[Nfd-dev] git rebase question

[Junxiao Shi]

Dear folks

Recently, Alex has been suggesting that commits in a feature branch (such
as NFD management refactor, NDNLP implementation, etc) should not be merged
until all commits are ready, and developers may start working on an
unmerged parent commit.
This would require the developer to rebase their commits, if the parent
commit changes.
I’m reluctant to do that, but prefers to wait for the parent commit to be
merged before starting the next commit, because I had a lot of trouble in
rebasing.

Specifically, my trouble starts with this situation:

   - commit1 is already merged.
   - commit2a is an unmerged commit on Gerrit, which is based on commit1.
   - commit3 is the commit that I’m working on, which is based on commit2a.
   - Now commit2a is modified, and the new patchset is commit2b, whose
   parent is still commit1.
   - I want to rebase commit3 on top of commit2b.

The situation can be re-created with the following git commands:
git init
touch file1
git add file1
git commit -m "commit1"
git checkout -b branch2
touch file2a
git add file2a
git commit -m "commit2a"
git checkout -b branch3
touch file3
git add file3
git commit -m "commit3"
git checkout branch2
git rm file2a
touch file2b
git add file2b
git commit -a --amend -m "commit2b"
git checkout branch3
git rebase branch2

Expected: `git log branch3` shows commit1-commit2b-commit3
Actual: `git log branch3` shows commit1-commit2b-commit2a-commit3

git doesn't seem to recognize that commit2b is a replacement of commit2a,
and therefore keeps both.
This happens only if there's no conflict between commit2a and commit2b.
When there's a conflict, git would tell me to run `git rebase --skip` which
would give the correct results.

If Alex or another git guru can help me solve this problem, I would be
happy to start using unmerged parent commits.

Yours, Junxiao
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