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* Constraint simplification loop now depends on `ExpansionFuel`Apoorv Ingle2023-03-062-72/+113
| | | | | | | | | | | | | | instead of a boolean flag for `CDictCan.cc_pend_sc`. Pending givens get a fuel of 3 while Wanted and quantified constraints get a fuel of 1. This helps pending given constraints to keep up with pending wanted constraints in case of `UndecidableSuperClasses` and superclass expansions while simplifying the infered type. Adds 3 dynamic flags for controlling the fuels for each type of constraints `-fgivens-expansion-fuel` for givens `-fwanteds-expansion-fuel` for wanteds and `-fqcs-expansion-fuel` for quantified constraints Fixes #21909 Added Tests T21909, T21909b Added Note [Expanding Recursive Superclasses and ExpansionFuel]
* Don't specialise incoherent instance applicationsGergő Érdi2023-02-273-37/+40
| | | | | | | | | | | | | | Using incoherent instances, there can be situations where two occurrences of the same overloaded function at the same type use two different instances (see #22448). For incoherently resolved instances, we must mark them with `nospec` to avoid the specialiser rewriting one to the other. This marking is done during the desugaring of the `WpEvApp` wrapper. Fixes #22448 Metric Increase: T15304
* Narrow the dont-decompose-newtype testSimon Peyton Jones2023-02-163-165/+152
| | | | | | | | | | | | | | | | | | | | | | | | | | Following #22924 this patch narrows the test that stops us decomposing newtypes. The key change is the use of noGivenNewtypeReprEqs in GHC.Tc.Solver.Canonical.canTyConApp. We went to and fro on the solution, as you can see in #22924. The result is carefully documented in Note [Decomoposing newtype equalities] On the way I had revert most of commit 3e827c3f74ef76d90d79ab6c4e71aa954a1a6b90 Author: Richard Eisenberg <rae@cs.brynmawr.edu> Date: Mon Dec 5 10:14:02 2022 -0500 Do newtype unwrapping in the canonicaliser and rewriter See Note [Unwrap newtypes first], which has the details. It turns out that (a) 3e827c3f makes GHC behave worse on some recursive newtypes (see one of the tests on this commit) (b) the finer-grained test (namely noGivenNewtypeReprEqs) renders 3e827c3f unnecessary
* Introduce warning for loopy superclass solvesheaf2023-02-143-53/+93
| | | | | | | | | | | | | | | | | Commit aed1974e completely re-engineered the treatment of loopy superclass dictionaries in instance declarations. Unfortunately, it has the potential to break (albeit in a rather minor way) user code. To alleviate migration concerns, this commit re-introduces the old behaviour. Any reliance on this old behaviour triggers a warning, controlled by `-Wloopy-superclass-solve`. The warning text explains that GHC might produce bottoming evidence, and provides a migration strategy. This allows us to provide a graceful migration period, alerting users when they are relying on this unsound behaviour. Fixes #22912 #22891 #20666 #22894 #22905
* Do newtype unwrapping in the canonicaliser and rewriterRichard Eisenberg2023-01-263-74/+187
| | | | | | See Note [Unwrap newtypes first], which has the details. Close #22519.
* Refactor the treatment of loopy superclass dictswip/T20666Richard Eisenberg2023-01-114-84/+136
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch completely re-engineers how we deal with loopy superclass dictionaries in instance declarations. It fixes #20666 and #19690 The highlights are * Recognise that the loopy-superclass business should use precisely the Paterson conditions. This is much much nicer. See Note [Recursive superclasses] in GHC.Tc.TyCl.Instance * With that in mind, define "Paterson-smaller" in Note [Paterson conditions] in GHC.Tc.Validity, and the new data type `PatersonSize` in GHC.Tc.Utils.TcType, along with functions to compute and compare PatsonSizes * Use the new PatersonSize stuff when solving superclass constraints See Note [Solving superclass constraints] in GHC.Tc.TyCl.Instance * In GHC.Tc.Solver.Monad.lookupInInerts, add a missing call to prohibitedSuperClassSolve. This was the original cause of #20666. * Treat (TypeError "stuff") as having PatersonSize zero. See Note [Paterson size for type family applications] in GHC.Tc.Utils.TcType. * Treat the head of a Wanted quantified constraint in the same way as the superclass of an instance decl; this is what fixes #19690. See GHC.Tc.Solver.Canonical Note [Solving a Wanted forall-constraint] (Thanks to Matthew Craven for this insight.) This entailed refactoring the GivenSc constructor of CtOrigin a bit, to say whether it comes from an instance decl or quantified constraint. * Some refactoring way in which redundant constraints are reported; we don't want to complain about the extra, apparently-redundant constraints that we must add to an instance decl because of the loopy-superclass thing. I moved some work from GHC.Tc.Errors to GHC.Tc.Solver. * Add a new section to the user manual to describe the loopy superclass issue and what rules it follows.
