builtin/history: split handling of ref updates into two phases

The function `handle_reference_updates()` is used by git-history(1) to
update all references that refer to commits that have been rewritten. As
such, it performs two steps:

  - It gathers the references that need to be updated in the first
    place.

  - It prepares and commits the reference transaction.

In a subsequent commit we'll want to handle those two steps separately.
Prepare for this by splitting up the function into two.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

builtin/history.c

@@ -333,21 +333,17 @@ static int handle_ref_update(struct ref_transaction *transaction,
 				      NULL, NULL, 0, reflog_msg, err);
 }
 
-static int handle_reference_updates(struct rev_info *revs,
-				    enum ref_action action,
-				    struct commit *original,
-				    struct commit *rewritten,
-				    const char *reflog_msg,
-				    int dry_run,
-				    enum replay_empty_commit_action empty)
+static int compute_pending_ref_updates(struct rev_info *revs,
+				       enum ref_action action,
+				       struct commit *original,
+				       struct commit *rewritten,
+				       enum replay_empty_commit_action empty,
+				       struct replay_result *result)
 {
 	const struct name_decoration *decoration;
 	struct replay_revisions_options opts = {
 		.empty = empty,
 	};
-	struct replay_result result = { 0 };
-	struct ref_transaction *transaction = NULL;
-	struct strbuf err = STRBUF_INIT;
 	char hex[GIT_MAX_HEXSZ + 1];
 	bool detached_head;
 	int head_flags = 0;
@@ -359,34 +355,13 @@ static int handle_reference_updates(struct rev_info *revs,
 
 	opts.onto = oid_to_hex_r(hex, &rewritten->object.oid);
 
-	ret = replay_revisions(revs, &opts, &result);
+	ret = replay_revisions(revs, &opts, result);
 	if (ret)
-		goto out;
+		return ret;
 
 	if (action != REF_ACTION_BRANCHES && action != REF_ACTION_HEAD)
 		BUG("unsupported ref action %d", action);
 
-	if (!dry_run) {
-		transaction = ref_store_transaction_begin(get_main_ref_store(revs->repo), 0, &err);
-		if (!transaction) {
-			ret = error(_("failed to begin ref transaction: %s"), err.buf);
-			goto out;
-		}
-	}
-
-	for (size_t i = 0; i < result.updates_nr; i++) {
-		ret = handle_ref_update(transaction,
-					result.updates[i].refname,
-					&result.updates[i].new_oid,
-					&result.updates[i].old_oid,
-					reflog_msg, &err);
-		if (ret) {
-			ret = error(_("failed to update ref '%s': %s"),
-				    result.updates[i].refname, err.buf);
-			goto out;
-		}
-	}
-
 	/*
 	 * `replay_revisions()` only updates references that are
 	 * ancestors of `rewritten`, so we need to manually
@@ -414,14 +389,43 @@ static int handle_reference_updates(struct rev_info *revs,
 		    !detached_head)
 			continue;
 
+		ALLOC_GROW(result->updates, result->updates_nr + 1, result->updates_alloc);
+		result->updates[result->updates_nr].refname = xstrdup(decoration->name);
+		result->updates[result->updates_nr].old_oid = original->object.oid;
+		result->updates[result->updates_nr].new_oid = rewritten->object.oid;
+		result->updates_nr++;
+	}
+
+	return 0;
+}
+
+static int apply_pending_ref_updates(struct repository *repo,
+				     const struct replay_result *result,
+				     const char *reflog_msg,
+				     int dry_run)
+{
+	struct ref_transaction *transaction = NULL;
+	struct strbuf err = STRBUF_INIT;
+	int ret;
+
+	if (!dry_run) {
+		transaction = ref_store_transaction_begin(get_main_ref_store(repo),
+							  0, &err);
+		if (!transaction) {
+			ret = error(_("failed to begin ref transaction: %s"), err.buf);
+			goto out;
+		}
+	}
+
+	for (size_t i = 0; i < result->updates_nr; i++) {
 		ret = handle_ref_update(transaction,
-					decoration->name,
-					&rewritten->object.oid,
-					&original->object.oid,
+					result->updates[i].refname,
+					&result->updates[i].new_oid,
+					&result->updates[i].old_oid,
 					reflog_msg, &err);
 		if (ret) {
 			ret = error(_("failed to update ref '%s': %s"),
-				    decoration->name, err.buf);
+				    result->updates[i].refname, err.buf);
 			goto out;
 		}
 	}
@@ -435,11 +439,33 @@ static int handle_reference_updates(struct rev_info *revs,
 
 out:
 	ref_transaction_free(transaction);
-	replay_result_release(&result);
 	strbuf_release(&err);
 	return ret;
 }
 
+static int handle_reference_updates(struct rev_info *revs,
+				    enum ref_action action,
+				    struct commit *original,
+				    struct commit *rewritten,
+				    const char *reflog_msg,
+				    int dry_run,
+				    enum replay_empty_commit_action empty)
+{
+	struct replay_result result = { 0 };
+	int ret;
+
+	ret = compute_pending_ref_updates(revs, action, original, rewritten,
+					  empty, &result);
+	if (ret)
+		goto out;
+
+	ret = apply_pending_ref_updates(revs->repo, &result, reflog_msg, dry_run);
+
+out:
+	replay_result_release(&result);
+	return ret;
+}
+
 static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)