[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, 6 insertions, 2 deletions

diff --git a/diff-files.c b/diff-files.c
index 3f20e7eee..b840b35d1 100644
--- a/diff-files.c
+++ b/diff-files.c
@@ -15,6 +15,7 @@ static int diff_setup_opt = 0;
 static int diff_score_opt = 0;
 static const char *pickaxe = NULL;
 static int pickaxe_opts = 0;
+static int diff_break_opt = -1;
 static int silent = 0;
 
 static void show_unmerge(const char *path)
@@ -57,6 +58,8 @@ int main(int argc, const char **argv)
 			pickaxe = argv[1] + 2;
 		else if (!strcmp(argv[1], "--pickaxe-all"))
 			pickaxe_opts = DIFF_PICKAXE_ALL;
+		else if (!strncmp(argv[1], "-B", 2))
+			diff_break_opt = diff_scoreopt_parse(argv[1]);
 		else if (!strncmp(argv[1], "-M", 2)) {
 			diff_score_opt = diff_scoreopt_parse(argv[1]);
 			detect_rename = DIFF_DETECT_RENAME;
@@ -116,9 +119,10 @@ int main(int argc, const char **argv)
 		show_modified(oldmode, mode, ce->sha1, null_sha1,
 			      ce->name);
 	}
-	diffcore_std(argv + 1,
+	diffcore_std((1 < argc) ? argv + 1 : NULL,
 		     detect_rename, diff_score_opt,
-		     pickaxe, pickaxe_opts);
+		     pickaxe, pickaxe_opts,
+		     diff_break_opt);
 	diff_flush(diff_output_format, 1);
 	return 0;
 }