WIP: Compute constant expressions in resolution.

pkg/compiler/lib/src/constant_system_dart.dart

Index: pkg/compiler/lib/src/constant_system_dart.dart
diff --git a/pkg/compiler/lib/src/constant_system_dart.dart b/pkg/compiler/lib/src/constant_system_dart.dart
index 4a15ac9aff7cba10487fe95cb9a8086619ee39ea..25adefb1f6060d04db817a7aaf8466489132746b 100644
--- a/pkg/compiler/lib/src/constant_system_dart.dart
+++ b/pkg/compiler/lib/src/constant_system_dart.dart
@@ -9,6 +9,9 @@ import 'compiler.dart' show
 import 'constants/constant_system.dart';
 import 'constants/values.dart';
 import 'dart_types.dart';
+import 'elements/elements.dart' show
+    ClassElement,
+    FieldElement;
 import 'tree/tree.dart' show
     DartString;
 
@@ -319,6 +322,22 @@ class EqualsOperation implements BinaryOperation {
   apply(left, right) => left == right;
 }
 
+class NotEqualsOperation implements BinaryOperation {
+  final String name = '!=';
+  const NotEqualsOperation();
+
+  @override
+  ConstantValue fold(ConstantValue left, ConstantValue right) {
+    BoolConstantValue result = const EqualsOperation().fold(left, right);
+    if (result != null) {
+      result = result.negate();
+    }
+    return result;
+  }
+
+  apply(left, right) => left != right;
+}
+
 class IdentityOperation implements BinaryOperation {
   final String name = '===';
   const IdentityOperation();
@@ -388,6 +407,7 @@ class DartConstantSystem extends ConstantSystem {
   final multiply = const MultiplyOperation();
   final negate = const NegateOperation();
   final not = const NotOperation();
+  final notEqual = const NotEqualsOperation();
   final shiftLeft = const ShiftLeftOperation();
   final shiftRight = const ShiftRightOperation();
   final subtract = const SubtractOperation();
@@ -437,6 +457,20 @@ class DartConstantSystem extends ConstantSystem {
         compiler.backend.typeImplementation.computeType(compiler.resolution));
   }
 
+  @override
+  ConstantValue createSymbol(Compiler compiler, String text) {
+    // TODO(johnniwinther): Create a backend agnostic value.
+    InterfaceType type = compiler.symbolClass.rawType;
+    ConstantValue argument = createString(new DartString.literal(text));
+    Map<FieldElement, ConstantValue> fields = <FieldElement, ConstantValue>{};
+    compiler.symbolImplementationClass.forEachInstanceField(
+        (ClassElement enclosingClass, FieldElement field) {
+      fields[field] = argument;
+    });
+    assert(fields.length == 1);
+    return new ConstructedConstantValue(type, fields);
+  }
+
   bool isInt(ConstantValue constant) => constant.isInt;
   bool isDouble(ConstantValue constant) => constant.isDouble;
   bool isString(ConstantValue constant) => constant.isString;