thodg/libgit2

diff --git a/include/git2/tag.h b/include/git2/tag.h
index c47e341..c751a13 100644
--- a/include/git2/tag.h
+++ b/include/git2/tag.h
@@ -140,7 +140,8 @@ GIT_EXTERN(const char *) git_tag_message(git_tag *t);
  * @param repo Repository where to store the tag
  *
  * @param tag_name Name for the tag; this name is validated
- * for consistency
+ * for consistency. It should also not conflict with an 
+ * already existing tag name
  *
  * @param target OID to which this tag points; note that no
  *	validation is done on this OID. Use the _o version of this
@@ -202,6 +203,78 @@ GIT_EXTERN(int) git_tag_create_frombuffer(
 		git_repository *repo,
 		const char *buffer);
 
+/**
+ * Create a new tag in the repository from an OID
+ * and overwrite an already existing tag reference, if any.
+ *
+ * @param oid Pointer where to store the OID of the
+ *	newly created tag
+ *
+ * @param repo Repository where to store the tag
+ *
+ * @param tag_name Name for the tag; this name is validated
+ * for consistency.
+ *
+ * @param target OID to which this tag points; note that no
+ *	validation is done on this OID. Use the _fo version of this
+ *	method to assure a proper object is being tagged
+ *
+ * @param target_type Type of the tagged OID; note that no
+ *	validation is performed here either
+ *
+ * @param tagger Signature of the tagger for this tag, and
+ *  of the tagging time
+ *
+ * @param message Full message for this tag
+ *
+ * @return 0 on success; error code otherwise.
+ *	A tag object is written to the ODB, and a proper reference
+ *	is written in the /refs/tags folder, pointing to it
+ */
+GIT_EXTERN(int) git_tag_create_f(
+		git_oid *oid,
+		git_repository *repo,
+		const char *tag_name,
+		const git_oid *target,
+		git_otype target_type,
+		const git_signature *tagger,
+		const char *message);
+
+/**
+ * Create a new tag in the repository from an existing
+ * `git_object` instance and overwrite an already existing 
+ * tag reference, if any.
+ *
+ * This method replaces the `target` and `target_type`
+ * paremeters of `git_tag_create_f` by a single instance
+ * of a `const git_object *`, which is assured to be
+ * a proper object in the ODB and hence will create
+ * a valid tag
+ *
+ * @see git_tag_create_f
+ */
+GIT_EXTERN(int) git_tag_create_fo(
+		git_oid *oid,
+		git_repository *repo,
+		const char *tag_name,
+		const git_object *target,
+		const git_signature *tagger,
+		const char *message);
+
+/**
+ * Delete an existing tag reference.
+ *
+ * @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 on success; error code otherwise.
+ */
+GIT_EXTERN(int) git_tag_delete(
+		git_repository *repo,
+		const char *tag_name);
+
 /** @} */
 GIT_END_DECL
 #endif
diff --git a/src/tag.c b/src/tag.c
index 5982a05..ef58e09 100644
--- a/src/tag.c
+++ b/src/tag.c
@@ -153,38 +153,61 @@ static int parse_tag_buffer(git_tag *tag, const char *buffer, const char *buffer
 	return GIT_SUCCESS;
 }
 
-int git_tag_create_o(
-		git_oid *oid,
-		git_repository *repo,
-		const char *tag_name,
-		const git_object *target,
-		const git_signature *tagger,
-		const char *message)
+static int retreive_tag_reference(git_reference **tag_reference_out, char *ref_name_out, git_repository *repo, const char *tag_name)
 {
-	return git_tag_create(
-		oid, repo, tag_name, 
-		git_object_id(target),
-		git_object_type(target),
-		tagger, message);
+	git_reference *tag_ref;
+	int error;
+
+	git__joinpath(ref_name_out, GIT_REFS_TAGS_DIR, tag_name);
+	error = git_reference_lookup(&tag_ref, repo, ref_name_out);
+	if (error < GIT_SUCCESS)
+		return error;
+
+	*tag_reference_out = tag_ref;
+
+	return GIT_SUCCESS;
 }
 
