rebase: introduce inmemory rebasing

Introduce the ability to rebase in-memory or in a bare repository.

When `rebase_options.inmemory` is specified, the resultant `git_rebase`
session will not be persisted to disk.  Callers may still analyze
the rebase operations, resolve any conflicts against the in-memory
index and create the commits.  Neither `HEAD` nor the working
directory will be updated during this process.

1 files changed, 250 insertions, 117 deletions

diff --git a/src/rebase.c b/src/rebase.c
index 17536c030..54affd6e2 100644
--- a/src/rebase.c
+++ b/src/rebase.c
@@ -63,17 +63,23 @@ struct git_rebase {
 	char *state_path;
 
 	int head_detached : 1,
+		inmemory : 1,
 		quiet : 1,
 		started : 1;
 
-	char *orig_head_name;
+	git_array_t(git_rebase_operation) operations;
+	size_t current;
+
+	/* Used by in-memory rebase */
+	git_commit *last_commit;
+	git_index *last_index;
+
+	/* Used by regular (not in-memory) merge-style rebase */
 	git_oid orig_head_id;
+	char *orig_head_name;
 
 	git_oid onto_id;
 	char *onto_name;
-
-	git_array_t(git_rebase_operation) operations;
-	size_t current;
 };
 
 #define GIT_REBASE_STATE_INIT {0}
@@ -393,6 +399,9 @@ done:
 
 static int rebase_cleanup(git_rebase *rebase)
 {
+	if (!rebase || rebase->inmemory)
+		return 0;
+
 	return git_path_isdir(rebase->state_path) ?
 		git_futils_rmdir_r(rebase->state_path, NULL, GIT_RMDIR_REMOVE_FILES) :
 		0;
@@ -601,61 +610,65 @@ static int rebase_init_merge(
 	const git_annotated_commit *upstream,
 	const git_annotated_commit *onto)
 {
-	if (rebase_init_operations(rebase, repo, branch, upstream, onto) < 0)
-		return -1;
-
-	rebase->onto_name = git__strdup(rebase_onto_name(onto));
-	GITERR_CHECK_ALLOC(rebase->onto_name);
-
-	return 0;
-}
-
-static int rebase_init(
-	git_rebase *rebase,
-	git_repository *repo,
-	const git_annotated_commit *branch,
-	const git_annotated_commit *upstream,
-	const git_annotated_commit *onto)
-{
 	git_reference *head_ref = NULL;
-	git_annotated_commit *head_branch = NULL;
+	git_commit *onto_commit = NULL;
+	git_buf reflog = GIT_BUF_INIT;
 	git_buf state_path = GIT_BUF_INIT;
 	int error;
 
+	GIT_UNUSED(upstream);
+
 	if ((error = git_buf_joinpath(&state_path, repo->path_repository, REBASE_MERGE_DIR)) < 0)
 		goto done;
 
-	if (!branch) {
-		if ((error = git_repository_head(&head_ref, repo)) < 0 ||
-			(error = git_annotated_commit_from_ref(&head_branch, repo, head_ref)) < 0)
-			goto done;
-
-		branch = head_branch;
-	}
-
-	rebase->repo = repo;
-	rebase->type = GIT_REBASE_TYPE_MERGE;
 	rebase->state_path = git_buf_detach(&state_path);
+	GITERR_CHECK_ALLOC(rebase->state_path);
+
 	rebase->orig_head_name = git__strdup(branch->ref_name ? branch->ref_name : ORIG_DETACHED_HEAD);
+	GITERR_CHECK_ALLOC(rebase->orig_head_name);
+
+	rebase->onto_name = git__strdup(rebase_onto_name(onto));
+	GITERR_CHECK_ALLOC(rebase->onto_name);
+
 	rebase->quiet = rebase->options.quiet;
 
 	git_oid_cpy(&rebase->orig_head_id, git_annotated_commit_id(branch));
 	git_oid_cpy(&rebase->onto_id, git_annotated_commit_id(onto));
 
-	if (!rebase->orig_head_name || !rebase->state_path)
-		return -1;
-
-	error = rebase_init_merge(rebase, repo, branch, upstream, onto);
-
-	git_buf_free(&state_path);
+	if ((error = rebase_setupfiles(rebase)) < 0 ||
+		(error = git_buf_printf(&reflog,
+			"rebase: checkout %s", rebase_onto_name(onto))) < 0 ||
+		(error = git_commit_lookup(
+			&onto_commit, repo, git_annotated_commit_id(onto))) < 0 ||
+		(error = git_checkout_tree(repo,
+			(git_object *)onto_commit, &rebase->options.checkout_options)) < 0 ||
+		(error = git_reference_create(&head_ref, repo, GIT_HEAD_FILE,
+			git_annotated_commit_id(onto), 1, reflog.ptr)) < 0)
+		goto done;
 
 done:
 	git_reference_free(head_ref);
-	git_annotated_commit_free(head_branch);
+	git_commit_free(onto_commit);
+	git_buf_free(&reflog);
+	git_buf_free(&state_path);
 
 	return error;
 }
 
+static int rebase_init_inmemory(
+	git_rebase *rebase,
+	git_repository *repo,
+	const git_annotated_commit *branch,
+	const git_annotated_commit *upstream,
+	const git_annotated_commit *onto)
+{
+	GIT_UNUSED(branch);
+	GIT_UNUSED(upstream);
+
+	return git_commit_lookup(
+		&rebase->last_commit, repo, git_annotated_commit_id(onto));
+}
+
 int git_rebase_init(
 	git_rebase **out,
 	git_repository *repo,
@@ -665,9 +678,9 @@ int git_rebase_init(
 	const git_rebase_options *given_opts)
 {
 	git_rebase *rebase = NULL;
-	git_buf reflog = GIT_BUF_INIT;
-	git_commit *onto_commit = NULL;
+	git_annotated_commit *head_branch = NULL;
 	git_reference *head_ref = NULL;
+	bool inmemory = (given_opts && given_opts->inmemory);
 	int error;
 
 	assert(repo && (upstream || onto));
@@ -677,39 +690,51 @@ int git_rebase_init(
 	if (!onto)
 		onto = upstream;
 
-	if ((error = rebase_check_versions(given_opts)) < 0 ||
-		(error = git_repository__ensure_not_bare(repo, "rebase")) < 0 ||
-		(error = rebase_ensure_not_in_progress(repo)) < 0 ||
-		(error = rebase_ensure_not_dirty(repo, true, true, GIT_ERROR)) < 0 ||
-		(error = git_commit_lookup(
-			&onto_commit, repo, git_annotated_commit_id(onto))) < 0)
-		return error;
+	if ((error = rebase_check_versions(given_opts)) < 0)
+		goto done;
+
+	if (!inmemory) {
+		if ((error = git_repository__ensure_not_bare(repo, "rebase")) < 0 ||
+			(error = rebase_ensure_not_in_progress(repo)) < 0 ||
+			(error = rebase_ensure_not_dirty(repo, true, true, GIT_ERROR)) < 0)
+			goto done;
+	}
+
+	if (!branch) {
+		if ((error = git_repository_head(&head_ref, repo)) < 0 ||
+			(error = git_annotated_commit_from_ref(&head_branch, repo, head_ref)) < 0)
+			goto done;
+
+		branch = head_branch;
+	}
 
 	rebase = rebase_alloc(given_opts);
+	GITERR_CHECK_ALLOC(rebase);
 
-	if ((error = rebase_init(
-			rebase, repo, branch, upstream, onto)) < 0 ||
-		(error = rebase_setupfiles(rebase)) < 0 ||
-		(error = git_buf_printf(&reflog,
-			"rebase: checkout %s", rebase_onto_name(onto))) < 0 ||
-		(error = git_checkout_tree(
-			repo, (git_object *)onto_commit, &rebase->options.checkout_options)) < 0 ||
-		(error = git_reference_create(&head_ref, repo, GIT_HEAD_FILE,
-			git_annotated_commit_id(onto), 1, reflog.ptr)) < 0)
+	rebase->repo = repo;
+	rebase->inmemory = inmemory;
+	rebase->type = GIT_REBASE_TYPE_MERGE;
+
+	if ((error = rebase_init_operations(rebase, repo, branch, upstream, onto)) < 0)
 		goto done;
 
