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

11 files changed, 176 insertions, 30 deletions

diff --git a/src/libcore/clone.rs b/src/libcore/clone.rs
index d25f498b99e..5c83dd79bd7 100644
--- a/src/libcore/clone.rs
+++ b/src/libcore/clone.rs
@@ -135,3 +135,63 @@ pub struct AssertParamIsClone<T: Clone + ?Sized> { _field: ::marker::PhantomData
            reason = "deriving hack, should not be public",
            issue = "0")]
 pub struct AssertParamIsCopy<T: Copy + ?Sized> { _field: ::marker::PhantomData<T> }
+
+/// Implementations of `Clone` for primitive types.
+///
+/// Implementations that cannot be described in Rust
+/// are implemented in `SelectionContext::copy_clone_conditions()` in librustc.
+#[cfg(not(stage0))]
+mod impls {
+
+    use super::Clone;
+
+    macro_rules! impl_clone {
+        ($($t:ty)*) => {
+            $(
+                #[stable(feature = "rust1", since = "1.0.0")]
+                impl Clone for $t {
+                    fn clone(&self) -> Self {
+                        *self
+                    }
+                }
+            )*
+        }
+    }
+
+    impl_clone! {
+        usize u8 u16 u32 u64 u128
+        isize i8 i16 i32 i64 i128
+        f32 f64
+        bool char
+    }
+
+    #[stable(feature = "never_type", since = "1.26.0")]
+    impl Clone for ! {
+        fn clone(&self) -> Self {
+            *self
+        }
+    }
+
+    #[stable(feature = "rust1", since = "1.0.0")]
+    impl<T: ?Sized> Clone for *const T {
+        fn clone(&self) -> Self {
+            *self
+        }
+    }
+
+    #[stable(feature = "rust1", since = "1.0.0")]
+    impl<T: ?Sized> Clone for *mut T {
+        fn clone(&self) -> Self {
+            *self
+        }
+    }
+
+    // Shared references can be cloned, but mutable references *cannot*!
+    #[stable(feature = "rust1", since = "1.0.0")]
+    impl<'a, T: ?Sized> Clone for &'a T {
+        fn clone(&self) -> Self {
+            *self
+        }
+    }
+
+}
diff --git a/src/libcore/marker.rs b/src/libcore/marker.rs
index 7d0174a178a..008cb15131d 100644
--- a/src/libcore/marker.rs
+++ b/src/libcore/marker.rs
@@ -593,3 +593,43 @@ unsafe impl<'a, T: ?Sized> Freeze for &'a mut T {}
 /// This trait is automatically implemented for almost every type.
 #[unstable(feature = "pin", issue = "49150")]
 pub unsafe auto trait Unpin {}
+
+/// Implementations of `Copy` for primitive types.
+///
+/// Implementations that cannot be described in Rust
+/// are implemented in `SelectionContext::copy_clone_conditions()` in librustc.
+#[cfg(not(stage0))]
+mod copy_impls {
+
+    use super::Copy;
+
+    macro_rules! impl_copy {
+        ($($t:ty)*) => {
+            $(
+                #[stable(feature = "rust1", since = "1.0.0")]
+                impl Copy for $t {}
+            )*
+        }
+    }
+
+    impl_copy! {
+        usize u8 u16 u32 u64 u128
+        isize i8 i16 i32 i64 i128
+        f32 f64
+        bool char
+    }
+
+    #[stable(feature = "never_type", since = "1.26.0")]
+    impl Copy for ! {}
+
+    #[stable(feature = "rust1", since = "1.0.0")]
+    impl<T: ?Sized> Copy for *const T {}
+
+    #[stable(feature = "rust1", since = "1.0.0")]
+    impl<T: ?Sized> Copy for *mut T {}
+
+    // Shared references can be copied, but mutable references *cannot*!
+    #[stable(feature = "rust1", since = "1.0.0")]
+    impl<'a, T: ?Sized> Copy for &'a T {}
+
+}
diff --git a/src/librustc/traits/select.rs b/src/librustc/traits/select.rs
index 11daa96134c..8a585d6ac14 100644
--- a/src/librustc/traits/select.rs
+++ b/src/librustc/traits/select.rs
@@ -2061,11 +2061,15 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
 
         match self_ty.sty {
             ty::TyInfer(ty::IntVar(_)) | ty::TyInfer(ty::FloatVar(_)) |
+            ty::TyFnDef(..) | ty::TyFnPtr(_) | ty::TyError => {
+                Where(ty::Binder(Vec::new()))
+            }
+
             ty::TyUint(_) | ty::TyInt(_) | ty::TyBool | ty::TyFloat(_) |
-            ty::TyFnDef(..) | ty::TyFnPtr(_) | ty::TyChar |
-            ty::TyRawPtr(..) | ty::TyError | ty::TyNever |
+            ty::TyChar | ty::TyRawPtr(..) | ty::TyNever |
             ty::TyRef(_, ty::TypeAndMut { ty: _, mutbl: hir::MutImmutable }) => {
-                Where(ty::Binder(Vec::new()))
+                // Implementations provided in libcore
+                None
             }
 
