Rustdoc generate files for items not used in documentation

[GuillaumeGomez]

As demonstrated in the following codes:

// @!has 'foo/hidden/index.html'

// The following two should not fail!
// @!has 'foo/hidden/inner/index.html'
// @!has 'foo/hidden/inner/trait.Foo.html'
#[doc(hidden)]
pub mod hidden {
    pub mod inner {
        pub trait Foo {
            /// Hello, world!
            fn test();
        }
    }
}

// @has 'foo/visible/index.html'
// @has 'foo/visible/trait.Foo.html'
#[doc(inline)]
pub use hidden::inner as visible;

// @has 'foo/struct.Bar.html'
// @count - '//*[@id="impl-Foo-for-Bar"]' 1
pub struct Bar;

impl visible::Foo for Bar {
    fn test() {}
}

And the other example:

// None of the following checks should fail.
// @!has 'foo/hidden/index.html'
// @!has 'foo/hidden/inner/index.html'
// @!has 'foo/hidden/inner/trait.Foo.html'
#[doc(hidden)]
pub mod hidden {
    pub mod inner {
        pub trait Foo {
            /// Hello, world!
            fn test();
        }
    }
}

// @has 'foo/trait.Foo.html'
#[doc(inline)]
pub use hidden::inner::Foo;

// @has 'foo/struct.Bar.html'
// @count - '//*[@id="impl-Foo-for-Bar"]' 1
pub struct Bar;

impl Foo for Bar {
    fn test() {}
}

Examples come from #111249.

[GuillaumeGomez]

Also, don't forget to update issue-111064-reexport-trait-from-hidden-2.rs.

[notriddle]

All assertions in this test case pass:

#![crate_name="foo"]

// @!has "foo/struct.Foo.html"
#[doc(hidden)]
pub struct Foo;

// @has "foo/struct.Bar.html"
pub use crate::Foo as Bar;

// @!has "foo/struct.Baz.html"
#[doc(hidden)]
pub use crate::Foo as Baz;

This test case fails:

#![crate_name="foo"]

// This assertion fails. The file gets generated.
// @!has "foo/foo/index.html"
#[doc(hidden)]
pub mod foo {}

// This assertion passes.
// @has "foo/bar/index.html"
pub use crate::foo as bar;

// This assertion also fails. The file gets generated.
// @!has "foo/baz/index.html"
#[doc(hidden)]
pub use crate::foo as baz;