Fix identifyWidgetExpression() for Flutter.

Probably a bit pessimistic approach, allow only cases that we know
to be valid and useful.

R=brianwilkerson@google.com

Bug: flutter/flutter-intellij#2714
Change-Id: I8835c03d919c1f00a986ff3ef677c7f69995682f
Reviewed-on: https://dart-review.googlesource.com/c/80985
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analysis_server/lib/src/utilities/flutter.dart

@@ -229,12 +229,18 @@ InstanceCreationExpression identifyNewExpression(AstNode node) {
 
 /**
  * Attempt to find and return the closest expression that encloses the [node]
- * and is a Flutter `Widget`.  Return `null` if nothing found.
+ * and is an independent Flutter `Widget`.  Return `null` if nothing found.
  */
 Expression identifyWidgetExpression(AstNode node) {
   for (; node != null; node = node.parent) {
     if (isWidgetExpression(node)) {
-      return node;
+      var parent = node.parent;
+      if (parent is ArgumentList ||
+          parent is ListLiteral ||
+          parent is NamedExpression && parent.expression == node ||
+          parent is Statement) {
+        return node;
+      }
     }
     if (node is ArgumentList || node is Statement || node is FunctionBody) {
       return null;

pkg/analysis_server/test/services/correction/assist_test.dart

@@ -5014,6 +5014,60 @@ class FakeFlutter {\r
     }
   }
 
+  test_flutterWrapWidget_OK_prefixedIdentifier_identifier() async {
+    addFlutterPackage();
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+abstract class Foo extends Widget {
+  Widget bar;
+}
+
+main(Foo foo) {
+  return foo./*caret*/bar;
+}
+''');
+    _setCaretLocation();
+    await assertHasAssist(DartAssistKind.FLUTTER_WRAP_GENERIC, '''
+import 'package:flutter/widgets.dart';
+
+abstract class Foo extends Widget {
+  Widget bar;
+}
+
+main(Foo foo) {
+  return widget(child: foo./*caret*/bar);
+}
+''');
+  }
+
+  test_flutterWrapWidget_OK_prefixedIdentifier_prefix() async {
+    addFlutterPackage();
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+abstract class Foo extends Widget {
+  Widget bar;
+}
+
+main(Foo foo) {
+  return /*caret*/foo.bar;
+}
+''');
+    _setCaretLocation();
+    await assertHasAssist(DartAssistKind.FLUTTER_WRAP_GENERIC, '''
+import 'package:flutter/widgets.dart';
+
+abstract class Foo extends Widget {
+  Widget bar;
+}
+
+main(Foo foo) {
+  return /*caret*/widget(child: foo.bar);
+}
+''');
+  }
+
   test_flutterWrapWidget_OK_singleLine1() async {
     addFlutterPackage();
     await resolveTestUnit('''

pkg/analysis_server/test/src/utilities/flutter_test.dart

@@ -90,22 +90,7 @@ var w = new Foo();
     expect(getWidgetPresentationText(w), isNull);
   }
 
-  test_identifyWidgetExpression_identifier() async {
-    await resolveTestUnit('''
-import 'package:flutter/widgets.dart';
-
-main() {
-  var text = new Text('abc');
-  text;
-}
-''');
-    {
-      Expression expression = findNodeAtString("text;");
-      expect(identifyWidgetExpression(expression), expression);
-    }
-  }
-
-  test_identifyWidgetExpression_instanceCreation() async {
+  test_identifyWidgetExpression_node_instanceCreation() async {
     await resolveTestUnit('''
 import 'package:flutter/widgets.dart';
 
@@ -155,7 +140,7 @@ class MyWidget extends StatelessWidget {
     }
   }
 
-  test_identifyWidgetExpression_invocation() async {
+  test_identifyWidgetExpression_node_invocation() async {
     await resolveTestUnit('''
 import 'package:flutter/widgets.dart';
 
@@ -185,7 +170,7 @@ Text createText(String txt) => new Text(txt);
     }
   }
 
-  test_identifyWidgetExpression_namedExpression() async {
+  test_identifyWidgetExpression_node_namedExpression() async {
     await resolveTestUnit('''
 import 'package:flutter/widgets.dart';
 
@@ -199,6 +184,50 @@ Text createEmptyText() => new Text('');
     expect(identifyWidgetExpression(childExpression), isNull);
   }
 
+  test_identifyWidgetExpression_node_prefixedIdentifier_identifier() async {
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+abstract class Foo extends Widget {
+  Widget bar;
+}
+
+main(Foo foo) {
+  foo.bar; // ref
+}
+''');
+    SimpleIdentifier bar = findNodeAtString('bar; // ref');
+    expect(identifyWidgetExpression(bar), bar.parent);
+  }
+
+  test_identifyWidgetExpression_node_prefixedIdentifier_prefix() async {
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+abstract class Foo extends Widget {
+  Widget bar;
+}
+
+main(Foo foo) {
+  foo.bar; // ref
+}
+''');
+    SimpleIdentifier foo = findNodeAtString('foo.bar');
+    expect(identifyWidgetExpression(foo), foo.parent);
+  }
+
+  test_identifyWidgetExpression_node_simpleIdentifier() async {
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+main(Widget widget) {
+  widget; // ref
+}
+''');
+    Expression expression = findNodeAtString('widget; // ref');
+    expect(identifyWidgetExpression(expression), expression);
+  }
+
   test_identifyWidgetExpression_null() async {
     await resolveTestUnit('''
 import 'package:flutter/widgets.dart';
@@ -222,6 +251,72 @@ Text createEmptyText() => new Text('');
     }
   }
 
+  test_identifyWidgetExpression_parent_argumentList() async {
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+main() {
+  var text = new Text('abc');
+  useWidget(text); // ref
+}
+
+void useWidget(Widget w) {}
+''');
+    Expression expression = findNodeAtString("text); // ref");
+    expect(identifyWidgetExpression(expression), expression);
+  }
+
+  test_identifyWidgetExpression_parent_expressionStatement() async {
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+main(Widget widget) {
+  widget; // ref
+}
+''');
+    Expression expression = findNodeAtString("widget; // ref");
+    expect(identifyWidgetExpression(expression), expression);
+  }
+
+  test_identifyWidgetExpression_parent_listLiteral() async {
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+main(Widget widget) {
+  return [widget]; // ref
+}
+''');
+    Expression expression = findNodeAtString("widget]; // ref");
+    expect(identifyWidgetExpression(expression), expression);
+  }
+
+  test_identifyWidgetExpression_parent_namedExpression() async {
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+main() {
+  var text = new Text('abc');
+  useWidget(child: text); // ref
+}
+
+void useWidget({Widget child}) {}
+''');
+    Expression expression = findNodeAtString("text); // ref");
+    expect(identifyWidgetExpression(expression), expression);
+  }
+
+  test_identifyWidgetExpression_parent_returnStatement() async {
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+main(Widget widget) {
+  return widget; // ref
+}
+''');
+    Expression expression = findNodeAtString("widget; // ref");
+    expect(identifyWidgetExpression(expression), expression);
+  }
+
   test_isWidget() async {
     await resolveTestUnit('''
 import 'package:flutter/widgets.dart';