Commit 25ee60cd authored by Committed by Marge Bot
Synchronize ClsInst.doTyConApp with TcTypeable validity checks (#15862)
Issue #15862 demonstrated examples of type constructors on which `TcTypeable.tyConIsTypeable` would return `False`, but the `Typeable` constraint solver in `ClsInst` (in particular, `doTyConApp`) would try to generate `Typeable` evidence for anyway, resulting in disaster. This incongruity was caused by the fact that `doTyConApp` was using a weaker validity check than `tyConIsTypeable` to determine if a type constructor warrants `Typeable` evidence or not. The solution, perhaps unsurprisingly, is to use `tyConIsTypeable` in `doTyConApp` instead. To avoid import cycles between `ClsInst` and `TcTypeable`, I factored out `tyConIsTypeable` into its own module, `TcTypeableValidity`. Fixes #15862.
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