thodg/libgit2

diff --git a/include/git2.h b/include/git2.h
index 704fb58..f749760 100644
--- a/include/git2.h
+++ b/include/git2.h
@@ -14,6 +14,7 @@
 #include "git2/branch.h"
 #include "git2/buffer.h"
 #include "git2/checkout.h"
+#include "git2/cherrypick.h"
 #include "git2/clone.h"
 #include "git2/commit.h"
 #include "git2/common.h"
diff --git a/include/git2/cherrypick.h b/include/git2/cherrypick.h
new file mode 100644
index 0000000..7c48e66
--- /dev/null
+++ b/include/git2/cherrypick.h
@@ -0,0 +1,88 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_git_cherrypick_h__
+#define INCLUDE_git_cherrypick_h__
+
+#include "common.h"
+#include "types.h"
+#include "merge.h"
+
+/**
+ * @file git2/cherrypick.h
+ * @brief Git cherry-pick routines
+ * @defgroup git_cherrypick Git cherry-pick routines
+ * @ingroup Git
+ * @{
+ */
+GIT_BEGIN_DECL
+
+typedef struct {
+	unsigned int version;
+
+	/** For merge commits, the "mainline" is treated as the parent. */
+	unsigned int mainline;
+
+	git_merge_options merge_opts;
+	git_checkout_options checkout_opts;
+} git_cherry_pick_options;
+
+#define GIT_CHERRY_PICK_OPTIONS_VERSION 1
+#define GIT_CHERRY_PICK_OPTIONS_INIT {GIT_CHERRY_PICK_OPTIONS_VERSION, 0, GIT_MERGE_OPTIONS_INIT, GIT_CHECKOUT_OPTIONS_INIT}
+
+/**
+ * Initializes a `git_cherry_pick_options` with default values. Equivalent to
+ * creating an instance with GIT_CHERRY_PICK_OPTIONS_INIT.
+ *
+ * @param opts the `git_cherry_pick_options` instance to initialize.
+ * @param version the version of the struct; you should pass
+ *        `GIT_CHERRY_PICK_OPTIONS_VERSION` here.
+ * @return Zero on success; -1 on failure.
+ */
+GIT_EXTERN(int) git_cherry_pick_init_opts(
+	git_cherry_pick_options* opts,
+	int version);
+
+/**
+ * Cherry-picks the given commit against the given "our" commit, producing an
+ * index that reflects the result of the cherry-pick.
+ *
+ * The returned index must be freed explicitly with `git_index_free`.
+ *
+ * @param out pointer to store the index result in
+ * @param repo the repository that contains the given commits
+ * @param cherry_pick_commit the commit to cherry-pick
+ * @param our_commit the commit to revert against (eg, HEAD)
+ * @param mainline the parent of the revert commit, if it is a merge
+ * @param merge_tree_opts the merge tree options (or null for defaults)
+ * @return zero on success, -1 on failure.
+ */
+GIT_EXTERN(int) git_cherry_pick_commit(
+	git_index **out,
+	git_repository *repo,
+	git_commit *cherry_pick_commit,
+	git_commit *our_commit,
+	unsigned int mainline,
+	const git_merge_options *merge_options);
+
+/**
+ * Cherry-pick the given commit, producing changes in the index and working directory.
+ *
+ * @param repo the repository to cherry-pick
+ * @param commit the commit to cherry-pick
+ * @param cherry_pick_options the cherry-pick options (or null for defaults)
+ * @return zero on success, -1 on failure.
+ */
+GIT_EXTERN(int) git_cherry_pick(
+	git_repository *repo,
+	git_commit *commit,
+	const git_cherry_pick_options *cherry_pick_options);
+
+/** @} */
+GIT_END_DECL
+
+#endif
+
diff --git a/include/git2/errors.h b/include/git2/errors.h
index bcf2f80..e22f0d8 100644
--- a/include/git2/errors.h
+++ b/include/git2/errors.h
@@ -86,6 +86,7 @@ typedef enum {
 	GITERR_FILTER,
 	GITERR_REVERT,
 	GITERR_CALLBACK,
+	GITERR_CHERRYPICK,
 } git_error_t;
 
 /**
diff --git a/src/cherrypick.c b/src/cherrypick.c
new file mode 100644
index 0000000..67a2c6a
--- /dev/null
+++ b/src/cherrypick.c
@@ -0,0 +1,230 @@
+/*
+* Copyright (C) the libgit2 contributors. All rights reserved.
