- Feb 03, 2024
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Apoorv Ingle authored- Fixes #18324 #20020 #23147 #22788 #15598 #22086 #21206 - The change is detailed in - Note [Expanding HsDo with HsExpansion] in `GHC.Tc.Gen.Do` - Note [Doing HsExpansion in the Renamer vs Typechecker] in `GHC.Rename.Expr` expains the rational of doing expansions in type checker as opposed to in the renamer - Adds new datatypes: - `GHC.Hs.Expr.XXExprGhcRn`: new datatype makes this expansion work easier 1. Expansion bits for Expressions, Statements and Patterns in (`ExpandedThingRn`) 2. `PopErrCtxt` a special GhcRn Phase only artifcat to pop the previous error message in the error context stack - `GHC.Basic.Origin` now tracks the reason for expansion in case of Generated This is useful for type checking cf. `GHC.Tc.Gen.Expr.tcExpr` case for `HsLam` - Kills `HsExpansion` and `HsExpanded` as we have inlined them in `XXExprGhcRn` and `XXExprGhcTc` - Ensures warnings such as 1. Pattern match checks 2. Failable patterns 3. non-() return in body statements are preserved - Kill `HsMatchCtxt` in favor of `TcMatchAltChecker` - Testcases: * T18324 T20020 T23147 T22788 T15598 T22086 * T23147b (error message check), * DoubleMatch (match inside a match for pmc check) * pattern-fails (check pattern match with non-refutable pattern, eg. newtype) * Simple-rec (rec statements inside do statment) * T22788 (code snippet from #22788) * DoExpanion1 (Error messages for body statments) * DoExpansion2 (Error messages for bind statements) * DoExpansion3 (Error messages for let statements) Also repoint haddock to the right submodule so that the test (haddockHypsrcTest) pass Metric Increase 'compile_time/bytes allocated': T9020 The testcase is a pathalogical example of a `do`-block with many statements that do nothing. Given that we are expanding the statements into function binds, we will have to bear a (small) 2% cost upfront in the compiler to unroll the statements.
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- Jan 20, 2024
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- Jan 14, 2024
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Pmc: COMPLETE pragmas associated with Family TyCons should apply to representation TyCons as well (#24326) Fixes #24326.
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- Dec 06, 2023
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Before, the source location would point at the surrounding function definition, causing the confusion in #24234. I also took the opportunity to introduce a new `LazyPatCtx :: HsMatchContext _` to make the warning message say "irrefutable pattern" instead of "pattern binding".
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- Jul 26, 2023
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It adds a warning -Wincomplete-record-selectors for usages of a record field access function (either a record selector or getField @"rec"), while trying to silence the warning whenever it can be sure that a constructor without the record field would not be invoked (which would otherwise cause the program to fail). For example: data T = T1 | T2 {x :: Bool} f a = x a -- this would throw an error g T1 = True g a = x a -- this would not throw an error h :: HasField "x" r Bool => r -> Bool h = getField @"x" j :: T -> Bool j = h -- this would throw an error because of the `HasField` -- constraint being solved See the tests DsIncompleteRecSel* and TcIncompleteRecSel for more examples of the warning. See Note [Detecting incomplete record selectors] in GHC.HsToCore.Expr for implementation details
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- Jul 18, 2023
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Some patterns introduce no new information to the pattern-match checker (such as plain variable or wildcard patterns). We can thus skip doing any pattern-match checking on them when the sole purpose for doing so was introducing new long-distance information. See Note [Boring patterns] in GHC.Hs.Pat. Doing this avoids regressing in performance now that we do additional pattern-match checking inside do notation.
