Stabilize `#![feature(const_if_match)]` and `#![feature(const_loop)]` #72437

ecstatic-morse · 2020-05-21T21:26:16Z

if and match expressions as well as the short-circuiting logic operators && and || will become legal in all const contexts. 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 #57175). As a result, let bindings can be used alongside short-circuiting logic in those initializers.

Resolves #49146.

Ideally, we would resolve 🐳 #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 #52000, otherwise people will have no recourse except recursion for iterative const fn.

r? @oli-obk

ecstatic-morse · 2020-05-21T21:56:24Z

While writing this, I found and fixed a bug in the HIR const-checker: It wasn't requiring allow_internal_unstable for rustc_const_stable functions, just the feature gates. I will probably split this out as part of an upcoming refactoring of the fn_queries module.

Manishearth · 2020-06-03T23:47:20Z

ping @oli-obk

oli-obk · 2020-06-04T07:52:28Z

This is waiting for someone from @rust-lang/lang starting the FCP on #52000 as we (wg-const-eval) would like to stabilize looping at the same time as branching so ppl don't have to resort to recursion.

Manishearth · 2020-06-04T22:46:22Z

Ah, gotcha. Thanks!

KodrAus · 2020-06-11T00:28:06Z

There’s now a FCP on #52000

jhpratt · 2020-06-11T00:30:08Z

*proposed FCP. Still needs a few checkboxes.

bors · 2020-06-15T11:48:31Z

☔ The latest upstream changes (presumably #73367) made this pull request unmergeable. Please resolve the merge conflicts.

oli-obk · 2020-06-16T09:38:06Z

Please adjust this PR to also stabilize const_loop. The FCP on the tracking issue has been started, imo we should get this merged immediately and revert if the FCP leads to blocking concerns before it finishes.

mark-i-m · 2020-06-26T01:15:38Z

FCP on #52000 has completed!

oli-obk · 2020-06-30T15:25:08Z

oops, too late: rust-lang/reference#842

…r=jonas-schievink Advertise correct stable version for const control flow rust-lang#72437 was opened before the 1.45 release but merged afterwards. These will be stable in 1.46.

`const_if_match` and `const_loop` has been stabilized by <rust-lang/rust#72437>.

`const_if_match` and `const_loop` have been stabilized by <rust-lang/rust#72437>.

…]` from example code `const_if_match` and `const_loop` have been stabilized by <rust-lang/rust#72437>.

…r=jonas-schievink Advertise correct stable version for const control flow rust-lang#72437 was opened before the 1.45 release but merged afterwards. These will be stable in 1.46.

Make more primitive integer methods const Now that rust-lang#72437 has been merged and `const_if_match` is stable, these methods can be stabilized const. The methods are grouped in commits according to feature names: * `const_nonzero_int_methods` - `NonZero*::new` * some `const_checked_int_methods` - `{i*,u*}::checked_add` - `{i*,u*}::checked_sub` - `{i*,u*}::checked_mul` - `{i*,u*}::checked_neg` - `{i*,u*}::checked_shl` - `{i*,u*}::checked_shr` - `i*::checked_abs` * `const_saturating_int_methods` - `{i*,u*}::saturating_add` - `{i*,u*}::saturating_sub` - `{i*,u*}::saturating_mul` - `i*::saturating_neg` - `i*::saturating_abs` * `const_int_sign` - `i*::signum` * `const_ascii_ctype_on_intrinsics` - `{char,u8}::is_ascii_alphabetic` - `{char,u8}::is_ascii_uppercase` - `{char,u8}::is_ascii_lowercase` - `{char,u8}::is_ascii_alphanumeric` - `{char,u8}::is_ascii_digit` - `{char,u8}::is_ascii_hexdigit` - `{char,u8}::is_ascii_punctuation` - `{char,u8}::is_ascii_graphic` - `{char,u8}::is_ascii_whitespace` - `{char,u8}::is_ascii_control`

