RFC: Allow boolean literals as `cfg` predicates by clubby789 · Pull Request #3695 · rust-lang/rfcs

clubby789 · 2024-09-16T14:02:39Z

This RFC proposes allowing boolean literals as cfg predicates, e.g. cfg(true) and cfg(false).

Tracking:

Tracking issue for RFC 3695: Allow boolean literals as cfg predicates rust#131204

clarfonthey · 2024-09-16T14:59:19Z

Also worth noting that, in addition to cfg(any()) meaning cfg(false), cfg(all()) means cfg(true) as well. So, both technically have easy versions, but I agree that true and false care clearer.

text/0000-cfg_boolean_literal.md

joshtriplett · 2024-09-16T15:08:25Z

This is simple, straightforward, solves an existing problem, and has no compatibility issues.

@rfcbot merge

rfcbot · 2024-09-16T15:08:28Z

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

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), 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!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

text/0000-cfg_boolean_literal.md

Co-authored-by: lolbinarycat <dogedoge61+github@gmail.com>

text/0000-cfg_boolean_literal.md

kennytm · 2024-09-16T21:08:28Z

the RFC should mention somewhere that the raw identifiers r#true and r#false continue to work:

rustc --cfg false --check-cfg 'cfg(r#false, values(none()))' 1.rs
#     ^~~~~~~~~~~

// 1.rs
#![deny(warnings)]

#[expect(unexpected_cfgs)]
mod a {
  #[cfg(r#true)]
  pub fn foo() {}
}

mod b {
  #[cfg(r#false)]
  pub fn bar() {}
}

fn main() { 
    b::bar()
}

nikomatsakis · 2024-09-16T21:49:16Z

Yes please. I'm always surprised I can't do cfg(false).

@rfcbot reviewed

clubby789 · 2024-09-17T10:06:03Z

Added a note about r#true/r#false

clubby789 · 2024-09-17T10:09:22Z

Also worth noting that, in addition to cfg(any()) meaning cfg(false), cfg(all()) means cfg(true) as well.

Mentioned this in a couple of places for completeness

lolbinarycat · 2024-09-18T02:59:33Z

probably should also mention cfg_attr for completeness

traviscross · 2024-09-18T04:15:01Z

@rfcbot reviewed

In particular, now that we're warning about #[cfg(False)], #[cfg(FALSE)], etc., this is somewhat more pressing.

rfcbot · 2024-09-18T04:15:14Z

🔔 This is now entering its final comment period, as per the review above. 🔔

clubby789 · 2024-10-03T14:30:33Z

Updated the name to cfg_boolean_literals: (rust-lang/rust#131034 (comment))

traviscross · 2024-10-04T06:41:30Z

The team has accepted this RFC, and it's now been merged.

Thanks to @clubby789 for writing this up and pushing it forward.

For further updates, follow the tracking issue:

Tracking issue for RFC 3695: Allow boolean literals as cfg predicates rust#131204

Implement RFC3695 Allow boolean literals as cfg predicates This PR implements rust-lang/rfcs#3695: allow boolean literals as cfg predicates, i.e. `cfg(true)` and `cfg(false)`. r? `@nnethercote` *(or anyone with parser knowledge)* cc `@clubby789`

Rollup merge of rust-lang#131034 - Urgau:cfg-true-false, r=nnethercote Implement RFC3695 Allow boolean literals as cfg predicates This PR implements rust-lang/rfcs#3695: allow boolean literals as cfg predicates, i.e. `cfg(true)` and `cfg(false)`. r? `@nnethercote` *(or anyone with parser knowledge)* cc `@clubby789`

lolbinarycat · 2025-04-11T07:45:16Z

for posterity, here is the IRLO thread that lead to this RFC: https://internals.rust-lang.org/t/cfg-none-for-disabling-code/21520

