RFC 2383: Stabilize lint_reasons in Clippy 🖇️

Author: xFrednet

src/tools/clippy/CHANGELOG.md

@@ -1943,7 +1943,7 @@ Released 2022-05-19
   [#8218](https://github.com/rust-lang/rust-clippy/pull/8218)
 * [`needless_match`]
   [#8471](https://github.com/rust-lang/rust-clippy/pull/8471)
-* [`allow_attributes_without_reason`] (Requires `#![feature(lint_reasons)]`)
+* [`allow_attributes_without_reason`]
   [#8504](https://github.com/rust-lang/rust-clippy/pull/8504)
 * [`print_in_format_impl`]
   [#8253](https://github.com/rust-lang/rust-clippy/pull/8253)

src/tools/clippy/book/src/lint_configuration.md

@@ -669,6 +669,8 @@ The minimum rust version that the project supports. Defaults to the `rust-versio
 
 ---
 **Affected lints:**
+* [`allow_attributes`](https://rust-lang.github.io/rust-clippy/master/index.html#allow_attributes)
+* [`allow_attributes_without_reason`](https://rust-lang.github.io/rust-clippy/master/index.html#allow_attributes_without_reason)
 * [`almost_complete_range`](https://rust-lang.github.io/rust-clippy/master/index.html#almost_complete_range)
 * [`approx_constant`](https://rust-lang.github.io/rust-clippy/master/index.html#approx_constant)
 * [`assigning_clones`](https://rust-lang.github.io/rust-clippy/master/index.html#assigning_clones)

src/tools/clippy/clippy_config/src/conf.rs

@@ -265,7 +265,7 @@ define_Conf! {
     ///
     /// Suppress lints whenever the suggested change would cause breakage for other crates.
     (avoid_breaking_exported_api: bool = true),
-    /// Lint: MANUAL_SPLIT_ONCE, MANUAL_STR_REPEAT, CLONED_INSTEAD_OF_COPIED, REDUNDANT_FIELD_NAMES, OPTION_MAP_UNWRAP_OR, REDUNDANT_STATIC_LIFETIMES, FILTER_MAP_NEXT, CHECKED_CONVERSIONS, MANUAL_RANGE_CONTAINS, USE_SELF, MEM_REPLACE_WITH_DEFAULT, MANUAL_NON_EXHAUSTIVE, OPTION_AS_REF_DEREF, MAP_UNWRAP_OR, MATCH_LIKE_MATCHES_MACRO, MANUAL_STRIP, MISSING_CONST_FOR_FN, UNNESTED_OR_PATTERNS, FROM_OVER_INTO, PTR_AS_PTR, IF_THEN_SOME_ELSE_NONE, APPROX_CONSTANT, DEPRECATED_CFG_ATTR, INDEX_REFUTABLE_SLICE, MAP_CLONE, BORROW_AS_PTR, MANUAL_BITS, ERR_EXPECT, CAST_ABS_TO_UNSIGNED, UNINLINED_FORMAT_ARGS, MANUAL_CLAMP, MANUAL_LET_ELSE, UNCHECKED_DURATION_SUBTRACTION, COLLAPSIBLE_STR_REPLACE, SEEK_FROM_CURRENT, SEEK_REWIND, UNNECESSARY_LAZY_EVALUATIONS, TRANSMUTE_PTR_TO_REF, ALMOST_COMPLETE_RANGE, NEEDLESS_BORROW, DERIVABLE_IMPLS, MANUAL_IS_ASCII_CHECK, MANUAL_REM_EUCLID, MANUAL_RETAIN, TYPE_REPETITION_IN_BOUNDS, TUPLE_ARRAY_CONVERSIONS, MANUAL_TRY_FOLD, MANUAL_HASH_ONE, ITER_KV_MAP, MANUAL_C_STR_LITERALS, ASSIGNING_CLONES, LEGACY_NUMERIC_CONSTANTS.
+    /// Lint: MANUAL_SPLIT_ONCE, MANUAL_STR_REPEAT, CLONED_INSTEAD_OF_COPIED, REDUNDANT_FIELD_NAMES, OPTION_MAP_UNWRAP_OR, REDUNDANT_STATIC_LIFETIMES, FILTER_MAP_NEXT, CHECKED_CONVERSIONS, MANUAL_RANGE_CONTAINS, USE_SELF, MEM_REPLACE_WITH_DEFAULT, MANUAL_NON_EXHAUSTIVE, OPTION_AS_REF_DEREF, MAP_UNWRAP_OR, MATCH_LIKE_MATCHES_MACRO, MANUAL_STRIP, MISSING_CONST_FOR_FN, UNNESTED_OR_PATTERNS, FROM_OVER_INTO, PTR_AS_PTR, IF_THEN_SOME_ELSE_NONE, APPROX_CONSTANT, DEPRECATED_CFG_ATTR, INDEX_REFUTABLE_SLICE, MAP_CLONE, BORROW_AS_PTR, MANUAL_BITS, ERR_EXPECT, CAST_ABS_TO_UNSIGNED, UNINLINED_FORMAT_ARGS, MANUAL_CLAMP, MANUAL_LET_ELSE, UNCHECKED_DURATION_SUBTRACTION, COLLAPSIBLE_STR_REPLACE, SEEK_FROM_CURRENT, SEEK_REWIND, UNNECESSARY_LAZY_EVALUATIONS, TRANSMUTE_PTR_TO_REF, ALMOST_COMPLETE_RANGE, NEEDLESS_BORROW, DERIVABLE_IMPLS, MANUAL_IS_ASCII_CHECK, MANUAL_REM_EUCLID, MANUAL_RETAIN, TYPE_REPETITION_IN_BOUNDS, TUPLE_ARRAY_CONVERSIONS, MANUAL_TRY_FOLD, MANUAL_HASH_ONE, ITER_KV_MAP, MANUAL_C_STR_LITERALS, ASSIGNING_CLONES, LEGACY_NUMERIC_CONSTANTS, ALLOW_ATTRIBUTES, ALLOW_ATTRIBUTES_WITHOUT_REASON.
     ///
     /// The minimum rust version that the project supports. Defaults to the `rust-version` field in `Cargo.toml`
     #[default_text = ""]

