Implement type inference of getters/setters based on inheritance.

pkg/analyzer/test/src/task/strong/front_end_inference_test.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 434 matching lines @@
   visitMapLiteral(MapLiteral node) {
     super.visitMapLiteral(node);
     if (node.typeArguments == null) {
       DartType type = node.staticType;
       if (type is InterfaceType) {
         _recordTypeArguments(node.offset, type.typeArguments);
       }
     }
   }
 
+  @override
+  visitMethodDeclaration(MethodDeclaration node) {
+    super.visitMethodDeclaration(node);
+    if (node.element.enclosingElement is ClassElement) {
+      if (node.isGetter && node.returnType == null) {
+        _recordTopType(node.name.offset, node.element.returnType);
+      }
+      if (node.isSetter) {
+        for (var parameter in node.parameters.parameters) {
+          if (parameter.element.hasImplicitType) {

[scheglov, 2017/06/18 23:03:43]

Would "parameter.type == null" work?
It would be consistent with the returnType check.

[Paul Berry, 2017/06/18 23:34:31]

I considered that too, but it wouldn't work because FormalParameter doesn't have
a getter `type`.  The reason is because of function-typed formal parameters,
which have `returnType` and `parameters` getters rather than a `type` getter.

I suppose I could have done:

  var parameterElement = parameter.element;
  if (parameterElement is SimpleFormalParameter && parameterElement.type ==
null)

But it seemed simpler to just use `hasImplicitType`.

I've added a comment explaining this.

[Paul Berry, 2017/06/19 18:18:27]

After further experimentation it turns out that ParameterElement.hasImplicitType
has a bug where it returns `true` for a function-typed parameter without an
explicit return type.  So this code is no good either until we fix the bug.

I'll send out a bug fix and add some more test cases.

+            _recordTopType(parameter.identifier.offset, parameter.element.type);
+          }
+        }
+      }
+    }
+  }
+
   visitMethodInvocation(MethodInvocation node) {
     super.visitMethodInvocation(node);
     if (node.typeArguments == null) {
       var inferredTypeArguments = _getInferredFunctionTypeArguments(
               node.function.staticType,
               node.staticInvokeType,
               node.typeArguments)
           .toList();
       if (inferredTypeArguments.isNotEmpty) {
         _recordTypeArguments(node.methodName.offset, inferredTypeArguments);
@@ skipping 99 matching lines @@
 
   /// Based on DDC code generator's `_recoverTypeArguments`
   Iterable<DartType> _recoverTypeArguments(FunctionType g, FunctionType f) {
     assert(identical(g.element, f.element));
     assert(g.typeFormals.isNotEmpty && f.typeFormals.isEmpty);
     assert(g.typeFormals.length + g.typeArguments.length ==
         f.typeArguments.length);
     return f.typeArguments.skip(g.typeArguments.length);
   }
 }