Stabilize lint_reasons in rustc (RFC 2383)

compiler/rustc_feature/src/accepted.rs

@@ -188,6 +188,8 @@ declare_features! (
     (accepted, item_like_imports, "1.15.0", Some(35120), None),
     /// Allows `if/while p && let q = r && ...` chains.
     (accepted, let_chains, "1.64.0", Some(53667), None),
+    /// Allows using `reason` in lint attributes and the `#[expect(lint)]` lint check.
+    (accepted, lint_reasons, "1.64.0", Some(54503), None),
     /// Allows `break {expr}` with a value inside `loop`s.
     (accepted, loop_break_value, "1.19.0", Some(37339), None),
     /// Allows use of `?` as the Kleene "at most one" operator in macros.

compiler/rustc_feature/src/active.rs

@@ -428,8 +428,6 @@ declare_features! (
     (active, let_else, "1.56.0", Some(87335), None),
     /// Allows `#[link(..., cfg(..))]`.
     (active, link_cfg, "1.14.0", Some(37406), None),
-    /// Allows using `reason` in lint attributes and the `#[expect(lint)]` lint check.
-    (active, lint_reasons, "1.31.0", Some(54503), None),
     /// Give access to additional metadata about declarative macro meta-variables.
     (active, macro_metavar_expr, "1.61.0", Some(83527), None),
     /// Allows `#[marker]` on certain traits allowing overlapping implementations.

compiler/rustc_feature/src/builtin_attrs.rs

@@ -301,9 +301,8 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ungated!(
         allow, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
     ),
-    gated!(
-        expect, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk,
-        lint_reasons, experimental!(expect)
+    ungated!(
+        expect, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
     ),
     ungated!(
         forbid, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk

compiler/rustc_lint/src/expect.rs

@@ -4,18 +4,13 @@ use rustc_hir::HirId;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::{lint::LintExpectation, ty::TyCtxt};
 use rustc_session::lint::LintExpectationId;
-use rustc_span::symbol::sym;
 use rustc_span::Symbol;
 
 pub(crate) fn provide(providers: &mut Providers) {
     *providers = Providers { check_expectations, ..*providers };
 }
 
 fn check_expectations(tcx: TyCtxt<'_>, tool_filter: Option<Symbol>) {
-    if !tcx.sess.features_untracked().enabled(sym::lint_reasons) {
-        return;
-    }
-
     let fulfilled_expectations = tcx.sess.diagnostic().steal_fulfilled_expectation_ids();
     let lint_expectations = &tcx.lint_levels(()).lint_expectations;
 

compiler/rustc_lint/src/levels.rs

@@ -17,7 +17,7 @@ use rustc_session::lint::{
     builtin::{self, FORBIDDEN_LINT_GROUPS, SINGLE_USE_LIFETIMES, UNFULFILLED_LINT_EXPECTATIONS},
     Level, Lint, LintExpectationId, LintId,
 };
-use rustc_session::parse::{add_feature_diagnostics, feature_err};
+use rustc_session::parse::add_feature_diagnostics;
 use rustc_session::Session;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::{Span, DUMMY_SP};
@@ -306,15 +306,6 @@ impl<'s> LintLevelsBuilder<'s> {
                     ast::MetaItemKind::NameValue(ref name_value) => {
                         if item.path == sym::reason {
                             if let ast::LitKind::Str(rationale, _) = name_value.kind {
-                                if !self.sess.features_untracked().lint_reasons {
-                                    feature_err(
-                                        &self.sess.parse_sess,
-                                        sym::lint_reasons,
-                                        item.span,
-                                        "lint reasons are experimental",
-                                    )
-                                    .emit();
-                                }
                                 reason = Some(rationale);
                             } else {
                                 bad_attr(name_value.span)

compiler/rustc_lint_defs/src/builtin.rs

@@ -503,8 +503,6 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust
-    /// #![feature(lint_reasons)]
-    ///
     /// #[expect(unused_variables)]
     /// let x = 10;
     /// println!("{}", x);
@@ -530,8 +528,7 @@ declare_lint! {
     /// [#54503]: https://github.com/rust-lang/rust/issues/54503
     pub UNFULFILLED_LINT_EXPECTATIONS,
     Warn,
-    "unfulfilled lint expectation",
-    @feature_gate = rustc_span::sym::lint_reasons;
+    "unfulfilled lint expectation"
 }
 
 declare_lint! {

src/doc/rustc/src/lints/levels.md

@@ -1,12 +1,13 @@
 # Lint Levels
 
-In `rustc`, lints are divided into five *levels*:
+In `rustc`, lints are divided into six *levels*:
 
 1. allow
-2. warn
-3. force-warn
-4. deny
-5. forbid
+2. expect
+3. warn
+4. force-warn
+5. deny
+6. forbid
 
 Each lint has a default level (explained in the lint listing later in this
 chapter), and the compiler has a default warning level. First, let's explain
@@ -33,6 +34,40 @@ But this code violates the `missing_docs` lint.
 These lints exist mostly to be manually turned on via configuration, as we'll
 talk about later in this section.
 
