thodg/libgit2

diff --git a/src/refdb_fs.c b/src/refdb_fs.c
index f494afa..25316fe 100644
--- a/src/refdb_fs.c
+++ b/src/refdb_fs.c
@@ -992,18 +992,54 @@ out:
 static int maybe_append_head(refdb_fs_backend *backend, const git_reference *ref, const git_signature *who, const char *message)
 {
 	int error;
-	git_oid old_id;
-	git_reference *head;
+	git_oid old_id = {{0}};
+	git_reference *tmp = NULL, *head = NULL, *peeled = NULL;
+	const char *name;
 
-	error = git_reference_name_to_id(&old_id, backend->repo, ref->name);
-	if (!git_branch_is_head(ref))
+	if (ref->type == GIT_REF_SYMBOLIC)
 		return 0;
 
-	if ((error = git_reference_lookup(&head, backend->repo, "HEAD")) < 0)
+	/* if we can't resolve, we use {0}*40 as old id */
+	git_reference_name_to_id(&old_id, backend->repo, ref->name);
+
+	if ((error = git_reference_lookup(&head, backend->repo, GIT_HEAD_FILE)) < 0)
 		return error;
 
+	if (git_reference_type(head) == GIT_REF_OID)
+		goto cleanup;
+
+	if ((error = git_reference_lookup(&tmp, backend->repo, GIT_HEAD_FILE)) < 0)
+		goto cleanup;
+
+	/* Go down the symref chain until we find the branch */
+	while (git_reference_type(tmp) == GIT_REF_SYMBOLIC) {
+		error = git_reference_lookup(&peeled, backend->repo, git_reference_symbolic_target(tmp));
+		if (error < 0)
+			break;
+
+		git_reference_free(tmp);
+		tmp = peeled;
+	}
+
+	if (error == GIT_ENOTFOUND) {
+		error = 0;
+		name = git_reference_symbolic_target(tmp);
+	} else if (error < 0) {
+		goto cleanup;
+	} else {
+		name = git_reference_name(tmp);
+	}
+
+	if (error < 0)
+		goto cleanup;
+
+	if (strcmp(name, ref->name))
+		goto cleanup;
+
 	error = reflog_append(backend, head, &old_id, git_reference_target(ref), who, message);
 
+cleanup:
+	git_reference_free(tmp);
 	git_reference_free(head);
 	return error;
 }
@@ -1021,6 +1057,8 @@ static int refdb_fs_backend__write(
 	refdb_fs_backend *backend = (refdb_fs_backend *)_backend;
 	git_filebuf file = GIT_FILEBUF_INIT;
 	int error = 0, cmp = 0;
+	const char *new_target = NULL;
+	const git_oid *new_id = NULL;
 
 	assert(backend);
 
@@ -1041,6 +1079,21 @@ static int refdb_fs_backend__write(
 		goto on_error;
 	}
 
+	if (ref->type == GIT_REF_SYMBOLIC)
+		new_target = ref->target.symbolic;
+	else
+		new_id = &ref->target.oid;
+
+	error = cmp_old_ref(&cmp, _backend, ref->name, new_id, new_target);
+	if (error < 0 && error != GIT_ENOTFOUND)
+		goto on_error;
+
+	/* Don't update if we have the same value */
+	if (!error && !cmp) {
+		error = 0;
+		goto on_error; /* not really error */
+	}
+
 	if (should_write_reflog(backend->repo, ref->name)) {
 		if ((error = reflog_append(backend, ref, NULL, NULL, who, message)) < 0)
 			goto on_error;
@@ -1555,11 +1608,10 @@ success:
 /* Append to the reflog, must be called under reference lock */
 static int reflog_append(refdb_fs_backend *backend, const git_reference *ref, const git_oid *old, const git_oid *new, const git_signature *who, const char *message)
 {
-	int error, is_symbolic, was_symbolic = 0;
+	int error, is_symbolic;
 	git_oid old_id = {{0}}, new_id = {{0}};
 	git_buf buf = GIT_BUF_INIT, path = GIT_BUF_INIT;
 	git_repository *repo = backend->repo;
-	git_reference *current_ref = NULL;
 
 	is_symbolic = ref->type == GIT_REF_SYMBOLIC;
 
