Rewrite blocks of single operator into just a single operator.

lib/compiler/implementation/dart_backend/backend.dart

 // Copyright (c) 2012, 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.
 
 const bool REMOVE_ASSERTS = false;
 
 class ElementAst {
   final Node ast;
   final TreeElements treeElements;
 
@@ skipping 64 matching lines @@
         if (send !== null) {
           Element element = originalTreeElements[send];
           if (REMOVE_ASSERTS && element === compiler.assertMethod) {
             return true;
           }
         }
       }
       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()));
     }
 
     return rewriteFunctionExpression(node, rewriteBody(node.body));
   }
 }
 
 class DartBackend extends Backend {
   final List<CompilerTask> tasks;
@@ skipping 331 matching lines @@
 }
 
 compareElements(e0, e1) {
   int result = compareBy((e) => e.getLibrary().uri.toString())(e0, e1);
   if (result != 0) return result;
   return compareBy((e) => e.position().charOffset)(e0, e1);
 }
 
 List<Element> sortElements(Collection<Element> elements) =>
     sorted(elements, compareElements);