Spurious access error inheriting from a generic Java class with a protected constructor

[retronym]

⚡ tail sandbox/{Test.java,sub.scala} && printf "\n" && javac -d /tmp sandbox/Test.java && scalac -d /tmp -cp /tmp sandbox/sub.scala
==> sandbox/Test.java <==
package p1;

public class Test {
    protected Test() {}
}
==> sandbox/sub.scala <==
package p2

class C extends p1.Test()

Add a type parameter:

⚡ tail sandbox/{Test.java,sub.scala} && printf "\n" && javac -d /tmp sandbox/Test.java && scalac -d /tmp -cp /tmp sandbox/sub.scala
==> sandbox/Test.java <==
package p1;

public class Test<T> {
    protected Test() {}
}
==> sandbox/sub.scala <==
package p2

class C extends p1.Test()

sandbox/sub.scala:3: error: constructor Test in class Test cannot be accessed in package p2
 Access to protected constructor Test not permitted because
 enclosing package p2 is not a subclass of
 class Test in package p1 where target is defined
class C extends p1.Test()
                   ^
one error found

[lrytz]

The error only shows if no type arguments are provided, i.e.,

package p2
class C extends p1.Test[String]()

compiles

[lrytz]

Maybe caused by a cycle (just a guess, I didn't look if that's actually the order of events in the typer): to infer the type argument in the supertype (p1.Test[Nothing]) the typer looks at the constructor call Test(), which triggers accessibility checking, which looks at the incomplete supertype.

[paulp]

Once known as SI-6617.

[paulp]

And then, in later years, as SI-10122.

[SethTisue]

closing as duplicate, then. scala/bug#6617, scala/bug#10122