@@ -1569,47 +1621,33 @@ static int reflog_append(refdb_fs_backend *backend, const git_reference *ref, co
 	    !(old && new))
 		return 0;
 
-	error = git_reference_lookup(&current_ref, repo, ref->name);
-	if (error < 0 && error != GIT_ENOTFOUND)
-		return error;
-
-	if (current_ref)
-		was_symbolic = current_ref->type == GIT_REF_SYMBOLIC;
-
 	/* From here on is_symoblic also means that it's HEAD */
 
 	if (old) {
 		git_oid_cpy(&old_id, old);
-	} else if (!was_symbolic) {
+	} else {
 		error = git_reference_name_to_id(&old_id, repo, ref->name);
-		if (error == GIT_ENOTFOUND) {
-			memset(&old_id, 0, sizeof(git_oid));
-			error = 0;
-		}
-
-		if (error < 0)
+		if (error < 0 && error != GIT_ENOTFOUND)
 			return error;
 	}
 
-	if (is_symbolic) {
-		error = git_reference_name_to_id(&new_id, repo, git_reference_symbolic_target(ref));
-		if (error != 0 && error != GIT_ENOTFOUND)
-			goto cleanup;
-		/* detaching HEAD does not create an entry */
-		if (error == GIT_ENOTFOUND) {
-			error = 0;
-			goto cleanup;
-		}
+	if (new) {
+		git_oid_cpy(&new_id, new);
+	} else {
+		if (!is_symbolic) {
+			git_oid_cpy(&new_id, git_reference_target(ref));
+		} else {
+			error = git_reference_name_to_id(&new_id, repo, git_reference_symbolic_target(ref));
+			if (error < 0 && error != GIT_ENOTFOUND)
+				return error;
+			/* detaching HEAD does not create an entry */
+			if (error == GIT_ENOTFOUND)
+				return 0;
 
-		giterr_clear();
+			giterr_clear();
+		}
 	}
 
-
-	if (new)
-		git_oid_cpy(&new_id, new);
-	else if (!is_symbolic)
-		git_oid_cpy(&new_id, git_reference_target(ref));
-
 	if ((error = serialize_reflog_entry(&buf, &old_id, &new_id, who, message)) < 0)
 		goto cleanup;
 
diff --git a/tests/refs/reflog/reflog.c b/tests/refs/reflog/reflog.c
index 149e982..a50d40a 100644
--- a/tests/refs/reflog/reflog.c
+++ b/tests/refs/reflog/reflog.c
@@ -237,3 +237,27 @@ void test_refs_reflog_reflog__append_to_HEAD_when_changing_current_branch(void)
 
