Re: How to find the commit that erase a change

From: Junio C Hamano <gitster@pobox.com>
Date: Oct 9, 2019, 03:02 UTC
Message-ID: <xmqqmuealiy3.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <5e12e2d8.1ed16.16dae58d6ac.Coremail.wuzhouhui14@mails.ucas.ac.cn>

wuzhouhui <wuzhouhui14@mails.ucas.ac.cn> writes:

> I have a file which contains complicated change history. When I use
>     git log -p file
> to see all changes made in this file, I found that a change disappeared
> for no reason.

"git log [-p] <pathspec>" is not about seeing *all* changes made to the path(s) that match the pathspec. Especially when your history has merges, the command is to give you _one_ simplest explanation as to how the contents of the path(s) came to be in the shape you see in HEAD.

So for example, if you have a history like this (time flows from left to right):

    O-----A-----B----M-----N
           \        /
            \      /
             X----Y

where A or B did *not* touch "file", X added a definition of func() to "file", Y reverted the change X made to "file", M made a natural merge between B and Y and N did not touch "file", "git log N file" would not even show the existence of commits X or Y. In the larger picture, at ancient time O, the file started without func(), and none of the commits A, B, M or N felt the need to add it and as the result, N does not need the unwanted func(). So "file's contents are the same since O throughout the history reaching N" is given as _one_ simplest explanation.

The "--full-history" option may help, though.