Add revision information to plan.json

[fgaz]

Closes #6186

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Template Α: This PR modifies behaviour or interface

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QA Notes

• cd to any project that uses packages from hackage
• Run cabal build --dry all to produce a plan.json
• inspect dist-newstyle/cache/plan.json
  • it should contain a pkg-revision field under all remote-repo or secure-repo packages
  • the field should correspond to the latest hackage revision published before the used index-state

[geekosaur]

Tests would be nice, granting that we'd have to find a stable repo that has revision fields.

[fgaz]

I'm trying to write one using withRemoteRepo

[fgaz]

Okay, this should work, please have a look ^_^

[mpickering]

Perhaps the revision should be adjacent to "repo" in the RepoTarballPackage but either way it seems good to get the info into the plan.json somehow.

[fgaz]

I put it there because I thought it didn't apply to all repo types (RepoLocalNoIndex in particular), but indeed it's a bit weird to have it inside repo.
And even though I don't really see a use case for exposing revisions from local repos, I don't see any disadvantage either, so maybe I should just do it.

[geekosaur]

"If it's there, someone will come up with a use for it". And consistent behavior is generally a good thing.

[fgaz]

Now I wonder if we should just have it at top level, next to pkg-name and pkg-version.
It's just a field that can be extracted from any cabal file that contains it anyway

[mpickering]

Now I wonder if we should just have it at top level, next to pkg-name and pkg-version. It's just a field that can be extracted from any cabal file that contains it anyway

That doesn't seem too bad to me.