strbuf_check_branch_ref(): a helper to check a refname for a branch

This allows a common calling sequence

	strbuf_branchname(&ref, name);
	strbuf_splice(&ref, 0, 0, "refs/heads/", 11);
	if (check_ref_format(ref.buf))
		die(...);

to be refactored into

	if (strbuf_check_branch_ref(&ref, name))
		die(...);

Signed-off-by: Junio C Hamano <gitster@pobox.com>

branch.c

@@ -135,10 +135,7 @@ void create_branch(const char *head,
 	struct strbuf ref = STRBUF_INIT;
 	int forcing = 0;
 
-	strbuf_branchname(&ref, name);
-	strbuf_splice(&ref, 0, 0, "refs/heads/", 11);
-
-	if (check_ref_format(ref.buf))
+	if (strbuf_check_branch_ref(&ref, name))
 		die("'%s' is not a valid branch name.", name);
 
 	if (resolve_ref(ref.buf, sha1, 1, NULL)) {

builtin-branch.c

@@ -468,14 +468,10 @@ static void rename_branch(const char *oldname, const char *newname, int force)
 	if (!oldname)
 		die("cannot rename the current branch while not on any.");
 
-	strbuf_branchname(&oldref, oldname);
-	strbuf_splice(&oldref, 0, 0, "refs/heads/", 11);
-	if (check_ref_format(oldref.buf))
+	if (strbuf_check_branch_ref(&oldref, oldname))
 		die("Invalid branch name: '%s'", oldname);
 
-	strbuf_branchname(&newref, newname);
-	strbuf_splice(&newref, 0, 0, "refs/heads/", 11);
-	if (check_ref_format(newref.buf))
+	if (strbuf_check_branch_ref(&newref, newname))
 		die("Invalid branch name: '%s'", newname);
 
 	if (resolve_ref(newref.buf, sha1, 1, NULL) && !force)

builtin-check-ref-format.c

@@ -11,9 +11,8 @@ int cmd_check_ref_format(int argc, const char **argv, const char *prefix)
 {
 	if (argc == 3 && !strcmp(argv[1], "--branch")) {
 		struct strbuf sb = STRBUF_INIT;
-		strbuf_branchname(&sb, argv[2]);
-		strbuf_splice(&sb, 0, 0, "refs/heads/", 11);
-		if (check_ref_format(sb.buf))
+
+		if (strbuf_check_branch_ref(&sb, argv[2]))
 			die("'%s' is not a valid branch name", argv[2]);
 		printf("%s\n", sb.buf + 11);
 		exit(0);

builtin-checkout.c

@@ -733,12 +733,11 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 
 	if (opts.new_branch) {
 		struct strbuf buf = STRBUF_INIT;
-		strbuf_addstr(&buf, "refs/heads/");
-		strbuf_addstr(&buf, opts.new_branch);
+		if (strbuf_check_branch_ref(&buf, opts.new_branch))
+			die("git checkout: we do not like '%s' as a branch name.",
+			    opts.new_branch);
 		if (!get_sha1(buf.buf, rev))
 			die("git checkout: branch %s already exists", opts.new_branch);
-		if (check_ref_format(buf.buf))
-			die("git checkout: we do not like '%s' as a branch name.", opts.new_branch);
 		strbuf_release(&buf);
 	}
 

strbuf.c

@@ -1,4 +1,5 @@
 #include "cache.h"
+#include "refs.h"
 
 int prefixcmp(const char *str, const char *prefix)
 {
@@ -366,3 +367,10 @@ int strbuf_branchname(struct strbuf *sb, const char *name)
 	strbuf_add(sb, name, len);
 	return len;
 }
+
+int strbuf_check_branch_ref(struct strbuf *sb, const char *name)
+{
+	strbuf_branchname(sb, name);
+	strbuf_splice(sb, 0, 0, "refs/heads/", 11);
+	return check_ref_format(sb->buf);
+}

strbuf.h

@@ -132,5 +132,6 @@ extern void stripspace(struct strbuf *buf, int skip_comments);
 extern int launch_editor(const char *path, struct strbuf *buffer, const char *const *env);
 
 extern int strbuf_branchname(struct strbuf *sb, const char *name);
+extern int strbuf_check_branch_ref(struct strbuf *sb, const char *name);
 
 #endif /* STRBUF_H */