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Add proc_macro to the extern prelude. #7700

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Dec 16, 2019

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ehuss
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@ehuss ehuss commented Dec 12, 2019

This makes it so that a proc-macro library can use the proc_macro crate without the extern crate proc_macro; item on the 2018 edition. This is the Cargo half of rust-lang/rust#64882.

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r? @alexcrichton

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Dec 12, 2019
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r=me, but I think this may need to be gated?

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ehuss commented Dec 12, 2019

Oops. I assume you mean in the test?

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Oh! I believe beta/stable are failing because --extern isn't stable, so we'll need to do some brief version detection to pass --extern proc_macro to proc-macro crates.

I also see that this is a new language feature, but I believe this has already been signed off by all the requisite teams, so we should be good to go when CI is ready

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ehuss commented Dec 13, 2019

Sorry, I was being dumb. I added a dynamic test in the same fashion as the old pipeline test. Does that seem reasonable?

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@bors: r+

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bors commented Dec 16, 2019

📌 Commit 4d64eb9 has been approved by alexcrichton

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 16, 2019
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bors commented Dec 16, 2019

⌛ Testing commit 4d64eb9 with merge ad4122a...

bors added a commit that referenced this pull request Dec 16, 2019
Add proc_macro to the extern prelude.

This makes it so that a proc-macro library can use the `proc_macro` crate without the `extern crate proc_macro;` item on the 2018 edition.  This is the Cargo half of rust-lang/rust#64882.
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bors commented Dec 16, 2019

☀️ Test successful - checks-azure
Approved by: alexcrichton
Pushing ad4122a to master...

@bors bors merged commit 4d64eb9 into rust-lang:master Dec 16, 2019
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Mar 13, 2020
Version 1.42.0 (2020-03-12)
==========================

Language
--------
- [You can now use the slice pattern syntax with subslices.][67712] e.g.
  ```rust
  fn foo(words: &[&str]) {
      match words {
          ["Hello", "World", "!", ..] => println!("Hello World!"),
          ["Foo", "Bar", ..] => println!("Baz"),
          rest => println!("{:?}", rest),
      }
  }
  ```
- [You can now use `#[repr(transparent)]` on univariant `enum`s.][68122] Meaning
  that you can create an enum that has the exact layout and ABI of the type
  it contains.
- [There are some *syntax-only* changes:][67131]
   - `default` is syntactically allowed before items in `trait` definitions.
   - Items in `impl`s (i.e. `const`s, `type`s, and `fn`s) may syntactically
     leave out their bodies in favor of `;`.
   - Bounds on associated types in `impl`s are now syntactically allowed
     (e.g. `type Foo: Ord;`).
   - `...` (the C-variadic type) may occur syntactically directly as the type of
      any function parameter.

  These are still rejected *semantically*, so you will likely receive an error
  but these changes can be seen and parsed by procedural macros and
  conditional compilation.

Compiler
--------
- [Added tier 2* support for `armv7a-none-eabi`.][68253]
- [Added tier 2 support for `riscv64gc-unknown-linux-gnu`.][68339]
- [`Option::{expect,unwrap}` and
   `Result::{expect, expect_err, unwrap, unwrap_err}` now produce panic messages
   pointing to the location where they were called, rather than
   `core`'s internals. ][67887]

* Refer to Rust's [platform support page][forge-platform-support] for more
information on Rust's tiered platform support.

Libraries
---------
- [`iter::Empty<T>` now implements `Send` and `Sync` for any `T`.][68348]
- [`Pin::{map_unchecked, map_unchecked_mut}` no longer require the return type
   to implement `Sized`.][67935]
- [`io::Cursor` now derives `PartialEq` and `Eq`.][67233]
- [`Layout::new` is now `const`.][66254]
- [Added Standard Library support for `riscv64gc-unknown-linux-gnu`.][66899]


Stabilized APIs
---------------
- [`CondVar::wait_while`]
- [`CondVar::wait_timeout_while`]
- [`DebugMap::key`]
- [`DebugMap::value`]
- [`ManuallyDrop::take`]
- [`matches!`]
- [`ptr::slice_from_raw_parts_mut`]
- [`ptr::slice_from_raw_parts`]

Cargo
-----
- [You no longer need to include `extern crate proc_macro;` to be able to
  `use proc_macro;` in the `2018` edition.][cargo/7700]

Compatibility Notes
-------------------
- [`Error::description` has been deprecated, and its use will now produce a
  warning.][66919] It's recommended to use `Display`/`to_string` instead.
- [`use $crate;` inside macros is now a hard error.][37390] The compiler
  emitted forward compatibility warnings since Rust 1.14.0.
- [As previously announced, this release reduces the level of support for
  32-bit Apple targets to tier 3.][apple-32bit-drop]. This means that the
  source code is still available to build, but the targets are no longer tested
  and no release binary is distributed by the Rust project. Please refer to the
  linked blog post for more information.

[37390]: rust-lang/rust#37390
[68253]: rust-lang/rust#68253
[68348]: rust-lang/rust#68348
[67935]: rust-lang/rust#67935
[68339]: rust-lang/rust#68339
[68122]: rust-lang/rust#68122
[67712]: rust-lang/rust#67712
[67887]: rust-lang/rust#67887
[67131]: rust-lang/rust#67131
[67233]: rust-lang/rust#67233
[66899]: rust-lang/rust#66899
[66919]: rust-lang/rust#66919
[66254]: rust-lang/rust#66254
[cargo/7700]: rust-lang/cargo#7700
[`DebugMap::key`]: https://doc.rust-lang.org/stable/std/fmt/struct.DebugMap.html#method.key
[`DebugMap::value`]: https://doc.rust-lang.org/stable/std/fmt/struct.DebugMap.html#method.value
[`ManuallyDrop::take`]: https://doc.rust-lang.org/stable/std/mem/struct.ManuallyDrop.html#method.take
[`matches!`]: https://doc.rust-lang.org/stable/std/macro.matches.html
[`ptr::slice_from_raw_parts_mut`]: https://doc.rust-lang.org/stable/std/ptr/fn.slice_from_raw_parts_mut.html
[`ptr::slice_from_raw_parts`]: https://doc.rust-lang.org/stable/std/ptr/fn.slice_from_raw_parts.html
[`CondVar::wait_while`]: https://doc.rust-lang.org/stable/std/sync/struct.Condvar.html#method.wait_while
[`CondVar::wait_timeout_while`]: https://doc.rust-lang.org/stable/std/sync/struct.Condvar.html#method.wait_timeout_while
facebook-github-bot pushed a commit to facebook/buck that referenced this pull request Nov 4, 2020
Summary:
Rebase of D21840371 with `throws InterruptedException` added to unbreak RustBinaryIntegrationTest.java.

 ---

This diff updates Buck's behavior to match the behavior of Cargo 1.42+ ([rust-lang/cargo#7700](rust-lang/cargo#7700)) to no longer require procedural macro crates to specify "extern crate proc_macro". See the release announcement of this change in https://blog.rust-lang.org/2020/03/12/Rust-1.42.html#use-proc_macrotokenstream-now-works.

Buck technically has no lower compiler version bound on its rustc support, so if someone requires support for rustc <1.42 in Buck then we can consider introducing a buckconfig to opt out of --extern=proc_macro.

Reviewed By: jsgf

fbshipit-source-id: 74fac22e9a67e6967151ab7e38f7e97be7300a4d
@ehuss ehuss added this to the 1.42.0 milestone Feb 6, 2022
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