Subject: bug in git diff --unified=0 ?

From: "Shawn O. Pearce" <[email-masked]>
Date: Sat, 2 May 2009 16:47:01 -0700

I can't decide if this is a bug in JGit, or a bug in CGit, or just
an area where the patch format is very unclear.

The following 2 patches are identical, but use different context:

git diff --unified=1:

    diff --git a/X b/X
    index a3648a1..2d44096 100644
    --- a/X
    +++ b/X
    @@ -2,2 +2,3 @@
     b
    +c
     d
    @@ -16,4 +17,2 @@
     q
    -r
    -s
     t

git diff --unified=0:

    diff --git a/X b/X
    index a3648a1..2d44096 100644
    --- a/X
    +++ b/X
    @@ -2,0 +3 @@
    +c
    @@ -17,2 +17,0 @@
    -r
    -s
    
Now lets look at JGit's output of that last patch, unified=0:

    diff --git a/X b/X
    index a3648a1..2d44096 100644
    --- a/X
    +++ b/X
    @@ -3,0 +3,1 @@
    +c
    @@ -17,2 +18,0 @@
    -r
    -s

Notice that `git diff --unified=1` said the first hunk started on
line 2 of the pre-image, as the 2nd line of the file is the context
line "b\n".  I call that correct.

However, `git diff --unified=0` said the first hunk started on line
2 of the pre-image, but there is no pre-image mentioned.  JGit says
it starts on line 3 of the pre-image, because the script is adding
a "c\n" on line 3.

The exact opposite behavior can be seen in the 2nd hunk, where we
delete lines.  Again, `git diff --unified=0` seems to behave as
though we had 1 line of context, but we don't.

-- 
Shawn.