[dart2js] Add subtyping of record types against Record interface

- Fix bug with nullable record type, e.g. `(int,int)?`.

Change-Id: Ie8006e8ec3a9ffd675519df2ab7b4d101d8d5dcd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/262843
Reviewed-by: Mayank Patke <fishythefish@google.com>
Commit-Queue: Stephen Adams <sra@google.com>

Author: rakudrama

pkg/compiler/lib/src/common/elements.dart

@@ -50,6 +50,9 @@ abstract class CommonElements {
   /// The `Function` class defined in 'dart:core'.
   late final ClassEntity functionClass = _findClass(coreLibrary, 'Function');
 
+  /// The `Record` class defined in 'dart:core'.
+  late final ClassEntity recordClass = _findClass(coreLibrary, 'Record');
+
   /// The `Resource` class defined in 'dart:core'.
   late final ClassEntity resourceClass = _findClass(coreLibrary, 'Resource');
 
@@ -239,6 +242,9 @@ abstract class CommonElements {
   /// The `Null` type defined in 'dart:core'.
   InterfaceType get nullType => _getRawType(nullClass);
 
+  /// The `Record` type defined in 'dart:core'.
+  InterfaceType get recordType => _getRawType(recordClass);
+
   /// The `Type` type defined in 'dart:core'.
   InterfaceType get typeType => _getRawType(typeClass);
 

pkg/compiler/lib/src/elements/types.dart

@@ -2308,10 +2308,12 @@ abstract class DartTypes {
       //
       // TODO(50081): Reference rules to updated specification
       // https://github.com/dart-lang/language/blob/master/resources/type-system/subtyping.md#rules
-      //
-      // TODO(50081): record is subtype of interface `Record`.
-      if (s is RecordType) {
-        if (t is! RecordType) return false;
+
+      // Record Type/Record:
+      if (s is RecordType && t == commonElements.recordType) return true;
+
+      // Record Type/Record Type:
+      if (s is RecordType && t is RecordType) {
         if (s.shape != t.shape) return false;
         List<DartType> sFields = s.fields;
         List<DartType> tFields = t.fields;

pkg/compiler/lib/src/ir/visitors.dart

@@ -179,7 +179,7 @@ class DartTypeConverter extends ir.DartTypeVisitor<DartType> {
       for (final type in positional) visitType(type),
       for (final namedType in named) visitType(namedType.type)
     ].toList(growable: false);
-    return _dartTypes.recordType(shape, fields);
+    return _convertNullability(_dartTypes.recordType(shape, fields), node);
   }
 
   @override

sdk/lib/_internal/js_shared/lib/rti.dart

@@ -3003,10 +3003,12 @@ bool _isSubtype(Object? universe, Rti s, Object? sEnv, Rti t, Object? tEnv) {
   //
   // TODO(50081): Reference rules to updated specification
   // https://github.com/dart-lang/language/blob/master/resources/type-system/subtyping.md#rules
-  //
-  // TODO(50081): record is subtype of interface `Record`.
-  if (sKind == Rti.kindRecord) {
-    if (tKind != Rti.kindRecord) return false;
+
+  // Record Type/Record:
+  if (sKind == Rti.kindRecord && isRecordInterfaceType(t)) return true;
+
+  // Record Type/Record Type:
+  if (sKind == Rti.kindRecord && tKind == Rti.kindRecord) {
     return _isRecordSubtype(universe, s, sEnv, t, tEnv);
   }
 
@@ -3267,6 +3269,7 @@ bool isNullType(Rti t) =>
 bool isFunctionType(Rti t) => _Utils.isIdentical(t, TYPE_REF<Function>());
 bool isJsFunctionType(Rti t) =>
     _Utils.isIdentical(t, TYPE_REF<JavaScriptFunction>());
+bool isRecordInterfaceType(Rti t) => _Utils.isIdentical(t, TYPE_REF<Record>());
 
 class _Utils {
   static bool asBool(Object? o) => JS('bool', '#', o);