Support proper unparse of is and is!.

lib/compiler/implementation/tree/unparser.dart

Index: lib/compiler/implementation/tree/unparser.dart
diff --git a/lib/compiler/implementation/tree/unparser.dart b/lib/compiler/implementation/tree/unparser.dart
index 05b24260254451bb67f314f740ba13b5e4956b95..dc922882d01240cd834b166bfdad765f3255d26a 100644
--- a/lib/compiler/implementation/tree/unparser.dart
+++ b/lib/compiler/implementation/tree/unparser.dart
@@ -181,16 +181,28 @@ class Unparser implements Visitor {
 
 
   unparseSendPart(Send node) {
+    Operator op = node.selector.asOperator();
+    bool isCheck = op !== null && op.source.stringValue == 'is';
+    // is check requires trailing space if it's not is! form.

[ahe, 2012/05/29 13:40:07]

Not a proper sentence. First word should be capitalized.

[Anton Muhin, 2012/05/31 14:44:44]

Now obsolete.

+    bool requiresSpace = isCheck && node.arguments.head is! Send;

[ahe, 2012/05/29 13:40:07]

The style we use is this:

node.arguments.head is !Send

The space is before the !.

[Bob Nystrom, 2012/05/30 21:46:51]

This was a surprise to me. In SEA I think we all use "foo is! Foo". But indeed
there are twice as many uses of "is !" than "is! " in the repo. I will clarify
this in the style guide so we are consistently using "is !".

[Anton Muhin, 2012/05/31 14:44:44]

That was a surprise for me as well.

On 2012/05/30 21:46:51, Bob Nystrom wrote:

+
     if (node.isPrefix) {
       visit(node.selector);
     }
     if (node.receiver !== null) {
       visit(node.receiver);
-      if (node.selector is !Operator) sb.add('.');
+      if (op === null) {
+        sb.add('.');
+      } else if (isCheck) {
+        sb.add(' ');
+      }
     }
     if (!node.isPrefix) {
       visit(node.selector);
     }
+    if (requiresSpace) {

[ahe, 2012/05/29 13:40:07]

This expression:

1 is !Object

Is printed as:

1 is!Object

If you change this into "if (isCheck) {", the expression is printed correctly.
This makes the code simpler because you can remove two lines (186 and 187).

[Anton Muhin, 2012/05/31 14:44:44]

Yes, that was planned as I thought that preferred form is 'is!' and in this case
we can save on a space here.

On 2012/05/29 13:40:07, ahe wrote:

+      sb.add(' ');
+    }
   }
 
   visitSend(Send node) {