Add PrefixElement.scope to API.

Change-Id: Ie673f521301d6ddc1b40d86ef7c02544f07e53fb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/154160
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

pkg/analyzer/CHANGELOG.md

@@ -6,7 +6,7 @@
 * Added `InterfaceType.allSupertypes`.
 * Added `InterfaceType.asInstanceOf(ClassElement)`.
 * Removed deprecated internal `bogus-disabled` and `bogus-enabled`.
-* Added `Scope` and `LibraryElement.scope`.
+* Added `Scope`, `LibraryElement.scope`, and `PrefixElement.scope`.
 
 ## 0.39.12
 * Deprecated `canUseSummaries` in `DartSdkManager` constructor.

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

@@ -1579,6 +1579,11 @@ abstract class ParameterElement
 abstract class PrefixElement implements Element {
   @override
   LibraryElement get enclosingElement;
+
+  /// Return the name lookup scope for this import prefix. It consists of
+  /// elements imported into the enclosing library with this prefix. The
+  /// namespace combinators of the import directives are taken into account.
+  Scope get scope;
 }
 
 /// A variable that might be subject to type promotion.  This might be a local

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

@@ -6958,6 +6958,9 @@ mixin ParameterElementMixin implements ParameterElement {
 
 /// A concrete implementation of a [PrefixElement].
 class PrefixElementImpl extends ElementImpl implements PrefixElement {
+  /// The scope of this prefix, `null` if it has not been created yet.
+  PrefixScope _scope;
+
   /// Initialize a newly created method element to have the given [name] and
   /// [nameOffset].
   PrefixElementImpl(String name, int nameOffset) : super(name, nameOffset);
@@ -6992,6 +6995,9 @@ class PrefixElementImpl extends ElementImpl implements PrefixElement {
     return super.nameOffset;
   }
 
+  @override
+  Scope get scope => _scope ??= PrefixScope(this);
+
   @override
   T accept<T>(ElementVisitor<T> visitor) => visitor.visitPrefixElement(this);
 

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

@@ -7,6 +7,7 @@ import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/scope.dart';
 import 'package:analyzer/src/dart/ast/token.dart';
+import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/resolver/scope.dart' as impl;
 import 'package:meta/meta.dart';
 
@@ -26,3 +27,89 @@ class LibraryScope implements Scope {
     return _implScope.lookup(identifier, _libraryElement);
   }
 }
+
+class PrefixScope implements Scope {
+  final PrefixElement _element;
+  final Map<String, Element> _getters = {};
+  final Map<String, Element> _setters = {};
+
+  PrefixScope(this._element) {
+    for (var import in _element.enclosingElement.imports) {
+      if (import.prefix == _element) {
+        var elements = impl.NamespaceBuilder().getImportedElements(import);
+        elements.forEach(_add);
+      }
+    }
+  }
+
+  @override
+  Element lookup({@required String id, @required bool setter}) {
+    var map = setter ? _setters : _getters;
+    return map[id];
+  }
+
+  void _add(Element element) {
+    var setter = element is PropertyAccessorElement && element.isSetter;
+    _addTo(
+      map: setter ? _setters : _getters,
+      element: element,
+    );
+  }
+
+  void _addTo({
+    @required Map<String, Element> map,
+    @required Element element,
+  }) {
+    var id = element.displayName;
+
+    var existing = map[id];
+    if (existing != null && existing != element) {
+      map[id] = _merge(existing, element);
+      return;
+    }
+
+    map[id] = element;
+  }
+
+  Element _merge(Element existing, Element other) {
+    if (_isSdkElement(existing)) {
+      if (!_isSdkElement(other)) {
+        return other;
+      }
+    } else {
+      if (_isSdkElement(other)) {
+        return existing;
+      }
+    }
+
+    var conflictingElements = <Element>{};
+    _addElement(conflictingElements, existing);
+    _addElement(conflictingElements, other);
+
+    var definingLibrary = _element.enclosingElement;
+    return MultiplyDefinedElementImpl(
+      definingLibrary.context,
+      definingLibrary.session,
+      conflictingElements.first.name,
+      conflictingElements.toList(),
+    );
+  }
+
+  static void _addElement(
+    Set<Element> conflictingElements,
+    Element element,
+  ) {
+    if (element is MultiplyDefinedElementImpl) {
+      conflictingElements.addAll(element.conflictingElements);
+    } else {
+      conflictingElements.add(element);
+    }
+  }
+
+  static bool _isSdkElement(Element element) {
+    if (element is NeverElementImpl) {
+      return true;
+    }
+    return element.library.isInSdk;
+  }
+}

pkg/analyzer/lib/src/dart/resolver/scope.dart

@@ -666,6 +666,19 @@ class NamespaceBuilder {
     return Namespace(definedNames);
   }
 
+  /// Return elements imported with the given [element].
+  Iterable<Element> getImportedElements(ImportElement element) {
+    var importedLibrary = element.importedLibrary;
+
+    // If the URI is invalid.
+    if (importedLibrary == null) {
+      return [];
+    }
+
+    var map = _getExportMapping(importedLibrary);
+    return _applyCombinators(map, element.combinators).values;
+  }
+
   /// Add all of the names in the given [namespace] to the table of
   /// [definedNames].
   void _addAllFromNamespace(