"Expected exactly one original SHA, found 0" error while trying to amend to non-HEAD merge commit

[brandondong]

Describe the bug

"Expected exactly one original SHA, found 0" error while trying to amend to non-HEAD merge commit

To Reproduce
Steps to reproduce the behavior:

Run:

git init
touch base && git add . && git commit -m "Base commit"
git checkout -b a
git branch b
touch a && git add . && git commit -m "a"
git checkout b
touch b && git add . && git commit -m "b"
git merge a -m "Merge a into b"
touch c && git add . && git commit -m "c"
touch d && git add .
lazygit

Then, navigate to the commits panel and to the "Merge a into b" commit. Perform "Amend commit with staged changes" (A).

Upon doing so, I receive this error:

lazygit/pkg/utils/rebase_todo.go

Line 235 in e1c3ef6

return nil, fmt.Errorf("Expected exactly one original SHA, found %d", originalShaCount)

and am left with a fixup commit containing the new file, d.

Expected behavior
I'd expect the amend to just work. It works if commit "c" did not exist.

Screenshots

Version info:
Run lazygit --version and paste the result here

> lazygit --version
commit=v0.40.2, build date=2023-08-12T17:47:33Z, build source=binaryRelease, version=0.40.2, os=linux, arch=amd64, git version=2.44.0

Run git --version and paste the result here

> git --version
git version 2.44.0

Additional context
Add any other context about the problem here.

Note: please try updating to the latest version or manually building the latest master to see if the issue still occurs.

[stefanhaller]

Thanks for the detailed report, it's easy to reproduce.

It's not a regression in 0.41.0, it happens in earlier versions too, which makes it a little less urgent to fix. I'll see if I can come up with a reliable way to fix it next week; if not, we might just have to disable the command for merge commits.

There are several workarounds; the easiest might be to press shift-F instead of shift-A to create a fixup commit for the merge commit, then move it down to right after the merge commit using ctrl-j, and then press f there to squash it into its parent.

[brandondong]

I had some spare time to look into this and it turned out to just be a simple one-liner. #3510