Force a space after empty list literal.

lib/compiler/implementation/tree/unparser.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.
 
 // Returns null if no need to rename a node.
 typedef String Renamer(Node node);
 
 String unparse(Node node) {
   Unparser unparser = new Unparser();
   unparser.unparse(node);
@@ skipping 202 matching lines @@
 
   visitNewExpression(NewExpression node) {
     addToken(node.newToken);
     visit(node.send);
   }
 
   visitLiteralList(LiteralList node) {
     if (node.constKeyword !== null) add(node.constKeyword.value);
     visit(node.typeArguments);
     visit(node.elements);
+    // If list is empty, emit space after [] to disambiguate cases like []==[].
+    if (node.elements.isEmpty()) sb.add(' ');
   }
 
   visitModifiers(Modifiers node) => node.visitChildren(this);
 
   /**
    * Unparses given NodeList starting from specific node.
    */
   unparseNodeListFrom(NodeList node, Link<Node> from) {
     if (from.isEmpty()) return;
     String delimiter = (node.delimiter === null) ? "" : "${node.delimiter}";
@@ skipping 274 matching lines @@
       sb.add(' ');
     }
     visit(node.name);
     if (node.typeParameters !== null) {
       visit(node.typeParameters);
     }
     visit(node.formals);
     add(node.endToken.value);
   }
 }