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Re: Request to add option to interactive rebase to preserve latest commit date




Peter Krefting <peter@xxxxxxxxxxxxxxxx> writes:

> Junio C Hamano:
>
>>> Using interactive rebase has one flaw IMHO and that is the way it
>>> handles dating its commit. Can you add an option to interactive rebase
>>> that would make it use the date from the commit that is most recent
>>> and not the date from the commit that is the oldest?
>>
>> I am not sure what you mean by this.  If you interactively rebase
>> the topmost two commits (assuming that since three commits ago, you
>> have a linear history):
>
> I sort of assume that this is when merging several fixup! or squash!
> commits. I often end up adding lines the code to date these with the
> current date, but the date of the last fixup'ed or squash'ed commit
> would probably be better.

Ah, I see.  So if you have (time flows left to right, as usual):

	A---B---C

where B and C are fixup for A, the question is what's the author
ident and author time should be for the resulting single commit.

I think we currently use the ident and time from the original A, and
that is the only right thing to do, as I view

	$ git commit -m A
	$ edit
	$ git commit -a --fixup HEAD ;# create B to fix A
	$ edit
	$ git commit -a --fixup HEAD^ ;# create C to fix A
	$ git rebase --autosquash -i HEAD~3 ;# squash B and C into A

as merely a different way to do the following:

	$ git commit -m A
	$ edit
	$ edit further ;# working tree has an equivalent of C
	$ git commit --amend -a

The principle is "the bulk of the work was done in A, no matter what
is done incrementally by squashing in or amending small refinements;
the primary authorship date and time stays the same as the original".

When the person who is correcting other's change with --amend makes
a contribution that is substantial enough such that the amended HEAD
no longer resembles the original HEAD, there is a mechanism to let
the amender take authorship, i.e. do this at the last step instead

	$ git commit --reset-author --amend -a

in the second sequence.  I do not think there currently is an
equivalent in "rebase -i" language to do so.  

I am still not convinced it is a good idea, but I can see how
another verb that behaves like existing "fixup" or "squash" but use
the authorship not from the updated but from the updating commit
might seem useful.