When += (and similar operations) are converted to = + ,

frog/minfrog

 #!/usr/bin/env node
 //  ********** Library dart:core **************
 //  ********** Natives dart:core **************
 /**
  * Generates a dynamic call stub for a function.
  * Our goal is to create a stub method like this on-the-fly:
  *   function($0, $1, capture) { return this($0, $1, true, capture); }
  *
  * This stub then replaces the dynamic one on Function, with one that is
  * specialized for that particular function, taking into account its default
@@ skipping 3503 matching lines @@
   else {
     target = node.target.visit(this);
   }
   return target.invoke$4(this, name, position, this._makeArgs(node.arguments));
 }
 MethodGenerator.prototype.visitIndexExpression = function(node) {
   var target = this.visitValue(node.target);
   var index = this.visitValue(node.index);
   return target.invoke$4(this, ':index', node, new Arguments(null, [index]));
 }
+MethodGenerator.prototype._expressionNeedsParens = function(e) {
+  return ((e instanceof BinaryExpression) || (e instanceof ConditionalExpression) || (e instanceof PostfixExpression) || this._isUnaryIncrement(e));
+}
 MethodGenerator.prototype.visitBinaryExpression = function(node, isVoid) {
   var kind = node.op.kind;
   if (kind == 35/*TokenKind.AND*/ || kind == 34/*TokenKind.OR*/) {
     var x = this.visitTypedValue(node.x, $globals.world.nonNullBool);
     var y = this.visitTypedValue(node.y, $globals.world.nonNullBool);
     var code = ('' + x.get$code() + ' ' + node.op + ' ' + y.get$code());
     if (x.get$isConst() && y.get$isConst()) {
       var value = (kind == 35/*TokenKind.AND*/) ? x.get$actualValue() && y.get$actualValue() : x.get$actualValue() || y.get$actualValue();
       return EvaluatedValue.EvaluatedValue$factory($globals.world.nonNullBool, value, ('' + value), node.span);
     }
@@ skipping 33 matching lines @@
     var name = TokenKind.binaryMethodName(node.op.kind);
     if (node.op.kind == 49/*TokenKind.NE*/) {
       name = ':ne';
     }
     if (name == null) {
       $globals.world.internalError(('unimplemented binary op ' + node.op), node.span);
       return;
     }
     return x.invoke$4(this, name, node, new Arguments(null, [y]));
   }
+  else if ((assignKind != 0) && this._expressionNeedsParens(node.y)) {
+    return this._visitAssign(assignKind, node.x, new ParenExpression(node.y, node.y.span), node, to$call$1(null), isVoid);
+  }
   else {
     return this._visitAssign(assignKind, node.x, node.y, node, to$call$1(null), isVoid);
   }
 }
 MethodGenerator.prototype._visitAssign = function(kind, xn, yn, position, captureOriginal, isVoid) {
   if (captureOriginal == null) {
     captureOriginal = (function (x) {
       return x;
     })
     ;
@@ skipping 389 matching lines @@
   var $0;
   var type = node.type.type;
   if (!!(($0 = node.value) && $0.is$List())) {
     var items = [];
     var $$list = node.value;
     for (var $$i = node.value.iterator$0(); $$i.hasNext$0(); ) {
       var item = $$i.next$0();
       var val = this.visitValue(item);
       val.invoke$4(this, 'toString', item, Arguments.get$EMPTY());
       var code = val.get$code();
-      if ((item instanceof BinaryExpression) || (item instanceof ConditionalExpression) || (item instanceof PostfixExpression) || this._isUnaryIncrement(item)) {
+      if (this._expressionNeedsParens(item)) {
         code = ('(' + code + ')');
       }
       if ($eq(items.get$length(), 0) || ($ne(code, "''") && $ne(code, '""'))) {
         items.add$1(code);
       }
     }
     return new Value(type, ('(' + Strings.join(items, " + ") + ')'), node.span, true);
   }
   var text = node.text;
   if (type.get$isString()) {
@@ skipping 9324 matching lines @@
   $globals._NO_COLOR = '\u001b[0m';
   $globals._RED_COLOR = '\u001b[31m';
 }
 var const$0 = new EnvMap()/*const EnvMap()*/;
 var const$2 = new EmptyQueueException()/*const EmptyQueueException()*/;
 var const$3 = new _DeletedKeySentinel()/*const _DeletedKeySentinel()*/;
 var const$8 = new NoMoreElementsException()/*const NoMoreElementsException()*/;
 var $globals = {};
 $static_init();
 main();