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Stabilize let bindings and destructuring in constants and const fn #57175

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merged 7 commits into from Jan 12, 2019

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@oli-obk
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@oli-obk oli-obk commented Dec 28, 2018

r? @Centril

This PR stabilizes the following features in constants and const functions:

  • irrefutable destructuring patterns (e.g. const fn foo((x, y): (u8, u8)) { ... })
  • let bindings (e.g. let x = 1;)
  • mutable let bindings (e.g. let mut x = 1;)
  • assignment (e.g. x = y) and assignment operator (e.g. x += y) expressions, even where the assignment target is a projection (e.g. a struct field or index operation like x[3] = 42)
  • expression statements (e.g. 3;)

This PR does explicitly not stabilize:

  • mutable references (i.e. &mut T)
  • dereferencing mutable references
  • refutable patterns (e.g. Some(x))
  • operations on UnsafeCell types (as that would need raw pointers and mutable references and such, not because it is explicitly forbidden. We can't explicitly forbid it as such values are OK as long as they aren't mutated.)
  • We are not stabilizing let bindings in constants that use && and || short circuiting operations. These are treated as & and | inside const and static items right now. If we stopped treating them as & and | after stabilizing let bindings, we'd break code like let mut x = false; false && { x = true; false };. So to use let bindings in constants you need to change && and || to & and | respectively.
@cramertj

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@cramertj cramertj commented Dec 28, 2018

I don't see #53515 mentioned here-- isn't this a blocker to stabilization? (or does #56160 somehow gate the problematic behavior?)

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@oli-obk oli-obk commented Dec 28, 2018

I don't see #53515 mentioned here-- isn't this a blocker to stabilization? (or does #56160 somehow gate the problematic behavior?)

yes, we're preventing both let bindings and short circuiting operators from being used within the same constant https://github.com/rust-lang/rust/search?utf8=%E2%9C%93&q=control_flow_destroyed&type=

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@cramertj cramertj commented Dec 28, 2018

I see, e.g. this test here.

src/libsyntax/feature_gate.rs Outdated Show resolved Hide resolved
src/test/run-pass/ctfe/locals-in-const-fn.rs Outdated Show resolved Hide resolved
src/test/ui/issues/issue-32829-2.rs Show resolved Hide resolved
src/test/ui/unsafe/ranged_ints2_const.rs Outdated Show resolved Hide resolved
src/test/ui/unsafe/ranged_ints3_const.rs Outdated Show resolved Hide resolved
src/test/ui/unsafe/ranged_ints4_const.rs Outdated Show resolved Hide resolved
@Centril Centril requested a review from RalfJung Dec 29, 2018
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@Centril Centril commented Dec 29, 2018

Assigning over to:
r? @nikomatsakis
for review of the code changes since I primarily looked at tests.

@cramertj I will write up a stabilization report in a bit either as a separate issue or in this PR and I'll fcp merge that one.

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@Centril Centril commented Dec 30, 2018

Stabilization proposal

I propose that we stabilize #![feature(const_let)].

@rfcbot merge

Tracking issue: #48821
Version target: 1.33 (2019-01-15 => beta, 2019-03-01 => stable).

What is stabilized

In the following places:

We stabilize:

  • expression statements (e.g. 3;)

  • irrefutable destructuring patterns; for example:

    let (x, y) = expr;
    const fn foo([x, y]: [u8; 2]) {}
  • let bindings including mut ones; for example:

    let x = 42;
    let x: u8;
    let mut x: u8;
    let mut x = 24;
  • assignment (e.g. x = y) and assignment operator (e.g. x += y) expressions, even where the assignment target is a projection (e.g. a struct field or index operation like x[3] = 42).

