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haskell/error-messages: Chain of recommending Language Extensions

Motivation

The error message to enable FunctionalDependencies is not given until MultiParamTypeClasses is enabled. This is less ergonomic, than recommending directly FunctionalDependencies MultiParamTypeClasses, in cases where it should be obvious for the compiler.

See these:

Proposal

When GHC recommends any language extension, test if there would be follow-up extensions needed to resolve the same error.

Optional

One of:

- Deduplicate the list when there are implied Extensions in the list of recommendations
- Add all extensions explicitly, even if they are implied by another one.
Edited by ikervagyok
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