[Git][ghc/ghc][wip/T25965] 11 commits: Refactor Handling of Multiple Default Declarations

Simon Peyton Jones pushed to branch wip/T25965 at Glasgow Haskell Compiler / GHC Commits: e0f3ff11 by Patrick at 2025-04-17T04:31:12-04:00 Refactor Handling of Multiple Default Declarations Fixes: #25912, #25914, #25934 Previously, GHC discarded all loaded defaults (tcg_default) when local defaults were encountered during typechecking. According to the exportable-named-default proposal (sections 2.4.2 and 2.4.3), local defaults should be merged into tcg_default, retaining any defaults already present while overriding where necessary. Key Changes: * Introduce DefaultProvenance to track the origin of default declarations (local, imported, or built-in), replacing the original cd_module in ClassDefaults with cd_provenance :: DefaultProvenance. * Rename tcDefaults to tcDefaultDecls, limiting its responsibility to only converting renamed class defaults into ClassDefaults. * Add extendDefaultEnvWithLocalDefaults to merge local defaults into the environment, with proper duplication checks: - Duplicate local defaults for a class trigger an error. - Local defaults override imported or built-in defaults. * Update and add related notes: Note [Builtin class defaults], Note [DefaultProvenance]. * Add regression tests: T25912, T25914, T25934. Thanks sam and simon for the help on this patch. Co-authored-by: sheaf - - - - - 386f1854 by Teo Camarasu at 2025-04-17T04:31:55-04:00 template-haskell: Remove `addrToByteArrayName` and `addrToByteArray` These were part of the implementation of the `Lift ByteArray` instance and were errornously exported because this module lacked an explicit export list. They have no usages on Hackage. Resolves #24782 - - - - - b96e2f77 by Sylvain Henry at 2025-04-18T20:46:33-04:00 RTS: remove target info and fix host info (#24058) The RTS isn't a compiler, hence it doesn't have a target and we remove the reported target info displayed by "+RTS --info". We also fix the host info displayed by "+RTS --info": the host of the RTS is the RTS-building compiler's target, not the compiler's host (wrong when doing cross-compilation). - - - - - 6d9965f4 by Sylvain Henry at 2025-04-18T20:46:33-04:00 RTS: remove build info As per the discussion in !13967, there is no reason to tag the RTS with information about the build platform. - - - - - d52e9b3f by Vladislav Zavialov at 2025-04-18T20:47:15-04:00 Diagnostics: remove the KindMismatch constructor (#25957) The KindMismatch constructor was only used as an intermediate representation in pretty-printing. Its removal addresses a problem detected by the "codes" test case: [GHC-89223] is untested (constructor = KindMismatch) In a concious deviation from the usual procedure, the error code GHC-89223 is removed entirely rather than marked as Outdated. The reason is that it never was user-facing in the first place. - - - - - e2f2f9d0 by Vladislav Zavialov at 2025-04-20T10:53:39-04:00 Add name for -Wunusable-unpack-pragmas This warning had no name or flag and was triggered unconditionally. Now it is part of -Wdefault. In GHC.Tc.TyCl.tcTyClGroupsPass's strict mode, we now have to force-enable this warning to ensure that detection of flawed groups continues to work even if the user disables the warning with the -Wno-unusable-unpack-pragmas option. Test case: T3990c Also, the misnamed BackpackUnpackAbstractType is now called UnusableUnpackPragma. - - - - - 6caa6508 by Adam Gundry at 2025-04-20T10:54:22-04:00 Fix specialisation of incoherent instances (fixes #25883) GHC normally assumes that class constraints are canonical, meaning that the specialiser is allowed to replace one dictionary argument with another provided that they have the same type. The `-fno-specialise-incoherents` flag alters INCOHERENT instance definitions so that they will prevent specialisation in some cases, by inserting `nospec`. This commit fixes a bug in 7124e4ad76d98f1fc246ada4fd7bf64413ff2f2e, which treated some INCOHERENT instance matches as if `-fno-specialise-incoherents` was in effect, thereby unnecessarily preventing specialisation. In addition it updates the relevant `Note [Rules for instance lookup]` and adds a new `Note [Canonicity for incoherent matches]`. - - - - - 0426fd6c by Adam Gundry at 2025-04-20T10:54:23-04:00 Add regression test for #23429 - - - - - eec96527 by Adam Gundry at 2025-04-20T10:54:23-04:00 user's guide: update specification of overlapping/incoherent instances The description of the instance resolution algorithm in the user's guide was slightly out of date, because it mentioned in-scope given constraints only at the end, whereas the implementation checks for their presence before any of the other steps. This also adds a warning to the user's guide about the impact of incoherent instances on specialisation, and more clearly documents some of the other