Elements. Add LibraryElement2.getXyz(name) methods.

Change-Id: I51a5d5bcf4a2837ae2f891eca15f3769dadcf54e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/396627
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

pkg/analyzer/lib/dart/element/element2.dart

@@ -1528,6 +1528,35 @@ abstract class LibraryElement2 implements Element2, Annotatable {
 
   /// Returns the class defined in this library that has the given [name].
   ClassElement2? getClass2(String name);
+
+  /// Returns the enum defined in this library that has the given [name].
+  EnumElement2? getEnum2(String name);
+
+  /// Returns the extension defined in this library that has the given [name].
+  ExtensionElement2? getExtension(String name);
+
+  /// Returns the extension type defined in this library that has the
+  /// given [name].
+  ExtensionTypeElement2? getExtensionType(String name);
+
+  /// Returns the getter defined in this library that has the given [name].
+  GetterElement? getGetter(String name);
+
+  /// Returns the mixin defined in this library that has the given [name].
+  MixinElement2? getMixin2(String name);
+
+  /// Returns the setter defined in this library that has the given [name].
+  SetterElement? getSetter(String name);
+
+  /// Returns the function defined in this library that has the given [name].
+  TopLevelFunctionElement? getTopLevelFunction(String name);
+
+  /// Returns the top-level variable defined in this library that has the
+  /// given [name].
+  TopLevelVariableElement2? getTopLevelVariable(String name);
+
+  /// Returns the type alias defined in this library that has the given [name].
+  TypeAliasElement2? getTypeAlias(String name);
 }
 
 /// An `export` directive within a library fragment.

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

@@ -6838,12 +6838,7 @@ class LibraryElementImpl extends ElementImpl
 
   @override
   ClassElement2? getClass2(String name) {
-    for (var class_ in classes) {
-      if (class_.name3 == name) {
-        return class_;
-      }
-    }
-    return null;
+    return _getElementByName(classes, name);
   }
 
   EnumElement? getEnum(String name) {
@@ -6856,6 +6851,26 @@ class LibraryElementImpl extends ElementImpl
     return null;
   }
 
+  @override
+  EnumElement2? getEnum2(String name) {
+    return _getElementByName(enums, name);
+  }
+
+  @override
+  ExtensionElement2? getExtension(String name) {
+    return _getElementByName(extensions, name);
+  }
+
+  @override
+  ExtensionTypeElement2? getExtensionType(String name) {
+    return _getElementByName(extensionTypes, name);
+  }
+
+  @override
+  GetterElement? getGetter(String name) {
+    return _getElementByName(getters, name);
+  }
+
   MixinElement? getMixin(String name) {
     for (var unitElement in units) {
       var element = unitElement.getMixin(name);
@@ -6866,6 +6881,31 @@ class LibraryElementImpl extends ElementImpl
     return null;
   }
 
+  @override
+  MixinElement2? getMixin2(String name) {
+    return _getElementByName(mixins, name);
+  }
+
+  @override
+  SetterElement? getSetter(String name) {
+    return _getElementByName(setters, name);
+  }
+
+  @override
+  TopLevelFunctionElement? getTopLevelFunction(String name) {
+    return _getElementByName(functions, name);
+  }
+
+  @override
+  TopLevelVariableElement2? getTopLevelVariable(String name) {
+    return _getElementByName(topLevelVariables, name);
+  }
+
+  @override
+  TypeAliasElement2? getTypeAlias(String name) {
+    return _getElementByName(typeAliases, name);
+  }
+
   /// Return `true` if [reference] comes only from deprecated exports.
   bool isFromDeprecatedExport(ExportedReference reference) {
     if (reference is ExportedReferenceExported) {
@@ -6898,6 +6938,13 @@ class LibraryElementImpl extends ElementImpl
     }
     return prefixes.toList(growable: false);
   }
+
+  static T? _getElementByName<T extends Element2>(
+    List<T> elements,
+    String name,
+  ) {
+    return elements.firstWhereOrNull((e) => e.name3 == name);
+  }
 }
 
 class LibraryExportElementImpl extends _ExistingElementImpl