-int git_tag_create(
+static int tag_create(
 		git_oid *oid,
 		git_repository *repo,
 		const char *tag_name,
 		const git_oid *target,
 		git_otype target_type,
 		const git_signature *tagger,
-		const char *message)
+		const char *message,
+		int allow_ref_overwrite)
 {
 	size_t final_size = 0;
 	git_odb_stream *stream;
 
 	const char *type_str;
 	char *tagger_str;
+	git_reference *new_ref;
+
+	char ref_name[MAX_GITDIR_TREE_STRUCTURE_PATH_LENGTH];
 
 	int type_str_len, tag_name_len, tagger_str_len, message_len;
-	int error;
+	int error, should_update_ref = 0;
+
+	/** Ensure the tag name doesn't conflict with an already existing 
+	    reference unless overwriting has explictly been requested **/
+	error = retreive_tag_reference(&new_ref, ref_name, repo, tag_name);
+
+	switch (error) {
+	case GIT_SUCCESS:
+		if (!allow_ref_overwrite)
+			return GIT_EEXISTS;	
+		should_update_ref = 1;
+		
+		/* Fall trough */
+
+	case GIT_ENOTFOUND: 
+		break;
+
+	default:
+		return error;
+	}
 
 	type_str = git_object_type2string(target_type);
 
@@ -222,13 +245,14 @@ int git_tag_create(
 	error = stream->finalize_write(oid, stream);
 	stream->free(stream);
 
-	if (error == GIT_SUCCESS) {
-		char ref_name[512];
-		git_reference *new_ref;
-		git__joinpath(ref_name, GIT_REFS_TAGS_DIR, tag_name);
-		error = git_reference_create_oid(&new_ref, repo, ref_name, oid);
-	}
+	if (error < GIT_SUCCESS)
+		return error;
 
+	if (!should_update_ref)
+		error = git_reference_create_oid(&new_ref, repo, ref_name, oid);
+	else
+		error = git_reference_set_oid(new_ref, oid);
+	
 	return error;
 }
 
@@ -261,6 +285,81 @@ cleanup:
 	return error;
 }
 
+int git_tag_create_o(
+		git_oid *oid,
+		git_repository *repo,
+		const char *tag_name,
+		const git_object *target,
+		const git_signature *tagger,
+		const char *message)
+{
+	return tag_create(
+		oid, repo, tag_name, 
+		git_object_id(target),
+		git_object_type(target),
+		tagger, message, 0);
+}
+
+int git_tag_create(
+		git_oid *oid,
+		git_repository *repo,
+		const char *tag_name,
+		const git_oid *target,
+		git_otype target_type,
+		const git_signature *tagger,
+		const char *message)
+{
+	return tag_create(
+		oid, repo, tag_name, 
+		target,
+		target_type,
+		tagger, message, 0);
+}
+
+int git_tag_create_fo(
+		git_oid *oid,
+		git_repository *repo,
+		const char *tag_name,
+		const git_object *target,
+		const git_signature *tagger,
+		const char *message)
+{
+	return tag_create(
+		oid, repo, tag_name, 
+		git_object_id(target),
+		git_object_type(target),
+		tagger, message, 1);
+}
+
+int git_tag_create_f(
+		git_oid *oid,
+		git_repository *repo,
+		const char *tag_name,
+		const git_oid *target,
+		git_otype target_type,
+		const git_signature *tagger,
+		const char *message)
+{
+	return tag_create(
+		oid, repo, tag_name, 
+		target,
+		target_type,
+		tagger, message, 1);
+}
+
+int git_tag_delete(git_repository *repo, const char *tag_name)
+{
+	int error;
+	git_reference *tag_ref;
+	char ref_name[MAX_GITDIR_TREE_STRUCTURE_PATH_LENGTH];
+
+	error = retreive_tag_reference(&tag_ref, ref_name, repo, tag_name);
+	if (error < GIT_SUCCESS)
+		return error;
+
+	return git_reference_delete(tag_ref);
+}
+
 int git_tag__parse(git_tag *tag, git_odb_object *obj)
 {
 	assert(tag);
diff --git a/tests/t08-tag.c b/tests/t08-tag.c
index 70eeb28..5bd3e14 100644
--- a/tests/t08-tag.c
+++ b/tests/t08-tag.c
@@ -58,6 +58,9 @@ BEGIN_TEST(read0, "read and parse a tag from the repository")
 
 	must_be_true(git_oid_cmp(&id_commit, git_commit_id(commit)) == 0);
 
+	git_tag_close(tag1);
+	git_tag_close(tag2);
+	git_commit_close(commit);
 	git_repository_free(repo);
 END_TEST
 
@@ -72,20 +75,19 @@ BEGIN_TEST(write0, "write a tag to the repository and read it again")
 	git_oid target_id, tag_id;
 	const git_signature *tagger;
 	git_reference *ref_tag;
-	/* char hex_oid[41]; */
 
 	must_pass(git_repository_open(&repo, REPOSITORY_FOLDER));
 
 	git_oid_mkstr(&target_id, tagged_commit);
 
