thodg/libgit2

diff --git a/include/git2/commit.h b/include/git2/commit.h
index a08cf1c..8b03df0 100644
--- a/include/git2/commit.h
+++ b/include/git2/commit.h
@@ -117,6 +117,17 @@ GIT_EXTERN(const char *) git_commit_message(const git_commit *commit);
 GIT_EXTERN(const char *) git_commit_message_raw(const git_commit *commit);
 
 /**
+ * Get the short "summary" of the git commit message.
+ *
+ * The returned message is the summary of the commit, comprising the
+ * first paragraph of the message with whitespace trimmed and squashed.
+ *
+ * @param commit a previously loaded commit.
+ * @return the summary of a commit or NULL on error
+ */
+GIT_EXTERN(const char *) git_commit_summary(git_commit *commit);
+
+/**
  * Get the commit time (i.e. committer time) of a commit.
  *
  * @param commit a previously loaded commit.
diff --git a/include/git2/errors.h b/include/git2/errors.h
index be7a31d..f1a8ea1 100644
--- a/include/git2/errors.h
+++ b/include/git2/errors.h
@@ -71,6 +71,7 @@ typedef enum {
 	GITERR_MERGE,
 	GITERR_SSH,
 	GITERR_FILTER,
+	GITERR_REVERT,
 } git_error_t;
 
 /**
diff --git a/include/git2/revert.h b/include/git2/revert.h
new file mode 100644
index 0000000..fe84238
--- /dev/null
+++ b/include/git2/revert.h
@@ -0,0 +1,52 @@
+/*
+ * 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_revert_h__
+#define INCLUDE_git_revert_h__
+
+#include "common.h"
+#include "types.h"
+#include "merge.h"
+
+/**
+ * @file git2/revert.h
+ * @brief Git revert routines
+ * @defgroup git_revert Git revert 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_tree_opts merge_tree_opts;
+	git_checkout_opts checkout_opts;
+} git_revert_opts;
+
+#define GIT_REVERT_OPTS_VERSION 1
+#define GIT_REVERT_OPTS_INIT {GIT_REVERT_OPTS_VERSION, 0, GIT_MERGE_TREE_OPTS_INIT, GIT_CHECKOUT_OPTS_INIT}
+
+/**
+* Reverts the given commits, producing changes in the working directory.
+*
+* @param repo the repository to revert
+* @param commits the commits to revert
+* @param commits_len the number of commits to revert
+* @param flags merge flags
+*/
+GIT_EXTERN(int) git_revert(
+	git_repository *repo,
+	git_commit *commit,
+	const git_revert_opts *given_opts);
+
+/** @} */
+GIT_END_DECL
+#endif
+
diff --git a/src/commit.c b/src/commit.c
index 91b60bb..bbb76f3 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 d452e29..efb080b 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 1158679..c31a935 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 d7d1c67..b240f6c 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 0000000..34ba343
--- /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 0000000..ed39121
--- /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
diff --git a/tests/commit/commit.c b/tests/commit/commit.c
index 8f071ff..4af9190 100644
--- a/tests/commit/commit.c
+++ b/tests/commit/commit.c
@@ -1,4 +1,6 @@
 #include "clar_libgit2.h"
+#include "commit.h"
+#include "git2/commit.h"
 
 static git_repository *_repo;
 
@@ -44,3 +46,30 @@ void test_commit_commit__create_unexisting_update_ref(void)
 	git_signature_free(s);
 	git_reference_free(ref);
 }
+
