Merge branch 'ps/history' into seen

"git history" history rewriting UI.

Comments?

* ps/history:
  builtin/history: implement "split" subcommand
  cache-tree: allow writing in-memory index as tree
  add-patch: add support for in-memory index patching
  add-patch: remove dependency on "add-interactive" subsystem
  add-patch: split out `struct interactive_options`
  add-patch: split out header from "add-interactive.h"
  builtin/history: implement "reword" subcommand
  builtin: add new "history" command
  replay: stop using `the_repository`
  replay: extract logic to pick commits
  wt-status: provide function to expose status for trees

7 files changed, 619 insertions, 159 deletions

diff --git a/builtin/add.c b/builtin/add.c
index 32709794b3..6f1e213052 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -31,7 +31,7 @@ static const char * const builtin_add_usage[] = {
 	NULL
 };
 static int patch_interactive, add_interactive, edit_interactive;
-static struct add_p_opt add_p_opt = ADD_P_OPT_INIT;
+static struct interactive_options interactive_opts = INTERACTIVE_OPTIONS_INIT;
 static int take_worktree_changes;
 static int add_renormalize;
 static int pathspec_file_nul;
@@ -160,7 +160,7 @@ static int refresh(struct repository *repo, int verbose, const struct pathspec *
 int interactive_add(struct repository *repo,
 		    const char **argv,
 		    const char *prefix,
-		    int patch, struct add_p_opt *add_p_opt)
+		    int patch, struct interactive_options *interactive_opts)
 {
 	struct pathspec pathspec;
 	int ret;
@@ -172,9 +172,9 @@ int interactive_add(struct repository *repo,
 		       prefix, argv);
 
 	if (patch)
-		ret = !!run_add_p(repo, ADD_P_ADD, add_p_opt, NULL, &pathspec);
+		ret = !!run_add_p(repo, ADD_P_ADD, interactive_opts, NULL, &pathspec);
 	else
-		ret = !!run_add_i(repo, &pathspec, add_p_opt);
+		ret = !!run_add_i(repo, &pathspec, interactive_opts);
 
 	clear_pathspec(&pathspec);
 	return ret;
@@ -256,8 +256,8 @@ static struct option builtin_add_options[] = {
 	OPT_GROUP(""),
 	OPT_BOOL('i', "interactive", &add_interactive, N_("interactive picking")),
 	OPT_BOOL('p', "patch", &patch_interactive, N_("select hunks interactively")),
-	OPT_DIFF_UNIFIED(&add_p_opt.context),
-	OPT_DIFF_INTERHUNK_CONTEXT(&add_p_opt.interhunkcontext),
+	OPT_DIFF_UNIFIED(&interactive_opts.context),
+	OPT_DIFF_INTERHUNK_CONTEXT(&interactive_opts.interhunkcontext),
 	OPT_BOOL('e', "edit", &edit_interactive, N_("edit current diff and apply")),
 	OPT__FORCE(&ignored_too, N_("allow adding otherwise ignored files"), 0),
 	OPT_BOOL('u', "update", &take_worktree_changes, N_("update tracked files")),
@@ -400,9 +400,9 @@ int cmd_add(int argc,
 	prepare_repo_settings(repo);
 	repo->settings.command_requires_full_index = 0;
 
-	if (add_p_opt.context < -1)
+	if (interactive_opts.context < -1)
 		die(_("'%s' cannot be negative"), "--unified");
-	if (add_p_opt.interhunkcontext < -1)
+	if (interactive_opts.interhunkcontext < -1)
 		die(_("'%s' cannot be negative"), "--inter-hunk-context");
 
 	if (patch_interactive)
@@ -412,11 +412,11 @@ int cmd_add(int argc,
 			die(_("options '%s' and '%s' cannot be used together"), "--dry-run", "--interactive/--patch");
 		if (pathspec_from_file)
 			die(_("options '%s' and '%s' cannot be used together"), "--pathspec-from-file", "--interactive/--patch");
-		exit(interactive_add(repo, argv + 1, prefix, patch_interactive, &add_p_opt));
+		exit(interactive_add(repo, argv + 1, prefix, patch_interactive, &interactive_opts));
 	} else {
-		if (add_p_opt.context != -1)
+		if (interactive_opts.context != -1)
 			die(_("the option '%s' requires '%s'"), "--unified", "--interactive/--patch");
-		if (add_p_opt.interhunkcontext != -1)
+		if (interactive_opts.interhunkcontext != -1)
 			die(_("the option '%s' requires '%s'"), "--inter-hunk-context", "--interactive/--patch");
 	}
 
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 66b69df6e6..c09065cc61 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -546,7 +546,7 @@ static int checkout_paths(const struct checkout_opts *opts,
 
 	if (opts->patch_mode) {
 		enum add_p_mode patch_mode;
-		struct add_p_opt add_p_opt = {
+		struct interactive_options interactive_opts = {
 			.context = opts->patch_context,
 			.interhunkcontext = opts->patch_interhunk_context,
 		};
@@ -575,7 +575,7 @@ static int checkout_paths(const struct checkout_opts *opts,
 		else
 			BUG("either flag must have been set, worktree=%d, index=%d",
 			    opts->checkout_worktree, opts->checkout_index);
-		return !!run_add_p(the_repository, patch_mode, &add_p_opt,
+		return !!run_add_p(the_repository, patch_mode, &interactive_opts,
 				   rev, &opts->pathspec);
 	}
 