+## expect
+
+Sometimes, it can be helpful to suppress lints, but at the same time ensure that
+the code in question still emits them. The 'expect' level does exactly this. If
+the lint in question is not emitted, the `unfulfilled_lint_expectation` lint
+triggers on the `expect` attribute, notifying you that the expectation is no
+longer fulfilled.
+
+```rust
+fn main() {
+    #[expect(unused_variables)]
+    let unused = "Everyone ignores me";
+
+    #[expect(unused_variables)]
+    let used = "I'm useful";
+    println!("The `used` value is equal to: {:?}", used);
+}
+```
+
+This will produce the following warning:
+
+```txt
+warning: this lint expectation is unfulfilled
+ --> src/main.rs:7:14
+  |
+7 |     #[expect(unused_variables)]
+  |              ^^^^^^^^^^^^^^^^
+  |
+  = note: `#[warn(unfulfilled_lint_expectations)]` on by default
+```
+
+This level can only be defined via the `#[expect]` attribute and not via the
+console. Lints with the special 'force-warn' lint will still be emitted as usual.
+
 ## warn
 
 The 'warn' lint level will produce a warning if you violate the lint. For example,
@@ -240,6 +275,24 @@ And use multiple attributes together:
 pub fn foo() {}
 ```
 
+All lint attributes support an additional `reason` parameter, to give context why
+a certain attribute was added. This reason will be displayed as part of the lint
+message, if the lint is emitted at the defined level.
+
+```rust
+use std::path::PathBuf;
+
+pub fn get_path() -> PathBuf {
+    #[allow(unused_mut, reason = "this is only modified on some platforms")]
+    let mut file_name = PathBuf::from("git");
+
+    #[cfg(target_os = "windows")]
+    file_name.set_extension("exe");
+
+    file_name
+}
+```
+
 ### Capping lints
 
 `rustc` supports a flag, `--cap-lints LEVEL` that sets the "lint cap level."

src/test/rustdoc-ui/expect-tool-lint-rfc-2383.rs

@@ -1,5 +1,4 @@
 // check-pass
-#![feature(lint_reasons)]
 
 //! This file tests the `#[expect]` attribute implementation for tool lints. The same
 //! file is used to test clippy and rustdoc. Any changes to this file should be synced

src/test/rustdoc-ui/expect-tool-lint-rfc-2383.stderr

@@ -1,25 +1,25 @@
 warning: this lint expectation is unfulfilled
-  --> $DIR/expect-tool-lint-rfc-2383.rs:16:11
+  --> $DIR/expect-tool-lint-rfc-2383.rs:15:11
    |
 LL | #![expect(rustdoc::missing_crate_level_docs)]
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(unfulfilled_lint_expectations)]` on by default
 
 warning: this lint expectation is unfulfilled
-  --> $DIR/expect-tool-lint-rfc-2383.rs:71:14
+  --> $DIR/expect-tool-lint-rfc-2383.rs:70:14
    |
 LL |     #[expect(rustdoc::broken_intra_doc_links)]
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: this lint expectation is unfulfilled
-  --> $DIR/expect-tool-lint-rfc-2383.rs:76:14
+  --> $DIR/expect-tool-lint-rfc-2383.rs:75:14
    |
 LL |     #[expect(rustdoc::invalid_html_tags)]
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: this lint expectation is unfulfilled
-  --> $DIR/expect-tool-lint-rfc-2383.rs:81:14
+  --> $DIR/expect-tool-lint-rfc-2383.rs:80:14
    |
 LL |     #[expect(rustdoc::bare_urls)]
    |              ^^^^^^^^^^^^^^^^^^

src/test/ui/empty/empty-attributes.rs

@@ -1,5 +1,3 @@
-#![feature(lint_reasons)]
-
 #![deny(unused_attributes)]
 #![allow()] //~ ERROR unused attribute
 #![expect()] //~ ERROR unused attribute

src/test/ui/empty/empty-attributes.stderr

@@ -1,66 +1,66 @@
 error: unused attribute
-  --> $DIR/empty-attributes.rs:11:1
+  --> $DIR/empty-attributes.rs:9:1
    |
 LL | #[repr()]
    | ^^^^^^^^^ help: remove this attribute
    |
 note: the lint level is defined here
-  --> $DIR/empty-attributes.rs:3:9
+  --> $DIR/empty-attributes.rs:1:9
    |
 LL | #![deny(unused_attributes)]
    |         ^^^^^^^^^^^^^^^^^
    = note: attribute `repr` with an empty list has no effect
 
 error: unused attribute
-  --> $DIR/empty-attributes.rs:14:1
+  --> $DIR/empty-attributes.rs:12:1