+void assert_commit_summary(const char *expected, const char *given)
+{
+	git_commit *dummy;
+
+	cl_assert(dummy = git__calloc(1, sizeof(struct git_commit)));
+
+	dummy->raw_message = git__strdup(given);
+	cl_assert_equal_s(expected, git_commit_summary(dummy));
+
+	git_commit__free(dummy);
+}
+
+void test_commit_commit__summary(void)
+{
+	assert_commit_summary("One-liner with no trailing newline", "One-liner with no trailing newline");
+	assert_commit_summary("One-liner with trailing newline", "One-liner with trailing newline\n");
+	assert_commit_summary("Trimmed leading&trailing newlines", "\n\nTrimmed leading&trailing newlines\n\n");
+	assert_commit_summary("First paragraph only", "\nFirst paragraph only\n\n(There are more!)");
+	assert_commit_summary("First paragraph with  unwrapped trailing\tlines", "\nFirst paragraph\nwith  unwrapped\ntrailing\tlines\n\n(Yes, unwrapped!)");
+	assert_commit_summary("\tLeading \ttabs", "\tLeading\n\ttabs\n\nis preserved");
+	assert_commit_summary(" Leading  Spaces", " Leading\n Spaces\n\nare preserved");
+	assert_commit_summary("Trailing tabs\tare removed", "Trailing tabs\tare removed\t\t");
+	assert_commit_summary("Trailing spaces  are removed", "Trailing spaces  are removed  ");
+	assert_commit_summary("Trailing tabs", "Trailing tabs\t\n\nare removed");
+	assert_commit_summary("Trailing spaces", "Trailing spaces \n\nare removed");
+}
diff --git a/tests/resources/revert/.gitted/HEAD b/tests/resources/revert/.gitted/HEAD
new file mode 100644
index 0000000..cb43805
--- /dev/null
+++ b/tests/resources/revert/.gitted/HEAD
@@ -0,0 +1 @@
+ref: refs/heads/master
diff --git a/tests/resources/revert/.gitted/config b/tests/resources/revert/.gitted/config
new file mode 100644
index 0000000..454e576
--- /dev/null
+++ b/tests/resources/revert/.gitted/config
@@ -0,0 +1,8 @@
+[core]
+	repositoryformatversion = 0
+	filemode = false
+	bare = false
+	logallrefupdates = true
+	symlinks = false
+	ignorecase = true
+	hideDotFiles = dotGitOnly
diff --git a/tests/resources/revert/.gitted/index b/tests/resources/revert/.gitted/index
new file mode 100644
index 0000000..87419ff
Binary files /dev/null and b/tests/resources/revert/.gitted/index differ
diff --git a/tests/resources/revert/.gitted/info/exclude b/tests/resources/revert/.gitted/info/exclude
new file mode 100644
index 0000000..f006809
--- /dev/null
+++ b/tests/resources/revert/.gitted/info/exclude
@@ -0,0 +1,6 @@
+# git ls-files --others --exclude-from=.git/info/exclude
+# Lines that start with '#' are comments.
+# For a project mostly in C, the following would be a good set of
+# exclude patterns (uncomment them if you want to use them):
+# *.[oa]
+# *~
diff --git a/tests/resources/revert/.gitted/objects/0a/a8c7e40d342fff78d60b29a4ba8e993ed79c51 b/tests/resources/revert/.gitted/objects/0a/a8c7e40d342fff78d60b29a4ba8e993ed79c51
new file mode 100644
index 0000000..5c811ef
--- /dev/null
+++ b/tests/resources/revert/.gitted/objects/0a/a8c7e40d342fff78d60b29a4ba8e993ed79c51
@@ -0,0 +1,2 @@
+x
��K
+�0@]�s
%�4?q�
�@2�Ѐ�@���3�{��{$��
�itf@��L9��1��OI��K�c���drY��X��c����s���W>��R�]ʸ���	�Gଭ���x�	U�:jz�/��?
