Fixes issues in string interpolation tests

frog/gen.dart

 // Copyright (c) 2011, 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.
 
 /**
  * Top level generator object for writing code and keeping track of
  * dependencies.
  *
  * Should have two compilation models, but only one implemented so far.
  *
@@ skipping 2095 matching lines @@
   visitSuperExpression(SuperExpression node) {
     return _makeSuperValue(node);
   }
 
   visitNullExpression(NullExpression node) {
     // TODO(jimhug): should be passing node.span
     // TODO(jimhug): Can we do better than var for the type?
     return new EvaluatedValue(world.varType, null, 'null', null);
   }
 
+  _isUnaryIncrement(Expression item) {
+    if (item is UnaryExpression) {
+      UnaryExpression u = item;
+      return u.op.kind == TokenKind.INCR || u.op.kind == TokenKind.DECR;
+    } else {
+      return false;
+    }
+  }
+
   visitLiteralExpression(LiteralExpression node) {
     // All Literal types are filled in at parse time, so no need to resolve.
     var type = node.type.type;
     assert(type != null);
 
     if (node.value is List) {
       var items = [];
       for (var item in node.value) {
         var val = visitValue(item);
         val.invoke(this, 'toString', item, Arguments.EMPTY);
 
         // TODO(jimhug): Ensure this solves all precedence problems.
+        // TODO(jmesserly): We could be smarter about prefix/postfix, but we'd
+        // need to know if it will compile to a ++ or to some sort of += form.
         var code = val.code;
-        if (item is BinaryExpression || item is ConditionalExpression) {
+        if (item is BinaryExpression || item is ConditionalExpression
+            || item is PostfixExpression || _isUnaryIncrement(item)) {
           code = '(${code})';
         }
         items.add(code);
       }
       return new Value(type, '(${Strings.join(items, " + ")})', node.span);
     }
 
     var text = node.text;
     // TODO(jimhug): Confirm that only strings need possible translation
     if (type.isString) {
@@ skipping 132 matching lines @@
       result.add(new Value(world.varType, '\$$i', null, /*needsTemp:*/false));
     }
     for (int i = bareCount; i < length; i++) {
       var name = getName(i);
       if (name == null) name = '\$$i';
       result.add(new Value(world.varType, name, null, /*needsTemp:*/false));
     }
     return new Arguments(nodes, result);
   }
 }