* Drop support for kind constraints.wip/p547Richard Eisenberg2022-12-241-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | This implements proposal 547 and closes ticket #22298. See the proposal and ticket for motivation. Compiler perf improves a bit Metrics: compile_time/bytes allocated ------------------------------------- CoOpt_Singletons(normal) -2.4% GOOD T12545(normal) +1.0% T13035(normal) -13.5% GOOD T18478(normal) +0.9% T9872d(normal) -2.2% GOOD geo. mean -0.2% minimum -13.5% maximum +1.0% Metric Decrease: CoOpt_Singletons T13035 T9872d
* Fix an assertion check in addToEqualCtListSimon Peyton Jones2022-12-211-9/+17
| | | | | | | The old assertion saw that a constraint ct could rewrite itself (of course it can) and complained (stupid). Fixes #22645
* Be more careful in GHC.Tc.Solver.Interact.solveOneFromTheOtherSimon Peyton Jones2022-11-303-45/+52
| | | | | | | | We were failing to account for the cc_pend_sc flag in this important function, with the result that we expanded superclasses forever. Fixes #22516.
* Killing cc_fundeps, streamlining kind equality orientation, and type ↵Apoorv Ingle2022-11-292-89/+245
| | | | | | | | | | | | | | | | | | | | equality processing order Fixes: #217093 Associated to #19415 This change * Flips the orientation of the the generated kind equality coercion in canEqLHSHetero; * Removes `cc_fundeps` in CDictCan as the check was incomplete; * Changes `canDecomposableTyConAppOk` to ensure we process kind equalities before type equalities and avoiding a call to `canEqLHSHetero` while processing wanted TyConApp equalities * Adds 2 new tests for validating the change - testsuites/typecheck/should_compile/T21703.hs and - testsuites/typecheck/should_fail/T19415b.hs (a simpler version of T19415.hs) * Misc: Due to the change in the equality direction some error messages now have flipped type mismatch errors * Changes in Notes: - Note [Fundeps with instances, and equality orientation] supercedes Note [Fundeps with instances] - Added Note [Kind Equality Orientation] to visualize the kind flipping - Added Note [Decomposing Dependent TyCons and Processing Wanted Equalties]
* Fix decomposition of TyConAppswip/T22331Simon Peyton Jones2022-11-253-219/+320
| | | | | | | | | | | | | | | | Ticket #22331 showed that we were being too eager to decompose a Wanted TyConApp, leading to incompleteness in the solver. To understand all this I ended up doing a substantial rewrite of the old Note [Decomposing equalities], now reborn as Note [Decomposing TyConApp equalities]. Plus rewrites of other related Notes. The actual fix is very minor and actually simplifies the code: in `can_decompose` in `GHC.Tc.Solver.Canonical.canTyConApp`, we now call `noMatchableIrreds`. A closely related refactor: we stop trying to use the same "no matchable givens" function here as in `matchClassInst`. Instead split into two much simpler functions.
* Scrub some no-warning pragmas.M Farkas-Dyck2022-11-234-6/+1
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* Type vs Constraint: finally nailedSimon Peyton Jones2022-11-115-189/+179
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This big patch addresses the rats-nest of issues that have plagued us for years, about the relationship between Type and Constraint. See #11715/#21623. The main payload of the patch is: * To introduce CONSTRAINT :: RuntimeRep -> Type * To make TYPE and CONSTRAINT distinct throughout the compiler Two overview Notes in GHC.Builtin.Types.Prim * Note [TYPE and CONSTRAINT] * Note [Type and Constraint are not apart] This is the main complication. The specifics * New primitive types (GHC.Builtin.Types.Prim) - CONSTRAINT - ctArrowTyCon (=>) - tcArrowTyCon (-=>) - ccArrowTyCon (==>) - funTyCon FUN -- Not new See Note [Function type constructors and FunTy] and Note [TYPE and CONSTRAINT] * GHC.Builtin.Types: - New type Constraint = CONSTRAINT LiftedRep - I also stopped nonEmptyTyCon being built-in; it only needs to be wired-in * Exploit the fact that Type and Constraint are distinct throughout GHC - Get rid of tcView in favour of coreView. - Many tcXX functions become XX functions. e.g. tcGetCastedTyVar --> getCastedTyVar * Kill off Note [ForAllTy and typechecker equality], in (old) GHC.Tc.Solver.Canonical. It said that typechecker-equality should ignore the specified/inferred