Generated documentation should display implicit trait implementations

[frewsxcv]

use std::fmt;

struct A;

impl fmt::Display for A {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "A")
    }
}

In this example, I'm able to call let a = A; a.to_string() since A implements fmt::Display. The generated documentation doesn't mention anything about to_string. It'd be great if the documentation displayed all available methods for a given structure.

[frewsxcv]

FYI, this implementation exists in case people were confused about the description above:

impl<T> ToString for T where T: Display + ?Sized

https://doc.rust-lang.org/std/string/trait.ToString.html

[GuillaumeGomez]

I'll take a look.

[GuillaumeGomez]

I've been looking for a few days and here are my current issues:

• I don't know how I can get information on trait impls in sub crates.
• I don't know how I can resolve the genericity "issue" (being able to know if a trait impl is also done on the type I'm looking for).

[cbreeden]

I have been working through the source code for method resolution (ie: how rustc resolves A.to_string() in this example) while working on reference documentation for the "dot" operator. See 36427.

I am under the impression that most of the logic found in the source for method resolution can translate to listing out implicit trait implementations. I'll take a look after I'm finsihed with the documentation, but if anyone else is curious to give it a stab, take a look at reference links found in 36427.

[frewsxcv]

Awesome, thanks for sharing @cbreeden! I've been wanting to look into this issue, but I'm still reading through the librustdoc module. I haven't (yet) made any progress on this issue. Will update here if I do.

[HybridEidolon]

How would this information be shown for generic types? i.e. Thing<B> and impl<T: Debug> Debug for Thing<T> {} -- a separate section saying something like "When B is Debug..."?

[frewsxcv]

@HybridEidolon Is there any reason you can think of why the shouldn't go in the already existing "Trait Implementations" section?

[GuillaumeGomez]

@HybridEidolon: For the moment, "everyone" wants it. If your issue is just for the output wording, we can always resolve the type name before printing.

[GuillaumeGomez]

I'll give a serious look into this to settle this matter once and for all.