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.

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))]