distinction when comparein two ForAllTys. But that wsa only weakly supported and (worse) implies that we need a separate typechecker equality, different from core equality. No no no. * GHC.Core.TyCon: kill off FunTyCon in data TyCon. There was no need for it, and anyway now we have four of them! * GHC.Core.TyCo.Rep: add two FunTyFlags to FunCo See Note [FunCo] in that module. * GHC.Core.Type. Lots and lots of changes driven by adding CONSTRAINT. The key new function is sORTKind_maybe; most other changes are built on top of that. See also `funTyConAppTy_maybe` and `tyConAppFun_maybe`. * Fix a longstanding bug in GHC.Core.Type.typeKind, and Core Lint, in kinding ForAllTys. See new tules (FORALL1) and (FORALL2) in GHC.Core.Type. (The bug was that before (forall (cv::t1 ~# t2). blah), where blah::TYPE IntRep, would get kind (TYPE IntRep), but it should be (TYPE LiftedRep). See Note [Kinding rules for types] in GHC.Core.Type. * GHC.Core.TyCo.Compare is a new module in which we do eqType and cmpType. Of course, no tcEqType any more. * GHC.Core.TyCo.FVs. I moved some free-var-like function into this module: tyConsOfType, visVarsOfType, and occCheckExpand. Refactoring only. * GHC.Builtin.Types. Compiletely re-engineer boxingDataCon_maybe to have one for each /RuntimeRep/, rather than one for each /Type/. This dramatically widens the range of types we can auto-box. See Note [Boxing constructors] in GHC.Builtin.Types The boxing types themselves are declared in library ghc-prim:GHC.Types. GHC.Core.Make. Re-engineer the treatment of "big" tuples (mkBigCoreVarTup etc) GHC.Core.Make, so that it auto-boxes unboxed values and (crucially) types of kind Constraint. That allows the desugaring for arrows to work; it gathers up free variables (including dictionaries) into tuples. See Note [Big tuples] in GHC.Core.Make. There is still work to do here: #22336. But things are better than before. * GHC.Core.Make. We need two absent-error Ids, aBSENT_ERROR_ID for types of kind Type, and aBSENT_CONSTRAINT_ERROR_ID for vaues of kind Constraint. Ditto noInlineId vs noInlieConstraintId in GHC.Types.Id.Make; see Note [inlineId magic]. * GHC.Core.TyCo.Rep. Completely refactor the NthCo coercion. It is now called SelCo, and its fields are much more descriptive than the single Int we used to have. A great improvement. See Note [SelCo] in GHC.Core.TyCo.Rep. * GHC.Core.RoughMap.roughMatchTyConName. Collapse TYPE and CONSTRAINT to a single TyCon, so that the rough-map does not distinguish them. * GHC.Core.DataCon - Mainly just improve documentation * Some significant renamings: GHC.Core.Multiplicity: Many --> ManyTy (easier to grep for) One --> OneTy GHC.Core.TyCo.Rep TyCoBinder --> GHC.Core.Var.PiTyBinder GHC.Core.Var TyCoVarBinder --> ForAllTyBinder AnonArgFlag --> FunTyFlag ArgFlag --> ForAllTyFlag GHC.Core.TyCon TyConTyCoBinder --> TyConPiTyBinder Many functions are renamed in consequence e.g. isinvisibleArgFlag becomes isInvisibleForAllTyFlag, etc * I refactored FunTyFlag (was AnonArgFlag) into a simple, flat data type data FunTyFlag = FTF_T_T -- (->) Type -> Type | FTF_T_C -- (-=>) Type -> Constraint | FTF_C_T -- (=>) Constraint -> Type | FTF_C_C -- (==>) Constraint -> Constraint * GHC.Tc.Errors.Ppr. Some significant refactoring in the TypeEqMisMatch case of pprMismatchMsg. * I made the tyConUnique field of TyCon strict, because I saw code with lots of silly eval's. That revealed that GHC.Settings.Constants.mAX_SUM_SIZE can only be 63, because we pack the sum tag into a 6-bit field. (Lurking bug squashed.) Fixes * #21530 Updates haddock submodule slightly. Performance changes ~~~~~~~~~~~~~~~~~~~ I was worried that compile times would get worse, but after some careful profiling we are down to a geometric mean 0.1% increase in allocation (in perf/compiler). That seems fine. There is a big runtime improvement in T10359 Metric Decrease: LargeRecord MultiLayerModulesTH_OneShot T13386 T13719 Metric Increase: T8095
* Define `Infinite` list and use where appropriate.M Farkas-Dyck2022-11-082-11/+13
| | | | | | | | Also add perf test for infinite list fusion. In particular, in `GHC.Core`, often we deal with infinite lists of roles. Also in a few locations we deal with infinite lists of names. Thanks to simonpj for helping to write the Note [Fusion for `Infinite` lists].
* TyEq:N assertion: only for saturated applicationssheaf2022-10-191-5/+15
| | | | | | | | | | The assertion that checked TyEq:N in canEqCanLHSFinish incorrectly triggered in the case of an unsaturated newtype TyCon heading the RHS, even though we can't unwrap such an application. Now, we only trigger an assertion failure in case of a saturated application of a newtype TyCon. Fixes #22310
* matchLocalInst: do domination analysissheaf2022-09-283-84/+213
| | | | | | | | | | | | | | | | | | | | | | | | | | When multiple Given quantified constraints match a Wanted, and there is a quantified constraint that dominates all others, we now pick it to solve the Wanted. See Note [Use only the best matching quantified constraint]. For example: [G] d1: forall a b. ( Eq a, Num b, C a b ) => D a b [G] d2: forall a . C a Int => D a Int [W] {w}: D a Int When solving the Wanted, we find that both Givens match, but we pick the second, because it has a weaker precondition, C a Int, compared to (Eq a, Num Int, C a Int). We thus say that d2 dominates d1; see Note [When does a quantified instance dominate another?]. This domination test is done purely in terms of superclass expansion, in the function GHC.Tc.Solver.Interact.impliedBySCs. We don't attempt to do a full round of constraint solving; this simple check suffices for now. Fixes #22216 and #22223
* Fix typosKrzysztof Gogolewski2022-09-141-1/+1
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* Fix typosEric Lindblad2022-09-144-15/+15
| | | | | | | This fixes various typos and spelling mistakes in the compiler. Fixes #21891
* Add diagnostic codessheaf2022-09-131-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This MR adds diagnostic codes, assigning unique numeric codes to error and warnings, e.g. error: [GHC-53633] Pattern match is redundant This is achieved as follows: - a type family GhcDiagnosticCode that gives the diagnostic code for each diagnostic constructor, - a type family ConRecursInto that specifies whether to recur into an argument of the constructor to obtain a more fine-grained code (e.g. different error codes for different 'deriving' errors), - generics machinery to generate the value-level function assigning each diagnostic its error code; see Note [Diagnostic codes using generics] in GHC.Types.Error.Codes. The upshot is that, to add a new diagnostic code, contributors only need to modify the two type families mentioned above. All logic relating to diagnostic codes is thus contained to the GHC.Types.Error.Codes module, with no code duplication. This MR also refactors error message datatypes a bit, ensuring we can derive Generic for them, and cleans up the logic around constraint solver reports by splitting up 'TcSolverReportInfo' into separate datatypes (see #20772). Fixes #21684
* Remove TCvSubst and use Subst for both term and type-level substYiyun Liu2022-08-043-14/+12
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch removes the TCvSubst data type and instead uses Subst as the environment for both term and type level substitution. This change is partially motivated by the existential type proposal, which will introduce types that contain expressions and therefore forces us to carry around an "IdSubstEnv" even when substituting for types. It also reduces the amount of code because "Subst" and "TCvSubst" share a lot of common operations. There isn't any noticeable impact on performance (geo. mean for ghc/alloc is around 0.0% but we have -94 loc and one less data type to worry abount). Currently, the "TCvSubst" data type for substitution on types is identical to the "Subst" data type except the former doesn't store "IdSubstEnv". Using "Subst" for type-level substitution means there will be a redundant field stored in the data type. However, in cases where the substitution starts from the expression, using "Subst" for type-level substitution saves us from having to project "Subst" into a "TCvSubst". This probably explains why the allocation is mostly even despite the redundant field. The patch deletes "TCvSubst" and moves "Subst" and its relevant functions from "GHC.Core.Subst" into "GHC.Core.TyCo.Subst". Substitution on expressions is still defined in "GHC.Core.Subst" so we don't have to expose the definition of "Expr" in the hs-boot file that "GHC.Core.TyCo.Subst" must import to refer to "IdSubstEnv" (whose codomain is "CoreExpr"). Most functions named fooTCvSubst are renamed into fooSubst with a few exceptions (e.g. "isEmptyTCvSubst" is a distinct function from "isEmptySubst"; the former ignores the emptiness of "IdSubstEnv"). These exceptions mainly exist for performance reasons and will go away when "Expr" and "Type" are mutually recursively defined (we won't be able to take those shortcuts if we can't make the assumption that expressions don't appear in types).
* Get the in-scope set right in FamInstEnv.injectiveBranchesSimon Peyton Jones2022-07-252-15/+26
| | | | | | | | | | | | | There was an assert error, as Gergo pointed out in #21896. I fixed this by adding an InScopeSet argument to tcUnifyTyWithTFs. And also to GHC.Core.Unify.niFixTCvSubst. I also took the opportunity to get a couple more InScopeSets right, and to change some substTyUnchecked into substTy. This MR touches a lot of other files, but only because I also took the opportunity to introduce mkInScopeSetList, and use it.