according to various people on tech-pkg@, there are no problems with the Firefox build Version 1.46.0 (2020-08-27) ========================== Language -------- - [`if`, `match`, and `loop` expressions can now be used in const functions.][72437] - [Additionally you are now also able to coerce and cast to slices (`&[T]`) in const functions.][73862] - [The `#[track_caller]` attribute can now be added to functions to use the function's caller's location information for panic messages.][72445] - [Recursively indexing into tuples no longer needs parentheses.][71322] E.g. `x.0.0` over `(x.0).0`. - [`mem::transmute` can now be used in static and constants.][72920] **Note** You currently can't use `mem::transmute` in constant functions. Compiler -------- - [You can now use the `cdylib` target on Apple iOS and tvOS platforms.][73516] - [Enabled static "Position Independent Executables" by default for `x86_64-unknown-linux-musl`.][70740] Libraries --------- - [`mem::forget` is now a `const fn`.][73887] - [`String` now implements `From<char>`.][73466] - [The `leading_ones`, and `trailing_ones` methods have been stabilised for all integer types.][73032] - [`vec::IntoIter<T>` now implements `AsRef<[T]>`.][72583] - [All non-zero integer types (`NonZeroU8`) now implement `TryFrom` for their zero-able equivalent (e.g. `TryFrom<u8>`).][72717] - [`&[T]` and `&mut [T]` now implement `PartialEq<Vec<T>>`.][71660] - [`(String, u16)` now implements `ToSocketAddrs`.][73007] - [`vec::Drain<'_, T>` now implements `AsRef<[T]>`.][72584] Stabilized APIs --------------- - [`Option::zip`] - [`vec::Drain::as_slice`] Cargo ----- Added a number of new environment variables that are now available when compiling your crate. - [`CARGO_BIN_NAME` and `CARGO_CRATE_NAME`][cargo/8270] Providing the name of the specific binary being compiled and the name of the crate. - [`CARGO_PKG_LICENSE`][cargo/8325] The license from the manifest of the package. - [`CARGO_PKG_LICENSE_FILE`][cargo/8387] The path to the license file. Compatibility Notes ------------------- - [The target configuration option `abi_blacklist` has been renamed to `unsupported_abis`.][74150] The old name will still continue to work. - [Rustc will now warn if you cast a C-like enum that implements `Drop`.][72331] This was previously accepted but will become a hard error in a future release. - [Rustc will fail to compile if you have a struct with `#[repr(i128)]` or `#[repr(u128)]`.][74109] This representation is currently only allowed on `enum`s. - [Tokens passed to `macro_rules!` are now always captured.][73293] This helps ensure that spans have the correct information, and may cause breakage if you were relying on receiving spans with dummy information. - [The InnoSetup installer for Windows is no longer available.][72569] This was a legacy installer that was replaced by a MSI installer a few years ago but was still being built. - [`{f32, f64}::asinh` now returns the correct values for negative numbers.][72486] - [Rustc will no longer accept overlapping trait implementations that only differ in how the lifetime was bound.][72493] - [Rustc now correctly relates the lifetime of an existential associated type.][71896] This fixes some edge cases where `rustc` would erroneously allow you to pass a shorter lifetime than expected. - [Rustc now dynamically links to `libz` (also called `zlib`) on Linux.][74420] The library will need to be installed for `rustc` to work, even though we expect it to be already available on most systems. - [Tests annotated with `#[should_panic]` are broken on ARMv7 while running under QEMU.][74820] - [Pretty printing of some tokens in procedural macros changed.][75453] The exact output returned by rustc's pretty printing is an unstable implementation detail: we recommend any macro relying on it to switch to a more robust parsing system. [75453]: rust-lang/rust#75453 [74820]: rust-lang/rust#74820 [74420]: rust-lang/rust#74420 [74109]: rust-lang/rust#74109 [74150]: rust-lang/rust#74150 [73862]: rust-lang/rust#73862 [73887]: rust-lang/rust#73887 [73466]: rust-lang/rust#73466 [73516]: rust-lang/rust#73516 [73293]: rust-lang/rust#73293 [73007]: rust-lang/rust#73007 [73032]: rust-lang/rust#73032 [72920]: rust-lang/rust#72920 [72569]: rust-lang/rust#72569 [72583]: rust-lang/rust#72583 [72584]: rust-lang/rust#72584 [72717]: rust-lang/rust#72717 [72437]: rust-lang/rust#72437 [72445]: rust-lang/rust#72445 [72486]: rust-lang/rust#72486 [72493]: rust-lang/rust#72493 [72331]: rust-lang/rust#72331 [71896]: rust-lang/rust#71896 [71660]: rust-lang/rust#71660 [71322]: rust-lang/rust#71322 [70740]: rust-lang/rust#70740 [cargo/8270]: rust-lang/cargo#8270 [cargo/8325]: rust-lang/cargo#8325 [cargo/8387]: rust-lang/cargo#8387 [`Option::zip`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.zip [`vec::Drain::as_slice`]: https://doc.rust-lang.org/stable/std/vec/struct.Drain.html#method.as_slice