What is not stabilized

  • mutable references (i.e. &mut T) and borrows (i.e. &mut x)
  • dereferencing mutable references
  • refutable patterns (e.g. Some(x))
  • operations on UnsafeCell types (as that would need raw pointers, mutable references, and such, not because it is explicitly forbidden. We cannot explicitly forbid it as such values are OK as long as they aren't mutated.)
  • We are not stabilizing let bindings in const contexts that use && and || short circuiting operations. These are treated as & and | inside const and static items right now. If we stopped treating them as & and | after stabilizing let bindings, we'd break code like let mut x = false; false && { x = true; false };. So to use let bindings in constants you need to change && and || to & and | respectively.

Divergences from RFC

  • See the note above about && and ||. These are control flow operations which should be stabilized in let bindings when we otherwise stabilize && with other control flow in the places aforementioned.
  • The RFC does not explicitly mention assignment and expression statements. However, as these are a natural consequence of having let bindings, it might as well be implied.

Tests

The tests can be primarily seen in the PR itself. Here are some of them:

Motivation

From the RFC:

It makes writing const fns much more like writing regular functions and is not possible right now because the old constant evaluator was a constant folder that could only process expressions. With the miri const evaluator this feature exists but is still disallowed.

As for motivations to do this now despite the lack of stable control flow,
given let bindings and assignments we may still:

  • Make overflowing_add into const fns on stable.

  • Write things such as:

    const fn bar() -> [u32; 500] {
        let mut foo = [0; 500];
        foo[3] = 42;
        foo
    }

History

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@rfcbot rfcbot commented Dec 30, 2018

Team member @Centril has proposed to merge this. The next step is review by the rest of the tagged teams:

No concerns currently listed.

Once a majority of reviewers approve (and none object), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

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@scottmcm scottmcm commented Dec 31, 2018

Since we already had ugly let statements by just making another function, I'm glad to see real ones.

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@cramertj cramertj commented Jan 2, 2019

Two clarifications here:

  • Why is that we're banning let in combination with && and || rather than making it work? Is there something challenging about implementing the short-circuiting behavior? Or is this just because we haven't yet stabilized const_if?

We are not stabilizing let bindings in const contexts that use && and || short circuiting operations. These are treated as & and | inside const and static items right now.

  • "[T]reated as & and |" (which I normally associated with std::ops::BitAnd) just means that they do not yet short-circuit, right?
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@Centril Centril commented Jan 2, 2019

  • Why is that we're banning let in combination with && and || rather than making it work? Is there something challenging about implementing the short-circuiting behavior? Or is this just because we haven't yet stabilized const_if?

@oli-obk knows better than me, but the gist of it is that we haven't implemented match or other control flow yet so it's not even stabilization; on nightly you cannot even write:

#![feature(const_fn)]

const fn foo() {
    match 0 { // error[E0019]: constant function contains unimplemented expression type
        1 => {}
        _ => {}
    };
}

And we can think of && as equivalent to:

match lhs { false => false, true => rhs }

Meanwhile, || can be thought of as:

match lhs { false => rhs, true => true }

I think the main hurdle is just doing the work, which we eventually will, but it will take its time.

  • "[T]reated as & and |" (which I normally associated with std::ops::BitAnd) just means that they do not yet short-circuit, right?

Yep, and sadly we already support a buggy, non-short-circuiting, version of && and || in const items but not in const fn; once we do get control flow working in in const eval we can stabilize && and || in const fn as well.

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@alexreg alexreg commented Jan 5, 2019

@oli-obk knows better than me, but the gist of it is that we haven't implemented match or other control flow yet so it's not even stabilization; on nightly you cannot even write:

This is correct. It requires control-flow support, which does not exist whatsoever yet. I'm hoping @oli-obk can pick up where eddyb left off with this. I can help perhaps.

