Merge branch 'sa/replay-atomic-ref-updates' into jch

"git replay" (experimental) learned to perform ref updates itself
in a transaction by default, instead of emitting where each refs
should point at and leaving the actual update to another command.

* sa/replay-atomic-ref-updates:
  replay: add replay.refAction config option
  replay: make atomic ref updates the default behavior
  replay: use die_for_incompatible_opt2() for option validation

Author: gitster

Documentation/config/replay.adoc

@@ -0,0 +1,11 @@
+replay.refAction::
+	Specifies the default mode for handling reference updates in
+	`git replay`. The value can be:
++
+--
+	* `update`: Update refs directly using an atomic transaction (default behavior).
+	* `print`: Output update-ref commands for pipeline use.
+--
++
+This setting can be overridden with the `--ref-action` command-line option.
+When not configured, `git replay` defaults to `update` mode.

Documentation/git-replay.adoc

@@ -9,15 +9,16 @@ git-replay - EXPERIMENTAL: Replay commits on a new base, works with bare repos t
 SYNOPSIS
 --------
 [verse]
-(EXPERIMENTAL!) 'git replay' ([--contained] --onto <newbase> | --advance <branch>) <revision-range>...
+(EXPERIMENTAL!) 'git replay' ([--contained] --onto <newbase> | --advance <branch>) [--ref-action[=<mode>]] <revision-range>...
 
 DESCRIPTION
 -----------
 
 Takes ranges of commits and replays them onto a new location. Leaves
-the working tree and the index untouched, and updates no references.
-The output of this command is meant to be used as input to
-`git update-ref --stdin`, which would update the relevant branches
+the working tree and the index untouched. By default, updates the
+relevant references using an atomic transaction (all refs update or
+none). Use `--ref-action=print` to avoid automatic ref updates and
+instead get update commands that can be piped to `git update-ref --stdin`
 (see the OUTPUT section below).
 
 THIS COMMAND IS EXPERIMENTAL. THE BEHAVIOR MAY CHANGE.
@@ -29,18 +30,29 @@ OPTIONS
 	Starting point at which to create the new commits.  May be any
 	valid commit, and not just an existing branch name.
 +
-When `--onto` is specified, the update-ref command(s) in the output will
-update the branch(es) in the revision range to point at the new
-commits, similar to the way how `git rebase --update-refs` updates
-multiple branches in the affected range.
+When `--onto` is specified, the branch(es) in the revision range will be
+updated to point at the new commits, similar to the way `git rebase --update-refs`
+updates multiple branches in the affected range.
 
 --advance <branch>::
 	Starting point at which to create the new commits; must be a
 	branch name.
 +
-When `--advance` is specified, the update-ref command(s) in the output
-will update the branch passed as an argument to `--advance` to point at
-the new commits (in other words, this mimics a cherry-pick operation).
+The history is replayed on top of the <branch> and <branch> is updated to
+point at the tip of the resulting history. This is different from `--onto`,
+which uses the target only as a starting point without updating it.
+
+--ref-action[=<mode>]::
+	Control how references are updated. The mode can be:
++
+--
+	* `update` (default): Update refs directly using an atomic transaction.
+	  All refs are updated or none are (all-or-nothing behavior).
+	* `print`: Output update-ref commands for pipeline use. This is the
+	  traditional behavior where output can be piped to `git update-ref --stdin`.
+--
++
+The default mode can be configured via the `replay.refAction` configuration variable.
 
 <revision-range>::
 	Range of commits to replay. More than one <revision-range> can
@@ -54,8 +66,11 @@ include::rev-list-options.adoc[]
 OUTPUT
 ------
 
-When there are no conflicts, the output of this command is usable as
-input to `git update-ref --stdin`.  It is of the form:
+By default, or with `--ref-action=update`, this command produces no output on
+success, as refs are updated directly using an atomic transaction.
+
+When using `--ref-action=print`, the output is usable as input to
+`git update-ref --stdin`. It is of the form:
 
 	update refs/heads/branch1 ${NEW_branch1_HASH} ${OLD_branch1_HASH}
 	update refs/heads/branch2 ${NEW_branch2_HASH} ${OLD_branch2_HASH}
@@ -81,40 +96,44 @@ To simply rebase `mybranch` onto `target`:
 
 ------------
 $ git replay --onto target origin/main..mybranch
+------------
+
+The refs are updated atomically and no output is produced on success.
+
+To see what would be updated without actually updating:
+
+------------
+$ git replay --ref-action=print --onto target origin/main..mybranch
 update refs/heads/mybranch ${NEW_mybranch_HASH} ${OLD_mybranch_HASH}
 ------------
 
 To cherry-pick the commits from mybranch onto target:
 
 ------------
 $ git replay --advance target origin/main..mybranch
-update refs/heads/target ${NEW_target_HASH} ${OLD_target_HASH}
 ------------
 
 Note that the first two examples replay the exact same commits and on
 top of the exact same new base, they only differ in that the first
-provides instructions to make mybranch point at the new commits and
-the second provides instructions to make target point at them.
+updates mybranch to point at the new commits and the second updates
+target to point at them.
 
 What if you have a stack of branches, one depending upon another, and
 you'd really like to rebase the whole set?
 
 ------------
 $ git replay --contained --onto origin/main origin/main..tipbranch
-update refs/heads/branch1 ${NEW_branch1_HASH} ${OLD_branch1_HASH}
-update refs/heads/branch2 ${NEW_branch2_HASH} ${OLD_branch2_HASH}
-update refs/heads/tipbranch ${NEW_tipbranch_HASH} ${OLD_tipbranch_HASH}
 ------------
 
+All three branches (`branch1`, `branch2`, and `tipbranch`) are updated
+atomically.
+
 When calling `git replay`, one does not need to specify a range of
 commits to replay using the syntax `A..B`; any range expression will
 do:
 
 ------------
 $ git replay --onto origin/main ^base branch1 branch2 branch3
-update refs/heads/branch1 ${NEW_branch1_HASH} ${OLD_branch1_HASH}
-update refs/heads/branch2 ${NEW_branch2_HASH} ${OLD_branch2_HASH}
-update refs/heads/branch3 ${NEW_branch3_HASH} ${OLD_branch3_HASH}
 ------------
 
 This will simultaneously rebase `branch1`, `branch2`, and `branch3`,

builtin/replay.c

@@ -8,6 +8,7 @@
 #include "git-compat-util.h"
 
 #include "builtin.h"
+#include "config.h"
 #include "environment.h"
 #include "hex.h"
 #include "lockfile.h"
@@ -20,6 +21,11 @@
 #include <oidset.h>
 #include <tree.h>
 
+enum ref_action_mode {
+	REF_ACTION_UPDATE,
+	REF_ACTION_PRINT,
+};
+
 static const char *short_commit_name(struct repository *repo,
 				     struct commit *commit)
 {
@@ -284,6 +290,54 @@ static struct commit *pick_regular_commit(struct repository *repo,
 	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"))
+		return REF_ACTION_UPDATE;
+	if (!strcmp(ref_action, "print"))
+		return REF_ACTION_PRINT;
+	die(_("invalid %s value: '%s'"), source, ref_action);
+}
+
+static enum ref_action_mode get_ref_action_mode(struct repository *repo, const char *ref_action)
+{
+	const char *config_value = NULL;
+
+	/* Command line option takes precedence */
+	if (ref_action)
+		return parse_ref_action_mode(ref_action, "--ref-action");
+
+	/* Check config value */
+	if (!repo_config_get_string_tmp(repo, "replay.refAction", &config_value))
+		return parse_ref_action_mode(config_value, "replay.refAction");
+
+	/* Default to update mode */
+	return REF_ACTION_UPDATE;
+}
+
+static int handle_ref_update(enum ref_action_mode mode,
+			     struct ref_transaction *transaction,
+			     const char *refname,
+			     const struct object_id *new_oid,
+			     const struct object_id *old_oid,
+			     const char *reflog_msg,
+			     struct strbuf *err)
+{
+	switch (mode) {
+	case REF_ACTION_PRINT:
+		printf("update %s %s %s\n",
+		       refname,
+		       oid_to_hex(new_oid),
+		       oid_to_hex(old_oid));
+		return 0;
+	case REF_ACTION_UPDATE:
+		return ref_transaction_update(transaction, refname, new_oid, old_oid,
+					      NULL, NULL, 0, reflog_msg, err);
+	default:
+		BUG("unknown ref_action_mode %d", mode);
+	}
+}
+
 int cmd_replay(int argc,
 	       const char **argv,
 	       const char *prefix,
@@ -294,6 +348,8 @@ int cmd_replay(int argc,
 	struct commit *onto = NULL;
 	const char *onto_name = NULL;
 	int contained = 0;
+	const char *ref_action = NULL;
+	enum ref_action_mode ref_mode;
 
 	struct rev_info revs;
 	struct commit *last_commit = NULL;
@@ -302,12 +358,15 @@ int cmd_replay(int argc,
 	struct merge_result result;
 	struct strset *update_refs = NULL;
 	kh_oid_map_t *replayed_commits;
+	struct ref_transaction *transaction = NULL;
+	struct strbuf transaction_err = STRBUF_INIT;
+	struct strbuf reflog_msg = STRBUF_INIT;
 	int ret = 0;
 
