Generic function monomorphization is incorrectly done.

[esdrubal]

The following script should not fail on the assert.

script;

use std::assert::*;

trait Trait {
    fn method(self) -> u64;
}

impl Trait for u64 {
    fn method(self) -> u64{
        42
    }
}

struct CallTrait<V> {}

#[inline(never)]
fn call_trait<T>(t: T) -> u64 where T: Trait {
    t.method()
}

impl<K> CallTrait<K> where K: Trait {
    pub fn call_trait(self, key: K) -> u64 {
        call_trait(key)
    }
}

fn main() -> bool {
    let _  = call_trait(1);
    let ct = CallTrait::<u64> {};
    assert(ct.call_trait(1) == 42);
    true
}

In the generated IR we can see that call_trait_7 is returning undef:

entry fn main() -> bool, !1 {
    entry():
    v0 = const u64 1, !2
    v1 = call call_trait_0(v0), !3
    v2 = const u64 1, !4
    v3 = call call_trait_7(v2), !7
    v4 = const u64 42, !8
    v5 = cmp eq v3 v4, !9
    v6 = const bool false, !11
    v7 = cmp eq v5 v6, !15
    cbr v7, assert_2_block0(), assert_2_block1(), !16

    assert_2_block0():
    v8 = const u64 18446744073709486084, !18
    revert v8, !22

    assert_2_block1():
    v9 = const bool true, !23
    ret bool v9
}

fn call_trait_0(t !24: u64) -> u64, !27 {
    entry(t: u64):
    v0 = const u64 42, !28
    ret u64 v0
}

fn call_trait_7(t !24: u64) -> u64, !29 {
    entry(t: u64):
    v0 = const u64 undef
    ret u64 v0
}

We should make sure that the compiler no longer fails silently while compiling generic methods.

[tritao]

Do you know if this is a frontend or codegen issue?

I've seen IR gen happily insert undef before instead of asserting, when given IR that is not fully correctly typed. Just something to keep in mind.

[esdrubal]

This looks like a frontend bug that the backend could catch.

Here is the line of code that is adding the undef, I tried to replace it by a compile error but it is required as it says on the comments for diverging control flow and implicit returns. https://github.com/FuelLabs/sway/blob/0d45b890c9eaa75b88093a9a4cbecbf5ca8c0731/sway-core/src/ir_generation/compile.rs#L491-L496