Interdiff between amended commits

Interdiff between amended commits

[Stefan Haller]

I'd like to show an interdiff between two commits, e.g. when a commit
was amended.

I'm aware of the "intercommit" alias in the git wiki:

  $ git show commit1 > .git/commit1 && git show commit2 > .git/commit2 && interdiff .git/commit[12]

It only works for simple cases though, and I'd also like to avoid the
dependency to an external tool if possible.

So one thing I came up with is this:

  git checkout commit1^
  git cherry-pick --no-commit commit2
  git diff --cached

Two problems:

1) It requires a non-bare clone. At the place where I need it (on a
   server that sends commit emails) I only have a bare clone, so ideally
   I'd like something that doesn't need a working directory at all.

2) I'm not sure what to do if the cherry-pick doesn't apply cleanly.
   (The interdiff command has the same problem, of course).
   I don't even know what information I want to see in that case;
   anybody have an idea?

Any other thoughts about this are appreciated.


-- 
Stefan Haller
Berlin, Germany
http://www.haller-berlin.de/

Re: Interdiff between amended commits

[Michael J Gruber]

Stefan Haller venit, vidit, dixit 13.04.2011 13:54:
> I'd like to show an interdiff between two commits, e.g. when a commit
> was amended.
> 
> I'm aware of the "intercommit" alias in the git wiki:
> 
>   $ git show commit1 > .git/commit1 && git show commit2 > .git/commit2 && interdiff .git/commit[12]
> 

This basically computes the diff between two patches, using a tool which
groks the patch format.

> It only works for simple cases though, and I'd also like to avoid the
> dependency to an external tool if possible.

You could use git diff --no-index instead, so that would work in really
simple cases only, probably.

> 
> So one thing I came up with is this:
> 
>   git checkout commit1^
>   git cherry-pick --no-commit commit2
>   git diff --cached

That does something completely different. It compares the tree of
commit1^ with the tree of (commit1^ with commit2's patch applied). I
don't see how commit1's patch plays any role here.

Depending on what your actual use case, you may be happier with "git
diff commit1 commit2". Alternatively, you may produce a fake merge with
parents commit1 and commit2 and tree commit1^ and look at "show -R -c"
for that. Sounds weird, I know ;)

Michael

Re: Interdiff between amended commits

[Stefan Haller]

Michael J Gruber <git@drmicha.warpmail.net> wrote:

> > So one thing I came up with is this:
> > 
> >   git checkout commit1^
> >   git cherry-pick --no-commit commit2
> >   git diff --cached
> 
> That does something completely different. It compares the tree of
> commit1^ with the tree of (commit1^ with commit2's patch applied). I
> don't see how commit1's patch plays any role here.

Sorry, that was just a typo.  I meant

  git diff --cached commit1

as the last line, of course.

Alternatively, I could do it the other way round, by saying

  git checkout commit2^
  git cherry-pick --no-commit commit1
  git diff --cached -R commit2

That should produce the same result (except maybe for the line numbers
in the hunk headers), as long as the cherry-pick didn't have conflicts.

> Depending on what your actual use case, you may be happier with "git
> diff commit1 commit2"

No, that's not what I want (except when commit1 and commit2 have the
same parent).  This would also show the differences between the parents
of commit1 and commit2; I don't want to include those.

My actual use case is that I have a central repository that sends out
commit emails; when someone does an interactive rebase and amends a
commit in the middle of a branch, I want to match up corresponding
commits based on their subject line, and then send an email showing how
the diff for that commit changed.


-- 
Stefan Haller
Berlin, Germany
http://www.haller-berlin.de/

Re: Interdiff between amended commits

[Michael J Gruber]

Stefan Haller venit, vidit, dixit 14.04.2011 10:09:
> Michael J Gruber <git@drmicha.warpmail.net> wrote:
> 
>>> So one thing I came up with is this:
>>>
>>>   git checkout commit1^
>>>   git cherry-pick --no-commit commit2
>>>   git diff --cached
>>
>> That does something completely different. It compares the tree of
>> commit1^ with the tree of (commit1^ with commit2's patch applied). I
>> don't see how commit1's patch plays any role here.
> 
> Sorry, that was just a typo.  I meant
> 
>   git diff --cached commit1
> 
> as the last line, of course.
> 
> Alternatively, I could do it the other way round, by saying
> 
>   git checkout commit2^
>   git cherry-pick --no-commit commit1
>   git diff --cached -R commit2
> 
> That should produce the same result (except maybe for the line numbers
> in the hunk headers), as long as the cherry-pick didn't have conflicts.
> 
>> Depending on what your actual use case, you may be happier with "git
>> diff commit1 commit2"
> 
> No, that's not what I want (except when commit1 and commit2 have the
> same parent).  This would also show the differences between the parents
> of commit1 and commit2; I don't want to include those.
> 
> My actual use case is that I have a central repository that sends out
> commit emails; when someone does an interactive rebase and amends a
> commit in the middle of a branch, I want to match up corresponding
> commits based on their subject line, and then send an email showing how
> the diff for that commit changed.

In that case, "git diff --no-index" on the two patches (i.e. the alias
you found with "interdiff" replaced) may be worth a try. We should be
able to teach our diff machinery about our diffs :) I mean, see userdiff
and funcname.

Michael