+*
+* This file is part of libgit2, distributed under the GNU GPL v2 with
+* a Linking Exception. For full terms see the included COPYING file.
+*/
+
+#include "common.h"
+#include "repository.h"
+#include "filebuf.h"
+#include "merge.h"
+#include "vector.h"
+
+#include "git2/types.h"
+#include "git2/merge.h"
+#include "git2/cherrypick.h"
+#include "git2/commit.h"
+#include "git2/sys/commit.h"
+
+#define GIT_CHERRY_PICK_FILE_MODE		0666
+
+static int write_cherry_pick_head(
+	git_repository *repo,
+	const char *commit_oidstr)
+{
+	git_filebuf file = GIT_FILEBUF_INIT;
+	git_buf file_path = GIT_BUF_INIT;
+	int error = 0;
+
+	if ((error = git_buf_joinpath(&file_path, repo->path_repository, GIT_CHERRY_PICK_HEAD_FILE)) >= 0 &&
+		(error = git_filebuf_open(&file, file_path.ptr, GIT_FILEBUF_FORCE, GIT_CHERRY_PICK_FILE_MODE)) >= 0 &&
+		(error = git_filebuf_printf(&file, "%s\n", commit_oidstr)) >= 0)
+		error = git_filebuf_commit(&file);
+
+	if (error < 0)
+		git_filebuf_cleanup(&file);
+
+	git_buf_free(&file_path);
+
+	return error;
+}
+
+static int write_merge_msg(
+	git_repository *repo,
+	const char *commit_msg)
+{
+	git_filebuf file = GIT_FILEBUF_INIT;
+	git_buf file_path = GIT_BUF_INIT;
+	int error = 0;
+
+	if ((error = git_buf_joinpath(&file_path, repo->path_repository, GIT_MERGE_MSG_FILE)) < 0 ||
+		(error = git_filebuf_open(&file, file_path.ptr, GIT_FILEBUF_FORCE, GIT_CHERRY_PICK_FILE_MODE)) < 0 ||
+		(error = git_filebuf_printf(&file, "%s", commit_msg)) < 0)
+		goto cleanup;
+
+	error = git_filebuf_commit(&file);
+
+cleanup:
+	if (error < 0)
+		git_filebuf_cleanup(&file);
+
+	git_buf_free(&file_path);
+
+	return error;
+}
+
+static int cherry_pick_normalize_opts(
+	git_repository *repo,
+	git_cherry_pick_options *opts,
+	const git_cherry_pick_options *given,
+	const char *their_label)
+{
+	int error = 0;
+	unsigned int default_checkout_strategy = GIT_CHECKOUT_SAFE_CREATE |
+		GIT_CHECKOUT_ALLOW_CONFLICTS;
+
+	GIT_UNUSED(repo);
+
+	if (given != NULL)
+		memcpy(opts, given, sizeof(git_cherry_pick_options));
+	else {
+		git_cherry_pick_options default_opts = GIT_CHERRY_PICK_OPTIONS_INIT;
+		memcpy(opts, &default_opts, sizeof(git_cherry_pick_options));
+	}
+
+	if (!opts->checkout_opts.checkout_strategy)
+		opts->checkout_opts.checkout_strategy = default_checkout_strategy;
+
+	if (!opts->checkout_opts.our_label)
+		opts->checkout_opts.our_label = "HEAD";
+
+	if (!opts->checkout_opts.their_label)
+		opts->checkout_opts.their_label = their_label;
+
+	return error;
+}
+
+static int cherry_pick_state_cleanup(git_repository *repo)
+{
+	const char *state_files[] = { GIT_CHERRY_PICK_HEAD_FILE, GIT_MERGE_MSG_FILE };
+
+	return git_repository__cleanup_files(repo, state_files, ARRAY_SIZE(state_files));
+}
+
+static int cherry_pick_seterr(git_commit *commit, const char *fmt)
+{
+	char commit_oidstr[GIT_OID_HEXSZ + 1];
+
+	giterr_set(GITERR_CHERRYPICK, fmt,
+		git_oid_tostr(commit_oidstr, GIT_OID_HEXSZ + 1, git_commit_id(commit)));
+
+	return -1;
+}
+
+int git_cherry_pick_commit(
+	git_index **out,
+	git_repository *repo,
+	git_commit *cherry_pick_commit,
+	git_commit *our_commit,
+	unsigned int mainline,
+	const git_merge_options *merge_opts)
+{
+	git_commit *parent_commit = NULL;
+	git_tree *parent_tree = NULL, *our_tree = NULL, *cherry_pick_tree = NULL;
+	int parent = 0, error = 0;
+
