Clear stale elements in an unresolved TypeName

BUG=#25855
[email protected]

Review URL: https://codereview.chromium.org/1745413002 .

Author: Brian Slesinsky

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

@@ -11633,6 +11633,7 @@ class TypeResolverVisitor extends ScopedVisitor {
   Object visitTypeName(TypeName node) {
     super.visitTypeName(node);
     Identifier typeName = node.name;
+    _setElement(typeName, null); // Clear old Elements from previous run.
     TypeArgumentList argumentList = node.typeArguments;
     Element element = nameScope.lookup(typeName, definingLibrary);
     if (element == null) {
@@ -11781,8 +11782,6 @@ class TypeResolverVisitor extends ScopedVisitor {
     if (!elementValid) {
       if (element is MultiplyDefinedElement) {
         _setElement(typeName, element);
-      } else {
-        _setElement(typeName, null);
       }
       typeName.staticType = _undefinedType;
       node.type = _undefinedType;
@@ -11847,7 +11846,6 @@ class TypeResolverVisitor extends ScopedVisitor {
               StaticWarningCode.NOT_A_TYPE, typeName, [typeName.name]);
         }
       }
-      _setElement(typeName, null);
       typeName.staticType = _dynamicType;
       node.type = _dynamicType;
       return null;
@@ -12348,25 +12346,19 @@ class TypeResolverVisitor extends ScopedVisitor {
   }
 
   /**
-   * If the given [element] is not `null`, set `staticElement` of the
-   * [typeName] to it.  If the [typeName] is a prefixed identifier, and the
-   * prefix can be resolved to a not `null` element, set also the
-   * `staticElement` of the prefix.
+   * Records the new Element for a TypeName's Identifier.
+   *
+   * A null may be passed in to indicate that the element can't be resolved.
+   * (During a re-run of a task, it's important to clear any previous value
+   * of the element.)
    */
   void _setElement(Identifier typeName, Element element) {
     if (typeName is SimpleIdentifier) {
-      if (element != null) {
-        typeName.staticElement = element;
-      }
+      typeName.staticElement = element;
     } else if (typeName is PrefixedIdentifier) {
-      if (element != null) {
-        typeName.identifier.staticElement = element;
-      }
+      typeName.identifier.staticElement = element;
       SimpleIdentifier prefix = typeName.prefix;
-      Element prefixElement = nameScope.lookup(prefix, definingLibrary);
-      if (prefixElement != null) {
-        prefix.staticElement = prefixElement;
-      }
+      prefix.staticElement = nameScope.lookup(prefix, definingLibrary);
     }
   }
 

pkg/analyzer/test/generated/resolver_test.dart

@@ -12,6 +12,8 @@ import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/context/context.dart';
+import 'package:analyzer/src/dart/ast/ast.dart'
+    show SimpleIdentifierImpl, PrefixedIdentifierImpl;
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/member.dart';
 import 'package:analyzer/src/dart/element/type.dart';
@@ -17074,6 +17076,30 @@ class TypeResolverVisitorTest {
     _listener.assertNoErrors();
   }
 
+  void test_visitTypeName_noParameters_noArguments_undefined() {
+    SimpleIdentifier id = AstFactory.identifier3("unknown")
+      ..staticElement = new _StaleElement();
+    TypeName typeName = new TypeName(id, null);
+    _resolveNode(typeName, []);
+    expect(typeName.type, UndefinedTypeImpl.instance);
+    expect(typeName.name.staticElement, null);
+    _listener.assertErrorsWithCodes([StaticWarningCode.UNDEFINED_CLASS]);
+  }
+
+  void test_visitTypeName_prefixed_noParameters_noArguments_undefined() {
+    SimpleIdentifier prefix = AstFactory.identifier3("unknownPrefix")
+      ..staticElement = new _StaleElement();
+    SimpleIdentifier suffix = AstFactory.identifier3("unknownSuffix")
+      ..staticElement = new _StaleElement();
+    TypeName typeName =
+        new TypeName(AstFactory.identifier(prefix, suffix), null);
+    _resolveNode(typeName, []);
+    expect(typeName.type, UndefinedTypeImpl.instance);
+    expect(prefix.staticElement, null);
+    expect(suffix.staticElement, null);
+    _listener.assertErrorsWithCodes([StaticWarningCode.UNDEFINED_CLASS]);
+  }
+
   void test_visitTypeName_parameters_arguments() {
     ClassElement classA = ElementFactory.classElement2("A", ["E"]);
     ClassElement classB = ElementFactory.classElement2("B");
@@ -17233,6 +17259,21 @@ class _SimpleResolverTest_localVariable_types_invoked
   }
 }
 
+/**
+ * Represents an element left over from a previous resolver run.
+ *
+ * A _StaleElement should always be replaced with either null or a new Element.
+ */
+class _StaleElement extends ElementImpl {
+  _StaleElement() : super("_StaleElement", -1);
+
+  @override
+  accept(_) => throw "_StaleElement shouldn't be visited";
+
+  @override
+  get kind => throw "_StaleElement's kind shouldn't be accessed";
+}
+
 /**
  * Shared infrastructure for [StaticTypeAnalyzer2Test] and
  * [StrongModeStaticTypeAnalyzer2Test].