in src/CodegenFile.hack [204:216]
public function rekeyManualSection(string $old_key, string $new_key): this {
if ($this->rekey === null) {
$this->rekey = dict[];
}
$rekey = $this->rekey;
if (!C\contains_key($rekey, $new_key)) {
$rekey[$new_key] = vec[$old_key];
} else {
$rekey[$new_key][] = $old_key;
}
$this->rekey = $rekey;
return $this;
}