Frontend: Constant evaluation allows extension methods.

[lrhn]

Example:

extension on Object {
  int operator~() => 42;
}

main() {
 const Object o = Object();
 const int x = ~o;
 print(x);
}

The front-end constant evaluator does not catch that we try to invoke an extension member here, but instead crashes. Backends report this crash, here the VM:

$ dart extbad.dart
Unhandled exception:
'file:///usr/local/google/home/lrn/dart/co/sdk/dev/extbad.dart': error: Invocation of _extension#0|~
#0      _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:305:19)
#1      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:172:12)

The constant evaluator should not allow ~ to be used in constant expression except when invoking the instance member ~ of int.

The specification is being updated to specify this clearly, but it has always been the intention that user code invocations cannot occur in constant expressions.

[johnniwinther]

@askeksa-google can you take a look at this?

[askeksa-google]

Fix in https://dart-review.googlesource.com/c/sdk/+/123247

Test case fails in the analyzer. Filed #39149 for the analyzer bug.