src/tools/clippy/clippy_config/src/msrvs.rs

@@ -17,6 +17,7 @@ macro_rules! msrv_aliases {
 
 // names may refer to stabilized feature flags or library items
 msrv_aliases! {
+    1,81,0  { LINT_REASONS_STABILIZATION }
     1,77,0 { C_STR_LITERALS }
     1,76,0 { PTR_FROM_REF }
     1,71,0 { TUPLE_ARRAY_CONVERSIONS, BUILD_HASHER_HASH_ONE }

src/tools/clippy/clippy_lints/src/allow_attributes.rs

@@ -0,0 +1,26 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::is_from_proc_macro;
+use rustc_ast::{AttrStyle, Attribute};
+use rustc_errors::Applicability;
+use rustc_lint::{LateContext, LintContext};
+use rustc_middle::lint::in_external_macro;
+use super::ALLOW_ATTRIBUTES;
+
+// Separate each crate's features.
+pub fn check<'cx>(cx: &LateContext<'cx>, attr: &'cx Attribute) {
+    if !in_external_macro(cx.sess(), attr.span)
+        && let AttrStyle::Outer = attr.style
+        && let Some(ident) = attr.ident()
+        && !is_from_proc_macro(cx, &attr)
+    {
+        span_lint_and_sugg(
+            cx,
+            ALLOW_ATTRIBUTES,
+            ident.span,
+            "#[allow] attribute found",
+            "replace it with",
+            "expect".into(),
+            Applicability::MachineApplicable,
+        );
+    }
+}

src/tools/clippy/clippy_lints/src/attrs/allow_attributes.rs

@@ -8,11 +8,6 @@ use rustc_span::sym;
 use rustc_span::symbol::Symbol;
 
 pub(super) fn check<'cx>(cx: &LateContext<'cx>, name: Symbol, items: &[NestedMetaItem], attr: &'cx Attribute) {
-    // Check for the feature
-    if !cx.tcx.features().lint_reasons {
-        return;
-    }
-
     // Check if the reason is present
     if let Some(item) = items.last().and_then(NestedMetaItem::meta_item)
         && let MetaItemKind::NameValue(_) = &item.kind

src/tools/clippy/clippy_lints/src/attrs/allow_attributes_without_reason.rs

@@ -1,6 +1,7 @@
 //! checks for attributes
 
 mod allow_attributes_without_reason;
+mod allow_attributes;
 mod blanket_clippy_restriction_lints;
 mod deprecated_cfg_attr;
 mod deprecated_semver;
@@ -14,11 +15,11 @@ mod unnecessary_clippy_cfg;
 mod useless_attribute;
 mod utils;
 
