refs: consolidate remote name validation

In preparation for a future patch, extract from remote.c a function that
validates possible remote names so that its rules can be used
consistently in other places.

Helped-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Sean Barag <sean@barag.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/remote.c

@@ -194,8 +194,7 @@ static int add(int argc, const char **argv)
 	if (remote_is_configured(remote, 1))
 		die(_("remote %s already exists."), name);
 
-	strbuf_addf(&buf2, "refs/heads/test:refs/remotes/%s/test", name);
-	if (!valid_fetch_refspec(buf2.buf))
+	if (!valid_remote_name(name))
 		die(_("'%s' is not a valid remote name"), name);
 
 	strbuf_addf(&buf, "remote.%s.url", name);
@@ -696,11 +695,9 @@ static int mv(int argc, const char **argv)
 	if (remote_is_configured(newremote, 1))
 		die(_("remote %s already exists."), rename.new_name);
 
-	strbuf_addf(&buf, "refs/heads/test:refs/remotes/%s/test", rename.new_name);
-	if (!valid_fetch_refspec(buf.buf))
+	if (!valid_remote_name(rename.new_name))
 		die(_("'%s' is not a valid remote name"), rename.new_name);
 
-	strbuf_reset(&buf);
 	strbuf_addf(&buf, "remote.%s", rename.old_name);
 	strbuf_addf(&buf2, "remote.%s", rename.new_name);
 	if (git_config_rename_section(buf.buf, buf2.buf) < 1)

refspec.c

@@ -201,6 +201,16 @@ int valid_fetch_refspec(const char *fetch_refspec_str)
 	return ret;
 }
 
+int valid_remote_name(const char *name)
+{
+	int result;
+	struct strbuf refspec = STRBUF_INIT;
+	strbuf_addf(&refspec, "refs/heads/test:refs/remotes/%s/test", name);
+	result = valid_fetch_refspec(refspec.buf);
+	strbuf_release(&refspec);
+	return result;
+}
+
 void refspec_ref_prefixes(const struct refspec *rs,
 			  struct strvec *ref_prefixes)
 {

refspec.h

@@ -60,6 +60,7 @@ void refspec_appendn(struct refspec *rs, const char **refspecs, int nr);
 void refspec_clear(struct refspec *rs);
 
 int valid_fetch_refspec(const char *refspec);
+int valid_remote_name(const char *name);
 
 struct strvec;
 /*