Pkgsrc changes: * Portability patches for Illumos have been intregrated upstream, so are no longer needed in pkgsrc. * Adjust one other patch, and update vendor/libc cargo checksum. Upstream changes: Version 1.46.0 (2020-08-27) ========================== Language -------- - [`if`, `match`, and `loop` expressions can now be used in const functions.] [72437] - [Additionally you are now also able to coerce and cast to slices (`&[T]`) in const functions.][73862] - [The `#[track_caller]` attribute can now be added to functions to use the function's caller's location information for panic messages.][72445] - [Recursively indexing into tuples no longer needs parentheses.][71322] E.g. `x.0.0` over `(x.0).0`. - [`mem::transmute` can now be used in static and constants.][72920] **Note** You currently can't use `mem::transmute` in constant functions. Compiler -------- - [You can now use the `cdylib` target on Apple iOS and tvOS platforms.][73516] - [Enabled static "Position Independent Executables" by default for `x86_64-unknown-linux-musl`.][70740] Libraries --------- - [`mem::forget` is now a `const fn`.][73887] - [`String` now implements `From<char>`.][73466] - [The `leading_ones`, and `trailing_ones` methods have been stabilised for all integer types.][73032] - [`vec::IntoIter<T>` now implements `AsRef<[T]>`.][72583] - [All non-zero integer types (`NonZeroU8`) now implement `TryFrom` for their zero-able equivalent (e.g. `TryFrom<u8>`).][72717] - [`&[T]` and `&mut [T]` now implement `PartialEq<Vec<T>>`.][71660] - [`(String, u16)` now implements `ToSocketAddrs`.][73007] - [`vec::Drain<'_, T>` now implements `AsRef<[T]>`.][72584] Stabilized APIs --------------- - [`Option::zip`] - [`vec::Drain::as_slice`] Cargo ----- Added a number of new environment variables that are now available when compiling your crate. - [`CARGO_BIN_NAME` and `CARGO_CRATE_NAME`][cargo/8270] Providing the name of the specific binary being compiled and the name of the crate. - [`CARGO_PKG_LICENSE`][cargo/8325] The license from the manifest of the package. - [`CARGO_PKG_LICENSE_FILE`][cargo/8387] The path to the license file. Compatibility Notes ------------------- - [The target configuration option `abi_blacklist` has been renamed to `unsupported_abis`.][74150] The old name will still continue to work. - [Rustc will now warn if you have a C-like enum that implements `Drop`.][72331] This was previously accepted but will become a hard error in a future release. - [Rustc will fail to compile if you have a struct with `#[repr(i128)]` or `#[repr(u128)]`.][74109] This representation is currently only allowed on `enum`s. - [Tokens passed to `macro_rules!` are now always captured.][73293] This helps ensure that spans have the correct information, and may cause breakage if you were relying on receiving spans with dummy information. - [The InnoSetup installer for Windows is no longer available.][72569] This was a legacy installer that was replaced by a MSI installer a few years ago but was still being built. - [`{f32, f64}::asinh` now returns the correct values for negative numbers.] [72486] - [Rustc will no longer accept overlapping trait implementations that only differ in how the lifetime was bound.][72493] - [Rustc now correctly relates the lifetime of an existential associated type.][71896] This fixes some edge cases where `rustc` would erroneously allow you to pass a shorter lifetime than expected. - [Rustc now dynamically links to `libz` (also called `zlib`) on Linux.][74420] The library will need to be installed for `rustc` to work, even though we expect it to be already available on most systems. - [Tests annotated with `#[should_panic]` are broken on ARMv7 while running under QEMU.][74820] - [Pretty printing of some tokens in procedural macros changed.][75453] The exact output returned by rustc's pretty printing is an unstable implementation detail: we recommend any macro relying on it to switch to a more robust parsing system. [75453]: rust-lang/rust#75453 [74820]: rust-lang/rust#74820 [74420]: rust-lang/rust#74420 [74109]: rust-lang/rust#74109 [74150]: rust-lang/rust#74150 [73862]: rust-lang/rust#73862 [73887]: rust-lang/rust#73887 [73466]: rust-lang/rust#73466 [73516]: rust-lang/rust#73516 [73293]: rust-lang/rust#73293 [73007]: rust-lang/rust#73007 [73032]: rust-lang/rust#73032 [72920]: rust-lang/rust#72920 [72569]: rust-lang/rust#72569 [72583]: rust-lang/rust#72583 [72584]: rust-lang/rust#72584 [72717]: rust-lang/rust#72717 [72437]: rust-lang/rust#72437 [72445]: rust-lang/rust#72445 [72486]: rust-lang/rust#72486 [72493]: rust-lang/rust#72493 [72331]: rust-lang/rust#72331 [71896]: rust-lang/rust#71896 [71660]: rust-lang/rust#71660 [71322]: rust-lang/rust#71322 [70740]: rust-lang/rust#70740 [cargo/8270]: rust-lang/cargo#8270 [cargo/8325]: rust-lang/cargo#8325 [cargo/8387]: rust-lang/cargo#8387 [`Option::zip`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.zip [`vec::Drain::as_slice`]: https://doc.rust-lang.org/stable/std/vec/struct.Drain.html#method.as_slice

