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Merge commits for single-commit PRs helpfully record which PR # was merged if you need to review/audit the PR sometime later, if nothing else.

u801e 6y ago
The original commit could be amended to include that information.
- WorldMaker 6y ago
  The point of using a "proper" merge commit would be to avoid amending/rebasing the original commit and allow the original commit to live as-developed in the final branch.
  - u801e 6y ago
    The only thing changing in the original commit is to include a reference to the PR number in the commit message. There would be no change to the tree referenced by the commit.
    - WorldMaker 6y ago
      It's an entirely different commit at that point. If work has already started in another branch based on the original commit (for whatever reason), it can cause merge problems down the road. Again, you are likely going to suggest that you can just rebase this other branch on top of the modified commit, but that's still sweeping possible merge commits under the rug, and again just because that rebase is usually automatic including that the tree references should be the same doesn't mean it is always automatic or doesn't have dangerous repercussions (including training junior devs to rebase often and giving them plenty of ammo for avoidable footguns).
      - u801e 6y ago
        I'm talking about a single commit PR in Github or Gitlab. If it's based on the latest version of the base branch, then amending it to include the PR number would allow Github to generate a link to the PR page associated with that commit. That would make the merge commit superfluous at that point. So something like: git commit --amend and editing the commit message. This doesn't introduce any further change to the tree associated with the commit.
        rectang 6y ago
        But because the commit has different metadata after amending, it now has a different SHA and is a different commit. For illustration, a minor inconvenience of amending the commit is that `git branch -d my-feature-branch` no longer succeeds for the original branch, because it looks for the actual commit SHA, not the tree. You may not care about the effects of changing the commit, but those effects are real and other people care.
        u801e 6y ago
        Assuming you were the one who amended the commit before pushing it up to the remote, there's no reason that you would not be able to delete the branch because your local working copy has already updated contents of .git/refs/heads/my-feature-branch. For those who have cloned the repo for testing, they can simply run git checkout my-feature-branch; git fetch origin; git reset --hard @{u} to get their local repo in sync with the remote. So there's no reason that amending the commit will affect anyone until they branch off of the repo to do their own work. But that's nothing that a rebase can't fix.
        rectang 6y ago
        Yes, of course there are workarounds; no matter what scenario you or I come up with, the other will be able to propose a different way of doing things. I chose a deliberately trivial example because I was illustrating a fundamental aspect of Git's design, not trying to stump you. But we're talking past each other.

u801e 6y ago

The original commit could be amended to include that information.

WorldMaker 6y ago
The point of using a "proper" merge commit would be to avoid amending/rebasing the original commit and allow the original commit to live as-developed in the final branch.
- u801e 6y ago
  The only thing changing in the original commit is to include a reference to the PR number in the commit message. There would be no change to the tree referenced by the commit.
  - WorldMaker 6y ago
    It's an entirely different commit at that point. If work has already started in another branch based on the original commit (for whatever reason), it can cause merge problems down the road. Again, you are likely going to suggest that you can just rebase this other branch on top of the modified commit, but that's still sweeping possible merge commits under the rug, and again just because that rebase is usually automatic including that the tree references should be the same doesn't mean it is always automatic or doesn't have dangerous repercussions (including training junior devs to rebase often and giving them plenty of ammo for avoidable footguns).
    - u801e 6y ago
      I'm talking about a single commit PR in Github or Gitlab. If it's based on the latest version of the base branch, then amending it to include the PR number would allow Github to generate a link to the PR page associated with that commit. That would make the merge commit superfluous at that point. So something like: git commit --amend and editing the commit message. This doesn't introduce any further change to the tree associated with the commit.
      - rectang 6y ago
        But because the commit has different metadata after amending, it now has a different SHA and is a different commit. For illustration, a minor inconvenience of amending the commit is that `git branch -d my-feature-branch` no longer succeeds for the original branch, because it looks for the actual commit SHA, not the tree. You may not care about the effects of changing the commit, but those effects are real and other people care.
        u801e 6y ago
        Assuming you were the one who amended the commit before pushing it up to the remote, there's no reason that you would not be able to delete the branch because your local working copy has already updated contents of .git/refs/heads/my-feature-branch. For those who have cloned the repo for testing, they can simply run git checkout my-feature-branch; git fetch origin; git reset --hard @{u} to get their local repo in sync with the remote. So there's no reason that amending the commit will affect anyone until they branch off of the repo to do their own work. But that's nothing that a rebase can't fix.
        rectang 6y ago
        Yes, of course there are workarounds; no matter what scenario you or I come up with, the other will be able to propose a different way of doing things. I chose a deliberately trivial example because I was illustrating a fundamental aspect of Git's design, not trying to stump you. But we're talking past each other.