builtin/branch: consolidate action-picking logic in cmd_branch()

Consolidate the logic for deciding when to create a new branch in
cmd_branch(), and save the result for reuse. Besides making the function
more explicit, this allows us to validate options that can only be used
when creating a branch. Such an option does not exist yet, but one will
be introduced in a subsequent commit.

Helped-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Glen Choo <chooglen@google.com>
Reviewed-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/branch.c

@@ -616,14 +616,15 @@ static int edit_branch_description(const char *branch_name)
 
 int cmd_branch(int argc, const char **argv, const char *prefix)
 {
-	int delete = 0, rename = 0, copy = 0, force = 0, list = 0;
-	int show_current = 0;
-	int reflog = 0, edit_description = 0;
-	int quiet = 0, unset_upstream = 0;
+	/* possible actions */
+	int delete = 0, rename = 0, copy = 0, list = 0,
+	    unset_upstream = 0, show_current = 0, edit_description = 0;
 	const char *new_upstream = NULL;
+	int noncreate_actions = 0;
+	/* possible options */
+	int reflog = 0, quiet = 0, icase = 0, force = 0;
 	enum branch_track track;
 	struct ref_filter filter;
-	int icase = 0;
 	static struct ref_sorting *sorting;
 	struct string_list sorting_options = STRING_LIST_INIT_DUP;
 	struct ref_format format = REF_FORMAT_INIT;
@@ -708,8 +709,10 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 	    filter.reachable_from || filter.unreachable_from || filter.points_at.nr)
 		list = 1;
 
-	if (!!delete + !!rename + !!copy + !!new_upstream + !!show_current +
-	    list + edit_description + unset_upstream > 1)
+	noncreate_actions = !!delete + !!rename + !!copy + !!new_upstream +
+			    !!show_current + !!list + !!edit_description +
+			    !!unset_upstream;
+	if (noncreate_actions > 1)
 		usage_with_options(builtin_branch_usage, options);
 
 	if (filter.abbrev == -1)
@@ -849,7 +852,7 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		strbuf_addf(&buf, "branch.%s.merge", branch->name);
 		git_config_set_multivar(buf.buf, NULL, NULL, CONFIG_FLAGS_MULTI_REPLACE);
 		strbuf_release(&buf);
-	} else if (argc > 0 && argc <= 2) {
+	} else if (!noncreate_actions && argc > 0 && argc <= 2) {
 		if (filter.kind != FILTER_REFS_BRANCHES)
 			die(_("The -a, and -r, options to 'git branch' do not take a branch name.\n"
 				  "Did you mean to use: -a|-r --list <pattern>?"));