Spurious implicit argument ambiguity #7999
Description
minimized code
trait TC[F[_]]
object TC {
implicit def instance1: TC[[x] =>> Int => x] = new TC[[x] =>> Int => x] {}
implicit def instance2: TC[List] = new TC[List] {}
}
case class Foo[F[_], A](value: F[A]) {
def bar(other: Foo[F, A])(implicit F: TC[F]): Foo[F, A] = other
}
val xs = List(1, 2, 3)
def foo1 = Foo(xs).bar(Foo(xs))
def foo2 = Foo(xs).bar(foo1)
def foo3 = Foo(xs).bar(Foo(xs)).bar(Foo(xs))
def foo4 = Foo(xs).bar(Foo(xs).bar(Foo[List, Int](xs)))
def foo5 = Foo(xs).bar(Foo(xs).bar(Foo(xs)))Compilation output
-- Error: Foo.scala:17:43 ------------------------------------------------------
17 |def foo5 = Foo(xs).bar(Foo(xs).bar(Foo(xs)))
| ^
|ambiguous implicit arguments: both method instance1 in object TC and method instance2 in object TC match type TC[F] of parameter F of method bar in class Foo
1 error foundexpectation
This is another attempt to minimize something I'm running into in the Cats tests. As in #7993 the Scala 2 equivalent compiles as expected.
It might be worth noting that if instance1 is TC[Option] or even TC[[x] =>> x => Int], Dotty has no problem with this. I tried minimizing with my own trait Func[-A, +B] but couldn't get it to error.