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@bors bors commented Jan 12, 2019

📌 Commit 6c62322 has been approved by nikomatsakis

Centril added a commit to Centril/rust that referenced this pull request Jan 12, 2019
…nikomatsakis

Stabilize `let` bindings and destructuring in constants and const fn

r? @Centril

This PR stabilizes the following features in constants and `const` functions:

* irrefutable destructuring patterns (e.g. `const fn foo((x, y): (u8, u8)) { ... }`)
* `let` bindings (e.g. `let x = 1;`)
* mutable `let` bindings (e.g. `let mut x = 1;`)
* assignment (e.g. `x = y`) and assignment operator (e.g. `x += y`) expressions, even where the assignment target is a projection (e.g. a struct field or index operation like `x[3] = 42`)
* expression statements (e.g. `3;`)

This PR does explicitly *not* stabilize:

* mutable references (i.e. `&mut T`)
* dereferencing mutable references
* refutable patterns (e.g. `Some(x)`)
* operations on `UnsafeCell` types (as that would need raw pointers and mutable references and such, not because it is explicitly forbidden. We can't explicitly forbid it as such values are OK as long as they aren't mutated.)
* We are not stabilizing `let` bindings in constants that use `&&` and `||` short circuiting operations. These are treated as `&` and `|` inside `const` and `static` items right now. If we stopped treating them as `&` and `|` after stabilizing `let` bindings, we'd break code like `let mut x = false; false && { x = true; false };`. So to use `let` bindings in constants you need to change `&&` and `||` to `&` and `|` respectively.
bors added a commit that referenced this pull request Jan 12, 2019
Rollup of 26 pull requests

Successful merges:

 - #56425 (Redo the docs for Vec::set_len)
 - #56906 (Issue #56905)
 - #57042 (Don't call `FieldPlacement::count` when count is too large)
 - #57175 (Stabilize `let` bindings and destructuring in constants and const fn)
 - #57192 (Change std::error::Error trait documentation to talk about `source` instead of `cause`)
 - #57296 (Fixed the link to the ? operator)
 - #57368 (Use CMAKE_{C,CXX}_COMPILER_LAUNCHER for ccache)
 - #57400 (Rustdoc: update Source Serif Pro and replace Heuristica italic)
 - #57417 (rustdoc: use text-based doctest parsing if a macro is wrapping main)
 - #57433 (Add link destination for `read-ownership`)
 - #57434 (Remove `CrateNum::Invalid`.)
 - #57441 (Supporting backtrace for x86_64-fortanix-unknown-sgx.)
 - #57450 (actually take a slice in this example)
 - #57459 (Reference tracking issue for inherent associated types in diagnostic)
 - #57463 (docs: Fix some 'second-edition' links)
 - #57466 (Remove outdated comment)
 - #57493 (use structured suggestion when casting a reference)
 - #57498 (make note of one more normalization that Paths do)
 - #57499 (note that FromStr does not work for borrowed types)
 - #57505 (Remove submodule step from README)
 - #57510 (Add a profiles section to the manifest)
 - #57511 (Fix undefined behavior)
 - #57519 (Correct RELEASES.md for 1.32.0)
 - #57522 (don't unwrap unexpected tokens in `format!`)
 - #57530 (Fixing a typographical error.)
 - #57535 (Stabilise irrefutable if-let and while-let patterns)

Failed merges:

r? @ghost
@bors bors merged commit 6c62322 into rust-lang:master Jan 12, 2019
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Details
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Mar 3, 2019
Pkgsrc changes:
 * Bump required rust version to build to 1.32.0.
 * Adapt patches to changed file locations.
 * Since we now patch some more vendor/ modules, doctor the corresponding
   .cargo-checksum.json files accordingly

Upstream changes:

