Converting JSBoolean to bool fails in dart2js

[simolus3]

Consider this simple snippet:

import 'dart:js_interop';

void main() {
  print(globalContext.equals(globalContext).toDart);
}

As .equals is declared to return a JSBoolean, it needs to be converted to Dart with toDart. dart2js seems to disagree on that though, and pretends equals returns a bool directly:

> ~/bin/dart-sdk/dev/bin/dart compile js tool/repro.dart 
tool/repro.dart:4:45:
Error: The getter 'toDart' isn't defined for the class 'bool'.
  print(globalContext.equals(globalContext).toDart);
                                            ^^^^^^
Error: Compilation failed.

Happens on 3.3.0 stable and I've also tested this on 3.4.0-160.0.dev. Casting to bool works, but all the documentation very strongly discourages that.

[sigmundch]

cc @srujzs

I can repro locally, but oddly it doesn't cause an issue in dartpad, not sure why.

What's strange is that the public API is declared to return JSBoolean in dart:js_interop, but to return a bool on the patch-files (both js_shared and wasm).

[sigmundch]

(thanks @simolus3 for the nice short repro, BTW)

[srujzs]

Thanks for filing!

Yeah, it looks like the patch files use bool but the publicly-visible API uses JSBoolean. The tests in https://dart-review.googlesource.com/c/sdk/+/341140 must have sidestepped this issue on all the web compilers. I'm guessing the usage of identical in package:expect might have made this unintentionally work on dart2wasm, but not sure. This affects several other relational operators too like lessThan.

I'll upload a change. Not sure if this would be considered a breaking change, but we can discuss in the CL.

I can repro locally, but oddly it doesn't cause an issue in dartpad, not sure why.

I'm seeing a separate error in dartpad in the console:

Uncaught TypeError: Cannot read properties of null (reading 'postMessage')