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The preceding commit re-enabled pattern-match checking inside record updates. This revealed that #21360 was in fact NOT fixed by e74fc066. This commit makes sure we correctly propagate long-distance information in do blocks, e.g. in ```haskell data T = A { fld :: Int } | B f :: T -> Maybe T f r = do a@A{} <- Just r Just $ case a of { A _ -> A 9 } ``` we need to propagate the fact that "a" is headed by the constructor "A" to see that the case expression "case a of { A _ -> A 9 }" cannot fail. Fixes #21360
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Commit e74fc066 refactored the handling of record updates to use the HsExpanded mechanism. This meant that the pattern matching inherent to a record update was considered to be "generated code", and thus we stopped emitting "incomplete record update" warnings entirely. This commit changes the "data Origin = Source | Generated" datatype, adding a field to the Generated constructor to indicate whether we still want to perform pattern-match checking. We also have to do a bit of plumbing with HsCase, to record that the HsCase arose from an HsExpansion of a RecUpd, so that the error message continues to mention record updates as opposed to a generic "incomplete pattern matches in case" error. Finally, this patch also changes the way we handle inaccessible code warnings. Commit e74fc066 was also a regression in this regard, as we were emitting "inaccessible code" warnings for case statements spuriously generated when desugaring a record update (remember: the desugaring mechanism happens before typechecking; it thus can't take into account e.g. GADT information in order to decide which constructors to include in the RHS of the desugaring of the record update). We fix this by changing the mechanism through which we disable inaccessible code warnings: we now check whether we are in generated code in GHC.Tc.Utils.TcMType.newImplication in order to determine whether to emit inaccessible code warnings. Fixes #23520 Updates haddock submodule, to avoid incomplete record update warnings
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- Jul 15, 2023
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This patch finally (I hope) nails the question of whether (forall a. ty) and (forall a -> ty) are `eqType`: they aren't! There is a long discussion in #22762, plus useful Notes: * Note [ForAllTy and type equality] in GHC.Core.TyCo.Compare * Note [Comparing visiblities] in GHC.Core.TyCo.Compare * Note [ForAllCo] in GHC.Core.TyCo.Rep It also establishes a helpful new invariant for ForAllCo, and ForAllTy, when the bound variable is a CoVar:in that case the visibility must be coreTyLamForAllTyFlag. All this is well documented in revised Notes.
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- Jul 05, 2023
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Numerous tests make use of CUSKs (complete user-supplied kinds), a legacy feature scheduled for deprecation. In order to proceed with the said deprecation, the tests have been updated to use SAKS instead (standalone kind signatures). This also allows us to remove the Haskell2010 language pragmas that were added in 115cd3c8 to work around the lack of CUSKs in GHC2021.
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- May 25, 2023
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When desugaring generated pattern matches, we skip pattern match checks. However, this ended up also discarding long-distance information, which might be needed for user-written sub-expressions. Example: ```haskell okay (GADT di) cd = let sr_field :: () sr_field = case getFooBar di of { Foo -> () } in case cd of { SomeRec _ -> SomeRec sr_field } ``` With sr_field a generated FunBind, we still want to propagate the outer long-distance information from the GADT pattern match into the checks for the user-written RHS of sr_field. Fixes #23445
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- May 23, 2023
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This refactoring makes a substantial improvement in the structure of the type-checker's constraint solver: #23070. Specifically: * Introduced the SolverStage monad. See GHC.Tc.Solver.Monad Note [The SolverStage monad] * Make each solver pipeline (equalities, dictionaries, irreds etc) deal with updating the inert set, as a separate SolverStage. There is sometimes special stuff to do, and it means that each full pipeline can have type SolverStage Void, indicating that they never return anything. * Made GHC.Tc.Solver.Equality.zonkEqTypes into a SolverStage. Much nicer. * Combined the remnants of GHC.Tc.Solver.Canonical and GHC.Tc.Solver.Interact into a new module GHC.Tc.Solver.Solve. (Interact and Canonical are removed.) * Gave the same treatment to dictionary and irred constraints as I have already done for equality constraints: * New types (akin to EqCt): IrredCt and DictCt * Ct is now just a simple sum type data Ct = CDictCan DictCt | CIrredCan IrredCt | CEqCan