You’re spot on.
However it’s clearly a missing feature that Git/Mercurial can’t tag diffs as “passes” or “bisectsble”.
This is especially annoying when you want to merge a stack of commits and the top passes all tests but the middle does not. It’s a monumental and valueless waste of time to fix the middle of the stack. But it’s required if you want to maintain bisectability.
It’s very annoying and wasteful. :(
I have only been in one place where "rebase" is used regularly, and now that I'm a little more familiar with it, I don't mind using it to bring in changes from a parent branch into a working branch, if the working branch hasn't been pushed to origin. It still weirds me out somewhat, and I don't see why a simple merge can't just be the preferred way.-
I have, however, seen "squashing" regularly (and my current position uses it as well as rebasing) -- and I don't particularly like it, because sometimes I put in notes and trials that get "lost" as the task progresses, but nonetheless might be helpful for future work. While it's often standard to delete "squashed" branches, I cannot help but think that, for history-minded folks like me, a good compromise would be to "squash and keep" -- so that the individual commits don't pollute the parent branch, while the details are kept around for anyone needing to review them.
Having said that, I've never been in a position where I felt like I need to "forcibly" push for my preferences. I just figure I might as well just "go with the flow", even if a tiny bit of me dies every time I squash or rebase something, or delete a branch upon merging!
But not linked together and those "closed" branches are mixed in with the current ones.
Instead, try out "git merge --no-ff" to merge back into master (forcing a merge commit to exist even if a fast-forward was possible) and "git log --first-parent" to only look at those merge commits. Kinda squash-like, but with all the commits still there.
I think every commit that gets merged to main should be an atomic believed-to-work thing. Not only does this make bisect way more effective, but it's a much better narrative for others to read. You should write code to be as readable by others as possible, and your git history likewise.
git bisect should operate on bisectable commits. Which may not be all commits. Git is missing information. This is, imho, a flaw in Git.
The thing is, I don't even bisect that often... the discipline necessary to maintain that in your source code heavily overlaps with the disciplines to prevent code regression and bugs in the first place, but when I do finally use it, it can pay for itself in literally one shot once a year, because we get bisect out for the biggest, most mysterious bugs, the ones that I know from experience can involve devs staring at code for potentially weeks, and while I'm yet to have a bisect that points at a one-line commit, I've definitely had it hand us multiple-day's-worth of clue in one shot.
If I was maintaining that discipline just for bisect we might quibble with the cost/benefits, but since there's a lot of other reasons to maintain that discipline anyhow, it's a big win for those sorts of disciplines.