Version 1.33.0 (2019-02-28)
==========================

Language
--------
- [You can now use the `cfg(target_vendor)` attribute.][57465] E.g.
  `#[cfg(target_vendor="apple")] fn main() { println!("Hello Apple!"); }`
- [Integer patterns such as in a match expression can now be exhaustive.][56362]
  E.g. You can have match statement on a `u8` that covers `0..=255` and
  you would no longer be required to have a `_ => unreachable!()` case.
- [You can now have multiple patterns in `if let` and `while let`
  expressions.][57532] You can do this with the same syntax as a `match`
  expression. E.g.
  ```rust
  enum Creature {
      Crab(String),
      Lobster(String),
      Person(String),
  }

  fn main() {
      let state = Creature::Crab("Ferris");

      if let Creature::Crab(name) | Creature::Person(name) = state {
          println!("This creature's name is: {}", name);
      }
  }
  ```
- [You can now have irrefutable `if let` and `while let` patterns.][57535]
  Using this feature will by default produce a warning as this behaviour
  can be unintuitive. E.g. `if let _ = 5 {}`
- [You can now use `let` bindings, assignments, expression statements,
  and irrefutable pattern destructuring in const functions.][57175]
- [You can now call unsafe const functions.][57067] E.g.
  ```rust
  const unsafe fn foo() -> i32 { 5 }
  const fn bar() -> i32 {
      unsafe { foo() }
  }
  ```
- [You can now specify multiple attributes in a `cfg_attr` attribute.][57332]
  E.g. `#[cfg_attr(all(), must_use, optimize)]`
- [You can now specify a specific alignment with the `#[repr(packed)]`
  attribute.][57049] E.g. `#[repr(packed(2))] struct Foo(i16, i32);` is a
  struct with an alignment of 2 bytes and a size of 6 bytes.
- [You can now import an item from a module as an `_`.][56303] This allows you
  to import a trait's impls, and not have the name in the namespace. E.g.
  ```rust
  use std::io::Read as _;

  // Allowed as there is only one `Read` in the module.
  pub trait Read {}
  ```
- [You may now use `Rc`, `Arc`, and `Pin` as method receivers][56805].

Compiler
--------
- [You can now set a linker flavor for `rustc` with the `-Clinker-flavor`
  command line argument.][56351]
- [The mininum required LLVM version has been bumped to 6.0.][56642]
- [Added support for the PowerPC64 architecture on FreeBSD.][57615]
- [The `x86_64-fortanix-unknown-sgx` target support has been upgraded to
  tier 2 support.][57130] Visit the [platform support][platform-support]
  page for information on Rust's platform support.
- [Added support for the `thumbv7neon-linux-androideabi` and
  `thumbv7neon-unknown-linux-gnueabihf` targets.][56947]
- [Added support for the `x86_64-unknown-uefi` target.][56769]

Libraries
---------
- [The methods `overflowing_{add, sub, mul, shl, shr}` are now `const`
  functions for all numeric types.][57566]
- [The methods `rotate_left`, `rotate_right`, and `wrapping_{add, sub, mul,
  shl, shr}`
  are now `const` functions for all numeric types.][57105]
- [The methods `is_positive` and `is_negative` are now `const` functions for
  all signed numeric types.][57105]
- [The `get` method for all `NonZero` types is now `const`.][57167]
- [The methods `count_ones`, `count_zeros`, `leading_zeros`, `trailing_zeros`,
  `swap_bytes`, `from_be`, `from_le`, `to_be`, `to_le` are now `const` for all
  numeric types.][57234]
- [`Ipv4Addr::new` is now a `const` function][57234]

Stabilized APIs
---------------
- [`unix::FileExt::read_exact_at`]
- [`unix::FileExt::write_all_at`]
- [`Option::transpose`]
- [`Result::transpose`]
- [`convert::identity`]
- [`pin::Pin`]
- [`marker::Unpin`]
- [`marker::PhantomPinned`]
- [`Vec::resize_with`]
- [`VecDeque::resize_with`]
- [`Duration::as_millis`]
- [`Duration::as_micros`]
- [`Duration::as_nanos`]


Cargo
-----
- [Cargo should now rebuild a crate if a file was modified during the initial
  build.][cargo/6484]

Compatibility Notes
-------------------
- The methods `str::{trim_left, trim_right, trim_left_matches,
  trim_right_matches}` are now deprecated in the standard library, and their
  usage will now produce a warning.  Please use the `str::{trim_start,
  trim_end, trim_start_matches, trim_end_matches}` methods instead.
- The `Error::cause` method has been deprecated in favor of `Error::source`
  which supports downcasting.