\ No newline at end of file
diff --git a/tests/resources/revert/.gitted/objects/0a/b09ea6d4c3634bdf6c221626d8b6f7dd890767 b/tests/resources/revert/.gitted/objects/0a/b09ea6d4c3634bdf6c221626d8b6f7dd890767
new file mode 100644
index 0000000..c050e5a
Binary files /dev/null and b/tests/resources/revert/.gitted/objects/0a/b09ea6d4c3634bdf6c221626d8b6f7dd890767 differ
diff --git a/tests/resources/revert/.gitted/objects/0c/db66192ee192f70f891f05a47636057420e871 b/tests/resources/revert/.gitted/objects/0c/db66192ee192f70f891f05a47636057420e871
new file mode 100644
index 0000000..31c107f
Binary files /dev/null and b/tests/resources/revert/.gitted/objects/0c/db66192ee192f70f891f05a47636057420e871 differ
diff --git a/tests/resources/revert/.gitted/objects/0f/5bfcf58c558d865da6be0281d7795993646cee b/tests/resources/revert/.gitted/objects/0f/5bfcf58c558d865da6be0281d7795993646cee
new file mode 100644
index 0000000..fb4fc76
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diff --git a/tests/resources/revert/.gitted/objects/13/ee9cd5d8e1023c218e0e1ea684ec0c582b5050 b/tests/resources/revert/.gitted/objects/13/ee9cd5d8e1023c218e0e1ea684ec0c582b5050
new file mode 100644
index 0000000..aed4647
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diff --git a/tests/resources/revert/.gitted/refs/heads/master b/tests/resources/revert/.gitted/refs/heads/master
new file mode 100644
index 0000000..d3850da
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@@ -0,0 +1 @@
+2d440f2b3147d3dc7ad1085813478d6d869d5a4d
diff --git a/tests/resources/revert/.gitted/refs/heads/merges b/tests/resources/revert/.gitted/refs/heads/merges
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index 0000000..6533a94
--- /dev/null
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+5acdc74af27172ec491d213ee36cea7eb9ef2579
diff --git a/tests/resources/revert/.gitted/refs/heads/merges-branch b/tests/resources/revert/.gitted/refs/heads/merges-branch
new file mode 100644
index 0000000..febb29c
--- /dev/null
+++ b/tests/resources/revert/.gitted/refs/heads/merges-branch
@@ -0,0 +1 @@
+13ee9cd5d8e1023c218e0e1ea684ec0c582b5050
diff --git a/tests/resources/revert/.gitted/refs/heads/reverted-branch b/tests/resources/revert/.gitted/refs/heads/reverted-branch
new file mode 100644
index 0000000..16bb7a2
--- /dev/null
+++ b/tests/resources/revert/.gitted/refs/heads/reverted-branch
@@ -0,0 +1 @@
+52c95c4264245469a0617e289a7d737f156826b4
diff --git a/tests/resources/revert/file1.txt b/tests/resources/revert/file1.txt
new file mode 100644
index 0000000..84b2259
--- /dev/null
+++ b/tests/resources/revert/file1.txt
@@ -0,0 +1,14 @@
+!File one!
+!File one!
+File one!
+File one
+File one
+File one
+File one
+File one
+File one
+File one
+File one!
+!File one!
+!File one!
+!File one!
diff --git a/tests/resources/revert/file2.txt b/tests/resources/revert/file2.txt
new file mode 100644
index 0000000..acb5747
--- /dev/null
+++ b/tests/resources/revert/file2.txt
@@ -0,0 +1,16 @@
+File two
+File two
+File two
+File two
+File two
+File two
+File two
+File two
+File two
+File two
+File two
+File two
+File two
+File two
+File two
+File two
diff --git a/tests/resources/revert/file3.txt b/tests/resources/revert/file3.txt
new file mode 100644
index 0000000..b033059
--- /dev/null
+++ b/tests/resources/revert/file3.txt
@@ -0,0 +1,16 @@
+File three
+File three
+File three
+File three
+File three
+File three
+File three
+File three
+File three
+File three
+File three
+File three
+File three
+File three
+File three
+File three
diff --git a/tests/resources/revert/file6.txt b/tests/resources/revert/file6.txt
new file mode 100644
index 0000000..5c0cd5d
--- /dev/null
+++ b/tests/resources/revert/file6.txt
@@ -0,0 +1,14 @@
+File six, actually!
