Infer type of extract index expressions.

pkg/analyzer/lib/src/summary/link.dart

 // Copyright (c) 2016, 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.
 
 /**
  * This library is capable of producing linked summaries from unlinked
  * ones (or prelinked ones).  It functions by building a miniature
  * element model to represent the contents of the summaries, and then
  * scanning the element model to gather linked information and adding
  * it to the summary data structures.
@@ skipping 1773 matching lines @@
         case UnlinkedConstOperation.assignToRef:
           _doAssignToRef();
           break;
         case UnlinkedConstOperation.assignToProperty:
           _doAssignToProperty();
           break;
         case UnlinkedConstOperation.assignToIndex:
           _doAssignToIndex();
           break;
         case UnlinkedConstOperation.extractIndex:
-          stack.length -= 2;
-          // TODO(paulberry): implement.
-          stack.add(DynamicTypeImpl.instance);
+          _doExtractIndex();
           break;
         case UnlinkedConstOperation.invokeMethodRef:
           _doInvokeMethodRef();
           break;
         case UnlinkedConstOperation.invokeMethod:
           _doInvokeMethod();
           break;
         case UnlinkedConstOperation.cascadeSectionBegin:
           stack.add(stack.last);
           break;
@@ skipping 110 matching lines @@
 
   void _doConditional() {
     DartType elseType = stack.removeLast();
     DartType thenType = stack.removeLast();
     stack.removeLast();
     DartType type = _leastUpperBound(thenType, elseType);
     type = _dynamicIfNull(type);
     stack.add(type);
   }
 
+  void _doExtractIndex() {
+    stack.removeLast(); // index
+    DartType target = stack.removeLast();
+    stack.add(() {
+      if (target is InterfaceType) {
+        MethodElement method = target.lookUpMethod('[]', library);
+        if (method != null) {
+          return method.returnType;
+        }
+      }
+      return DynamicTypeImpl.instance;
+    }());
+  }
+
   void _doExtractProperty() {
     DartType target = stack.removeLast();
     String propertyName = _getNextString();
     stack.add(() {
       if (target is InterfaceType) {
         PropertyAccessorElement getter =
             target.lookUpGetter(propertyName, library);
         if (getter != null) {
           return getter.returnType;
         }
@@ skipping 2008 matching lines @@
           List<int> implicitFunctionTypeIndices) =>
       DynamicTypeImpl.instance;
 
   ReferenceableElementForLink getContainedName(String name) {
     return new NonstaticMemberElementForLink(_constNode);
   }
 
   @override
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }