interesting consequence of this design is that more data constructors require wrappers. This is because the workers always expect the first arguments to be the universal tyvars followed by the existential tyvars, so when the user writes the tyvars in a different order, a wrapper type is needed to swizzle the tyvars around to match the order that the worker expects. For more details, refer to `Note [Data con wrappers and GADT syntax]` in `MkId.hs`. Test Plan: ./validate Reviewers: austin, goldfire, bgamari, simonpj Reviewed By: goldfire, simonpj Subscribers: ezyang, goldfire, rwbarton, thomie GHC Trac Issues: #11721, #13848 Differential Revision: https://phabricator.haskell.org/D3687
* Also show types that subsume a hole as valid substitutions for that hole.Matthías Páll Gissurarson2017-09-211-0/+12
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This builds on the previous "Valid substitutions include..." functionality, but add subsumption checking as well, so that the suggested valid substitutions show not only exact matches, but also identifiers that fit the hole by virtue of subsuming the type of the hole (i.e. being more general than the type of the hole). Building on the previous example, in the given program ``` ps :: String -> IO () ps = putStrLn ps2 :: a -> IO () ps2 _ = putStrLn "hello, world" main :: IO () main = _ "hello, world" ``` The results would be something like ``` • Found hole: _ :: [Char] -> IO () • In the expression: _ In the expression: _ "hello, world" In an equation for ‘main’: main = _ "hello, world" • Relevant bindings include main :: IO () (bound at t1.hs:8:1) Valid substitutions include ps :: String -> IO () (defined at t1.hs:2:1) ps2 :: forall a. a -> IO () (defined at t1.hs:5:1) putStrLn :: String -> IO () (imported from ‘Prelude’ at t1.hs:1:1 (and originally defined in ‘System.IO’)) fail :: forall (m :: * -> *). Monad m => forall a. String -> m a (imported from ‘Prelude’ at t1.hs:1:1 (and originally defined in ‘GHC.Base’)) mempty :: forall a. Monoid a => a (imported from ‘Prelude’ at t1.hs:1:1 (and originally defined in ‘GHC.Base’)) print :: forall a. Show a => a -> IO () (imported from ‘Prelude’ at t1.hs:1:1 (and originally defined in ‘System.IO’)) (Some substitutions suppressed; use -fmax-valid-substitutions=N or -fno-max-valid-substitutions) ``` Signed-off-by: Matthías Páll Gissurarson <mpg@mpg.is> Modified according to suggestions from Simon PJ Accept tests that match the expectations, still a few to look better at Swithced to using tcLookup, after sit down with SPJ at ICFP. Implications are WIP. Now works with polymorphism and constraints! We still need to merge the latest master, before we can make a patch. Wrap the type of the hole, instead of implication shenanigans, As per SPJs suggestion, this is simpler and feels closer to what we actually want to do. Updated tests with the new implementation Remove debugging trace and update documentation Reviewers: austin, bgamari Reviewed By: bgamari Subscribers: RyanGlScott, rwbarton, thomie Differential Revision: https://phabricator.haskell.org/D3930
* Suggest how to fix illegally nested foralls in GADT constructor type signaturesRyan Scott2017-08-173-1/+55
| | | | | | | | | | | | | | | | | | Summary: Although the code from #12087 isn't accepted by GHC, we can at least do a better job of letting users know what the problem is, and how to fix it. Test Plan: make test TEST=T12087 Reviewers: goldfire, austin, bgamari Reviewed By: goldfire Subscribers: rwbarton, thomie GHC Trac Issues: #12087 Differential Revision: https://phabricator.haskell.org/D3851
* Improve error messages around kind mismatches.Richard Eisenberg2017-07-271-3/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Previously, when canonicalizing (or unifying, in uType) a heterogeneous equality, we emitted a kind equality and used the resulting coercion to cast one side of the heterogeneous equality. While sound, this led to terrible error messages. (See the bugs listed below.) The problem is that using the coercion built from the emitted kind equality is a bit like a wanted rewriting a wanted. The solution is to keep heterogeneous equalities as irreducible. See Note [Equalities with incompatible kinds] in TcCanonical. This commit also removes a highly suspicious switch to FM_SubstOnly when flattening in the kinds of a type variable. I have no idea why this was there, other than as a holdover from pre-TypeInType. I've not left a Note because there is simply no reason I can conceive of that the FM_SubstOnly should be there. One challenge with this patch is that the emitted derived equalities might get emitted several times: when a heterogeneous equality is in an implication and then gets floated out from the implication, the Derived is present both in and out of the implication. This causes a duplicate error message. (Test case: typecheck/should_fail/T7368) Solution: track the provenance of Derived constraints and refuse to float out a constraint that has an insoluble Derived. Lastly, this labels one test (dependent/should_fail/RAE_T32a) as expect_broken, because the problem is really #12919. The different handling of constraints in this patch exposes the error. This fixes bugs #11198, #12373, #13530, and #13610. test cases: typecheck/should_fail/{T8262,T8603,tcail122,T12373,T13530,T13610}
* Some tidying up of type pretty-printingSimon Peyton Jones2017-05-261-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | Triggered by the changes in #13677, I ended up doing a bit of refactoring in type pretty-printing. * We were using TyOpPrec and FunPrec rather inconsitently, so I made it consisent. * That exposed the fact that we were a bit undecided about whether to print a + b -> c + d vs (a+b) -> (c+d) and similarly a ~ [b] => blah vs (a ~ [b]) => blah I decided to make TyOpPrec and FunPrec compare equal (in BasicTypes), so (->) is treated as equal precedence with other type operators, so you get the unambiguous forms above, even though they have more parens. We could readily reverse this decision. See Note [Type operator precedence] in BasicTypes * I fixed a bug in pretty-printing of HsType where some parens were omitted by mistake.
