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Better document the implementors of Clone and Copy #48171

Merged
merged 5 commits into from
Apr 4, 2018
Merged

Better document the implementors of Clone and Copy #48171

merged 5 commits into from
Apr 4, 2018

Commits on Mar 27, 2018

  1. 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 rust-lang#25893
    @FraGag
    FraGag committed Mar 27, 2018
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  2. Document builtin implementations of Clone and Copy 

    There are types that implement `Clone` and `Copy` but are not mentioned
in the documentation, because the implementations are provided by the
compiler. They are types of variants that cannot be fully covered by
trait implementations in Rust code, because the language is not
expressive enough.
    @FraGag
    FraGag committed Mar 27, 2018
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  3. Add #[inline] to Clone impls for primitive types

    @FraGag
    FraGag committed Mar 27, 2018
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  4. Strengthen the repeat-trusted-len test 

    Simply checking for the presence of `llvm.memset` is too brittle because
this instrinsic can be used for seemingly trivial operations, such as
zero-initializing a `RawVec`.
    @FraGag
    FraGag committed Mar 27, 2018
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  5. Update liblibc submodule to the 0.2.40 release

    @FraGag
    FraGag committed Mar 27, 2018
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