thodg/libgit2

diff --git a/include/git2/tag.h b/include/git2/tag.h
index f82a6c9..a9773be 100644
--- a/include/git2/tag.h
+++ b/include/git2/tag.h
@@ -144,6 +144,10 @@ GIT_EXTERN(const char *) git_tag_message(const git_tag *tag);
  * The message will not be cleaned up. This can be achieved
  * through `git_message_prettify()`.
  *
+ * The tag name will be checked for validity. You must avoid
+ * the characters '~', '^', ':', '\\', '?', '[', and '*', and the
+ * sequences ".." and "@{" which have special meaning to revparse.
+ *
  * @param oid Pointer where to store the OID of the
  * newly created tag. If the tag already exists, this parameter
  * will be the oid of the existing tag, and the function will
@@ -165,7 +169,7 @@ GIT_EXTERN(const char *) git_tag_message(const git_tag *tag);
  *
  * @param force Overwrite existing references
  *
- * @return 0 or an error code
+ * @return 0 on success, GIT_EINVALIDSPEC or an error code
  *	A tag object is written to the ODB, and a proper reference
  *	is written in the /refs/tags folder, pointing to it
  */
@@ -200,6 +204,9 @@ GIT_EXTERN(int) git_tag_create_frombuffer(
  * this target object. If `force` is true and a reference
  * already exists with the given name, it'll be replaced.
  *
+ * The tag name will be checked for validity.
+ * See `git_tag_create()` for rules about valid names.
+ *
  * @param oid Pointer where to store the OID of the provided
  * target object. If the tag already exists, this parameter
  * will be filled with the oid of the existing pointed object
@@ -216,7 +223,7 @@ GIT_EXTERN(int) git_tag_create_frombuffer(
  *
  * @param force Overwrite existing references
  *
- * @return 0 or an error code
+ * @return 0 on success, GIT_EINVALIDSPEC or an error code
  *	A proper reference is written in the /refs/tags folder,
  * pointing to the provided target object
  */
@@ -230,12 +237,15 @@ GIT_EXTERN(int) git_tag_create_lightweight(
 /**
  * Delete an existing tag reference.
  *
+ * The tag name will be checked for validity.
+ * See `git_tag_create()` for rules about valid names.
+ *
  * @param repo Repository where lives the tag
  *
  * @param tag_name Name of the tag to be deleted;
  * this name is validated for consistency.
  *
- * @return 0 or an error code
+ * @return 0 on success, GIT_EINVALIDSPEC or an error code
  */
 GIT_EXTERN(int) git_tag_delete(
 	git_repository *repo,
diff --git a/src/tag.c b/src/tag.c
index 606afd6..94915ad 100644
--- a/src/tag.c
+++ b/src/tag.c
@@ -251,7 +251,7 @@ static int git_tag_create__internal(
 
 	error = retrieve_tag_reference_oid(oid, &ref_name, repo, tag_name);
 	if (error < 0 && error != GIT_ENOTFOUND)
-		return -1;
+		goto cleanup;
 
 	/** Ensure the tag name doesn't conflict with an already existing
 	 *	reference unless overwriting has explictly been requested **/
@@ -269,6 +269,7 @@ static int git_tag_create__internal(
 
 	error = git_reference_create(&new_ref, repo, ref_name.ptr, oid, allow_ref_overwrite);
 
+cleanup:
 	git_reference_free(new_ref);
 	git_buf_free(&ref_name);
 	return error;
@@ -384,7 +385,7 @@ int git_tag_delete(git_repository *repo, const char *tag_name)
 	git_buf_free(&ref_name);
 
 	if (error < 0)
-		return -1;
+		return error;
 
 	return git_reference_delete(tag_ref);
 }
diff --git a/tests-clar/object/tag/write.c b/tests-clar/object/tag/write.c
index ad6ca76..eb0ac28 100644
--- a/tests-clar/object/tag/write.c
+++ b/tests-clar/object/tag/write.c
@@ -88,7 +88,6 @@ void test_object_tag_write__overwrite(void)
 
 	git_object_free(target);
 	git_signature_free(tagger);
-
 }
 
 void test_object_tag_write__replace(void)
@@ -190,3 +189,33 @@ void test_object_tag_write__delete(void)
 
 	git_reference_free(ref_tag);
 }
+
+void test_object_tag_write__creating_with_an_invalid_name_returns_EINVALIDSPEC(void)
+{
+	git_oid target_id, tag_id;
+	git_signature *tagger;
+	git_object *target;
+
+	git_oid_fromstr(&target_id, tagged_commit);
+	cl_git_pass(git_object_lookup(&target, g_repo, &target_id, GIT_OBJ_COMMIT));
+
+	cl_git_pass(git_signature_new(&tagger, tagger_name, tagger_email, 123456789, 60));
+
+	cl_assert_equal_i(GIT_EINVALIDSPEC,
+		git_tag_create(&tag_id, g_repo,
+		  "Inv@{id", target, tagger, tagger_message, 0)
+	);
+
+	cl_assert_equal_i(GIT_EINVALIDSPEC,
+		git_tag_create_lightweight(&tag_id, g_repo,
+		  "Inv@{id", target, 0)
+	);
+
+	git_object_free(target);
+	git_signature_free(tagger);
+}
+
+void test_object_tag_write__deleting_with_an_invalid_name_returns_EINVALIDSPEC(void)
+{
+	cl_assert_equal_i(GIT_EINVALIDSPEC, git_tag_delete(g_repo, "Inv@{id"));
+}