Zubin pushed to branch wip/9.12.3-backports at Glasgow Haskell Compiler / GHC Commits: 91db1d51 by Zubin Duggal at 2025-09-16T08:52:56+00:00 QuickLook: do a shape test before unifying This commit ensures we do a shape test before unifying. This ensures we don't try to unify a TyVarTv with a non-tyvar, e.g. alpha[tyv] := Int Fixes #25950 (cherry picked from commit a4c0c8d32e8c29364062b199abe19b033e3d4381) Co-authored-by: sheaf <sam.derbyshire@gmail.com> - - - - - 4 changed files: - compiler/GHC/Tc/Gen/App.hs - + testsuite/tests/typecheck/should_fail/T25950.hs - + testsuite/tests/typecheck/should_fail/T25950.stderr - testsuite/tests/typecheck/should_fail/all.T Changes: ===================================== compiler/GHC/Tc/Gen/App.hs ===================================== @@ -2040,6 +2040,10 @@ qlUnify ty1 ty2 go_flexi1 kappa ty2 -- ty2 is zonked | -- See Note [QuickLook unification] (UQL1) simpleUnifyCheck UC_QuickLook kappa ty2 + , checkTopShape (metaTyVarInfo kappa) ty2 + -- NB: don't forget to do a shape check, as we might be dealing + -- with an ordinary metavariable (and not a quick-look instantiation variable). + -- (Forgetting this led to #25950.) = do { co <- unifyKind (Just (TypeThing ty2)) ty2_kind kappa_kind -- unifyKind: see (UQL2) in Note [QuickLook unification] -- and (MIV2) in Note [Monomorphise instantiation variables] ===================================== testsuite/tests/typecheck/should_fail/T25950.hs ===================================== @@ -0,0 +1,6 @@ +{-# LANGUAGE PartialTypeSignatures #-} + +module T25950 where + +fails :: _ => a +fails = id $ () ===================================== testsuite/tests/typecheck/should_fail/T25950.stderr ===================================== @@ -0,0 +1,9 @@ +T25950.hs:6:9: error: [GHC-25897] + • Couldn't match expected type ‘a’ with actual type ‘()’ + ‘a’ is a rigid type variable bound by + the inferred type of fails :: a + at T25950.hs:5:1-15 + • In the expression: id $ () + In an equation for ‘fails’: fails = id $ () + • Relevant bindings include fails :: a (bound at T25950.hs:6:1) + ===================================== testsuite/tests/typecheck/should_fail/all.T ===================================== @@ -724,6 +724,7 @@ test('T17594c', normal, compile_fail, ['']) test('T17594d', normal, compile_fail, ['']) test('T17594g', normal, compile_fail, ['']) +test('T25950', normal, compile_fail, ['']) test('T24470a', normal, compile_fail, ['']) test('T24553', normal, compile_fail, ['']) test('T23739b', normal, compile_fail, ['']) View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/91db1d51d2d53346612fe843e863cd71... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/91db1d51d2d53346612fe843e863cd71... You're receiving this email because of your account on gitlab.haskell.org.