Merge branch 'cc/git-replay'

Introduce "git replay", a tool meant on the server side without
working tree to recreate a history.

* cc/git-replay:
  replay: stop assuming replayed branches do not diverge
  replay: add --contained to rebase contained branches
  replay: add --advance or 'cherry-pick' mode
  replay: use standard revision ranges
  replay: make it a minimal server side command
  replay: remove HEAD related sanity check
  replay: remove progress and info output
  replay: add an important FIXME comment about gpg signing
  replay: change rev walking options
  replay: introduce pick_regular_commit()
  replay: die() instead of failing assert()
  replay: start using parse_options API
  replay: introduce new builtin
  t6429: remove switching aspects of fast-rebase

1 files changed, 446 insertions, 0 deletions

diff --git a/builtin/replay.c b/builtin/replay.c
new file mode 100644
index 0000000000..6bc4b47f09
--- /dev/null
+++ b/builtin/replay.c
@@ -0,0 +1,446 @@
+/*
+ * "git replay" builtin command
+ */
+
+#define USE_THE_INDEX_VARIABLE
+#include "git-compat-util.h"
+
+#include "builtin.h"
+#include "environment.h"
+#include "hex.h"
+#include "lockfile.h"
+#include "merge-ort.h"
+#include "object-name.h"
+#include "parse-options.h"
+#include "refs.h"
+#include "revision.h"
+#include "strmap.h"
+#include <oidset.h>
+#include <tree.h>
+
+static const char *short_commit_name(struct commit *commit)
+{
+	return repo_find_unique_abbrev(the_repository, &commit->object.oid,
+				       DEFAULT_ABBREV);
+}
+
+static struct commit *peel_committish(const char *name)
+{
+	struct object *obj;
+	struct object_id oid;
+
+	if (repo_get_oid(the_repository, name, &oid))
+		return NULL;
+	obj = parse_object(the_repository, &oid);
+	return (struct commit *)repo_peel_to_type(the_repository, name, 0, obj,
+						  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 tree *tree,
+				    struct commit *based_on,
+				    struct commit *parent)
+{
+	struct object_id ret;
+	struct object *obj;
+	struct commit_list *parents = NULL;
+	char *author;
+	char *sign_commit = NULL; /* FIXME: cli users might want to sign again */
+	struct commit_extra_header *extra;
+	struct strbuf msg = STRBUF_INIT;
+	const char *out_enc = get_commit_output_encoding();
+	const char *message = repo_logmsg_reencode(the_repository, 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"));
+		return NULL;
+	}
+	free(author);
+	strbuf_release(&msg);
+
+	obj = parse_object(the_repository, &ret);
+	return (struct commit *)obj;
+}
+
+struct ref_info {
+	struct commit *onto;
+	struct strset positive_refs;
+	struct strset negative_refs;
+	int positive_refexprs;
+	int negative_refexprs;
+};
+
+static void get_ref_information(struct rev_cmdline_info *cmd_info,
+				struct ref_info *ref_info)
+{
+	int i;
+
+	ref_info->onto = NULL;
+	strset_init(&ref_info->positive_refs);
+	strset_init(&ref_info->negative_refs);
+	ref_info->positive_refexprs = 0;
+	ref_info->negative_refexprs = 0;
+
+	/*
+	 * When the user specifies e.g.
+	 *   git replay origin/main..mybranch
+	 *   git replay ^origin/next mybranch1 mybranch2
+	 * we want to be able to determine where to replay the commits.  In
+	 * these examples, the branches are probably based on an old version
+	 * of either origin/main or origin/next, so we want to replay on the
+	 * newest version of that branch.  In contrast we would want to error
+	 * out if they ran
+	 *   git replay ^origin/master ^origin/next mybranch
+	 *   git replay mybranch~2..mybranch
+	 * the first of those because there's no unique base to choose, and
+	 * the second because they'd likely just be replaying commits on top
+	 * of the same commit and not making any difference.