-	*out = rebase;
+	if (inmemory)
+		error = rebase_init_inmemory(rebase, repo, branch, upstream, onto);
+	else
+		rebase_init_merge(rebase, repo, branch ,upstream, onto);
+
+	if (error == 0)
+		*out = rebase;
 
 done:
 	git_reference_free(head_ref);
+	git_annotated_commit_free(head_branch);
+
 	if (error < 0) {
 		rebase_cleanup(rebase);
 		git_rebase_free(rebase);
 	}
 
-	git_commit_free(onto_commit);
-	git_buf_free(&reflog);
-
 	return error;
 }
 
@@ -764,9 +789,6 @@ static int rebase_next_merge(
 
 	*out = NULL;
 
-	if ((error = rebase_movenext(rebase)) < 0)
-		goto done;
-
 	operation = git_array_get(rebase->operations, rebase->current);
 
 	if ((error = git_commit_lookup(&current_commit, rebase->repo, &operation->id)) < 0 ||
@@ -812,6 +834,46 @@ done:
 	return error;
 }
 
+static int rebase_next_inmemory(
+	git_rebase_operation **out,
+	git_rebase *rebase)
+{
+	git_commit *current_commit = NULL, *parent_commit = NULL;
+	git_tree *current_tree = NULL, *head_tree = NULL, *parent_tree = NULL;
+	git_rebase_operation *operation;
+	git_index *index = NULL;
+	int error;
+
+	*out = NULL;
+
+	operation = git_array_get(rebase->operations, rebase->current);
+
+	if ((error = git_commit_lookup(&current_commit, rebase->repo, &operation->id)) < 0 ||
+		(error = git_commit_tree(&current_tree, current_commit)) < 0 ||
+		(error = git_commit_parent(&parent_commit, current_commit, 0)) < 0 ||
+		(error = git_commit_tree(&parent_tree, parent_commit)) < 0 ||
+		(error = git_commit_tree(&head_tree, rebase->last_commit)) < 0 ||
+		(error = git_merge_trees(&index, rebase->repo, parent_tree, head_tree, current_tree, NULL)) < 0)
+		goto done;
+
+	git_index_free(rebase->last_index);
+	rebase->last_index = index;
+	operation->index = index;
+	index = NULL;
+
+	*out = operation;
+
+done:
+	git_commit_free(current_commit);
+	git_commit_free(parent_commit);
+	git_tree_free(current_tree);
+	git_tree_free(head_tree);
+	git_tree_free(parent_tree);
+	git_index_free(index);
+
+	return error;
+}
+
 int git_rebase_next(
 	git_rebase_operation **out,
 	git_rebase *rebase)
@@ -820,66 +882,55 @@ int git_rebase_next(
 
 	assert(out && rebase);
 
-	switch (rebase->type) {
-	case GIT_REBASE_TYPE_MERGE:
+	if ((error = rebase_movenext(rebase)) < 0)
+		return error;
+
+	if (rebase->inmemory)
+		error = rebase_next_inmemory(out, rebase);
+	else if (rebase->type == GIT_REBASE_TYPE_MERGE)
 		error = rebase_next_merge(out, rebase);
-		break;
-	default:
+	else
 		abort();
-	}
 
 	return error;
 }
 
-static int rebase_commit_merge(
-	git_oid *commit_id,
+static int rebase_commit__create(
+	git_commit **out,
 	git_rebase *rebase,
+	git_index *index,
+	git_commit *parent_commit,
 	const git_signature *author,
 	const git_signature *committer,
 	const char *message_encoding,
 	const char *message)
 {
-	git_index *index = NULL;
-	git_reference *head = NULL;
-	git_commit *current_commit = NULL, *head_commit = NULL, *commit = NULL;
 	git_rebase_operation *operation;
-	git_tree *head_tree = NULL, *tree = NULL;
-	git_diff *diff = NULL;
-	git_oid tree_id;
-	git_buf reflog_msg = GIT_BUF_INIT;
-	char old_idstr[GIT_OID_HEXSZ], new_idstr[GIT_OID_HEXSZ];
+	git_commit *current_commit = NULL, *commit = NULL;
+	git_tree *parent_tree = NULL, *tree = NULL;
+	git_oid tree_id, commit_id;
 	int error;
 
 	operation = git_array_get(rebase->operations, rebase->current);
-	assert(operation);
-
-	if ((error = git_repository_index(&index, rebase->repo)) < 0)
-		goto done;
 
 	if (git_index_has_conflicts(index)) {
-		giterr_set(GITERR_REBASE, "Conflicts have not been resolved");
+		giterr_set(GITERR_REBASE, "conflicts have not been resolved");
 		error = GIT_EUNMERGED;
 		goto done;
 	}
 
