[PATCH] Add -B flag to diff-* brothers.

A new diffcore transformation, diffcore-break.c, is introduced.

When the -B flag is given, a patch that represents a complete
rewrite is broken into a deletion followed by a creation.  This
makes it easier to review such a complete rewrite patch.

The -B flag takes the same syntax as the -M and -C flags to
specify the minimum amount of non-source material the resulting
file needs to have to be considered a complete rewrite, and
defaults to 99% if not specified.

As the new test t4008-diff-break-rewrite.sh demonstrates, if a
file is a complete rewrite, it is broken into a delete/create
pair, which can further be subjected to the usual rename
detection if -M or -C is used.  For example, if file0 gets
completely rewritten to make it as if it were rather based on
file1 which itself disappeared, the following happens:

    The original change looks like this:

	file0     --> file0' (quite different from file0)
	file1     --> /dev/null

    After diffcore-break runs, it would become this:

	file0     --> /dev/null
	/dev/null --> file0'
	file1     --> /dev/null

    Then diffcore-rename matches them up:

	file1     --> file0'

The internal score values are finer grained now.  Earlier
maximum of 10000 has been raised to 60000; there is no user
visible changes but there is no reason to waste available bits.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 9 insertions, 3 deletions

diff --git a/diffcore.h b/diffcore.h
index 032902ac7..dc0f21db9 100644
--- a/diffcore.h
+++ b/diffcore.h
@@ -8,8 +8,9 @@
  * (e.g. diffcore-rename, diffcore-pickaxe).  Never include this header
  * in anything else.
  */
-#define MAX_SCORE 10000
-#define DEFAULT_MINIMUM_SCORE 5000
+#define MAX_SCORE 60000
+#define DEFAULT_RENAME_SCORE 30000 /* rename/copy similarity minimum (50%) */
+#define DEFAULT_BREAK_SCORE  59400 /* minimum for break to happen (99%)*/
 
 #define RENAME_DST_MATCHED 01
 
@@ -40,14 +41,19 @@ struct diff_filepair {
 	struct diff_filespec *one;
 	struct diff_filespec *two;
 	unsigned short int score;
-	char source_stays; /* all of R/C are copies */
 	char status; /* M C R N D U (see Documentation/diff-format.txt) */
+	unsigned source_stays : 1; /* all of R/C are copies */
+	unsigned broken_pair : 1;
 };
 #define DIFF_PAIR_UNMERGED(p) \
 	(!DIFF_FILE_VALID((p)->one) && !DIFF_FILE_VALID((p)->two))
 
 #define DIFF_PAIR_RENAME(p) (strcmp((p)->one->path, (p)->two->path))
 
+#define DIFF_PAIR_BROKEN(p) \
+	( (!DIFF_FILE_VALID((p)->one) != !DIFF_FILE_VALID((p)->two)) && \
+	  ((p)->broken_pair != 0) )
+
 #define DIFF_PAIR_TYPE_CHANGED(p) \
 	((S_IFMT & (p)->one->mode) != (S_IFMT & (p)->two->mode))