`uninitialized` accepted, but `_` isn't

[durban]

Compiler version

3.3.5

Minimized code

This works:

package com.example

class Foo {
  var bar: String =
    scala.compiletime.uninitialized
}

But this doesn't:

package com.example

class Foo {
  var bar: String =
    _
}

Output

[error] -- [E017] Syntax Error: ...
[error] 5 |    _
[error]    |    ^
[error]    |    Unbound placeholder parameter; incorrect use of _
[error]    |
[error]    | longer explanation available when compiling with `-explain`
[error] one error found

Expectation

I expected both to work.

[som-snytt]

With significant indentation, it looks like

class Foo {
  var bar: String = {
    _
  }
}

which errors the same way. It works with -no-indent.