Simon Peyton Jones pushed to branch wip/T26115 at Glasgow Haskell Compiler / GHC Commits: 8b731e3c by Matthew Pickering at 2025-07-21T13:36:43-04:00 level imports: Fix infinite loop with cyclic module imports I didn't anticipate that downsweep would run before we checked for cyclic imports. Therefore we need to use the reachability function which handles cyclic graphs. Fixes #26087 - - - - - d751a9f1 by Pierre Thierry at 2025-07-21T13:37:28-04:00 Fix documentation about deriving from generics - - - - - 460ad5b1 by Simon Peyton Jones at 2025-07-22T16:04:11+01:00 Renaming around predicate types .. we were (as it turned out) abstracting over type-class selectors in SPECIALISATION rules! Wibble isEqPred - - - - - 2f87efe4 by Simon Peyton Jones at 2025-07-22T16:04:11+01:00 Refactor of Specialise.hs This patch just tidies up `specHeader` a bit, removing one of its many results, and adding some comments. No change in behaviour. Also add a few more `HasDebugCallStack` contexts. - - - - - 36c79389 by Simon Peyton Jones at 2025-07-22T16:04:11+01:00 Improve treatment of SPECIALISE pragmas -- again! This MR does another major refactor of the way that SPECIALISE pragmas work, to fix #26115, #26116, #26117. * We now /always/ solve forall-constraints in an all-or-nothing way. See Note [Solving a Wanted forall-constraint] in GHC.Tc.Solver.Solve This means we might have unsolved quantified constraints, which need to be reported. See `inert_insts` in `getUnsolvedInerts`. * I refactored the short-cut solver for type classes to work by recursively calling the solver rather than by having a little baby solver that kept being not clever enough. See Note [Shortcut solving] in GHC.Tc.Solver.Dict * I totally rewrote the desugaring of SPECIALISE pragmas, again. The new story is in Note [Desugaring new-form SPECIALISE pragmas] in GHC.HsToCore.Binds Both old-form and new-form SPECIALISE pragmas now route through the same function `dsSpec_help`. The tricky function `decomposeRuleLhs` is now used only for user-written RULES, not for SPECIALISE pragmas. * I improved `solveOneFromTheOther` to account for rewriter sets. Previously it would solve a non-rewritten dict from a rewritten one. For equalities we were already dealing with this, in Some incidental refactoring * A small refactor: `ebv_tcvs` in `EvBindsBar` now has a list of coercions, rather than a set of tyvars. We just delay taking the free vars. * GHC.Core.FVs.exprFVs now returns /all/ free vars. Use `exprLocalFVs` for Local vars. Reason: I wanted another variant for /evidence/ variables. * Ues `EvId` in preference to `EvVar`. (Evidence variables are always Ids.) Rename `isEvVar` to `isEvId`. * I moved `inert_safehask` out of `InertCans` and into `InertSet` where it more properly belongs. Compiler-perf changes: * There was a palpable bug (#26117) which this MR fixes in newWantedEvVar, which bypassed all the subtle overlapping-Given and shortcutting logic. (See the new `newWantedEvVar`.) Fixing this but leads to extra dictionary bindings; they are optimised away quickly but they made CoOpt_Read allocate 3.6% more. * Hpapily T15164 improves. * The net compiler-allocation change is 0.0% Metric Decrease: T15164 Metric Increase: CoOpt_Read T12425 - - - - - f60424fa by Simon Peyton Jones at 2025-07-22T16:27:24+01:00 Solve forall-constraints immediately, or not at all This MR refactors the constraint solver to solve forall-constraints immediately, rather than emitting an implication constraint to be solved later. The most immediate motivation was that when solving quantified constraints in SPECIALISE pragmas, we really really don't want to leave behind half- solved implications. Also it's in tune with the approach of the new short-cut solver, which recursively invokes the solver. It /also/ saves quite a bit of plumbing; e.g - The `wl_implics` field of `WorkList` is gone, - The types of `solveSimpleWanteds` and friends are simplified. - An EvFun contains binding, rather than an EvBindsVar ref-cell that will in the future contain bindings. That makes `evVarsOfTerm` simpler. Much nicer. It also improves error messages a bit. All described in Note [Solving a Wanted forall-constraint] in GHC.Tc.Solver.Solve. One tiresome point: in the tricky case of `inferConstraintsCoerceBased` we make a forall-constraint. This we /do/ want to partially solve, so we can infer a suitable