gitattributes export-subst and software versioning

Periodically, I wonder if there is some better way for managing tagged releases for software in git. Current state of the art seems to be "write a custom Makefile that takes a version and seds out the existing version, then runs git tag for you". Inelegant solutions also abound; people release code that does not build properly unless you build it from a git checkout so it can run git describe. (There are half a dozen individually popular but mutually exclusive python ecosystems for this, in fact, all of them varying degrees of broken.)

git does have a way to automatically insert metadata via the export-subst attribute on a file, but it's very awkward to use and you cannot get much info out of it.

# get tags into a file, only on exact match:

$ cat VERSION $Format:%d$ $Format:%D$

$ git archive HEAD | bsdtar -xOf - VERSION
   (HEAD -> master, tag: 1.0)
HEAD -> master, tag: 1.0

With sufficient regex, you can get a release out of this, but it doesn't work if you try getting an autogenerated tarball for a commit that isn't exactly a release.

$ git commit --allow-empty -m ...
$ git archive HEAD | bsdtar -xOf - VERSION
   (HEAD -> master)
HEAD -> master

I think it would be much, much nicer if there was a format placeholder for git describe.

It doesn't even need option support -- the default output in most cases could be a replacement for or fall back to existing invocations of the "git" program, followed by post-processing with e.g. "sed".

However, the existence of current pretty formats such as %C() or %(trailer:options) implies that options could be passed in a git-describe format too. e.g. %(describe:--long --tags --match="v*")

Thoughts?