-	if ((error = rebase_ensure_not_dirty(rebase->repo, false, true, GIT_EUNMERGED)) < 0 ||
-		(error = git_commit_lookup(&current_commit, rebase->repo, &operation->id)) < 0 ||
-		(error = git_repository_head(&head, rebase->repo)) < 0 ||
-		(error = git_reference_peel((git_object **)&head_commit, head, GIT_OBJ_COMMIT)) < 0 ||
-		(error = git_commit_tree(&head_tree, head_commit)) < 0 ||
-		(error = git_diff_tree_to_index(&diff, rebase->repo, head_tree, index, NULL)) < 0)
+	if ((error = git_commit_lookup(&current_commit, rebase->repo, &operation->id)) < 0 ||
+		(error = git_commit_tree(&parent_tree, parent_commit)) < 0 ||
+		(error = git_index_write_tree_to(&tree_id, index, rebase->repo)) < 0 ||
+		(error = git_tree_lookup(&tree, rebase->repo, &tree_id)) < 0)
 		goto done;
 
-	if (git_diff_num_deltas(diff) == 0) {
-		giterr_set(GITERR_REBASE, "This patch has already been applied");
+	if (git_oid_equal(&tree_id, git_tree_id(parent_tree))) {
+		giterr_set(GITERR_REBASE, "this patch has already been applied");
 		error = GIT_EAPPLIED;
 		goto done;
 	}
 
-	if ((error = git_index_write_tree(&tree_id, index)) < 0 ||
-		(error = git_tree_lookup(&tree, rebase->repo, &tree_id)) < 0)
-		goto done;
-
 	if (!author)
 		author = git_commit_author(current_commit);
 
@@ -888,30 +939,104 @@ static int rebase_commit_merge(
 		message = git_commit_message(current_commit);
 	}
 
-	if ((error = git_commit_create(commit_id, rebase->repo, NULL, author,
-			committer, message_encoding, message, tree, 1,
-			(const git_commit **)&head_commit)) < 0 ||
-		(error = git_commit_lookup(&commit, rebase->repo, commit_id)) < 0 ||
+	if ((error = git_commit_create(&commit_id, rebase->repo, NULL, author,
+		committer, message_encoding, message, tree, 1,
+		(const git_commit **)&parent_commit)) < 0 ||
+		(error = git_commit_lookup(&commit, rebase->repo, &commit_id)) < 0)
+		goto done;
+
+	*out = commit;
+
+done:
+	if (error < 0)
+		git_commit_free(commit);
+
+	git_commit_free(current_commit);
+	git_tree_free(parent_tree);
+	git_tree_free(tree);
+
+	return error;
+}
+
+static int rebase_commit_merge(
+	git_oid *commit_id,
+	git_rebase *rebase,
+	const git_signature *author,
+	const git_signature *committer,
+	const char *message_encoding,
+	const char *message)
+{
+	git_rebase_operation *operation;
+	git_reference *head = NULL;
+	git_commit *head_commit = NULL, *commit = NULL;
+	git_index *index = NULL;
+	char old_idstr[GIT_OID_HEXSZ], new_idstr[GIT_OID_HEXSZ];
+	int error;
+
+	operation = git_array_get(rebase->operations, rebase->current);
+	assert(operation);
+
+	if ((error = rebase_ensure_not_dirty(rebase->repo, false, true, GIT_EUNMERGED)) < 0 ||
+		(error = git_repository_head(&head, rebase->repo)) < 0 ||
+		(error = git_reference_peel((git_object **)&head_commit, head, GIT_OBJ_COMMIT)) < 0 ||
+		(error = git_repository_index(&index, rebase->repo)) < 0 ||
+		(error = rebase_commit__create(&commit, rebase, index, head_commit,
+			author, committer, message_encoding, message)) < 0 ||
 		(error = git_reference__update_for_commit(
-			rebase->repo, NULL, "HEAD", commit_id, "rebase")) < 0)
+			rebase->repo, NULL, "HEAD", git_commit_id(commit), "rebase")) < 0)
 		goto done;
 