[55982]: rust-lang/rust#55982
[56303]: rust-lang/rust#56303
[56351]: rust-lang/rust#56351
[56362]: rust-lang/rust#56362
[56642]: rust-lang/rust#56642
[56769]: rust-lang/rust#56769
[56805]: rust-lang/rust#56805
[56947]: rust-lang/rust#56947
[57049]: rust-lang/rust#57049
[57067]: rust-lang/rust#57067
[57105]: rust-lang/rust#57105
[57130]: rust-lang/rust#57130
[57167]: rust-lang/rust#57167
[57175]: rust-lang/rust#57175
[57234]: rust-lang/rust#57234
[57332]: rust-lang/rust#57332
[57465]: rust-lang/rust#57465
[57532]: rust-lang/rust#57532
[57535]: rust-lang/rust#57535
[57566]: rust-lang/rust#57566
[57615]: rust-lang/rust#57615
[cargo/6484]: rust-lang/cargo#6484
[`unix::FileExt::read_exact_at`]: https://doc.rust-lang.org/std/os/unix/fs/trait.FileExt.html#method.read_exact_at
[`unix::FileExt::write_all_at`]: https://doc.rust-lang.org/std/os/unix/fs/trait.FileExt.html#method.write_all_at
[`Option::transpose`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.transpose
[`Result::transpose`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.transpose
[`convert::identity`]: https://doc.rust-lang.org/std/convert/fn.identity.html
[`pin::Pin`]: https://doc.rust-lang.org/std/pin/struct.Pin.html
[`marker::Unpin`]: https://doc.rust-lang.org/stable/std/marker/trait.Unpin.html
[`marker::PhantomPinned`]: https://doc.rust-lang.org/nightly/std/marker/struct.PhantomPinned.html
[`Vec::resize_with`]: https://doc.rust-lang.org/std/vec/struct.Vec.html#method.resize_with
[`VecDeque::resize_with`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.resize_with
[`Duration::as_millis`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.as_millis
[`Duration::as_micros`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.as_micros
[`Duration::as_nanos`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.as_nanos
[platform-support]: https://forge.rust-lang.org/platform-support.html
@Centril Centril added this to the 1.33 milestone Apr 26, 2019
jperkin added a commit to joyent/pkgsrc that referenced this pull request Jun 20, 2019
Pkgsrc changes:
 * Bump required rust version to build to 1.32.0.
 * Adapt patches to changed file locations.
 * Since we now patch some more vendor/ modules, doctor the corresponding
   .cargo-checksum.json files accordingly

Upstream changes:

Version 1.33.0 (2019-02-28)
==========================

Language
--------
- [You can now use the `cfg(target_vendor)` attribute.][57465] E.g.
  `#[cfg(target_vendor="apple")] fn main() { println!("Hello Apple!"); }`
- [Integer patterns such as in a match expression can now be exhaustive.][56362]
  E.g. You can have match statement on a `u8` that covers `0..=255` and
  you would no longer be required to have a `_ => unreachable!()` case.
- [You can now have multiple patterns in `if let` and `while let`
  expressions.][57532] You can do this with the same syntax as a `match`
  expression. E.g.
  ```rust
  enum Creature {
      Crab(String),
      Lobster(String),
      Person(String),
  }

  fn main() {
      let state = Creature::Crab("Ferris");

      if let Creature::Crab(name) | Creature::Person(name) = state {
          println!("This creature's name is: {}", name);
      }
  }
  ```
- [You can now have irrefutable `if let` and `while let` patterns.][57535]
  Using this feature will by default produce a warning as this behaviour
  can be unintuitive. E.g. `if let _ = 5 {}`
- [You can now use `let` bindings, assignments, expression statements,
  and irrefutable pattern destructuring in const functions.][57175]
- [You can now call unsafe const functions.][57067] E.g.
  ```rust
  const unsafe fn foo() -> i32 { 5 }
  const fn bar() -> i32 {
      unsafe { foo() }
  }
  ```
- [You can now specify multiple attributes in a `cfg_attr` attribute.][57332]
  E.g. `#[cfg_attr(all(), must_use, optimize)]`
- [You can now specify a specific alignment with the `#[repr(packed)]`
  attribute.][57049] E.g. `#[repr(packed(2))] struct Foo(i16, i32);` is a
  struct with an alignment of 2 bytes and a size of 6 bytes.
- [You can now import an item from a module as an `_`.][56303] This allows you
  to import a trait's impls, and not have the name in the namespace. E.g.
  ```rust
  use std::io::Read as _;

  // Allowed as there is only one `Read` in the module.
  pub trait Read {}
  ```
- [You may now use `Rc`, `Arc`, and `Pin` as method receivers][56805].

