thodg/libgit2

diff --git a/include/git2/index.h b/include/git2/index.h
index bca9791..8e1a7e5 100644
--- a/include/git2/index.h
+++ b/include/git2/index.h
@@ -215,9 +215,12 @@ GIT_EXTERN(int) git_index_read_tree(git_index *index, git_tree *tree);
  * The index instance cannot be bare, and needs to be associated
  * to an existing repository.
  *
+ * The index must not contain any file in conflict.
+ *
  * @param oid Pointer where to store the OID of the written tree
  * @param index Index to write
- * @return 0 or an error code
+ * @return 0 on success, GIT_EUNMERGED when the index is not clean
+ * or an error code
  */
 GIT_EXTERN(int) git_index_write_tree(git_oid *oid, git_index *index);
 
@@ -228,10 +231,13 @@ GIT_EXTERN(int) git_index_write_tree(git_oid *oid, git_index *index);
  * letting the user choose the repository where the tree will
  * be written.
  *
+ * The index must not contain any file in conflict.
+ *
  * @param oid Pointer where to store OID of the the written tree
  * @param index Index to write
  * @param repo Repository where to write the tree
- * @return 0 or an error code
+ * @return 0 on success, GIT_EUNMERGED when the index is not clean
+ * or an error code
  */
 GIT_EXTERN(int) git_index_write_tree_to(git_oid *oid, git_index *index, git_repository *repo);
 
@@ -431,6 +437,13 @@ GIT_EXTERN(int) git_index_conflict_remove(git_index *index, const char *path);
  */
 GIT_EXTERN(void) git_index_conflict_cleanup(git_index *index);
 
+/**
+ * Determine if the index contains entries representing file conflicts.
+ *
+ * @return 1 if at least one conflict is found, 0 otherwise.
+ */
+GIT_EXTERN(int) git_index_has_conflicts(git_index *index);
+
 /**@}*/
 
 /** @name Resolve Undo (REUC) index entry manipulation.
diff --git a/src/index.c b/src/index.c
index fed067c..06bbcac 100644
--- a/src/index.c
+++ b/src/index.c
@@ -959,6 +959,21 @@ void git_index_conflict_cleanup(git_index *index)
 	git_vector_remove_matching(&index->entries, index_conflicts_match);
 }
 
+int git_index_has_conflicts(git_index *index)
+{
+	unsigned int i;
+	git_index_entry *entry;
+
+	assert(index);
+
+	git_vector_foreach(&index->entries, i, entry) {
+		if (index_entry_stage(entry) > 0)
+			return 1;
+	}
+
+	return 0;
+}
+
 unsigned int git_index_reuc_entrycount(git_index *index)
 {
 	assert(index);
diff --git a/src/tree.c b/src/tree.c
index 46b4a6d..7b47af3 100644
--- a/src/tree.c
+++ b/src/tree.c
@@ -497,6 +497,12 @@ int git_tree__write_index(git_oid *oid, git_index *index, git_repository *repo)
 
 	assert(oid && index && repo);
 
+	if (git_index_has_conflicts(index)) {
+		giterr_set(GITERR_INDEX,
+			"Cannot create a tree from a not fully merged index.");
+		return GIT_EUNMERGED;
+	}
+
 	if (index->tree != NULL && index->tree->entries >= 0) {
 		git_oid_cpy(oid, &index->tree->oid);
 		return 0;
diff --git a/tests-clar/index/conflicts.c b/tests-clar/index/conflicts.c
index 59df257..e101b16 100644
--- a/tests-clar/index/conflicts.c
+++ b/tests-clar/index/conflicts.c
@@ -180,8 +180,12 @@ void test_index_conflicts__remove_all_conflicts(void)
 
 	cl_assert(git_index_entrycount(repo_index) == 8);
 
+	cl_assert_equal_i(true, git_index_has_conflicts(repo_index));
+
 	git_index_conflict_cleanup(repo_index);
 
+	cl_assert_equal_i(false, git_index_has_conflicts(repo_index));
+
 	cl_assert(git_index_entrycount(repo_index) == 2);
 
