6 files changed, 274 insertions, 8 deletions

diff --git a/src/commit.c b/src/commit.c
index 91b60bbb2..bbb76f350 100644
--- a/src/commit.c
+++ b/src/commit.c
@@ -31,6 +31,7 @@ void git_commit__free(void *_commit)
 	git__free(commit->raw_header);
 	git__free(commit->raw_message);
 	git__free(commit->message_encoding);
+	git__free(commit->summary);
 
 	git__free(commit);
 }
@@ -286,6 +287,34 @@ const char *git_commit_message(const git_commit *commit)
 	return message;
 }
 
+const char *git_commit_summary(git_commit *commit)
+{
+	git_buf summary = GIT_BUF_INIT;
+	const char *msg, *space;
+
+	assert(commit);
+
+	if (!commit->summary) {
+		for (msg = git_commit_message(commit), space = NULL; *msg; ++msg) {
+			if (msg[0] == '\n' && (!msg[1] || msg[1] == '\n'))
+				break;
+			else if (msg[0] == '\n')
+				git_buf_putc(&summary, ' ');
+			else if (git__isspace(msg[0]))
+				space = space ? space : msg;
+			else if (space) {
+				git_buf_put(&summary, space, (msg - space) + 1);
+				space = NULL;
+			} else
+				git_buf_putc(&summary, *msg);
+		}
+
+		commit->summary = git_buf_detach(&summary);
+	}
+
+	return commit->summary;
+}
+
 int git_commit_tree(git_tree **tree_out, const git_commit *commit)
 {
 	assert(commit);
diff --git a/src/commit.h b/src/commit.h
index d452e2975..efb080b50 100644
--- a/src/commit.h
+++ b/src/commit.h
@@ -26,6 +26,8 @@ struct git_commit {
 	char *message_encoding;
 	char *raw_message;
 	char *raw_header;
+
+	char *summary;
 };
 
 void git_commit__free(void *commit);
diff --git a/src/merge.c b/src/merge.c
index 115867971..c31a935b0 100644
--- a/src/merge.c
+++ b/src/merge.c
@@ -1206,7 +1206,7 @@ static git_merge_diff *merge_diff_from_index_entries(
 
 /* Merge trees */
 
-static int merge_index_insert_conflict(
+static int merge_diff_list_insert_conflict(
 	git_merge_diff_list *diff_list,
 	struct merge_diff_df_data *merge_df_data,
 	const git_index_entry *tree_items[3])
@@ -1222,7 +1222,7 @@ static int merge_index_insert_conflict(
 	return 0;
 }
 
-static int merge_index_insert_unmodified(
+static int merge_diff_list_insert_unmodified(
 	git_merge_diff_list *diff_list,
 	const git_index_entry *tree_items[3])
 {
@@ -1252,7 +1252,7 @@ int git_merge_diff_list__find_differences(
 	size_t i, j;
 	int error = 0;
 
-	assert(diff_list && our_tree && their_tree);
+	assert(diff_list && (our_tree || their_tree));
 
 	if ((error = git_iterator_for_tree(&iterators[TREE_IDX_ANCESTOR], (git_tree *)ancestor_tree, GIT_ITERATOR_DONT_IGNORE_CASE, NULL, NULL)) < 0 ||
 		(error = git_iterator_for_tree(&iterators[TREE_IDX_OURS], (git_tree *)our_tree, GIT_ITERATOR_DONT_IGNORE_CASE, NULL, NULL)) < 0 ||
@@ -1262,6 +1262,7 @@ int git_merge_diff_list__find_differences(
 	/* Set up the iterators */
 	for (i = 0; i < 3; i++) {
 		error = git_iterator_current(&items[i], iterators[i]);
+
 		if (error < 0 && error != GIT_ITEROVER)
 			goto done;
 	}
@@ -1313,9 +1314,9 @@ int git_merge_diff_list__find_differences(
 			break;
 
 		if (cur_item_modified)
-			error = merge_index_insert_conflict(diff_list, &df_data, cur_items);
+			error = merge_diff_list_insert_conflict(diff_list, &df_data, cur_items);
 		else
-			error = merge_index_insert_unmodified(diff_list, cur_items);
+			error = merge_diff_list_insert_unmodified(diff_list, cur_items);
 		if (error < 0)
 			goto done;
 
