[PATCH] Diff-helper update

This patch adds a framework and a stub implementation of rename
detection to diff-helper program.

The current stub code is just enough to detect pure renames in
diff-tree output and not fancier.  The plan is perhaps to use
the same delta code when Nico's delta storage patch is merged
for similarity evaluation purposes.

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

diff-helper.c

@@ -21,6 +21,129 @@ static int matches_pathspec(const char *name, const char **spec, int cnt)
 	return 0;
 }
 
+static int detect_rename = 0;
+
+/*
+ * We do not detect circular renames.  Just hold created and deleted
+ * entries and later attempt to match them up.  If they do not match,
+ * then spit them out as deletes or creates as original.
+ */
+
+static struct diff_spec_hold {
+	struct diff_spec_hold *next;
+	struct diff_spec_hold *matched;
+	struct diff_spec old, new;
+	char path[1];
+} *createdfile, *deletedfile;
+
+static void hold_spec(const char *path,
+		      struct diff_spec *old, struct diff_spec *new)
+{
+	struct diff_spec_hold **list, *elem;
+	list = (! old->file_valid) ? &createdfile : &deletedfile;
+	elem = xmalloc(sizeof(*elem) + strlen(path));
+	strcpy(elem->path, path);
+	elem->next = *list;
+	*list = elem;
+	elem->old = *old;
+	elem->new = *new;
+	elem->matched = 0;
+}
+
+#define MINIMUM_SCORE 7000
+int estimate_similarity(struct diff_spec *one, struct diff_spec *two)
+{
+	/* Return how similar they are, representing the score as an
+	 * integer between 0 and 10000.
+	 *
+	 * This version is very dumb and detects exact matches only.
+	 * Wnen Nico's delta stuff gets in, I'll use the delta
+	 * algorithm to estimate the similarity score in core.
+	 */
+
+	if (one->sha1_valid && two->sha1_valid &&
+	    !memcmp(one->blob_sha1, two->blob_sha1, 20))
+		return 10000;
+	return 0;
+}
+
+static void flush_renames(const char **spec, int cnt, int reverse)
+{
+	struct diff_spec_hold *rename_src, *rename_dst, *elem;
+	struct diff_spec_hold *leftover = NULL;
+	int score, best_score;
+
+	while (createdfile) {
+		rename_dst = createdfile;
+		createdfile = rename_dst->next;
+		best_score = MINIMUM_SCORE;
+		rename_src = NULL;
+		for (elem = deletedfile;
+		     elem;
+		     elem = elem->next) {
+			if (elem->matched)
+				continue;
+			score = estimate_similarity(&elem->old,
+						    &rename_dst->new);
+			if (best_score < score) {
+				rename_src = elem;
+				best_score = score;
+			}
+		}
+		if (rename_src) {
+			rename_src->matched = rename_dst;
+			rename_dst->matched = rename_src;
+
+			if (!cnt ||
+			    matches_pathspec(rename_src->path, spec, cnt) ||
+			    matches_pathspec(rename_dst->path, spec, cnt)) {
+				if (reverse)
+					run_external_diff(rename_dst->path,
+							  rename_src->path,
+							  &rename_dst->new,
+							  &rename_src->old);
+				else
+					run_external_diff(rename_src->path,
+							  rename_dst->path,
+							  &rename_src->old,
+							  &rename_dst->new);
+			}
+		}
+		else {
+			rename_dst->next = leftover;
+			leftover = rename_dst;
+		}
+	}
+
+	/* unmatched deletes */
+	for (elem = deletedfile; elem; elem = elem->next) {
+		if (elem->matched)
+			continue;
+		if (!cnt ||
+		    matches_pathspec(elem->path, spec, cnt)) {
+			if (reverse)
+				run_external_diff(elem->path, NULL,
+						  &elem->new, &elem->old);
+			else
+				run_external_diff(elem->path, NULL,
+						  &elem->old, &elem->new);
+		}
+	}
+
+	/* unmatched creates */
+	for (elem = leftover; elem; elem = elem->next) {
+		if (!cnt ||
+		    matches_pathspec(elem->path, spec, cnt)) {
+			if (reverse)
+				run_external_diff(elem->path, NULL,
+						  &elem->new, &elem->old);
+			else
+				run_external_diff(elem->path, NULL,
+						  &elem->old, &elem->new);
+		}
+	}
+}
+
 static int parse_oneside_change(const char *cp, struct diff_spec *one,
 				char *path)
 {
@@ -100,17 +223,24 @@ static int parse_diff_raw_output(const char *buf,
 	default:
 		return -1;
 	}
+
+	if (detect_rename && old.file_valid != new.file_valid) {
+		/* hold these */
+		hold_spec(path, &old, &new);
+		return 0;
+	}
+
 	if (!cnt || matches_pathspec(path, spec, cnt)) {
 		if (reverse)
-			run_external_diff(path, &new, &old);
+			run_external_diff(path, NULL, &new, &old);
 		else
-			run_external_diff(path, &old, &new);
+			run_external_diff(path, NULL, &old, &new);
 	}
 	return 0;
 }
 
 static const char *diff_helper_usage =
-"git-diff-helper [-R] [-z] paths...";
+	"git-diff-helper [-r] [-R] [-z] paths...";
 
 int main(int ac, const char **av) {
 	struct strbuf sb;
@@ -124,6 +254,8 @@ int main(int ac, const char **av) {
 			reverse = 1;
 		else if (av[1][1] == 'z')
 			line_termination = 0;
+		else if (av[1][1] == 'r')
+			detect_rename = 1;
 		else
 			usage(diff_helper_usage);
 		ac--; av++;
@@ -139,5 +271,8 @@ int main(int ac, const char **av) {
 		if (status)
 			fprintf(stderr, "cannot parse %s\n", sb.buf);
 	}
+
+	if (detect_rename)
+		flush_renames(av+1, ac-1, reverse);
 	return 0;
 }