Rollup merge of #138632 - clubby789:stabilize-cfg-boolean-lit, r=davidtwco,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](#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.

Author: matthiaskrgr

compiler/rustc_attr_parsing/src/attributes/cfg.rs

@@ -7,7 +7,6 @@ use rustc_session::config::ExpectedValues;
 use rustc_session::lint::BuiltinLintDiag;
 use rustc_session::lint::builtin::UNEXPECTED_CFGS;
 use rustc_session::parse::feature_err;
-use rustc_span::symbol::kw;
 use rustc_span::{Span, Symbol, sym};
 
 use crate::session_diagnostics::{self, UnsupportedLiteralReason};
@@ -89,20 +88,6 @@ pub fn eval_condition(
     let cfg = match cfg {
         MetaItemInner::MetaItem(meta_item) => meta_item,
         MetaItemInner::Lit(MetaItemLit { kind: LitKind::Bool(b), .. }) => {
-            if let Some(features) = features {
-                // we can't use `try_gate_cfg` as symbols don't differentiate between `r#true`
-                // and `true`, and we want to keep the former working without feature gate
-                gate_cfg(
-                    &(
-                        if *b { kw::True } else { kw::False },
-                        sym::cfg_boolean_literals,
-                        |features: &Features| features.cfg_boolean_literals(),
-                    ),
-                    cfg.span(),
-                    sess,
-                    features,
-                );
-            }
             return *b;
         }
         _ => {

compiler/rustc_feature/src/accepted.rs

@@ -95,6 +95,8 @@ declare_features! (
     (accepted, c_unwind, "1.81.0", Some(74990)),
     /// Allows `#[cfg_attr(predicate, multiple, attributes, here)]`.
     (accepted, cfg_attr_multi, "1.33.0", Some(54881)),
+    /// Allows the use of `#[cfg(<true/false>)]`.
+    (accepted, cfg_boolean_literals, "CURRENT_RUSTC_VERSION", Some(131204)),
     /// Allows the use of `#[cfg(doctest)]`, set when rustdoc is collecting doctests.
     (accepted, cfg_doctest, "1.40.0", Some(62210)),
     /// Enables `#[cfg(panic = "...")]` config key.

compiler/rustc_feature/src/unstable.rs

@@ -391,8 +391,6 @@ declare_features! (
     (unstable, async_trait_bounds, "1.85.0", Some(62290)),
     /// Allows using C-variadics.
     (unstable, c_variadic, "1.34.0", Some(44930)),
-    /// Allows the use of `#[cfg(<true/false>)]`.
-    (unstable, cfg_boolean_literals, "1.83.0", Some(131204)),
     /// Allows the use of `#[cfg(contract_checks)` to check if contract checks are enabled.
     (unstable, cfg_contract_checks, "1.86.0", Some(128044)),
     /// Allows the use of `#[cfg(overflow_checks)` to check if integer overflow behaviour.

src/doc/unstable-book/src/language-features/cfg-boolean-literals.md

@@ -3789,35 +3789,6 @@ The tracking issue for this feature is: [#64797]
 [#64797]: https://github.com/rust-lang/rust/issues/64797
 
 ------------------------
-"##,
-        default_severity: Severity::Allow,
-        warn_since: None,
-        deny_since: None,
-    },
-    Lint {
-        label: "cfg_boolean_literals",
-        description: r##"# `cfg_boolean_literals`
-
-The tracking issue for this feature is: [#131204]
-
-[#131204]: https://github.com/rust-lang/rust/issues/131204
-
-------------------------
-
-The `cfg_boolean_literals` feature makes it possible to use the `true`/`false`
-literal as cfg predicate. They always evaluate to true/false respectively.
-
-## Examples
-
-```rust
-#![feature(cfg_boolean_literals)]
-
-#[cfg(true)]
-const A: i32 = 5;
-
-#[cfg(all(false))]
-const A: i32 = 58 * 89;
-```
 "##,
         default_severity: Severity::Allow,
         warn_since: None,

src/tools/rust-analyzer/crates/ide-db/src/generated/lints.rs

@@ -2,7 +2,7 @@
 
 fn main() {}
 
-#[cfg(FALSE)]
+#[cfg(false)]
 fn syntax() {
     let _ = #[attr] [];
     let _ = #[attr] [0];

tests/pretty/ast-stmt-expr-attr.rs

@@ -4,5 +4,5 @@
 
 fn main() {}
 
-#[cfg(FALSE)]
+#[cfg(false)]
 enum Foo { pub V, }

tests/pretty/enum-variant-vis.rs

@@ -1,6 +1,6 @@
 //@ pp-exact
 
-#[cfg(FALSE)]
+#[cfg(false)]
 fn simple_attr() {
 
     #[attr]
@@ -10,21 +10,21 @@ fn simple_attr() {
     if true {}
 }
 
-#[cfg(FALSE)]
+#[cfg(false)]
 fn if_else_chain() {
 
     #[first_attr]
     if true {} else if false {} else {}
 }
 
-#[cfg(FALSE)]
+#[cfg(false)]
 fn if_let() {
 
     #[attr]
     if let Some(_) = Some(true) {}
 }
 
-#[cfg(FALSE)]
+#[cfg(false)]
 fn let_attr_if() {
     let _ = #[attr] if let _ = 0 {};
     let _ = #[attr] if true {};

tests/pretty/if-attr.rs

@@ -4,7 +4,7 @@
 
 fn main() {}
 
-#[cfg(FALSE)]
+#[cfg(false)]
 extern "C" {
     static X: u8;
     type X;
@@ -14,7 +14,7 @@ extern "C" {
     pub fn foo();
 }
 