@@ -902,7 +902,8 @@ static int merge_working_tree(const struct checkout_opts *opts,
 					   0);
 			init_ui_merge_options(&o, the_repository);
 			o.verbosity = 0;
-			work = write_in_core_index_as_tree(the_repository);
+			work = write_in_core_index_as_tree(the_repository,
+							   the_repository->index);
 
 			ret = reset_tree(new_tree,
 					 opts, 1,
diff --git a/builtin/commit.c b/builtin/commit.c
index 0243f17d53..640495cc57 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -123,7 +123,7 @@ static const char *edit_message, *use_message;
 static char *fixup_message, *fixup_commit, *squash_message;
 static const char *fixup_prefix;
 static int all, also, interactive, patch_interactive, only, amend, signoff;
-static struct add_p_opt add_p_opt = ADD_P_OPT_INIT;
+static struct interactive_options interactive_opts = INTERACTIVE_OPTIONS_INIT;
 static int edit_flag = -1; /* unspecified */
 static int quiet, verbose, no_verify, allow_empty, dry_run, renew_authorship;
 static int config_commit_verbose = -1; /* unspecified */
@@ -356,9 +356,9 @@ static const char *prepare_index(const char **argv, const char *prefix,
 	const char *ret;
 	char *path = NULL;
 
-	if (add_p_opt.context < -1)
+	if (interactive_opts.context < -1)
 		die(_("'%s' cannot be negative"), "--unified");
-	if (add_p_opt.interhunkcontext < -1)
+	if (interactive_opts.interhunkcontext < -1)
 		die(_("'%s' cannot be negative"), "--inter-hunk-context");
 
 	if (is_status)
@@ -407,7 +407,7 @@ static const char *prepare_index(const char **argv, const char *prefix,
 		old_index_env = xstrdup_or_null(getenv(INDEX_ENVIRONMENT));
 		setenv(INDEX_ENVIRONMENT, the_repository->index_file, 1);
 
-		if (interactive_add(the_repository, argv, prefix, patch_interactive, &add_p_opt) != 0)
+		if (interactive_add(the_repository, argv, prefix, patch_interactive, &interactive_opts) != 0)
 			die(_("interactive add failed"));
 
 		the_repository->index_file = old_repo_index_file;
@@ -432,9 +432,9 @@ static const char *prepare_index(const char **argv, const char *prefix,
 		ret = get_lock_file_path(&index_lock);
 		goto out;
 	} else {
-		if (add_p_opt.context != -1)
+		if (interactive_opts.context != -1)
 			die(_("the option '%s' requires '%s'"), "--unified", "--interactive/--patch");
-		if (add_p_opt.interhunkcontext != -1)
+		if (interactive_opts.interhunkcontext != -1)
 			die(_("the option '%s' requires '%s'"), "--inter-hunk-context", "--interactive/--patch");
 	}
 
