Add some more ignore_errors for 3.21

Author: fredemmott

src/TypeSpec/__Private/from_type_structure.php

@@ -17,7 +17,9 @@
 use namespace Facebook\TypeAssert;
 
 function from_type_structure<T>(TypeStructure<T> $ts): TypeSpec<T> {
+  /* HH_IGNORE_ERROR[4108] 3.21 is not aware of optional_shape_field */
   if ($ts['optional_shape_field'] ?? false) {
+    /* HH_IGNORE_ERROR[4108] 3.21 is not aware of optional_shape_field */
     $ts['optional_shape_field'] = false;
     return new OptionalSpec(from_type_structure($ts));
   }
@@ -114,6 +116,7 @@ function from_type_structure<T>(TypeStructure<T> $ts): TypeSpec<T> {
           ($_k, $field_ts) ==> from_type_structure($field_ts),
           ($k, $_v) ==> $k,
         ),
+        /* HH_IGNORE_ERROR[4108] 3.21 is not aware of allows_unknown_fields */
         ($ts['allows_unknown_fields'] ?? !ShapeSpec::STRICT_SHAPES)
           ? UnknownFieldsMode::ALLOW
           : UnknownFieldsMode::DENY,

tests/fixtures/TypeConstants.php

@@ -43,6 +43,8 @@ class TypeConstants {
   const type TShapeWithOneField = shape(
     'someString' => string,
   );
+
+  /* HH_IGNORE_ERROR[0003] no unknown shape fields in 3.21 */
   const type TShapeWithOneFieldAndImplicitSubtypes = shape(
     'someString' => string,
     ...