diff: make more cases implicit --no-index

When specifying an absolute path, or a relative path pointing outside
the working tree, do not fail, but roll your own diffopt parsing,
and execute a --no-index diff.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

builtin-diff-files.c

@@ -23,7 +23,10 @@ int cmd_diff_files(int argc, const char **argv, const char *prefix)
 	git_config(git_default_config); /* no "diff" UI options */
 	rev.abbrev = 0;
 
-	argc = setup_revisions(argc, argv, &rev, NULL);
+	if (!setup_diff_no_index(&rev, argc, argv, nongit, prefix))
+		argc = 0;
+	else
+		argc = setup_revisions(argc, argv, &rev, NULL);
 	if (!rev.diffopt.output_format)
 		rev.diffopt.output_format = DIFF_FORMAT_RAW;
 	return run_diff_files_cmd(&rev, argc, argv);

builtin-diff.c

@@ -215,7 +215,10 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 	git_config(git_diff_ui_config);
 	init_revisions(&rev, prefix);
 
-	argc = setup_revisions(argc, argv, &rev, NULL);
+	if (!setup_diff_no_index(&rev, argc, argv, nongit, prefix))
+		argc = 0;
+	else
+		argc = setup_revisions(argc, argv, &rev, NULL);
 	if (!rev.diffopt.output_format) {
 		rev.diffopt.output_format = DIFF_FORMAT_PATCH;
 		if (diff_setup_done(&rev.diffopt) < 0)

diff-lib.c

@@ -200,6 +200,60 @@ static int handle_diff_files_args(struct rev_info *revs,
 	return 0;
 }
 
+static int is_outside_repo(const char *path, int nongit, const char *prefix)
+{
+	int i;
+	if (nongit || !strcmp(path, "-") || path[0] == '/')
+		return 1;
+	if (prefixcmp(path, "../"))
+		return 0;
+	if (!prefix)
+		return 1;
+	for (i = strlen(prefix); !prefixcmp(path, "../"); ) {
+		while (i > 0 && prefix[i - 1] != '/')
+			i--;
+		if (--i < 0)
+			return 1;
+		path += 3;
+	}
+	return 0;
+}
+
+int setup_diff_no_index(struct rev_info *revs,
+		int argc, const char ** argv, int nongit, const char *prefix)
+{
+	int i;
+	for (i = 1; i < argc; i++)
+		if (argv[i][0] != '-')
+			break;
+		else if (!strcmp(argv[i], "--")) {
+			i++;
+			break;
+		} else if (i < argc - 3 && !strcmp(argv[i], "--no-index")) {
+			i = argc - 3;
+			break;
+		}
+	if (argc != i + 2 || (!is_outside_repo(argv[i + 1], nongit, prefix) &&
+				!is_outside_repo(argv[i], nongit, prefix)))
+		return -1;
+
+	diff_setup(&revs->diffopt);
+	for (i = 1; i < argc - 2; )
+		if (!strcmp(argv[i], "--no-index"))
+			i++;
+		else {
+			int j = diff_opt_parse(&revs->diffopt,
+					argv + i, argc - i);
+			if (!j)
+				die("invalid diff option/value: %s", argv[i]);
+			i += j;
+		}
+	revs->diffopt.paths = argv + argc - 2;
+	revs->diffopt.nr_paths = 2;
+	revs->max_count = -2;
+	return 0;
+}
+
 int run_diff_files_cmd(struct rev_info *revs, int argc, const char **argv)
 {
 	int silent_on_removed;

diff.h

@@ -222,6 +222,8 @@ extern void diff_flush(struct diff_options*);
 extern const char *diff_unique_abbrev(const unsigned char *, int);
 
 extern int run_diff_files(struct rev_info *revs, int silent_on_removed);
+extern int setup_diff_no_index(struct rev_info *revs,
+		int argc, const char ** argv, int nongit, const char *prefix);
 extern int run_diff_files_cmd(struct rev_info *revs, int argc, const char **argv);
 
 extern int run_diff_index(struct rev_info *revs, int cached);