The implementation of compiling OR patterns is incorrect

[yorickpeterse]

Gleam uses the flatten_or function from https://github.com/yorickpeterse/pattern-matching-in-rust. I recently found out this implementation is incorrect, as it doesn't account for patterns such as foo or foo (i.e. OR patterns that bind variables in their branches). While such patterns are nonsensical (= they're always true), it would trigger a panic here.

The fix is to expand OR patterns earlier, before pushing bindings/wildcards out of the patterns. This is implemented here. The new setup could probably be improved performance wise, but as far as I can determine it works well enough.

For some additional background information, see inko-lang/inko#679 and inko-lang/inko#599 which is how I found out about this.

[michallepicki]

@lpil should this be fixed before 1.0 as well?

[lpil]

It doesn't have to be I don't think. I've not yet verified that this impacts us as we use or patterns in a limited way currently.

[yorickpeterse]

@lpil Patterns such as this are unlikely to be found in the field, as you'd have to write something like this (using Inko syntax here):

match whatever {
  case 10 -> ...
  case a or a -> ...
}

This means it's not urgent by any means, as in the worst case you'd just run into a panic 😃

[lpil]

Ah! Thank you! 💜