[interop] Add support for Intersection types

web_generator/lib/src/ast/types.dart

@@ -146,6 +146,41 @@ class UnionType extends DeclarationType {
   }
 }
 
+class IntersectionType extends DeclarationType {
+  final List<Type> types;
+
+  @override
+  bool isNullable = false;
+
+  @override
+  String declarationName;
+
+  IntersectionType({required this.types, required String name})
+      : declarationName = name;
+
+  @override
+  ID get id => ID(type: 'type', name: types.map((t) => t.id.name).join('&'));
+
+  @override
+  Declaration get declaration =>
+      _IntersectionDeclaration(name: declarationName, types: types);
+
+  @override
+  Reference emit([TypeOptions? options]) {
+    return TypeReference((t) => t
+      ..symbol = declarationName
+      ..isNullable = (options?.nullable ?? false) || isNullable);
+  }
+
+  @override
+  int get hashCode => Object.hashAllUnordered(types);
+
+  @override
+  bool operator ==(Object other) {
+    return other is TupleType && other.types.every(types.contains);
+  }
+}
+
 class HomogenousEnumType<T extends LiteralType, D extends Declaration>
     extends UnionType implements DeclarationType {
   final List<T> _types;
@@ -557,25 +592,27 @@ class _ConstructorDeclaration extends CallableDeclaration
   }
 }
 
-// TODO: Merge properties/methods of related types
-class _UnionDeclaration extends NamedDeclaration
+sealed class _UnionOrIntersectionDeclaration extends NamedDeclaration
     implements ExportableDeclaration {
   @override
   bool get exported => true;
 
   @override
-  ID get id => ID(type: 'union', name: name);
-
-  bool isNullable;
+  ID get id;
 
   List<Type> types;
 
   List<GenericType> typeParameters;
 
-  _UnionDeclaration(
+  @override
+  String name;
+
+  @override
+  String? dartName;
+
+  _UnionOrIntersectionDeclaration(
       {required this.name,
       this.types = const [],
-      this.isNullable = false,
       List<GenericType>? typeParams})
       : typeParameters = typeParams ?? [] {
     if (typeParams == null) {
@@ -588,26 +625,42 @@ class _UnionDeclaration extends NamedDeclaration
     }
   }
 
-  @override
-  String? dartName;
-
-  @override
-  String name;
-
-  @override
-  Spec emit([covariant DeclarationOptions? options]) {
+  Spec _emit(
+      {covariant DeclarationOptions? options,
+      bool extendTypes = false,
+      bool isNullable = false}) {
     options ??= DeclarationOptions();
 
     final repType =
         getLowestCommonAncestorOfTypes(types, isNullable: isNullable);
 
+    final extendees = <Type>[];
+    if (extendTypes) {
+      // check if any types are primitive
+      // TODO: We can be much smarter about this, but this works best so far
+      if (types.any((t) {
+            final jsAltType = getJSTypeAlternative(t);
+            return jsAltType is BuiltinType &&
+                _nonObjectRepTypeTypes.contains(jsAltType.name);
+          }) ||
+          (repType is BuiltinType && repType.name == 'JSAny')) {
+        extendees.add(
+            BuiltinType.primitiveType(PrimitiveType.any, isNullable: false));
+      } else {
+        extendees.addAll(types.map(getJSTypeAlternative));
+      }
+    } else {
+      extendees.add(repType);
+    }
+
     return ExtensionType((e) => e
       ..name = name
       ..primaryConstructorName = '_'
       ..representationDeclaration = RepresentationDeclaration((r) => r
         ..name = '_'
         ..declaredRepresentationType = repType.emit(options?.toTypeOptions()))
-      ..implements.addAll([repType.emit(options?.toTypeOptions())])
+      ..implements
+          .addAll(extendees.map((e) => e.emit(options?.toTypeOptions())))
       ..types
           .addAll(typeParameters.map((t) => t.emit(options?.toTypeOptions())))
       ..methods.addAll(types.map((t) {
@@ -719,3 +772,45 @@ class _EnumObjDeclaration extends NamedDeclaration
   @override
   ID get id => ID(type: 'enum-rep', name: name);
 }
+
+List<String> _nonObjectRepTypeTypes = [
+  'JSAny',
+  'JSString',
+  'JSBoolean',
+  'JSNumber',
+  'JSSymbol',
+  'JSBigInt'
+];
+
+class _IntersectionDeclaration extends _UnionOrIntersectionDeclaration {
+  @override
+  bool get exported => true;
+
+  @override
+  ID get id => ID(type: 'intersection', name: name);
+
+  _IntersectionDeclaration({required super.name, super.types}) : super();
+
+  @override
+  Spec emit([covariant DeclarationOptions? options]) {
+    return super._emit(options: options, extendTypes: true);
+  }
+}
+
+class _UnionDeclaration extends _UnionOrIntersectionDeclaration {
+  @override
+  bool get exported => true;
+
+  @override
+  ID get id => ID(type: 'union', name: name);
+
+  bool isNullable;
+
+  _UnionDeclaration({required super.name, super.types, this.isNullable = false})
+      : super();
+
+  @override
+  Spec emit([covariant DeclarationOptions? options]) {
+    return super._emit(options: options, isNullable: isNullable);
+  }
+}

