Rustdoc doesn't see trait implementations inside of functions

It's possible to define trait implementations inside of functions in Rust. This is useful not too often, but particularly nice if you have a macro that both defines trait implementation and calls some initialization for a given type.

Anyway, the following code is valid in Rust itself:

pub struct S;

pub fn a() {
    impl From<u8> for S {
        fn from(_: u8) -> S {
            S
        }
    }
}

But Rustdoc doesn't generate documentation for a given trait, despite it being visible to Rust itself, and being immediately available and unique across entire crate.

I can move impl out of the function and then it gets seen by Rustdoc, but this is rather inconvenient when impl is generated as part of a bigger macro.

The scope of the implementation is only inside the function and so cannot be used outside of it and so shouldn't be documented. Also, macro != functions. If you make an implementation inside a macro, it's documented.

Closing it then, don't hesitate to reopen it if I missed something.

The scope of the implementation is only inside the function and so cannot be used outside of it and so shouldn't be documented.

No, this is exactly the problem I was referring to - impl is not scoped. In Rust itself it's visible across entire codebase despite being declared inside of a function.

Also, macro != functions. If you make an implementation inside a macro, it's documented.

I referred to macro only because I'm using them inside of such function to generate both impl and a call to some other function.

@GuillaumeGomez

To enhance the example above:

pub struct S;

pub fn a() {
    impl From<u8> for S {
        fn from(_: u8) -> S {
            S
        }
    }
}

fn main() {
    let s = S::from(10u8);
}

^^ From works here as expected, as well as other crates that depend on this one, can use it, which is why it's important to have it documented.

@GuillaumeGomez

don't hesitate to reopen it if I missed something

(GitHub doesn't allow non-members to reopen issues closed by others.)

doesn't allow non-members to reopen issues closed by others

Indeed, thanks for reopening this!

@petrochenkov

Thanks for reopening it @petrochenkov.

@RReverser: That's completely crazy. Another example just for the fun:

pub struct S;

trait Foo {
    fn foo(&self) {}
}

pub fn a() {
    impl Foo for S {
    }
}

fn main() {
    S.foo();
}

So rustdoc should document these implementations as well. Thanks for opening the issue!

Got bit by this. rustdoc were simply unable to find a trait implementation defined in a function which cargo build picked up fine https://docs.rs/crate/serde_state/0.4.2/builds/77728 . Thought I was going crazy for second there.

I've opened #53162 to fix this.

Auto merge of #53162 - QuietMisdreavus:crouching-impl-hidden-trait, r…

Rollup merge of rust-lang#53162 - QuietMisdreavus:crouching-impl-hidd…

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Rustdoc doesn't see trait implementations inside of functions #41480

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Rustdoc doesn't see trait implementations inside of functions #41480

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GuillaumeGomez commented on Apr 25, 2017

RReverser commented on Apr 25, 2017

RReverser commented on Apr 25, 2017

petrochenkov commented on Apr 25, 2017

RReverser commented on Apr 25, 2017

GuillaumeGomez commented on Apr 25, 2017

Marwes commented on Nov 29, 2017

QuietMisdreavus commented on Aug 7, 2018

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