Git bisect with merged commits

I have a history that looks like this:

* 3830e61 Add data escaping.              (Bad)
* 0f5e148 Improve function for getting page template.
*   aaf8dc5 Merge branch 'navigation'
|\
| * 3e667f8 Add icons.
| * 43a07b1 Add menu styles.              (Breaks)
| * 107ca95 Add Responsive Nav.           (Good)
* | ea3d736 Add ‘Admin’ notice.
* | 17ca0bb Update placeholder text.
|/
* f52cc34 Add featured image.
* 2abd954 Style placeholders.

I am trying to learn more and git bisect, but am having trouble with this history. I know that 107ca95 is good and 3830e61 is bad. When I run a git bisect, commits 107ca95..3e667f8 are ignored. I happen to know that 43a07b1 is the commit that introduced a regression, but it is never evaluated.

Here is roughly what I've done:

git checkout master
git bisect start
git bisect bad
git bisect good 107ca95
git bisect bad (multiple times)

No matter what I do, 107ca95..3e667f8 are never checked out to be tested.

Is there any way that I can essentially "flatten" the history during the bisect to test those commits? I know I can use an interactive rebase to flatten the history, but I do not want to have to do that.

This is a very old but unanswered question. I decided to investigate, and found that I could show that the behavior of Git is different to what the question says it is. One explanation is that Git improved the algorithm for bisect, or that the questioner made a mistake in marking commits.

> I am trying to learn more and git bisect, but am having trouble with this history. I know that 107ca95 is good and 3830e61 is bad. When I run a git bisect, commits 107ca95..3e667f8 are ignored. I happen to know that 43a07b1 is the commit that introduced a regression, but it is never evaluated.

I wrote some code to check whether it is evaluated or not. My test shows that it is evaluated. Run the code below and verify that a commit with message Add menu styles. appears.

Further comments:

• "commits 107ca95..3e667f8 are ignored": Please note, that the commit you marked as "good" will not be evaluated because git already knows it to be good.
• Please read the section "Bisection Algorithm" in this article by Christian Couder. Also the section "Checking merge bases" might be relevant.
• As mentioned above, the question was certainly using a different version then the one I used (Question is from 2013, Git 2.11 is from 2016).

Bisect run output

• Notice that first 'Add Admin notice' is checked (line 4) because that provides the most information. (Read "Checking merge bases" from article mentioned above.)
• From then on, it bisects the linear history as would be expected.

This is already answered

Basic idea - to find which commit from feature-branch breaks your master, you will have to reapply it on top of ea3d736 - relevant master HEAD.

Following is an example (from git doc)of test script which does that for you:

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.

You can select the range of commits with the "git start" command. The synopsis of the command is:

git bisect start <bad> <good>

In your specific case I think the right command would be:

git bisect start 3830e61 107ca95