why does github show current date instead of real date of an ammended commit?

Question

I amended a commit in a github repository (wrong version in a Changelog file) some days later after the commit was pushed. When I do a git log I see that the amended commit still has the date of the original commit as it should, but in github it shows the current date instead of the original commit date as git log does. Why is this ?

Answer 1

Firstly, commits in git are immutable; you cannot in fact edit a commit. When you use commands such as commit --amend, cherry-pick, or rebase, what happens is that git creates a new commit, based on the original commit.

This new commit stores two sets of information:

• The "author" name and e-mail address, and "date authored", copied from the original commit
• The "committer" name and e-mail address, and "date committed", for the newly created commit

In fact, all commits have both sets of fields, it's just that they're generally the same, because a normal commit is "authored" and "committed" simultaneously.

What you're seeing is that "git log" on the command line is defaulting to show only the author information, and Github is defaulting to show the committer information. As far as I know, Github has no option to see both (despite its popularity, Github is actually quite a limited UI), but on the command line, you can see both at once with various formatting options, most simply:

git log --format=fuller