fix inference of object members when a method has no target

we incorrectly thought `toString()` was a call to `Object.toString()`

See dart-archive/dev_compiler#349 for more context

[email protected]

Review URL: https://codereview.chromium.org//1368793004 .

Author: John Messerly

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

@@ -1762,6 +1762,15 @@ class StaticTypeAnalyzer extends SimpleAstVisitor<Object> {
    * being called is one of the object methods.
    */
   bool _inferMethodInvocationObject(MethodInvocation node) {
+    // If we have a call like `toString()` don't infer it.
+    //
+    // Either: it's really `this.toString()` and we shouldn't need inference,
+    // or it's a call to a function that happens to be called `toString()` and
+    // we shouldn't infer.
+    if (node.target == null) {
+      return false;
+    }
+
     // Object methods called on dynamic targets can have their types improved.
     String name = node.methodName.name;
     MethodElement inferredElement =

pkg/analyzer/test/generated/resolver_test.dart

@@ -12172,6 +12172,20 @@ main() {
         code, typeProvider.dynamicType, typeProvider.intType);
   }
 
+  void test_localVariableInference_declaredType_disabled_for_toString() {
+    String name = 'toString';
+    String code = '''
+main() {
+  dynamic $name = () => null;
+  $name(); // marker
+}''';
+    SimpleIdentifier identifier = _findMarkedIdentifier(code, "$name = ");
+    expect(identifier.staticType, typeProvider.dynamicType);
+    SimpleIdentifier call = _findMarkedIdentifier(code, "(); // marker");
+    expect(call.staticType, typeProvider.dynamicType);
+    expect((call.parent as Expression).staticType, typeProvider.dynamicType);
+  }
+
   void test_localVariableInference_noInitializer_disabled() {
     String code = r'''
 main() {