+File four!
+File four!
+File four!
+File four!
+File four!
+File four!
+File four!
+File four!
+File four!
+File four!
+File four!
+File four!
+File four!
diff --git a/tests/revert/revert.c b/tests/revert/revert.c
new file mode 100644
index 0000000..4a45190
--- /dev/null
+++ b/tests/revert/revert.c
@@ -0,0 +1,364 @@
+#include "clar.h"
+#include "clar_libgit2.h"
+
+#include "buffer.h"
+#include "fileops.h"
+#include "git2/revert.h"
+
+#include "../merge/merge_helpers.h"
+
+#define TEST_REPO_PATH "revert"
+
+static git_repository *repo;
+static git_index *repo_index;
+
+// Fixture setup and teardown
+void test_revert_revert__initialize(void)
+{
+	repo = cl_git_sandbox_init(TEST_REPO_PATH);
+	git_repository_index(&repo_index, repo);
+}
+
+void test_revert_revert__cleanup(void)
+{
+	git_index_free(repo_index);
+	cl_git_sandbox_cleanup();
+}
+
+/* git reset --hard 72333f47d4e83616630ff3b0ffe4c0faebcc3c45
+ * git revert --no-commit d1d403d22cbe24592d725f442835cf46fe60c8ac */
+void test_revert_revert__automerge(void)
+{
+	git_commit *head, *commit;
+	git_oid head_oid, revert_oid;
+
+	struct merge_index_entry merge_index_entries[] = {
+		{ 0100644, "caf99de3a49827117bb66721010eac461b06a80c", 0, "file1.txt" },
+		{ 0100644, "0ab09ea6d4c3634bdf6c221626d8b6f7dd890767", 0, "file2.txt" },
+		{ 0100644, "f4e107c230d08a60fb419d19869f1f282b272d9c", 0, "file3.txt" },
+		{ 0100644, "0f5bfcf58c558d865da6be0281d7795993646cee", 0, "file6.txt" },
+	};
+
+	git_oid_fromstr(&head_oid, "72333f47d4e83616630ff3b0ffe4c0faebcc3c45");
+	cl_git_pass(git_commit_lookup(&head, repo, &head_oid));
+	cl_git_pass(git_reset(repo, (git_object *)head, GIT_RESET_HARD));
+
+	git_oid_fromstr(&revert_oid, "d1d403d22cbe24592d725f442835cf46fe60c8ac");
+	cl_git_pass(git_commit_lookup(&commit, repo, &revert_oid));
+	cl_git_pass(git_revert(repo, commit, NULL));
+
+	cl_assert(merge_test_index(repo_index, merge_index_entries, 4));
+
+	git_commit_free(commit);
+	git_commit_free(head);
+}
+
+/* git revert --no-commit 72333f47d4e83616630ff3b0ffe4c0faebcc3c45 */
+void test_revert_revert__conflicts(void)
+{
+	git_reference *head_ref;
+	git_commit *head, *commit;
+	git_oid revert_oid;
+	git_buf conflicting_buf = GIT_BUF_INIT;
+
+	struct merge_index_entry merge_index_entries[] = {
+		{ 0100644, "7731926a337c4eaba1e2187d90ebfa0a93659382", 1, "file1.txt" },
+		{ 0100644, "4b8fcff56437e60f58e9a6bc630dd242ebf6ea2c", 2, "file1.txt" },
+		{ 0100644, "3a3ef367eaf3fe79effbfb0a56b269c04c2b59fe", 3, "file1.txt" },
+		{ 0100644, "0ab09ea6d4c3634bdf6c221626d8b6f7dd890767", 0, "file2.txt" },
+		{ 0100644, "f4e107c230d08a60fb419d19869f1f282b272d9c", 0, "file3.txt" },
