Upstream git-survey(1) as a native replacement for git-sizer(1)

Derrick Stolee has proposed a new git-survey(1) command that gathers metrics around a repository's on-disk state. This tool would be the first step towards a native replacement for git-sizer(1).

Having such low-level information would help us to surface more information about repositories. Potential usecases are as part of RepositoryInfo() or the upcoming repository dashboard. The info would be helpful to get a general sense of how well we will be able to serve a specific repository.

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