Comment (by Roland Haas):

I must have been sleeping when I wrote that patch. While git does not provide the full set of $Foo$ tags that svn provides, the one it does provide is $Id$ which resolves to the git hash. So really instead of the overly complex TeX code I could have just as well put $Id$ into the LaTeX file, and added

*.tex ident

to .gitattributes. This is described in https://git-scm.com/book/en/v2/Customizing-Git-Git-Attributes#_keyword_expansion and I had even read that page before / while writing the code in the pull request.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2330/include-date-of-build-and-git-hash-in