diff-files: do not play --no-index games

Being able to say "git diff A B" outside a git repository and getting a
colourful version of "diff -u A B" may be nice, but such a cute hack
should not give bogus results to scripts that want to give two paths,
either or both of which happen to have been removed from the work tree,
to "git diff-files".
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-diff-files.txt

@@ -8,7 +8,7 @@ git-diff-files - Compares files in the working tree and the index
 
 SYNOPSIS
 --------
-'git-diff-files' [-q] [-0|-1|-2|-3|-c|--cc|--no-index] [<common diff options>] [<path>...]
+'git-diff-files' [-q] [-0|-1|-2|-3|-c|--cc] [<common diff options>] [<path>...]
 
 DESCRIPTION
 -----------
@@ -36,9 +36,6 @@ omit diff output for unmerged entries and just show "Unmerged".
 	diff, similar to the way 'diff-tree' shows a merge
 	commit with these flags.
 
---no-index::
-	Compare the two given files / directories.
-
 -q::
 	Remain silent even on nonexistent files
 

builtin-diff-files.c

@@ -10,26 +10,54 @@
 #include "builtin.h"
 
 static const char diff_files_usage[] =
-"git-diff-files [-q] [-0/-1/2/3 |-c|--cc|--no-index] [<common diff options>] [<path>...]"
+"git-diff-files [-q] [-0/-1/2/3 |-c|--cc] [<common diff options>] [<path>...]"
 COMMON_DIFF_OPTIONS_HELP;
 
 int cmd_diff_files(int argc, const char **argv, const char *prefix)
 {
 	struct rev_info rev;
-	int nongit;
 	int result;
+	unsigned options = 0;
 
-	prefix = setup_git_directory_gently(&nongit);
 	init_revisions(&rev, prefix);
 	git_config(git_diff_basic_config); /* no "diff" UI options */
 	rev.abbrev = 0;
 
-	if (!setup_diff_no_index(&rev, argc, argv, nongit, prefix))
-		argc = 0;
-	else
-		argc = setup_revisions(argc, argv, &rev, NULL);
+	argc = setup_revisions(argc, argv, &rev, NULL);
+	while (1 < argc && argv[1][0] == '-') {
+		if (!strcmp(argv[1], "--base"))
+			rev.max_count = 1;
+		else if (!strcmp(argv[1], "--ours"))
+			rev.max_count = 2;
+		else if (!strcmp(argv[1], "--theirs"))
+			rev.max_count = 3;
+		else if (!strcmp(argv[1], "-q"))
+			options |= DIFF_SILENT_ON_REMOVED;
+		else
+			usage(diff_files_usage);
+		argv++; argc--;
+	}
 	if (!rev.diffopt.output_format)
 		rev.diffopt.output_format = DIFF_FORMAT_RAW;
-	result = run_diff_files_cmd(&rev, argc, argv);
+
+	/*
+	 * Make sure there are NO revision (i.e. pending object) parameter,
+	 * rev.max_count is reasonable (0 <= n <= 3), and
+	 * there is no other revision filtering parameters.
+	 */
+	if (rev.pending.nr ||
+	    rev.min_age != -1 || rev.max_age != -1 ||
+	    3 < rev.max_count)
+		usage(diff_files_usage);
+
+	if (rev.max_count == -1 &&
+	    (rev.diffopt.output_format & DIFF_FORMAT_PATCH))
+		rev.combine_merges = rev.dense_combined_merges = 1;
+
+	if (read_cache() < 0) {
+		perror("read_cache");
+		return -1;
+	}
+	result = run_diff_files(&rev, options);
 	return diff_result_code(&rev.diffopt, result);
 }

git.c

@@ -293,7 +293,7 @@ static void handle_internal_command(int argc, const char **argv)
 		{ "count-objects", cmd_count_objects, RUN_SETUP },
 		{ "describe", cmd_describe, RUN_SETUP },
 		{ "diff", cmd_diff },
-		{ "diff-files", cmd_diff_files },
+		{ "diff-files", cmd_diff_files, RUN_SETUP },
 		{ "diff-index", cmd_diff_index, RUN_SETUP },
 		{ "diff-tree", cmd_diff_tree, RUN_SETUP },
 		{ "fast-export", cmd_fast_export, RUN_SETUP },