EqCt | CQuantCan QCInst | CNonCanonical CtEvidence * inert_dicts can now have the better type DictMap DictCt, instead of DictMap Ct; and similarly inert_irreds. * Significantly simplified the treatment of implicit parameters. Previously we had a number of special cases * interactGivenIP, an entire function * special case in maybeKickOut * special case in findDict, when looking up dictionaries But actually it's simpler than that. When adding a new Given, implicit parameter constraint to the InertSet, we just need to kick out any existing inert constraints that mention that implicit parameter. The main work is done in GHC.Tc.Solver.InertSet.delIPDict, along with its auxiliary GHC.Core.Predicate.mentionsIP. See Note [Shadowing of implicit parameters] in GHC.Tc.Solver.Dict. * Add a new fast-path in GHC.Tc.Errors.Hole.tcCheckHoleFit. See Note [Fast path for tcCheckHoleFit]. This is a big win in some cases: test hard_hole_fits gets nearly 40% faster (at compile time). * Add a new fast-path for solving /boxed/ equality constraints (t1 ~ t2). See Note [Solving equality classes] in GHC.Tc.Solver.Dict. This makes a big difference too: test T17836 compiles 40% faster. * Implement the PermissivePlan of #23413, which concerns what happens with insoluble Givens. Our previous treatment was wildly inconsistent as that ticket pointed out. A part of this, I simplified GHC.Tc.Validity.checkAmbiguity: now we simply don't run the ambiguity check at all if -XAllowAmbiguousTypes is on. Smaller points: * In `GHC.Tc.Errors.misMatchOrCND` instead of having a special case for insoluble /occurs/ checks, broaden in to all insouluble constraints. Just generally better. See Note [Insoluble mis-match] in that module. As noted above, compile time perf gets better. Here are the changes over 0.5% on Fedora. (The figures are slightly larger on Windows for some reason.) Metrics: compile_time/bytes allocated ------------------------------------- LargeRecord(normal) -0.9% MultiLayerModulesTH_OneShot(normal) +0.5% T11822(normal) -0.6% T12227(normal) -1.8% GOOD T12545(normal) -0.5% T13035(normal) -0.6% T15703(normal) -1.4% GOOD T16875(normal) -0.5% T17836(normal) -40.7% GOOD T17836b(normal) -12.3% GOOD T17977b(normal) -0.5% T5837(normal) -1.1% T8095(normal) -2.7% GOOD T9020(optasm) -1.1% hard_hole_fits(normal) -37.0% GOOD geo. mean -1.3% minimum -40.7% maximum +0.5% Metric Decrease: T12227 T15703 T17836 T17836b T8095 hard_hole_fits LargeRecord T9198 T13035
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- Mar 30, 2023
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- Feb 21, 2023
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Ryan Scott authored
The data constructors for a `type data` declaration don't exist at the value level, so we don't want GHC to warn users to match on them. Fixes #22964.
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- Dec 14, 2022
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We were missing a call to `decideBangHood` in the pattern-match checker. There is another call in `matchWrapper.mk_eqn_info` which seems redundant but really is not; see `Note [Desugaring -XStrict matches in Pmc]`. Fixes #21761.
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- Nov 25, 2022
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Before this patch, GHC unconditionally printed ticks before promoted data constructors: ghci> type T = True -- unticked (user-written) ghci> :kind! T T :: Bool = 'True -- ticked (compiler output) After this patch, GHC prints ticks only when necessary: ghci> type F = False -- unticked (user-written) ghci> :kind! F F :: Bool = False -- unticked (compiler output) ghci> data False -- introduce ambiguity ghci> :kind! F F :: Bool = 'False -- ticked by necessity (compiler output) The old behavior can be enabled by -fprint-redundant-promotion-ticks. Summary of changes: * Rename PrintUnqualified to NamePprCtx * Add QueryPromotionTick to it * Consult the GlobalRdrEnv to decide whether to print a tick (see mkPromTick) * Introduce -fprint-redundant-promotion-ticks Co-authored-by:Artyom Kuznetsov <hi@wzrd.ht>
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- Nov 11, 2022
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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
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- Sep 13, 2022
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- Aug 26, 2022
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This patch massages the keys used in the `TmOracle` `CoreMap` to ensure that dictionaries of coherent classes give the same key. That is, whenever we have an expression we want to insert or lookup in the `TmOracle` `CoreMap`, we first replace any dictionary `$dict_abcd :: ct` with a value of the form `error @ct`. This allows us to common-up view pattern functions with required constraints whose arguments differed only in the uniques of the dictionaries they were provided, thus fixing #21662. This is a rather ad-hoc change to the keys used in the `TmOracle` `CoreMap`. In the long run, we would probably want to use a different representation for the keys instead of simply using `CoreExpr` as-is. This more ambitious plan is outlined in #19272. Fixes #21662 Updates unix submodule
