Direct stack merge creates one merge commit instead of one per PR

[kj-lml]

Description

When merging a two-PR stack via GitHub's web UI using Create a merge commit, only one merge commit is created, although both PRs are marked as merged.

I used GitHub.com (Free plan, public test repository). All PR creation and merging operations were performed through the web UI, not the CLI.

Expected vs. actual

According to the official documentation, one merge commit should be created per PR.

However, merging PRs 1 and 2 together produced only one merge commit.

Comparison tests

All tests were performed in the same repository using the GitHub web UI.

Repository: https://github.com/kj-lml/stacked-renshu

• Merge entire stack (PR 1, PR 2) using Merge commit: 1 merge commit
• Merge PRs individually (PR 4, PR 5) using Merge commit: 2 merge commits
• Merge entire stack (PR 7, PR 8) using Squash: 2 squash commits

Git history

Command:

git log --first-parent --oneline -n 20 origin/main

Output:

4db4de9 y (#8)
3217fec x (#7)
cb91647 Merge pull request #5 from kj-lml/4
9776eec Merge pull request #4 from kj-lml/3
05525c8 Merge pull request #2 from kj-lml/2
12ff45f 1st

The merge commit for PR 2 has the following parents:

05525c8 12ff45f 047ded7 Merge pull request #2 from kj-lml/2

This confirms that the first stack merge created only one merge commit on the first-parent history.

Screenshots

1. Squash entire stack (PRs 7 and 8):

2. Merge entire stack (PRs 1 and 2):

3. Git Graph showing all three results:

Question

The issue appears to occur specifically when merging an entire stack using the merge-commit method.

Could you clarify whether this is a bug or an intentional difference between direct stack merges and individual PR merges?