…r=RalfJung Update E0744 about control flow in `const` contexts to accurately describe when the error is triggered and why This PR fixes rust-lang#79083. `const fn` currently supports `if`, `match`, `loop`, and `while` in terms of control flow. The error relating to control flow in `const` contexts currently states that those control flow constructs are not allowed in `const` contexts. That is no longer true, as RFC 2342 and 2344 were [stabilized](rust-lang#72437). `for` loops, however, as well as `?` and `.await` are still not allowed, so I changed the error message to be more descriptive of the error as it is not just control flow that could trigger this error. I also added links to tracking issues that mark things that are blocking the usage of these expressions.

rust-highfive assigned oli-obk May 21, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 21, 2020

jonas-schievink added relnotes Marks issues that should be documented in the release notes of the next release. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels May 21, 2020

jonas-schievink added this to the 1.45 milestone May 21, 2020

KodrAus mentioned this pull request May 28, 2020

Rework structured value casting rust-lang/log#396

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mystor mentioned this pull request Jun 7, 2020

Make AtomicRef::new const fn mystor/atomic_ref#2

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const-evaluation rust-lang/lang-team#22

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Mark AtomicCell::is_lock_free() as const fn? crossbeam-rs/crossbeam#531

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zslayton mentioned this pull request Jun 30, 2020

Promote the header byte jump table to a constant amazon-ion/ion-rust#4

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Upgrade percent-encoding to 2.x and base64 to 0.12. rwf2/Rocket#1349

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boards/opentitan: Build OpenTitan with target device specific parameters tock/tock#1741

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yvt added a commit to r3-os/r3 that referenced this pull request Jul 9, 2020

chore: update the target compiler version to nightly-2020-07-07

a23c3f6

`const_if_match` and `const_loop` has been stabilized by <rust-lang/rust#72437>.

yvt added a commit to r3-os/r3 that referenced this pull request Jul 9, 2020

chore: update the target compiler version to nightly-2020-07-07

16ed714

`const_if_match` and `const_loop` have been stabilized by <rust-lang/rust#72437>.

yvt added a commit to r3-os/r3 that referenced this pull request Jul 9, 2020

doc: remove #![feature(const_loop)] and `#![feature(const_if_match)…

39ad732

…]` from example code `const_if_match` and `const_loop` have been stabilized by <rust-lang/rust#72437>.

Perlmint mentioned this pull request Aug 6, 2020

lazy_static 제거할 수 있는 곳 제거하기 skyser2003/ditto_bot_rust#8

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chenrui333 mentioned this pull request Sep 1, 2020

rust-analyzer 2020-08-31 Homebrew/homebrew-core#60465

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jrincayc mentioned this pull request Sep 4, 2020

Rust 1.46 now allows more features in const fn rust-lang/reference#883

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More constfn! stm32-rs/stm32h7xx-hal#137

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ThePuzzlemaker mentioned this pull request Nov 16, 2020

Update E0744 about control flow in const contexts to accurately describe when the error is triggered and why #79087

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Dependency on Crate "bs58" sets Minimum Rust Version to > 1.46 ChainSafe/forest#992

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Add more const fn functions svartalf/rust-macaddr#4

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jyn514 mentioned this pull request Oct 13, 2021

Tracking issue for RFC 2342, "Allow if and match in constants" #49146

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Stabilize `#![feature(const_if_match)]` and `#![feature(const_loop)]` #72437

Stabilize `#![feature(const_if_match)]` and `#![feature(const_loop)]` #72437

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ecstatic-morse commented May 21, 2020 •

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oli-obk commented Jun 30, 2020

Stabilize #![feature(const_if_match)] and #![feature(const_loop)] #72437

Stabilize #![feature(const_if_match)] and #![feature(const_loop)] #72437

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Stabilize `#![feature(const_if_match)]` and `#![feature(const_loop)]` #72437

Stabilize `#![feature(const_if_match)]` and `#![feature(const_loop)]` #72437

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ecstatic-morse commented May 21, 2020 •

edited