Automatic commit squashing

Thu Jun 16 14:12:15 UTC 2016

Note that if github is squashing the commits when it lands into Master, I
*believe* that this breaks the ancestry with your local branch. So it isn't
a matter of "the history just isn't present in the master branch", but "it
looks like a completely independent commit revision, and you have no
obvious way to associate it with the branch that you have at all".

It may be that git adds information to the commit ('this commit is a rollup
of hash deadbeef") in which case the git tool could look it up.

I don't know the github UI around this. If I do "git merge --squash" then
it leaves me with an uncommitted tree with the file contents updated, and
then I can do "git commit -m new-content"

And then if I try to do:
$ git branch -d test-branch
error: The branch 'test-branch' is not fully merged.
If you are sure you want to delete it, run 'git branch -D test-branch'

Which indicates to me that it intentionally forgets everything about all of
your commits, which mean *you* need to know when it got merged so that you
can prune your branches, because the tool isn't going to track what has and
hasn't been merged.

(I don't know about other people, but because of the delays of waiting for
reviews and merge bot bouncing things, it can take a while for something to
actually land. I often have branches that sit for a while, and it is easy
for me to not be 100% sure if that quick bugfix I did last week actually
made it through to master, and having 'git branch -d ' as a short hand was
quite useful.)

Note that if we are going to go with "only 1 commit for each thing landed",
then I do think that using github's squash feature is probably better than
rebasing your branches. Because if we just rebase your branch, then you end
up with 2 revisions that represent your commit (the one you proposed, and
the merge revision), vs just having the "revision of master that represents
your changes rebased onto master". We could 'fast forward when possible'
but that just means there is a window where sometimes you rebased your
branch and it landed fast enough to be only 1 commit, vs someone else
landed a change just before you and now you have a merge commit. I would
like us to be consistent.

For people who do want to throw away history with a rebase, what's your
feeling on whether there should be a merge commit (the change as I proposed
it) separate from the change-as-it-landed-on-master. I mean, if you're
getting rid of the history, the the change-as-I-proposed-it (and personally
tested it) doesn't really matter, right? And the bot tests the
change-as-it-landed.

John
=:->

On Thu, Jun 16, 2016 at 4:20 PM, Ian Booth <ian.booth at canonical.com> wrote:

>
>
> On 16/06/16 19:04, David Cheney wrote:
> > Counter suggestion: the bot refuses to accept PR's that contain more
> > than one commit, then it's up to the submitter to prepare it in any
> > way that they feel appropriate.
> >
>
> Please no. I do not want to be forced to alter my local history.
>
> I was hopeful that having the landing bot / github squash commits would
> satisfy
> those people what did not want to use git log --first-parent to present a
> sanitised view of commits, but allow me to retain the history in my
> branches
> locally so I could look back on what I did and when and how (if needed).
>
> If the default github behaviour is not sufficient, perhaps we can add some
> tooling in the merge bot to do the squashing prior to merging.
>
>
> > On Thu, Jun 16, 2016 at 6:44 PM, roger peppe <roger.peppe at canonical.com>
> wrote:
> >> Squashed commits are nice, but there's something worth watching
> >> out for: currently the merge commit is committed with the text
> >> that's in the github PR, but when a squashed commit is made, this
> >> text is ignored and only the text in the actual proposed commit ends up
> >> in the history. This surprised me (I often edit the PR description
> >> as the review continues) so worth being aware of, I think.
> >>
> >>   cheers,
> >>     rog.
> >>
> >> On 16 June 2016 at 02:12, Menno Smits <menno.smits at canonical.com>
> wrote:
> >>> Hi everyone,
> >>>
> >>> Following on from the recent thread about commit squashing and commit
> >>> message quality, the idea of automatically squashing commit at merge
> time
> >>> has been raised. The idea is that the merge bot would automatically
> squash
> >>> commits for a pull request into a single commit, using the PR
> description as
> >>> the commit message.
> >>>
> >>> With this in place, developers can commit locally using any approach
> they
> >>> prefer. The smaller commits they make as they work won't be part of the
> >>> history the team interacts with in master.
> >>>
> >>> When using autosquashing the quality of pull request descriptions
> should get
> >>> even more scrutiny during reviews. The quality of PR descriptions is
> already
> >>> important as they are used for merge commits but with autosquashing in
> place
> >>> they will be the *only* commit message.
> >>>
> >>> Autosquashing can be achieved technically by either having the merge
> bot do
> >>> the squashing itself, or by taking advantage of Github's feature to do
> this
> >>> (currently in preview mode):
> >>>
> >>> https://developer.github.com/changes/2016-04-01-squash-api-preview/
> >>>
> >>> We need to ensure that the squashed commits are attributed to the
> correct
> >>> author (i.e. not jujubot). I'm not sure what we do with pull requests
> which
> >>> contain work from multiple authors. There doesn't seem to be an
> established
> >>> approach for this.
> >>>
> >>> Thoughts?
> >>>
> >>> - Menno
> >>>
> >>>
> >>>
> >>>
> >>> --
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> >>
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