diff.c: respect diff.renames config option

diff.renames is mentioned several times in the documentation,
but to my surprise it didn't do anything before this patch.

Also add the --no-renames option to override this from the
command-line.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/config.txt

@@ -114,6 +114,11 @@ diff.renameLimit::
 	The number of files to consider when performing the copy/rename
 	detection; equivalent to the git diff option '-l'.
 
+diff.renames::
+	Tells git to detect renames.  If set to any boolean value, it
+	will enable basic rename detection.  If set to "copies" or
+	"copy", it will detect copies, as well.
+
 format.headers::
 	Additional email headers to include in a patch to be submitted
 	by mail.  See gitlink:git-format-patch[1].

diff.c

@@ -13,6 +13,7 @@
 
 static int use_size_cache;
 
+static int diff_detect_rename_default = 0;
 static int diff_rename_limit_default = -1;
 static int diff_use_color_default = 0;
 
@@ -120,6 +121,16 @@ int git_diff_config(const char *var, const char *value)
 			diff_use_color_default = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "diff.renames")) {
+		if (!value)
+			diff_detect_rename_default = DIFF_DETECT_RENAME;
+		else if (!strcasecmp(value, "copies") ||
+			 !strcasecmp(value, "copy"))
+			diff_detect_rename_default = DIFF_DETECT_COPY;
+		else if (git_config_bool(var,value))
+			diff_detect_rename_default = DIFF_DETECT_RENAME;
+		return 0;
+	}
 	if (!strncmp(var, "diff.color.", 11)) {
 		int slot = parse_diff_color_slot(var, 11);
 		diff_colors[slot] = parse_diff_color_value(value, var);
@@ -1431,6 +1442,7 @@ void diff_setup(struct diff_options *options)
 	options->change = diff_change;
 	options->add_remove = diff_addremove;
 	options->color_diff = diff_use_color_default;
+	options->detect_rename = diff_detect_rename_default;
 }
 
 int diff_setup_done(struct diff_options *options)
@@ -1617,6 +1629,8 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 		options->xdl_opts |= XDF_IGNORE_WHITESPACE;
 	else if (!strcmp(arg, "-b") || !strcmp(arg, "--ignore-space-change"))
 		options->xdl_opts |= XDF_IGNORE_WHITESPACE_CHANGE;
+	else if (!strcmp(arg, "--no-renames"))
+		options->detect_rename = 0;
 	else
 		return 0;
 	return 1;