-#[cfg(FALSE)]
+#[cfg(false)]
 trait T {
     const X: u8;
     type X;
@@ -30,7 +30,7 @@ trait T {
     pub default fn foo();
 }
 
-#[cfg(FALSE)]
+#[cfg(false)]
 impl T for S {
     const X: u8;
     type X;

tests/pretty/nested-item-vis-defaultness.rs

@@ -1,6 +1,5 @@
 //@ check-pass
 
-#![feature(cfg_boolean_literals)]
 #![feature(doc_cfg)]
 
 #[doc(cfg(false))]

tests/rustdoc-ui/cfg-boolean-literal.rs

@@ -1,10 +1,6 @@
 // #138113: rustdoc didn't gate unstable predicates inside `doc(cfg(..))`
 #![feature(doc_cfg)]
 
-// `cfg_boolean_literals`
-#[doc(cfg(false))] //~ ERROR `cfg(false)` is experimental and subject to change
-pub fn cfg_boolean_literals() {}
-
 // `cfg_version`
 #[doc(cfg(sanitize = "thread"))] //~ ERROR `cfg(sanitize)` is experimental and subject to change
 pub fn cfg_sanitize() {}

tests/rustdoc-ui/doc-cfg-unstable.rs

@@ -1,15 +1,5 @@
-error[E0658]: `cfg(false)` is experimental and subject to change
-  --> $DIR/doc-cfg-unstable.rs:5:11
-   |
-LL | #[doc(cfg(false))]
-   |           ^^^^^
-   |
-   = note: see issue #131204 <https://github.com/rust-lang/rust/issues/131204> for more information
-   = help: add `#![feature(cfg_boolean_literals)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
 error[E0658]: `cfg(sanitize)` is experimental and subject to change
-  --> $DIR/doc-cfg-unstable.rs:9:11
+  --> $DIR/doc-cfg-unstable.rs:5:11
    |
 LL | #[doc(cfg(sanitize = "thread"))]
    |           ^^^^^^^^^^^^^^^^^^^
@@ -18,6 +8,6 @@ LL | #[doc(cfg(sanitize = "thread"))]
    = help: add `#![feature(cfg_sanitize)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
 For more information about this error, try `rustc --explain E0658`.

tests/rustdoc-ui/doc-cfg-unstable.stderr

@@ -1,4 +1,4 @@
 fn main() {
-    #[cfg(FALSE)]
+    #[cfg(false)]
     <() as module>::mac!(); //~ ERROR macros cannot use qualified paths
 }

tests/ui/associated-types/associated-type-macro.rs

@@ -11,7 +11,7 @@ fn f() {
     };
 }
 
-#[cfg(FALSE)]
+#[cfg(false)]
 fn g() {
     let _ = async {
         for await _i in core::async_iter::from_iter(0..3) {

tests/ui/async-await/feature-async-for-loop.rs

@@ -3,11 +3,11 @@
 struct S;
 
 impl S {
-    #[cfg(FALSE)]
+    #[cfg(false)]
     unsafe async fn g() {} //~ ERROR expected one of `extern` or `fn`, found keyword `async`
 }
 
-#[cfg(FALSE)]
+#[cfg(false)]
 unsafe async fn f() {} //~ ERROR expected one of `extern` or `fn`, found keyword `async`
 
 fn main() {}

tests/ui/async-await/no-unsafe-async.rs

@@ -1,5 +1,5 @@
-// Ensure that `-Z crate-attr=cfg(FALSE)` can comment out the whole crate
-//@ compile-flags: --crate-type=lib -Zcrate-attr=cfg(FALSE)
+// Ensure that `-Z crate-attr=cfg(false)` can comment out the whole crate
+//@ compile-flags: --crate-type=lib -Zcrate-attr=cfg(false)
 //@ check-pass
 
 // NOTE: duplicate items are load-bearing

tests/ui/attributes/z-crate-attr/cfg-false.rs

@@ -1,6 +1,6 @@
 //@ check-pass
 
-#[cfg(FALSE)]
+#[cfg(false)]
 auto trait Foo {}
 //~^ WARN `auto` traits are unstable
 //~| WARN unstable syntax can change at any point in the future, causing a hard error!

tests/ui/auto-traits/pre-cfg.rs

@@ -1,4 +1,4 @@
-// `#![no_std]` on a fully unconfigured crate is respected if it's placed before `cfg(FALSE)`.
+// `#![no_std]` on a fully unconfigured crate is respected if it's placed before `cfg(false)`.
 // This crate has no such attribute, therefore this crate does link to libstd.
 
