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  1. 01 8月, 2020 1 次提交
  3. 30 7月, 2020 20 次提交
  5. 29 7月, 2020 19 次提交
    • B
      Auto merge of #72488 - KodrAus:stabilize/const_type_id, r=nikomatsakis · 6fd4c3f2
      由 bors 提交于 
      Stabilize const_type_id feature

The tracking issue for `const_type_id` points to the ill-fated #41875. So I'm re-energizing `TypeId` shenanigans by opening this one up to see if there's anything blocking us from stabilizing the constification of type ids.

Will wait for CI before pinging teams/groups.

-----

This PR stabilizes the `const_type_id` feature, which allows `TypeId::of` (and the underlying unstable intrinsic) to be called in constant contexts.

There are some [sanity tests](https://github.com/rust-lang/rust/blob/master/src/test/ui/consts/const-typeid-of-rpass.rs) that demonstrate its usage, but I’ve included some more below.

As a simple example, you could create a constant item that contains some type ids:

```rust
use std::any::TypeId;

const TYPE_IDS: [TypeId; 2] = [
    TypeId::of::<u32>(),
    TypeId::of::<i32>(),
];

assert_eq!(TypeId::of::<u32>(), TYPE_IDS[0]);
```

Type ids can also now appear in associated constants. You could create a trait that associates each type with its constant type id:

```rust
trait Any where Self: 'static {
    const TYPE_ID: TypeId = TypeId::of::<Self>();
}

impl<T: 'static> Any for T { }

assert_eq!(TypeId::of::<usize>(), usize::TYPE_ID);
```

`TypeId::of` is generic, which we saw above in the way the generic `Self` argument was used. This has some implications for const evaluation. It means we can make trait impls evaluate differently depending on information that wasn't directly passed through the trait system. This violates the _parametricity_ property, which requires all instances of a generic function to behave the same way with respect to its generic parameters. That's not unique to `TypeId::of`, other generic const functions based on compiler intrinsics like `mem::align_of` can also violate parametricity. In practice Rust doesn't really have type parametricity anyway since it monomorphizes generics into concrete functions, so violating it using type ids isn’t new.

As an example of how impls can behave differently, you could combine constant type ids with the `const_if_match` feature to dispatch calls based on the type id of the generic `Self`, rather than based on information about `Self` that was threaded through trait bounds. It's like a rough-and-ready form of specialization:

```rust
#![feature(const_if_match)]

trait Specialized where Self: 'static {
    // An associated constant that determines the function to call
    // at compile-time based on `TypeId::of::<Self>`.
    const CALL: fn(&Self) = {
        const USIZE: TypeId = TypeId::of::<usize>();

        match TypeId::of::<Self>() {
            // Use a closure for `usize` that transmutes the generic `Self` to
            // a concrete `usize` and dispatches to `Self::usize`.
            USIZE => |x| Self::usize(unsafe { &*(x as *const Self as *const usize) }),
            // For other types, dispatch to the generic `Self::default`.
            _ => Self::default,
        }
    };

    fn call(&self) {
        // Call the function we determined at compile-time
        (Self::CALL)(self)
    }

    fn default(x: &Self);
    fn usize(x: &usize);
}

// Implement our `Specialized` trait for any `Debug` type.
impl<T: fmt::Debug + 'static> Specialized for T {
    fn default(x: &Self) {
        println!("default: {:?}", x);
    }

    fn usize(x: &usize) {
        println!("usize: {:?}", x);
    }
}

// Will print "usize: 42"
Specialized::call(&42usize);

// Will print "default: ()"
Specialized::call(&());
```

