Give strong preference to type variable names in scope when reporting hole contexts
When using ScopedTypeVariables with typed holes, I want GHC to bend over backwards to preserve the names of type variables that the user has chosen to bring into scope. I can't immediately reproduce the situations I've run into recently where that hasn't happened, but sometimes I've had a signature like
foo :: forall bar . ...
foo = ... _ ...and yet the typed hole message shows that bar has been lost in unification and replaced by some unrelated name. I would very much prefer if this never happened.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.10.2 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |