thodg/libgit2

diff --git a/include/git2/checkout.h b/include/git2/checkout.h
index 0bac569..b4f9ad0 100644
--- a/include/git2/checkout.h
+++ b/include/git2/checkout.h
@@ -81,7 +81,8 @@ typedef struct git_checkout_opts {
  * @param repo repository to check out (must be non-bare)
  * @param opts specifies checkout options (may be NULL)
  * @param stats structure through which progress information is reported
- * @return 0 on success, GIT_ERROR otherwise (use giterr_last for information
+ * @return 0 on success, GIT_EORPHANEDHEAD when HEAD points to a non existing
+ * branch, GIT_ERROR otherwise (use giterr_last for information
  * about the error)
  */
 GIT_EXTERN(int) git_checkout_head(
diff --git a/include/git2/repository.h b/include/git2/repository.h
index 025a0a9..32a2f64 100644
--- a/include/git2/repository.h
+++ b/include/git2/repository.h
@@ -272,7 +272,8 @@ GIT_EXTERN(int) git_repository_init_ext(
  * @param head_out pointer to the reference which will be retrieved
  * @param repo a repository object
  *
- * @return 0 on success; error code otherwise
+ * @return 0 on success, GIT_EORPHANEDHEAD when HEAD points to a non existing
+ * branch, an error code otherwise
  */
 GIT_EXTERN(int) git_repository_head(git_reference **head_out, git_repository *repo);
 
@@ -562,7 +563,8 @@ GIT_EXTERN(int) git_repository_set_head_detached(
  * Otherwise, the HEAD will be detached and point to the peeled Commit.
  *
  * @param repo Repository pointer
- * @return 0 on success, or an error code
+ * @return 0 on success, GIT_EORPHANEDHEAD when HEAD points to a non existing
+ * branchor an error code
  */
 GIT_EXTERN(int) git_repository_detach_head(
 	git_repository* repo);
diff --git a/src/branch.c b/src/branch.c
index d9fa9eb..9913145 100644
--- a/src/branch.c
+++ b/src/branch.c
@@ -274,7 +274,7 @@ int git_branch_is_head(
 
 	error = git_repository_head(&head, git_reference_owner(branch));
 
-	if (error == GIT_ENOTFOUND)
+	if (error == GIT_EORPHANEDHEAD)
 		return false;
 
 	if (error < 0)
diff --git a/src/checkout.c b/src/checkout.c
index 4782f77..b56b459 100644
--- a/src/checkout.c
+++ b/src/checkout.c
@@ -430,17 +430,23 @@ int git_checkout_head(
 	git_checkout_opts *opts,
 	git_indexer_stats *stats)
 {
+	git_reference *head;
 	int error;
-	git_tree *tree = NULL;
+	git_object *tree = NULL;
 
 	assert(repo);
 
-	if (git_repository_head_tree(&tree, repo) < 0)
-		return -1;
+	if ((error = git_repository_head(&head, repo)) < 0)
+		return error;
+	
+	if ((error = git_reference_peel(&tree, head, GIT_OBJ_TREE)) < 0)
+		goto cleanup;
 
-	error = git_checkout_tree(repo, (git_object *)tree, opts, stats);
+	error = git_checkout_tree(repo, tree, opts, stats);
 
-	git_tree_free(tree);
+cleanup:
+	git_reference_free(head);
+	git_object_free(tree);
 
 	return error;
 }
diff --git a/src/repository.c b/src/repository.c
index 5f7fa3c..db0888a 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -1206,7 +1206,11 @@ int git_repository_head_detached(git_repository *repo)
 
 int git_repository_head(git_reference **head_out, git_repository *repo)
 {
-	return git_reference_lookup_resolved(head_out, repo, GIT_HEAD_FILE, -1);
+	int error;
+
+	error = git_reference_lookup_resolved(head_out, repo, GIT_HEAD_FILE, -1);
+
+	return error == GIT_ENOTFOUND ? GIT_EORPHANEDHEAD : error;
 }
 
 int git_repository_head_orphan(git_repository *repo)
@@ -1217,7 +1221,7 @@ int git_repository_head_orphan(git_repository *repo)
 	error = git_repository_head(&ref, repo);
 	git_reference_free(ref);
 
-	if (error == GIT_ENOTFOUND)
+	if (error == GIT_EORPHANEDHEAD)
 		return 1;
 
 	if (error < 0)
@@ -1519,14 +1523,14 @@ int git_repository_detach_head(
 	git_reference *old_head = NULL,
 		*new_head = NULL;
 	git_object *object = NULL;
-	int error = -1;
+	int error;
 
 	assert(repo);
 
-	if (git_repository_head(&old_head, repo) < 0)
-		return -1;
+	if ((error = git_repository_head(&old_head, repo)) < 0)
+		return error;
 
-	if (git_object_lookup(&object, repo, git_reference_oid(old_head), GIT_OBJ_COMMIT) < 0)
+	if ((error = git_object_lookup(&object, repo, git_reference_oid(old_head), GIT_OBJ_COMMIT)) < 0)
 		goto cleanup;
 
 	error = git_reference_create_oid(&new_head, repo, GIT_HEAD_FILE, git_reference_oid(old_head), 1);
diff --git a/tests-clar/checkout/head.c b/tests-clar/checkout/head.c
new file mode 100644
index 0000000..f2f81e5
--- /dev/null
+++ b/tests-clar/checkout/head.c
@@ -0,0 +1,24 @@
+#include "clar_libgit2.h"
+#include "refs.h"
+
+static git_repository *g_repo;
+
+void test_checkout_head__initialize(void)
+{
+	g_repo = cl_git_sandbox_init("testrepo");
+}
+
+void test_checkout_head__cleanup(void)
+{
+	cl_git_sandbox_cleanup();
+}
+
+void test_checkout_head__checking_out_an_orphaned_head_returns_GIT_EORPHANEDHEAD(void)
+{
+	git_reference *head;
+
+	cl_git_pass(git_reference_create_symbolic(&head, g_repo, GIT_HEAD_FILE, "refs/heads/hide/and/seek", 1));
+	git_reference_free(head);
+
+	cl_assert_equal_i(GIT_EORPHANEDHEAD, git_checkout_head(g_repo, NULL, NULL));
+}
diff --git a/tests-clar/refs/branches/delete.c b/tests-clar/refs/branches/delete.c
index 1a97dc8..99af44e 100644
--- a/tests-clar/refs/branches/delete.c
+++ b/tests-clar/refs/branches/delete.c
@@ -50,6 +50,18 @@ void test_refs_branches_delete__can_delete_a_branch_even_if_HEAD_is_missing(void
 	cl_git_pass(git_branch_delete(branch));
 }
 
+void test_refs_branches_delete__can_delete_a_branch_when_HEAD_is_orphaned(void)
+{
+	git_reference *head;
+	git_reference *branch;
+
+	cl_git_pass(git_reference_create_symbolic(&head, repo, GIT_HEAD_FILE, "refs/heads/hide/and/seek", 1));
+	git_reference_free(head);
+
+	cl_git_pass(git_branch_lookup(&branch, repo, "br2", GIT_BRANCH_LOCAL));
+	cl_git_pass(git_branch_delete(branch));
+}
+
 void test_refs_branches_delete__can_delete_a_branch_pointed_at_by_detached_HEAD(void)
 {
 	git_reference *master, *head, *branch;
diff --git a/tests-clar/refs/branches/ishead.c b/tests-clar/refs/branches/ishead.c
index c40a431..0d57f00 100644
--- a/tests-clar/refs/branches/ishead.c
+++ b/tests-clar/refs/branches/ishead.c
@@ -22,6 +22,30 @@ void test_refs_branches_ishead__can_tell_if_a_branch_is_pointed_at_by_HEAD(void)
 	cl_assert_equal_i(true, git_branch_is_head(branch));
 }
 
+static void make_head_orphaned(void)
+{
+	git_reference *head;
+
+	cl_git_pass(git_reference_create_symbolic(&head, repo, GIT_HEAD_FILE, "refs/heads/hide/and/seek", 1));
+	git_reference_free(head);
+}
+
+void test_refs_branches_ishead__can_properly_handle_orphaned_HEAD(void)
+{
+	git_repository_free(repo);
+
+	repo = cl_git_sandbox_init("testrepo.git");
+
+	make_head_orphaned();
+
+	cl_git_pass(git_reference_lookup(&branch, repo, "refs/heads/master"));
+
+	cl_assert_equal_i(false, git_branch_is_head(branch));
+
+	cl_git_sandbox_cleanup();
+	repo = NULL;
+}
+
 void test_refs_branches_ishead__can_tell_if_a_branch_is_not_pointed_at_by_HEAD(void)
 {
 	cl_git_pass(git_reference_lookup(&branch, repo, "refs/heads/br2"));
diff --git a/tests-clar/repo/head.c b/tests-clar/repo/head.c
index 64dec69..4113289 100644
--- a/tests-clar/repo/head.c
+++ b/tests-clar/repo/head.c
@@ -33,18 +33,26 @@ void test_repo_head__head_detached(void)
 	git_reference_free(ref);
 }
 
+static void make_head_orphaned(void)
+{
+	git_reference *head;
+
+	cl_git_pass(git_reference_create_symbolic(&head, repo, GIT_HEAD_FILE, "refs/heads/hide/and/seek", 1));
+	git_reference_free(head);
+}
+
 void test_repo_head__head_orphan(void)
 {
 	git_reference *ref;
 
 	cl_assert(git_repository_head_orphan(repo) == 0);
 
-	/* orphan HEAD */
-	cl_git_pass(git_reference_create_symbolic(&ref, repo, "HEAD", "refs/heads/orphan", 1));
+	make_head_orphaned();
+
 	cl_assert(git_repository_head_orphan(repo) == 1);
-	git_reference_free(ref);
 
-	/* take the reop back to it's original state */
+
+	/* take the repo back to it's original state */
 	cl_git_pass(git_reference_create_symbolic(&ref, repo, "HEAD", "refs/heads/master", 1));
 	cl_assert(git_repository_head_orphan(repo) == 0);
 
@@ -59,7 +67,7 @@ void test_repo_head__set_head_Attaches_HEAD_to_un_unborn_branch_when_the_branch_
 
 	cl_assert_equal_i(false, git_repository_head_detached(repo));
 
-	cl_assert_equal_i(GIT_ENOTFOUND, git_repository_head(&head, repo));
+	cl_assert_equal_i(GIT_EORPHANEDHEAD, git_repository_head(&head, repo));
 }
 
 void test_repo_head__set_head_Returns_ENOTFOUND_when_the_reference_doesnt_exist(void)
@@ -163,3 +171,19 @@ void test_repo_head__detach_head_Fails_if_HEAD_and_point_to_a_non_commitish(void
 
 	git_reference_free(head);
 }
+
+void test_repo_head__detaching_an_orphaned_head_returns_GIT_EORPHANEDHEAD(void)
+{
+	make_head_orphaned();
+
+	cl_assert_equal_i(GIT_EORPHANEDHEAD, git_repository_detach_head(repo));
+}
+
+void test_repo_head__retrieving_an_orphaned_head_returns_GIT_EORPHANEDHEAD(void)
+{
+	git_reference *head;
+
+	make_head_orphaned();
+
+	cl_assert_equal_i(GIT_EORPHANEDHEAD, git_repository_head(&head, repo));
+}