Type ids have some edges that this stabilization exposes to more contexts. It's possible for type ids to collide (but this is a bug). Since they can change between compiler versions, it's never valid to cast a type id to its underlying value.
      6fd4c3f2
    • X
      Move mir-opt tests to toplevel · f07607f4
      由 Xavier Denis 提交于
      f07607f4
    • R
      Moved structs/enums with repr(C) to LLVM types into ffi.rs crates · 5b2e2b25
      由 Rich Kadel 提交于 
      Some were in librustc_codegen_llvm, but others are not tied to LLVM, so
I put them in a new crate: librustc_codegen_ssa/coverageinfo/ffi.rs
      5b2e2b25
    • T
      Fix broken link in unstable book `plugin` · ab166cff
      由 Takayuki Nakata 提交于
      ab166cff
    • B
      Auto merge of #72049 - mati865:mingw-lld, r=petrochenkov · 584e83dd
      由 bors 提交于 
      MinGW: enable dllexport/dllimport

Fixes (only when using LLD) https://github.com/rust-lang/rust/issues/50176
Fixes https://github.com/rust-lang/rust/issues/72319

This makes `windows-gnu` on pair with `windows-msvc` when it comes to symbol exporting.
For MinGW it means both good things like correctly working dllimport/dllexport, ability to link with LLD and bad things like https://github.com/rust-lang/rust/issues/27438.

Not sure but maybe this should land behind unstable compiler option (`-Z`) or environment variable?
      584e83dd
    • R
      fence docs: fix example Mutex · 897149a8
      由 Ralf Jung 提交于
      897149a8
    • M
      Add test for #50176 · 87abd656
      由 Mateusz Mikuła 提交于
      87abd656
    • M
      MinGW: emit dllexport/dllimport by rustc · db9a84a1
      由 Mateusz Mikuła 提交于 
      This fixes various cases where LD could not guess dllexport correctly and greatly improves compatibility with LLD which is not going to support linker scripts anytime soon
      db9a84a1
    • X
      add crate name to mir dumps · 86be22eb
      由 Xavier Denis 提交于
      86be22eb
    • B
      Auto merge of #74900 - tmiasko:doc-open, r=Mark-Simulacrum · 06e7b93f
      由 bors 提交于 
      Fix opening docs for std crates with ./x.py doc --open library/*

The directories for core, alloc, std, proc_macro, and test crates now
correspond directly to the crate name, and stripping the "lib" prefix is
no longer necessary.
      06e7b93f
    • T
      Fix opening docs for std crates with ./x.py doc --open library/* · 6b4c739f
      由 Tomasz Miąsko 提交于 
      The directories for core, alloc, std, proc_macro, and test crates now
correspond directly to the crate name and stripping the "lib" prefix is
no longer necessary.
      6b4c739f
    • J
      Fix some typos in src/librustdoc/clean/auto_trait.rs · 82766cb7
      由 Josh Triplett 提交于
      82766cb7
    • O
      Address review comments · b81d164f
      由 Oliver Scherer 提交于
      b81d164f
    • S
      Remove deprecated unstable `{Box,Rc,Arc}::into_raw_non_null` functions · 1fb67363
      由 Simon Sapin 提交于 
      FCP: https://github.com/rust-lang/rust/issues/47336#issuecomment-619369613
      1fb67363
    • B
      Auto merge of #74896 - imbolc:patch-1, r=kennytm · 0dd362ec
      由 bors 提交于 
      Update `fs::remove_file` docs

Mention that absence of file causes an error
      0dd362ec
    • T
      Link to syntax section when referencing it · 1b4a6a51
      由 Tomasz Miąsko 提交于
      1b4a6a51
    • L
      Explain why inline default ToString impl · 27e1b063
      由 Lzu Tao 提交于
      27e1b063
    • I
      Update `fs::remove_file` docs · c4e44d73
      由 Imbolc 提交于 
      Mention that absence of file causes an error
      c4e44d73
    • B
      Auto merge of #74887 - Mark-Simulacrum:cache-non-exhaustive, r=petrochenkov · 10c37570
      由 bors 提交于 
      Cache non-exhaustive separately from attributes

This prevents cross-crate attribute loading from metadata just for non_exhaustive checking; cross-crate attribute loading implies disk reading and is relatively slow.
      10c37570