Comment by xixixao

15 hours ago

Conflicts spawn most likely because PR A was squashed, and once you squash Git doesn't know that PR B's ancestors commits are the same thing as the squashed commit on main.

No idea if this feature fixes this.

Edit: Hopefully `gh stack sync` does the rebasing correctly (rebase --onto with the PR A's last commit as base)

2 comments

xixixao

Reply
akersten  15 hours ago

> Conflicts spawn most likely because PR A was squashed, and once you squash Git doesn't know that PR B's ancestors commits are the same thing as the squashed commit on main.

Yeah, and I kind of see how git gets confused because the squashed commits essentially disappear. But I don't know why the rebase can't be smart when it sees that file content between the eventual destination commit (the squash) is the same as the tip of the branch (instead of rebasing one commit at a time).

  • skydhash  10 hours ago

    Because at first your have this

      main <- PR A <- PR B

    Then you'll have

      main, squashed A
      \
       \-> PR A -> PR B

    The tip of B is the list of changes of both A and B, while the tip of main is now the squashed version of the changes of A. Unless a branch tracks the end of A in the PR B, It looks like more you want to apply A and B on top of A again.

    A quick analogy to math

      main is X
  A is 3
  B is 5

    Before you have X + 3 + 5 which was equivalent to X + 8, but then when you squash A on on X, it looks like (X + 3) + (3 + 5) from `main`'s point of view, while from B, it should be X + (3 + 5). So you need to rebase B to remove its 3 so that it can be (X + 3) + 5.

    Branches only store the commits at the top. The rest is found using the parent metadata in each commits (a linked list. Squashing A does not remove its commits. It creates a new one, and the tip of `main` as its parent and set the new commit as the tip of `main`. But the list of commits in B still refer to the old tip of `main` as their ancestor and still includes the old commits of A. Which is why you can't merge the PR because it would have applies the commits of A twice.