reftable/merged: refactor seeking of records

The code to seek reftable records in the merged table code is quite hard
to read and does not conform to our coding style in multiple ways:

  - We have multiple exit paths where we release resources even though
    that is not really necessary.

  - We use a scoped error variable `e` which is hard to reason about.
    This variable is not required at all.

  - We allocate memory in the variable declarations, which is easy to
    miss.

Refactor the function so that it becomes more maintainable in the
future.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

reftable/merged.c

@@ -238,50 +238,38 @@ static int merged_table_seek_record(struct reftable_merged_table *mt,
 				    struct reftable_iterator *it,
 				    struct reftable_record *rec)
 {
-	struct reftable_iterator *iters = reftable_calloc(
-		mt->stack_len, sizeof(*iters));
 	struct merged_iter merged = {
-		.stack = iters,
 		.typ = reftable_record_type(rec),
 		.hash_id = mt->hash_id,
 		.suppress_deletions = mt->suppress_deletions,
 		.key = STRBUF_INIT,
 		.entry_key = STRBUF_INIT,
 	};
-	int n = 0;
-	int err = 0;
-	int i = 0;
-	for (i = 0; i < mt->stack_len && err == 0; i++) {
-		int e = reftable_table_seek_record(&mt->stack[i], &iters[n],
-						   rec);
-		if (e < 0) {
-			err = e;
-		}
-		if (e == 0) {
-			n++;
-		}
-	}
-	if (err < 0) {
-		int i = 0;
-		for (i = 0; i < n; i++) {
-			reftable_iterator_destroy(&iters[i]);
-		}
-		reftable_free(iters);
-		return err;
+	struct merged_iter *p;
+	int err;
+
+	REFTABLE_CALLOC_ARRAY(merged.stack, mt->stack_len);
+	for (size_t i = 0; i < mt->stack_len; i++) {
+		err = reftable_table_seek_record(&mt->stack[i],
+						 &merged.stack[merged.stack_len], rec);
+		if (err < 0)
+			goto out;
+		if (!err)
+			merged.stack_len++;
 	}
 
-	merged.stack_len = n;
 	err = merged_iter_init(&merged);
-	if (err < 0) {
+	if (err < 0)
+		goto out;
+
+	p = reftable_malloc(sizeof(struct merged_iter));
+	*p = merged;
+	iterator_from_merged_iter(it, p);
+
+out:
+	if (err < 0)
 		merged_iter_close(&merged);
-		return err;
-	} else {
-		struct merged_iter *p =
-			reftable_malloc(sizeof(struct merged_iter));
-		*p = merged;
-		iterator_from_merged_iter(it, p);
-	}
-	return 0;
+	return err;
 }
 
 int reftable_merged_table_seek_ref(struct reftable_merged_table *mt,