[Git][ghc/ghc][master] Valid hole fits: don't suggest unsafeCoerce (#17940)

[Marge Bot (@marge-bot)]

Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC


Commits:
a0ccef7a by Krzysztof Gogolewski at 2023-09-08T04:05:42-04:00
Valid hole fits: don't suggest unsafeCoerce (#17940)

- - - - -


4 changed files:

- compiler/GHC/Tc/Errors/Hole.hs
- + testsuite/tests/typecheck/should_fail/T17940.hs
- + testsuite/tests/typecheck/should_fail/T17940.stderr
- testsuite/tests/typecheck/should_fail/all.T


Changes:

=====================================
compiler/GHC/Tc/Errors/Hole.hs
=====================================
@@ -48,7 +48,7 @@ import GHC.Core.DataCon
 import GHC.Core.Predicate( Pred(..), classifyPredType, eqRelRole )
 import GHC.Types.Name
 import GHC.Types.Name.Reader
-import GHC.Builtin.Names ( gHC_ERR )
+import GHC.Builtin.Names ( gHC_ERR, uNSAFE_COERCE )
 import GHC.Types.Id
 import GHC.Types.Var.Set
 import GHC.Types.Var.Env
@@ -823,8 +823,8 @@ tcFilterHoleFits limit typed_hole ht@(hole_ty, _) candidates =
                               _ -> discard_it }
                _ -> discard_it }
         where
-          -- We want to filter out undefined and the likes from GHC.Err
-          not_trivial id = nameModule_maybe (idName id) /= Just gHC_ERR
+          -- We want to filter out undefined and the likes from GHC.Err (#17940)
+          not_trivial id = nameModule_maybe (idName id) `notElem` [Just gHC_ERR, Just uNSAFE_COERCE]
 
           lookup :: HoleFitCandidate -> TcM (Maybe (Id, Type))
           lookup (IdHFCand id) = return (Just (id, idType id))


=====================================
testsuite/tests/typecheck/should_fail/T17940.hs
=====================================
@@ -0,0 +1,7 @@
+{-# LANGUAGE MagicHash #-}
+module T17940 where
+
+import GHC.Exts
+
+index# :: ByteArray# -> Int# -> Word8#
+index# a i = _ (indexWord8Array# a i)


=====================================
testsuite/tests/typecheck/should_fail/T17940.stderr
=====================================
@@ -0,0 +1,17 @@
+
+T17940.hs:7:14: error: [GHC-88464]
+    • Found hole: _ :: Word8# -> Word8#
+    • In the expression: _ (indexWord8Array# a i)
+      In an equation for ‘index#’: index# a i = _ (indexWord8Array# a i)
+    • Relevant bindings include
+        i :: Int# (bound at T17940.hs:7:10)
+        a :: ByteArray# (bound at T17940.hs:7:8)
+        index# :: ByteArray# -> Int# -> Word8# (bound at T17940.hs:7:1)
+      Valid hole fits include
+        notWord8# :: Word8# -> Word8#
+          (imported from ‘GHC.Exts’ at T17940.hs:4:1-15
+           (and originally defined in ‘GHC.Prim’))
+        coerce :: forall a b. Coercible a b => a -> b
+          with coerce @Word8# @Word8#
+          (imported from ‘GHC.Exts’ at T17940.hs:4:1-15
+           (and originally defined in ‘GHC.Prim’))


=====================================
testsuite/tests/typecheck/should_fail/all.T
=====================================
@@ -700,3 +700,4 @@ test('T22684', normal, compile_fail, [''])
 test('T23514a', normal, compile_fail, [''])
 test('T22478c', normal, compile_fail, [''])
 test('T23776', normal, compile, ['']) # to become an error in GHC 9.12
+test('T17940', normal, compile_fail, [''])



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/a0ccef7a44def216da92a0436249789c363a6f91

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/a0ccef7a44def216da92a0436249789c363a6f91
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