Strict equality CanEqual derivation fails for classes in which type argument is not used for equality

Compiler version

Scala 3.1.1

Minimized code

import scala.language.strictEquality

case class MyClass[A](value: String)(val a: A) derives CanEqual

class Something {}

val a = MyClass[Something]("some")(new Something())
val b = MyClass[Something]("some")(new Something())

println(a == b)

Output

Values of types Playground.MyClass[Playground.Something] and Playground.MyClass[Playground.Something] cannot be compared with == or !=.
I found:

    Playground.MyClass.derived$CanEqual[Playground.Something, Playground.Something](
      /* missing */summon[CanEqual[Playground.Something, Playground.Something]]
    )

But no implicit values were found that match type CanEqual[Playground.Something, Playground.Something].

Expectation

Something is not part of case class universal equality check so it shouldn’t be part of multiversal equality constraint either

[SimY4]

@spameggo you need to enable strict quality via:

import scala.language.strictEquality

[bishabosha]

Something is not part of case class universal equality check so it shouldn’t be part of multiversal equality constraint either

ok so in this case you would want a feature change so that CanEqual derivation can analyse the equals method - this is hard in general, but making it specialised for this one use case of “if user does not define custom equals, and generic type parameter does not appear in primary constructor of case class” could be possible