-use clippy_config::msrvs::Msrv;
+use clippy_config::msrvs::{self, Msrv};
 use rustc_ast::{Attribute, MetaItemKind, NestedMetaItem};
 use rustc_hir::{ImplItem, Item, ItemKind, TraitItem};
 use rustc_lint::{EarlyContext, EarlyLintPass, LateContext, LateLintPass};
-use rustc_session::{declare_lint_pass, impl_lint_pass};
+use rustc_session::impl_lint_pass;
 use rustc_span::sym;
 use utils::{is_lint_level, is_relevant_impl, is_relevant_item, is_relevant_trait};
 
@@ -272,23 +273,17 @@ declare_clippy_lint! {
     /// ### What it does
     /// Checks for attributes that allow lints without a reason.
     ///
-    /// (This requires the `lint_reasons` feature)
-    ///
     /// ### Why restrict this?
     /// Justifying each `allow` helps readers understand the reasoning,
     /// and may allow removing `allow` attributes if their purpose is obsolete.
     ///
     /// ### Example
     /// ```no_run
-    /// #![feature(lint_reasons)]
-    ///
     /// #![allow(clippy::some_lint)]
     /// ```
     ///
     /// Use instead:
     /// ```no_run
-    /// #![feature(lint_reasons)]
-    ///
     /// #![allow(clippy::some_lint, reason = "False positive rust-lang/rust-clippy#1002020")]
     /// ```
     #[clippy::version = "1.61.0"]
@@ -297,6 +292,41 @@ declare_clippy_lint! {
     "ensures that all `allow` and `expect` attributes have a reason"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for usage of the `#[allow]` attribute and suggests replacing it with
+    /// the `#[expect]` (See [RFC 2383](https://rust-lang.github.io/rfcs/2383-lint-reasons.html))
+    ///
+    /// This lint only warns outer attributes (`#[allow]`), as inner attributes
+    /// (`#![allow]`) are usually used to enable or disable lints on a global scale.
+    ///
+    /// ### Why is this bad?
+    /// `#[expect]` attributes suppress the lint emission, but emit a warning, if
+    /// the expectation is unfulfilled. This can be useful to be notified when the
+    /// lint is no longer triggered.
+    ///
+    /// ### Example
+    /// ```rust,ignore
+    /// #[allow(unused_mut)]
+    /// fn foo() -> usize {
+    ///    let mut a = Vec::new();
+    ///    a.len()
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust,ignore
+    /// #[expect(unused_mut)]
+    /// fn foo() -> usize {
+    ///     let mut a = Vec::new();
+    ///     a.len()
+    /// }
+    /// ```
+    #[clippy::version = "1.70.0"]
+    pub ALLOW_ATTRIBUTES,
+    restriction,
+    "`#[allow]` will not trigger if a warning isn't found. `#[expect]` triggers if there are no warnings."
+}
+
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for `#[should_panic]` attributes without specifying the expected panic message.
@@ -469,7 +499,12 @@ declare_clippy_lint! {
     "duplicated attribute"
 }
 
-declare_lint_pass!(Attributes => [
+#[derive(Clone)]
+pub struct Attributes {
+    msrv: Msrv,
+}
+
+impl_lint_pass!(Attributes => [
     ALLOW_ATTRIBUTES_WITHOUT_REASON,
     INLINE_ALWAYS,
     DEPRECATED_SEMVER,
@@ -480,6 +515,13 @@ declare_lint_pass!(Attributes => [
     DUPLICATED_ATTRIBUTES,
 ]);
 