effects of `-XIncoherentInstances`. - - - - - a00eeaec by Matthew Craven at 2025-04-20T10:55:03-04:00 Fix bytecode generation for `tagToEnum# <LITERAL>` Fixes #25975. - - - - - 5c976307 by Simon Peyton Jones at 2025-04-20T22:39:35+01:00 Fix infelicities in the Specialiser On the way to #23109 (unary classes) I discovered some infelicities (or maybe tiny bugs, I forget) in the type-class specialiser. I also tripped over #25965, an outright bug in the rule matcher Specifically: * Refactor: I enhanced `wantCallsFor`, whih previously always said `True`, to discard calls of class-ops, data constructors etc. This is a bit more efficient; and it means we don't need to worry about filtering them out later. * Fix: I tidied up some tricky logic that eliminated redundant specialisations. It wasn't working correctly. See the expanded Note [Specialisations already covered], and (MP3) in Note [Specialising polymorphic dictionaries]. See also the new top-level `alreadyCovered` function, which now goes via `GHC.Core.Rules.ruleLhsIsMoreSpecific` I also added a useful Note [The (CI-KEY) invariant] * Fix #25965: fixed a tricky bug in the `go_fam_fam` in `GHC.Core.Unify.uVarOrFam`, which allows matching to succeed without binding all type varibles. I enhanced Note [Apartness and type families] some more * #25703. This ticket "just works" with -fpolymorphic-specialisation; but I was surprised that it worked! In this MR I added documentation to Note [Interesting dictionary arguments] to explain; and tests to ensure it stays fixed. - - - - - 73 changed files: - compiler/GHC/Core/InstEnv.hs - compiler/GHC/Core/Opt/Specialise.hs - compiler/GHC/Core/Rules.hs - compiler/GHC/Core/Unify.hs - compiler/GHC/Driver/Flags.hs - compiler/GHC/Driver/Session.hs - compiler/GHC/IfaceToCore.hs - compiler/GHC/StgToByteCode.hs - compiler/GHC/Tc/Errors/Ppr.hs - compiler/GHC/Tc/Errors/Types.hs - compiler/GHC/Tc/Gen/Default.hs - compiler/GHC/Tc/Gen/Export.hs - compiler/GHC/Tc/Module.hs - compiler/GHC/Tc/Solver/Dict.hs - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Tc/TyCl.hs - compiler/GHC/Tc/Utils/Env.hs - compiler/GHC/Tc/Utils/Monad.hs - compiler/GHC/Types/Basic.hs - compiler/GHC/Types/DefaultEnv.hs - compiler/GHC/Types/Error/Codes.hs - configure.ac - docs/users_guide/9.14.1-notes.rst - docs/users_guide/exts/instances.rst - docs/users_guide/using-warnings.rst - hadrian/src/Settings/Packages.hs - libraries/template-haskell/Language/Haskell/TH/Syntax.hs - libraries/template-haskell/changelog.md - rts/RtsUtils.c - testsuite/ghc-config/ghc-config.hs - + testsuite/tests/bytecode/T25975.hs - + testsuite/tests/bytecode/T25975.stdout - testsuite/tests/bytecode/all.T - + testsuite/tests/default/T25912.hs - + testsuite/tests/default/T25912.stdout - + testsuite/tests/default/T25912_helper.hs - + testsuite/tests/default/T25914.hs - + testsuite/tests/default/T25934.hs - testsuite/tests/default/all.T - testsuite/tests/default/default-fail03.stderr - testsuite/tests/diagnostic-codes/codes.stdout - testsuite/tests/interface-stability/template-haskell-exports.stdout - testsuite/tests/linters/notes.stdout - testsuite/tests/module/mod58.stderr - testsuite/tests/simplCore/should_compile/Makefile - testsuite/tests/simplCore/should_compile/T23307c.stderr - + testsuite/tests/simplCore/should_compile/T25703.hs - + testsuite/tests/simplCore/should_compile/T25703.stderr - + testsuite/tests/simplCore/should_compile/T25703a.hs - + testsuite/tests/simplCore/should_compile/T25703a.stderr - + testsuite/tests/simplCore/should_compile/T25883.hs - + testsuite/tests/simplCore/should_compile/T25883.substr-simpl - + testsuite/tests/simplCore/should_compile/T25883b.hs - + testsuite/tests/simplCore/should_compile/T25883b.substr-simpl - + testsuite/tests/simplCore/should_compile/T25883c.hs - + testsuite/tests/simplCore/should_compile/T25883c.substr-simpl - + testsuite/tests/simplCore/should_compile/T25883d.hs - + testsuite/tests/simplCore/should_compile/T25883d.stderr - + testsuite/tests/simplCore/should_compile/T25883d_import.hs - + testsuite/tests/simplCore/should_compile/T25965.hs - + testsuite/tests/simplCore/should_compile/T3990c.hs - + testsuite/tests/simplCore/should_compile/T3990c.stdout - testsuite/tests/simplCore/should_compile/all.T - testsuite/tests/simplCore/should_fail/T25672.stderr - + testsuite/tests/simplCore/should_run/T23429.hs - + testsuite/tests/simplCore/should_run/T23429.stdout - testsuite/tests/simplCore/should_run/all.T - testsuite/tests/typecheck/should_compile/T7050.stderr - testsuite/tests/typecheck/should_fail/T3966.stderr - + testsuite/tests/typecheck/should_fail/T3966b.hs - + testsuite/tests/typecheck/should_fail/T3966b.stderr - testsuite/tests/typecheck/should_fail/all.T - testsuite/tests/unboxedsums/unpack_sums_5.stderr The diff was not included because it is too large. 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