Adjust method parameters in noSuchMethod helper stubs

lib/src/compiler/code_generator.dart

Index: lib/src/compiler/code_generator.dart
diff --git a/lib/src/compiler/code_generator.dart b/lib/src/compiler/code_generator.dart
index bdbdbc6b3531ba7a55484df8c5a2cbe873002ef6..591f35669a21eb0a1fd0fba41d8475bd40f88dc3 100644
--- a/lib/src/compiler/code_generator.dart
+++ b/lib/src/compiler/code_generator.dart
@@ -94,6 +94,7 @@ class CodeGenerator extends GeneralizingAstVisitor
   final _dartxVar = new JS.Identifier('dartx');
   final _runtimeLibVar = new JS.Identifier('dart');
   final namedArgumentTemp = new JS.TemporaryId('opts');
+  final positionalArgumentsTemp = new JS.TemporaryId('positionalArgs');
 
   final _hasDeferredSupertype = new HashSet<ClassElement>();
 
@@ -1409,13 +1410,13 @@ class CodeGenerator extends GeneralizingAstVisitor
   ///           new dart.InvocationImpl('eatFood', [food])));
   ///     }
   JS.Method _implementMockMethod(ExecutableElement method) {
-    var positionalArgs = <JS.Identifier>[]
+    var normalArgs = <JS.Identifier>[]
       ..addAll(
-          method.type.normalParameterNames.map((a) => new JS.Identifier(a)))
+          method.type.normalParameterNames.map((a) => new JS.Identifier(a)));
+    var optionalArgs = <JS.Identifier>[]
       ..addAll(
           method.type.optionalParameterNames.map((a) => new JS.Identifier(a)));
-
-    var fnArgs = positionalArgs.toList();
+    var fnArgs = <JS.Identifier>[]..addAll(normalArgs)..addAll(optionalArgs);
 
     var invocationProps = <JS.Property>[];
     addProperty(String name, JS.Expression value) {
@@ -1438,18 +1439,41 @@ class CodeGenerator extends GeneralizingAstVisitor
       }
     }
 
-    var fnBody =
+    var posDecl = js.statement('let # = #;',
+        [positionalArgumentsTemp, new JS.ArrayInitializer(normalArgs)]);
+
+    var fnBody = <JS.Statement>[posDecl];
+
+    if (optionalArgs.length > 0) {
+      final argTemp = new JS.TemporaryId('arg');
+      // Optional arguments must only be passed on to noSuchMethod if they were
+      // actually passed here. This code loops through them, pushing the ones
+      // that were actually passed.
+      var existenceCheckLoop = js.statement(
+          'for (let arg of #) { if (# !== void 0) { #.push(#); } }', [

[srawlins, 2016/08/01 18:30:38]

I think I need help on this line: `arg` needs to be the JS.TemporaryId from line
1448, but if I use:

'for (let # of #) { if (# !== void 0) { #.push(#); } }', and uncomment that arg
on line 1454, then ddc produces this error:

Error in MiniJsParser:
for (let # of #) { if (# !== void 0) { #.push(#); } }
         ^
         Expected ALPHA

#0      MiniJsParser.error (package:dev_compiler/src/js_ast/builder.dart:730:5)
#1      MiniJsParser.expectCategory
(package:dev_compiler/src/js_ast/builder.dart:693:30)
...

Any ideas?

+        //argTemp,
+        new JS.ArrayInitializer(optionalArgs),
+        argTemp,
+        positionalArgumentsTemp,
+        argTemp,
+      ]);
+      fnBody.add(existenceCheckLoop);
+    }
+
+    var nSMCall =
         js.call('this.noSuchMethod(new dart.InvocationImpl(#, #, #))', [
       _elementMemberName(method),
-      new JS.ArrayInitializer(positionalArgs),
+      positionalArgumentsTemp,
       new JS.ObjectInitializer(invocationProps)
     ]);
 
     if (!method.returnType.isDynamic) {
-      fnBody = js.call('#._check(#)', [_emitType(method.returnType), fnBody]);
+      nSMCall = js.call('#._check(#)', [_emitType(method.returnType), nSMCall]);
     }
 
-    var fn = new JS.Fun(fnArgs, js.statement('{ return #; }', [fnBody]),
+    fnBody.add(js.statement('return #', [nSMCall]));
+
+    var fn = new JS.Fun(fnArgs, js.statement('{ # }', [_statement(fnBody)]),
         typeParams: _emitTypeFormals(method.type.typeFormals));
 
     // TODO(jmesserly): generic type arguments will get dropped.