+impl Attributes {
+    #[must_use]
+    pub fn new(msrv: Msrv) -> Self {
+        Self { msrv }
+    }
+}
+
 impl<'tcx> LateLintPass<'tcx> for Attributes {
     fn check_crate(&mut self, cx: &LateContext<'tcx>) {
         blanket_clippy_restriction_lints::check_command_line(cx);
@@ -492,8 +534,15 @@ impl<'tcx> LateLintPass<'tcx> for Attributes {
                 if is_lint_level(ident.name, attr.id) {
                     blanket_clippy_restriction_lints::check(cx, ident.name, items);
                 }
+                if matches!(ident.name, sym::allow) {
+                    if self.msrv.meets(msrvs::LINT_REASONS_STABILIZATION) {
+                        allow_attributes::check(cx, attr);
+                    }
+                }
                 if matches!(ident.name, sym::allow | sym::expect) {
-                    allow_attributes_without_reason::check(cx, ident.name, items, attr);
+                    if self.msrv.meets(msrvs::LINT_REASONS_STABILIZATION) {
+                        allow_attributes_without_reason::check(cx, ident.name, items, attr);
+                    }
                 }
                 if items.is_empty() || !attr.has_name(sym::deprecated) {
                     return;
@@ -537,6 +586,8 @@ impl<'tcx> LateLintPass<'tcx> for Attributes {
             inline_always::check(cx, item.span, item.ident.name, cx.tcx.hir().attrs(item.hir_id()));
         }
     }
+
+    extract_msrv_attr!(LateContext);
 }
 
 pub struct EarlyAttributes {

src/tools/clippy/clippy_lints/src/attrs/mod.rs

@@ -38,7 +38,6 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     #[cfg(feature = "internal")]
     crate::utils::internal_lints::unsorted_clippy_utils_paths::UNSORTED_CLIPPY_UTILS_PATHS_INFO,
     crate::absolute_paths::ABSOLUTE_PATHS_INFO,
-    crate::allow_attributes::ALLOW_ATTRIBUTES_INFO,
     crate::almost_complete_range::ALMOST_COMPLETE_RANGE_INFO,
     crate::approx_const::APPROX_CONSTANT_INFO,
     crate::arc_with_non_send_sync::ARC_WITH_NON_SEND_SYNC_INFO,
@@ -49,6 +48,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::assertions_on_result_states::ASSERTIONS_ON_RESULT_STATES_INFO,
     crate::assigning_clones::ASSIGNING_CLONES_INFO,
     crate::async_yields_async::ASYNC_YIELDS_ASYNC_INFO,
+    crate::attrs::ALLOW_ATTRIBUTES_INFO,
     crate::attrs::ALLOW_ATTRIBUTES_WITHOUT_REASON_INFO,
     crate::attrs::BLANKET_CLIPPY_RESTRICTION_LINTS_INFO,
     crate::attrs::DEPRECATED_CFG_ATTR_INFO,

src/tools/clippy/clippy_lints/src/declared_lints.rs

@@ -6,7 +6,7 @@
 #![feature(if_let_guard)]
 #![feature(iter_intersperse)]
 #![feature(let_chains)]
-#![feature(lint_reasons)]
+#![cfg_attr(bootstrap, feature(lint_reasons))]
 #![feature(never_type)]
 #![feature(rustc_private)]
 #![feature(stmt_expr_attributes)]
@@ -73,7 +73,6 @@ mod renamed_lints;
 
 // begin lints modules, do not remove this comment, it’s used in `update_lints`
 mod absolute_paths;
-mod allow_attributes;
 mod almost_complete_range;
 mod approx_const;
 mod arc_with_non_send_sync;
@@ -699,7 +698,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(|_| Box::new(mut_reference::UnnecessaryMutPassed));
     store.register_late_pass(|_| Box::<significant_drop_tightening::SignificantDropTightening<'_>>::default());
     store.register_late_pass(|_| Box::new(len_zero::LenZero));
-    store.register_late_pass(|_| Box::new(attrs::Attributes));
+    store.register_late_pass(move |_| Box::new(attrs::Attributes::new(msrv())));
     store.register_late_pass(|_| Box::new(blocks_in_conditions::BlocksInConditions));
     store.register_late_pass(|_| Box::new(unicode::Unicode));
     store.register_late_pass(|_| Box::new(uninit_vec::UninitVec));
@@ -1065,7 +1064,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(|_| Box::new(needless_maybe_sized::NeedlessMaybeSized));
     store.register_late_pass(|_| Box::new(redundant_async_block::RedundantAsyncBlock));
     store.register_late_pass(|_| Box::new(let_with_type_underscore::UnderscoreTyped));
-    store.register_late_pass(|_| Box::new(allow_attributes::AllowAttribute));
     store.register_late_pass(move |_| Box::new(manual_main_separator_str::ManualMainSeparatorStr::new(msrv())));
     store.register_late_pass(|_| Box::new(unnecessary_struct_initialization::UnnecessaryStruct));
     store.register_late_pass(move |_| {