The protected keyword makes it impossible for the subclass to use the default value of the superclass constructor

[makingthematrix]

Compiler version

I was able to narrow down the time when the bug originated to somewhere between 3.3.0-RC1-bin-20221122-794818b-NIGHTLY and 3.3.0-RC1. The bug is still present in 3.3.0-RC2.

Minimized code

  class Foo protected (foo: Int = 0) { }
  class Bar extends Foo

Output

In Scala 3.2.1 the above code compiles.
Bar extends Foo without providing a value for foo, but there is the default value 0 in the superclass constructor so all is good.

In Scala 3.3.0-RC1/RC2 (but not yet in the nightly I specified above) it fails with:

[error]    |  class Bar extends Foo
[error]    |                    ^^^
[error]    |missing argument for parameter foo of constructor Foo in class Foo: (foo: Int): 
[error] one error found

It compiles again either if I remove protected from the superclass constructor, or if I provide the value for foo explicitly:

class Foo(foo: Int = 0) { } // this is ok
class Bar extends Foo 
// ---
class Foo protected (foo: Int = 0) { }
class Bar extends Foo(0) // this is ok

Expectation

The original minimized code should compile.

[SethTisue]

I'm curious which PR is responsible.

[soronpo]

I'm more curious how the community build and CI didn't catch this sort of thing

[mbovel]

Bisected to #16538.

[SethTisue]

fyi @dwijnand