Unable to call other trait methods in `impl Trait with ...`?

Development
1

This does not work:

trait UnderlyingBuffer {
  read_u8(Self, Int) -> Byte?
  read_u16_be(Self, Int) -> Int?
}

impl UnderlyingBuffer for Bytes with read_u8(self, idx : Int) -> Byte? {
  if idx < 0 || idx >= self.length() {
    return None
  }
  Some(self[idx])
}

impl UnderlyingBuffer for Bytes with read_u16_be(self, idx : Int) -> Int? {
  let b1 = self.read_u8(idx)?      // E4015: Type Bytes has no method read_u8
  let b2 = self.read_u8(idx + 1)?  // E4015: Type Bytes has no method read_u8
  b1.to_int().lsl(8).lor(b2.to_int())
}

Neither does this:

fn UnderlyingBuffer::read_u8(self : Bytes, idx : Int) -> Byte? {
  if idx < 0 || idx >= self.length() {
    return None
  }
  Some(self[idx])
}

fn UnderlyingBuffer::read_u16_be(self : Bytes, idx : Int) -> Int? {
  let b1 = self.read_u8(idx)?      // E4015: Type Bytes has no method read_u8
  let b2 = self.read_u8(idx + 1)?  // E4015: Type Bytes has no method read_u8
  b1.to_int().lsl(8).lor(b2.to_int())
}

While this, umm… it’s an ICE

impl UnderlyingBuffer for Bytes

fn read_u8(self : Bytes, idx : Int) -> Byte? {
  if idx < 0 || idx >= self.length() {
    return None
  }
  Some(self[idx])
}

fn read_u16_be(self : Bytes, idx : Int) -> Int? {
  let b1 = self.read_u8(idx)?
  let b2 = self.read_u8(idx + 1)?
  b1.to_int().lsl(8).lor(b2.to_int())
}

failed: moonc check -error-format json [...] -target wasm-gc
Fatal error: exception File "lib/xml/typing/toplevel_typer.ml", line 1343, characters 32-38: Assertion failed
error: failed when checking

This is the only way I found for it to work, but it’s too verbose IMHO:

fn UnderlyingBuffer::read_u16_be(self : Bytes, idx : Int) -> Int? {
  let b1 = UnderlyingBuffer::read_u8(self, idx)?
  let b2 = UnderlyingBuffer::read_u8(self, idx + 1)?
  Some(b1.to_int().lsl(8).lor(b2.to_int()))
}