-#![cfg(FALSE)]
+#![cfg(false)]

tests/ui/cfg/auxiliary/cfg_false_lib.rs

@@ -1,5 +1,5 @@
-// `#![no_std]` on a fully unconfigured crate is respected if it's placed before `cfg(FALSE)`.
+// `#![no_std]` on a fully unconfigured crate is respected if it's placed before `cfg(false)`.
 // Therefore this crate does link to libstd.
 
-#![cfg(FALSE)]
+#![cfg(false)]
 #![no_std]

tests/ui/cfg/auxiliary/cfg_false_lib_no_std_after.rs

@@ -1,8 +1,8 @@
-// `#![no_std]` on a fully unconfigured crate is respected if it's placed before `cfg(FALSE)`.
+// `#![no_std]` on a fully unconfigured crate is respected if it's placed before `cfg(false)`.
 // Therefore this crate doesn't link to libstd.
 
 //@ no-prefer-dynamic
 
 #![no_std]
 #![crate_type = "lib"]
-#![cfg(FALSE)]
+#![cfg(false)]

tests/ui/cfg/auxiliary/cfg_false_lib_no_std_before.rs

@@ -1,8 +1,8 @@
 pub mod inner {
-    #[cfg(FALSE)]
+    #[cfg(false)]
     pub fn uwu() {}
 
-    #[cfg(FALSE)]
+    #[cfg(false)]
     pub mod doesnt_exist {
         pub fn hello() {}
     }

tests/ui/cfg/auxiliary/cfged_out.rs

@@ -0,0 +1,14 @@
+/// Test that placing a `cfg(true)` and `cfg(false)` on the same item result in
+//. it being disabled.`
+
+#[cfg(false)]
+#[cfg(true)]
+fn foo() {}
+
+#[cfg(true)]
+#[cfg(false)]
+fn foo() {}
+
+fn main() {
+    foo();  //~ ERROR cannot find function `foo` in this scope
+}

tests/ui/cfg/both-true-false.rs

@@ -0,0 +1,9 @@
+error[E0425]: cannot find function `foo` in this scope
+  --> $DIR/both-true-false.rs:13:5
+   |
+LL |     foo();
+   |     ^^^ not found in this scope
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0425`.

tests/ui/cfg/both-true-false.stderr

@@ -1,10 +1,10 @@
-// Features above `cfg(FALSE)` are in effect in a fully unconfigured crate (issue #104633).
+// Features above `cfg(false)` are in effect in a fully unconfigured crate (issue #104633).
 
 //@ check-pass
 //@ compile-flags: --crate-type lib
 
 #![feature(decl_macro)]
-#![cfg(FALSE)]
+#![cfg(false)]
 #![feature(box_patterns)]
 
 macro mac() {} // OK

tests/ui/cfg/cfg-false-feature.rs

@@ -3,7 +3,7 @@
 // check that cfg correctly chooses between the macro impls (see also
 // cfg-macros-foo.rs)
 
-#[cfg(FALSE)]
+#[cfg(false)]
 #[macro_use]
 mod foo {
     macro_rules! bar {

tests/ui/cfg/cfg-macros-notfoo.rs

@@ -11,7 +11,7 @@ fn foo(f: Foo) {
         Foo::Bar => {},
         #[cfg(not(FALSE))]
         Foo::Baz => {},
-        #[cfg(FALSE)]
+        #[cfg(false)]
         Basdfwe => {}
     }
 }

tests/ui/cfg/cfg-match-arm.rs

@@ -6,7 +6,7 @@
 #[cfg_eval]
 fn main() {
     #[cfg_eval]
-    let _ = #[cfg(FALSE)] 0;
+    let _ = #[cfg(false)] 0;
     //~^ ERROR removing an expression is not supported in this position
     //~| ERROR expected expression, found `;`
     //~| ERROR removing an expression is not supported in this position

tests/ui/cfg/cfg-stmt-recovery.rs

@@ -1,19 +1,19 @@
 error: removing an expression is not supported in this position
   --> $DIR/cfg-stmt-recovery.rs:9:13
    |
-LL |     let _ = #[cfg(FALSE)] 0;
+LL |     let _ = #[cfg(false)] 0;
    |             ^^^^^^^^^^^^^
 
 error: expected expression, found `;`
   --> $DIR/cfg-stmt-recovery.rs:9:28
    |
-LL |     let _ = #[cfg(FALSE)] 0;
+LL |     let _ = #[cfg(false)] 0;
    |                            ^ expected expression
 
 error: removing an expression is not supported in this position
   --> $DIR/cfg-stmt-recovery.rs:9:13
    |
-LL |     let _ = #[cfg(FALSE)] 0;
+LL |     let _ = #[cfg(false)] 0;
    |             ^^^^^^^^^^^^^
 
 error: aborting due to 3 previous errors