@@ -1742,8 +1742,8 @@ int cmd_commit(int argc,
 		OPT_BOOL('i', "include", &also, N_("add specified files to index for commit")),
 		OPT_BOOL(0, "interactive", &interactive, N_("interactively add files")),
 		OPT_BOOL('p', "patch", &patch_interactive, N_("interactively add changes")),
-		OPT_DIFF_UNIFIED(&add_p_opt.context),
-		OPT_DIFF_INTERHUNK_CONTEXT(&add_p_opt.interhunkcontext),
+		OPT_DIFF_UNIFIED(&interactive_opts.context),
+		OPT_DIFF_INTERHUNK_CONTEXT(&interactive_opts.interhunkcontext),
 		OPT_BOOL('o', "only", &only, N_("commit only specified files")),
 		OPT_BOOL('n', "no-verify", &no_verify, N_("bypass pre-commit and commit-msg hooks")),
 		OPT_BOOL(0, "dry-run", &dry_run, N_("show what would be committed")),
diff --git a/builtin/history.c b/builtin/history.c
new file mode 100644
index 0000000000..cae841707d
--- /dev/null
+++ b/builtin/history.c
@@ -0,0 +1,561 @@
+#define USE_THE_REPOSITORY_VARIABLE
+
+#include "builtin.h"
+#include "cache-tree.h"
+#include "commit-reach.h"
+#include "commit.h"
+#include "config.h"
+#include "editor.h"
+#include "environment.h"
+#include "gettext.h"
+#include "hex.h"
+#include "oidmap.h"
+#include "parse-options.h"
+#include "path.h"
+#include "read-cache.h"
+#include "refs.h"
+#include "replay.h"
+#include "reset.h"
+#include "revision.h"
+#include "run-command.h"
+#include "sequencer.h"
+#include "strvec.h"
+#include "tree.h"
+#include "wt-status.h"
+
+#define GIT_HISTORY_REWORD_USAGE N_("git history reword <commit>")
+#define GIT_HISTORY_SPLIT_USAGE  N_("git history split <commit> [--] [<pathspec>...]")
+
+static int collect_commits(struct repository *repo,
+			   struct commit *old_commit,
+			   struct commit *new_commit,
+			   struct strvec *out)
+{
+	struct setup_revision_opt revision_opts = {
+		.assume_dashdash = 1,
+	};
+	struct strvec revisions = STRVEC_INIT;
+	struct commit *child;
+	struct rev_info rev = { 0 };
+	int ret;
+
+	repo_init_revisions(repo, &rev, NULL);
+	strvec_push(&revisions, "");
+	strvec_push(&revisions, oid_to_hex(&new_commit->object.oid));
+	if (old_commit)
+		strvec_pushf(&revisions, "^%s", oid_to_hex(&old_commit->object.oid));
+
+	setup_revisions_from_strvec(&revisions, &rev, &revision_opts);
+	if (revisions.nr != 1 || prepare_revision_walk(&rev)) {
+		ret = error(_("revision walk setup failed"));
+		goto out;
+	}
+
+	while ((child = get_revision(&rev))) {
+		if (old_commit && !child->parents)
+			BUG("revision walk did not find child commit");
+		if (child->parents && child->parents->next) {
+			ret = error(_("cannot rearrange commit history with merges"));
+			goto out;
+		}
+
+		strvec_push(out, oid_to_hex(&child->object.oid));
+
+		if (child->parents && old_commit &&
+		    commit_list_contains(old_commit, child->parents))
+			break;
+	}
+
+	/*
+	 * Revisions are in newest-order-first. We have to reverse the
+	 * array though so that we pick the oldest commits first.
+	 */
+	for (size_t i = 0, j = out->nr - 1; i < j; i++, j--)
+		SWAP(out->v[i], out->v[j]);
+
+	ret = 0;
+
+out:
+	strvec_clear(&revisions);
+	release_revisions(&rev);
+	reset_revision_walk();
+	return ret;
+}
+
+static void replace_commits(struct strvec *commits,
+			    const struct object_id *commit_to_replace,
+			    const struct object_id *replacements,
+			    size_t replacements_nr)
+{
+	char commit_to_replace_oid[GIT_MAX_HEXSZ + 1];
+	struct strvec replacement_oids = STRVEC_INIT;
+	bool found = false;
+
+	oid_to_hex_r(commit_to_replace_oid, commit_to_replace);
+	for (size_t i = 0; i < replacements_nr; i++)
+		strvec_push(&replacement_oids, oid_to_hex(&replacements[i]));
+
+	for (size_t i = 0; i < commits->nr; i++) {
+		if (strcmp(commits->v[i], commit_to_replace_oid))
+			continue;
+		strvec_splice(commits, i, 1, replacement_oids.v, replacement_oids.nr);
+		found = true;
+		break;
+	}
+	if (!found)
+		BUG("could not find commit to replace");
+
+	strvec_clear(&replacement_oids);
+}
+
+static int apply_commits(struct repository *repo,
+			 const struct strvec *commits,
+			 struct commit *onto,
+			 struct commit *orig_head,
+			 const char *action)
+{
+	struct reset_head_opts reset_opts = { 0 };
+	struct strbuf buf = STRBUF_INIT;
+	int ret;
+
+	for (size_t i = 0; i < commits->nr; i++) {
+		struct object_id commit_id;
+		struct commit *commit;
+		const char *end;
+
+		if (parse_oid_hex_algop(commits->v[i], &commit_id, &end,
+					repo->hash_algo)) {
+			ret = error(_("invalid object ID: %s"), commits->v[i]);
+			goto out;
+		}
+
+		commit = lookup_commit(repo, &commit_id);
+		if (!commit || repo_parse_commit(repo, commit)) {
+			ret = error(_("failed to look up commit: %s"), oid_to_hex(&commit_id));
+			goto out;
+		}
+
+		if (!onto) {
+			onto = commit;
+		} else {
+			struct tree *tree = repo_get_commit_tree(repo, commit);
+			onto = replay_create_commit(repo, tree, commit, onto);
+			if (!onto)
+				break;
+		}
+	}
+
+	reset_opts.oid = &onto->object.oid;
+	strbuf_addf(&buf, "%s: switch to rewritten %s", action, oid_to_hex(reset_opts.oid));
+	reset_opts.flags = RESET_HEAD_REFS_ONLY | RESET_ORIG_HEAD;
+	reset_opts.orig_head = &orig_head->object.oid;
+	reset_opts.default_reflog_action = action;
+	if (reset_head(repo, &reset_opts) < 0) {
+		ret = error(_("could not switch to %s"), oid_to_hex(reset_opts.oid));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&buf);
+	return ret;
+}
+
+static void change_data_free(void *util, const char *str UNUSED)
+{
+	struct wt_status_change_data *d = util;
+	free(d->rename_source);
+	free(d);
+}
+
+static int fill_commit_message(struct repository *repo,
+			       const struct object_id *old_tree,
+			       const struct object_id *new_tree,
+			       const char *default_message,
+			       const char *action,
