Re: Distinguishing trivial and non-trivial merge commits

From: Jonathan Nieder <jrnieder@gmail.com>
Date: May 2, 2010, 20:29 UTC
Message-ID: <20100502202943.GB16746@progeny.tock>
In-Reply-To: <19421.54064.178345.489772@winooski.ccs.neu.edu>

Eli Barzilay wrote:

> On May  2, Jonathan Nieder wrote:

Show 7 quoted lines

>> Note that most conflicts will not show up here: if the merge result
>> matches either parent, then git diff --cc and friends will not
>> consider it interesting at all.
>
> Isn't that a good definition of a trivial commit?  I'm not talking
> about the whole commit -- just any file that is not identical to one
> of its parents.

[...]

> For my purpose, I basically just want
> to know whether there was manual tweaking involved in the merge.

diff --name-only follows exactly the example heuristic you described. It still does not catch all manual merge resolutions[1].

Sometimes two branches introduce different changes to completely separate parts of a file. This is not a conflict, and diff --cc will correctly report the merge as trivial (whereas diff --name-only does not pay enough attention to do the same).

On the other hand, sometimes two branches introduce conflicting changes, but the correct resolution for each conflict hunk is to pick one as winner. Though simple, this can be error-prone, because rejecting one change from branch A might end up breaking another change that was accepted from the same branch. diff --cc examines only the selected revision and its parents and for all it knows, this is just another trivial merge.

>  git show --pretty=format:"" --name-only "$r" | grep -q "."
>    --> test if it's trivial

I would have expected

	git show --name-only --exit-code --quiet "$r"

to take care of this, but apparently it always exits zero. Probably no one had tried it before.

> (My script generally "compensates" for git being fast by running a ton
> of them for each email...)

:)

Jonathan

[1] http://thread.gmane.org/gmane.comp.version-control.git/89415