Incorrectly constructed trees when inlining with bound type parameters

[anatoliykmetyuk]

minimized code

trait Foo { def f(x: Int): Any }

inline def f[T <: Foo]: T = (??? match {
  case t: T => t.f(10)
}).asInstanceOf[T]

@main def Test = f

Says:

-- Error: ../pg/i3.scala:4:18 --------------------------------------------------
4 |  case t: T => t.f(10)
  |               ^^^^^^^
  |     undefined: t.f # 1201: TermRef(TermRef(NoPrefix,val t),f) at frontend
one error found

expectation

It should compile.

[odersky]

The problem is that the type parameter to Test is instantiated to Nothing, which means the body of f can no longer be typed since it contains a selection t.f where t has type Nothing.

It's not quite clear what's the best remedy here:

• disallow all instantiations of type params of inline methods with a bottom type? This could make useful programs illegal.

• or try to improve the error message. But in light of all the situations where a Nothing type could creep in and mess things up it looks hard to do a complete job. And not sure it's worth it in light of the added complexity this would cause.

[odersky]

On hold until someone has figured out what to do here.

[odersky]

We now get:

  |               value f is not a member of Nothing

which is correct since the scrutinee ??? is of type Nothing.

If we fix the program to

rait Foo { def f(x: Int): Any }

inline def f[T <: Foo]: T = ((??? : Foo) match {
  case t: T => t.f(10)
}).asInstanceOf[T]

@main def Test = f

we get:

- Error: ../new/test.scala:7:17 -----------------------------------------------
7 |@main def Test = f
  |                 ^
  |f cannot be accessed as a member of (t : Nothing) from module class test$package$.
  |-----------------------------------------------------------------------------
  |Inline stack trace
  |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  |This location contains code that was inlined from test.scala:4
4 |  case t: T => t.f(10)
  |               ^^^
   -----------------------------------------------------------------------------
1 error found

This looks also correct to me.