 	cl_assert_equal_i(nlogs_after, nlogs + 1);
 }
+
+void test_refs_reflog_reflog__do_not_append_when_no_update(void)
+{
+	size_t nlogs, nlogs_after;
+	git_reference *ref, *ref2;
+	git_reflog *log;
+
+	cl_git_pass(git_reflog_read(&log, g_repo, "HEAD"));
+	nlogs = git_reflog_entrycount(log);
+	git_reflog_free(log);
+
+	cl_git_pass(git_reference_lookup(&ref, g_repo, "refs/heads/master"));
+	cl_git_pass(git_reference_create(&ref2, g_repo, "refs/heads/master",
+					 git_reference_target(ref), 1, NULL, NULL));
+
+	git_reference_free(ref);
+	git_reference_free(ref2);
+
+	cl_git_pass(git_reflog_read(&log, g_repo, "HEAD"));
+	nlogs_after = git_reflog_entrycount(log);
+	git_reflog_free(log);
+
+	cl_assert_equal_i(nlogs_after, nlogs);
+}
diff --git a/tests/repo/head.c b/tests/repo/head.c
index d88fd90..79892a3 100644
--- a/tests/repo/head.c
+++ b/tests/repo/head.c
@@ -269,3 +269,201 @@ void test_repo_head__setting_head_updates_reflog(void)
 	git_object_free(tag);
 	git_signature_free(sig);
 }
+
+static void assert_head_reflog(git_repository *repo, size_t idx,
+			       const char *old_id, const char *new_id, const char *message)
+{
+	git_reflog *log;
+	const git_reflog_entry *entry;
+	char id_str[GIT_OID_HEXSZ + 1] = {0};
+
+	cl_git_pass(git_reflog_read(&log, repo, GIT_HEAD_FILE));
+	entry = git_reflog_entry_byindex(log, idx);
+
+	git_oid_fmt(id_str, git_reflog_entry_id_old(entry));
+	cl_assert_equal_s(old_id, id_str);
+
+	git_oid_fmt(id_str, git_reflog_entry_id_new(entry));
+	cl_assert_equal_s(new_id, id_str);
+
+	cl_assert_equal_s(message, git_reflog_entry_message(entry));
+
+	git_reflog_free(log);
+}
+
+void test_repo_head__detaching_writes_reflog(void)
+{
+	git_signature *sig;
+	git_oid id;
+	const char *msg;
+
+	cl_git_pass(git_signature_now(&sig, "me", "foo@example.com"));
+
+	msg = "message1";
+	git_oid_fromstr(&id, "e90810b8df3e80c413d903f631643c716887138d");
+	cl_git_pass(git_repository_set_head_detached(repo, &id, sig, msg));
+	assert_head_reflog(repo, 0, "a65fedf39aefe402d3bb6e24df4d4f5fe4547750",
+			   "e90810b8df3e80c413d903f631643c716887138d", msg);
+
+	msg = "message2";
+	cl_git_pass(git_repository_set_head(repo, "refs/heads/haacked", sig, msg));
+	assert_head_reflog(repo, 0, "e90810b8df3e80c413d903f631643c716887138d",
+			   "258f0e2a959a364e40ed6603d5d44fbb24765b10", msg);
+
+	git_signature_free(sig);
+}
+
+void test_repo_head__orphan_branch_does_not_count(void)
+{
+	git_signature *sig;
+	git_oid id;
+	const char *msg;
+
+	cl_git_pass(git_signature_now(&sig, "me", "foo@example.com"));
+
+	/* Have something known */
+	msg = "message1";
+	git_oid_fromstr(&id, "e90810b8df3e80c413d903f631643c716887138d");
+	cl_git_pass(git_repository_set_head_detached(repo, &id, sig, msg));
+	assert_head_reflog(repo, 0, "a65fedf39aefe402d3bb6e24df4d4f5fe4547750",
+			   "e90810b8df3e80c413d903f631643c716887138d", msg);
+
+	/* Switching to an orphan branch does not write tot he reflog */
+	cl_git_pass(git_repository_set_head(repo, "refs/heads/orphan", sig, "ignored message"));
+	assert_head_reflog(repo, 0, "a65fedf39aefe402d3bb6e24df4d4f5fe4547750",
+			   "e90810b8df3e80c413d903f631643c716887138d", msg);
+
+	/* And coming back, we set the source to zero */
+	msg = "message2";
+	cl_git_pass(git_repository_set_head(repo, "refs/heads/haacked", sig, msg));
+	assert_head_reflog(repo, 0, "0000000000000000000000000000000000000000",
+			   "258f0e2a959a364e40ed6603d5d44fbb24765b10", msg);
+
+	git_signature_free(sig);
+}
+
+void test_repo_head__set_to_current_target(void)
+{
+	git_signature *sig;
+	const char *msg;
+	git_reflog *log;
+	size_t nentries, nentries_after;
+
+	cl_git_pass(git_reflog_read(&log, repo, GIT_HEAD_FILE));
+	nentries = git_reflog_entrycount(log);
+	git_reflog_free(log);
+
+	cl_git_pass(git_signature_now(&sig, "me", "foo@example.com"));
+
+	msg = "message 1";
+	cl_git_pass(git_repository_set_head(repo, "refs/heads/haacked", sig, msg));
+	cl_git_pass(git_repository_set_head(repo, "refs/heads/haacked", sig, msg));
+
+	cl_git_pass(git_reflog_read(&log, repo, GIT_HEAD_FILE));
+	nentries_after = git_reflog_entrycount(log);
+	git_reflog_free(log);
+
+	cl_assert_equal_i(nentries + 1, nentries_after);
+
+	git_signature_free(sig);
+
+}
+
+void test_repo_head__branch_birth(void)
+{
+	git_signature *sig;
+	git_oid id;
+	git_tree *tree;
+	git_reference *ref;
+	const char *msg;
+	git_reflog *log;
+	size_t nentries, nentries_after;
+
+	cl_git_pass(git_reflog_read(&log, repo, GIT_HEAD_FILE));
+	nentries = git_reflog_entrycount(log);
+	git_reflog_free(log);
+
+	cl_git_pass(git_signature_now(&sig, "me", "foo@example.com"));
+
+	cl_git_pass(git_repository_head(&ref, repo));
+	cl_git_pass(git_reference_peel((git_object **) &tree, ref, GIT_OBJ_TREE));
+	git_reference_free(ref);
+
+	msg = "message 1";
+	cl_git_pass(git_repository_set_head(repo, "refs/heads/orphan", sig, msg));
+
+	cl_git_pass(git_reflog_read(&log, repo, GIT_HEAD_FILE));
+	nentries_after = git_reflog_entrycount(log);
+	git_reflog_free(log);
+
+	cl_assert_equal_i(nentries, nentries_after);
+
+	msg = "message 2";
+	cl_git_pass(git_commit_create(&id, repo, "HEAD", sig, sig, NULL, msg, tree, 0, NULL));
+
+	git_tree_free(tree);
+
+	cl_git_pass(git_reflog_read(&log, repo, "refs/heads/orphan"));
+	cl_assert_equal_i(1, git_reflog_entrycount(log));
+	git_reflog_free(log);
+
+	cl_git_pass(git_reflog_read(&log, repo, GIT_HEAD_FILE));
+	nentries_after = git_reflog_entrycount(log);
+	git_reflog_free(log);
+
+	cl_assert_equal_i(nentries + 1, nentries_after);
+
+	git_signature_free(sig);
+
+}
+
+static size_t entrycount(git_repository *repo, const char *name)
+{
+	git_reflog *log;
+	size_t ret;
+
+	cl_git_pass(git_reflog_read(&log, repo, name));
+	ret = git_reflog_entrycount(log);
+	git_reflog_free(log);
+
+	return ret;
+}
+
+void test_repo_head__symref_chain(void)
+{
+	git_signature *sig;
+	git_oid id;
+	git_tree *tree;
+	git_reference *ref;
+	const char *msg;
+	size_t nentries, nentries_master;
+
+	nentries = entrycount(repo, GIT_HEAD_FILE);
+
+	cl_git_pass(git_signature_now(&sig, "me", "foo@example.com"));
+
+	cl_git_pass(git_repository_head(&ref, repo));
+	cl_git_pass(git_reference_peel((git_object **) &tree, ref, GIT_OBJ_TREE));
+	git_reference_free(ref);
+
+	nentries_master = entrycount(repo, "refs/heads/master");
+
+	msg = "message 1";
+	cl_git_pass(git_reference_symbolic_create(&ref, repo, "refs/heads/master", "refs/heads/foo", 1, sig, msg));
+	git_reference_free(ref);
+
+	cl_assert_equal_i(0, entrycount(repo, "refs/heads/foo"));
+	cl_assert_equal_i(nentries, entrycount(repo, GIT_HEAD_FILE));
+	cl_assert_equal_i(nentries_master, entrycount(repo, "refs/heads/master"));
+
+	msg = "message 2";
+	cl_git_pass(git_commit_create(&id, repo, "HEAD", sig, sig, NULL, msg, tree, 0, NULL));
+	git_tree_free(tree);
+
+	cl_assert_equal_i(1, entrycount(repo, "refs/heads/foo"));
+	cl_assert_equal_i(nentries +1, entrycount(repo, GIT_HEAD_FILE));
+	cl_assert_equal_i(nentries_master, entrycount(repo, "refs/heads/master"));
+
+	git_signature_free(sig);
+
+}