* Generalize breakTyVarCycle to work with TyFamLHSRichard Eisenberg2022-05-263-68/+99
| | | | | | | | | | | | | | | | | The function breakTyVarCycle_maybe has been installed in a dark corner of GHC to catch some gremlins (a.k.a. occurs-check failures) who lurk there. But it previously only caught gremlins of the form (a ~ ... F a ...), where some of our intrepid users have spawned gremlins of the form (G a ~ ... F (G a) ...). This commit improves breakTyVarCycle_maybe (and renames it to breakTyEqCycle_maybe) to catch the new gremlins. Happily, the change is remarkably small. The gory details are in Note [Type equality cycles]. Test cases: typecheck/should_compile/{T21515,T21473}.
* Consider the stage of typeable evidence when checking stage restrictionMatthew Pickering2022-05-222-11/+77
| | | | | | | | | | | | | | We were considering all Typeable evidence to be "BuiltinInstance"s which meant the stage restriction was going unchecked. In-fact, typeable has evidence and so we need to apply the stage restriction. This is complicated by the fact we don't generate typeable evidence and the corresponding DFunIds until after typechecking is concluded so we introcue a new `InstanceWhat` constructor, BuiltinTypeableInstance which records whether the evidence is going to be local or not. Fixes #21547
* TcPlugin: access to irreducible givens + fix passed ev_binds_varPavol Vargovcik2022-05-162-6/+13
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* Fix several note referencesKrzysztof Gogolewski2022-05-021-1/+1
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* Fix unification of ConcreteTvs, removing IsRefl#sheaf2022-04-284-70/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch fixes the unification of concrete type variables. The subtlety was that unifying concrete metavariables is more subtle than other metavariables, as decomposition is possible. See the Note [Unifying concrete metavariables], which explains how we unify a concrete type variable with a type 'ty' by concretising 'ty', using the function 'GHC.Tc.Utils.Concrete.concretise'. This can be used to perform an eager syntactic check for concreteness, allowing us to remove the IsRefl# special predicate. Instead of emitting two constraints `rr ~# concrete_tv` and `IsRefl# rr concrete_tv`, we instead concretise 'rr'. If this succeeds we can fill 'concrete_tv', and otherwise we directly emit an error message to the typechecker environment instead of deferring. We still need the error message to be passed on (instead of directly thrown), as we might benefit from further unification in which case we will need to zonk the stored types. To achieve this, we change the 'wc_holes' field of 'WantedConstraints' to 'wc_errors', which stores general delayed errors. For the moement, a delayed error is either a hole, or a syntactic equality error. hasFixedRuntimeRep_MustBeRefl is now hasFixedRuntimeRep_syntactic, and hasFixedRuntimeRep has been refactored to directly return the most useful coercion for PHASE 2 of FixedRuntimeRep. This patch also adds a field ir_frr to the InferResult datatype, holding a value of type Maybe FRROrigin. When this value is not Nothing, this means that we must fill the ir_ref field with a type which has a fixed RuntimeRep. When it comes time to fill such an ExpType, we ensure that the type has a fixed RuntimeRep by performing a representation-polymorphism check with the given FRROrigin This is similar to what we already do to ensure we fill an Infer ExpType with a type of the correct TcLevel. This allows us to properly perform representation-polymorphism checks on 'Infer' 'ExpTypes'. The fillInferResult function had to be moved to GHC.Tc.Utils.Unify to avoid a cyclic import now that it calls hasFixedRuntimeRep. This patch also changes the code in matchExpectedFunTys to make use of the coercions, which is now possible thanks to the previous change. This implements PHASE 2 of FixedRuntimeRep in some situations. For example, the test cases T13105 and T17536b are now both accepted. Fixes #21239 and #21325 ------------------------- Metric Decrease: T18223 T5631 -------------------------
* Add Red Herring to Note [What might equal later?]Richard Eisenberg2022-03-283-87/+130
| | | | Close #21208.
