[llvm-dev] Phabricator -> GitHub PRs?

[David Greene via llvm-dev]

Christian Kühnel <kuhnel at google.com> writes:

>> It's not quite that simple though.  In general most PRs will need to be
>> rebased just before merging to maintain linear history.
>
>
> That depends on how frequent merge conflicts are. In my other projects that
> wasn't really an issue. I rarely had to rebase something manually.

It has little to do with merge conflicts.  Because LLVM requires
fast-forward merges, everything has to be rebased after something else
gets merged.

>> What happens then?  Would things need to pass another build before
>> the "final merge?"
>>
>> If so, then something needs to keep a list of pending PRs waiting for
>> "final merge."  This quickly gets very hairy as pending PRs have to
>> constantly be rebased and rebuilt as other PRs land.
>
> Some projects have a flag they set and let some bot do the manual work:
> Rebase, re-test and then automatically merge.
> I do not expect this to be perfect, it should rather be much better than
> today in slipping new bugs into master.

I agree the process can be improved.  But at some point builders are
going to be backed up as each PR gets rebased and then rebuilt just
before merging.  Probably we will have to punt an assume that if the
rebase is clean, it can just be merged in without another build.  We
will miss some small cases where non-conflicting code interacts in bad
ways but as you said, no system is perfect.

                       -David