Compiler
--------
- [You can now set a linker flavor for `rustc` with the `-Clinker-flavor`
  command line argument.][56351]
- [The mininum required LLVM version has been bumped to 6.0.][56642]
- [Added support for the PowerPC64 architecture on FreeBSD.][57615]
- [The `x86_64-fortanix-unknown-sgx` target support has been upgraded to
  tier 2 support.][57130] Visit the [platform support][platform-support]
  page for information on Rust's platform support.
- [Added support for the `thumbv7neon-linux-androideabi` and
  `thumbv7neon-unknown-linux-gnueabihf` targets.][56947]
- [Added support for the `x86_64-unknown-uefi` target.][56769]

Libraries
---------
- [The methods `overflowing_{add, sub, mul, shl, shr}` are now `const`
  functions for all numeric types.][57566]
- [The methods `rotate_left`, `rotate_right`, and `wrapping_{add, sub, mul,
  shl, shr}`
  are now `const` functions for all numeric types.][57105]
- [The methods `is_positive` and `is_negative` are now `const` functions for
  all signed numeric types.][57105]
- [The `get` method for all `NonZero` types is now `const`.][57167]
- [The methods `count_ones`, `count_zeros`, `leading_zeros`, `trailing_zeros`,
  `swap_bytes`, `from_be`, `from_le`, `to_be`, `to_le` are now `const` for all
  numeric types.][57234]
- [`Ipv4Addr::new` is now a `const` function][57234]

Stabilized APIs
---------------
- [`unix::FileExt::read_exact_at`]
- [`unix::FileExt::write_all_at`]
- [`Option::transpose`]
- [`Result::transpose`]
- [`convert::identity`]
- [`pin::Pin`]
- [`marker::Unpin`]
- [`marker::PhantomPinned`]
- [`Vec::resize_with`]
- [`VecDeque::resize_with`]
- [`Duration::as_millis`]
- [`Duration::as_micros`]
- [`Duration::as_nanos`]


Cargo
-----
- [Cargo should now rebuild a crate if a file was modified during the initial
  build.][cargo/6484]

Compatibility Notes
-------------------
- The methods `str::{trim_left, trim_right, trim_left_matches,
  trim_right_matches}` are now deprecated in the standard library, and their
  usage will now produce a warning.  Please use the `str::{trim_start,
  trim_end, trim_start_matches, trim_end_matches}` methods instead.
- The `Error::cause` method has been deprecated in favor of `Error::source`
  which supports downcasting.

