remote: validate refspecs before adding to config

When we moved from acting on the instance to acting on the
configuration, we dropped the validation of the passed refspec, which
can lead to writing an invalid refspec to the configuration. Bring that
validation back.

include/git2/remote.h

@@ -168,7 +168,7 @@ GIT_EXTERN(int) git_remote_set_pushurl(git_repository *repo, const char *remote,
  * @param repo the repository in which to change the configuration
  * @param remote the name of the remote to change
  * @param refspec the new fetch refspec
- * @return 0 or an error value
+ * @return 0, GIT_EINVALIDSPEC if refspec is invalid or an error value
  */
 GIT_EXTERN(int) git_remote_add_fetch(git_repository *repo, const char *remote, const char *refspec);
 
@@ -192,7 +192,7 @@ GIT_EXTERN(int) git_remote_get_fetch_refspecs(git_strarray *array, const git_rem
  * @param repo the repository in which to change the configuration
  * @param remote the name of the remote to change
  * @param refspec the new push refspec
- * @return 0 or an error value
+ * @return 0, GIT_EINVALIDSPEC if refspec is invalid or an error value
  */
 GIT_EXTERN(int) git_remote_add_push(git_repository *repo, const char *remote, const char *refspec);
 

src/remote.c

@@ -97,6 +97,7 @@ static int write_add_refspec(git_repository *repo, const char *name, const char
 {
 	git_config *cfg;
 	git_buf var = GIT_BUF_INIT;
+	git_refspec spec;
 	const char *fmt;
 	int error;
 
@@ -108,6 +109,15 @@ static int write_add_refspec(git_repository *repo, const char *name, const char
 	if ((error = ensure_remote_name_is_valid(name)) < 0)
 		return error;
 
+	if ((error = git_refspec__parse(&spec, refspec, fetch)) < 0) {
+		if (giterr_last()->klass != GITERR_NOMEMORY)
+			error = GIT_EINVALIDSPEC;
+
+		return error;
+	}
+
+	git_refspec__free(&spec);
+
 	if ((error = git_buf_printf(&var, fmt, name)) < 0)
 		return error;
 

tests/network/remote/remotes.c

@@ -128,6 +128,8 @@ void test_network_remote_remotes__add_fetchspec(void)
 	cl_assert_equal_s(git_refspec_dst(_refspec), "refs/*");
 	cl_assert_equal_s(git_refspec_string(_refspec), "refs/*:refs/*");
 	cl_assert_equal_b(_refspec->push, false);
+
+	cl_git_fail_with(GIT_EINVALIDSPEC, git_remote_add_fetch(_repo, "test", "refs/*/foo/*:refs/*"));
 }
 
 void test_network_remote_remotes__dup(void)