Simon Peyton Jones pushed to branch wip/T25440 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 - - - - - 1a6a4b1e by Simon Peyton Jones at 2025-04-18T17:42:14+01:00 Track rewriter sets more accurately in constraint solving The key change, which fixed #25440, is to call `recordRewriter` in GHC.Tc.Solver.Rewrite.rewrite_exact_fam_app. This missing call meant that we were secretly rewriting a Wanted with a Wanted, but not really noticing; and that led to a very bad error message, as you can see in the ticket. But of course that led me into rabbit hole of other refactoring around the RewriteSet code: * Improve Notes [Wanteds rewrite Wanteds] * Zonk the RewriterSet in `zonkCtEvidence` rather than only in GHC.Tc.Errors. This is tidier anyway (e.g. de-clutters debug output), and helps with the next point. * In GHC.Tc.Solver.Equality.inertsCanDischarge, don't replace a constraint with no rewriters with an equal constraint that has many. See See (CE4) in Note [Combining equalities] * Move zonkRewriterSet and friends from GHC.Tc.Zonk.Type into GHC.Tc.Zonk.TcType, where they properly belong. A handful of tests get better error messages. For some reason T24984 gets 12% less compiler allocation -- good Metric Decrease: T24984 - - - - - 33 changed files: - compiler/GHC/IfaceToCore.hs - compiler/GHC/Tc/Errors.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/Default.hs - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Tc/Solver/Monad.hs - compiler/GHC/Tc/Solver/Rewrite.hs - compiler/GHC/Tc/Types/Constraint.hs - compiler/GHC/Tc/Utils/Env.hs - compiler/GHC/Tc/Utils/TcMType.hs - compiler/GHC/Tc/Zonk/TcType.hs - compiler/GHC/Tc/Zonk/Type.hs - compiler/GHC/Types/DefaultEnv.hs - libraries/template-haskell/Language/Haskell/TH/Syntax.hs - libraries/template-haskell/changelog.md - + 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/indexed-types/should_fail/T3330c.stderr - testsuite/tests/indexed-types/should_fail/T4174.stderr - testsuite/tests/indexed-types/should_fail/T8227.stderr - testsuite/tests/interface-stability/template-haskell-exports.stdout - testsuite/tests/linters/notes.stdout - testsuite/tests/module/mod58.stderr - testsuite/tests/typecheck/should_fail/T18851.stderr The diff was not included because it is too large. View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/be011dacff5ef7a07d59ecd52ef5c6e... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/be011dacff5ef7a07d59ecd52ef5c6e... You're receiving this email because of your account on gitlab.haskell.org.