+			       struct strbuf *out)
+{
+	const char *path = git_path_commit_editmsg();
+	const char *hint =
+		_("Please enter the commit message for the %s changes."
+		  " Lines starting\nwith '%s' will be ignored.\n");
+	struct wt_status s;
+
+	strbuf_addstr(out, default_message);
+	strbuf_addch(out, '\n');
+	strbuf_commented_addf(out, comment_line_str, hint, action, comment_line_str);
+	write_file_buf(path, out->buf, out->len);
+
+	wt_status_prepare(repo, &s);
+	FREE_AND_NULL(s.branch);
+	s.ahead_behind_flags = AHEAD_BEHIND_QUICK;
+	s.commit_template = 1;
+	s.colopts = 0;
+	s.display_comment_prefix = 1;
+	s.hints = 0;
+	s.use_color = 0;
+	s.whence = FROM_COMMIT;
+	s.committable = 1;
+
+	s.fp = fopen(git_path_commit_editmsg(), "a");
+	if (!s.fp)
+		return error_errno(_("could not open '%s'"), git_path_commit_editmsg());
+
+	wt_status_collect_changes_trees(&s, old_tree, new_tree);
+	wt_status_print(&s);
+	wt_status_collect_free_buffers(&s);
+	string_list_clear_func(&s.change, change_data_free);
+
+	strbuf_reset(out);
+	if (launch_editor(path, out, NULL)) {
+		fprintf(stderr, _("Please supply the message using the -m option.\n"));
+		return -1;
+	}
+	strbuf_stripspace(out, comment_line_str);
+
+	cleanup_message(out, COMMIT_MSG_CLEANUP_ALL, 0);
+
+	if (!out->len) {
+		fprintf(stderr, _("Aborting commit due to empty commit message.\n"));
+		return -1;
+	}
+
+	return 0;
+}
+
+static int cmd_history_reword(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_REWORD_USAGE,
+		NULL,
+	};
+	struct option options[] = {
+		OPT_END(),
+	};
+	struct strbuf final_message = STRBUF_INIT;
+	struct commit *original_commit, *parent, *head;
+	struct strvec commits = STRVEC_INIT;
+	struct object_id parent_tree_oid, original_commit_tree_oid;
+	struct object_id rewritten_commit;
+	struct commit_list *from_list = NULL;
+	const char *original_message, *original_body, *ptr;
+	char *original_author = NULL;
+	size_t len;
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+	if (argc != 1) {
+		ret = error(_("command expects a single revision"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	original_commit = lookup_commit_reference_by_name(argv[0]);
+	if (!original_commit) {
+		ret = error(_("commit to be reworded cannot be found: %s"), argv[0]);
+		goto out;
+	}
+	original_commit_tree_oid = repo_get_commit_tree(repo, original_commit)->object.oid;
+
+	parent = original_commit->parents ? original_commit->parents->item : NULL;
+	if (parent) {
+		if (repo_parse_commit(repo, parent)) {
+			ret = error(_("unable to parse commit %s"),
+				    oid_to_hex(&parent->object.oid));
+			goto out;
+		}
+		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
+	} else {
+		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	}
+
+	head = lookup_commit_reference_by_name("HEAD");
+	if (!head) {
+		ret = error(_("could not resolve HEAD to a commit"));
+		goto out;
+	}
+
+	commit_list_append(original_commit, &from_list);
+	if (!repo_is_descendant_of(repo, head, from_list)) {
+		ret = error (_("split commit must be reachable from current HEAD commit"));
+		goto out;
+	}
+
+	/*
+	 * Collect the list of commits that we'll have to reapply now already.
+	 * This ensures that we'll abort early on in case the range of commits
+	 * contains merges, which we do not yet handle.
+	 */
+	ret = collect_commits(repo, parent, head, &commits);
+	if (ret < 0)
+		goto out;
+
+	/* We retain authorship of the original commit. */
+	original_message = repo_logmsg_reencode(repo, original_commit, NULL, NULL);
+	ptr = find_commit_header(original_message, "author", &len);
+	if (ptr)
+		original_author = xmemdupz(ptr, len);
+	find_commit_subject(original_message, &original_body);
+
+	ret = fill_commit_message(repo, &parent_tree_oid, &original_commit_tree_oid,
+				  original_body, "reworded", &final_message);
+	if (ret < 0)
+		goto out;
+
+	ret = commit_tree(final_message.buf, final_message.len, &original_commit_tree_oid,
+			  original_commit->parents, &rewritten_commit, original_author, NULL);
+	if (ret < 0) {
+		ret = error(_("failed writing reworded commit"));
+		goto out;
+	}
+
+	replace_commits(&commits, &original_commit->object.oid, &rewritten_commit, 1);
+
+	ret = apply_commits(repo, &commits, parent, head, "reword");
+	if (ret < 0)
+		goto out;
+
+	ret = 0;
+
+out:
+	strbuf_release(&final_message);
+	free_commit_list(from_list);
+	strvec_clear(&commits);
+	free(original_author);
+	return ret;
+}
+
+static int split_commit(struct repository *repo,
+			struct commit *original_commit,
+			struct pathspec *pathspec,
+			struct object_id *out)
+{
+	struct interactive_options interactive_opts = INTERACTIVE_OPTIONS_INIT;
+	struct strbuf index_file = STRBUF_INIT, split_message = STRBUF_INIT;
+	struct child_process read_tree_cmd = CHILD_PROCESS_INIT;
+	struct index_state index = INDEX_STATE_INIT(repo);
+	struct object_id original_commit_tree_oid, parent_tree_oid;
+	const char *original_message, *original_body, *ptr;
+	char original_commit_oid[GIT_MAX_HEXSZ + 1];
+	char *original_author = NULL;
+	struct commit_list *parents = NULL;
+	struct commit *first_commit;
+	struct tree *split_tree;
+	size_t len;
+	int ret;
+
+	if (original_commit->parents)
+		parent_tree_oid = *get_commit_tree_oid(original_commit->parents->item);
+	else
+		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	original_commit_tree_oid = *get_commit_tree_oid(original_commit);
+
+	/*
+	* Construct the first commit. This is done by taking the original
+	* commit parent's tree and selectively patching changes from the diff
+	* between that parent and its child.
+	*/
+	repo_git_path_replace(repo, &index_file, "%s", "history-split.index");
+
+	read_tree_cmd.git_cmd = 1;
+	strvec_pushf(&read_tree_cmd.env, "GIT_INDEX_FILE=%s", index_file.buf);
