Mailing list + git format-patch + git apply can generate author != committer
In projects like the Linux kernel where patches are:
generating a single new commit with different author and committer:
- the author is who wrote the patch
- the committer is who is a project maintainer, and who merged the patch
See for example this randomly selected patch and the corresponding commit:
Git web interfaces like GitHub and GitLab may or may not generate author != committer
Since Git(Hub|Lab) hold both the upstream and the fork repositories on a the same machine, they can automatically do anything that you can do locally as well, including either of:
Create a merge commit.
Does not generate author != committer.
Keeps the SHA or the new commit intact, and creates a new commit:
* Merge commit (committer == author == project maintainer)
|\
| * Feature commit (committer == author == contributor)
|/
* Old master (random committer and author)
Historically, this was the first available method on GitHub.
Locally, this is done with git merge --no-ff.
This produces two commits per pull request, and keeps a fork in the git history.
rebase on top of master
GitHub also hacks the commits to set committer == whoever pressed the merge button. This is not mandatory, and not even done by default locally by git rebase, but it gives accountability to the project maintainer.
The git tree now looks like:
* Feature commit (committer == maintainer, author == contributor)
|
* Old master (random committer and author)
which is exactly like that of the git apply email patches.
On GitHub currently:
- you choose the method when merging via the dropdown on the merge button
- methods can be enabled or disabled on the repo settings by the owner
https://help.github.com/articles/about-merge-methods-on-github/
How to set the committer of a new commit?
The best I could find was using the environment variables to override the committer:
GIT_COMMITTER_NAME='a' GIT_COMMITTER_EMAIL='a' git commit --author 'a <a>'
How to get the committer and commit date of a given commit?
Only author data shows by default on git log.
To see the committer date you can either:
format the log specifically for that:
git log --pretty='%cn %cd' -n1 HEAD
where cn and cd stand for Committer Name and Committer Date
use the fuller predefined format:
git log --format=fuller
See also: How to configure 'git log' to show 'commit date'
go low level and show the entire commit data:
git cat-file -p HEAD
How to set the committer date of a new commit?
git commit --date only sets the author date: for the committer date the best I could find was with the environment variable:
GIT_COMMITTER_DATE='2000-01-01T00:00:00+0000' git commit --date='2000-01-01T00:00:00+0000'
See also: What is the difference between author and committer in Git?
How Git stores author vs committer internally?
See: What is the file format of a git commit object?
Basically, the commit is a text file, and it contains two line separated fields:
author {author_name} <{author_email}> {author_date_seconds} {author_date_timezone}
committer {committer_name} <{committer_email}> {committer_date_seconds} {committer_date_timezone}
This makes it clear that both are two completely independent data entries in the commit object.
