feature request: expanding type synonyms in error messages

Type errors sometimes becoming confusing because of synonyms, for example, expected type and found type sometimes use different synonyms or sometimes only one of them use a synonym etc.

We discussed this in the mailing list: https://mail.haskell.org/pipermail/ghc-devs/2015-June/009247.html And also moved it to the Wiki to collect examples: https://wiki.haskell.org/Expanding_type_synonyms_in_error_messages_proposal

I'm currently working on a patch, I made some progress and I'll hopefully submit something for reviews in a couple of days.

This ticket is for further discussions and keep track of the progress.

Trac metadata

Trac field	Value
Version
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	Compiler (Type checker)
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