 	for (i = 0; i < git_index_entrycount(repo_index); i++) {
diff --git a/tests-clar/object/tree/duplicateentries.c b/tests-clar/object/tree/duplicateentries.c
new file mode 100644
index 0000000..27e1e2b
--- /dev/null
+++ b/tests-clar/object/tree/duplicateentries.c
@@ -0,0 +1,157 @@
+#include "clar_libgit2.h"
+#include "tree.h"
+
+static git_repository *_repo;
+
+void test_object_tree_duplicateentries__initialize(void) {
+   _repo = cl_git_sandbox_init("testrepo");
+}
+
+void test_object_tree_duplicateentries__cleanup(void) {
+   cl_git_sandbox_cleanup();
+}
+
+/*
+ * $ git show --format=raw refs/heads/dir
+ * commit 144344043ba4d4a405da03de3844aa829ae8be0e
+ * tree d52a8fe84ceedf260afe4f0287bbfca04a117e83
+ * parent cf80f8de9f1185bf3a05f993f6121880dd0cfbc9
+ * author Ben Straub <bstraub@github.com> 1343755506 -0700
+ * committer Ben Straub <bstraub@github.com> 1343755506 -0700
+ * 
+ *     Change a file mode
+ * 
+ * diff --git a/a/b.txt b/a/b.txt
+ * old mode 100644
+ * new mode 100755
+ *
+ * $ git ls-tree d52a8fe84ceedf260afe4f0287bbfca04a117e83
+ * 100644 blob a8233120f6ad708f843d861ce2b7228ec4e3dec6    README
+ * 040000 tree 4e0883eeeeebc1fb1735161cea82f7cb5fab7e63    a
+ * 100644 blob 45b983be36b73c0788dc9cbcb76cbb80fc7bb057    branch_file.txt
+ * 100644 blob a71586c1dfe8a71c6cbf6c129f404c5642ff31bd    new.txt
+ */
+
+static void tree_checker(
+	git_oid *tid,
+	const char *expected_sha,
+	git_filemode_t expected_filemode)
+{
+	git_tree *tree;
+	const git_tree_entry *entry;
+	git_oid oid;
+
+	cl_git_pass(git_tree_lookup(&tree, _repo, tid));
+	cl_assert_equal_i(1, git_tree_entrycount(tree));
+	entry = git_tree_entry_byindex(tree, 0);
+
+	cl_git_pass(git_oid_fromstr(&oid, expected_sha));
+
+	cl_assert_equal_i(0, git_oid_cmp(&oid, git_tree_entry_id(entry)));
+	cl_assert_equal_i(expected_filemode, git_tree_entry_filemode(entry));
+
+	git_tree_free(tree);
+}
+
+static void tree_creator(git_oid *out, void (*fn)(git_treebuilder *))
+{
+	git_treebuilder *builder;
+
+	cl_git_pass(git_treebuilder_create(&builder, NULL));
+
+	fn(builder);
+
+	cl_git_pass(git_treebuilder_write(out, _repo, builder));
+	git_treebuilder_free(builder);
+}
+
+static void two_blobs(git_treebuilder *bld)
+{
+	git_oid oid;
+	const git_tree_entry *entry;
+	
+	cl_git_pass(git_oid_fromstr(&oid,
+		"a8233120f6ad708f843d861ce2b7228ec4e3dec6"));	/* blob oid (README) */
+
+	cl_git_pass(git_treebuilder_insert(
+		&entry,	bld, "duplicate", &oid,
+		GIT_FILEMODE_BLOB));
+
+	cl_git_pass(git_oid_fromstr(&oid,
+		"a71586c1dfe8a71c6cbf6c129f404c5642ff31bd"));	/* blob oid (new.txt) */
+
+	cl_git_pass(git_treebuilder_insert(
+		&entry,	bld, "duplicate", &oid,
+		GIT_FILEMODE_BLOB));
+}
+
+static void one_blob_and_one_tree(git_treebuilder *bld)
+{
+	git_oid oid;
+	const git_tree_entry *entry;
+	
+	cl_git_pass(git_oid_fromstr(&oid,
+		"a8233120f6ad708f843d861ce2b7228ec4e3dec6"));	/* blob oid (README) */
+
+	cl_git_pass(git_treebuilder_insert(
+		&entry,	bld, "duplicate", &oid,
+		GIT_FILEMODE_BLOB));
+
+	cl_git_pass(git_oid_fromstr(&oid,
+		"4e0883eeeeebc1fb1735161cea82f7cb5fab7e63"));	/* tree oid (a) */
+
+	cl_git_pass(git_treebuilder_insert(
+		&entry,	bld, "duplicate", &oid,
+		GIT_FILEMODE_TREE));
+}
+
+void test_object_tree_duplicateentries__cannot_create_a_duplicate_entry_through_the_treebuilder(void)
+{
+	git_oid tid;
+
+	tree_creator(&tid, two_blobs);
+	tree_checker(&tid, "a71586c1dfe8a71c6cbf6c129f404c5642ff31bd", GIT_FILEMODE_BLOB);
+	
+	tree_creator(&tid, one_blob_and_one_tree);
+	tree_checker(&tid, "4e0883eeeeebc1fb1735161cea82f7cb5fab7e63", GIT_FILEMODE_TREE);
+}
+
+void add_fake_conflicts(git_index *index)
+{
+	git_index_entry ancestor_entry, our_entry, their_entry;
+
+	memset(&ancestor_entry, 0x0, sizeof(git_index_entry));
+	memset(&our_entry, 0x0, sizeof(git_index_entry));
+	memset(&their_entry, 0x0, sizeof(git_index_entry));
+
+	ancestor_entry.path = "duplicate";
+	ancestor_entry.mode = GIT_FILEMODE_BLOB;
+	ancestor_entry.flags |= (1 << GIT_IDXENTRY_STAGESHIFT);
+	git_oid_fromstr(&ancestor_entry.oid, "a8233120f6ad708f843d861ce2b7228ec4e3dec6");
+
+	our_entry.path = "duplicate";
+	our_entry.mode = GIT_FILEMODE_BLOB;
+	ancestor_entry.flags |= (2 << GIT_IDXENTRY_STAGESHIFT);
+	git_oid_fromstr(&our_entry.oid, "45b983be36b73c0788dc9cbcb76cbb80fc7bb057");
+
+	their_entry.path = "duplicate";
+	their_entry.mode = GIT_FILEMODE_BLOB;
+	ancestor_entry.flags |= (3 << GIT_IDXENTRY_STAGESHIFT);
+	git_oid_fromstr(&their_entry.oid, "a71586c1dfe8a71c6cbf6c129f404c5642ff31bd");
+
+	cl_git_pass(git_index_conflict_add(index, &ancestor_entry, &our_entry, &their_entry));
+}
+
+void test_object_tree_duplicateentries__cannot_create_a_duplicate_entry_building_a_tree_from_a_index_with_conflicts(void)
+{
+	git_index *index;
+	git_oid tid;
+
+	cl_git_pass(git_repository_index(&index, _repo));
+
+	add_fake_conflicts(index); 
+
+	cl_assert_equal_i(GIT_EUNMERGED, git_index_write_tree(&tid, index));
+
+	git_index_free(index);
+}