+	strvec_push(&read_tree_cmd.args, "read-tree");
+	strvec_push(&read_tree_cmd.args, oid_to_hex(&parent_tree_oid));
+	ret = run_command(&read_tree_cmd);
+	if (ret < 0)
+		goto out;
+
+	ret = read_index_from(&index, index_file.buf, repo->gitdir);
+	if (ret < 0) {
+		ret = error(_("failed reading temporary index"));
+		goto out;
+	}
+
+	oid_to_hex_r(original_commit_oid, &original_commit->object.oid);
+	ret = run_add_p_index(repo, &index, index_file.buf, &interactive_opts,
+			      original_commit_oid, pathspec);
+	if (ret < 0)
+		goto out;
+
+	split_tree = write_in_core_index_as_tree(repo, &index);
+	if (!split_tree) {
+		ret = error(_("failed split tree"));
+		goto out;
+	}
+
+	unlink(index_file.buf);
+
+	/*
+	* We disallow the cases where either the split-out commit or the
+	* original commit would become empty. Consequently, if we see that the
+	* new tree ID matches either of those trees we abort.
+	*/
+	if (oideq(&split_tree->object.oid, &parent_tree_oid)) {
+		ret = error(_("split commit is empty"));
+		goto out;
+	} else if (oideq(&split_tree->object.oid, &original_commit_tree_oid)) {
+		ret = error(_("split commit tree matches original commit"));
+		goto out;
+	}
+
+	/* We retain authorship of the original commit. */
+	original_message = repo_logmsg_reencode(repo, original_commit, NULL, NULL);
+	ptr = find_commit_header(original_message, "author", &len);
+	if (ptr)
+		original_author = xmemdupz(ptr, len);
+
+	ret = fill_commit_message(repo, &parent_tree_oid, &split_tree->object.oid,
+				  "", "split-out", &split_message);
+	if (ret < 0)
+		goto out;
+
+	ret = commit_tree(split_message.buf, split_message.len, &split_tree->object.oid,
+			  original_commit->parents, &out[0], original_author, NULL);
+	if (ret < 0) {
+		ret = error(_("failed writing split-out commit"));
+		goto out;
+	}
+
+	/*
+	* The second commit is much simpler to construct, as we can simply use
+	* the original commit details, except that we adjust its parent to be
+	* the newly split-out commit.
+	*/
+	find_commit_subject(original_message, &original_body);
+	first_commit = lookup_commit_reference(repo, &out[0]);
+	commit_list_append(first_commit, &parents);
+
+	ret = commit_tree(original_body, strlen(original_body), &original_commit_tree_oid,
+			  parents, &out[1], original_author, NULL);
+	if (ret < 0) {
+		ret = error(_("failed writing second commit"));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	if (index_file.len)
+		unlink(index_file.buf);
+	strbuf_release(&split_message);
+	strbuf_release(&index_file);
+	free_commit_list(parents);
+	free(original_author);
+	release_index(&index);
+	return ret;
+}
+
+static int cmd_history_split(int argc,
+			     const char **argv,
+			     const char *prefix,
+			     struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SPLIT_USAGE,
+		NULL,
+	};
+	struct option options[] = {
+		OPT_END(),
+	};
+	struct oidmap rewritten_commits = OIDMAP_INIT;
+	struct commit *original_commit, *parent, *head;
+	struct strvec commits = STRVEC_INIT;
+	struct commit_list *from_list = NULL;
+	struct object_id split_commits[2];
+	struct pathspec pathspec = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+	if (argc < 1) {
+		ret = error(_("command expects a revision"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	original_commit = lookup_commit_reference_by_name(argv[0]);
+	if (!original_commit) {
+		ret = error(_("commit to be split cannot be found: %s"), argv[0]);
+		goto out;
+	}
+
+	parent = original_commit->parents ? original_commit->parents->item : NULL;
+	if (parent && repo_parse_commit(repo, parent)) {
+		ret = error(_("unable to parse commit %s"),
+			    oid_to_hex(&parent->object.oid));
+		goto out;
+	}
+
+	head = lookup_commit_reference_by_name("HEAD");
+	if (!head) {
+		ret = error(_("could not resolve HEAD to a commit"));
+		goto out;
+	}
+
+	commit_list_append(original_commit, &from_list);
+	if (!repo_is_descendant_of(repo, head, from_list)) {
+		ret = error(_("split commit must be reachable from current HEAD commit"));
+		goto out;
+	}
+
+	parse_pathspec(&pathspec, 0,
+		PATHSPEC_PREFER_FULL | PATHSPEC_SYMLINK_LEADING_PATH | PATHSPEC_PREFIX_ORIGIN,
+		prefix, argv + 1);
+
+	/*
+	 * Collect the list of commits that we'll have to reapply now already.
+	 * This ensures that we'll abort early on in case the range of commits
+	 * contains merges, which we do not yet handle.
+	 */
+	ret = collect_commits(repo, parent, head, &commits);
+	if (ret < 0)
+		goto out;
+
+	/*
+	 * Then we split up the commit and replace the original commit with the
+	 * new ones.
+	 */
+	ret = split_commit(repo, original_commit, &pathspec, split_commits);
+	if (ret < 0)
+		goto out;
+
+	replace_commits(&commits, &original_commit->object.oid,
+			split_commits, ARRAY_SIZE(split_commits));
+
+	ret = apply_commits(repo, &commits, parent, head, "split");
+	if (ret < 0)
+		goto out;
+
+	ret = 0;
+
+out:
+	oidmap_clear(&rewritten_commits, 0);
+	free_commit_list(from_list);
+	clear_pathspec(&pathspec);
+	strvec_clear(&commits);
+	return ret;
+}
+
+int cmd_history(int argc,
+		const char **argv,
+		const char *prefix,
+		struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_REWORD_USAGE,
+		GIT_HISTORY_SPLIT_USAGE,
+		NULL,
+	};
+	parse_opt_subcommand_fn *fn = NULL;
+	struct option options[] = {
+		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
+		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_END(),
+	};
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+	return fn(argc, argv, prefix, repo);
+}
diff --git a/builtin/replay.c b/builtin/replay.c
index 6606a2c94b..f974a8c963 100644
--- a/builtin/replay.c
+++ b/builtin/replay.c
@@ -2,7 +2,6 @@
  * "git replay" builtin command
  */
 
