In the current documentation about the `Copy` marker trait, there is a section
about "additional implementors", which list additional implementors of the `Copy` trait.
The fact that shared references are also `Copy` is mixed with another point,
which makes it hard to recognize and make it seem not as important.

This clarifies the fact that shared references are also `Copy`, by mentioning it as a
separate item in the list of "additional implementors".

In the current documentation about the `Copy` marker trait, there is a section
with examples of structs that can implement `Copy`. Currently there is no example for
showing that shared references (`&T`) are also `Copy`.
It is worth to have a dedicated example for `&T` being `Copy`, because shared
references are an integral part of the language and it being `Copy` is not as
intuitive as other types that share this behaviour like `i32` or `bool`.

The example picks up on the previous non-`Copy` struct and shows that
structs can be `Copy`, even when they hold a shared reference to a non-`Copy` type.

Co-authored-by: Joshua Nelson <[email protected]>

Co-authored-by: Joshua Nelson <[email protected]>

Co-authored-by: Poliorcetics <[email protected]>

Code blocks in doc comments are compiled and run, so we show `Copy` works in this example.

Co-authored-by: Poliorcetics <[email protected]>

* Impl IntoInner rather than AsInner for Ipv4Addr
* Add some comments
* Add test to show endiannes of Ipv4Addr display

Adds a seen set to structurally_same_type to avoid recursing
indefinitely when a reference or pointer member introduces a cycle in
the visited types.

That cache is unlikely to be particularly useful within a single
invocation of structurally_same_type, especially compared to memoizing
results across _all_ invocations of that function.

Co-authored-by: Bastian Kauschke <[email protected]>

Fixes rust-lang#42474.

This adds another `derive` for a `Copy`able struct, so that we are
consistent with `derive` annotations.

…bnik

See also X-Link mem::{swap, take, replace}

Since it's easy to end up at one of these functions when you really wanted the other one, cross link them with descriptions of why you'd want to use them.

docs(marker/copy): provide example for `&T` being `Copy`

### Edited 2020-08-16 (most recent)
In the current documentation about the `Copy` marker trait, there is a section
with examples of structs that can implement `Copy`. Currently there is no example for
showing that shared references (`&T`) are also `Copy`.
It is worth to have a dedicated example for `&T` being `Copy`, because shared
references are an integral part of the language and it being `Copy` is not as
intuitive as other types that share this behaviour like `i32` or `bool`.

The example picks up on the previous non-`Copy` struct and shows that
structs can be `Copy`, even when they hold a shared reference to a non-`Copy` type.

-----------------------------------------
### Edited 2020-08-02, 3:28 p.m.
I've just realized that it says "in addition to the **implementors listed below**", which makes this PR kind of "wrong", because `&T` is indeed in the "implementors listed below".
Maybe we can instead show an example with `&T` in the [When can my type be Copy](https://doc.rust-lang.org/std/marker/trait.Copy.html#when-can-my-type-be-copy) section.

What I really want to achieve is that it becomes more obvious that `&T` is also `Copy`, because, I think, it is very valuable to know and it wasn't obvious for me, until I read something about it in a forum post.

What do you think? I would create another PR for that.
**Please feel free to close this PR.**

-----------------------------------
### Original post
In the current documentation about the `Copy` marker trait, there is a section
about "additional implementors", which list additional implementors of the `Copy` trait.
The fact that shared references are also `Copy` is mixed with another point,
which makes it hard to recognize and make it seem not as important.

This clarifies the fact that shared references are also `Copy`, by mentioning it as a
separate item in the list of "additional implementors".

…crum

Minor changes to Ipv4Addr

Minor changes to Ipv4Addr

* Impl IntoInner rather than AsInner for Ipv4Addr
* Add some comments
* Add test to show endiannes of Ipv4Addr display

Capture output from threads spawned in tests

Fixes rust-lang#42474.

r? @dtolnay since you expressed interest in this, but feel free to redirect if you aren't the right person anymore.

…rk-Simulacrum

BTreeMap: check some invariants in unit tests

…-75412, r=Dylan-DPC

Fix documentation error

This should fix rust-lang#75412. Just a quick >= to > sign replacement.

…erflow, r=lcnr

Fix clashing_extern_declarations stack overflow for recursive types.

Fixes rust-lang#75512.

Adds a seen set to `structurally_same_type` to avoid recursing indefinitely for types which contain values of the same type through a pointer or reference.

…r=jyn514

Move to intra doc links for keyword documentation

Helps with rust-lang#75080.

@rustbot modify labels: T-doc, A-intra-doc-links, T-rustdoc

…aumeGomez

Fix intra-doc links for inherent impls that are both lang items and not the default impl

I found in rust-lang#75464 (comment) that `str::to_uppercase()` doesn't resolve while `str::trim()` does. The only real difference is that `to_uppercase` is defined in `alloc`, while trim is defined in `core`. It turns out that rustdoc was ignoring `lang_items.str_alloc_impl()` - it saw them in `collect_trait_impls`, but not for intra-doc links.

This uses the same `impls` for all parts of rustdoc, so that there can be no more inconsistency. It does have the slight downside that the matches are no longer exhaustive but it will be very clear if a new lang item is missed because it will panic when you try to document it (and if you don't document it, does rustdoc really need to know about it?).

~~This needs a test case (probably just `str::to_uppercase`).~~ Added.

This is best reviewed commit-by-commit.

r? @GuillaumeGomez

…e, r=jyn514

Add doc examples coverage

r? @jyn514