             ty::TyDynamic(..) | ty::TyStr | ty::TySlice(..) |
diff --git a/src/librustc/ty/util.rs b/src/librustc/ty/util.rs
index afe977d10ba..22f851a908b 100644
--- a/src/librustc/ty/util.rs
+++ b/src/librustc/ty/util.rs
@@ -197,7 +197,14 @@ impl<'tcx> ty::ParamEnv<'tcx> {
         // FIXME: (@jroesch) float this code up
         tcx.infer_ctxt().enter(|infcx| {
             let (adt, substs) = match self_type.sty {
+                // These types used to have a builtin impl.
+                // Now libcore provides that impl.
+                ty::TyUint(_) | ty::TyInt(_) | ty::TyBool | ty::TyFloat(_) |
+                ty::TyChar | ty::TyRawPtr(..) | ty::TyNever |
+                ty::TyRef(_, ty::TypeAndMut { ty: _, mutbl: hir::MutImmutable }) => return Ok(()),
+
                 ty::TyAdt(adt, substs) => (adt, substs),
+
                 _ => return Err(CopyImplementationError::NotAnAdt),
             };
 
diff --git a/src/librustc_typeck/diagnostics.rs b/src/librustc_typeck/diagnostics.rs
index 1f882676f61..691e0ffb6a5 100644
--- a/src/librustc_typeck/diagnostics.rs
+++ b/src/librustc_typeck/diagnostics.rs
@@ -1918,16 +1918,16 @@ differs from the behavior for `&T`, which is always `Copy`).
 
 E0206: r##"
 You can only implement `Copy` for a struct or enum. Both of the following
-examples will fail, because neither `i32` (primitive type) nor `&'static Bar`
-(reference to `Bar`) is a struct or enum:
+examples will fail, because neither `[u8; 256]` nor `&'static mut Bar`
+(mutable reference to `Bar`) is a struct or enum:
 
 ```compile_fail,E0206
-type Foo = i32;
+type Foo = [u8; 256];
 impl Copy for Foo { } // error
 
 #[derive(Copy, Clone)]
 struct Bar;
-impl Copy for &'static Bar { } // error
+impl Copy for &'static mut Bar { } // error
 ```
 "##,
 
diff --git a/src/test/run-make-fulldeps/atomic-lock-free/atomic_lock_free.rs b/src/test/run-make-fulldeps/atomic-lock-free/atomic_lock_free.rs
index b41e8e9226b..54f888b3796 100644
--- a/src/test/run-make-fulldeps/atomic-lock-free/atomic_lock_free.rs
+++ b/src/test/run-make-fulldeps/atomic-lock-free/atomic_lock_free.rs
@@ -23,6 +23,8 @@ trait Copy {}
 #[lang = "freeze"]
 trait Freeze {}
 
+impl<T: ?Sized> Copy for *mut T {}
+
 #[cfg(target_has_atomic = "8")]
 pub unsafe fn atomic_u8(x: *mut u8) {
     atomic_xadd(x, 1);
diff --git a/src/test/run-make-fulldeps/simd-ffi/simd.rs b/src/test/run-make-fulldeps/simd-ffi/simd.rs
index 94b91c711cc..21411a35e3c 100644
--- a/src/test/run-make-fulldeps/simd-ffi/simd.rs
+++ b/src/test/run-make-fulldeps/simd-ffi/simd.rs
@@ -75,6 +75,9 @@ pub trait Sized { }
 #[lang = "copy"]
 pub trait Copy { }
 
+impl Copy for f32 {}
+impl Copy for i32 {}
+
 pub mod marker {
     pub use Copy;
 }
diff --git a/src/test/ui/coherence-impls-copy.rs b/src/test/ui/coherence-impls-copy.rs
index 51f43d27c34..f48790d1f40 100644
--- a/src/test/ui/coherence-impls-copy.rs
+++ b/src/test/ui/coherence-impls-copy.rs
@@ -12,6 +12,10 @@
 
 use std::marker::Copy;
 
+impl Copy for i32 {}
+//~^ ERROR conflicting implementations of trait `std::marker::Copy` for type `i32`:
+//~| ERROR only traits defined in the current crate can be implemented for arbitrary types
+
 enum TestE {
   A
 }
@@ -35,14 +39,14 @@ impl Copy for (MyType, MyType) {}
 //~| ERROR only traits defined in the current crate can be implemented for arbitrary types
 
 impl Copy for &'static NotSync {}
-//~^ ERROR the trait `Copy` may not be implemented for this type
+//~^ ERROR conflicting implementations of trait `std::marker::Copy` for type `&NotSync`:
 
 impl Copy for [MyType] {}
 //~^ ERROR the trait `Copy` may not be implemented for this type
 //~| ERROR only traits defined in the current crate can be implemented for arbitrary types
 
