dart2js: Make functions that appear to be unreachable throw.

sdk/lib/_internal/js_runtime/lib/js_helper.dart

Index: sdk/lib/_internal/js_runtime/lib/js_helper.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/js_helper.dart b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
index 2a91a2e34eb8247d1cd3d27c368125f8aa4b176a..91049cda0fe66872d542cdc2d79fdb2ac2b06f45 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
@@ -2396,8 +2396,12 @@ abstract class Closure implements Function {
                      jsArguments,
                      String propertyName) {
     JS_EFFECT(() {

[Siggi Cherem (dart-lang), 2015/09/04 17:46:23]

When we declare JS_EFFECT, does it mean that we ignore the rest of the possible
effects in the body of this function during type-inference?

Or we add these because we can't otherwise see the effects within the `JS`
blocks below?

(I assume it's more the latter? If so, would it be worth moving the JS_EFFECT
block down and have one next to each of the expressions that causes the effect?)

[sra1, 2015/09/04 21:01:53]

No.
Yes.
JS_EFFECT pretends the code is called in resolution and type inference but omits
the code in building the IR.
It is almost the same as writing  if (false) { ... }
but I assume that resolution and type inference might one day see through that.

I'd be happy to use a different mechanism but it is less painful that writing
special case code to have the same effect in resolution, and type inference.

-      BoundClosure.receiverOf(JS('BoundClosure', 'void 0'));
-      BoundClosure.selfOf(JS('BoundClosure', 'void 0'));
+      // The functions are called here to model the calls from JS forms below.
+      // The types in the JS forms in the arguments are propagated in type
+      // inference.
+      BoundClosure.receiverOf(JS('BoundClosure', '0'));

[Siggi Cherem (dart-lang), 2015/09/04 17:46:23]

what's the reason you need to change `void 0` to 0?

[sra1, 2015/09/04 21:01:52]

I don't need to.  'void 0' is just as arcane as '0'.
I can change them back.

[Siggi Cherem (dart-lang), 2015/09/04 21:04:30]

no need, just wanted to make sure I didn't miss anything important.

+      BoundClosure.selfOf(JS('BoundClosure', '0'));
+      getType(JS('int', '0'));
     });
     // TODO(ahe): All the place below using \$ should be rewritten to go
     // through the namer.