Pattern match cases that follow wildcard patterns aren't always marked as unreachable

[Yorick Peterse]

Please describe the bug

When one or more pattern match cases follow a case that uses a wildcard pattern, these patterns aren't always correctly marked as unreachable.

This issue also affects Gleam (gleam-lang/gleam#2651), suggesting it's a problem with the underlying algorithm from https://github.com/yorickpeterse/pattern-matching-in-rust.

The issue seems to be specific to literals, i.e. patterns that are treated as having an infinite range. The following works as expected:

class enum Letter {
  case A
  case B
  case C
  case D
}

class async Main {
  fn async main {
    match Letter.A {
      case A -> 'one'
      case B -> 'two'
      case _ -> 'else'
      case C -> 'three'
    }
  }
}

Please list the exact steps necessary to reproduce the bug

Save the following as test.inko:

class async Main {
  fn async main {
    match 42 {
      case 1 -> 'one'
      case 2 -> 'two'
      case _ -> 'else'
      case 3 -> 'three'
    }
  }
}

Now run inko check test.inko. This should produce a warning that the case 3 -> 'three' line is unreachable, but instead no warnings are produced.

Operating system

Fedora 39

Inko version

main

Rust version

1.77.1