Re: How to fork a file (git cp ?)

From: Junio C Hamano <gitster@pobox.com>
Date: May 4, 2011, 21:02 UTC
Message-ID: <7viptqdvrf.fsf@alter.siamese.dyndns.org>
In-Reply-To: <4DC19955.7040503@kdbg.org>

Johannes Sixt <j6t@kdbg.org> writes:

Show 7 quoted lines

> Am 04.05.2011 19:56, schrieb Mikhail T.:
>> I need to add a new thing to our project. The thing will be similar to
>> what already exists. I'd like to "derive" the new files from the
>> existing ones -- without altering them and by preserving the
>> change-history.
>
> You cannot. Git does not have such a thing as "copy-with-preserved-history".

Well, if you come from the mindset that a "file" has an identity (hence there is a distinction between "This file used to be called A and at one point was renamed to B which is the name we see today" and "Some time ago somebody created a file B with the same contents as A and then removed A at the same time"), "copy" would not make much sense. What identity does a new file B gets when you create it by copying from A?

The same identity, or a different one? What happens when you later refactor the redundant part from these two files to create a common third file C? What identity does C have?

> You just cp the file and git add it. But you will not be able to follow
> a history of the file.

Correct. You cannot follow a history of _the file_, as there is no such thing.

You can still follow the history of contents, though. If you did a refactor like the one in the above example, "blame -L <range>" would follow the contents just fine. The command is a 80% satisfactory implementation of Linus's grand vision expressed in one of the most important message in the git mailing list archive:

    http://thread.gmane.org/gmane.comp.version-control.git/27/focus=217