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

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merged 14 commits into from
Jun 29, 2020

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@ecstatic-morse ecstatic-morse commented May 21, 2020

Quoting from the stabilization report:

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

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 21, 2020
@jonas-schievink 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 jonas-schievink added this to the 1.45 milestone May 21, 2020
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ecstatic-morse commented May 21, 2020

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.

@crlf0710 crlf0710 added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 30, 2020
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ping @oli-obk

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oli-obk commented Jun 4, 2020

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.

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Ah, gotcha. Thanks!

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KodrAus commented Jun 11, 2020

There’s now a FCP on #52000

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jhpratt commented Jun 11, 2020

*proposed FCP. Still needs a few checkboxes.

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bors commented Jun 15, 2020

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

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oli-obk commented Jun 16, 2020

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.

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FCP on #52000 has completed!

@oli-obk oli-obk added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 26, 2020
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@ecstatic-morse ecstatic-morse force-pushed the stabilize-const-if-match branch 2 times, most recently from 402ed30 to 072247e Compare June 26, 2020 19:51
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@ecstatic-morse ecstatic-morse force-pushed the stabilize-const-if-match branch 3 times, most recently from 41cc4d6 to 63078c3 Compare June 26, 2020 22:28
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oli-obk commented Jun 30, 2020

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

Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this pull request Jun 30, 2020
…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.
Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this pull request Jul 1, 2020
…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.
yvt added a commit to r3-os/r3 that referenced this pull request Jul 9, 2020
`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
`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
…]` from example code

`const_if_match` and `const_loop` have been stabilized by
<rust-lang/rust#72437>.
Manishearth added a commit to Manishearth/rust that referenced this pull request Jul 22, 2020
…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.
Manishearth added a commit to Manishearth/rust that referenced this pull request Jul 22, 2020
…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.
Manishearth added a commit to Manishearth/rust that referenced this pull request Jul 22, 2020
…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.
Manishearth added a commit to Manishearth/rust that referenced this pull request Jul 22, 2020
…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.
Manishearth added a commit to Manishearth/rust that referenced this pull request Jul 22, 2020
…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.
Manishearth added a commit to Manishearth/rust that referenced this pull request Jul 22, 2020
…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.
Manishearth added a commit to Manishearth/rust that referenced this pull request Jul 27, 2020
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`
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Aug 30, 2020
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
@ecstatic-morse ecstatic-morse deleted the stabilize-const-if-match branch October 6, 2020 01:42
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Oct 30, 2020
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
m-ou-se added a commit to m-ou-se/rust that referenced this pull request Nov 16, 2020
…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.
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merged-by-bors This PR was explicitly merged by bors. relnotes Marks issues that should be documented in the release notes of the next release. S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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Successfully merging this pull request may close these issues.

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