* Fix isLiftedType_maybe and handle falloutsheaf2022-03-141-0/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | As #20837 pointed out, `isLiftedType_maybe` returned `Just False` in many situations where it should return `Nothing`, because it didn't take into account type families or type variables. In this patch, we fix this issue. We rename `isLiftedType_maybe` to `typeLevity_maybe`, which now returns a `Levity` instead of a boolean. We now return `Nothing` for types with kinds of the form `TYPE (F a1 ... an)` for a type family `F`, as well as `TYPE (BoxedRep l)` where `l` is a type variable. This fix caused several other problems, as other parts of the compiler were relying on `isLiftedType_maybe` returning a `Just` value, and were now panicking after the above fix. There were two main situations in which panics occurred: 1. Issues involving the let/app invariant. To uphold that invariant, we need to know whether something is lifted or not. If we get an answer of `Nothing` from `isLiftedType_maybe`, then we don't know what to do. As this invariant isn't particularly invariant, we can change the affected functions to not panic, e.g. by behaving the same in the `Just False` case and in the `Nothing` case (meaning: no observable change in behaviour compared to before). 2. Typechecking of data (/newtype) constructor patterns. Some programs involving patterns with unknown representations were accepted, such as T20363. Now that we are stricter, this caused further issues, culminating in Core Lint errors. However, the behaviour was incorrect the whole time; the incorrectness only being revealed by this change, not triggered by it. This patch fixes this by overhauling where the representation polymorphism involving pattern matching are done. Instead of doing it in `tcMatches`, we instead ensure that the `matchExpected` functions such as `matchExpectedFunTys`, `matchActualFunTySigma`, `matchActualFunTysRho` allow return argument pattern types which have a fixed RuntimeRep (as defined in Note [Fixed RuntimeRep]). This ensures that the pattern matching code only ever handles types with a known runtime representation. One exception was that patterns with an unknown representation type could sneak in via `tcConPat`, which points to a missing representation-polymorphism check, which this patch now adds. This means that we now reject the program in #20363, at least until we implement PHASE 2 of FixedRuntimeRep (allowing type families in RuntimeRep positions). The aforementioned refactoring, in which checks have been moved to `matchExpected` functions, is a first step in implementing PHASE 2 for patterns. Fixes #20837
* Make inert_cycle_breakers into a stack.Richard Eisenberg2022-03-022-18/+75
| | | | Close #20231.
* Introduce ConcreteTv metavariablessheaf2022-03-023-230/+77
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch introduces a new kind of metavariable, by adding the constructor `ConcreteTv` to `MetaInfo`. A metavariable with `ConcreteTv` `MetaInfo`, henceforth a concrete metavariable, can only be unified with a type that is concrete (that is, a type that answers `True` to `GHC.Core.Type.isConcrete`). This solves the problem of dangling metavariables in `Concrete#` constraints: instead of emitting `Concrete# ty`, which contains a secret existential metavariable, we simply emit a primitive equality constraint `ty ~# concrete_tv` where `concrete_tv` is a fresh concrete metavariable. This means we can avoid all the complexity of canonicalising `Concrete#` constraints, as we can just re-use the existing machinery for `~#`. To finish things up, this patch then removes the `Concrete#` special predicate, and instead introduces the special predicate `IsRefl#` which enforces that a coercion is reflexive. Such a constraint is needed because the canonicaliser is quite happy to rewrite an equality constraint such as `ty ~# concrete_tv`, but such a rewriting is not handled by the rest of the compiler currently, as we need to make use of the resulting coercion, as outlined in the FixedRuntimeRep plan. The big upside of this approach (on top of simplifying the code) is that we can now selectively implement PHASE 2 of FixedRuntimeRep, by changing individual calls of `hasFixedRuntimeRep_MustBeRefl` to `hasFixedRuntimeRep` and making use of the obtained coercion.
* Kill derived constraintsRichard Eisenberg2022-02-236-1453/+968
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Co-authored by: Sam Derbyshire Previously, GHC had three flavours of constraint: Wanted, Given, and Derived. This removes Derived constraints. Though serving a number of purposes, the most important role of Derived constraints was to enable better error messages. This job has been taken over by the new RewriterSets, as explained in Note [Wanteds rewrite wanteds] in GHC.Tc.Types.Constraint. Other knock-on effects: - Various new Notes as I learned about under-described bits of GHC - A reshuffling around the AST for implicit-parameter bindings, with better integration with TTG. - Various improvements around fundeps. These were caused by the fact that, previously, fundep constraints were all Derived, and Derived constraints would get dropped. Thus, an unsolved Derived didn't stop compilation. Without Derived, this is no longer possible, and so we have to be considerably more careful around