rustdoc search doesn't handle non-trait `impl`s in a different module to the type definition

[huonw]

std::path::Path has some methods impl'd in std::rt::io::fs; searching for, e.g., exists links to std::rt::io::fs::Path as if the struct was defined there.

[huonw]

Self contained example:

#[crate_id="10284"];

pub mod foo {
    pub struct Bar;
}

pub mod bar {
    impl ::foo::Bar {
        pub fn baz(&self) {}
    }
}

Searching for baz in the generated docs links to a nonexistent page.

[edwardw]

This is surprisingly arcane. The method index is built here and it depends on the order of parsing. I had a fix but a seemingly irrelevant syntactical change easily broke it:

#[crate_id="10284"];

pub mod bar {
    impl ::foo::Zar {
        pub fn baz(&self) {}
    }
}

pub mod foo {
    pub struct Zar;
}

For the same reason, the fix also didn't work for Path::stat given in #12728: std::io::fs is parsed before std::path::posix::Path so the poor Path::stat couldn't find the right parent node.

[edwardw]

r?