-#define USE_THE_REPOSITORY_VARIABLE
 #define DISABLE_SIGN_COMPARE_WARNINGS
 
 #include "git-compat-util.h"
@@ -16,6 +15,7 @@
 #include "object-name.h"
 #include "parse-options.h"
 #include "refs.h"
+#include "replay.h"
 #include "revision.h"
 #include "strmap.h"
 #include <oidset.h>
@@ -26,13 +26,6 @@ enum ref_action_mode {
 	REF_ACTION_PRINT,
 };
 
-static const char *short_commit_name(struct repository *repo,
-				     struct commit *commit)
-{
-	return repo_find_unique_abbrev(repo, &commit->object.oid,
-				       DEFAULT_ABBREV);
-}
-
 static struct commit *peel_committish(struct repository *repo, const char *name)
 {
 	struct object *obj;
@@ -45,59 +38,6 @@ static struct commit *peel_committish(struct repository *repo, const char *name)
 						  OBJ_COMMIT);
 }
 
-static char *get_author(const char *message)
-{
-	size_t len;
-	const char *a;
-
-	a = find_commit_header(message, "author", &len);
-	if (a)
-		return xmemdupz(a, len);
-
-	return NULL;
-}
-
-static struct commit *create_commit(struct repository *repo,
-				    struct tree *tree,
-				    struct commit *based_on,
-				    struct commit *parent)
-{
-	struct object_id ret;
-	struct object *obj = NULL;
-	struct commit_list *parents = NULL;
-	char *author;
-	char *sign_commit = NULL; /* FIXME: cli users might want to sign again */
-	struct commit_extra_header *extra = NULL;
-	struct strbuf msg = STRBUF_INIT;
-	const char *out_enc = get_commit_output_encoding();
-	const char *message = repo_logmsg_reencode(repo, based_on,
-						   NULL, out_enc);
-	const char *orig_message = NULL;
-	const char *exclude_gpgsig[] = { "gpgsig", NULL };
-
-	commit_list_insert(parent, &parents);
-	extra = read_commit_extra_headers(based_on, exclude_gpgsig);
-	find_commit_subject(message, &orig_message);
-	strbuf_addstr(&msg, orig_message);
-	author = get_author(message);
-	reset_ident_date();
-	if (commit_tree_extended(msg.buf, msg.len, &tree->object.oid, parents,
-				 &ret, author, NULL, sign_commit, extra)) {
-		error(_("failed to write commit object"));
-		goto out;
-	}
-
-	obj = parse_object(repo, &ret);
-
-out:
-	repo_unuse_commit_buffer(the_repository, based_on, message);
-	free_commit_extra_headers(extra);
-	free_commit_list(parents);
-	strbuf_release(&msg);
-	free(author);
-	return (struct commit *)obj;
-}
-
 struct ref_info {
 	struct commit *onto;
 	struct strset positive_refs;
@@ -246,50 +186,6 @@ static void determine_replay_mode(struct repository *repo,
 	strset_clear(&rinfo.positive_refs);
 }
 
-static struct commit *mapped_commit(kh_oid_map_t *replayed_commits,
-				    struct commit *commit,
-				    struct commit *fallback)
-{
-	khint_t pos = kh_get_oid_map(replayed_commits, commit->object.oid);
-	if (pos == kh_end(replayed_commits))
-		return fallback;
-	return kh_value(replayed_commits, pos);
-}
-
-static struct commit *pick_regular_commit(struct repository *repo,
-					  struct commit *pickme,
-					  kh_oid_map_t *replayed_commits,
-					  struct commit *onto,
-					  struct merge_options *merge_opt,
-					  struct merge_result *result)
-{
-	struct commit *base, *replayed_base;
-	struct tree *pickme_tree, *base_tree;
-
-	base = pickme->parents->item;
-	replayed_base = mapped_commit(replayed_commits, base, onto);
-
-	result->tree = repo_get_commit_tree(repo, replayed_base);
-	pickme_tree = repo_get_commit_tree(repo, pickme);
-	base_tree = repo_get_commit_tree(repo, base);
-
-	merge_opt->branch1 = short_commit_name(repo, replayed_base);
-	merge_opt->branch2 = short_commit_name(repo, pickme);
-	merge_opt->ancestor = xstrfmt("parent of %s", merge_opt->branch2);
-
-	merge_incore_nonrecursive(merge_opt,
-				  base_tree,
-				  result->tree,
-				  pickme_tree,
-				  result);
-
-	free((char*)merge_opt->ancestor);
-	merge_opt->ancestor = NULL;
-	if (!result->clean)
-		return NULL;
-	return create_commit(repo, result->tree, pickme, replayed_base);
-}
-
 static enum ref_action_mode parse_ref_action_mode(const char *ref_action, const char *source)
 {
 	if (!ref_action || !strcmp(ref_action, "update"))
@@ -495,8 +391,8 @@ int cmd_replay(int argc,
 		if (commit->parents->next)
 			die(_("replaying merge commits is not supported yet!"));
 