+	 */
+	for (i = 0; i < cmd_info->nr; i++) {
+		struct rev_cmdline_entry *e = cmd_info->rev + i;
+		struct object_id oid;
+		const char *refexpr = e->name;
+		char *fullname = NULL;
+		int can_uniquely_dwim = 1;
+
+		if (*refexpr == '^')
+			refexpr++;
+		if (repo_dwim_ref(the_repository, refexpr, strlen(refexpr), &oid, &fullname, 0) != 1)
+			can_uniquely_dwim = 0;
+
+		if (e->flags & BOTTOM) {
+			if (can_uniquely_dwim)
+				strset_add(&ref_info->negative_refs, fullname);
+			if (!ref_info->negative_refexprs)
+				ref_info->onto = lookup_commit_reference_gently(the_repository,
+										&e->item->oid, 1);
+			ref_info->negative_refexprs++;
+		} else {
+			if (can_uniquely_dwim)
+				strset_add(&ref_info->positive_refs, fullname);
+			ref_info->positive_refexprs++;
+		}
+
+		free(fullname);
+	}
+}
+
+static void determine_replay_mode(struct rev_cmdline_info *cmd_info,
+				  const char *onto_name,
+				  const char **advance_name,
+				  struct commit **onto,
+				  struct strset **update_refs)
+{
+	struct ref_info rinfo;
+
+	get_ref_information(cmd_info, &rinfo);
+	if (!rinfo.positive_refexprs)
+		die(_("need some commits to replay"));
+	if (onto_name && *advance_name)
+		die(_("--onto and --advance are incompatible"));
+	else if (onto_name) {
+		*onto = peel_committish(onto_name);
+		if (rinfo.positive_refexprs <
+		    strset_get_size(&rinfo.positive_refs))
+			die(_("all positive revisions given must be references"));
+	} else if (*advance_name) {
+		struct object_id oid;
+		char *fullname = NULL;
+
+		*onto = peel_committish(*advance_name);
+		if (repo_dwim_ref(the_repository, *advance_name, strlen(*advance_name),
+			     &oid, &fullname, 0) == 1) {
+			*advance_name = fullname;
+		} else {
+			die(_("argument to --advance must be a reference"));
+		}
+		if (rinfo.positive_refexprs > 1)
+			die(_("cannot advance target with multiple sources because ordering would be ill-defined"));
+	} else {
+		int positive_refs_complete = (
+			rinfo.positive_refexprs ==
+			strset_get_size(&rinfo.positive_refs));
+		int negative_refs_complete = (
+			rinfo.negative_refexprs ==
+			strset_get_size(&rinfo.negative_refs));
+		/*
+		 * We need either positive_refs_complete or
+		 * negative_refs_complete, but not both.
+		 */
+		if (rinfo.negative_refexprs > 0 &&
+		    positive_refs_complete == negative_refs_complete)
+			die(_("cannot implicitly determine whether this is an --advance or --onto operation"));
+		if (negative_refs_complete) {
+			struct hashmap_iter iter;
+			struct strmap_entry *entry;
+
+			if (rinfo.negative_refexprs == 0)
+				die(_("all positive revisions given must be references"));
+			else if (rinfo.negative_refexprs > 1)
+				die(_("cannot implicitly determine whether this is an --advance or --onto operation"));
+			else if (rinfo.positive_refexprs > 1)
+				die(_("cannot advance target with multiple source branches because ordering would be ill-defined"));
+
+			/* Only one entry, but we have to loop to get it */
+			strset_for_each_entry(&rinfo.negative_refs,
+					      &iter, entry) {
+				*advance_name = entry->key;
+			}
+		} else { /* positive_refs_complete */
+			if (rinfo.negative_refexprs > 1)
+				die(_("cannot implicitly determine correct base for --onto"));
+			if (rinfo.negative_refexprs == 1)
+				*onto = rinfo.onto;
+		}
+	}
+	if (!*advance_name) {
+		*update_refs = xcalloc(1, sizeof(**update_refs));
+		**update_refs = rinfo.positive_refs;
+		memset(&rinfo.positive_refs, 0, sizeof(**update_refs));
+	}
+	strset_clear(&rinfo.negative_refs);
+	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 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(the_repository, replayed_base);
+	pickme_tree = repo_get_commit_tree(the_repository, pickme);
+	base_tree = repo_get_commit_tree(the_repository, base);
+
+	merge_opt->branch1 = short_commit_name(replayed_base);
+	merge_opt->branch2 = short_commit_name(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(result->tree, pickme, replayed_base);
+}
+
+int cmd_replay(int argc, const char **argv, const char *prefix)
+{
+	const char *advance_name = NULL;
+	struct commit *onto = NULL;
+	const char *onto_name = NULL;
+	int contained = 0;
+
+	struct rev_info revs;
+	struct commit *last_commit = NULL;
+	struct commit *commit;
+	struct merge_options merge_opt;
+	struct merge_result result;
+	struct strset *update_refs = NULL;
+	kh_oid_map_t *replayed_commits;
+	int ret = 0;
+
+	const char * const replay_usage[] = {
+		N_("(EXPERIMENTAL!) git replay "
+		   "([--contained] --onto <newbase> | --advance <branch>) "
+		   "<revision-range>..."),
+		NULL
+	};
+	struct option replay_options[] = {
+		OPT_STRING(0, "advance", &advance_name,
+			   N_("branch"),
+			   N_("make replay advance given branch")),
+		OPT_STRING(0, "onto", &onto_name,
+			   N_("revision"),
+			   N_("replay onto given commit")),
+		OPT_BOOL(0, "contained", &contained,
+			 N_("advance all branches contained in revision-range")),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, prefix, replay_options, replay_usage,
+			     PARSE_OPT_KEEP_ARGV0 | PARSE_OPT_KEEP_UNKNOWN_OPT);
+
+	if (!onto_name && !advance_name) {
+		error(_("option --onto or --advance is mandatory"));
+		usage_with_options(replay_usage, replay_options);
+	}
+
+	if (advance_name && contained)
+		die(_("options '%s' and '%s' cannot be used together"),
+		    "--advance", "--contained");
+
+	repo_init_revisions(the_repository, &revs, prefix);
+
+	/*
+	 * Set desired values for rev walking options here. If they
+	 * are changed by some user specified option in setup_revisions()
+	 * below, we will detect that below and then warn.
