2.13.2: @uncheckedVariance is ignored in type member definitions

[neko-kai]

reproduction steps

To reproduce execute:

git clone https://github.com/7mind/izumi.git
cd izumi
git checkout bug/no-unchecked-variance
sbt compile

problem

Unchecked variance annotations are ignored and variance errors abort compilation:

[error] izumi/distage/distage-core-api/src/main/scala/izumi/distage/model/definition/DIResource.scala:776:12: contravariant type RR occurs in invariant position in type [-RR, +EE, +AA]F0[RR @scala.annotation.unchecked.uncheckedVariance,EE @scala.annotation.unchecked.uncheckedVariance,AA @scala.annotation.unchecked.uncheckedVariance] of type F
[error]       type F[-RR, +EE, +AA] = F0[RR @v, EE @v, AA @v]
[error]            ^
[error] izumi/distage/distage-core-api/src/main/scala/izumi/distage/model/definition/DIResource.scala:801:12: contravariant type RR occurs in invariant position in type [-RR, +EE, +AA]F0[RR @scala.annotation.unchecked.uncheckedVariance,EE @scala.annotation.unchecked.uncheckedVariance,AA @scala.annotation.unchecked.uncheckedVariance] @scala.annotation.unchecked.uncheckedVariance of type F
[error]       type F[-RR, +EE, +AA] = F0[RR @v, EE @v, AA @v] @v
[error]            ^

Minimized example (https://scastie.scala-lang.org/NupT3nqjS6qGhHIIAYaA3A):

import scala.annotation.unchecked.uncheckedVariance

trait T {
  type F[+_]
}
object T {
  implicit def fromUnchecked[F0[_]]: T { type F[+A] = F0[A @uncheckedVariance] } = new T {
    type F[+A] = F0[A @uncheckedVariance]
  }
}

covariant type A occurs in invariant position in type [+A]F0[A @scala.annotation.unchecked.uncheckedVariance] of type F

expectation

Expected code to compile as in 2.13.1.

[neko-kai]

Unchecked variance annotation was prompted by buggy implicit search involving variant higher-kinded types, the bug still persist in 2.13.2 so trying to remove uncheckedVariance didn't work:

git clone https://github.com/7mind/izumi.git
cd izumi
git checkout bug/variant-implicit-search
sbt distage-core/test:compile

[error] izumi/distage/distage-core/src/test/scala/izumi/distage/injector/ZIOHasInjectionTest.scala:163:49: could not find implicit ResourceTag for ZIOHasInjectionTest.this.ResourceHasImpl[zio.ZIO]!
[error] could not find implicit value for Tag[ZIOHasInjectionTest.this.ResourceHasImpl[zio.ZIO]]. Did you forget to put on a Tag, TagK or TagKK context bound on one of the parameters in ZIOHasInjectionTest.this.ResourceHasImpl[zio.ZIO]? e.g. def x[T: Tag, F[_]: TagK] = ...
[error]
[error]
[error] <trace>:
[error]   deriving Tag for ZIOHasInjectionTest.this.ResourceHasImpl[zio.ZIO], dealiased: ZIOHasInjectionTest.this.ResourceHasImpl[zio.ZIO]:
[error]   succeeded for: ZIOHasInjectionTest.this.ResourceHasImpl[zio.ZIO]
[error]         make[Trait2].named("classbased").fromHas[ResourceHasImpl[ZIO]]
[error]                                                 ^
[error] izumi/distage/distage-core/src/test/scala/izumi/distage/injector/ZIOHasInjectionTest.scala:222:29: could not find implicit ResourceTag for ZIOHasInjectionTest.this.ResourceHasImpl[F]!
[error] could not find implicit value for Tag[ZIOHasInjectionTest.this.ResourceHasImpl[F]]. Did you forget to put on a Tag, TagK or TagKK context bound on one of the parameters in ZIOHasInjectionTest.this.ResourceHasImpl[F]? e.g. def x[T: Tag, F[_]: TagK] = ...
[error]
[error]
[error] <trace>:
[error]   deriving Tag for ZIOHasInjectionTest.this.ResourceHasImpl[F], dealiased: ZIOHasInjectionTest.this.ResourceHasImpl[F]:
[error]   succeeded for: ZIOHasInjectionTest.this.ResourceHasImpl[F]
[error]         make[Trait2].fromHas[ResourceHasImpl[F]]
[error]                             ^
[error] two errors found

I can't seem to find any workaround to compile this code under 2.13.2

[joroKr21]

I didn't know you can use @uncheckedVariance like that

[joroKr21]

@neko-kai can you open another issue for the implicit search problem?
Is it fixed in Dotty?

[neko-kai]

will do

[neko-kai]

@joroKr21 Posted - #11970, yes, it's fixed in Dotty.