-		last_commit = pick_regular_commit(repo, commit, replayed_commits,
-						  onto, &merge_opt, &result);
+		last_commit = replay_pick_regular_commit(repo, commit, replayed_commits,
+							 onto, &merge_opt, &result);
 		if (!last_commit)
 			break;
 
diff --git a/builtin/reset.c b/builtin/reset.c
index ed35802af1..088449e120 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -346,7 +346,7 @@ int cmd_reset(int argc,
 	struct object_id oid;
 	struct pathspec pathspec;
 	int intent_to_add = 0;
-	struct add_p_opt add_p_opt = ADD_P_OPT_INIT;
+	struct interactive_options interactive_opts = INTERACTIVE_OPTIONS_INIT;
 	const struct option options[] = {
 		OPT__QUIET(&quiet, N_("be quiet, only report errors")),
 		OPT_BOOL(0, "no-refresh", &no_refresh,
@@ -371,8 +371,8 @@ int cmd_reset(int argc,
 			       PARSE_OPT_OPTARG,
 			       option_parse_recurse_submodules_worktree_updater),
 		OPT_BOOL('p', "patch", &patch_mode, N_("select hunks interactively")),
-		OPT_DIFF_UNIFIED(&add_p_opt.context),
-		OPT_DIFF_INTERHUNK_CONTEXT(&add_p_opt.interhunkcontext),
+		OPT_DIFF_UNIFIED(&interactive_opts.context),
+		OPT_DIFF_INTERHUNK_CONTEXT(&interactive_opts.interhunkcontext),
 		OPT_BOOL('N', "intent-to-add", &intent_to_add,
 				N_("record only the fact that removed paths will be added later")),
 		OPT_PATHSPEC_FROM_FILE(&pathspec_from_file),
@@ -423,9 +423,9 @@ int cmd_reset(int argc,
 		oidcpy(&oid, &tree->object.oid);
 	}
 
-	if (add_p_opt.context < -1)
+	if (interactive_opts.context < -1)
 		die(_("'%s' cannot be negative"), "--unified");
-	if (add_p_opt.interhunkcontext < -1)
+	if (interactive_opts.interhunkcontext < -1)
 		die(_("'%s' cannot be negative"), "--inter-hunk-context");
 
 	prepare_repo_settings(the_repository);
@@ -436,12 +436,12 @@ int cmd_reset(int argc,
 			die(_("options '%s' and '%s' cannot be used together"), "--patch", "--{hard,mixed,soft}");
 		trace2_cmd_mode("patch-interactive");
 		update_ref_status = !!run_add_p(the_repository, ADD_P_RESET,
-						&add_p_opt, rev, &pathspec);
+						&interactive_opts, rev, &pathspec);
 		goto cleanup;
 	} else {
-		if (add_p_opt.context != -1)
+		if (interactive_opts.context != -1)
 			die(_("the option '%s' requires '%s'"), "--unified", "--patch");
-		if (add_p_opt.interhunkcontext != -1)
+		if (interactive_opts.interhunkcontext != -1)
 			die(_("the option '%s' requires '%s'"), "--inter-hunk-context", "--patch");
 	}
 
diff --git a/builtin/stash.c b/builtin/stash.c
index 948eba06fb..3b50905233 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -1306,7 +1306,7 @@ done:
 
 static int stash_patch(struct stash_info *info, const struct pathspec *ps,
 		       struct strbuf *out_patch, int quiet,
-		       struct add_p_opt *add_p_opt)
+		       struct interactive_options *interactive_opts)
 {
 	int ret = 0;
 	struct child_process cp_read_tree = CHILD_PROCESS_INIT;
@@ -1331,7 +1331,7 @@ static int stash_patch(struct stash_info *info, const struct pathspec *ps,
 	old_index_env = xstrdup_or_null(getenv(INDEX_ENVIRONMENT));
 	setenv(INDEX_ENVIRONMENT, the_repository->index_file, 1);
 
-	ret = !!run_add_p(the_repository, ADD_P_STASH, add_p_opt, NULL, ps);
+	ret = !!run_add_p(the_repository, ADD_P_STASH, interactive_opts, NULL, ps);
 
 	the_repository->index_file = old_repo_index_file;
 	if (old_index_env && *old_index_env)
@@ -1427,7 +1427,8 @@ done:
 }
 
 static int do_create_stash(const struct pathspec *ps, struct strbuf *stash_msg_buf,
-			   int include_untracked, int patch_mode, struct add_p_opt *add_p_opt,
+			   int include_untracked, int patch_mode,
+			   struct interactive_options *interactive_opts,
 			   int only_staged, struct stash_info *info, struct strbuf *patch,
 			   int quiet)
 {
@@ -1509,7 +1510,7 @@ static int do_create_stash(const struct pathspec *ps, struct strbuf *stash_msg_b
 		untracked_commit_option = 1;
 	}
 	if (patch_mode) {
-		ret = stash_patch(info, ps, patch, quiet, add_p_opt);
+		ret = stash_patch(info, ps, patch, quiet, interactive_opts);
 		if (ret < 0) {
 			if (!quiet)
 				fprintf_ln(stderr, _("Cannot save the current "
@@ -1595,7 +1596,8 @@ static int create_stash(int argc, const char **argv, const char *prefix UNUSED,
 }
 