…t, r=davidtwco,Urgau,traviscross Stabilize `cfg_boolean_literals` Closes rust-lang#131204 `@rustbot` labels +T-lang +I-lang-nominated This will end up conflicting with the test in rust-lang#138293 so whichever doesn't land first will need updating -- # Stabilization Report ## General design ### What is the RFC for this feature and what changes have occurred to the user-facing design since the RFC was finalized? [RFC 3695](rust-lang/rfcs#3695), none. ### What behavior are we committing to that has been controversial? Summarize the major arguments pro/con. None ### Are there extensions to this feature that remain unstable? How do we know that we are not accidentally committing to those? None ## Has a call-for-testing period been conducted? If so, what feedback was received? Yes; only positive feedback was received. ## Implementation quality ### Summarize the major parts of the implementation and provide links into the code (or to PRs) Implemented in [rust-lang#131034](rust-lang#131034). ### Summarize existing test coverage of this feature - [Basic usage, including `#[cfg()]`, `cfg!()` and `#[cfg_attr()]`](https://github.com/rust-lang/rust/blob/6d71251cf9e40326461f90f8ff9a7024706aea87/tests/ui/cfg/true-false.rs) - [`--cfg=true/false` on the command line being accessible via `r#true/r#false`](https://github.com/rust-lang/rust/blob/6d71251cf9e40326461f90f8ff9a7024706aea87/tests/ui/cfg/raw-true-false.rs) - [Interaction with the unstable `#[doc(cfg(..))]` feature](https://github.com/rust-lang/rust/tree/6d71251/tests/rustdoc-ui/cfg-boolean-literal.rs) - [Denying `--check-cfg=cfg(true/false)`](https://github.com/rust-lang/rust/tree/6d71251/tests/ui/check-cfg/invalid-arguments.rs) - Ensuring `--cfg false` on the command line doesn't change the meaning of `cfg(false)`: `tests/ui/cfg/cmdline-false.rs` - Ensuring both `cfg(true)` and `cfg(false)` on the same item result in it being disabled: `tests/ui/cfg/both-true-false.rs` ### What outstanding bugs in the issue tracker involve this feature? Are they stabilization-blocking? The above mentioned issue; it should not block as it interacts with another unstable feature. ### What FIXMEs are still in the code for that feature and why is it ok to leave them there? None ### Summarize contributors to the feature by name for recognition and assuredness that people involved in the feature agree with stabilization - `@clubby789` (RFC) - `@Urgau` (Implementation in rustc) ### Which tools need to be adjusted to support this feature. Has this work been done? `rustdoc`'s unstable`#[doc(cfg(..)]` has been updated to respect it. `cargo` has been updated with a forward compatibility lint to enable supporting it in cargo once stabilized. ## Type system and execution rules ### What updates are needed to the reference/specification? (link to PRs when they exist) A few lines to be added to the reference for configuration predicates, specified in the RFC.

Rollup merge of rust-lang#138632 - clubby789:stabilize-cfg-boolean-lit, r=davidtwco,Urgau,traviscross Stabilize `cfg_boolean_literals` Closes rust-lang#131204 `@rustbot` labels +T-lang +I-lang-nominated This will end up conflicting with the test in rust-lang#138293 so whichever doesn't land first will need updating -- # Stabilization Report ## General design ### What is the RFC for this feature and what changes have occurred to the user-facing design since the RFC was finalized? [RFC 3695](rust-lang/rfcs#3695), none. ### What behavior are we committing to that has been controversial? Summarize the major arguments pro/con. None ### Are there extensions to this feature that remain unstable? How do we know that we are not accidentally committing to those? None ## Has a call-for-testing period been conducted? If so, what feedback was received? Yes; only positive feedback was received. ## Implementation quality ### Summarize the major parts of the implementation and provide links into the code (or to PRs) Implemented in [rust-lang#131034](rust-lang#131034). ### Summarize existing test coverage of this feature - [Basic usage, including `#[cfg()]`, `cfg!()` and `#[cfg_attr()]`](https://github.com/rust-lang/rust/blob/6d71251cf9e40326461f90f8ff9a7024706aea87/tests/ui/cfg/true-false.rs) - [`--cfg=true/false` on the command line being accessible via `r#true/r#false`](https://github.com/rust-lang/rust/blob/6d71251cf9e40326461f90f8ff9a7024706aea87/tests/ui/cfg/raw-true-false.rs) - [Interaction with the unstable `#[doc(cfg(..))]` feature](https://github.com/rust-lang/rust/tree/6d71251/tests/rustdoc-ui/cfg-boolean-literal.rs) - [Denying `--check-cfg=cfg(true/false)`](https://github.com/rust-lang/rust/tree/6d71251/tests/ui/check-cfg/invalid-arguments.rs) - Ensuring `--cfg false` on the command line doesn't change the meaning of `cfg(false)`: `tests/ui/cfg/cmdline-false.rs` - Ensuring both `cfg(true)` and `cfg(false)` on the same item result in it being disabled: `tests/ui/cfg/both-true-false.rs` ### What outstanding bugs in the issue tracker involve this feature? Are they stabilization-blocking? The above mentioned issue; it should not block as it interacts with another unstable feature. ### What FIXMEs are still in the code for that feature and why is it ok to leave them there? None ### Summarize contributors to the feature by name for recognition and assuredness that people involved in the feature agree with stabilization - `@clubby789` (RFC) - `@Urgau` (Implementation in rustc) ### Which tools need to be adjusted to support this feature. Has this work been done? `rustdoc`'s unstable`#[doc(cfg(..)]` has been updated to respect it. `cargo` has been updated with a forward compatibility lint to enable supporting it in cargo once stabilized. ## Type system and execution rules ### What updates are needed to the reference/specification? (link to PRs when they exist) A few lines to be added to the reference for configuration predicates, specified in the RFC.