    |
 LL | #[target_feature()]
    | ^^^^^^^^^^^^^^^^^^^ help: remove this attribute
    |
    = note: attribute `target_feature` with an empty list has no effect
 
 error: unused attribute
-  --> $DIR/empty-attributes.rs:4:1
+  --> $DIR/empty-attributes.rs:2:1
    |
 LL | #![allow()]
    | ^^^^^^^^^^^ help: remove this attribute
    |
    = note: attribute `allow` with an empty list has no effect
 
 error: unused attribute
-  --> $DIR/empty-attributes.rs:5:1
+  --> $DIR/empty-attributes.rs:3:1
    |
 LL | #![expect()]
    | ^^^^^^^^^^^^ help: remove this attribute
    |
    = note: attribute `expect` with an empty list has no effect
 
 error: unused attribute
-  --> $DIR/empty-attributes.rs:6:1
+  --> $DIR/empty-attributes.rs:4:1
    |
 LL | #![warn()]
    | ^^^^^^^^^^ help: remove this attribute
    |
    = note: attribute `warn` with an empty list has no effect
 
 error: unused attribute
-  --> $DIR/empty-attributes.rs:7:1
+  --> $DIR/empty-attributes.rs:5:1
    |
 LL | #![deny()]
    | ^^^^^^^^^^ help: remove this attribute
    |
    = note: attribute `deny` with an empty list has no effect
 
 error: unused attribute
-  --> $DIR/empty-attributes.rs:8:1
+  --> $DIR/empty-attributes.rs:6:1
    |
 LL | #![forbid()]
    | ^^^^^^^^^^^^ help: remove this attribute
    |
    = note: attribute `forbid` with an empty list has no effect
 
 error: unused attribute
-  --> $DIR/empty-attributes.rs:9:1
+  --> $DIR/empty-attributes.rs:7:1
    |
 LL | #![feature()]
    | ^^^^^^^^^^^^^ help: remove this attribute

src/test/ui/lint/empty-lint-attributes.rs

@@ -1,5 +1,3 @@
-#![feature(lint_reasons)]
-
 // check-pass
 
 // Empty (and reason-only) lint attributes are legal—although we may want to

src/test/ui/lint/rfc-2383-lint-reason/avoid_delayed_good_path_ice.rs

@@ -1,5 +1,4 @@
 // check-pass
-#![feature(lint_reasons)]
 
 #[expect(drop_bounds)]
 fn trigger_rustc_lints<T: Drop>() {

src/test/ui/lint/rfc-2383-lint-reason/catch_multiple_lint_triggers.rs

@@ -1,7 +1,5 @@
 // check-pass
 
-#![feature(lint_reasons)]
-
 #![warn(unused)]
 
 // This expect attribute should catch all lint triggers

src/test/ui/lint/rfc-2383-lint-reason/crate_level_expect.rs

@@ -1,7 +1,5 @@
 // check-pass
 
-#![feature(lint_reasons)]
-
 #![warn(unused)]
 
 #![expect(unused_mut)]

src/test/ui/lint/rfc-2383-lint-reason/crate_level_expect.stderr

@@ -1,5 +1,5 @@
 warning: this lint expectation is unfulfilled
-  --> $DIR/crate_level_expect.rs:7:11
+  --> $DIR/crate_level_expect.rs:5:11
    |
 LL | #![expect(unused_mut)]
    |           ^^^^^^^^^^

src/test/ui/lint/rfc-2383-lint-reason/expect_inside_macro.rs

@@ -1,7 +1,5 @@
 // check-pass
 
-#![feature(lint_reasons)]
-
 #![warn(unused)]
 
 macro_rules! expect_inside_macro {

src/test/ui/lint/rfc-2383-lint-reason/expect_lint_from_macro.rs

@@ -1,7 +1,5 @@
 // check-pass
 
-#![feature(lint_reasons)]
-
 #![warn(unused_variables)]
 
 macro_rules! trigger_unused_variables_macro {

src/test/ui/lint/rfc-2383-lint-reason/expect_lint_from_macro.stderr

@@ -1,5 +1,5 @@
 warning: unused variable: `x`
-  --> $DIR/expect_lint_from_macro.rs:9:13
+  --> $DIR/expect_lint_from_macro.rs:7:13
    |
 LL |         let x = 0;
    |             ^ help: if this is intentional, prefix it with an underscore: `_x`
@@ -8,14 +8,14 @@ LL |     trigger_unused_variables_macro!();
    |     --------------------------------- in this macro invocation
    |
 note: the lint level is defined here
-  --> $DIR/expect_lint_from_macro.rs:5:9
+  --> $DIR/expect_lint_from_macro.rs:3:9
    |
 LL | #![warn(unused_variables)]
    |         ^^^^^^^^^^^^^^^^
    = note: this warning originates in the macro `trigger_unused_variables_macro` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 warning: unused variable: `x`
-  --> $DIR/expect_lint_from_macro.rs:9:13
+  --> $DIR/expect_lint_from_macro.rs:7:13
    |
 LL |         let x = 0;
    |             ^ help: if this is intentional, prefix it with an underscore: `_x`