Bug with branches/merges in submodules

Hello, I ran into a bug where commits are omitted from `git submodule summary` and friends when the submodule contains merge commits. Originally using 2.30.2, I can also reproduce this with a fresh build on the `next` branch (see attached bugreport). I would assume that this is not intentional, however I cannot find any relevant information on this. Feel free to contact me for extra details. Best regards, Mel

Thank you for filling out a Git bug report! Please answer the following questions to help us understand your issue.

What did you do before the bug happened? (Steps to reproduce your issue) Set up a submodule that has branches/merge commits: ```bash # create repository "child" mkdir child-repo cd child-repo git init touch initial.txt git add initial.txt git commit -m "initial child" cd .. # create repository "parent" mkdir parent cd parent git init # add submodule "child" to repository "parent" git submodule add ../child-repo/ child git commit -am "initial parent" cd child # make two commits in separate branches in "child" git switch -c "secondary" touch s1.txt git add s1.txt git commit -m "s1" git switch master touch m1.txt git add m1.txt git commit -m "m1" # merge branch "secondary" into "master" in "child" - this creates a merge commit git merge secondary --no-edit cd .. ``` Run `git diff --submodule=log` inside the "parent" repository.

What did you expect to happen? (Expected behavior) `git diff --submodule=log` should show all three commits added to the "child" submodule: ``` Submodule child XXXXXXX..YYYYYYY

```

What happened instead? (Actual behavior) `git diff --submodule=log` only shows commits from one ancestor of the merge commit: ``` Submodule child XXXXXXX..YYYYYYY

```

What's different between what you expected and what actually happened? All the commits added to the "secondary" branch are missing in `git diff --submodule=log`.

Anything else you want to add: The commit range shown by `git diff --submodule=log` is correct: `cd child; git log XXXXXXX..YYYYYYY` shows the correct list of commits.

This bug also affects `git submodule summary`, and `git show --submodule=log` after the changes have been committed.

[System Info] git version: git version 2.32.0.262.g8c582fcd64 cpu: x86_64 built from commit: 8c582fcd643d12802e0a6d7e307890aa5b6b26e1 sizeof-long: 8 sizeof-size_t: 8 shell-path: /bin/sh uname: Linux 5.11.0-22-generic #23-Ubuntu SMP Thu Jun 17 00:34:23 UTC 2021 x86_64 compiler info: gnuc: 10.3 libc info: glibc: 2.33 $SHELL (typically, interactive shell): /bin/bash

[Enabled Hooks]

Hi Mel!

Thanks for writing in! Responses inline below.

Le 2021-07-07 à 09:13, Mel Dafert a écrit :

You are right that the doc seems to be quiet about that [1], [2].

Thanks for the reproducer. The behaviour for 'git log/show/diff' is due this line [3] and the behaviour for 'git submodule summary' to these lines [4] [5].

For 'git diff' and friends, it goes back to the addition of the '--submodule=log' option in 752c0c2492 (Add the --submodule option to the diff option family, 2009-10-19). (authored CC'ed). The use of '--first-parent' was discussed on the list when this was implemented [6]. I did not read the whole thing.

For 'git submodule summary', it goes back to the addition of the subcommand in 1cb639e6b0 (git-submodule summary: show commit summary, 2008-03-11). (author also CC'ed). The justification of the use of '--first-parent' was not really discussed as far as I could tell [7].

I personnally think it would be a good addition to be able to choose if yes or no '--first-parent' should be used.

Cheers,

Philippe.

[1] https://git-scm.com/docs/git-submodule#Documentation/git-submodule.txt-summary--cached--files-n--summary-limitltngtcommit--ltpathgt82308203 [2] https://git-scm.com/docs/git-diff#Documentation/git-diff.txt---submoduleltformatgt [3] https://github.com/git/git/blob/d486ca60a51c9cb1fe068803c3f540724e95e83a/submodule.c#L453 [4] https://github.com/git/git/blob/d486ca60a51c9cb1fe068803c3f540724e95e83a/builtin/submodule--helper.c#L1020-L1021 [5] https://github.com/git/git/blob/d486ca60a51c9cb1fe068803c3f540724e95e83a/builtin/submodule--helper.c#L1117-L1118 [6] https://lore.kernel.org/git/67a884457aeaead275612be10902a80726b2a7db.1254668669u.git.johannes.schindelin@gmx.de/t/#u [7] https://lore.kernel.org/git/?q=f%3Ayin+s%3A%280+submodule+summary+NOT%3ARe+%29+

Hello Philippe, Thank you for your reply, and the points to the mailing list.

The discussion you found [1] also suggested that as a future option.

In the original implementation, the first mention is [2], where the length of the message is discussed - I (and later discussions) assume that this just happened to be the preference of the author.

I would thus like to correct myself, and refile this as a feature request - it would be very helpful to me to have this as an option, possibly even with one that can be set in the config, similar to 'diff.submodule=log'.

I would be open to implementing this - I might need some mentoring, however, as this would be my first time contributing (and reading the git codebase).

Regards, Mel

[1] https://lore.kernel.org/git/67a884457aeaead275612be10902a80726b2a7db.1254668669u.git.johannes.schindelin@gmx.de/t/#u [2] https://lore.kernel.org/git/46dff0320803061750x70d059a2yaf1e5751e9c62150@mail.gmail.com/

Hi Mel,

Le 2021-07-14 à 07:07, Mel Dafert a écrit :

That would great! The page "Hacking Git" [1] has several pointers to interesting ressources to learn about the code and the contribution process. One of these is the "My First Contribution" tutorial. [2]

Cheers,

Philippe.

[1] https://git.github.io/Hacking-Git/ [2] https://git-scm.com/docs/MyFirstContribution