Re: [PATCH] mktag.c: improve verification of tagger field and tests

Brandon Casey [off-list ref] writes:

Eventually filter-branch along with the rest of git will be rewritten
in c and the need for many low-level git tools will vanish.

That holds true only for the tools shipped with git.git itself.  However,
you never should forget that people _script_ around git.  I do not see a
reason to stop supporting mktag in this discussion.

I would suggest:

 * make mktag.c a built-in first;

 * rename verify_tag() in mktag.c to verify_tag_buffer(), and update its
   implementation to tighten the format validation, perhaps along the
   lines you propose in your patch, and move it to tag.c.  By the way, I
   think tagger information should get the same validation as committer
   and author information gets elsewhere in the system;

 * add a call to verify_tag_buffer() you introduce above immediately
   before write_sha1_file() in builtin-tag.c, to make sure both programs
   produce valid tags, with the same definition of validity.