-	/* create signatures */
+	/* create signature */
 	tagger = git_signature_new(TAGGER_NAME, TAGGER_EMAIL, 123456789, 60);
 	must_be_true(tagger != NULL);
 
 	must_pass(git_tag_create(
 		&tag_id, /* out id */
 		repo,
-		"the-tag", /* do not update the HEAD */
+		"the-tag",
 		&target_id,
 		GIT_OBJ_COMMIT,
 		tagger,
@@ -94,6 +96,7 @@ BEGIN_TEST(write0, "write a tag to the repository and read it again")
 	git_signature_free((git_signature *)tagger);
 
 	must_pass(git_tag_lookup(&tag, repo, &tag_id));
+	must_be_true(git_oid_cmp(git_tag_target_oid(tag), &target_id) == 0);
 
 	/* Check attributes were set correctly */
 	tagger = git_tag_tagger(tag);
@@ -111,12 +114,136 @@ BEGIN_TEST(write0, "write a tag to the repository and read it again")
 
 	must_pass(remove_loose_object(REPOSITORY_FOLDER, (git_object *)tag));
 
+	git_tag_close(tag);
 	git_repository_free(repo);
 
 END_TEST
 
+BEGIN_TEST(write1, "write a tag to the repository which points to an unknown oid and read it again")
+	git_repository *repo;
+	git_tag *tag;
+	git_oid target_id, tag_id;
+	const git_signature *tagger;
+	git_reference *ref_tag;
+	git_object *zombie;
+
+	must_pass(git_repository_open(&repo, REPOSITORY_FOLDER));
+
+	git_oid_mkstr(&target_id, "deadbeef1b46c854b31185ea97743be6a8774479");
+
+	/* create signature */
+	tagger = git_signature_new(TAGGER_NAME, TAGGER_EMAIL, 123456789, 60);
+	must_be_true(tagger != NULL);
+
+	must_pass(git_tag_create(
+		&tag_id, /* out id */
+		repo,
+		"the-zombie-tag",
+		&target_id,
+		GIT_OBJ_COMMIT,
+		tagger,
+		TAGGER_MESSAGE));
+
+	git_signature_free((git_signature *)tagger);
+
+	must_pass(git_tag_lookup(&tag, repo, &tag_id));
+	
+	/* The non existent target can not be looked up */
+	must_fail(git_tag_target(&zombie, tag));
+
+	must_pass(git_reference_lookup(&ref_tag, repo, "refs/tags/the-zombie-tag"));
+	
+	must_pass(git_reference_delete(ref_tag));
+	must_pass(remove_loose_object(REPOSITORY_FOLDER, (git_object *)tag));
+
+	git_tag_close(tag);
+	git_repository_free(repo);
+
+END_TEST
+
+BEGIN_TEST(write2, "Attempt to write a tag bearing the same name than an already existing tag")
+	git_repository *repo;
+	git_oid target_id, tag_id;
+	const git_signature *tagger;
+
+	must_pass(git_repository_open(&repo, REPOSITORY_FOLDER));
+
+	git_oid_mkstr(&target_id, tagged_commit);
+
+	/* create signature */
+	tagger = git_signature_new(TAGGER_NAME, TAGGER_EMAIL, 123456789, 60);
+	must_be_true(tagger != NULL);
+
+	must_fail(git_tag_create(
+		&tag_id, /* out id */
+		repo,
+		"very-simple",
+		&target_id,
+		GIT_OBJ_COMMIT,
+		tagger,
+		TAGGER_MESSAGE));
+
+	git_signature_free((git_signature *)tagger);
+
+	git_repository_free(repo);
+
+END_TEST
+
+BEGIN_TEST(write3, "Replace an already existing tag")
+	git_repository *repo;
+	git_oid target_id, tag_id, old_tag_id;
+	const git_signature *tagger;
+	git_reference *ref_tag;
+
+	must_pass(open_temp_repo(&repo, REPOSITORY_FOLDER));
+
+	git_oid_mkstr(&target_id, tagged_commit);
+
+	must_pass(git_reference_lookup(&ref_tag, repo, "refs/tags/very-simple"));
+	git_oid_cpy(&old_tag_id, git_reference_oid(ref_tag));
+
+	/* create signature */
+	tagger = git_signature_new(TAGGER_NAME, TAGGER_EMAIL, 123456789, 60);
+	must_be_true(tagger != NULL);
+
+	must_pass(git_tag_create_f(
+		&tag_id, /* out id */
+		repo,
+		"very-simple",
+		&target_id,
+		GIT_OBJ_COMMIT,
+		tagger,
+		TAGGER_MESSAGE));
+
+	git_signature_free((git_signature *)tagger);
+
+	must_pass(git_reference_lookup(&ref_tag, repo, "refs/tags/very-simple"));
+	must_be_true(git_oid_cmp(git_reference_oid(ref_tag), &tag_id) == 0);
+	must_be_true(git_oid_cmp(git_reference_oid(ref_tag), &old_tag_id) != 0);
+
+	close_temp_repo(repo);
+
+END_TEST
+
+BEGIN_TEST(write4, "Delete an already existing tag")
+	git_repository *repo;
+	git_reference *ref_tag;
+
+	must_pass(open_temp_repo(&repo, REPOSITORY_FOLDER));
+
+	must_pass(git_tag_delete(repo,"very-simple"));
+
+	must_fail(git_reference_lookup(&ref_tag, repo, "refs/tags/very-simple"));
+
+	close_temp_repo(repo);
+
+END_TEST
 
