Various constant checks.

pkg/front_end/lib/src/fasta/kernel/body_builder.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.
 
 library fasta.body_builder;
 
 import '../fasta_codes.dart'
     show FastaMessage, codeExpectedButGot, codeExpectedFunctionBody;
 
 import '../parser/parser.dart' show FormalParameterType, MemberKind, optional;
@@ skipping 1528 matching lines @@
   void handleVoidKeyword(Token token) {
     debugEvent("VoidKeyword");
     push(const VoidType());
   }
 
   @override
   void handleAsOperator(Token operator, Token endToken) {
     debugEvent("AsOperator");
     DartType type = pop();
     Expression expression = popForValue();
-    push(new KernelAsExpression(expression, type)
-      ..fileOffset = offsetForToken(operator));
+    if (constantExpressionRequired) {
+      push(buildCompileTimeError(
+          "Not a constant expression.", operator.charOffset));
+    } else {
+      push(new KernelAsExpression(expression, type)
+        ..fileOffset = offsetForToken(operator));
+    }
   }
 
   @override
   void handleIsOperator(Token operator, Token not, Token endToken) {
     debugEvent("IsOperator");
     DartType type = pop();
     Expression operand = popForValue();
     bool isInverted = not != null;
     var offset = offsetForToken(operator);
     Expression isExpression = isInverted
         ? new KernelIsNotExpression(operand, type, offset)
         : new KernelIsExpression(operand, type)
       ..fileOffset = offset;
     if (operand is VariableGet) {
       typePromoter.handleIsCheck(isExpression, isInverted, operand.variable,
           type, functionNestingLevel);
     }
-    push(isExpression);
+    if (constantExpressionRequired) {
+      push(buildCompileTimeError(
+          "Not a constant expression.", operator.charOffset));
+    } else {
+      push(isExpression);
+    }
   }
 
   @override
   void handleConditionalExpression(Token question, Token colon) {
     debugEvent("ConditionalExpression");
     Expression elseExpression = popForValue();
     Expression thenExpression = popForValue();
     Expression condition = popForValue();
     push(new KernelConditionalExpression(
         condition, thenExpression, elseExpression));
@@ skipping 1322 matching lines @@
 
   Expression buildSimpleRead() {
     return handleAssignment(false);
   }
 
   Expression buildForEffect() {
     return handleAssignment(true);
   }
 
   Expression handleAssignment(bool voidContext) {
+    if (helper.constantExpressionRequired) {
+      return helper.buildCompileTimeError(
+          "Not a constant expression.", offsetForToken(token));
+    }
     if (identical("=", assignmentOperator)) {
       return accessor.buildAssignment(value, voidContext: voidContext);
     } else if (identical("+=", assignmentOperator)) {
       return accessor.buildCompoundAssignment(plusName, value,
           offset: offsetForToken(token), voidContext: voidContext);
     } else if (identical("-=", assignmentOperator)) {
       return accessor.buildCompoundAssignment(minusName, value,
           offset: offsetForToken(token), voidContext: voidContext);
     } else if (identical("*=", assignmentOperator)) {
       return accessor.buildCompoundAssignment(multiplyName, value,
@@ skipping 319 matching lines @@
     if (starToken == null) {
       return AsyncMarker.Async;
     } else {
       assert(identical(starToken.stringValue, "*"));
       return AsyncMarker.AsyncStar;
     }
   } else {
     return internalError("Unknown async modifier: $asyncToken");
   }
 }