Rustdoc does not show Into implementations, only From implementations

[shepmaster]

This code:

pub struct Hello;

impl Into<Hello> for String {
    fn into(self) -> Hello {
        Hello
    }
}

impl From<u8> for Hello {
    fn from(_: u8) -> Hello {
        Hello
    }
}

Documents the implementation of From (presumably because it's implemented for a local type), but not Into, (presumably because it's an implemented on a non-local type).

In many cases, this is "OK" because we build the whole documentation and so we can see the implementors of a trait. This doesn't work when the trait is in the standard library, which doesn't regenerate docs with cargo doc.

I'm sure this is a duplicate issue, I just haven't found it yet. This can serve as a signpost when we do!

/cc #33417, which will encourage more cases of implementing a trait we don't own parameterized with a type we do own for a type we don't own.

rustc 1.15.1 (021bd294c 2017-02-08)
binary: rustc
commit-hash: 021bd294c039bd54aa5c4aa85bcdffb0d24bc892
commit-date: 2017-02-08
host: x86_64-apple-darwin
release: 1.15.1
LLVM version: 3.9

[RReverser]

I can't even get all my From implementations documented :(

[QuietMisdreavus]

Duplicate of #25264