@@ -1325,6 +1326,7 @@ int git_merge_diff_list__find_differences(
 				continue;
 
 			error = git_iterator_advance(&items[i], iterators[i]);
+
 			if (error < 0 && error != GIT_ITEROVER)
 				goto done;
 		}
@@ -1569,7 +1571,7 @@ int git_merge_trees(
 	size_t i;
 	int error = 0;
 
-	assert(out && repo && our_tree && their_tree);
+	assert(out && repo && (our_tree || their_tree));
 
 	*out = NULL;
 
@@ -2268,7 +2270,7 @@ done:
 	return error;
 }
 
-static int merge_indexes(git_repository *repo, git_index *index_new)
+int git_merge__indexes(git_repository *repo, git_index *index_new)
 {
 	git_index *index_repo;
 	unsigned int index_repo_caps;
@@ -2440,7 +2442,7 @@ int git_merge(
 	/* TODO: recursive, octopus, etc... */
 
 	if ((error = git_merge_trees(&index_new, repo, ancestor_tree, our_tree, their_trees[0], &opts.merge_tree_opts)) < 0 ||
-		(error = merge_indexes(repo, index_new)) < 0 ||
+		(error = git_merge__indexes(repo, index_new)) < 0 ||
 		(error = git_repository_index(&index_repo, repo)) < 0 ||
 		(error = git_checkout_index(repo, index_repo, &opts.checkout_opts)) < 0)
 		goto on_error;
diff --git a/src/merge.h b/src/merge.h
index d7d1c67b7..b240f6c44 100644
--- a/src/merge.h
+++ b/src/merge.h
@@ -158,4 +158,6 @@ int git_merge__setup(
 	size_t their_heads_len,
 	unsigned int flags);
 