[55982]: rust-lang/rust#55982
[56303]: rust-lang/rust#56303
[56351]: rust-lang/rust#56351
[56362]: rust-lang/rust#56362
[56642]: rust-lang/rust#56642
[56769]: rust-lang/rust#56769
[56805]: rust-lang/rust#56805
[56947]: rust-lang/rust#56947
[57049]: rust-lang/rust#57049
[57067]: rust-lang/rust#57067
[57105]: rust-lang/rust#57105
[57130]: rust-lang/rust#57130
[57167]: rust-lang/rust#57167
[57175]: rust-lang/rust#57175
[57234]: rust-lang/rust#57234
[57332]: rust-lang/rust#57332
[57465]: rust-lang/rust#57465
[57532]: rust-lang/rust#57532
[57535]: rust-lang/rust#57535
[57566]: rust-lang/rust#57566
[57615]: rust-lang/rust#57615
[cargo/6484]: rust-lang/cargo#6484
[`unix::FileExt::read_exact_at`]: https://doc.rust-lang.org/std/os/unix/fs/trait.FileExt.html#method.read_exact_at
[`unix::FileExt::write_all_at`]: https://doc.rust-lang.org/std/os/unix/fs/trait.FileExt.html#method.write_all_at
[`Option::transpose`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.transpose
[`Result::transpose`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.transpose
[`convert::identity`]: https://doc.rust-lang.org/std/convert/fn.identity.html
[`pin::Pin`]: https://doc.rust-lang.org/std/pin/struct.Pin.html
[`marker::Unpin`]: https://doc.rust-lang.org/stable/std/marker/trait.Unpin.html
[`marker::PhantomPinned`]: https://doc.rust-lang.org/nightly/std/marker/struct.PhantomPinned.html
[`Vec::resize_with`]: https://doc.rust-lang.org/std/vec/struct.Vec.html#method.resize_with
[`VecDeque::resize_with`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.resize_with
[`Duration::as_millis`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.as_millis
[`Duration::as_micros`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.as_micros
[`Duration::as_nanos`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.as_nanos
[platform-support]: https://forge.rust-lang.org/platform-support.html
@oli-obk oli-obk deleted the oli-obk:const_let_stabilization branch Jun 15, 2020
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 27, 2020
…ch, r=oli-obk

Stabilize `#![feature(const_if_match)]`

Quoting from the [stabilization report](rust-lang#49146 (comment)):

> `if` and `match` expressions as well as the short-circuiting logic operators `&&` and `||` will become legal in all [const contexts](https://doc.rust-lang.org/reference/const_eval.html#const-context). A const context is any of the following:
>
> - The initializer of a `const`, `static`, `static mut` or enum discriminant.
> - The body of a `const fn`.
> - The value of a const generic (nightly only).
> - The length of an array type (`[u8; 3]`) or an array repeat expression (`[0u8; 3]`).
>
> Furthermore, the short-circuiting logic operators will no longer be lowered to their bitwise equivalents (`&` and `|` respectively) in `const` and `static` initializers (see rust-lang#57175). As a result, `let` bindings can be used alongside short-circuiting logic in those initializers.

Resolves rust-lang#49146.

Ideally, we would resolve 🐳 rust-lang#66753 before this lands on stable, so it might be worth pushing this back a release. Also, this means we should get the process started for rust-lang#52000, otherwise people will have no recourse except recursion for iterative `const fn`.

r? @oli-obk
Manishearth added a commit to Manishearth/rust that referenced this pull request Jun 27, 2020
…atch, r=oli-obk

Stabilize `#![feature(const_if_match)]`

Quoting from the [stabilization report](rust-lang#49146 (comment)):

> `if` and `match` expressions as well as the short-circuiting logic operators `&&` and `||` will become legal in all [const contexts](https://doc.rust-lang.org/reference/const_eval.html#const-context). A const context is any of the following:
>
> - The initializer of a `const`, `static`, `static mut` or enum discriminant.
> - The body of a `const fn`.
> - The value of a const generic (nightly only).
> - The length of an array type (`[u8; 3]`) or an array repeat expression (`[0u8; 3]`).
>
> Furthermore, the short-circuiting logic operators will no longer be lowered to their bitwise equivalents (`&` and `|` respectively) in `const` and `static` initializers (see rust-lang#57175). As a result, `let` bindings can be used alongside short-circuiting logic in those initializers.

Resolves rust-lang#49146.

