Document version availability for each language extension

A certain amount of "historical" information about language extensions is of sufficient practical utility to deserve a place in the GHC documentation. I believe that the documentation for each language extension should include

1. The GHC version in which it first appeared.
2. Any major changes that have been made to the extension since the previous major-major version. For example, the GHC 8.x.x documentation for any given language extension should include any major changes to it since 7.0.1.

At present, the only way I see to get this information is to dig through previous versions of the documentation and change logs, which is rather inefficient.

Trac metadata

Trac field	Value
Version	8.0.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Documentation
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changed milestone to %8.2.1

changed weight to 5

added Tfeature request Trac import documentation labels

Fwiw, there is LanguagePragmaHistory.

Replying to [ticket:12404#comment:122453 thomie]:

Fwiw, there is LanguagePragmaHistory.

Imitation is the sincerest form of flattery. I think this is something that belongs in the GHC documentation proper. And that list does not (yet) include many details on changes made to the extensions from version to version. There have been some wobbles around PolyKinds, for example, although I don't know the details, and several changes to PatternSynonyms from 7.8 to 8.0.

closed

As of eb8bc4da the users guide will include since annotations on nearly all language extension flags.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

added Pnormal label