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I don't bisect regularly, but when I do, it's usually trying to figure out what the original reason for introducing the code that is problematic is. The entire

I don't bisect regularly, but when I do, it's usually trying to figure out what the original reason for introducing the code that is problematic is. The entire point is on projects big enough, you may not be able to just "follow the logic" enough to know that your fix the to apparent bug isn't re-introducing some regression that was fixed previously. So bisect to me, is a way to figure out where and why the code was changed the way that it was, so I have a better understanding of the changes I can make going forward. That doesn't mean the change made in the past was correct and must be maintained (obviously something is broken), or that it might be that the obvious solution based on following the code logic is correct. But that doesn't mean I wasted time making sure I best understand the reasoning behind the changes made. But this is also why I don't resort to it very often, because it isn't necessary in all cases (I'd even say it isn't necessary in most cases). Bisect also allows you to see other changes made in the commit in question, and around that commit, so you get a better overall picture of the logic.

thom 5y ago
If you've got a codebase where the intent of the code isn't clear, where you can't track bugs, and where you can't fix them without being confident you're not breaking other stuff, surely those are all fundamental problems worth addressing?
- JoshuaDavid 5y ago
  Yes, but those things take time to address and in the meantime the need to make changes that address more immediate needs doesn't go away. Bisect specifically helps if you've got an easily reproducible bug in a hairy part of the codebase and you know that bug could be arbitrarily old but is on a path that recently started getting exercised much more often. I use it maybe once a month but when I do it is very nice to have that context of how the bug happened and any other places that might need to be fixed.
  - thom 5y ago
    Sure, but at that point there's a whole raft of practices that seem more important than 'having a nice commit history'.
    - JoshuaDavid 5y ago
      Bisect doesn't require a nice commit history, just a granular one (well, it doesn't require a granular one either but it's a bit less helpful if it lets you identify the problem commit as the +18000/-7000 LOC "Overhaul payment system <7 paragraph description of new payment system>" than if it drops you on the +3/-3 LOC "fix encoding bug <no description of what the bug is or what the fix does>") Edit: I should also add that if you use github, squash-merging pull requests is fine because you can pull down and check out the pull request branch and run bisect on that. Or more generally if you don't delete history and keep a record of what commits were squashed to make your giant commit, your friendly local maintenance programmer might grumble slightly but will still be able to work effectively. Just please avoid erasing history entirely.

thom 5y ago

If you've got a codebase where the intent of the code isn't clear, where you can't track bugs, and where you can't fix them without being confident you're not breaking other stuff, surely those are all fundamental problems worth addressing?

JoshuaDavid 5y ago
Yes, but those things take time to address and in the meantime the need to make changes that address more immediate needs doesn't go away. Bisect specifically helps if you've got an easily reproducible bug in a hairy part of the codebase and you know that bug could be arbitrarily old but is on a path that recently started getting exercised much more often. I use it maybe once a month but when I do it is very nice to have that context of how the bug happened and any other places that might need to be fixed.
- thom 5y ago
  Sure, but at that point there's a whole raft of practices that seem more important than 'having a nice commit history'.
  - JoshuaDavid 5y ago
    Bisect doesn't require a nice commit history, just a granular one (well, it doesn't require a granular one either but it's a bit less helpful if it lets you identify the problem commit as the +18000/-7000 LOC "Overhaul payment system <7 paragraph description of new payment system>" than if it drops you on the +3/-3 LOC "fix encoding bug <no description of what the bug is or what the fix does>") Edit: I should also add that if you use github, squash-merging pull requests is fine because you can pull down and check out the pull request branch and run bisect on that. Or more generally if you don't delete history and keep a record of what commits were squashed to make your giant commit, your friendly local maintenance programmer might grumble slightly but will still be able to work effectively. Just please avoid erasing history entirely.