Crash in rustboot on bad type conversion in ret

[jyasskin]

Given:

fn mk_int() -> uint {
  let int i = 3;
  ret i;
}
fn main() {
}

Rustboot crashes with:

Fatal error: exception Assert_failure("boot/me/trans.ml", 2988, 6)
Raised at file "boot/me/trans.ml", line 2989, characters 6-652
Called from file "boot/me/trans.ml", line 4442, characters 27-46
Called from file "boot/me/trans.ml", line 4055, characters 6-26
Re-raised at file "boot/me/trans.ml", line 4072, characters 11-104
Called from file "array.ml", line 117, characters 31-48
Called from file "boot/me/trans.ml", line 1974, characters 4-36
Called from file "boot/me/trans.ml", line 4604, characters 4-20
Called from file "boot/me/trans.ml", line 4999, characters 4-39
Called from file "boot/me/semant.ml", line 1435, characters 4-17
Called from file "boot/me/semant.ml", line 1561, characters 4-50
Called from file "boot/me/walk.ml", line 134, characters 4-9
Called from file "hashtbl.ml", line 145, characters 8-13
Called from file "hashtbl.ml", line 148, characters 4-19
Called from file "boot/me/walk.ml", line 135, characters 4-15
Called from file "array.ml", line 130, characters 31-51
Called from file "boot/driver/session.ml", line 60, characters 10-17
Called from file "boot/me/semant.ml", line 1861, characters 8-84
Called from file "boot/driver/main.ml", line 322, characters 9-26
Called from file "array.ml", line 117, characters 31-48
Called from file "boot/driver/main.ml", line 320, characters 4-366
Called from file "boot/driver/main.ml", line 404, characters 5-21

Changing the 'int' to 'uint' causes the correct "mismatched types" error (although the "expected" type isn't what I would have expected), and changing the 'uint' to 'int' makes the code compile fine, even if (say) an interface conversion is involved.

[graydon]

Bug in the new typechecker, it should catch that. Trans trapping late like that is no fun.

The residual behavior is what I'd expect though: changing int to uint makes it complain at the initialization point, yes? Because 3 is an int, not a uint. And changing uint to int makes it compile, because then everyone's dealing with ints everywhere and there's no error.

What did you mean by interface conversion?

[jyasskin]

I agree the residual behavior is right. I though it would "expect" uint (the function's return type) and find int, but instead it's the other way around. That's just a UI issue, though, nothing to do with correctness.

By interface conversion, I meant something like
type intfc = obj { fn foo(); };
obj impl() { fn foo() {} }
fn bar() -> intfc { ret impl(); }
where it needs to convert a concrete type to an interface type.

[graydon]

Missing semicolon in type.ml, plus test to catch regression. Closed by bacb8e6.