 impl Copy for &'static [NotSync] {}
-//~^ ERROR the trait `Copy` may not be implemented for this type
+//~^ ERROR conflicting implementations of trait `std::marker::Copy` for type `&[NotSync]`:
 //~| ERROR only traits defined in the current crate can be implemented for arbitrary types
 
 fn main() {
diff --git a/src/test/ui/coherence-impls-copy.stderr b/src/test/ui/coherence-impls-copy.stderr
index 5f9b0c62df2..24e7e85b1a9 100644
--- a/src/test/ui/coherence-impls-copy.stderr
+++ b/src/test/ui/coherence-impls-copy.stderr
@@ -1,35 +1,61 @@
-error[E0206]: the trait `Copy` may not be implemented for this type
-  --> $DIR/coherence-impls-copy.rs:29:15
+error[E0119]: conflicting implementations of trait `std::marker::Copy` for type `i32`:
+  --> $DIR/coherence-impls-copy.rs:15:1
    |
-LL | impl Copy for &'static mut MyType {}
-   |               ^^^^^^^^^^^^^^^^^^^ type is not a structure or enumeration
+LL | impl Copy for i32 {}
+   | ^^^^^^^^^^^^^^^^^
+   |
+   = note: conflicting implementation in crate `core`:
+           - impl std::marker::Copy for i32;
+
+error[E0119]: conflicting implementations of trait `std::marker::Copy` for type `&NotSync`:
+  --> $DIR/coherence-impls-copy.rs:41:1
+   |
+LL | impl Copy for &'static NotSync {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: conflicting implementation in crate `core`:
+           - impl<'a, T> std::marker::Copy for &'a T
+             where T: ?Sized;
+
+error[E0119]: conflicting implementations of trait `std::marker::Copy` for type `&[NotSync]`:
+  --> $DIR/coherence-impls-copy.rs:48:1
+   |
+LL | impl Copy for &'static [NotSync] {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: conflicting implementation in crate `core`:
+           - impl<'a, T> std::marker::Copy for &'a T
+             where T: ?Sized;
 
 error[E0206]: the trait `Copy` may not be implemented for this type
   --> $DIR/coherence-impls-copy.rs:33:15
    |
-LL | impl Copy for (MyType, MyType) {}
-   |               ^^^^^^^^^^^^^^^^ type is not a structure or enumeration
+LL | impl Copy for &'static mut MyType {}
+   |               ^^^^^^^^^^^^^^^^^^^ type is not a structure or enumeration
 
 error[E0206]: the trait `Copy` may not be implemented for this type
   --> $DIR/coherence-impls-copy.rs:37:15
    |
-LL | impl Copy for &'static NotSync {}
+LL | impl Copy for (MyType, MyType) {}
    |               ^^^^^^^^^^^^^^^^ type is not a structure or enumeration
 
 error[E0206]: the trait `Copy` may not be implemented for this type
-  --> $DIR/coherence-impls-copy.rs:40:15
+  --> $DIR/coherence-impls-copy.rs:44:15
    |
 LL | impl Copy for [MyType] {}
    |               ^^^^^^^^ type is not a structure or enumeration
 
-error[E0206]: the trait `Copy` may not be implemented for this type
-  --> $DIR/coherence-impls-copy.rs:44:15
+error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
+  --> $DIR/coherence-impls-copy.rs:15:1
    |
-LL | impl Copy for &'static [NotSync] {}
-   |               ^^^^^^^^^^^^^^^^^^ type is not a structure or enumeration
+LL | impl Copy for i32 {}
+   | ^^^^^^^^^^^^^^^^^ impl doesn't use types inside crate
+   |
+   = note: the impl does not reference any types defined in this crate
+   = note: define and implement a trait or new type instead
 
 error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
-  --> $DIR/coherence-impls-copy.rs:33:1
+  --> $DIR/coherence-impls-copy.rs:37:1
    |
 LL | impl Copy for (MyType, MyType) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl doesn't use types inside crate
@@ -38,7 +64,7 @@ LL | impl Copy for (MyType, MyType) {}
    = note: define and implement a trait or new type instead
 
 error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
-  --> $DIR/coherence-impls-copy.rs:40:1
+  --> $DIR/coherence-impls-copy.rs:44:1
    |
 LL | impl Copy for [MyType] {}
    | ^^^^^^^^^^^^^^^^^^^^^^ impl doesn't use types inside crate
@@ -47,7 +73,7 @@ LL | impl Copy for [MyType] {}
    = note: define and implement a trait or new type instead
 
 error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
-  --> $DIR/coherence-impls-copy.rs:44:1
+  --> $DIR/coherence-impls-copy.rs:48:1
    |
 LL | impl Copy for &'static [NotSync] {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl doesn't use types inside crate
@@ -55,7 +81,7 @@ LL | impl Copy for &'static [NotSync] {}
    = note: the impl does not reference any types defined in this crate
    = note: define and implement a trait or new type instead
 
-error: aborting due to 8 previous errors
+error: aborting due to 10 previous errors
 
-Some errors occurred: E0117, E0206.
+Some errors occurred: E0117, E0119, E0206.
 For more information about an error, try `rustc --explain E0117`.
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