Re: [WIP/RFH] format-patch: Allow diffs for first-parent history

[Jonathan Nieder <jrnieder@gmail.com>]

Michael J Gruber wrote:

> The attached patch teaches format-patch not to ignore merges (on
> "--first-parent"), but I failed to track how "diff-tree" sets options
> based on "-m"

With hindsight, here's a search result:

 $ git grep -e argv -- builtin/diff-tree.c
 int cmd_diff_tree(int argc, const char **argv, const char *prefix)
         argc = setup_revisions(argc, argv, opt, &s_r_opt);
                 const char *arg = *++argv;

So it's setup_revisions, in revision.c, which clears revs->ignore_merges
when -m is detected.

Maybe it should clear revs->no_merges while at it?  I can't see any
other meaningful meaning for

	git alias.lg "log --no-merges"
	git lg -m HEAD~2..HEAD

or

	git format-patch -m --first-parent HEAD~2..HEAD

Meanwhile I would also be happy to see --first-parent imply -m, though
that might be more controversial since -p -c --first-parent and
-p --cc --first-parent are also meaningful.