-	git_oid_fmt(old_idstr, git_commit_id(current_commit));
-	git_oid_fmt(new_idstr, commit_id);
+	git_oid_fmt(old_idstr, &operation->id);
+	git_oid_fmt(new_idstr, git_commit_id(commit));
+
+	if ((error = rebase_setupfile(rebase, REWRITTEN_FILE, O_CREAT|O_WRONLY|O_APPEND,
+		"%.*s %.*s\n", GIT_OID_HEXSZ, old_idstr, GIT_OID_HEXSZ, new_idstr)) < 0)
+		goto done;
 
-	error = rebase_setupfile(rebase, REWRITTEN_FILE, O_CREAT|O_WRONLY|O_APPEND,
-		"%.*s %.*s\n", GIT_OID_HEXSZ, old_idstr, GIT_OID_HEXSZ, new_idstr);
+	git_oid_cpy(commit_id, git_commit_id(commit));
 
 done:
-	git_buf_free(&reflog_msg);
-	git_commit_free(commit);
-	git_diff_free(diff);
-	git_tree_free(tree);
-	git_tree_free(head_tree);
-	git_commit_free(head_commit);
-	git_commit_free(current_commit);
-	git_reference_free(head);
 	git_index_free(index);
+	git_reference_free(head);
+	git_commit_free(head_commit);
+	git_commit_free(commit);
+	return error;
+}
+
+static int rebase_commit_inmemory(
+	git_oid *commit_id,
+	git_rebase *rebase,
+	const git_signature *author,
+	const git_signature *committer,
+	const char *message_encoding,
+	const char *message)
+{
+	git_rebase_operation *operation;
+	git_commit *commit = NULL;
+	int error = 0;
+
+	operation = git_array_get(rebase->operations, rebase->current);
+
+	assert(operation);
+	assert(operation->index);
+	assert(rebase->last_commit);
+
+	if ((error = rebase_commit__create(&commit, rebase, operation->index,
+		rebase->last_commit, author, committer, message_encoding, message)) < 0)
+		goto done;
+
+	git_index_free(rebase->last_index);
+	operation->index = NULL;
+	rebase->last_index = NULL;
+
+	git_commit_free(rebase->last_commit);
+	rebase->last_commit = commit;
+
+	git_oid_cpy(commit_id, git_commit_id(commit));
+
+done:
+	if (error < 0)
+		git_commit_free(commit);
 
 	return error;
 }
@@ -928,14 +1053,14 @@ int git_rebase_commit(
 
 	assert(rebase && committer);
 
-	switch (rebase->type) {
-	case GIT_REBASE_TYPE_MERGE:
+	if (rebase->inmemory)
+		error = rebase_commit_inmemory(
+			id, rebase, author, committer, message_encoding, message);
+	else if (rebase->type == GIT_REBASE_TYPE_MERGE)
 		error = rebase_commit_merge(
 			id, rebase, author, committer, message_encoding, message);
-		break;
-	default:
+	else
 		abort();
-	}
 
 	return error;
 }
@@ -948,6 +1073,9 @@ int git_rebase_abort(git_rebase *rebase)
 
 	assert(rebase);
 
+	if (rebase->inmemory)
+		return 0;
+
 	error = rebase->head_detached ?
 		git_reference_create(&orig_head_ref, rebase->repo, GIT_HEAD_FILE,
 			 &rebase->orig_head_id, 1, "rebase: aborting") :
@@ -1125,6 +1253,9 @@ int git_rebase_finish(
 
 	assert(rebase);
 
+	if (rebase->inmemory)
+		return 0;
+
 	git_oid_fmt(onto, &rebase->onto_id);
 
 	if ((error = git_buf_printf(&branch_msg, "rebase finished: %s onto %.*s",
@@ -1182,6 +1313,8 @@ void git_rebase_free(git_rebase *rebase)
 	if (rebase == NULL)
 		return;
 
+	git_index_free(rebase->last_index);
+	git_commit_free(rebase->last_commit);
 	git__free(rebase->onto_name);
 	git__free(rebase->orig_head_name);
 	git__free(rebase->state_path);