builtin/show-ref: refactor --exclude-existing options

It's not immediately obvious options which options are applicable to
what subcommand in git-show-ref(1) because all options exist as global
state. This can easily cause confusion for the reader.

Refactor options for the `--exclude-existing` subcommand to be contained
in a separate structure. This structure is stored on the stack and
passed down as required. Consequently, it clearly delimits the scope of
those options and requires the reader to worry less about global state.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

builtin/show-ref.c

@@ -19,8 +19,7 @@ static const char * const show_ref_usage[] = {
 };
 
 static int deref_tags, show_head, tags_only, heads_only, found_match, verify,
-	   quiet, hash_only, abbrev, exclude_arg;
-static const char *exclude_existing_arg;
+	   quiet, hash_only, abbrev;
 
 static void show_one(const char *refname, const struct object_id *oid)
 {
@@ -95,6 +94,15 @@ static int add_existing(const char *refname,
 	return 0;
 }
 
+struct exclude_existing_options {
+	/*
+	 * We need an explicit `enabled` field because it is perfectly valid
+	 * for `pattern` to be `NULL` even if `--exclude-existing` was given.
+	 */
+	int enabled;
+	const char *pattern;
+};
+
 /*
  * read "^(?:<anything>\s)?<refname>(?:\^\{\})?$" from the standard input,
  * and
@@ -104,11 +112,11 @@ static int add_existing(const char *refname,
  * (4) ignore if refname is a ref that exists in the local repository;
  * (5) otherwise output the line.
  */
-static int cmd_show_ref__exclude_existing(const char *match)
+static int cmd_show_ref__exclude_existing(const struct exclude_existing_options *opts)
 {
 	struct string_list existing_refs = STRING_LIST_INIT_DUP;
 	char buf[1024];
-	int matchlen = match ? strlen(match) : 0;
+	int patternlen = opts->pattern ? strlen(opts->pattern) : 0;
 
 	for_each_ref(add_existing, &existing_refs);
 	while (fgets(buf, sizeof(buf), stdin)) {
@@ -124,11 +132,11 @@ static int cmd_show_ref__exclude_existing(const char *match)
 		for (ref = buf + len; buf < ref; ref--)
 			if (isspace(ref[-1]))
 				break;
-		if (match) {
+		if (opts->pattern) {
 			int reflen = buf + len - ref;
-			if (reflen < matchlen)
+			if (reflen < patternlen)
 				continue;
-			if (strncmp(ref, match, matchlen))
+			if (strncmp(ref, opts->pattern, patternlen))
 				continue;
 		}
 		if (check_refname_format(ref, 0)) {
@@ -201,44 +209,46 @@ static int hash_callback(const struct option *opt, const char *arg, int unset)
 static int exclude_existing_callback(const struct option *opt, const char *arg,
 				     int unset)
 {
+	struct exclude_existing_options *opts = opt->value;
 	BUG_ON_OPT_NEG(unset);
-	exclude_arg = 1;
-	*(const char **)opt->value = arg;
+	opts->enabled = 1;
+	opts->pattern = arg;
 	return 0;
 }
 
-static const struct option show_ref_options[] = {
-	OPT_BOOL(0, "tags", &tags_only, N_("only show tags (can be combined with heads)")),
-	OPT_BOOL(0, "heads", &heads_only, N_("only show heads (can be combined with tags)")),
-	OPT_BOOL(0, "verify", &verify, N_("stricter reference checking, "
-		    "requires exact ref path")),
-	OPT_HIDDEN_BOOL('h', NULL, &show_head,
-			N_("show the HEAD reference, even if it would be filtered out")),
-	OPT_BOOL(0, "head", &show_head,
-	  N_("show the HEAD reference, even if it would be filtered out")),
-	OPT_BOOL('d', "dereference", &deref_tags,
-		    N_("dereference tags into object IDs")),
-	OPT_CALLBACK_F('s', "hash", &abbrev, N_("n"),
-		       N_("only show SHA1 hash using <n> digits"),
-		       PARSE_OPT_OPTARG, &hash_callback),
-	OPT__ABBREV(&abbrev),
-	OPT__QUIET(&quiet,
-		   N_("do not print results to stdout (useful with --verify)")),
-	OPT_CALLBACK_F(0, "exclude-existing", &exclude_existing_arg,
-		       N_("pattern"), N_("show refs from stdin that aren't in local repository"),
-		       PARSE_OPT_OPTARG | PARSE_OPT_NONEG, exclude_existing_callback),
-	OPT_END()
-};
-
 int cmd_show_ref(int argc, const char **argv, const char *prefix)
 {
+	struct exclude_existing_options exclude_existing_opts = {0};
+	const struct option show_ref_options[] = {
+		OPT_BOOL(0, "tags", &tags_only, N_("only show tags (can be combined with heads)")),
+		OPT_BOOL(0, "heads", &heads_only, N_("only show heads (can be combined with tags)")),
+		OPT_BOOL(0, "verify", &verify, N_("stricter reference checking, "
+			    "requires exact ref path")),
+		OPT_HIDDEN_BOOL('h', NULL, &show_head,
+				N_("show the HEAD reference, even if it would be filtered out")),
+		OPT_BOOL(0, "head", &show_head,
+		  N_("show the HEAD reference, even if it would be filtered out")),
+		OPT_BOOL('d', "dereference", &deref_tags,
+			    N_("dereference tags into object IDs")),
+		OPT_CALLBACK_F('s', "hash", &abbrev, N_("n"),
+			       N_("only show SHA1 hash using <n> digits"),
+			       PARSE_OPT_OPTARG, &hash_callback),
+		OPT__ABBREV(&abbrev),
+		OPT__QUIET(&quiet,
+			   N_("do not print results to stdout (useful with --verify)")),
+		OPT_CALLBACK_F(0, "exclude-existing", &exclude_existing_opts,
+			       N_("pattern"), N_("show refs from stdin that aren't in local repository"),
+			       PARSE_OPT_OPTARG | PARSE_OPT_NONEG, exclude_existing_callback),
+		OPT_END()
+	};
+
 	git_config(git_default_config, NULL);
 
 	argc = parse_options(argc, argv, prefix, show_ref_options,
 			     show_ref_usage, 0);
 
-	if (exclude_arg)
-		return cmd_show_ref__exclude_existing(exclude_existing_arg);
+	if (exclude_existing_opts.enabled)
+		return cmd_show_ref__exclude_existing(&exclude_existing_opts);
 	else if (verify)
 		return cmd_show_ref__verify(argv);
 	else