fundeps. - A nice little refactoring in GHC.Tc.Errors to center the work on a new datatype called ErrorItem. Constraints are converted into ErrorItems at the start of processing, and this allows for a little preprocessing before the main classification. - This commit also cleans up the behavior in generalisation around functional dependencies. Now, if a variable is determined by functional dependencies, it will not be quantified. This change is user facing, but it should trim down GHC's strange behavior around fundeps. - Previously, reportWanteds did quite a bit of work, even on an empty WantedConstraints. This commit adds a fast path. - Now, GHC will unconditionally re-simplify constraints during quantification. See Note [Unconditionally resimplify constraints when quantifying], in GHC.Tc.Solver. Close #18398. Close #18406. Solve the fundep-related non-confluence in #18851. Close #19131. Close #19137. Close #20922. Close #20668. Close #19665. ------------------------- Metric Decrease: LargeRecord T9872b T9872b_defer T9872d TcPlugin_RewritePerf -------------------------
* Fix some notesMatthew Pickering2022-02-082-3/+3
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* Relax TyEq:N: allow out-of-scope newtype DataConsheaf2022-02-081-8/+20
| | | | | | | | | | The 'bad_newtype' assertion in GHC.Tc.Solver.Canonical.canEqCanLHSFinish failed to account for the possibility that the newtype constructor might not be in scope, in which case we don't provide any guarantees about canonicalising away a newtype on the RHS of a representational equality. Fixes #21010
* Fix a few Note inconsistenciesBen Gamari2022-02-011-3/+3
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* Make typechecker trace less strictSimon Peyton Jones2022-01-311-2/+4
| | | | Fixes #21011
* Rework the handling of SkolemInfoMatthew Pickering2022-01-292-15/+18
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The main purpose of this patch is to attach a SkolemInfo directly to each SkolemTv. This fixes the large number of bugs which have accumulated over the years where we failed to report errors due to having "no skolem info" for particular type variables. Now the origin of each type varible is stored on the type variable we can always report accurately where it cames from. Fixes #20969 #20732 #20680 #19482 #20232 #19752 #10946 #19760 #20063 #13499 #14040 The main changes of this patch are: * SkolemTv now contains a SkolemInfo field which tells us how the SkolemTv was created. Used when reporting errors. * Enforce invariants relating the SkolemInfoAnon and level of an implication (ic_info, ic_tclvl) to the SkolemInfo and level of the type variables in ic_skols. * All ic_skols are TcTyVars -- Check is currently disabled * All ic_skols are SkolemTv * The tv_lvl of the ic_skols agrees with the ic_tclvl * The ic_info agrees with the SkolInfo of the implication. These invariants are checked by a debug compiler by checkImplicationInvariants. * Completely refactor kcCheckDeclHeader_sig which kept doing my head in. Plus, it wasn't right because it wasn't skolemising the binders as it decomposed the kind signature. The new story is described in Note [kcCheckDeclHeader_sig]. The code is considerably shorter than before (roughly 240 lines turns into 150 lines). It still has the same awkward complexity around computing arity as before, but that is a language design issue. See Note [Arity inference in kcCheckDeclHeader_sig] * I added new type synonyms MonoTcTyCon and PolyTcTyCon, and used them to be clear which TcTyCons have "finished" kinds etc, and which are monomorphic. See Note [TcTyCon, MonoTcTyCon, and PolyTcTyCon] * I renamed etaExpandAlgTyCon to splitTyConKind, becuase that's a better name, and it is very useful in kcCheckDeclHeader_sig, where eta-expansion isn't an issue. * Kill off the nasty `ClassScopedTvEnv` entirely. Co-authored-by: Simon Peyton Jones <simon.peytonjones@gmail.com>
* Set the TcLclEnv when solving a ForAll constraintSimon Peyton Jones2022-01-272-1/+11
| | | | | | | Fix a simple omission in GHC.Tc.Solver.Canonical.solveForAll, where we ended up with the wrong TcLclEnv captured in an implication. Result: unhelpful error message (#21006)
* Fix getHasGivenEqsSimon Peyton Jones2022-01-271-4/+7
| | | | | | | | | The second component is supposed to be "insoluble equalities arising from givens". But we were getting wanteds too; and that led to an outright duplication of constraints. It's not harmful, but it's not right either. I came across this when debugging something else. Easily fixed.
* Skip computing superclass origins for equalitiesRichard Eisenberg2021-12-281-4/+13
| | | | This yields a small, but measurable, performance improvement.
* Ensure new Ct/evidence invariantChristiaan Baaij2021-11-251-5/+5
| | | | | | | | | | The `ctev_pred` field of a `CtEvidence` is a just a cache for the type of the evidence. More precisely: * For Givens, `ctev_pred` = `varType ctev_evar` * For Wanteds, `ctev_pred` = `evDestType ctev_dest` This new invariant is needed because evidence can become part of a type, via `Castty ty kco`.
* Use local instances with least superclass depthRichard Eisenberg2021-11-123-50/+114
| | | | | | | | | | See new Note [Use only the best local instance] in GHC.Tc.Solver.Interact. This commit also refactors the InstSC/OtherSC mechanism slightly. Close #20582.
