Parse shorthand refspecs as valid

Relax the ONELEVEL ref naming rules so the refspec parsing code can
ask for 'master' to be considered valid.

include/git2/refs.h

@@ -422,6 +422,13 @@ typedef enum {
 	 * (e.g., foo/<star>/bar but not foo/bar<star>).
 	 */
 	GIT_REF_FORMAT_REFSPEC_PATTERN = (1 << 1),
+
+	/**
+	 * Interpret the name as part of a refspec in shorthand form
+	 * so the `ONELEVEL` naming rules aren't enforced and 'master'
+	 * becomes a valid name.
+	 */
+	GIT_REF_FORMAT_REFSPEC_SHORTHAND = (1 << 2),
 } git_reference_normalize_t;
 
 /**

src/refs.c

@@ -752,6 +752,7 @@ int git_reference__normalize_name(
 		goto cleanup;
 
 	if ((segments_count == 1 ) &&
+	    !(flags & GIT_REF_FORMAT_REFSPEC_SHORTHAND) &&
 		!(is_all_caps_and_underscore(name, (size_t)segment_len) ||
 			((flags & GIT_REF_FORMAT_REFSPEC_PATTERN) && !strcmp("*", name))))
 			goto cleanup;

src/refspec.c

@@ -60,7 +60,7 @@ int git_refspec__parse(git_refspec *refspec, const char *input, bool is_fetch)
 
 	refspec->pattern = is_glob;
 	refspec->src = git__strndup(lhs, llen);
-	flags = GIT_REF_FORMAT_ALLOW_ONELEVEL
+	flags = GIT_REF_FORMAT_ALLOW_ONELEVEL | GIT_REF_FORMAT_REFSPEC_SHORTHAND
 		| (is_glob ? GIT_REF_FORMAT_REFSPEC_PATTERN : 0);
 
 	if (is_fetch) {

tests-clar/network/refspecs.c

@@ -81,4 +81,7 @@ void test_network_refspecs__parsing(void)
 
 	assert_refspec(GIT_DIRECTION_FETCH, "refs/heads/*/for-linus:refs/remotes/mine/*", true);
 	assert_refspec(GIT_DIRECTION_PUSH, "refs/heads/*/for-linus:refs/remotes/mine/*", true);
+
+	assert_refspec(GIT_DIRECTION_FETCH, "master", true);
+	assert_refspec(GIT_DIRECTION_PUSH, "master", true);
 }