+		{ 0100644, "0f5bfcf58c558d865da6be0281d7795993646cee", 0, "file6.txt" },
+	};
+
+	git_oid_fromstr(&revert_oid, "72333f47d4e83616630ff3b0ffe4c0faebcc3c45");
+
+	cl_git_pass(git_repository_head(&head_ref, repo));
+	cl_git_pass(git_reference_peel((git_object **)&head, head_ref, GIT_OBJ_COMMIT));
+	cl_git_pass(git_reset(repo, (git_object *)head, GIT_RESET_HARD));
+
+	cl_git_pass(git_commit_lookup(&commit, repo, &revert_oid));
+	cl_git_pass(git_revert(repo, commit, NULL));
+
+	cl_assert(merge_test_index(repo_index, merge_index_entries, 6));
+
+	cl_git_pass(git_futils_readbuffer(&conflicting_buf,
+		TEST_REPO_PATH "/file1.txt"));
+	cl_assert(strcmp(conflicting_buf.ptr, "!File one!\n" \
+		"!File one!\n" \
+		"File one!\n" \
+		"File one\n" \
+		"File one\n" \
+		"File one\n" \
+		"File one\n" \
+		"File one\n" \
+		"File one\n" \
+		"File one\n" \
+		"<<<<<<< HEAD\n" \
+		"File one!\n" \
+		"!File one!\n" \
+		"!File one!\n" \
+		"!File one!\n" \
+		"=======\n" \
+		"File one\n" \
+		"File one\n" \
+		"File one\n" \
+		"File one\n" \
+		">>>>>>> parent of 72333f4... automergeable changes\n") == 0);
+
+	git_commit_free(commit);
+	git_commit_free(head);
+	git_reference_free(head_ref);
+	git_buf_free(&conflicting_buf);
+}
+
+/* git reset --hard 39467716290f6df775a91cdb9a4eb39295018145
+ * git revert --no-commit ebb03002cee5d66c7732dd06241119fe72ab96a5
+*/
+void test_revert_revert__orphan(void)
+{
+	git_commit *head, *commit;
+	git_oid head_oid, revert_oid;
+
+	struct merge_index_entry merge_index_entries[] = {
+		{ 0100644, "296a6d3be1dff05c5d1f631d2459389fa7b619eb", 0, "file-mainline.txt" },
+	};
+
+	git_oid_fromstr(&head_oid, "39467716290f6df775a91cdb9a4eb39295018145");
+	cl_git_pass(git_commit_lookup(&head, repo, &head_oid));
+	cl_git_pass(git_reset(repo, (git_object *)head, GIT_RESET_HARD));
+
+	git_oid_fromstr(&revert_oid, "ebb03002cee5d66c7732dd06241119fe72ab96a5");
+	cl_git_pass(git_commit_lookup(&commit, repo, &revert_oid));
+	cl_git_pass(git_revert(repo, commit, NULL));
+
+	cl_assert(merge_test_index(repo_index, merge_index_entries, 1));
+
+	git_commit_free(commit);
+	git_commit_free(head);
+}
+
+/* git reset --hard 72333f47d4e83616630ff3b0ffe4c0faebcc3c45
+ * git revert --no-commit d1d403d22cbe24592d725f442835cf46fe60c8ac */
+void test_revert_revert__conflict_use_ours(void)
+{
+	git_commit *head, *commit;
+	git_oid head_oid, revert_oid;
+	git_revert_opts opts = GIT_REVERT_OPTS_INIT;
+
+	opts.merge_tree_opts.automerge_flags = GIT_MERGE_AUTOMERGE_NONE;
+	opts.checkout_opts.checkout_strategy = GIT_CHECKOUT_SAFE | GIT_CHECKOUT_USE_OURS;
+
+	struct merge_index_entry merge_index_entries[] = {
