Commit cabal file

[brandon-leapyear]

:sparkles: This is an old work account. Please reference @brandonchinn178 for all future communication :sparkles:

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This allows people to specify ghc-source-gen as an extra-dep via git commit:

# stack.yaml
extra-deps:
  - github: google/ghc-source-gen
    commit: 1234567890abcdef

For example, it's useful now, to be able to use the HEAD of ghc-source-gen without waiting for a Hackage release. But this only works if the repo has .cabal committed. (more info: https://www.fpcomplete.com/blog/storing-generated-cabal-files/)

Also added a check in CI to ensure that the cabal file has been updated. I also simplified the CI config with Circle CI's new parameterized jobs syntax, which also fixes some bugs (e.g. the build-ghc-9.0 job specified the wrong cache keys when restoring, so it was previously always a cache miss)

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[brandon-leapyear]

:sparkles: This is an old work account. Please reference @brandonchinn178 for all future communication :sparkles:

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@googlebot I signed it!

[blackgnezdo]

Thanks @brandon-leapyear, this is an awesome cleanup!