Change PR strategy from rebase to merge?

[RalfJung]

rust-lang repositories usually "merge" their PRs rather than rebasing them. This repo is an exception. According to @Amanieu, it's been like that for a while and it is unclear why.

IMO we should switch this repo to use "merge" rather than "rebase". However I also just realized that this repo doesn't use bors, is that somehow related to the use of rebases?

[lu-zero]

I think it started that way, at least since I started contributing it was setup to favour rebase over merge.

On why some prefer a way or another, it mainly boils down to having bisect tools behave better on the linear history than the tree one, IMHO. I'm not even sure if now git bisect and friends behave nicely or they are still a bit surprising to use.

[bjorn3]

git bisect --first-parent will bisect individual PR's if you use merge instead of rebase. This works much better if not every commit is guaranteed to build as you don't have to do git bisect skip on every commit that doesn't build.

[RalfJung]

Yeah, bisecting works rust fine on the main rustc repo.

[BurntSushi]

This was almost certainly my doing. I started this project in the beforetime, when the Rust project had much less process and structure and tooling. I believe it was originally created at http://github.com/BurntSushi/stdsimd and then moved into rust-lang. (The redirect is still there!)

This also explains why it was set to rebase, because I use rebase for all of my projects. I try to treat source history like I treat source code. That is, that it should be cultivated and optimized for humans looking to understand the logical transformations that the source code has undergone. I generally find merge commits to be contrary to this goal.

Of course, with all that said, I haven't been involved with this project for a long time. So if it makes sense to the current maintainers, then I'm totally in favor of changing it to match most of how the rest of the project operates. But if you want to stick on rebase and are looking for precedent, rust-lang/regex has used rebase for many years now and there are no plans to change that.

[RalfJung]

This also explains why it was set to rebase, because I use rebase for all of my projects. I try to treat source history like I treat source code. That is, that it should be cultivated and optimized for humans looking to understand the logical transformations that the source code has undergone. I generally find merge commits to be contrary to this goal.

In my opinion, merge commits better reflect the history of the code, and thus are also better for humans looking at it to trace back what happened.

But I guess this is neither the time nor the place to discuss that. :)

[BurntSushi]

Yeah I mean obviously I disagree. I find merge commits bewildering, difficult to follow, messy and encouraging of poor commit hygiene.