[js_interop] No error to tear off the primary construcror of a JS ointerop type

[sgrekhov]

Thanks to @eernstg for pointing on this. There's no error if a primary constructor of a JS interop type is torn off.

For example there is no expected errors in the test below.

import 'dart:js_interop';

extension type ET._(JSObject _) implements JSObject {
}

@JS("ET")
extension type ET2(JSObject _) implements JSObject {
}

extension type ET3.p(JSObject _) implements JSObject {
}

main() {
  var c1 = ET._;
//         ^^^^^
// [analyzer] unspecified
// [web] unspecified

  var c2 = ET2.new;
//         ^^^^^^^
// [analyzer] unspecified
// [web] unspecified

  var c3 = ET3.p;
//         ^^^^^
// [analyzer] unspecified
// [web] unspecified
}

cc @srujzs
Dart SDK version: 3.10.0-edge.9f2218e4509210576abecc79d7184c94a3ad0e26 (main) (Fri Aug 8 20:46:19 2025 -0700) on "linux_x64"

[sgrekhov]

I believe I'm wrong here. Primary constructor of JS interop type is not external and therefore can be torn off. Sorry for the noise.

[srujzs]

Primary constructor of JS interop type is not external and therefore can be torn off.

Indeed. This applies to any other non-externals as well.

[eernstg]

Oh, of course. But then it should be possible to use the torn-off primary constructor (in particular, it should have a static type like TheExtensionType Function(RepresentationType) and a run-time type of RepresentationType Function(RepresentationType), and it should just return its argument).