[rs2bril] Duplicate variable names with different types compiled incorrectly.

[oflatt]

Rust files that re-use a name with a different type cause the rs2bril compiler to generate ill-typed bril.

Example:

fn main() {
  let x: f64 = 2.0;
  let x: i64 = 2;
}

[Pat-Lafon]

What bril code would you expect this to generate?

@main() {
  x: float = const 2.0;
  x: int = const 2;
}

We could generate this, but:

❯ bril2json < dupe.bril | brilck
new type int for x conflicts with old type float

(This might be a limitation of the type checking of brilck/brilirs to be fair)

[oflatt]

I wasn't sure if it's a limitation of type checking or an intended restriction.
One way to get around this is to generate fresh names for each x

[Pat-Lafon]

Hmm, it could work, but note that fresh names are tricky because I will now need to construct a control flow graph to understand what to re-write later uses of x to. Maybe one can show in most/all well-typed rust programs that one x dominates the other?

Somewhat unrelated but a fun example of bril typing that is probably not well supported(except by brili)

@main(cond: bool) {
  br cond .there .here;
.here:
  x: int = const 2;
  jmp .end;
.there:
  x: bool = const false;
.end:
  print x;
}

[oflatt]

Could we do the renaming over the rust ast?

Alternatively a lightweight solution for now that would be a lot better is to throw an error

[Pat-Lafon]

Hmm, I've punted and taken your solution of just throwing an error. Hopefully this isn't too limiting in terms of what rust programs are not accepted. There are probably better solutions.

[oflatt]

I'm perfectly happy with that solution, thanks for putting so much effort into improving it!