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- Jul 22, 2022
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The way record updates are typechecked/desugared changed in MR !7981. Because we desugar in the typechecker to a simple case expression, the pattern match checker becomes able to spot the long-distance information and avoid emitting an incorrect pattern match warning. Fixes #21360
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- Jun 06, 2022
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This commit fixes #20312 It deprecates "TypeInType" extension according to the following proposal: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0083-no-type-in-type.rst It has been already implemented. The migration strategy: 1. Disable TypeInType 2. Enable both DataKinds and PolyKinds extensions Metric Decrease: T16875
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- May 25, 2022
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This patch typechecks record updates by desugaring them inside the typechecker using the HsExpansion mechanism, and then typechecking this desugared result. Example: data T p q = T1 { x :: Int, y :: Bool, z :: Char } | T2 { v :: Char } | T3 { x :: Int } | T4 { p :: Float, y :: Bool, x :: Int } | T5 The record update `e { x=e1, y=e2 }` desugars as follows e { x=e1, y=e2 } ===> let { x' = e1; y' = e2 } in case e of T1 _ _ z -> T1 x' y' z T4 p _ _ -> T4 p y' x' The desugared expression is put into an HsExpansion, and we typecheck that. The full details are given in Note [Record Updates] in GHC.Tc.Gen.Expr. Fixes #2595 #3632 #10808 #10856 #16501 #18311 #18802 #21158 #21289 Updates haddock submodule
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- Apr 01, 2022
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Jakob Brünker authored
This commit implements proposal 302: \cases - Multi-way lambda expressions. This adds a new expression heralded by \cases, which works exactly like \case, but can match multiple apats instead of a single pat. Updates submodule haddock to support the ITlcases token. Closes #20768
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- Feb 26, 2022
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- Jan 17, 2022
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sheaf authored
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- Jan 03, 2022
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- Nov 17, 2021
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Since 8.10, when formatting a pattern match warning, we'd case split on a wildcard match such as ```hs foo :: [a] -> [a] foo [] = [] foo xs = ys where (_, ys@(_:_)) = splitAt 0 xs -- Pattern match(es) are non-exhaustive -- In a pattern binding: -- Patterns not matched: -- ([], []) -- ((_:_), []) ``` But that's quite verbose and distracts from which part of the pattern was actually the inexhaustive one. We'd prefer a wildcard for the first pair component here, like it used to be in GHC 8.8. On the other hand, case splitting is pretty handy for `-XEmptyCase` to know the different constructors we could've matched on: ```hs f :: Bool -> () f x = case x of {} -- Pattern match(es) are non-exhaustive -- In a pattern binding: -- Patterns not matched: -- False -- True ``` The solution is to communicate that we want a top-level case split to `generateInhabitingPatterns` for `-XEmptyCase`, which is exactly what this patch arranges. Details in `Note [Case split inhabiting patterns]`. Fixes #20642.
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- Nov 07, 2021
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Although I thought we were already set to handle unlifted datatypes correctly, it appears we weren't. #20631 showed that it's wrong to assume `vi_bot=IsNotBot` for `VarInfo`s of unlifted types from their inception if we don't follow up with an inhabitation test to see if there are any habitable constructors left. We can't trigger the test from `emptyVarInfo`, so now we instead fail early in `addBotCt` for variables of unlifted types. Fixed #20631.
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- Aug 15, 2021
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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
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- Jun 03, 2021
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This commit converts a bunch of HsToCore (Ds) messages to use the new GHC's diagnostic message infrastructure. In particular the DsMessage type has been expanded with a lot of type constructors, each encapsulating a particular error and warning emitted during desugaring. Due to the fact that levity polymorphism checking can happen both at the Ds and at the TcRn level, a new `TcLevityCheckDsMessage` constructor has been added to the `TcRnMessage` type.
