Git bisect with merged commits

Question

I have a history that looks like this:

* 3830e61 Add data escaping.              (Bad)
* 0f5e148 Improve function for getting page template.
*   aaf8dc5 Merge br         


        

Answer 1

Warning: the git bisect section regarding "Automatically bisect with temporary modifications" has been updated with Git 2.25 (Q1 2020).

(And git bisect --first-parent is available with Git 2.29+ -- Q4 2020)

It involves the step where you reapply the commit you are testing on top of your relevant master commit (which was ea3d736 in the OP's case)

The "git merge --no-commit" needs "--no-ff" if you do not want to move HEAD, which has been corrected in the manual page for "git bisect".

See commit 8dd327b (28 Oct 2019) by Mihail Atanassov (matana).
^{(Merged by Junio C Hamano -- gitster -- in commit fac9ab1, 01 Dec 2019)}

Documentation/git-bisect.txt: add --no-ff to merge command

^{Signed-off-by: Mihail Atanassov
Reviewed-by: Jonathan Nieder}

The hotfix application example uses git merge --no-commit to apply temporary changes to the working tree during a bisect operation.

In some situations this can be a fast-forward and merge will apply the hotfix branch's commits regardless of --no-commit (as documented in the git merge manual).

In the pathological case this will make a [git bisect](https://git-scm.com/docs/git-bisect) run invocation loop indefinitely between the first bisect step and the fast-forwarded post-merge HEAD.

Add --no-ff to the merge command to avoid this issue.

git merge mentions indeed:

Note that fast-forward updates do not create a merge commit and therefore there is no way to stop those merges with --no-commit.

Thus, if you want to ensure your branch is not changed or updated by the merge command, use --no-ff with --no-commit.