git cat-file warnings on bumped git revision

[mdkent]

Hiya! We are occasionally seeing some neat warnings out of our bundler deploys:

 ** [out :: yyy] Retrying git cat-file -e 803ce88710f853db3e310bca889912f22c6472d6 due to error (2/3): Bundler::Source::Git::GitCommandError Git error: command `git cat-file -e 803ce88710f853db3e310bca889912f22c6472d6` in directory /foo/bar/shared/bundle-rails4/ruby/x/cache/bundler/git/foo-c6395bcedd77f151eba090b253e0e7db95b5e961 has failed.
 ** [out :: yyy] If this error persists you could try removing the cache directory '/foo/bar/shared/bundle-rails4/ruby/x/cache/bundler/git/foo-b6395bcedd77f151eba090b253e0e7db95b5e961'
 ** [out :: yyy] Retrying git cat-file -e 803ce88710f853db3e310bca889912f22c6472d6 due to error (3/3): Bundler::Source::Git::GitCommandError Git error: command `git cat-file -e 803ce88710f853db3e310bca889912f22c6472d6` in directory /foo/bar/shared/bundle-rails4/ruby/x/cache/bundler/git/foo-c6395bcedd77f151eba090b253e0e7db95b5e961 has failed.
 ** [out :: yyy] If this error persists you could try removing the cache directory '/foo/bar/shared/bundle-rails4/ruby/x/cache/bundler/git/foo-b6395bcedd77f151eba090b253e0e7db95b5e961'

They seem to popup whenever we bump a git revision in the Gemfile.lock and deploy for the first time. They disappear on subsequent runs.

The issue appears to be caused by has_revision_cached? checking to see if it already has the reference in https://github.com/bundler/bundler/blob/master/lib/bundler/source/git/git_proxy.rb#L115-L121. This command correctly returns a non-zero exit status on the first run, which gets sent somewhat needlessly through the Bundler::Retry attempts.

The simplest solution is to just pass

          in_path { git("cat-file -e #{@revision}", false) }

to suppress the error output. The retry logic puts this particular command in a tough spot as it's expected to exit(1), but could also fail if github is having issues.

This user https://discussion.heroku.com/t/build-error-retrying-git-cat-file-e/448 is suffering the same issue.