+		{ 0100644, "3a3ef367eaf3fe79effbfb0a56b269c04c2b59fe", 1, "file1.txt" },
+		{ 0100644, "7731926a337c4eaba1e2187d90ebfa0a93659382", 2, "file1.txt" },
+		{ 0100644, "747726e021bc5f44b86de60e3032fd6f9f1b8383", 3, "file1.txt" },
+		{ 0100644, "0ab09ea6d4c3634bdf6c221626d8b6f7dd890767", 0, "file2.txt" },
+		{ 0100644, "f4e107c230d08a60fb419d19869f1f282b272d9c", 0, "file3.txt" },
+		{ 0100644, "0f5bfcf58c558d865da6be0281d7795993646cee", 0, "file6.txt" },
+	};
+
+	struct merge_index_entry merge_filesystem_entries[] = {
+		{ 0100644, "7731926a337c4eaba1e2187d90ebfa0a93659382", 0, "file1.txt" },
+		{ 0100644, "0ab09ea6d4c3634bdf6c221626d8b6f7dd890767", 0, "file2.txt" },
+		{ 0100644, "f4e107c230d08a60fb419d19869f1f282b272d9c", 0, "file3.txt" },
+		{ 0100644, "0f5bfcf58c558d865da6be0281d7795993646cee", 0, "file6.txt" },
+	};
+
+	git_oid_fromstr(&head_oid, "72333f47d4e83616630ff3b0ffe4c0faebcc3c45");
+	cl_git_pass(git_commit_lookup(&head, repo, &head_oid));
+	cl_git_pass(git_reset(repo, (git_object *)head, GIT_RESET_HARD));
+
+	git_oid_fromstr(&revert_oid, "d1d403d22cbe24592d725f442835cf46fe60c8ac");
+	cl_git_pass(git_commit_lookup(&commit, repo, &revert_oid));
+	cl_git_pass(git_revert(repo, commit, &opts));
+
+	cl_assert(merge_test_index(repo_index, merge_index_entries, 6));
+	cl_assert(merge_test_workdir(repo, merge_filesystem_entries, 4));
+
+	git_commit_free(commit);
+	git_commit_free(head);
+}
+
+/* git reset --hard cef56612d71a6af8d8015691e4865f7fece905b5
+ * git revert --no-commit 55568c8de5322ff9a95d72747a239cdb64a19965
+ */
+void test_revert_revert__rename_1_of_2(void)
+{
+	git_commit *head, *commit;
+	git_oid head_oid, revert_oid;
+	git_revert_opts opts = GIT_REVERT_OPTS_INIT;
+
+	opts.merge_tree_opts.flags |= GIT_MERGE_TREE_FIND_RENAMES;
+	opts.merge_tree_opts.rename_threshold = 50;
+
+	struct merge_index_entry merge_index_entries[] = {
+		{ 0100644, "747726e021bc5f44b86de60e3032fd6f9f1b8383", 0, "file1.txt" },
+		{ 0100644, "0ab09ea6d4c3634bdf6c221626d8b6f7dd890767", 0, "file2.txt" },
+		{ 0100644, "f4e107c230d08a60fb419d19869f1f282b272d9c", 0, "file3.txt" },
+		{ 0100644, "55acf326a69f0aab7a974ec53ffa55a50bcac14e", 3, "file4.txt" },
+		{ 0100644, "55acf326a69f0aab7a974ec53ffa55a50bcac14e", 1, "file5.txt" },
+		{ 0100644, "0f5bfcf58c558d865da6be0281d7795993646cee", 2, "file6.txt" },
+	};
+
+	git_oid_fromstr(&head_oid, "cef56612d71a6af8d8015691e4865f7fece905b5");
+	cl_git_pass(git_commit_lookup(&head, repo, &head_oid));
+	cl_git_pass(git_reset(repo, (git_object *)head, GIT_RESET_HARD));
+
+	git_oid_fromstr(&revert_oid, "55568c8de5322ff9a95d72747a239cdb64a19965");
+	cl_git_pass(git_commit_lookup(&commit, repo, &revert_oid));