context. (I'd be quite happy to force the user to write a context, bt I don't want to change behavior.) So we want to generate an /implication/ constraint in `emitPredSpecConstraints` rather than a /forall-constraint/ as we were doing before. Discussed in (WFA3) of the above Note. Incidental refactoring * `GHC.Tc.Deriv.Infer.inferConstraints` was consulting the state monad for the DerivEnv that the caller had just consulted. Nicer to pass it as an argument I think, so I have done that. No change in behaviour. - - - - - f1286410 by Simon Peyton Jones at 2025-07-22T16:27:24+01:00 Remove duplicated code in Ast.hs for evTermFreeVars This is just a tidy up. - - - - - 59d468c6 by Simon Peyton Jones at 2025-07-22T16:27:24+01:00 Small tc-tracing changes only - - - - - 83 changed files: - compiler/GHC/Core.hs - compiler/GHC/Core/FVs.hs - compiler/GHC/Core/Make.hs - compiler/GHC/Core/Opt/Arity.hs - compiler/GHC/Core/Opt/Specialise.hs - compiler/GHC/Core/Predicate.hs - compiler/GHC/Core/Rules.hs - compiler/GHC/Core/Subst.hs - compiler/GHC/Core/TyCo/Rep.hs - compiler/GHC/Core/Unfold/Make.hs - compiler/GHC/Core/Utils.hs - compiler/GHC/HsToCore/Binds.hs - compiler/GHC/HsToCore/Errors/Ppr.hs - compiler/GHC/HsToCore/Pmc/Solver/Types.hs - compiler/GHC/Iface/Ext/Ast.hs - compiler/GHC/Tc/Deriv.hs - compiler/GHC/Tc/Deriv/Infer.hs - compiler/GHC/Tc/Deriv/Utils.hs - compiler/GHC/Tc/Errors.hs - compiler/GHC/Tc/Errors/Ppr.hs - compiler/GHC/Tc/Gen/App.hs - compiler/GHC/Tc/Gen/Expr.hs - compiler/GHC/Tc/Gen/Pat.hs - compiler/GHC/Tc/Gen/Sig.hs - compiler/GHC/Tc/Solver.hs - compiler/GHC/Tc/Solver/Default.hs - compiler/GHC/Tc/Solver/Dict.hs - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Tc/Solver/InertSet.hs - compiler/GHC/Tc/Solver/Monad.hs - compiler/GHC/Tc/Solver/Rewrite.hs - compiler/GHC/Tc/Solver/Solve.hs - + compiler/GHC/Tc/Solver/Solve.hs-boot - compiler/GHC/Tc/Solver/Types.hs - compiler/GHC/Tc/TyCl/PatSyn.hs - compiler/GHC/Tc/Types/Constraint.hs - compiler/GHC/Tc/Types/Evidence.hs - compiler/GHC/Tc/Types/Origin.hs - compiler/GHC/Tc/Utils/Monad.hs - compiler/GHC/Tc/Utils/TcMType.hs - compiler/GHC/Tc/Utils/TcType.hs - compiler/GHC/Tc/Utils/Unify.hs - compiler/GHC/Tc/Validity.hs - compiler/GHC/Tc/Zonk/Type.hs - compiler/GHC/Types/Var.hs - compiler/GHC/Unit/Module/Graph.hs - libraries/base/src/GHC/Generics.hs - testsuite/tests/deriving/should_compile/T20815.hs - testsuite/tests/deriving/should_fail/T12768.stderr - testsuite/tests/deriving/should_fail/T1496.stderr - testsuite/tests/deriving/should_fail/T5498.stderr - testsuite/tests/deriving/should_fail/T7148.stderr - testsuite/tests/deriving/should_fail/T7148a.stderr - testsuite/tests/hiefile/should_run/HieQueries.stdout - testsuite/tests/impredicative/T17332.stderr - testsuite/tests/quantified-constraints/T15290a.stderr - testsuite/tests/quantified-constraints/T19690.stderr - testsuite/tests/quantified-constraints/T19921.stderr - testsuite/tests/quantified-constraints/T21006.stderr - testsuite/tests/roles/should_fail/RolesIArray.stderr - + testsuite/tests/simplCore/should_compile/T26115.hs - + testsuite/tests/simplCore/should_compile/T26115.stderr - + testsuite/tests/simplCore/should_compile/T26116.hs - + testsuite/tests/simplCore/should_compile/T26116.stderr - + testsuite/tests/simplCore/should_compile/T26117.hs - + testsuite/tests/simplCore/should_compile/T26117.stderr - testsuite/tests/simplCore/should_compile/all.T - + testsuite/tests/splice-imports/T26087.stderr - + testsuite/tests/splice-imports/T26087A.hs - + testsuite/tests/splice-imports/T26087B.hs - testsuite/tests/splice-imports/all.T - testsuite/tests/typecheck/should_compile/T12427a.stderr - testsuite/tests/typecheck/should_compile/T23171.hs - testsuite/tests/typecheck/should_compile/TcSpecPragmas.stderr - testsuite/tests/typecheck/should_fail/T14605.hs - testsuite/tests/typecheck/should_fail/T14605.stderr - testsuite/tests/typecheck/should_fail/T15801.stderr - testsuite/tests/typecheck/should_fail/T18640a.stderr - testsuite/tests/typecheck/should_fail/T18640b.stderr - testsuite/tests/typecheck/should_fail/T19627.stderr - testsuite/tests/typecheck/should_fail/T21530b.stderr - testsuite/tests/typecheck/should_fail/T22912.stderr - testsuite/tests/typecheck/should_fail/tcfail174.stderr The diff was not included because it is too large. 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