-	const char * const replay_usage[] = {
+	const char *const replay_usage[] = {
 		N_("(EXPERIMENTAL!) git replay "
 		   "([--contained] --onto <newbase> | --advance <branch>) "
-		   "<revision-range>..."),
+		   "[--ref-action[=<mode>]] <revision-range>..."),
 		NULL
 	};
 	struct option replay_options[] = {
@@ -319,6 +378,9 @@ int cmd_replay(int argc,
 			   N_("replay onto given commit")),
 		OPT_BOOL(0, "contained", &contained,
 			 N_("advance all branches contained in revision-range")),
+		OPT_STRING(0, "ref-action", &ref_action,
+			   N_("mode"),
+			   N_("control ref update behavior (update|print)")),
 		OPT_END()
 	};
 
@@ -330,9 +392,12 @@ int cmd_replay(int argc,
 		usage_with_options(replay_usage, replay_options);
 	}
 
-	if (advance_name_opt && contained)
-		die(_("options '%s' and '%s' cannot be used together"),
-		    "--advance", "--contained");
+	die_for_incompatible_opt2(!!advance_name_opt, "--advance",
+				  contained, "--contained");
+
+	/* Parse ref action mode from command line or config */
+	ref_mode = get_ref_action_mode(repo, ref_action);
+
 	advance_name = xstrdup_or_null(advance_name_opt);
 
 	repo_init_revisions(repo, &revs, prefix);
@@ -389,6 +454,24 @@ int cmd_replay(int argc,
 	determine_replay_mode(repo, &revs.cmdline, onto_name, &advance_name,
 			      &onto, &update_refs);
 
+	/* Build reflog message */
+	if (advance_name_opt)
+		strbuf_addf(&reflog_msg, "replay --advance %s", advance_name_opt);
+	else
+		strbuf_addf(&reflog_msg, "replay --onto %s",
+			    oid_to_hex(&onto->object.oid));
+
+	/* Initialize ref transaction if using update mode */
+	if (ref_mode == REF_ACTION_UPDATE) {
+		transaction = ref_store_transaction_begin(get_main_ref_store(repo),
+							  0, &transaction_err);
+		if (!transaction) {
+			ret = error(_("failed to begin ref transaction: %s"),
+				    transaction_err.buf);
+			goto cleanup;
+		}
+	}
+
 	if (!onto) /* FIXME: Should handle replaying down to root commit */
 		die("Replaying down to root commit is not supported yet!");
 
@@ -434,21 +517,41 @@ int cmd_replay(int argc,
 			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));
+				if (handle_ref_update(ref_mode, transaction,
+						      decoration->name,
+						      &last_commit->object.oid,
+						      &commit->object.oid,
+						      reflog_msg.buf,
+						      &transaction_err) < 0) {
+					ret = error(_("failed to update ref '%s': %s"),
+						    decoration->name, transaction_err.buf);
+					goto cleanup;
+				}
 			}
 			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));
+		if (handle_ref_update(ref_mode, transaction, advance_name,
+				      &last_commit->object.oid,
+				      &onto->object.oid,
+				      reflog_msg.buf,
+				      &transaction_err) < 0) {
+			ret = error(_("failed to update ref '%s': %s"),
+				    advance_name, transaction_err.buf);
+			goto cleanup;
+		}
+	}
+
+	/* Commit the ref transaction if we have one */
+	if (transaction && result.clean == 1) {
+		if (ref_transaction_commit(transaction, &transaction_err)) {
+			ret = error(_("failed to commit ref transaction: %s"),
+				    transaction_err.buf);
+			goto cleanup;
+		}
 	}
 
 	merge_finalize(&merge_opt, &result);
@@ -460,6 +563,10 @@ int cmd_replay(int argc,
 	ret = result.clean;
 
 cleanup:
+	if (transaction)
+		ref_transaction_free(transaction);
+	strbuf_release(&transaction_err);
+	strbuf_release(&reflog_msg);
 	release_revisions(&revs);
 	free(advance_name);