Support for HHVM 3.18

Author: fredemmott

examples/dorm/CodegenMutator.php

@@ -198,8 +198,8 @@ private function getCheckRequiredFieldsMethod(): CodegenMethod {
         'invariant',
         Vector {
           '$missing->isEmpty()',
-          '"The following required fields are missing: "'.
-            '.implode(", ", $missing)',
+          '"The following required fields are missing: %s"',
+          'implode(", ", $missing)',
         }
       );
 

src/CodegenFile.php

@@ -376,7 +376,8 @@ public function setNamespace(string $file_namespace): this {
   public function useNamespace(string $ns, ?string $as = null): this {
     invariant(
       !$this->useNamespaces->contains($ns),
-      $ns.' is already being used',
+      '%s is already being used',
+      $ns,
     );
     $this->useNamespaces[$ns] = $as;
     return $this;