 static int do_push_stash(const struct pathspec *ps, const char *stash_msg, int quiet,
-			 int keep_index, int patch_mode, struct add_p_opt *add_p_opt,
+			 int keep_index, int patch_mode,
+			 struct interactive_options *interactive_opts,
 			 int include_untracked, int only_staged)
 {
 	int ret = 0;
@@ -1667,7 +1669,7 @@ static int do_push_stash(const struct pathspec *ps, const char *stash_msg, int q
 	if (stash_msg)
 		strbuf_addstr(&stash_msg_buf, stash_msg);
 	if (do_create_stash(ps, &stash_msg_buf, include_untracked, patch_mode,
-			    add_p_opt, only_staged, &info, &patch, quiet)) {
+			    interactive_opts, only_staged, &info, &patch, quiet)) {
 		ret = -1;
 		goto done;
 	}
@@ -1841,7 +1843,7 @@ static int push_stash(int argc, const char **argv, const char *prefix,
 	const char *stash_msg = NULL;
 	char *pathspec_from_file = NULL;
 	struct pathspec ps;
-	struct add_p_opt add_p_opt = ADD_P_OPT_INIT;
+	struct interactive_options interactive_opts = INTERACTIVE_OPTIONS_INIT;
 	struct option options[] = {
 		OPT_BOOL('k', "keep-index", &keep_index,
 			 N_("keep index")),
@@ -1849,8 +1851,8 @@ static int push_stash(int argc, const char **argv, const char *prefix,
 			 N_("stash staged changes only")),
 		OPT_BOOL('p', "patch", &patch_mode,
 			 N_("stash in patch mode")),
-		OPT_DIFF_UNIFIED(&add_p_opt.context),
-		OPT_DIFF_INTERHUNK_CONTEXT(&add_p_opt.interhunkcontext),
+		OPT_DIFF_UNIFIED(&interactive_opts.context),
+		OPT_DIFF_INTERHUNK_CONTEXT(&interactive_opts.interhunkcontext),
 		OPT__QUIET(&quiet, N_("quiet mode")),
 		OPT_BOOL('u', "include-untracked", &include_untracked,
 			 N_("include untracked files in stash")),
@@ -1907,19 +1909,19 @@ static int push_stash(int argc, const char **argv, const char *prefix,
 	}
 
 	if (!patch_mode) {
-		if (add_p_opt.context != -1)
+		if (interactive_opts.context != -1)
 			die(_("the option '%s' requires '%s'"), "--unified", "--patch");
-		if (add_p_opt.interhunkcontext != -1)
+		if (interactive_opts.interhunkcontext != -1)
 			die(_("the option '%s' requires '%s'"), "--inter-hunk-context", "--patch");
 	}
 
-	if (add_p_opt.context < -1)
+	if (interactive_opts.context < -1)
 		die(_("'%s' cannot be negative"), "--unified");
-	if (add_p_opt.interhunkcontext < -1)
+	if (interactive_opts.interhunkcontext < -1)
 		die(_("'%s' cannot be negative"), "--inter-hunk-context");
 
 	ret = do_push_stash(&ps, stash_msg, quiet, keep_index, patch_mode,
-			    &add_p_opt, include_untracked, only_staged);
+			    &interactive_opts, include_untracked, only_staged);
 
 	clear_pathspec(&ps);
 	free(pathspec_from_file);
@@ -1944,7 +1946,7 @@ static int save_stash(int argc, const char **argv, const char *prefix,
 	const char *stash_msg = NULL;
 	struct pathspec ps;
 	struct strbuf stash_msg_buf = STRBUF_INIT;
-	struct add_p_opt add_p_opt = ADD_P_OPT_INIT;
+	struct interactive_options interactive_opts = INTERACTIVE_OPTIONS_INIT;
 	struct option options[] = {
 		OPT_BOOL('k', "keep-index", &keep_index,
 			 N_("keep index")),
@@ -1952,8 +1954,8 @@ static int save_stash(int argc, const char **argv, const char *prefix,
 			 N_("stash staged changes only")),
 		OPT_BOOL('p', "patch", &patch_mode,
 			 N_("stash in patch mode")),
-		OPT_DIFF_UNIFIED(&add_p_opt.context),
-		OPT_DIFF_INTERHUNK_CONTEXT(&add_p_opt.interhunkcontext),
+		OPT_DIFF_UNIFIED(&interactive_opts.context),
+		OPT_DIFF_INTERHUNK_CONTEXT(&interactive_opts.interhunkcontext),
 		OPT__QUIET(&quiet, N_("quiet mode")),
 		OPT_BOOL('u', "include-untracked", &include_untracked,
 			 N_("include untracked files in stash")),
@@ -1973,20 +1975,20 @@ static int save_stash(int argc, const char **argv, const char *prefix,
 
 	memset(&ps, 0, sizeof(ps));
 
-	if (add_p_opt.context < -1)
+	if (interactive_opts.context < -1)
 		die(_("'%s' cannot be negative"), "--unified");
-	if (add_p_opt.interhunkcontext < -1)
+	if (interactive_opts.interhunkcontext < -1)
 		die(_("'%s' cannot be negative"), "--inter-hunk-context");
 
 	if (!patch_mode) {
-		if (add_p_opt.context != -1)
+		if (interactive_opts.context != -1)
 			die(_("the option '%s' requires '%s'"), "--unified", "--patch");
-		if (add_p_opt.interhunkcontext != -1)
+		if (interactive_opts.interhunkcontext != -1)
 			die(_("the option '%s' requires '%s'"), "--inter-hunk-context", "--patch");
 	}
 
 	ret = do_push_stash(&ps, stash_msg, quiet, keep_index,
-			    patch_mode, &add_p_opt, include_untracked,
+			    patch_mode, &interactive_opts, include_untracked,
 			    only_staged);
 
 	strbuf_release(&stash_msg_buf);