0.20: support `git rebase --committer-date-is-author-date`

[lkraav]

There are some use cases where stg edit <some-earlier-patch> should keep all following timestamps intact, because let's say some system /etc configuration tracking automation failed and you just want to fixup a couple of errors, without altering anything else.

[chucklever]

This is probably related. According to:

https://stackoverflow.com/questions/2973996/git-rebase-without-changing-commit-timestamps/11179245

"git rebase" by default does not alter Author Dates. "stg rebase" does, but perhaps should not.

[chucklever]

The problem appears to be trans.push_patch (and its subroutines), not in 'stg rebase'.

• If the parent commit is unchanged and 'stg push' does not modify the patch, currently the Author date remains the same. This is the correct behavior.
• If the parent commit has changed, then currently push_patch updates Author date, even if the pushed patch itself is not modified by the push operation. This is a common situation during a rebase. I suggest that Author date should not be changed in this case.
• If the parent commit is unchanged and 'stg push' modifies the pushed patch, then currently the Author date remains the same. I suggest that in this case, the Author date should be refreshed.

[chucklever]

After updating to stgit-0.22, "stg rebase" and "stg push" behave correctly. Ignore my comments above, thanks.

[jpgrayson]

I'm triaging old issues and trying to make sense of this one. Do we believe, @lkraav @chucklever, that there is a change needed for StGit?

If there is a bug, what would be most helpful for me is a test case that illustrates the bug. As things stand, I'm not sure the scenarios in which stg edit does or does not alter the author date in a way that is not desired.

[lkraav]

My original issue is not about a bug, more of a feature.

I'd like to occasionally fix up a commit somewhere mid-tree with stg edit, without altering any date information for following commits as they are pushed back on the stack.

[jpgrayson]

Is this a fair example of the behavior you are interested in:

$ for p in a b c; do stg new -m $p; sleep 3; done
Now at patch "a"
Now at patch "b"
Now at patch "c"
$ for p in a b c; do echo "$p:"; stg show --diff-opts=--pretty=fuller $p | rg Date; done
a:
AuthorDate: Mon Apr 20 08:30:25 2020 -0400
CommitDate: Mon Apr 20 08:30:25 2020 -0400
b:
AuthorDate: Mon Apr 20 08:30:28 2020 -0400
CommitDate: Mon Apr 20 08:30:28 2020 -0400
c:
AuthorDate: Mon Apr 20 08:30:31 2020 -0400
CommitDate: Mon Apr 20 08:30:31 2020 -0400
$ stg edit -m "edit a" a
Popped c -- b
Pushing patch "b" ... done (empty)
Pushing patch "c" ... done (empty)
$ for p in a b c; do echo "$p:"; stg show --diff-opts=--pretty=fuller $p | rg Date; done
a:
AuthorDate: Mon Apr 20 08:30:25 2020 -0400
CommitDate: Mon Apr 20 08:30:58 2020 -0400  <-- New CommitDate
b:
AuthorDate: Mon Apr 20 08:30:28 2020 -0400
CommitDate: Mon Apr 20 08:30:58 2020 -0400  <-- New CommitDate
c:
AuthorDate: Mon Apr 20 08:30:31 2020 -0400
CommitDate: Mon Apr 20 08:30:58 2020 -0400  <-- New CommitDate

When editing patch at the bottom of the stack (patch a), all of the AuthorDates are preserved, but the CommitDates are all updated.

You are asking for an option to forge the CommitDate to remain the same as the AuthorDate. (Sorry to be so slow on the uptake)

I also see that --committer-date-is-author-date comes from git am and is also used by git rebase. It makes sense that if StGit was to have an option for this, we would use this name.

My next question is to which commands should have the --committer-date-is-author-date option? Any command that alters an existing patch, I think. So these commands:

• stg edit
• stg refresh
• stg import
• stg rebase
• stg pull
• stg pick
• stg fold

I buy this as a valid and useful StGit feature. I cannot promise when I may implement it though.

[lkraav]

👍 yep that looks correct.

stg edit and refresh get by far the most use here.

rebase is solid 3rd place, but I haven't found myself needing to alter default date arrangement there very much if at all.

[pcmoore]

For whatever it is worth, I have a small little shell wrapper around stg to workaround this (and do a few other things); it determines the commit date before editing and uses that to forcibly set the commit date using $GIT_COMMITTER_DATE when editing. Here is the relevant snippet from the wrapper:

function cmd_edit() {
        local rc=0

        # we only do this to workaround a problem where stgit v1.3 always
        # updates the commit date even if there are not textual changes

        # skip past the "edit" parameter
        shift

        # make sure we have at least one patch applied
        stg top >& /dev/null || return $?

        # try to find the commit date
        local commit=""
        local commit_date=""
        for i in "$@"; do
                stg id $i >& /dev/null
                rc=$?
                if [[ $rc -eq 0 ]]; then
                        commit=$i
                        break;
                fi
        done
        [[ $rc -ne 0 ]] && commit=$(stg top)
        commit_date=$(git show -s --format=%ci $(stg id $commit) 2> /dev/null)
        [[ -z $commit_date ]] && return 1

        # do the edit but force the commit date to the current value
        GIT_COMMITTER_DATE="$commit_date" stg edit "$@"
        return $?
}