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- Apr 29, 2021
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This gives a more precise type signature to `magicDict` as proposed in #16646. In addition, this replaces the constant-folding rule for `magicDict` in `GHC.Core.Opt.ConstantFold` with a special case in the desugarer in `GHC.HsToCore.Expr.dsHsWrapped`. I have also renamed `magicDict` to `withDict` in light of the discussion in https://mail.haskell.org/pipermail/ghc-devs/2021-April/019833.html. All of this has the following benefits: * `withDict` is now more type safe than before. Moreover, if a user applies `withDict` at an incorrect type, the special-casing in `dsHsWrapped` will now throw an error message indicating what the user did incorrectly. * `withDict` can now work with classes that have multiple type arguments, such as `Typeable @k a`. This means that `Data.Typeable.Internal.withTypeable` can now be implemented in terms of `withDict`. * Since the special-casing for `withDict` no longer needs to match on the structure of the expression passed as an argument to `withDict`, it no longer cares about the presence or absence of `Tick`s. In effect, this obsoletes the fix for #19667. The new `T16646` test case demonstrates the new version of `withDict` in action, both in terms of `base` functions defined in terms of `withDict` as well as in terms of functions from the `reflection` and `singletons` libraries. The `T16646Fail` test case demonstrates the error message that GHC throws when `withDict` is applied incorrectly. This fixes #16646. By adding more tests for `withDict`, this also fixes #19673 as a side effect.
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- Apr 02, 2021
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It appears that the issue has already been fixed. Judging by the use of a pattern synonym with a provided constraint, my bet is on 1793ca9d. Fixes #19622.
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- Mar 14, 2021
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This patch makes `guessConLikeUnivTyArgsFromResTy` consider required Thetas of PatSynCons, by treating them as Wanted constraints to be discharged with the constraints from the Nabla's TyState and saying "does not match the match type" if the Wanted constraints are unsoluble. It calls out into a new function `GHC.Tc.Solver.tcCheckWanteds` to do so. In pushing the failure logic around call sites of `initTcDsForSolver` inside it by panicking, I realised that there was a bunch of dead code surrounding `pmTopMoraliseType`: I was successfully able to delete the `NoChange` data constructor of `TopNormaliseTypeResult`. The details are in `Note [Matching against a ConLike result type]` and `Note [Instantiating a ConLike]. The regression test is in `T19475`. It's pretty much a fork of `T14422` at the moment. Co-authored-by:Cale Gibbard <cgibbard@gmail.com>
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- Mar 10, 2021
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- Mar 07, 2021
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Ben Gamari authored
This implements the BoxedRep proposal, refactoring the `RuntimeRep` hierarchy from: ```haskell data RuntimeRep = LiftedPtrRep | UnliftedPtrRep | ... ``` to ```haskell data RuntimeRep = BoxedRep Levity | ... data Levity = Lifted | Unlifted ``` Updates binary, haddock submodules. Closes #17526. Metric Increase: T12545
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- Mar 05, 2021
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Commit 2a942285 dramatically simplified the implementation and improved the performance of COMPLETE sets while making them applicable in more scenarios at the same time. But it turned out that there was a change in semantics that (to me unexpectedly) broke users' expectations (see #14422): They relied on the "type signature" of a COMPLETE pragma to restrict the scrutinee types of a pattern match for which they are applicable. This patch brings back that filtering, so the semantics is the same as it was in GHC 9.0. See the updated Note [Implementation of COMPLETE pragmas]. There are a few testsuite output changes (`completesig13`, `T14422`) which assert this change. Co-authored-by:
Sebastian Graf <sebastian.graf@kit.edu>
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- Mar 01, 2021
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Consider (`T18610`): ```hs f :: Bool -> Int f x = case (x, x) of (True, True) -> 1 (False, False) -> 2 (True, False) -> 3 -- Warning: Redundant ``` The third clause will be flagged as redundant. Nevertheless, the programmer might intend to keep the clause in order to avoid bitrot. After this patch, the programmer can write ```hs g :: Bool -> Int g x = case (x, x) of (True, True) -> 1 (False, False) -> 2 (True, False) | GHC.Exts.considerAccessible -> 3 -- No warning ``` And won't be bothered any longer. See also `Note [considerAccessible]` and the updated entries in the user's guide. Fixes #18610 and #19228.
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- Feb 27, 2021
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When desugaring large overloaded literals we now avoid computing the `Rational` value. Instead prefering to store the significant and exponent as given where reasonable and possible. See Note [FractionalLit representation] for details.
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- Feb 06, 2021
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