[PATCH] apply.c: tolerate diff from a dirty but unchanged path

[Junio C Hamano <junkio@cox.net>]

I just noticed a problem with empty "diff --git" header a dirty
but otherwise unmodified path spits out.  The problem is related
to an old topic:

    Re: [PATCH] Do not show empty diff in diff-cache uncached.
    >>>>> "LT" == Linus Torvalds <torvalds@osdl.org> writes:

    LT> On Sat, 28 May 2005, Junio C Hamano wrote:
    >> Recent diff-cache produces "diff --git" header internally before
    >> calling the "diff" command, which results in an empty diff for
    >> such a file, cluttering the output.  This patch fixes this.

    LT> I actually _expect_ that "git-diff-files" will show
    LT> files that don't match the index, even if they happen to
    LT> have the exact content that the index points to. It's
    LT> how I know whether the index is up-to-date or not.

I now agree with the reasoning and think showing an empty "diff
--git" header is a good thing.  I had something like this, while
fixing a rename/copy bug:

    ...
     #endif

     static void diff_resolve_rename_copy(void)
    diff --git a/diffcore-break.c b/diffcore-break.c
    diff --git a/diffcore-rename.c b/diffcore-rename.c
    --- a/diffcore-rename.c
    +++ b/diffcore-rename.c
    @@ -249,8 +249,12 @@ void diffcore_rename(int detect_rename, 
    ...

I touched diffcore-break.c and decided I should not change it so
I reverted, which is why the empty "diff --git" for that file
shows that the cache is dirty.  The problem is that currently,
"git-apply --stat" seems to barf reading such a patch.

Here is a proposed fix.

------------
apply.c: tolerate diff from a dirty but otherwise unchanged cache.

For such an entry, "diff --git" line without anything else is
output, but the next "diff --git" header is not really treated
as an unrecognized diff.

Signed-off-by: Junio C Hamano <junkio@cox.net>
---
diff --git a/apply.c b/apply.c
--- a/apply.c
+++ b/apply.c
@@ -343,7 +343,7 @@ static int gitdiff_dissimilarity(const c
  */
 static int gitdiff_unrecognized(const char *line, struct patch *patch)
 {
-	return -1;
+	return -2;
 }
 
 static char *git_header_name(char *line)
@@ -453,8 +453,12 @@ static int parse_git_header(char *line, 
 			int oplen = strlen(p->str);
 			if (len < oplen || memcmp(p->str, line, oplen))
 				continue;
-			if (p->fn(line + oplen, patch) < 0)
+			switch (p->fn(line + oplen, patch)) {
+			case -1:
 				return offset;
+			case -2:
+				return -1;
+			}
 			break;
 		}
 	}