diff: factor out add_diff_options()

Add a function for appending the parseopts member of struct diff_options
to a struct option array.  Use it in two sites instead of accessing the
parseopts member directly.  Decoupling callers from diff internals like
that allows us to change the latter.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/range-diff.c

@@ -47,7 +47,7 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 
 	repo_diff_setup(the_repository, &diffopt);
 
-	options = parse_options_concat(range_diff_options, diffopt.parseopts);
+	options = add_diff_options(range_diff_options, &diffopt);
 	argc = parse_options(argc, argv, prefix, options,
 			     builtin_range_diff_usage, PARSE_OPT_KEEP_DASHDASH);
 

diff-no-index.c

@@ -255,8 +255,7 @@ int diff_no_index(struct rev_info *revs,
 	};
 	struct option *options;
 
-	options = parse_options_concat(no_index_options,
-				       revs->diffopt.parseopts);
+	options = add_diff_options(no_index_options, &revs->diffopt);
 	argc = parse_options(argc, argv, revs->prefix, options,
 			     diff_no_index_usage, 0);
 	if (argc != 2) {

diff.c

@@ -5397,6 +5397,12 @@ static int diff_opt_rotate_to(const struct option *opt, const char *arg, int uns
 	return 0;
 }
 
+struct option *add_diff_options(const struct option *opts,
+				struct diff_options *options)
+{
+	return parse_options_concat(opts, options->parseopts);
+}
+
 static void prep_parse_options(struct diff_options *options)
 {
 	struct option parseopts[] = {

diff.h

@@ -539,6 +539,7 @@ int git_diff_ui_config(const char *var, const char *value, void *cb);
 #define diff_setup(diffopts) repo_diff_setup(the_repository, diffopts)
 #endif
 void repo_diff_setup(struct repository *, struct diff_options *);
+struct option *add_diff_options(const struct option *, struct diff_options *);
 int diff_opt_parse(struct diff_options *, const char **, int, const char *);
 void diff_setup_done(struct diff_options *);
 int git_config_rename(const char *var, const char *value);