Rewrite blocks of single operator into just a single operator.

lib/compiler/implementation/dart_backend/backend.dart

Index: lib/compiler/implementation/dart_backend/backend.dart
diff --git a/lib/compiler/implementation/dart_backend/backend.dart b/lib/compiler/implementation/dart_backend/backend.dart
index 0f9ec2b54a12308d9798526044d4b42cdb481b2d..e9af56a075b73bd0ec0d47a1505afc6f1a297342 100644
--- a/lib/compiler/implementation/dart_backend/backend.dart
+++ b/lib/compiler/implementation/dart_backend/backend.dart
@@ -82,13 +82,28 @@ class FunctionBodyRewriter extends CloningVisitor {
       return false;
     }
 
+    rewritTo(Statement statement) {

[Roman, 2012/09/21 12:10:27]

tryRewriteSingleStatementBlock?

[Anton Muhin, 2012/09/21 12:13:08]

There should be no references to single statement block as this will eventually
do all the kinds of rewrites.

And why try if it always returns something?

[Roman, 2012/09/21 12:16:00]

then just rewriteStatement?

side note: does 'try' mean 'sometimes return something'?

+      if (statement is Block) {
+        Link statements = statement.statements.nodes;
+        if (!statements.isEmpty() && statements.tail.isEmpty()) {
+          Statement single = statements.head;
+          bool isDeclaration =
+              single is VariableDefinitions || single is FunctionDeclaration;
+          if (!isDeclaration) return single;
+        }
+      }
+      return statement;
+    }
+
     rewriteBody(Statement body) {
       if (body is !Block) return visit(body);
       Block block = body;
       NodeList statements = block.statements;
       LinkBuilder<Statement> builder = new LinkBuilder<Statement>();
       for (Statement statement in statements.nodes) {
-        if (!shouldOmit(statement)) builder.addLast(visit(statement));
+        if (!shouldOmit(statement)) {
+          builder.addLast(visit(rewritTo(statement)));
+        }
       }
       return new Block(rewriteNodeList(statements, builder.toLink()));
     }