Add --strict switch to diff-cache to force SHA1 checking

@@ -1,6 +1,7 @@
 #include "cache.h"
 
 static int cached_only = 0;
+static int strict_checking = 0;
 static int line_termination = '\n';
 
 /* A file entry went away or appeared */

@@ -10,6 +11,26 @@
 	       sha1_to_hex(ce->sha1), ce->name, line_termination);
 }
 
+static int check_modified_signature(struct cache_entry *old, struct stat *st)
+{
+	void *map;
+	int ret = -1;
+	int fd = open(old->name, O_RDONLY);
+
+	if (fd < 0)
+		return -1;
+
+	map = mmap(NULL, st->st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	if (map != MAP_FAILED) {
+		ret = check_sha1_signature(old->sha1, map, st->st_size, "blob");
+		munmap(map, st->st_size);
+	}
+
+	close(fd);
+
+	return ret;
+}
+
 static int show_modified(struct cache_entry *old, struct cache_entry *new)
 {
 	unsigned int mode = ntohl(new->ce_mode), oldmode;

@@ -27,6 +48,12 @@
 		changed = cache_match_stat(new, &st);
 		if (changed) {
 			mode = st.st_mode;
+
+			if (strict_checking
+			    && mode == ntohl(old->ce_mode)
+			    && check_modified_signature(old, &st) == 0)
+				return 0;
+
 			sha1 = no_sha1;
 		}
 	}

@@ -85,7 +112,7 @@
 	}
 }
 
-static char *diff_cache_usage = "diff-cache [-r] [-z] [--cached] <tree sha1>";
+static char *diff_cache_usage = "diff-cache [-r] [-z] [--cached] [--strict] <tree sha1>";
 
 int main(int argc, char **argv)
 {

@@ -110,6 +137,10 @@
 			cached_only = 1;
 			continue;
 		}
+		if (!strcmp(arg, "--strict")) {
+			strict_checking = 1;
+			continue;
+		}
 		usage(diff_cache_usage);
 	}
 

@@ -76,7 +76,7 @@
 	# FIXME: Update ret based on what did we match. And take "$@"
 	# to account after all.
 	ret=
-	diff-cache -r -z $tree | xargs -0 gitdiff-do "$tree" uncommitted "$filter"
+	diff-cache -r -z --strict $tree | xargs -0 gitdiff-do "$tree" uncommitted "$filter"
 
 	if [ "$id1" != " " ]; then
 		rm $GIT_INDEX_FILE