+	 *
+	 * TODO: In the future we might want to either die(), or allow
+	 * some options changing these values if we think they could
+	 * be useful.
+	 */
+	revs.reverse = 1;
+	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+	revs.topo_order = 1;
+	revs.simplify_history = 0;
+
+	argc = setup_revisions(argc, argv, &revs, NULL);
+	if (argc > 1) {
+		ret = error(_("unrecognized argument: %s"), argv[1]);
+		goto cleanup;
+	}
+
+	/*
+	 * Detect and warn if we override some user specified rev
+	 * walking options.
+	 */
+	if (revs.reverse != 1) {
+		warning(_("some rev walking options will be overridden as "
+			  "'%s' bit in 'struct rev_info' will be forced"),
+			"reverse");
+		revs.reverse = 1;
+	}
+	if (revs.sort_order != REV_SORT_IN_GRAPH_ORDER) {
+		warning(_("some rev walking options will be overridden as "
+			  "'%s' bit in 'struct rev_info' will be forced"),
+			"sort_order");
+		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+	}
+	if (revs.topo_order != 1) {
+		warning(_("some rev walking options will be overridden as "
+			  "'%s' bit in 'struct rev_info' will be forced"),
+			"topo_order");
+		revs.topo_order = 1;
+	}
+	if (revs.simplify_history != 0) {
+		warning(_("some rev walking options will be overridden as "
+			  "'%s' bit in 'struct rev_info' will be forced"),
+			"simplify_history");
+		revs.simplify_history = 0;
+	}
+
+	determine_replay_mode(&revs.cmdline, onto_name, &advance_name,
+			      &onto, &update_refs);
+
+	if (!onto) /* FIXME: Should handle replaying down to root commit */
+		die("Replaying down to root commit is not supported yet!");
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto cleanup;
+	}
+
+	init_merge_options(&merge_opt, the_repository);
+	memset(&result, 0, sizeof(result));
+	merge_opt.show_rename_progress = 0;
+	last_commit = onto;
+	replayed_commits = kh_init_oid_map();
+	while ((commit = get_revision(&revs))) {
+		const struct name_decoration *decoration;
+		khint_t pos;
+		int hr;
+
+		if (!commit->parents)
+			die(_("replaying down to root commit is not supported yet!"));
+		if (commit->parents->next)
+			die(_("replaying merge commits is not supported yet!"));
+
+		last_commit = pick_regular_commit(commit, replayed_commits, onto,
+						  &merge_opt, &result);
+		if (!last_commit)
+			break;
+
+		/* Record commit -> last_commit mapping */
+		pos = kh_put_oid_map(replayed_commits, commit->object.oid, &hr);
+		if (hr == 0)
+			BUG("Duplicate rewritten commit: %s\n",
+			    oid_to_hex(&commit->object.oid));
+		kh_value(replayed_commits, pos) = last_commit;
+
+		/* Update any necessary branches */
+		if (advance_name)
+			continue;
+		decoration = get_name_decoration(&commit->object);
+		if (!decoration)
+			continue;
+		while (decoration) {
+			if (decoration->type == DECORATION_REF_LOCAL &&
+			    (contained || strset_contains(update_refs,
+							  decoration->name))) {
+				printf("update %s %s %s\n",
+				       decoration->name,
+				       oid_to_hex(&last_commit->object.oid),
+				       oid_to_hex(&commit->object.oid));
+			}
+			decoration = decoration->next;
+		}
+	}
+
+	/* In --advance mode, advance the target ref */
+	if (result.clean == 1 && advance_name) {
+		printf("update %s %s %s\n",
+		       advance_name,
+		       oid_to_hex(&last_commit->object.oid),
+		       oid_to_hex(&onto->object.oid));
+	}
+
+	merge_finalize(&merge_opt, &result);
+	kh_destroy_oid_map(replayed_commits);
+	if (update_refs) {
+		strset_clear(update_refs);
+		free(update_refs);
+	}
+	ret = result.clean;
+
+cleanup:
+	release_revisions(&revs);
+
+	/* Return */
+	if (ret < 0)
+		exit(128);
+	return ret ? 0 : 1;
+}