Elements. Implement children2 for specific Element2 subclasses.

Change-Id: Ief3864287beecb811bfcc1754e8ebcb0f4ccfdbb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/390080
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/dart/element/element.dart

@@ -298,6 +298,11 @@ class ClassElementImpl extends ClassOrMixinElementImpl
     return null;
   }
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   @override
   set constructors(List<ConstructorElementImpl> constructors) {
     assert(!isMixinApplication);
@@ -821,6 +826,11 @@ class CompilationUnitElementImpl extends UriReferencedElementImpl
         ...topLevelVariables,
       ];
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   @override
   List<Fragment> get children3 => children.cast<Fragment>();
 
@@ -1345,6 +1355,11 @@ class ConstructorElementImpl extends ExecutableElementImpl
     }
   }
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   /// Return the constant initializers for this element, which will be empty if
   /// there are no initializers, or `null` if there was an error in the source.
   List<ConstructorInitializer> get constantInitializers {
@@ -1897,6 +1912,9 @@ class DynamicElementImpl extends ElementImpl implements TypeDefiningElement {
     setModifier(Modifier.SYNTHETIC, true);
   }
 
+  @override
+  List<Element2> get children2 => const [];
+
   @override
   ElementKind get kind => ElementKind.DYNAMIC;
 
@@ -2370,9 +2388,6 @@ abstract class ElementImpl implements Element, Element2 {
   @override
   List<Element> get children => const [];
 
-  @override
-  List<Element2> get children2 => children.cast<Element2>();
-
   /// The length of the element's code, or `null` if the element is synthetic.
   int? get codeLength => _codeLength;
 
@@ -3375,6 +3390,11 @@ class EnumElementImpl extends InterfaceElementImpl
     return null;
   }
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   List<FieldElementImpl> get constants {
     return fields.where((field) => field.isEnumConstant).toList();
   }
@@ -3657,6 +3677,11 @@ class ExtensionElementImpl extends InstanceElementImpl
         ...typeParameters,
       ];
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   @override
   String get displayName => name ?? '';
 
@@ -3777,6 +3802,11 @@ class ExtensionTypeElementImpl extends InterfaceElementImpl
     return null;
   }
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   @override
   ExtensionTypeElement2 get element => super.element as ExtensionTypeElement2;
 
@@ -3833,6 +3863,11 @@ class FieldElementImpl extends PropertyInducingElementImpl
   /// [name] at the given [offset].
   FieldElementImpl(super.name, super.offset);
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   @override
   FieldElement get declaration => this;
 
@@ -4689,6 +4724,14 @@ class FunctionElementImpl extends ExecutableElementImpl
   /// [nameOffset]. This is used for function expressions, that have no name.
   FunctionElementImpl.forOffset(int nameOffset) : super("", nameOffset);
 
+  @override
+  List<Element2> get children2 {
+    if (enclosingElement3 is LibraryFragment) {
+      return element.children2;
+    }
+    throw StateError('Not an Element2');
+  }
+
   @override
   ExecutableElement get declaration => this;
 
@@ -4815,6 +4858,12 @@ class GenericFunctionTypeElementImpl extends _ExistingElementImpl
         ...parameters,
       ];
 
+  @override
+  List<Element2> get children2 {
+    // TODO(scheglov): implement
+    throw UnimplementedError();
+  }
+
   @override
   GenericFunctionTypeElement2 get element =>
       throw UnsupportedError('This is not a fragment');
@@ -5651,6 +5700,9 @@ class LabelElementImpl extends ElementImpl implements LabelElement {
   /// `switch` member.
   LabelElementImpl(String super.name, super.nameOffset, this._onSwitchMember);
 
+  @override
+  List<Element2> get children2 => const [];
+
   @override
   String get displayName => name;
 
@@ -5807,6 +5859,20 @@ class LibraryElementImpl extends LibraryOrAugmentationElementImpl
         ..._partUnits,
       ];
 
