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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2022-11-02 18:06:35 +0000 |
|---|---|---|
| committer | Simon Peyton Jones <simon.peytonjones@gmail.com> | 2022-11-25 22:31:27 +0000 |
| commit | d10dc6bdade0fdae879e5869038ce8378c2ce84f (patch) | |
| tree | e386af2c82a9e64b7c72275c2b7e9af36bea7f11 /testsuite/tests/typecheck | |
| parent | 13d627bbd0bc3dd30d672de341aa7f471be0aa2c (diff) | |
| download | haskell-d10dc6bdade0fdae879e5869038ce8378c2ce84f.tar.gz | |
Fix decomposition of TyConAppswip/T22331
Ticket #22331 showed that we were being too eager to decompose
a Wanted TyConApp, leading to incompleteness in the solver.
To understand all this I ended up doing a substantial rewrite
of the old Note [Decomposing equalities], now reborn as
Note [Decomposing TyConApp equalities]. Plus rewrites of other
related Notes.
The actual fix is very minor and actually simplifies the code: in
`can_decompose` in `GHC.Tc.Solver.Canonical.canTyConApp`, we now call
`noMatchableIrreds`. A closely related refactor: we stop trying to
use the same "no matchable givens" function here as in
`matchClassInst`. Instead split into two much simpler functions.
Diffstat (limited to 'testsuite/tests/typecheck')
| -rw-r--r-- | testsuite/tests/typecheck/should_compile/T22331.hs | 15 | ||||
| -rw-r--r-- | testsuite/tests/typecheck/should_compile/all.T | 1 |
2 files changed, 16 insertions, 0 deletions
diff --git a/testsuite/tests/typecheck/should_compile/T22331.hs b/testsuite/tests/typecheck/should_compile/T22331.hs new file mode 100644 index 0000000000..0454c97d7d --- /dev/null +++ b/testsuite/tests/typecheck/should_compile/T22331.hs @@ -0,0 +1,15 @@ +{-# LANGUAGE TypeFamilies #-} + +module T22331 where + +import Data.Coerce + +data family Fool a + +-- This works +joe :: Coercible (Fool a) (Fool b) => Fool a -> Fool b +joe = coerce + +-- This does not +bob :: Coercible (Fool a) (Fool b) => Fool b -> Fool a +bob = coerce diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T index 80738de7c1..46db37f854 100644 --- a/testsuite/tests/typecheck/should_compile/all.T +++ b/testsuite/tests/typecheck/should_compile/all.T @@ -850,3 +850,4 @@ test('T21951a', normal, compile, ['-Wredundant-strictness-flags']) test('T21951b', normal, compile, ['-Wredundant-strictness-flags']) test('T21550', normal, compile, ['']) test('T22310', normal, compile, ['']) +test('T22331', normal, compile, ['']) |