* Improve redundant-constraints warningRichard Eisenberg2021-11-123-59/+65
| | | | | | | | | | | | | | Previously, we reported things wrong with f :: (Eq a, Ord a) => a -> Bool f x = x == x saying that Eq a was redundant. This is fixed now, along with some simplification in Note [Replacement vs keeping]. There's a tiny bit of extra complexity in setImplicationStatus, but it's explained in Note [Tracking redundant constraints]. Close #20602
* Introduce Concrete# for representation polymorphism checkssheaf2021-10-175-33/+198
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | PHASE 1: we never rewrite Concrete# evidence. This patch migrates all the representation polymorphism checks to the typechecker, using a new constraint form Concrete# :: forall k. k -> TupleRep '[] Whenever a type `ty` must be representation-polymorphic (e.g. it is the type of an argument to a function), we emit a new `Concrete# ty` Wanted constraint. If this constraint goes unsolved, we report a representation-polymorphism error to the user. The 'FRROrigin' datatype keeps track of the context of the representation-polymorphism check, for more informative error messages. This paves the way for further improvements, such as allowing type families in RuntimeReps and improving the soundness of typed Template Haskell. This is left as future work (PHASE 2). fixes #17907 #20277 #20330 #20423 #20426 updates haddock submodule ------------------------- Metric Decrease: T5642 -------------------------
* Speed up valid hole-fits by adding early abort and checks.Matthías Páll Gissurarson2021-10-051-25/+43
| | | | | | | | | | | | | | By adding an early abort flag in `TcSEnv`, we can fail fast in the presence of insoluble constraints. This helps us avoid a lot of work in valid hole-fits, and we geta massive speed-up by avoiding a lot of useless work solving constraints that never come into play. Additionally, we add a simple check for degenerate hole types, such as when the type of the hole is an immutable type variable (as is the case when the hole is completely unconstrained). Then the only valid fits are the locals, so we can ignore the global candidates. This fixes #16875
* Use eqType, not tcEqType, in metavar kind checkRichard Eisenberg2021-10-021-1/+1
| | | | | | | | | | | | Close #20356. See addendum to Note [coreView vs tcView] in GHC.Core.Type for the details. Also killed old Note about metaTyVarUpdateOK, which has been gone for some time. test case: typecheck/should_fail/T20356
* Compare FunTys as if they were TyConApps.Richard Eisenberg2021-09-292-15/+42
| | | | | | | | | | | See Note [Equality on FunTys] in TyCoRep. Close #17675. Close #17655, about documentation improvements included in this patch. Close #19677, about a further mistake around FunTy. test cases: typecheck/should_compile/T19677
* Add and use new constructors to TcRnMessageAlfredo Di Napoli2021-09-071-8/+1
| | | | | | | | | | | | | This commit adds the following constructors to the TcRnMessage type and uses them to replace sdoc-based diagnostics in some parts of GHC (e.g. TcRnUnknownMessage). It includes: * Add TcRnMonomorphicBindings diagnostic * Convert TcRnUnknownMessage in Tc.Solver.Interact * Add and use the TcRnOrphanInstance constructor to TcRnMessage * Add TcRnFunDepConflict and TcRnDupInstanceDecls constructors to TcRnMessage * Add and use TcRnConflictingFamInstDecls constructor to TcRnMessage * Get rid of TcRnUnknownMessage from GHC.Tc.Instance.Family
* TcPlugins: solve and report contras simultaneouslysheaf2021-08-231-8/+11
| | | | | | | | | | | | This changes the TcPlugin datatype to allow type-checking plugins to report insoluble constraints while at the same time solve some other constraints. This allows better error messages, as the plugin can still simplify constraints, even when it wishes to report a contradiction. Pattern synonyms TcPluginContradiction and TcPluginOk are provided for backwards compatibility: existing type-checking plugins should continue to work without modification.
* Detect TypeError when checking for insolubilitysheaf2021-08-151-3/+9
| | | | | | | | | | | | | | | We detect insoluble Givens by making getInertInsols take into account TypeError constraints, on top of insoluble equalities such as Int ~ Bool (which it already took into account). This allows pattern matches with insoluble contexts to be reported as redundant (tyOracle calls tcCheckGivens which calls getInertInsols). As a bonus, we get to remove a workaround in Data.Typeable.Internal: we can directly use a NotApplication type family, as opposed to needing to cook up an insoluble equality constraint. Fixes #11503 #14141 #16377 #20180
* Add rewriting to typechecking pluginssheaf2021-08-133-54/+116
| | | | | | | | | | | | | | | | | | | | | | | | | | | Type-checking plugins can now directly rewrite type-families. The TcPlugin record is given a new field, tcPluginRewrite. The plugin specifies how to rewrite certain type-families with a value of type `UniqFM TyCon TcPluginRewriter`, where: type TcPluginRewriter = RewriteEnv -- Rewriter environment -> [Ct] -- Givens -> [TcType] -- type family arguments -> TcPluginM TcPluginRewriteResult data TcPluginRewriteResult = TcPluginNoRewrite | TcPluginRewriteTo { tcPluginRewriteTo :: Reduction , tcRewriterNewWanteds :: [Ct] } When rewriting an exactly-saturated type-family application, GHC will first query type-checking plugins for possible rewritings before proceeding. Includes some changes to the TcPlugin API, e.g. removal of the EvBindsVar parameter to the TcPluginM monad.
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