match expression ignores inline command

[antognini]

Minimized code

3.0.0-M3

object Inline1:
  inline def foo( i:Int): Int =
    inline if i == 0 then -1 
    else Math.abs(i)

  def bar(i:Int): Int = foo(i) // as expected, fails to compile
  //                    ^^^^^^
  // Cannot reduce `inline if` because its condition is not a constant value: i.==(0)


object Inline2:
  inline def foo( i:Int): Int =
    inline i match
      case 0     => -1
      case x:Int => Math.abs(x)
  
  def bar(i:Int): Int = foo(i) // a compilation error was expected, but none is reported

Expectation

inline is a command in Scala 3.0.0, not an implementation hint:
=> def bar() should fail in conjunction with inline match, as it does with inline if.

[odersky]

That's not how it is specified, and a lot of code relies on this behavior.

[SethTisue]

I think the current behavior is comprehensible, as follows. At compile time, case 0 isn't known to match, so the compiler proceeds to the next case, which does match. It may help to understand that here case 0 is a type test, not a runtime equality test. If it's the other semantics you wanted, inline if is available.

related: #13774 — there is some discussion there. It's probably better to discuss further on 13774 unless someone wants to make a case that this ticket is definitely different.