Hacker News Reader

Comment by phailhaus | Hacker News Reader

> assuming the PR contains atomic, logical commits

This is impossible to enforce or guarantee at scale. Squashing PRs, though, is practically fool-proof: PRs already represent a single, atomic unit of work that passes all CI checks and is safe to merge. No such thing is true (or should be!) of individual commits within that PR. Whether we like it or not, a branch commit really only represents a "save point" for a developer.

View on HN

What you say is impossible, we pretty successfully apply at ScyllaDB (see https://github.com/scylladb/scylladb/commits/master).

I'm not sure 100% of the commits compile & pass all tests - there may be some mistakes - but generally we're in a pretty good state, and the clean git log is being successfully used for bisecting.

If you want even larger scale - if I understand correctly, the Linux kernel practices a similar thing, which is where we got this practice from (ScyllaDB founders came from kernel development). And since Git was originally created to help developing Linux - that's where you want to look for good practices.

I also found the comment you replied to a little unconvincing. The remark concerning scale in particular did not hit home, as I would guess the vast majority of teams are <10 devs which I would hardly call 'scale'. I left my previous role for several reasons but one was the constant "Microsoft does x".. Microsoft has 100k devs, we had 5. Not the same.

The point is that you can try, but IMO it's wasted effort. Commits are immutable and really hard to manipulate retroactively, and humans are guaranteed to make mistakes. Why put so much effort into trying to make your commits atomic, when it's unlikely that they ever truly are?

Sure, you can git bisect to the exact commit that introduced a bug, but that commit was part of a larger PR, and you probably can't revert just that commit alone. So what was gained?

You can get the same guarantees without squashes with {log, bisect, blame} --first-parent and merge --no-ff (force all PRs to make merge commits). You can preserve more of the graph and use it to revisit "inside" of PRs when necessary.

So much this. Everyone needs to learn about --first-parent, it makes git log, git bisect, etc... so much more powerful and prevents people from just squashing PRs into giant mega-commits that make the history so much less useful.

I keep joking that all we need is one good Git GUI to go viral that defaults to --first-parent in every view and we might eventually convince more people they don't need to squash/rebase as much. One of these days I may even take the joke far enough along to prototype something.

What's the point? It's unlikely you'll be able to revert it in isolation. You can do the same thing with squashed PR's, except you also get a description of the overall work, all discussions related to it, and a higher likelihood that you can revert it in one piece.

First parent applies to revert, too (with the -m flag):

    git revert MERGECOMMITHASH -m 1 # revert to first parent of merge (revert changes of second parent/other branch)

You can include good descriptions in your PR merge commits including discussion comments and everything. Some PR tools automate that, some do not. I don't know any technical reason why any PR tool automation would create better squash merge commit messages than normal merge commit messages.

(ETA: Also you may want to reconsider your workflow if you rely on reverts that often. I had to look up the command argument, even though I knew it existed, because I haven't needed to do it in a while and I'm very thankful for that.)

Reply on news.ycombinator.com