Re: co-authoring commits

On Thu, Jun 18, 2015 at 11:25:44PM +0200, Jakub Narębski wrote:

Author and committer include datetime in the contents of the
field, which is used by Git for heuristics limiting walk. Coauthor
would have the same date as author, isn't it? If, after long
and involved discussion, we didn't add 'generation' field (for
easier cutting history walking), what chance adding 'coauthor'
has.

I don't think the two situations are comparable. I would (and did) argue
that a "generation" field is a bad header to bake in because of what it
means (it is redundant with the graph structure).

Whereas "co-author" is not a fundamentally bad; it's just not something
we chose to support early on, and it would have to be added now.

OTOH it would be nice to have support for .mailmap, and for
grepping... but the former could conceivably be added to the trailer
tool, the latter can be done with appropriate regexp in
"git log --grep=...".

I don't think we munge trailers during "git log" pretty-printing at all
now, but it is certainly something we could add (including mailmap-ing
them).  That doesn't seem like much more work than showing the co-author
field, and it's a lot more generally applicable (you could mailmap
S-O-B, Reviewed-by, and so forth).

Similarly, something like "git shortlog" would have to learn about
multiple authors under the "co-author" scheme. But likewise, it would
not be much more work to teach it something like:

  git shortlog --field=Reviewed-by

to handle an arbitrary trailer. And that is much more flexible.

I wonder what would break if one used 'Name <e@mai.l>, Name <em@i.l>'
as the author...

The "normal" parser we use for pretty-printing goes left-to-right and
will stop at the first ">", and show only the first author.

Older versions of git would then get the date wrong, complaining about
the ",". Newer versions parse the date from right-to-left to work around
such bogosities (especially things like "<foo <bar>>") and so will parse
back to the second ">".

Fsck will definitely complain about it.

-Peff