Ideally, we would resolve 🐳 rust-lang#66753 before this lands on stable, so it might be worth pushing this back a release. Also, this means we should get the process started for rust-lang#52000, otherwise people will have no recourse except recursion for iterative `const fn`.

r? @oli-obk
Dylan-DPC added a commit to Dylan-DPC/rust that referenced this pull request Jun 27, 2020
…atch, r=oli-obk

Stabilize `#![feature(const_if_match)]`

Quoting from the [stabilization report](rust-lang#49146 (comment)):

> `if` and `match` expressions as well as the short-circuiting logic operators `&&` and `||` will become legal in all [const contexts](https://doc.rust-lang.org/reference/const_eval.html#const-context). A const context is any of the following:
>
> - The initializer of a `const`, `static`, `static mut` or enum discriminant.
> - The body of a `const fn`.
> - The value of a const generic (nightly only).
> - The length of an array type (`[u8; 3]`) or an array repeat expression (`[0u8; 3]`).
>
> Furthermore, the short-circuiting logic operators will no longer be lowered to their bitwise equivalents (`&` and `|` respectively) in `const` and `static` initializers (see rust-lang#57175). As a result, `let` bindings can be used alongside short-circuiting logic in those initializers.

Resolves rust-lang#49146.

Ideally, we would resolve 🐳 rust-lang#66753 before this lands on stable, so it might be worth pushing this back a release. Also, this means we should get the process started for rust-lang#52000, otherwise people will have no recourse except recursion for iterative `const fn`.

r? @oli-obk
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 28, 2020
…ch, r=oli-obk

Stabilize `#![feature(const_if_match)]`

Quoting from the [stabilization report](rust-lang#49146 (comment)):

> `if` and `match` expressions as well as the short-circuiting logic operators `&&` and `||` will become legal in all [const contexts](https://doc.rust-lang.org/reference/const_eval.html#const-context). A const context is any of the following:
>
> - The initializer of a `const`, `static`, `static mut` or enum discriminant.
> - The body of a `const fn`.
> - The value of a const generic (nightly only).
> - The length of an array type (`[u8; 3]`) or an array repeat expression (`[0u8; 3]`).
>
> Furthermore, the short-circuiting logic operators will no longer be lowered to their bitwise equivalents (`&` and `|` respectively) in `const` and `static` initializers (see rust-lang#57175). As a result, `let` bindings can be used alongside short-circuiting logic in those initializers.

Resolves rust-lang#49146.

Ideally, we would resolve 🐳 rust-lang#66753 before this lands on stable, so it might be worth pushing this back a release. Also, this means we should get the process started for rust-lang#52000, otherwise people will have no recourse except recursion for iterative `const fn`.

r? @oli-obk
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 28, 2020
…ch, r=oli-obk

Stabilize `#![feature(const_if_match)]`

Quoting from the [stabilization report](rust-lang#49146 (comment)):

> `if` and `match` expressions as well as the short-circuiting logic operators `&&` and `||` will become legal in all [const contexts](https://doc.rust-lang.org/reference/const_eval.html#const-context). A const context is any of the following:
>
> - The initializer of a `const`, `static`, `static mut` or enum discriminant.
> - The body of a `const fn`.
> - The value of a const generic (nightly only).
> - The length of an array type (`[u8; 3]`) or an array repeat expression (`[0u8; 3]`).
>
> Furthermore, the short-circuiting logic operators will no longer be lowered to their bitwise equivalents (`&` and `|` respectively) in `const` and `static` initializers (see rust-lang#57175). As a result, `let` bindings can be used alongside short-circuiting logic in those initializers.

Resolves rust-lang#49146.

Ideally, we would resolve 🐳 rust-lang#66753 before this lands on stable, so it might be worth pushing this back a release. Also, this means we should get the process started for rust-lang#52000, otherwise people will have no recourse except recursion for iterative `const fn`.

r? @oli-obk
jonas-schievink added a commit to jonas-schievink/rust that referenced this pull request Nov 10, 2020
…jyn514

Use check-pass instead of build-pass in some consts ui test suits

Helps with rust-lang#62277

Changed tests modified by rust-lang#57175 because of the stabilization `#![feature(const_let)]`.
They should be compile-fail because the feature gate checking disallow the feature before stabilization. So the feature gate checking have nothing to do with codegen according to https://rustc-dev-guide.rust-lang.org/feature-gate-ck.html.
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9 participants