+	cl_git_pass(git_revert(repo, commit, &opts));
+
+	cl_assert(merge_test_index(repo_index, merge_index_entries, 6));
+
+	git_commit_free(commit);
+	git_commit_free(head);
+}
+
+/* git reset --hard 55568c8de5322ff9a95d72747a239cdb64a19965
+ * git revert --no-commit HEAD~1 */
+void test_revert_revert__rename(void)
+{
+	git_commit *head, *commit;
+	git_oid head_oid, revert_oid;
+	git_revert_opts opts = GIT_REVERT_OPTS_INIT;
+
+	opts.merge_tree_opts.flags |= GIT_MERGE_TREE_FIND_RENAMES;
+	opts.merge_tree_opts.rename_threshold = 50;
+
+	struct merge_index_entry merge_index_entries[] = {
+		{ 0100644, "55acf326a69f0aab7a974ec53ffa55a50bcac14e", 1, "file4.txt" },
+		{ 0100644, "55acf326a69f0aab7a974ec53ffa55a50bcac14e", 2, "file5.txt" },
+	};
+
+	struct merge_name_entry merge_name_entries[] = {
+		{ "file4.txt", "file5.txt", "" },
+	};
+
+	git_oid_fromstr(&head_oid, "55568c8de5322ff9a95d72747a239cdb64a19965");
+	cl_git_pass(git_commit_lookup(&head, repo, &head_oid));
+	cl_git_pass(git_reset(repo, (git_object *)head, GIT_RESET_HARD));
+
+	git_oid_fromstr(&revert_oid, "0aa8c7e40d342fff78d60b29a4ba8e993ed79c51");
+	cl_git_pass(git_commit_lookup(&commit, repo, &revert_oid));
+	cl_git_pass(git_revert(repo, commit, &opts));
+
+	cl_assert(merge_test_index(repo_index, merge_index_entries, 2));
+	cl_assert(merge_test_names(repo_index, merge_name_entries, 1));
+
+	git_commit_free(commit);
+	git_commit_free(head);
+}
+
+/* git revert --no-commit HEAD */
+void test_revert_revert__head(void)
+{
+	git_reference *head;
+	git_commit *commit;
+
+	struct merge_index_entry merge_index_entries[] = {
+		{ 0100644, "7731926a337c4eaba1e2187d90ebfa0a93659382", 0, "file1.txt" },
+		{ 0100644, "0ab09ea6d4c3634bdf6c221626d8b6f7dd890767", 0, "file2.txt" },
+		{ 0100644, "f4e107c230d08a60fb419d19869f1f282b272d9c", 0, "file3.txt" },
+		{ 0100644, "0f5bfcf58c558d865da6be0281d7795993646cee", 0, "file6.txt" },
+	};
+
+	/* HEAD is 2d440f2b3147d3dc7ad1085813478d6d869d5a4d */
+	cl_git_pass(git_repository_head(&head, repo));
+	cl_git_pass(git_reference_peel((git_object **)&commit, head, GIT_OBJ_COMMIT));
+	cl_git_pass(git_reset(repo, (git_object *)commit, GIT_RESET_HARD));
+	cl_git_pass(git_revert(repo, commit, NULL));
+
+	cl_assert(merge_test_index(repo_index, merge_index_entries, 4));
+	cl_assert(merge_test_workdir(repo, merge_index_entries, 4));
+
+	git_reference_free(head);
+	git_commit_free(commit);
+}
+
+void test_revert_revert__nonmerge_fails_mainline_specified(void)
+{
+	git_reference *head;
+	git_commit *commit;
+	git_revert_opts opts = GIT_REVERT_OPTS_INIT;
+
+	cl_git_pass(git_repository_head(&head, repo));
