t27c gen-rust: local bound to a bool-returning call is emitted as if (b) != 0

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What happens

t27c gen-rust emits if (b) != 0 when b is a local bound to the result of a bool-returning function, and rustc rejects it. The Zig backend (t27c gen) compiles the same spec.

Repro (rust_bool.t27):

module repro_rust_bool;
pub fn is_odd(x: u32) bool { return (x & 1) == 1; }
pub fn half_if_even(x: u32) u32 {
    const odd = is_odd(x);
    if (odd) { return x; }
    return x / 2;
}

t27c gen-rust rust_bool.t27 emits:

let odd = is_odd(x);
if (odd) != 0 {

and rustc fails with error[E0308]: mismatched types ... expected bool, found integer.

Where

bootstrap/src/compiler.rs on master 6111696:

• fn expr_is_bool_syntactically (line 23416) recognises comparisons, ! / not and bool literals, but has no ExprCall arm.
• So collect_bool_locals (line 23428, called at 26202) does not mark const odd = is_odd(x) as a bool local.
• expr_to_rust_cond (around 27146) then treats odd as an integer and wraps it as ({}) != 0.

The method expr_is_bool already handles ExprCall through self.bool_fns.contains(...); only the syntactic helper used for locals lacks it.

Suggested fix

Let the local inference consult bool_fns, for example by passing &self.bool_fns into collect_bool_locals / expr_is_bool_syntactically and treating ExprCall of a name in that set as bool. The repro should then compile with rustc --crate-type lib.

Workaround in use

Call the function inline in the condition: if (is_odd(x)) { ... }. Hit while writing specs/xilinx7/packets.t27.

Boundary

• specs/xilinx7/packets.t27
• bootstrap/src/compiler.rs