web_generator/lib/src/interop_gen/transform/transformer.dart

@@ -1268,7 +1268,8 @@ class Transformer {
             nonNullableUnionTypes.length != unionTypes.length;
 
         if (nonNullableUnionTypes.singleOrNull case final singleTypeNode?) {
-          return _transformType(singleTypeNode, isNullable: shouldBeNullable);
+          return _transformType(singleTypeNode,
+              isNullable: shouldBeNullable || (isNullable ?? false));
         }
 
         final types = nonNullableUnionTypes.map<Type>(_transformType).toList();
@@ -1307,7 +1308,8 @@ class Transformer {
         final expectedId = ID(type: 'type', name: idMap.join('|'));
 
         if (typeMap.containsKey(expectedId.toString())) {
-          return typeMap[expectedId.toString()] as UnionType;
+          return (typeMap[expectedId.toString()] as UnionType)
+            ..isNullable = (isNullable ?? false);
         }
 
         final name =
@@ -1323,6 +1325,50 @@ class Transformer {
         });
         return unType..isNullable = shouldBeNullable;
 
+      case TSSyntaxKind.IntersectionType:
+        final intersectionType = type as TSIntersectionTypeNode;
+        final intersectionTypes = intersectionType.types.toDart;
+        final nonNullableIntersectionTypes = intersectionTypes
+            .where((t) =>
+                t.kind != TSSyntaxKind.UndefinedKeyword &&
+                !(t.kind == TSSyntaxKind.LiteralType &&
+                    (t as TSLiteralTypeNode).literal.kind ==
+                        TSSyntaxKind.NullKeyword))
+            .toList();
+        final shouldBeNullable =
+            nonNullableIntersectionTypes.length != intersectionTypes.length;
+
+        if (shouldBeNullable) {
+          return BuiltinType.primitiveType(PrimitiveType.never,
+              isNullable: isNullable);
+        }
+
+        if (nonNullableIntersectionTypes.singleOrNull
+            case final singleTypeNode?) {
+          return _transformType(singleTypeNode, isNullable: isNullable);
+        }
+
+        final types =
+            nonNullableIntersectionTypes.map<Type>(_transformType).toList();
+
+        final idMap = types.map((t) => t.id.name);
+        final expectedId = ID(type: 'type', name: idMap.join('&'));
+        if (typeMap.containsKey(expectedId.toString())) {
+          return (typeMap[expectedId.toString()] as IntersectionType)
+            ..isNullable = (isNullable ?? false);
+        }
+
+        final intersectionHash = AnonymousHasher.hashUnion(idMap.toList());
+        final name = 'AnonymousIntersection_$intersectionHash';
+
+        final un = IntersectionType(types: types, name: name);
+
+        final unType = typeMap.putIfAbsent(expectedId.toString(), () {
+          namer.markUsed(name);
+          return un;
+        });
+
+        return unType..isNullable = isNullable ?? shouldBeNullable;
       case TSSyntaxKind.TupleType:
         // tuple type is array
         final tupleType = type as TSTupleTypeNode;
@@ -2332,12 +2378,13 @@ class Transformer {
             for (final t in t.types.where((t) => t is! BuiltinType))
               t.id.toString(): t
           });
-        case final UnionType u:
+        case UnionType(types: final uTypes, declaration: final uDecl) ||
+              IntersectionType(types: final uTypes, declaration: final uDecl):
           filteredDeclarations.addAll({
-            for (final t in u.types.where((t) => t is! BuiltinType))
+            for (final t in uTypes.where((t) => t is! BuiltinType))
               t.id.toString(): t
           });
-          filteredDeclarations.add(u.declaration);
+          filteredDeclarations.add(uDecl);
         case final DeclarationType d:
           filteredDeclarations.add(d.declaration);
           break;

web_generator/lib/src/js/typescript.types.dart

@@ -87,6 +87,7 @@ extension type const TSSyntaxKind._(num _) {
 
   // types
   static const TSSyntaxKind UnionType = TSSyntaxKind._(192);
+  static const TSSyntaxKind IntersectionType = TSSyntaxKind._(193);
   static const TSSyntaxKind TypeReference = TSSyntaxKind._(183);
   static const TSSyntaxKind ArrayType = TSSyntaxKind._(188);
   static const TSSyntaxKind LiteralType = TSSyntaxKind._(201);
@@ -158,6 +159,13 @@ extension type TSUnionTypeNode._(JSObject _) implements TSTypeNode {
   external TSNodeArray<TSTypeNode> get types;
 }
 
+@JS('IntersectionTypeNode')
+extension type TSIntersectionTypeNode._(JSObject _) implements TSTypeNode {
+  @redeclare
+  TSSyntaxKind get kind => TSSyntaxKind.IntersectionType;
+  external TSNodeArray<TSTypeNode> get types;
+}
+
 @JS('TypeQueryNode')
 extension type TSTypeQueryNode._(JSObject _) implements TSTypeNode {
   @redeclare