+	cl_git_pass(git_reference_peel((git_object **)&commit, head, GIT_OBJ_COMMIT));
+
+	opts.mainline = 1;
+	cl_must_fail(git_revert(repo, commit, &opts));
+	cl_assert(!git_path_exists(TEST_REPO_PATH "/.git/MERGE_MSG"));
+	cl_assert(!git_path_exists(TEST_REPO_PATH "/.git/REVERT_HEAD"));
+
+	git_reference_free(head);
+	git_commit_free(commit);
+}
+
+/* git reset --hard 5acdc74af27172ec491d213ee36cea7eb9ef2579
+ * git revert HEAD */
+void test_revert_revert__merge_fails_without_mainline_specified(void)
+{
+	git_commit *head;
+	git_oid head_oid;
+
+	git_oid_fromstr(&head_oid, "5acdc74af27172ec491d213ee36cea7eb9ef2579");
+	cl_git_pass(git_commit_lookup(&head, repo, &head_oid));
+	cl_git_pass(git_reset(repo, (git_object *)head, GIT_RESET_HARD));
+
+	cl_must_fail(git_revert(repo, head, NULL));
+	cl_assert(!git_path_exists(TEST_REPO_PATH "/.git/MERGE_MSG"));
+	cl_assert(!git_path_exists(TEST_REPO_PATH "/.git/REVERT_HEAD"));
+
+	git_commit_free(head);
+}
+
+/* git reset --hard 5acdc74af27172ec491d213ee36cea7eb9ef2579
+ * git revert HEAD -m1 --no-commit */
+void test_revert_revert__merge_first_parent(void)
+{
+	git_commit *head;
+	git_oid head_oid;
+	git_revert_opts opts = GIT_REVERT_OPTS_INIT;
+
+	opts.mainline = 1;
+
+	struct merge_index_entry merge_index_entries[] = {
+		{ 0100644, "296a6d3be1dff05c5d1f631d2459389fa7b619eb", 0, "file-mainline.txt" },
+		{ 0100644, "0cdb66192ee192f70f891f05a47636057420e871", 0, "file1.txt" },
+		{ 0100644, "73ec36fa120f8066963a0bc9105bb273dbd903d7", 0, "file2.txt" },
+	};
+
+	git_oid_fromstr(&head_oid, "5acdc74af27172ec491d213ee36cea7eb9ef2579");
+	cl_git_pass(git_commit_lookup(&head, repo, &head_oid));
+	cl_git_pass(git_reset(repo, (git_object *)head, GIT_RESET_HARD));
+
+	cl_git_pass(git_revert(repo, head, &opts));
+
+	cl_assert(merge_test_index(repo_index, merge_index_entries, 3));
+
+	git_commit_free(head);
+}
+
+void test_revert_revert__merge_second_parent(void)
+{
+	git_commit *head;
+	git_oid head_oid;
+	git_revert_opts opts = GIT_REVERT_OPTS_INIT;
+
+	opts.mainline = 2;
+
+	struct merge_index_entry merge_index_entries[] = {
+		{ 0100644, "33c6fd981c49a2abf2971482089350bfc5cda8ea", 0, "file-branch.txt" },
+		{ 0100644, "0cdb66192ee192f70f891f05a47636057420e871", 0, "file1.txt" },
+		{ 0100644, "73ec36fa120f8066963a0bc9105bb273dbd903d7", 0, "file2.txt" },
+	};
+
+	git_oid_fromstr(&head_oid, "5acdc74af27172ec491d213ee36cea7eb9ef2579");
+	cl_git_pass(git_commit_lookup(&head, repo, &head_oid));
+	cl_git_pass(git_reset(repo, (git_object *)head, GIT_RESET_HARD));
+
+	cl_git_pass(git_revert(repo, head, &opts));
+
+	cl_assert(merge_test_index(repo_index, merge_index_entries, 3));
+
+	git_commit_free(head);
+}