thodg/libgit2

diff --git a/include/git2/revwalk.h b/include/git2/revwalk.h
index aef0b5f..1bd6186 100644
--- a/include/git2/revwalk.h
+++ b/include/git2/revwalk.h
@@ -261,6 +261,30 @@ GIT_EXTERN(void) git_revwalk_free(git_revwalk *walk);
  */
 GIT_EXTERN(git_repository *) git_revwalk_repository(git_revwalk *walk);
 
+/**
+ * This is a callback function that user can provide to hide a
+ * commit and its parents. If the callback function returns non-zero value,
+ * then this commit and its parents will be hidden.
+ *
+ * @param commit_id oid of Commit
+ * @param payload User-specified pointer to data to be passed as data payload
+ */
+typedef int(*git_revwalk_hide_cb)(
+	const git_oid *commit_id,
+	void *payload);
+
+/**
+ * Adds a callback function to hide a commit and its parents
+ *
+ * @param walk the revision walker
+ * @param hide_cb  callback function to hide a commit and its parents
+ * @param payload  data payload to be passed to callback function
+ */
+GIT_EXTERN(int) git_revwalk_add_hide_cb(
+	git_revwalk *walk,
+	git_revwalk_hide_cb hide_cb,
+	void *payload);
+
 /** @} */
 GIT_END_DECL
 #endif
diff --git a/src/revwalk.c b/src/revwalk.c
index f037ee6..f010936 100644
--- a/src/revwalk.c
+++ b/src/revwalk.c
@@ -81,6 +81,9 @@ static int process_commit(git_revwalk *walk, git_commit_list_node *commit, int h
 {
 	int error;
 
+	if (!hide && walk->hide_cb)
+		hide = walk->hide_cb(&commit->oid, walk->hide_cb_payload);
+
 	if (hide && mark_uninteresting(commit) < 0)
 		return -1;
 
@@ -178,11 +181,6 @@ static int push_ref(git_revwalk *walk, const char *refname, int hide, int from_g
 	return push_commit(walk, &oid, hide, from_glob);
 }
 
-struct push_cb_data {
-	git_revwalk *walk;
-	int hide;
-};
-
 static int push_glob(git_revwalk *walk, const char *glob, int hide)
 {
 	int error = 0;
@@ -575,3 +573,25 @@ void git_revwalk_reset(git_revwalk *walk)
 	git_vector_clear(&walk->twos);
 }
 
+int git_revwalk_add_hide_cb(
+	git_revwalk *walk,
+	git_revwalk_hide_cb hide_cb,
+	void *payload)
+{
+	assert(walk);
+
+	if (walk->walking)
+		git_revwalk_reset(walk);
+
+	if (walk->hide_cb) {
+		/* There is already a callback added */
+		giterr_set(GITERR_INVALID, "There is already a callback added to hide commits in revision walker.");
+		return -1;
+	}
+
+	walk->hide_cb = hide_cb;
+	walk->hide_cb_payload = payload;
+
+	return 0;
+}
+
diff --git a/src/revwalk.h b/src/revwalk.h
index a0ce1ae..a0654f3 100644
--- a/src/revwalk.h
+++ b/src/revwalk.h
@@ -39,6 +39,10 @@ struct git_revwalk {
 	/* merge base calculation */
 	git_commit_list_node *one;
 	git_vector twos;
+
+	/* hide callback */
+	git_revwalk_hide_cb hide_cb;
+	void *hide_cb_payload;
 };
 
