[analyzer] Failure in language/constants_2018/constant_types_test/04

[eernstg]

CL https://dart-review.googlesource.com/c/sdk/+/214644 changed said test such that it expects to use a type variable in the initializer list of a constant constructor as a type literal without error:

class C<X> {
  final t;
  const C(): t = X;
}

This used to be a compile-time error, but with dart-lang/language#1860 it is no longer an error (a type variable used as an expression is a potentially constant expression).

This is part of the constructor-tearoffs feature bundle and part of the work requested in #47150.

NB: Due to a glitch in Gerrit (which has been reported), the change does not cause any buildbots to turn red, and there will not be an approval for the failure. This issue would have been the one to mention in that approval.

[eernstg]

/cc @scheglov.

[scheglov]

Do we allow type variables only when constructor-tearoffs is enabled for the library? Or always?

[eernstg]

This is all part of the constructor-tearoffs feature bundle, so it should only be enabled there.

[srawlins]

tests/language/const/instantiated_function_constant_test.dart exercises this new rule too.

[scheglov]

It seems that type variables were already allowed as "potentially constant type expression" for null safety.
https://github.com/dart-lang/language/blob/master/accepted/2.12/nnbd/feature-specification.md#const-objects

So, my understanding is that now we enable them as "potentially constant expression" when constructor-tearoffs is enabled. This seems to fix the language test.

[scheglov]

https://dart-review.googlesource.com/c/sdk/+/215014

[eernstg]

enable them as "potentially constant expression" when constructor-tearoffs is enabled

Exactly, thanks!