[Git][ghc/ghc][wip/T23070-unify] 3 commits: Add the Unsatisfiable class

[Simon Peyton Jones (@simonpj)]

Simon Peyton Jones pushed to branch wip/T23070-unify at Glasgow Haskell Compiler / GHC


Commits:
57277662 by sheaf at 2023-04-29T20:23:06+02:00
Add the Unsatisfiable class

This commit implements GHC proposal #433, adding the Unsatisfiable
class to the GHC.TypeError module. This provides an alternative to
TypeError for which error reporting is more predictable: we report it
when we are reporting unsolved Wanted constraints.

Fixes #14983 #16249 #16906 #18310 #20835

- - - - -
00a8a5ff by Torsten Schmits at 2023-04-30T03:45:09-04:00
Add structured error messages for GHC.Rename.Names

Tracking ticket: #20115

MR: !10336

This converts uses of `mkTcRnUnknownMessage` to newly added constructors
of `TcRnMessage`.

- - - - -
d38c4d93 by Simon Peyton Jones at 2023-04-30T22:45:31+01:00
Use the eager unifier in the constraint solver

This patch continues the refactoring of the constraint solver
described in #23070.

The Big Deal in this patch is to call the regular, eager unifier from the
constraint solver, when we want to create new equalities. This
replaces the existing, unifyWanted which amounted to
yet-another-unifier, so it reduces duplication of a rather subtle
piece of technology. See

  * Note [The eager unifier] in GHC.Tc.Utils.Unify
  * GHC.Tc.Solver.Monad.wrapUnifierTcS

I did lots of other refactoring along the way

* I simplified the treatment of right hand sides that contain CoercionHoles.
  Now, a constraint that contains a hetero-kind CoercionHole is non-canonical,
  and cannot be used for rewriting or unification alike.  This required me
  to add the ch_hertero_kind flag to CoercionHole, with consequent knock-on
  effects. See wrinkle (2) of `Note [Equalities with incompatible kinds]` in
  GHC.Tc.Solver.Equality.

* I refactored the StopOrContinue type to add StartAgain, so that after a
  fundep improvement (for example) we can simply start the pipeline again.

* I got rid of the unpleasant (and inefficient) rewriterSetFromType/Co functions.
  With Richard I concluded that they are never needed.

* I discovered Wrinkle (W1) in Note [Wanteds rewrite Wanteds] in
  GHC.Tc.Types.Constraint, and therefore now prioritise non-rewritten equalities.

Quite a few error messages change, I think always for the better.

Compiler runtime stays about the same, with one outlier: a 17% improvement in T17836

Metric Decrease:
    T17836
    T18223

- - - - -


27 changed files:

- compiler/GHC/Builtin/Names.hs
- compiler/GHC/Builtin/Types.hs
- compiler/GHC/Builtin/Types/Prim.hs
- compiler/GHC/Core/Coercion.hs
- compiler/GHC/Core/Coercion.hs-boot
- compiler/GHC/Core/Predicate.hs
- compiler/GHC/Core/Reduction.hs
- compiler/GHC/Core/TyCo/Rep.hs
- compiler/GHC/Core/TyCo/Subst.hs
- compiler/GHC/Core/Type.hs
- compiler/GHC/Data/Bag.hs
- compiler/GHC/HsToCore.hs
- compiler/GHC/Rename/Names.hs
- compiler/GHC/Tc/Errors.hs
- compiler/GHC/Tc/Errors/Ppr.hs
- compiler/GHC/Tc/Errors/Types.hs
- compiler/GHC/Tc/Gen/HsType.hs
- compiler/GHC/Tc/Gen/Rule.hs
- compiler/GHC/Tc/Instance/Class.hs
- compiler/GHC/Tc/Instance/FunDeps.hs
- compiler/GHC/Tc/Plugin.hs
- compiler/GHC/Tc/Solver.hs
- compiler/GHC/Tc/Solver/Canonical.hs
- compiler/GHC/Tc/Solver/Dict.hs
- compiler/GHC/Tc/Solver/Equality.hs
- compiler/GHC/Tc/Solver/InertSet.hs
- compiler/GHC/Tc/Solver/Interact.hs


The diff was not included because it is too large.


View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/68b73ac0a880e73cbc990acd1464848600c9703b...d38c4d93c18b531683de19e2057b476d7fd89ca1

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/68b73ac0a880e73cbc990acd1464848600c9703b...d38c4d93c18b531683de19e2057b476d7fd89ca1
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