+int git_merge__indexes(git_repository *repo, git_index *index_new);
+
 #endif
diff --git a/src/revert.c b/src/revert.c
new file mode 100644
index 000000000..34ba343b6
--- /dev/null
+++ b/src/revert.c
@@ -0,0 +1,217 @@
+/*
+* 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 "revert.h"
+
+#include "git2/types.h"
+#include "git2/merge.h"
+#include "git2/revert.h"
+#include "git2/commit.h"
+#include "git2/sys/commit.h"
+
+#define GIT_REVERT_FILE_MODE		0666
+
+static int write_revert_head(
+	git_repository *repo,
+	const git_commit *commit,
+	const char *commit_oidstr)
+{
+	git_filebuf file = GIT_FILEBUF_INIT;
+	git_buf file_path = GIT_BUF_INIT;
+	int error = 0;
+
+	assert(repo && commit);
+
+	if ((error = git_buf_joinpath(&file_path, repo->path_repository, GIT_REVERT_HEAD_FILE)) >= 0 &&
+		(error = git_filebuf_open(&file, file_path.ptr, GIT_FILEBUF_FORCE, GIT_REVERT_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 git_commit *commit,
+	const char *commit_oidstr,
+	const char *commit_msgline)
+{
+	git_filebuf file = GIT_FILEBUF_INIT;
+	git_buf file_path = GIT_BUF_INIT;
+	int error = 0;
+
+	assert(repo && commit);
+
+	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_REVERT_FILE_MODE)) < 0 ||
+		(error = git_filebuf_printf(&file, "Revert \"%s\"\n\nThis reverts commit %s.\n",
+		commit_msgline, commit_oidstr)) < 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 revert_normalize_opts(
+	git_repository *repo,
+	git_revert_opts *opts,
+	const git_revert_opts *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_revert_opts));
+	else {
+		git_revert_opts default_opts = GIT_REVERT_OPTS_INIT;
+		memcpy(opts, &default_opts, sizeof(git_revert_opts));
+	}
+
+	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;
+}
+
+int git_revert(
+	git_repository *repo,
+	git_commit *commit,
+	const git_revert_opts *given_opts)
+{
+	git_revert_opts opts;
+	git_commit *parent_commit = NULL;
+	git_tree *parent_tree = NULL, *our_tree = NULL, *revert_tree = NULL;
+	git_index *index_new = NULL, *index_repo = NULL;
+	char commit_oidstr[GIT_OID_HEXSZ + 1];
+	const char *commit_msg;
+	git_buf their_label = GIT_BUF_INIT;
+	int parent = 0;
+	int error = 0;
+
+	assert(repo && commit);
+
+	if ((error = git_repository__ensure_not_bare(repo, "revert")) < 0)
+		return error;
+
+	git_oid_fmt(commit_oidstr, git_commit_id(commit));
+	commit_oidstr[GIT_OID_HEXSZ] = '\0';
+
+	if ((commit_msg = git_commit_summary(commit)) == NULL) {
+		error = -1;
+		goto on_error;
+	}
+
+	if ((error = git_buf_printf(&their_label, "parent of %.7s... %s", commit_oidstr, commit_msg)) < 0 ||
+		(error = revert_normalize_opts(repo, &opts, given_opts, git_buf_cstr(&their_label))) < 0 ||
+		(error = write_revert_head(repo, commit, commit_oidstr)) < 0 ||
+		(error = write_merge_msg(repo, commit, commit_oidstr, commit_msg)) < 0 ||
+		(error = git_repository_head_tree(&our_tree, repo)) < 0 ||
+		(error = git_commit_tree(&revert_tree, commit)) < 0)
+		goto on_error;
+
+	if (git_commit_parentcount(commit) > 1) {
+		if (!opts.mainline) {
+			giterr_set(GITERR_REVERT,
+				"Mainline branch is not specified but %s is a merge commit",
+				commit_oidstr);
+			error = -1;
+			goto on_error;
+		}
+
+		parent = opts.mainline;
+	} else {
+		if (opts.mainline) {
+			giterr_set(GITERR_REVERT,
+				"Mainline branch was specified but %s is not a merge",
+				commit_oidstr);
+			error = -1;
+			goto on_error;
+		}
+
+		parent = git_commit_parentcount(commit);
+	}
+
+	if (parent &&
+		((error = git_commit_parent(&parent_commit, commit, (parent - 1))) < 0 ||
+		(error = git_commit_tree(&parent_tree, parent_commit)) < 0))
+		goto on_error;
+
+	if ((error = git_merge_trees(&index_new, repo, revert_tree, our_tree, parent_tree, &opts.merge_tree_opts)) < 0 ||
+		(error = git_merge__indexes(repo, index_new)) < 0 ||
+		(error = git_repository_index(&index_repo, repo)) < 0 ||
+		(error = git_checkout_index(repo, index_repo, &opts.checkout_opts)) < 0)
+		goto on_error;
+
+	goto done;
+
+on_error:
+	git_revert__cleanup(repo);
+
+done:
+	git_index_free(index_new);
+	git_index_free(index_repo);
+	git_tree_free(parent_tree);
+	git_tree_free(our_tree);
+	git_tree_free(revert_tree);
+	git_commit_free(parent_commit);
+	git_buf_free(&their_label);
+
+	return error;
+}
+
+int git_revert__cleanup(git_repository *repo)
+{
+	int error = 0;
+	git_buf revert_head_path = GIT_BUF_INIT,
+		merge_msg_path = GIT_BUF_INIT;
+
+	assert(repo);
+
+	if (git_buf_joinpath(&revert_head_path, repo->path_repository, GIT_REVERT_HEAD_FILE) < 0 ||
+		git_buf_joinpath(&merge_msg_path, repo->path_repository, GIT_MERGE_MSG_FILE) < 0)
+		return -1;
+
+	if (git_path_isfile(revert_head_path.ptr)) {
+		if ((error = p_unlink(revert_head_path.ptr)) < 0)
+			goto cleanup;
+	}
+
+	if (git_path_isfile(merge_msg_path.ptr))
+		(void)p_unlink(merge_msg_path.ptr);
+
+cleanup:
+	git_buf_free(&merge_msg_path);
+	git_buf_free(&revert_head_path);
+
+	return error;
+}
diff --git a/src/revert.h b/src/revert.h
new file mode 100644
index 000000000..ed3912198
--- /dev/null
+++ b/src/revert.h
@@ -0,0 +1,14 @@
+/*
+ * 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_revert_h__
+#define INCLUDE_revert_h__
+
+#include "git2/repository.h"
+
+int git_revert__cleanup(git_repository *repo);
+
+#endif