 git_commit_list_node *git_revwalk__commit_lookup(git_revwalk *walk, const git_oid *oid);
diff --git a/tests/revwalk/hidecb.c b/tests/revwalk/hidecb.c
new file mode 100644
index 0000000..c13a177
--- /dev/null
+++ b/tests/revwalk/hidecb.c
@@ -0,0 +1,198 @@
+#include "clar_libgit2.h"
+/*
+*   a4a7dce [0] Merge branch 'master' into br2
+|\
+| * 9fd738e [1] a fourth commit
+| * 4a202b3 [2] a third commit
+* | c47800c [3] branch commit one
+|/
+* 5b5b025 [5] another commit
+* 8496071 [4] testing
+*/
+static const char *commit_head = "a4a7dce85cf63874e984719f4fdd239f5145052f";
+
+static const char *commit_strs[] = {
+	"a4a7dce85cf63874e984719f4fdd239f5145052f", /* 0 */
+	"9fd738e8f7967c078dceed8190330fc8648ee56a", /* 1 */
+	"4a202b346bb0fb0db7eff3cffeb3c70babbd2045", /* 2 */
+	"c47800c7266a2be04c571c04d5a6614691ea99bd", /* 3 */
+	"8496071c1b46c854b31185ea97743be6a8774479", /* 4 */
+	"5b5b025afb0b4c913b4c338a42934a3863bf3644", /* 5 */
+};
+
+#define commit_count 6
+
+static git_oid commit_ids[commit_count];
+static git_oid _head_id;
+static git_repository *_repo;
+
+
+void test_revwalk_hidecb__initialize(void)
+{
+	int i;
+
+	cl_git_pass(git_repository_open(&_repo, cl_fixture("testrepo.git")));
+	cl_git_pass(git_oid_fromstr(&_head_id, commit_head));
+
+	for (i = 0; i < commit_count; i++)
+		cl_git_pass(git_oid_fromstr(&commit_ids[i], commit_strs[i]));
+
+}
+
+void test_revwalk_hidecb__cleanup(void)
+{
+	git_repository_free(_repo);
+	_repo = NULL;
+}
+
+/* Hide all commits */
+static int hide_every_commit_cb(const git_oid *commit_id, void *data)
+{
+	return 1;
+}
+
+/* Do not hide anything */
+static int hide_none_cb(const git_oid *commit_id, void *data)
+{
+	return 0;
+}
+
+/* Hide some commits */
+static int hide_commit_cb(const git_oid *commit_id, void *data)
+{
+	if (0 == git_oid_cmp(commit_id, &commit_ids[5]))
+		return 1;
+	else
+		return 0;
+
+}
+
+/* In payload data, pointer to a commit id is passed */
+static int hide_commit_use_payload_cb(const git_oid *commit_id, void *data)
+{
+	git_oid *hide_commit_id = data;
+	if (git_oid_cmp(commit_id, hide_commit_id) == 0)
+		return 1;
+	else
+		return 0;
+}
+
+void test_revwalk_hidecb__hide_all_cb(void)
+{
+	git_revwalk *walk;
+	git_oid id;
+
+	cl_git_pass(git_revwalk_new(&walk, _repo));
+	cl_git_pass(git_revwalk_add_hide_cb(walk, hide_every_commit_cb, NULL));
+	cl_git_pass(git_revwalk_push(walk, &_head_id));
+
+	/* First call to git_revwalk_next should return GIT_ITEROVER */
+	cl_assert_equal_i(GIT_ITEROVER, git_revwalk_next(&id, walk));
+
+	git_revwalk_free(walk);
+}
+
+
+void test_revwalk_hidecb__hide_none_cb(void)
+{
+	git_revwalk *walk;
+	int i, error;
+	git_oid id;
+
+	cl_git_pass(git_revwalk_new(&walk, _repo));
+	cl_git_pass(git_revwalk_add_hide_cb(walk, hide_none_cb, NULL));
+	cl_git_pass(git_revwalk_push(walk, &_head_id));
+
+	/* It should return all 6 commits */
+	i = 0;
+	while ((error = git_revwalk_next(&id, walk)) == 0)
+		i++;
+
+	cl_assert_equal_i(i, 6);
+	cl_assert_equal_i(error, GIT_ITEROVER);
+
+	git_revwalk_free(walk);
+}
+
+void test_revwalk_hidecb__add_hide_cb_multiple_times(void)
+{
+	git_revwalk *walk;
+
+	cl_git_pass(git_revwalk_new(&walk, _repo));
+	cl_git_pass(git_revwalk_add_hide_cb(walk, hide_every_commit_cb, NULL));
+	cl_git_fail(git_revwalk_add_hide_cb(walk, hide_every_commit_cb, NULL));
+
+	git_revwalk_free(walk);
+}
+
+void test_revwalk_hidecb__add_hide_cb_during_walking(void)
+{
+	git_revwalk *walk;
+	git_oid id;
+	int error;
+
+	cl_git_pass(git_revwalk_new(&walk, _repo));
+	cl_git_pass(git_revwalk_push(walk, &_head_id));
+
+	/* Start walking without adding hide callback */
+	cl_git_pass(git_revwalk_next(&id, walk));
+
+	/* Now add hide callback */
+	cl_git_pass(git_revwalk_add_hide_cb(walk, hide_none_cb, NULL));
+
+	/* walk should be reset */
+	error = git_revwalk_next(&id, walk);
+	cl_assert_equal_i(error, GIT_ITEROVER);
+
+	git_revwalk_free(walk);
+}
+
+void test_revwalk_hidecb__hide_some_commits(void)
+{
+	git_revwalk *walk;
+	git_oid id;
+	int i, error;
+
+	cl_git_pass(git_revwalk_new(&walk, _repo));
+	cl_git_pass(git_revwalk_push(walk, &_head_id));
+
+	/* Add hide callback */
+	cl_git_pass(git_revwalk_add_hide_cb(walk, hide_commit_cb, NULL));
+
+	i = 0;
+	while ((error = git_revwalk_next(&id, walk)) == 0) {
+		cl_assert_equal_i(git_oid_cmp(&id, &commit_ids[i]), 0);
+		i++;
+	}
+
+	cl_assert_equal_i(i, 4);
+	cl_assert_equal_i(error, GIT_ITEROVER);
+
+	git_revwalk_free(walk);
+}
+
+void test_revwalk_hidecb__test_payload(void)
+{
+	git_revwalk *walk;
+	git_oid id;
+	int i, error;
+
+	cl_git_pass(git_revwalk_new(&walk, _repo));
+	cl_git_pass(git_revwalk_push(walk, &_head_id));
+
+	/* Add hide callback, pass id of parent of initial commit as payload data */
+	cl_git_pass(git_revwalk_add_hide_cb(walk, hide_commit_use_payload_cb, &commit_ids[5]));
+
+	i = 0;
+	while ((error = git_revwalk_next(&id, walk)) == 0) {
+		cl_assert_equal_i(git_oid_cmp(&id, &commit_ids[i]), 0);
+		i++;
+	}
+
+	/* walker should return four commits */
+	cl_assert_equal_i(i, 4);
+	cl_assert_equal_i(error, GIT_ITEROVER);
+
+	git_revwalk_free(walk);
+}
+