Move some implementations of Clone and Copy to libcore

Add implementations of `Clone` and `Copy` for some primitive types to
libcore so that they show up in the documentation. The concerned types
are the following:

* All primitive signed and unsigned integer types (`usize`, `u8`, `u16`,
  `u32`, `u64`, `u128`, `isize`, `i8`, `i16`, `i32`, `i64`, `i128`);
* All primitive floating point types (`f32`, `f64`)
* `bool`
* `char`
* `!`
* Raw pointers (`*const T` and `*mut T`)
* Shared references (`&'a T`)

These types already implemented `Clone` and `Copy`, but the
implementation was provided by the compiler. The compiler no longer
provides these implementations and instead tries to look them up as
normal trait implementations. The goal of this change is to make the
implementations appear in the generated documentation.

For `Copy` specifically, the compiler would reject an attempt to write
an `impl` for the primitive types listed above with error `E0206`; this
error no longer occurs for these types, but it will still occur for the
other types that used to raise that error.

The trait implementations are guarded with `#[cfg(not(stage0))]` because
they are invalid according to the stage0 compiler. When the stage0
compiler is updated to a revision that includes this change, the
attribute will have to be removed, otherwise the stage0 build will fail
because the types mentioned above no longer implement `Clone` or `Copy`.

For type variants that are variadic, such as tuples and function
pointers, and for array types, the `Clone` and `Copy` implementations
are still provided by the compiler, because the language is not
expressive enough yet to be able to write the appropriate
implementations in Rust.

The initial plan was to add `impl` blocks guarded by `#[cfg(dox)]` to
make them apply only when generating documentation, without having to
touch the compiler. However, rustdoc's usage of the compiler still
rejected those `impl` blocks.

This is a [breaking-change] for users of `#![no_core]`, because they
will now have to supply their own implementations of `Clone` and `Copy`
for the primitive types listed above. The easiest way to do that is to
simply copy the implementations from `src/libcore/clone.rs` and
`src/libcore/marker.rs`.

Fixes #25893

2 files changed, 4 insertions, 4 deletions

diff --git a/src/test/ui/error-codes/E0206.rs b/src/test/ui/error-codes/E0206.rs
index da0370b301b..9b3d1b351dd 100644
--- a/src/test/ui/error-codes/E0206.rs
+++ b/src/test/ui/error-codes/E0206.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-type Foo = i32;
+type Foo = [u8; 256];
 
 impl Copy for Foo { }
 //~^ ERROR the trait `Copy` may not be implemented for this type
@@ -17,7 +17,7 @@ impl Copy for Foo { }
 #[derive(Copy, Clone)]
 struct Bar;
 
-impl Copy for &'static Bar { }
+impl Copy for &'static mut Bar { }
 //~^ ERROR the trait `Copy` may not be implemented for this type
 
 fn main() {
diff --git a/src/test/ui/error-codes/E0206.stderr b/src/test/ui/error-codes/E0206.stderr
index bbc0da2248f..f2c23b0767a 100644
--- a/src/test/ui/error-codes/E0206.stderr
+++ b/src/test/ui/error-codes/E0206.stderr
@@ -7,8 +7,8 @@ LL | impl Copy for Foo { }
 error[E0206]: the trait `Copy` may not be implemented for this type
   --> $DIR/E0206.rs:20:15
    |
-LL | impl Copy for &'static Bar { }
-   |               ^^^^^^^^^^^^ type is not a structure or enumeration
+LL | impl Copy for &'static mut Bar { }
+   |               ^^^^^^^^^^^^^^^^ type is not a structure or enumeration
 
 error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
   --> $DIR/E0206.rs:13:1