[llvm-dev] Committing with git

Tue Oct 29 07:24:12 PDT 2019

> At the dev meeting I heard Doug Gregor say something like, "what kind of dirty animals are you, you just push directly to master!?" Based on that, I think other communities may set up workflows where they push branches to places, and some automation rebases and updates master asynchronously, optionally conditioned on some (light) testing or approval.

Someone has already mentioned rust-lang/rust GitHub project in other thread related to GitHub migration: from their contribution guide (https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#pull-requests):

> After someone has reviewed your pull request, they will leave an annotation on the pull request with an r+. It will look something like this:
> @bors r+
> This tells @bors, our lovable integration bot, that your pull request has been approved. The PR then enters the merge queue, where @bors will run all the tests on every platform we support. If it all works out, @bors will merge your code into master and close the pull request.
> Depending on the scale of the change, you may see a slightly different form of r+:
> @bors r+ rollup
> The additional rollup tells @bors that this change is eligible for to be "rolled up". Changes that are rolled up are tested and merged at the same time, to speed the process up. Typically only small changes that are expected not to conflict with one another are rolled up.

Just an idea of possible automation which will contribute to stability of master on merges

From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Reid Kleckner via llvm-dev
Sent: Tuesday, October 29, 2019 3:21 AM
To: Nemanja Ivanovic <nemanja.i.ibm at gmail.com>
Cc: llvm-dev <llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] Committing with git

Yep, that's the case. I would say that we're no worse off than we were in terms of testing, as you note. Previously svn would let us racily commit to separate files without testing the new result. Now we're forced to observe the race.

At the dev meeting I heard Doug Gregor say something like, "what kind of dirty animals are you, you just push directly to master!?" Based on that, I think other communities may set up workflows where they push branches to places, and some automation rebases and updates master asynchronously, optionally conditioned on some (light) testing or approval.

Maybe we'll want something like that one day, but for now, we just have to pull, rebase, push, and hope.

On Mon, Oct 28, 2019 at 4:19 PM Nemanja Ivanovic via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Now that we have switched to git and I had to leave behind my wonderfully simple svn workflow I have noticed something curious when committing.

My typical workflow once my patch is approved on Phabricator has always been:
- Update my source tree to latest
- Apply the approved patch
- Rebuild
- Retest
- If all is well, commit

Having to update again after rebuilding/retesting was extremely rare since SVN only prevented the commit if I am modifying the same file(s) that have been modified upstream since my update.

So I tried replicating that workflow with git, but apparently that isn't really an option. Apparently git won't let me push if there have been any commits upstream at all between my last pull and my push. This means that I can never push from a fully tested state since it is almost impossible to find a window of 20-30 minutes without any commits (which is how long a rebuild/retest takes for me).

One might argue that this is no worse than what I had with SVN since I would commit on top of changes that already happened upstream. But this is not always the case. Namely, if an upstream commit modifies the same file, causing a semantic conflict, I would not end up committing with the old svn workflow whereas I would end up committing with the new git workflow.

I am not sure if this is something that can be solved (nor if it is something that needs to be solved) but I thought I would just bring it up.
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