upload: Add "branch-format" config option and commit tag

[jerry-skydio]

Branch-format will let you control how branches are named,
which has an effect on when branches collide. This can be
set on cmdline, from config file, or on a topic-by-topic
basis inside the commit text.

user+branch is the default today and will remain the default.
Branch names will never collide if using this, but you cannot
retarget to other base branches, and you must use Uploader: if
another user wants to push to this branch.

user allows retargeting prs to other base branches, but will
not allow multiple base-branches to be specified. if they are,
it will warn to specify user+branch instead.

branch will allow others to upload to the same pr, but uploader:
cannot be used.

none includes both limitations and features of user and branch.

I don't really believe there's good use cases for branch and none,
but i'm implementing them to be complete.

Fixes: #11

[jerry-skydio]

Reviews in this chain:
└#167 upload: Add "branch-format" config option and commit tag

[jerry-skydio]

#	head	base	diff	date	summary
0	6a9b2f55	29f86bf3	diff	Mar 13 13:29 PM	3 files changed, 37 insertions(+), 5 deletions(-)
1	ff9c9981	2d6c7c26	diff	Mar 13 13:40 PM	2 files changed, 3 insertions(+), 4 deletions(-)
2	e0d33ebc	2d6c7c26	diff	Mar 13 13:41 PM	1 file changed, 1 deletion(-)
3	02f6d399	573558fe	diff	Mar 13 13:46 PM	1 file changed, 17 insertions(+), 14 deletions(-)
4	7ed5f674	3a19895f	rebase	Mar 13 13:50 PM	0 files changed
5	3730eed6	3a19895f	diff	Mar 13 14:02 PM	1 file changed, 11 insertions(+), 2 deletions(-)
6	f60b13a9	e370a376	rebase	Mar 13 14:02 PM	0 files changed
7	051b8f7f	8c17f143	rebase	Mar 13 14:03 PM	0 files changed
8	83b6db28	98552230	diff	Mar 13 14:04 PM	1 file changed, 1 insertion(+), 1 deletion(-)
9	62c9a476	c51d4cb3	rebase	Mar 13 14:12 PM	0 files changed
10	1a5080fe	c4ee1e20	rebase	Mar 13 14:14 PM	0 files changed
11	a8eb317f	7ce245cb	rebase	Mar 13 14:15 PM	0 files changed
12	5952c05d	1dd80d5e	diff	Mar 13 14:17 PM	0 files changed
13	1ed3dddc	1dd80d5e	diff	Mar 13 14:19 PM	1 file changed, 1 insertion(+), 1 deletion(-)
14	dfdff148	c4ace457	diff	Mar 13 14:54 PM	1 file changed, 2 insertions(+), 1 deletion(-)

[aaron-skydio]

Does retargeting automatically with revup upload have the problem of spamming codeowners for changes in between the merge-base of the new and old bases, and the original PR branch? It can't atomically push the branch and change the base branch in github right? I guess I'm a little worried about recommending this if it's going to spam people like that

It seems super annoying but I guess might be possible to

1. upload the PR relative to the merge-base of the new and old base branches
2. change the base branch via the github API
3. maybe reupload on top of the actual new base branch

At least that's what I've done previously if I really wanted to retarget a PR

[jerry-skydio]

yes it probably will be spammy depending on which direction it retargets. ex 31.6-> master will be spammy because we need to push before updating the bb. the reverse will actually not be too spammy because with the new automerger we expect most of 31.6 to have merged into master already

i don't want to cherry-pick onto the merge base though because it's possible that changes will cherry-pick cleanly on each branch but not on their merge base

[jerry-skydio]

at this point i've seen enough limitations / spam in the codeowners system that i think the issue is more with it and not necessarily other tools.

whether we recommend it is maybe a different question but i think it's useful enough that there should be some way for revup to configure it