Re: Confused about "degenerate" combined diff for merge commits

From: Thomas Rast <trast@student.ethz.ch>
Date: Aug 15, 2010, 19:54 UTC
Message-ID: <201008152154.57578.trast@student.ethz.ch>
In-Reply-To: <1jna5yt.1pm42a3uw2yquM%lists@haller-berlin.de>

Stefan Haller wrote:

Show 17 quoted lines

> However, for some of these merge commits I see diff output such as this:
> 
> diff --cc Src/ClipBoard.cpp
> index 4357ea0,4357ea0..3fad79a
> --- a/Src/ClipBoard.cpp
> +++ b/Src/ClipBoard.cpp
> @@@ -71,7 -71,7 +71,7 @@@ AClipBoard* AClipBoard::SNew(
>   
>   AClipBoard* AClipBoard::SClipBoard()
>   {
> --  static AClipBoard* spClipBoard = SNew();
> ++  static TPtr<AClipBoard> spClipBoard = SNew();
>     return spClipBoard;
>   }
>   
> It looks like both merge parents had an identical diff here, so this is
> not a conflict; why does diff --cc even show this to me?

The --cc output has one column per parent, and if you removed all other +/-/space columns, then (for that hunk) you'd have a unified diff with that parent.

So I'd say the above means that both parents had

  static AClipBoard* spClipBoard = SNew();

but your merge result was

  static TPtr<AClipBoard> spClipBoard = SNew();

This is usually called an "evil merge" in git terms: it is introducing changes that are neither coming from one side, nor part of a benign merge resolution.

-- 
Thomas Rast
trast@{inf,student}.ethz.ch