[Git][ghc/ghc][wip/T22194-flags] 8 commits: GHCi.RemoteTypes: fix doc and avoid unsafeCoerce (#23201)

Simon Peyton Jones (@simonpj) gitlab at gitlab.haskell.org
Wed Apr 5 20:21:38 UTC 2023 


Simon Peyton Jones pushed to branch wip/T22194-flags at Glasgow Haskell Compiler / GHC


Commits:
eed0d930 by Sylvain Henry at 2023-04-04T11:09:15-04:00
GHCi.RemoteTypes: fix doc and avoid unsafeCoerce (#23201)

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071139c3 by Ryan Scott at 2023-04-04T11:09:51-04:00
Make INLINE pragmas for pattern synonyms work with TH

Previously, the code for converting `INLINE <name>` pragmas from TH splices
used `vNameN`, which assumed that `<name>` must live in the variable namespace.
Pattern synonyms, on the other hand, live in the constructor namespace. I've
fixed the issue by switching to `vcNameN` instead, which works for both the
variable and constructor namespaces.

Fixes #23203.

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7c16f3be by Krzysztof Gogolewski at 2023-04-04T17:13:00-04:00
Fix unification with oversaturated type families

unify_ty was incorrectly saying that F x y ~ T x are surely apart,
where F x y is an oversaturated type family and T x is a tyconapp.
As a result, the simplifier dropped a live case alternative (#23134).

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c165f079 by sheaf at 2023-04-04T17:13:40-04:00
Add testcase for #23192

This issue around solving of constraints arising from superclass
expansion using other constraints also borned from superclass expansion
was the topic of commit aed1974e. That commit made sure we don't emit
a "redundant constraint" warning in a situation in which removing the
constraint would cause errors.

Fixes #23192

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f0395a5b by Simon Peyton Jones at 2023-04-05T21:23:17+01:00
Major refactor in the handling of equality constraints

This MR substantially refactors the way in which the constraint
solver deals with equality constraints.  The big thing is:

* Intead of a pipeline in which we /first/ canonicalise and /then/
  interact (the latter including performing unification) the two steps
  are more closely integreated into one.  That avoids the current
  rather indirect communication between the two steps.

The proximate cause for this refactoring is fixing #22194, which involve
solving   [W] alpha[2] ~ Maybe (F beta[4])
by doing this:
          alpha[2] := Maybe delta[2]
          [W] delta[2] ~ F beta[4]
That is, we don't promote beta[4]!  This is very like introducing a cycle
breaker, and was very awkward to do before, but now it is all nice.
See GHC.Tc.Utils.Unify Note [Promotion and level-checking] and
Note [Family applications in canonical constraints].

The big change is this:

* Several canonicalisation checks (occurs-check, cycle-breaking,
  checking for concreteness) are combined into one new function:
     GHC.Tc.Utils.Unify.checkTyEqRhs

  This function is controlled by `TyEqFlags`, which says what to do
  for foralls, type families etc.

* `canEqCanLHSFinish` now sees if unification is possible, and if so,
  actually does it: see `canEqCanLHSFinish_try_unification`.

There are loads of smaller changes:

* The on-the-fly unifier `GHC.Tc.Utils.Unify.unifyType` has a
  cheap-and-cheerful version of `checkTyEqRhs`, called
  `simpleUnifyCheck`.  If `simpleUnifyCheck` succeeds, it can unify,
  otherwise it defers by emitting a constraint. This is simpler than
  before.

* I simplified the swapping code in `GHC.Tc.Solver.Equality.canEqCanLHS`.
  Especially the nasty stuff involving `swap_for_occurs` and
  `canEqTyVarFunEq`.  Much nicer now.  See
      Note [Orienting TyVarLHS/TyFamLHS]
      Note [Orienting TyFamLHS/TyFamLHS]

* Added `cteSkolemOccurs`, `cteConcrete`, and `cteCoercionHole` to the
  problems that can be discovered by `checkTyEqRhs`.

* I fixed #23199 `pickQuantifiablePreds`, which actually allows GHC to
  to accept both cases in #22194 rather than rejecting both.

Yet smaller:

* Added a `synIsConcrete` flag to `SynonymTyCon` (alongside `synIsFamFree`)
  to reduce the need for synonym expansion when checking concreteness.
  Use it in `isConcreteType`.

* Renamed `isConcrete` to `isConcreteType`

* Defined `GHC.Core.TyCo.FVs.isInjectiveInType` as a more efficient
  way to find if a particular type variable is used injectively than
  finding all the injective variables.  It is called in
  `GHC.Tc.Utils.Unify.definitely_poly`, which in turn is used quite a
  lot.

* Moved `rewriterView` to `GHC.Core.Type`, so we can use it from the
  constraint solver.

Fixes #22194, #23199

Compile times decrease by an average of 0.1%; but there is a 7.4%
drop in compiler allocation on T15703.

Metric Decrease:
    T15703

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b39504b9 by Simon Peyton Jones at 2023-04-05T21:23:17+01:00
Add some documentation about redundant constraints

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ca5971bd by Simon Peyton Jones at 2023-04-05T21:23:17+01:00
Make approximateWC a bit cleverer

This MR fixes
  #23224: making approximateWC more clever
  #23223: misleading error with partial type signatuers

See the long notes:

* Note [ApproximateWC] in GHC.Tc.Solver
* Note [Partial type signatures and the MR] in GHC.Tc.Gen.Bind

All this is delicate and ad-hoc -- but it /has/ to be: we are
talking about inferring a type for a binding in the presence of
GADTs, type families and whatnot: known difficult territory.
We just try as hard as we can.

The test #19106 becomes an error again, but with a better error
message; it's a very subtle case, conjured out of Richard's brain.

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96d5d693 by Simon Peyton Jones at 2023-04-05T21:23:17+01:00
Wibble partial type sigs

Needs better documentation

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19 changed files:

- compiler/GHC/Core/Opt/Simplify/Iteration.hs
- compiler/GHC/Core/TyCo/FVs.hs
- compiler/GHC/Core/TyCo/Rep.hs
- compiler/GHC/Core/TyCon.hs
- compiler/GHC/Core/Type.hs
- compiler/GHC/Core/Type.hs-boot
- compiler/GHC/Core/Unify.hs
- compiler/GHC/Data/Bag.hs
- compiler/GHC/Data/Maybe.hs
- compiler/GHC/Hs/Expr.hs
- compiler/GHC/Runtime/Interpreter.hs
- compiler/GHC/Tc/Errors.hs
- compiler/GHC/Tc/Errors/Ppr.hs
- compiler/GHC/Tc/Gen/Bind.hs
- compiler/GHC/Tc/Gen/Sig.hs
- compiler/GHC/Tc/Solver.hs
- compiler/GHC/Tc/Solver/Equality.hs
- compiler/GHC/Tc/Solver/InertSet.hs
- compiler/GHC/Tc/Solver/Monad.hs


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