Bug with duplicate impl blocks defined for the same type with different type parameters.

[nfurfaro]

The following code won't compile. The error is:

library bug;

pub trait Convert<T> {
    fn convert(t: T) -> Self;
}

pub struct A {
    a: u64,
}

pub struct B {
    b: u64,
}

pub struct C {
    c: u64,
}

impl Convert<B> for A {
    fn convert(t: B) -> Self {
        A {
            a: t.b
        }
    }
}

impl Convert<C> for A {
    fn convert(t: C) -> Self {
        A {
            a: t.c
        }
    }
}

[emilyaherbert]

This is not a bug---this case should not be allowed and it is true that these implementations are conflicting. This is because the generic type "B" is equivalent to the generic type "C", they are both "a generic type" without any additional information. i.e. when the user calls the method .convert::<bool>(..), how is the compiler to know which implementation of convert to use?

See here for this same case in Rust: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=293dbb6a1a51a2c06fba457340e430d6

We should make the error message more clear though---I will change this issue to reflect this.

[mohammadfawaz]

@emilyaherbert I think in @nfurfaro's example, B and C are not meant to be generic parameters. This is the use case that he's thinking of: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=dad181001f80f61c5fd47994f3e6e067

The use case here is being able to implement From for ContractId from multiple types.

[nfurfaro]

@mohammadfawaz is correct; sorry if my attempt at a simple repro is misleading and/or incorrect.

[emilyaherbert]

Oh I see, apologies for my mistake! Thanks so much for clarifying @mohammadfawaz and @nfurfaro.

Yes in this case the original bug description is correct 😄

[emilyaherbert]

sorry if my attempt at a simple repro is misleading and/or incorrect.

No no, just a brain fart on my end haha.

[nfurfaro]

@esdrubal It looks like you may have a fix for this in the works?
I'm blocked by this again, and it will keep happening with more frequency until resolved. :)

[esdrubal]

@nfurfaro yes #3676 should fix this. Updated it now to remove merge conflicts. I hope it will be merged soon.