 BEGIN_SUITE(tag)
 	ADD_TEST(read0);
-	ADD_TEST(write0); 
+	ADD_TEST(write0);
+	ADD_TEST(write1);
+	ADD_TEST(write2);
+	ADD_TEST(write3);
+	ADD_TEST(write4);
 END_SUITE
diff --git a/tests/t10-refs.c b/tests/t10-refs.c
index 413811c..b1124b3 100644
--- a/tests/t10-refs.c
+++ b/tests/t10-refs.c
@@ -227,9 +227,8 @@ BEGIN_TEST(create0, "create a new symbolic reference")
 	must_pass(git_reference_resolve(&resolved_ref, looked_up_ref));
 	must_be_true(git_oid_cmp(&id, git_reference_oid(resolved_ref)) == 0);
 
+	git_reference_delete(looked_up_ref);
 	git_repository_free(repo);
-
-	must_pass(gitfo_unlink(ref_path));	/* TODO: replace with git_reference_delete() when available */
 END_TEST
 
 BEGIN_TEST(create1, "create a deep symbolic reference")
@@ -250,9 +249,8 @@ BEGIN_TEST(create1, "create a deep symbolic reference")
 	must_pass(git_reference_resolve(&resolved_ref, looked_up_ref));
 	must_be_true(git_oid_cmp(&id, git_reference_oid(resolved_ref)) == 0);
 
+	git_reference_delete(looked_up_ref);
 	git_repository_free(repo);
-
-	must_pass(gitfo_unlink(ref_path));	/* TODO: replace with git_reference_delete() when available */
 END_TEST
 
 BEGIN_TEST(create2, "create a new OID reference")
@@ -290,9 +288,28 @@ BEGIN_TEST(create2, "create a new OID reference")
 	must_pass(git_reference_lookup(&looked_up_ref, repo, new_head));
 	must_be_true(git_oid_cmp(&id, git_reference_oid(looked_up_ref)) == 0);
 
+	git_reference_delete(looked_up_ref);
 	git_repository_free(repo);
+END_TEST
+
+BEGIN_TEST(create3, "Can not create a new OID reference which targets at an unknown id")
+	git_reference *new_reference, *looked_up_ref;
+	git_repository *repo;
+	git_oid id;
+
+	const char *new_head = "refs/heads/new-head";
+
+	git_oid_mkstr(&id, "deadbeef3f795b2b4353bcce3a527ad0a4f7f644");
+
+	must_pass(git_repository_open(&repo, REPOSITORY_FOLDER));
 
-	must_pass(gitfo_unlink(ref_path));	/* TODO: replace with git_reference_delete() when available */
+	/* Create and write the new object id reference */
+	must_fail(git_reference_create_oid(&new_reference, repo, new_head, &id));
+
+	/* Ensure the reference can't be looked-up... */
+	must_fail(git_reference_lookup(&looked_up_ref, repo, new_head));
+
+	git_repository_free(repo);
 END_TEST
 
 static const char *ref_name = "refs/heads/other";
@@ -892,6 +909,7 @@ BEGIN_SUITE(refs)
 	ADD_TEST(create0);
 	ADD_TEST(create1);
 	ADD_TEST(create2);
+	ADD_TEST(create3);
 
 	ADD_TEST(overwrite0);
 	ADD_TEST(overwrite1);