Tests for `void`.

pkg/compiler/lib/src/typechecker.dart

Index: pkg/compiler/lib/src/typechecker.dart
diff --git a/pkg/compiler/lib/src/typechecker.dart b/pkg/compiler/lib/src/typechecker.dart
index e7d66cef0e0d71b7a5edee1523b749060058a5af..6306b197c69578d8759fbd0357d667f12be42132 100644
--- a/pkg/compiler/lib/src/typechecker.dart
+++ b/pkg/compiler/lib/src/typechecker.dart
@@ -652,7 +652,9 @@ class TypeCheckerVisitor extends Visitor<ResolutionDartType> {
     if (Elements.isUnresolved(element)) return const ResolutionDynamicType();
     if (element.isGenerativeConstructor) {
       type = const ResolutionDynamicType();
-      returnType = const ResolutionVoidType();
+      // TODO(floitsch): would be nice to have the voidType directly on
+      // commonElements.
+      returnType = new ResolutionVoidType(commonElements.objectClass);
 
       element.functionSignature.forEachParameter((ParameterElement parameter) {
         if (parameter.isInitializingFormal) {
@@ -1693,6 +1695,10 @@ class TypeCheckerVisitor extends Visitor<ResolutionDartType> {
 
     final Node expression = node.expression;
 
+    // TODO(floitsch): would be nice if the voidType was directly accessible
+    // from `commonElements`.
+    ResolutionVoidType voidType =
+        new ResolutionVoidType(commonElements.objectClass);
     // Executing a return statement return e; [...] It is a static type warning
     // if the type of e may not be assigned to the declared return type of the
     // immediately enclosing function.
@@ -1706,8 +1712,10 @@ class TypeCheckerVisitor extends Visitor<ResolutionDartType> {
               commonElements.futureType(types.flatten(expressionType));
           expressionType = futureOfFlattenedType;
         }
+        // TODO(floitsch): this is probably where we want to have the checks
+        // that `void` must not have a `return` unless it returns void.
         if (expectedReturnType.isVoid &&
-            !types.isAssignable(expressionType, const ResolutionVoidType())) {
+            !types.isAssignable(expressionType, voidType)) {
           reportTypeWarning(expression, MessageKind.RETURN_VALUE_IN_VOID);
         } else {
           checkAssignable(expression, expressionType, expectedReturnType);
@@ -1715,8 +1723,10 @@ class TypeCheckerVisitor extends Visitor<ResolutionDartType> {
       }
     } else if (currentAsyncMarker != AsyncMarker.SYNC) {
       // `return;` is allowed.
-    } else if (!types.isAssignable(
-        expectedReturnType, const ResolutionVoidType())) {
+    } else if (!types.isAssignable(expectedReturnType, voidType)) {
+      // TODO(floitsch): this is probably where we want to have the checks
+      // that `void` must not have a `return` unless it returns void.
+
       // Let f be the function immediately enclosing a return statement of the
       // form 'return;' It is a static warning if both of the following
       // conditions hold: