Adds typechecking of return values

frog/gen.dart

Index: frog/gen.dart
diff --git a/frog/gen.dart b/frog/gen.dart
index 90853e227f8d2a48bccaf6d502dccb0c666fb023..2d74b3a03e9eee334294de98b308ba0bae1cddea 100644
--- a/frog/gen.dart
+++ b/frog/gen.dart
@@ -1103,12 +1103,15 @@ class MethodGenerator implements TreeVisitor {
    */
   bool visitReturnStatement(ReturnStatement node) {
     if (node.value == null) {
+      // This is essentially "return null".
+      // It can't issue a warning because every type is nullable.

[jimhug, 2011/11/11 15:02:02]

Isn't there a TODO here to fix the language <smile>

       writer.writeln('return;');
     } else {
       if (method.isConstructor) {
         world.error('return of value not allowed from constructor', node.span);
       }
-      writer.writeln('return ${visitValue(node.value).code};');
+      var value = visitTypedValue(node.value, method.returnType);

[jimhug, 2011/11/11 15:02:02]

I love the fact that this is essentially your entire real change and all the
rest is just fixing errors caught by the better checking!

+      writer.writeln('return ${value.code};');
     }
     return true;
   }