Squash merge: "---------" separator before Co-authored-by pushes trailers in the PR description out of git's trailer block

[mrt181]

What is happening

When a pull request is squash-merged with the default commit message "Pull request
title and description" and the PR has commits from more than one author, GitHub
appends the co-authors as a separate paragraph after a "---------" line:

feat: co-author test (#1)

Two authors, space-free reference.

Ref:AB#1415699

---------

Co-authored-by: Jane Doe <jane.doe@example.com>

git only reads the last paragraph of a message as its trailer block. Any trailer
written at the end of the PR description (here Ref:, but also Signed-off-by:,
Reviewed-by:, Fixes: etc.) is therefore no longer a trailer:

$ git log -1 --format='%(trailers:key=Ref,valueonly)'
(empty)
$ git log -1 --format=%B | git interpret-trailers --parse
Co-authored-by: Jane Doe <jane.doe@example.com>

Listing the co-author in the description directly under Ref: does not help:
GitHub appends its own block anyway and the co-author appears twice.

Steps to reproduce

1. Repository settings: allow squash merging, default message "Pull request
   title and description".
2. Open a PR with two commits by different authors and end the description with
   a trailer, e.g. Ref:AB#123.
3. Squash-merge with the default message (merge button or gh pr merge --squash).
4. Run git interpret-trailers --parse on the merge commit.

Expected

The description's trailers and the co-authors end up in one trailer block, e.g.

Ref:AB#123
Co-authored-by: Jane Doe <jane.doe@example.com>

Why it matters

Teams that squash-merge put work item references and other trailers in the PR
description because it becomes the commit message. Release tooling, changelog
generators and commit checks read them with git's trailer parsing
(%(trailers), git interpret-trailers). As soon as a PR has a co-author, those
trailers silently disappear from the history.

Suggestion

If the generated message already ends with a trailer block, append the
Co-authored-by lines to that block instead of adding "---------" and a new
paragraph. Alternatively, a repository setting to omit the separator.

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[kaluarachchiteshan]

Hi,

I can reproduce the logic from your description, and I'm not aware of a repository setting that removes the --------- separator. Here are workarounds, from least to most invasive.

1. Edit the commit message in the merge dialog

Before clicking "Confirm squash and merge", edit the message so the PR trailers and the co-author lines sit together in the final paragraph:

feat: co-author test (#1)

Two authors, space-free reference.

Ref:AB#1415699
Co-authored-by: Jane Doe <jane.doe@example.com>

GitHub may still append its own co-author block, so after merging check the result. This is manual, so it doesn't scale for a team.

2. Make the tooling not depend on git's trailer parser

If release tools, changelog generators or commit checks only need the work item reference, read it in a way that survives the separator:

# plain text match on the whole message
git log -1 --format=%B | grep -E '^Ref:'

# or take the reference from the PR instead of the commit
gh pr view 1 --json body --jq .body | grep -E '^Ref:'

For CI checks, validate the PR description via the API before merge, since that is where the author wrote the trailer.

3. Put the trailer where the parser looks

Some teams put required trailers in the PR title or in the first lines of the description (as Fixes #123-style references), because those survive regardless of what GitHub appends at the end. This depends on what your tools accept.

4. Change the merge strategy for multi-author PRs

• Rebase merge keeps each commit and its own trailers.
• Merge commit keeps the original commits, and the message GitHub writes for the merge commit doesn't use the --------- block.

Both change your history shape, so they may not fit a squash-only policy.

5. Post-merge fix (last resort)

Rewriting a merged commit on a protected default branch isn't appropriate, so I'd avoid it. Normalizing the message in the tooling (option 2) is safer.

6. Report it as feedback

This discussion is marked Closed, so it may not be read by the product team. The suggestion is clear and well-argued, so consider posting it again in the Community feedback category with the Product Feedback template, and include the exact before/after message. Your proposed fix (append co-authors to an existing trailer block, or add a setting to omit the separator) is a concrete request they can act on.