+  @override
+  List<Element2> get children2 {
+    return [
+      ...classes,
+      ...extensions,
+      ...extensionTypes,
+      ...functions,
+      ...mixins,
+      ...typeAliases,
+      ...getters,
+      ...topLevelVariables,
+    ];
+  }
+
   @override
   List<ClassElement2> get classes {
     var declarations = <ClassElement2>{};
@@ -6295,6 +6361,11 @@ class LibraryExportElementImpl extends _ExistingElementImpl
     required this.uri,
   }) : super(null, exportKeywordOffset);
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('Not an Element2');
+  }
+
   @override
   LibraryElementImpl? get exportedLibrary {
     var uri = this.uri;
@@ -6359,6 +6430,11 @@ class LibraryImportElementImpl extends _ExistingElementImpl
     required this.uri,
   }) : super(null, importKeywordOffset);
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('Not an Element2');
+  }
+
   @override
   CompilationUnitElementImpl get enclosingElement3 {
     return super.enclosingElement3 as CompilationUnitElementImpl;
@@ -6651,6 +6727,9 @@ class LocalVariableElementImpl extends NonParameterVariableElementImpl
   /// [offset].
   LocalVariableElementImpl(super.name, super.offset);
 
+  @override
+  List<Element2> get children2 => const [];
+
   LocalVariableElementImpl2 get element2 => _element2;
 
   @override
@@ -7405,6 +7484,11 @@ class MethodElementImpl extends ExecutableElementImpl
   /// given [offset].
   MethodElementImpl(super.name, super.offset);
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   @override
   MethodElement get declaration => this;
 
@@ -7567,6 +7651,11 @@ class MixinElementImpl extends ClassOrMixinElementImpl
     return null;
   }
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   @override
   MixinElement2 get element => super.element as MixinElement2;
 
@@ -8075,6 +8164,9 @@ class NeverElementImpl extends ElementImpl implements TypeDefiningElement {
     setModifier(Modifier.SYNTHETIC, true);
   }
 
+  @override
+  List<Element2> get children2 => const [];
+
   @override
   ElementKind get kind => ElementKind.NEVER;
 
@@ -8337,6 +8429,9 @@ class ParameterElementImpl extends VariableElementImpl
   @override
   List<Element> get children => parameters;
 
+  @override
+  List<Element2> get children2 => const [];
+
   @override
   List<Fragment> get children3 => const [];
 
@@ -8582,6 +8677,11 @@ class PartElementImpl extends _ExistingElementImpl
     required this.uri,
   }) : super(null, -1);
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('Not an Element2');
+  }
+
   @override
   CompilationUnitElementImpl get enclosingUnit {
     var enclosingLibrary = enclosingElement3 as LibraryElementImpl;
@@ -8652,6 +8752,9 @@ class PrefixElementImpl extends _ExistingElementImpl implements PrefixElement {
   /// [nameOffset].
   PrefixElementImpl(String super.name, super.nameOffset, {super.reference});
 
+  @override
+  List<Element2> get children2 => const [];
+
   @override
   String get displayName => name;
 
@@ -8868,6 +8971,11 @@ class PropertyAccessorElementImpl extends ExecutableElementImpl
     return null;
   }
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   @override
   PropertyAccessorElement? get correspondingGetter {
     if (isGetter) {
@@ -9543,6 +9651,11 @@ class TopLevelVariableElementImpl extends PropertyInducingElementImpl
   /// the given [name] and [offset].
   TopLevelVariableElementImpl(super.name, super.offset);
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   @override
   TopLevelVariableElement get declaration => this;
 
@@ -9713,6 +9826,11 @@ class TypeAliasElementImpl extends _ExistingElementImpl
   /// The aliased type, might be `null` if not yet linked.
   DartType? get aliasedTypeRaw => _aliasedType;
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   @override
   String get displayName => name;
 
@@ -10035,6 +10153,11 @@ class TypeParameterElementImpl extends ElementImpl
     }
   }
 
+  @override
+  List<Element2> get children2 {
+    throw StateError('This is a fragment');
+  }
+
   @override
   List<Fragment> get children3 => const [];