+	assert(out && repo && cherry_pick_commit && our_commit);
+
+	if (git_commit_parentcount(cherry_pick_commit) > 1) {
+		if (!mainline)
+			return cherry_pick_seterr(cherry_pick_commit,
+				"Mainline branch is not specified but %s is a merge commit");
+
+		parent = mainline;
+	} else {
+		if (mainline)
+			return cherry_pick_seterr(cherry_pick_commit,
+				"Mainline branch specified but %s is not a merge commit");
+
+		parent = git_commit_parentcount(cherry_pick_commit);
+	}
+
+	if (parent &&
+		((error = git_commit_parent(&parent_commit, cherry_pick_commit, (parent - 1))) < 0 ||
+		(error = git_commit_tree(&parent_tree, parent_commit)) < 0))
+		goto done;
+
+	if ((error = git_commit_tree(&cherry_pick_tree, cherry_pick_commit)) < 0 ||
+		(error = git_commit_tree(&our_tree, our_commit)) < 0)
+		goto done;
+
+	error = git_merge_trees(out, repo, parent_tree, our_tree, cherry_pick_tree, merge_opts);
+
+done:
+	git_tree_free(parent_tree);
+	git_tree_free(our_tree);
+	git_tree_free(cherry_pick_tree);
+	git_commit_free(parent_commit);
+
+	return error;
+}
+
+int git_cherry_pick(
+	git_repository *repo,
+	git_commit *commit,
+	const git_cherry_pick_options *given_opts)
+{
+	git_cherry_pick_options opts;
+	git_reference *our_ref = NULL;
+	git_commit *our_commit = NULL;
+	char commit_oidstr[GIT_OID_HEXSZ + 1];
+	const char *commit_msg, *commit_summary;
+	git_buf their_label = GIT_BUF_INIT;
+	git_index *index_new = NULL, *index_repo = NULL;
+	int error = 0;
+
+	assert(repo && commit);
+
+	GITERR_CHECK_VERSION(given_opts, GIT_CHERRY_PICK_OPTIONS_VERSION, "git_cherry_pick_options");
+
+	if ((error = git_repository__ensure_not_bare(repo, "cherry-pick")) < 0)
+		return error;
+
+	if ((commit_msg = git_commit_message(commit)) == NULL ||
+		(commit_summary = git_commit_summary(commit)) == NULL) {
+		error = -1;
+		goto on_error;
+	}
+
+	git_oid_fmt(commit_oidstr, git_commit_id(commit));
+
+	if ((error = write_merge_msg(repo, commit_msg)) < 0 ||
+		(error = git_buf_printf(&their_label, "%.7s... %s", commit_oidstr, commit_summary)) < 0 ||
+		(error = cherry_pick_normalize_opts(repo, &opts, given_opts, git_buf_cstr(&their_label))) < 0 ||
+		(error = write_cherry_pick_head(repo, commit_oidstr)) < 0 ||
+		(error = git_repository_head(&our_ref, repo)) < 0 ||
+		(error = git_reference_peel((git_object **)&our_commit, our_ref, GIT_OBJ_COMMIT)) < 0 ||
+		(error = git_cherry_pick_commit(&index_new, repo, commit, our_commit, opts.mainline, &opts.merge_opts)) < 0 ||
+		(error = git_merge__indexes(repo, index_new)) < 0 ||
+		(error = git_repository_index(&index_repo, repo)) < 0 ||
+		(error = git_merge__append_conflicts_to_merge_msg(repo, index_repo)) < 0 ||
+		(error = git_checkout_index(repo, index_repo, &opts.checkout_opts)) < 0)
+		goto on_error;
+
+	goto done;
+
+on_error:
+	cherry_pick_state_cleanup(repo);
+
+done:
+	git_index_free(index_new);
+	git_index_free(index_repo);
+	git_commit_free(our_commit);
+	git_reference_free(our_ref);
+	git_buf_free(&their_label);
+
+	return error;
+}
+
+int git_cherry_pick_init_opts(git_cherry_pick_options* opts, int version)
+{
+	if (version != GIT_CHERRY_PICK_OPTIONS_VERSION) {
+		giterr_set(GITERR_INVALID, "Invalid version %d for git_cherry_pick_options", version);
+		return -1;
+	} else {
+		git_cherry_pick_options o = GIT_CHERRY_PICK_OPTIONS_INIT;
+		memcpy(opts, &o, sizeof(o));
+		return 0;
+	}
+}