[Git][ghc/ghc][master] Assert that ctEvCoercion is called on an equality

[Marge Bot (@marge-bot)]

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


Commits:
0b11cdc0 by sheaf at 2024-10-31T08:38:55-04:00
Assert that ctEvCoercion is called on an equality

Calling 'ctEvCoercion' on non-equality constraints is always incorrect.
We add an assertion to this function to detect such cases; for example
a type-checking plugin might erroneously do this.

- - - - -


1 changed file:

- compiler/GHC/Tc/Types/Constraint.hs


Changes:

=====================================
compiler/GHC/Tc/Types/Constraint.hs
=====================================
@@ -2306,8 +2306,10 @@ ctEvExpr ev@(CtWanted { ctev_dest = HoleDest _ })
 ctEvExpr ev = evId (ctEvEvId ev)
 
 ctEvCoercion :: HasDebugCallStack => CtEvidence -> TcCoercion
-ctEvCoercion (CtGiven { ctev_evar = ev_id })
-  = mkCoVarCo ev_id
+ctEvCoercion _given@(CtGiven { ctev_evar = ev_id })
+  = assertPpr (isCoVar ev_id)
+    (text "ctEvCoercion used on non-equality Given constraint:" <+> ppr _given)
+  $ mkCoVarCo ev_id
 ctEvCoercion (CtWanted { ctev_dest = dest })
   | HoleDest hole <- dest
   = -- ctEvCoercion is only called on type equalities



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/0b11cdc022ce33d089db95b2b2e7c1f4bb326d37

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/0b11cdc022ce33d089db95b2b2e7c1f4bb326d37
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