* Re-engineer Given flatten-skolemsSimon Peyton Jones2017-05-262-10/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The big change here is to fix an outright bug in flattening of Givens, albeit one that is very hard to exhibit. Suppose we have the constraint forall a. (a ~ F b) => ..., (forall c. ....(F b)...) ... Then - we'll flatten the (F) b to a fsk, say (F b ~ fsk1) - we'll rewrite the (F b) inside the inner implication to 'fsk1' - when we leave the outer constraint we are suppose to unflatten; but that fsk1 will still be there - if we re-simplify the entire outer implication, we'll re-flatten the Given (F b) to, say, (F b ~ fsk2) Now we have two fsks standing for the same thing, and that is very wrong. Solution: make fsks behave more like fmvs: - A flatten-skolem is now a MetaTyVar, whose MetaInfo is FlatSkolTv - We "fill in" that meta-tyvar when leaving the implication - The old FlatSkol form of TcTyVarDetails is gone completely - We track the flatten-skolems for the current implication in a new field of InertSet, inert_fsks. See Note [The flattening story] in TcFlatten. In doing this I found various other things to fix: * I removed the zonkSimples from TcFlatten.unflattenWanteds; it wasn't needed. But I added one in TcSimplify.floatEqualities, which does the zonk precisely when it is needed. * Trac #13674 showed up a case where we had - an insoluble Given, e.g. a ~ [a] - the same insoluble Wanted a ~ [a] We don't use the Given to rewwrite the Wanted (obviously), but we therefore ended up reporting Can't deduce (a ~ [a]) from (a ~ [a]) which is silly. Conclusion: when reporting errors, make the occurs check "win" See Note [Occurs check wins] in TcErrors
* Ensure that insolubles are fully rewrittenSimon Peyton Jones2017-05-193-0/+16
| | | | | | | | | | | | | | | | I was alerted to this by Trac #12468 and #11325. We were treating insolubles (and "hole" constraints are treated as insoluble) inconsistently. In some places we were carefully rewriting them e.g. Note [Make sure that insolubles are fully rewritten] in TcCanonical. But in TcSimplify we weren't feeding them into the solver. As a result, "hole" constraints were not being rewritten, which some users found confusing, and I think rightly so. This patch also fixes a bug in TcSMonad.emitInsoluble, in which two different "hole" constriants could be treated (bogusly) as duplicates, thereby losing one.
* Typos in comments [ci skip]Gabor Greif2017-04-111-1/+1
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* Fix TcSimplify.decideQuantification for kind variablesSimon Peyton Jones2017-03-101-8/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | TcSimplify.decideQuantification was doing the Wrong Thing when "growing" the type variables to quantify over. We were trying to do this on a tyvar set where we'd split off the dependent type varaibles; and we just got it wrong. A kind variable wasn't being generalised properly, with confusing knock on consequences. All this led to Trac #13371 and Trac #13393. This commit tidies it all up: * The type TcDepVars is renamed as CandidateQTvs; and splitDepVarsOfType to candidateQTyVarsOfType * The code in TcSimplify.decideQuantification is simpler. It no longer does the tricky "grow" stuff over TcDepVars. Instead it use ordinary VarSets (thereby eliminating the nasty growThetaTyVarsDSet) and uses that to filter the result of candidateQTyVarsOfType. * I documented that candidateQTyVarsOfType returns the type variables in a good order in which to quantify, and rewrote it to use an accumulator pattern, so that we would predicatably get left-to-right ordering. In doing all this I also made UniqDFM behave a little more nicely: * When inserting an element that is there already, keep the old tag, while still overwriting with the new value. * This means that when doing udfmToList we get back elements in the order they were originally inserted, rather than in reverse order. It's not a big deal, but in a subsequent commit I use it to improve the order of type variables in inferred types. All this led to a lot of error message wibbles: - changing the order of quantified variables - changing the order in which instances are listed in GHCi - changing the tidying of variables in typechecker erors There's a submodule update for 'array' because one of its tests has an error-message change. I may not have associated all of them with the correct commit.
* tests: remove extra_files.py (#12223)Reid Barton2017-02-261-2/+2
| | | | | | | | | | | | The script I used is included as testsuite/driver/kill_extra_files.py, though at this point it is for mostly historical interest. Some of the tests in libraries/hpc relied on extra_files.py, so this commit includes an update to that submodule. One test in libraries/process also relies on extra_files.py, but we cannot update that submodule so easily, so for now we special-case it in the test driver.
* Remove clean_cmd and extra_clean usage from .T filesThomas Miedema2017-01-221-16/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | The `clean_cmd` and `extra_clean` setup functions don't do anything. Remove them from .T files. Created using https://github.com/thomie/refactor-ghc-testsuite. This diff is a test for the .T-file parser/processor/pretty-printer in that repository. find . -name '*.T' -exec ~/refactor-ghc-testsuite/Main "{}" \; Tests containing inline comments or multiline strings are not modified. Preparation for #12223. Test Plan: Harbormaster Reviewers: austin, hvr, simonmar, mpickering, bgamari Reviewed By: mpickering Subscribers: mpickering Differential Revision: https://phabricator.haskell.org/D3000 GHC Trac Issues: #12223
* Spelling fixes in comments [ci skip]Gabor Greif2017-01-181-1/+1
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* Take account of kinds in promoteTcTypeSimon Peyton Jones2016-10-241-3/+3
| | | | | | | | | One of the ASSERT failures in Trac #12762, namely the one for T4439, showed that I had not dealt correctly with promoting the kind of a type in promoteTcType. Happily I could fix this by simplifying InferRes (eliminating the ir_kind field), so things get better. And the ASSERT is fixed.
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