…dtwco,Urgau,traviscross Stabilize `cfg_boolean_literals` Closes #131204 `@rustbot` labels +T-lang +I-lang-nominated This will end up conflicting with the test in #138293 so whichever doesn't land first will need updating -- # Stabilization Report ## General design ### What is the RFC for this feature and what changes have occurred to the user-facing design since the RFC was finalized? [RFC 3695](rust-lang/rfcs#3695), none. ### What behavior are we committing to that has been controversial? Summarize the major arguments pro/con. None ### Are there extensions to this feature that remain unstable? How do we know that we are not accidentally committing to those? None ## Has a call-for-testing period been conducted? If so, what feedback was received? Yes; only positive feedback was received. ## Implementation quality ### Summarize the major parts of the implementation and provide links into the code (or to PRs) Implemented in [#131034](rust-lang/rust#131034). ### Summarize existing test coverage of this feature - [Basic usage, including `#[cfg()]`, `cfg!()` and `#[cfg_attr()]`](https://github.com/rust-lang/rust/blob/6d71251cf9e40326461f90f8ff9a7024706aea87/tests/ui/cfg/true-false.rs) - [`--cfg=true/false` on the command line being accessible via `r#true/r#false`](https://github.com/rust-lang/rust/blob/6d71251cf9e40326461f90f8ff9a7024706aea87/tests/ui/cfg/raw-true-false.rs) - [Interaction with the unstable `#[doc(cfg(..))]` feature](https://github.com/rust-lang/rust/tree/6d71251/tests/rustdoc-ui/cfg-boolean-literal.rs) - [Denying `--check-cfg=cfg(true/false)`](https://github.com/rust-lang/rust/tree/6d71251/tests/ui/check-cfg/invalid-arguments.rs) - Ensuring `--cfg false` on the command line doesn't change the meaning of `cfg(false)`: `tests/ui/cfg/cmdline-false.rs` - Ensuring both `cfg(true)` and `cfg(false)` on the same item result in it being disabled: `tests/ui/cfg/both-true-false.rs` ### What outstanding bugs in the issue tracker involve this feature? Are they stabilization-blocking? The above mentioned issue; it should not block as it interacts with another unstable feature. ### What FIXMEs are still in the code for that feature and why is it ok to leave them there? None ### Summarize contributors to the feature by name for recognition and assuredness that people involved in the feature agree with stabilization - `@clubby789` (RFC) - `@Urgau` (Implementation in rustc) ### Which tools need to be adjusted to support this feature. Has this work been done? `rustdoc`'s unstable`#[doc(cfg(..)]` has been updated to respect it. `cargo` has been updated with a forward compatibility lint to enable supporting it in cargo once stabilized. ## Type system and execution rules ### What updates are needed to the reference/specification? (link to PRs when they exist) A few lines to be added to the reference for configuration predicates, specified in the RFC.

### What does this PR try to resolve? This PR implements rust-lang/rfcs#3695: allow boolean literals as cfg predicates, i.e. `cfg(true)` and `cfg(false)`. ### How should we test and review this PR? The PR should be reviewed commit by commit and tested by looking at the tests and using `[target.'cfg(<true/false>)']` in `Cargo.toml`/`.cargo/config.toml`. ### Additional information I had to bump `cargo-platform` to `0.3.0` has we are changing `CfgExpr` enum in a semver incompatible change. We currently have (thks to #14671) a forward compatibility warning against `cfg(true/false)` as identifiers instead of keywords. ~~I choose a use a `Cargo.toml` feature (for the manifest) as well as a unstable CLI flag for the `.cargo/config.toml` part.~~ ~~Given the very small (two occurrences on Github Search) for [`cfg(true)`](https://github.com/search?q=lang%3Atoml+%2F%28%3F-i%29%5C%5Btarget%5C.%5B%27%22%5Dcfg.*true%2F&type=code) and [`cfg(false)`](https://github.com/search?q=lang%3Atoml+%2F%28%3F-i%29%5C%5Btarget%5C.%5B%27%22%5Dcfg.*false%2F&type=code), I choose to gate the feature under a error and not a warning.~~

