dart2js: Properly construct rti ast templates.

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index caff14a5c4939db59614fe90b186142d52a80ae0..f210452a62ca79f4c87100395718d62112933112 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -3564,7 +3564,7 @@ class SsaBuilder extends NewResolvedVisitor {
         templates.add(rti.getTypeRepresentationWithPlaceholders(argument, (variable) {

[floitsch, 2015/05/20 13:48:18]

long line.

[herhut, 2015/05/20 14:27:59]

Done.

           HInstruction runtimeType = addTypeVariableReference(variable);
           inputs.add(runtimeType);
-        }));
+        }, firstPlaceholderIndex : inputs.length));

[floitsch, 2015/05/20 13:48:18]

No space after "firstPlaceholderIndex".

I would prefer if it was more explicit.
That is, create an `int placeholderIndex = 0` outside.
Then, in the closure:

  // The runtimeType has one placeholder.
  assert(...);  // If you can find an easy way to check.
  placeholderIndex++;
  inputs.add(runtimeType);
}, firstPlaceholderIndex: placeholderIndex;

[herhut, 2015/05/20 14:27:59]

This constructs a template with holes and the corresponding inputs that will
later fill these holes when we generate the code. So there is always a one to
one mapping between inputs and holes. That is why the length of the inputs is
always the correct starting value. 

Using an explicit counter decouples this on the surface but the underlying
dependency is still there. How about a comment?

       }
       // TODO(sra): This is a fresh template each time.  We can't let the
       // template manager build them.