…dtwco,Urgau,traviscross Stabilize `cfg_boolean_literals` Closes #131204 `@rustbot` labels +T-lang +I-lang-nominated This will end up conflicting with the test in #138293 so whichever doesn't land first will need updating -- # Stabilization Report ## General design ### What is the RFC for this feature and what changes have occurred to the user-facing design since the RFC was finalized? [RFC 3695](rust-lang/rfcs#3695), none. ### What behavior are we committing to that has been controversial? Summarize the major arguments pro/con. None ### Are there extensions to this feature that remain unstable? How do we know that we are not accidentally committing to those? None ## Has a call-for-testing period been conducted? If so, what feedback was received? Yes; only positive feedback was received. ## Implementation quality ### Summarize the major parts of the implementation and provide links into the code (or to PRs) Implemented in [#131034](rust-lang/rust#131034). ### Summarize existing test coverage of this feature - [Basic usage, including `#[cfg()]`, `cfg!()` and `#[cfg_attr()]`](https://github.com/rust-lang/rust/blob/6d71251cf9e40326461f90f8ff9a7024706aea87/tests/ui/cfg/true-false.rs) - [`--cfg=true/false` on the command line being accessible via `r#true/r#false`](https://github.com/rust-lang/rust/blob/6d71251cf9e40326461f90f8ff9a7024706aea87/tests/ui/cfg/raw-true-false.rs) - [Interaction with the unstable `#[doc(cfg(..))]` feature](https://github.com/rust-lang/rust/tree/6d71251/tests/rustdoc-ui/cfg-boolean-literal.rs) - [Denying `--check-cfg=cfg(true/false)`](https://github.com/rust-lang/rust/tree/6d71251/tests/ui/check-cfg/invalid-arguments.rs) - Ensuring `--cfg false` on the command line doesn't change the meaning of `cfg(false)`: `tests/ui/cfg/cmdline-false.rs` - Ensuring both `cfg(true)` and `cfg(false)` on the same item result in it being disabled: `tests/ui/cfg/both-true-false.rs` ### What outstanding bugs in the issue tracker involve this feature? Are they stabilization-blocking? The above mentioned issue; it should not block as it interacts with another unstable feature. ### What FIXMEs are still in the code for that feature and why is it ok to leave them there? None ### Summarize contributors to the feature by name for recognition and assuredness that people involved in the feature agree with stabilization - `@clubby789` (RFC) - `@Urgau` (Implementation in rustc) ### Which tools need to be adjusted to support this feature. Has this work been done? `rustdoc`'s unstable`#[doc(cfg(..)]` has been updated to respect it. `cargo` has been updated with a forward compatibility lint to enable supporting it in cargo once stabilized. ## Type system and execution rules ### What updates are needed to the reference/specification? (link to PRs when they exist) A few lines to be added to the reference for configuration predicates, specified in the RFC.

…elmann Remove uses of `cfg({any()/all()})` ~~This implements the followup warning suggested in rust-lang/rfcs#3695 ~~Lint against an empty `cfg(any/all)`, suggest the boolean literal equivalents.~~ rust-lang#149791 (comment) Tracking issue: rust-lang#131204

Rollup merge of #149791 - clubby789:cfg-bool-lints, r=jdonszelmann Remove uses of `cfg({any()/all()})` ~~This implements the followup warning suggested in rust-lang/rfcs#3695 ~~Lint against an empty `cfg(any/all)`, suggest the boolean literal equivalents.~~ #149791 (comment) Tracking issue: #131204

Remove uses of `cfg({any()/all()})` ~~This implements the followup warning suggested in rust-lang/rfcs#3695 ~~Lint against an empty `cfg(any/all)`, suggest the boolean literal equivalents.~~ rust-lang/rust#149791 (comment) Tracking issue: rust-lang/rust#131204

clubby789 added 2 commits September 16, 2024 10:58

cfg boolean literals

2aa0e82

Add RFC PR number

599dc26

joshtriplett reviewed Sep 16, 2024

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