Add allow_attribute lint

CHANGELOG.md

@@ -4382,6 +4382,7 @@ Released 2018-09-13
 <!-- begin autogenerated links to lint list -->
 [`absurd_extreme_comparisons`]: https://rust-lang.github.io/rust-clippy/master/index.html#absurd_extreme_comparisons
 [`alloc_instead_of_core`]: https://rust-lang.github.io/rust-clippy/master/index.html#alloc_instead_of_core
+[`allow_attribute`]: https://rust-lang.github.io/rust-clippy/master/index.html#allow_attribute
 [`allow_attributes_without_reason`]: https://rust-lang.github.io/rust-clippy/master/index.html#allow_attributes_without_reason
 [`almost_complete_letter_range`]: https://rust-lang.github.io/rust-clippy/master/index.html#almost_complete_letter_range
 [`almost_complete_range`]: https://rust-lang.github.io/rust-clippy/master/index.html#almost_complete_range

clippy_lints/src/allow_attribute.rs

@@ -0,0 +1,91 @@
+use ast::{AttrStyle, MetaItemKind};
+use clippy_utils::{diagnostics::span_lint_and_sugg, source::snippet};
+use rustc_ast as ast;
+use rustc_errors::Applicability;
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::{symbol::Ident, BytePos};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Detects uses of the `#[allow]` attribute and suggests to replace it with the new `#[expect]` attribute implemented by `#![feature(lint_reasons)]` ([RFC 2383](https://rust-lang.github.io/rfcs/2383-lint-reasons.html))
+    /// ### Why is this bad?
+    /// Using `#[allow]` isn't bad, but `#[expect]` may be preferred as it lints if the code **doesn't** produce a warning.
+    /// ### Example
+    /// ```rust
+    /// #[allow(unused_mut)]
+    /// fn foo() -> usize {
+    ///    let mut a = Vec::new();
+    ///    a.len()
+    ///}
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// #[expect(unused_mut)]
+    /// fn foo() -> usize {
+    ///     let mut a = Vec::new();
+    ///     a.len()
+    /// }
+    /// ```
+    #[clippy::version = "1.69.0"]
+    pub ALLOW_ATTRIBUTE,
+    restriction,
+    "`#[allow]` will not trigger if a warning isn't found. `#[expect]` triggers if there are no warnings."
+}
+
+pub struct AllowAttribute {
+    pub lint_reasons_active: bool,
+}
+
+impl_lint_pass!(AllowAttribute => [ALLOW_ATTRIBUTE]);
+
+impl LateLintPass<'_> for AllowAttribute {
+    // Separate each crate's features.
+    fn check_crate_post(&mut self, _: &LateContext<'_>) {
+        self.lint_reasons_active = false;
+    }
+    fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
+        // Check inner attributes
+
+        if_chain! {
+            if let AttrStyle::Inner = attr.style;
+            if attr.ident()
+            .unwrap_or(Ident::with_dummy_span(sym!(empty))) // Will not trigger if doesn't have an ident.
+            .name == sym!(feature);
+            if let ast::AttrKind::Normal(normal) = &attr.kind;
+            if let Some(MetaItemKind::List(list)) = normal.item.meta_kind();
+            if list[0].ident().unwrap().name == sym!(lint_reasons);
+            then {
+                self.lint_reasons_active = true;
+            }
+        }
+
+        // Check outer attributes
+
+        if_chain! {
+            if let AttrStyle::Outer = attr.style;
+            if attr.ident()
+            .unwrap_or(Ident::with_dummy_span(sym!(empty))) // Will not trigger if doesn't have an ident.
+            .name == sym!(allow);
+            if self.lint_reasons_active;
+            then {
+                span_lint_and_sugg(
+                    cx,
+                    ALLOW_ATTRIBUTE,
+                    attr.span,
+                    "#[allow] attribute found",
+                    "replace it with",
+                    format!("#[expect{})]", snippet(
+                        cx,
+                        attr.ident().unwrap().span
+                        .with_lo(
+                            attr.ident().unwrap().span.hi() + BytePos(2) // Cut [(
+                        )
+                        .with_hi(
+                            attr.meta().unwrap().span.hi() - BytePos(2) // Cut )]
+                        )
+                        , "...")), Applicability::MachineApplicable);
+            }
+        }
+    }
+}

clippy_lints/src/declared_lints.rs

@@ -35,6 +35,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::utils::internal_lints::produce_ice::PRODUCE_ICE_INFO,
     #[cfg(feature = "internal")]
     crate::utils::internal_lints::unnecessary_def_path::UNNECESSARY_DEF_PATH_INFO,
+    crate::allow_attribute::ALLOW_ATTRIBUTE_INFO,
     crate::almost_complete_range::ALMOST_COMPLETE_RANGE_INFO,
     crate::approx_const::APPROX_CONSTANT_INFO,
     crate::as_conversions::AS_CONVERSIONS_INFO,

clippy_lints/src/lib.rs

@@ -67,6 +67,7 @@ mod declared_lints;
 mod renamed_lints;
 
 // begin lints modules, do not remove this comment, it’s used in `update_lints`
+mod allow_attribute;
 mod almost_complete_range;
 mod approx_const;
 mod as_conversions;
@@ -933,6 +934,11 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|_| Box::new(missing_assert_message::MissingAssertMessage));
     store.register_early_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_attribute::AllowAttribute {
+            lint_reasons_active: false,
+        })
+    });
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

tests/ui/allow_attribute.fixed

@@ -0,0 +1,18 @@
+// run-rustfix
+#![allow(unused)]
+#![warn(clippy::allow_attribute)]
+#![feature(lint_reasons)]
+
+fn main() {}
+
+// Using clippy::needless_borrow just as a placeholder, it isn't relevant.
+
+// Should lint
+#[expect(dead_code)]
+struct T1;
+
+struct T2; // Should not lint
+#[deny(clippy::needless_borrow)] // Should not lint
+struct T3;
+#[warn(clippy::needless_borrow)] // Should not lint
+struct T4;

tests/ui/allow_attribute.rs

@@ -0,0 +1,18 @@
+// run-rustfix
+#![allow(unused)]
+#![warn(clippy::allow_attribute)]
+#![feature(lint_reasons)]
+
+fn main() {}
+
+// Using clippy::needless_borrow just as a placeholder, it isn't relevant.
+
+// Should lint
+#[allow(dead_code)]
+struct T1;
+
+struct T2; // Should not lint
+#[deny(clippy::needless_borrow)] // Should not lint
+struct T3;
+#[warn(clippy::needless_borrow)] // Should not lint
+struct T4;

tests/ui/allow_attribute.stderr

@@ -0,0 +1,10 @@
+error: #[allow] attribute found
+  --> $DIR/allow_attribute.rs:11:1
+   |
+LL | #[allow(dead_code)]
+   | ^^^^^^^^^^^^^^^^^^^ help: replace it with: `#[expect(dead_code)]`
+   |
+   = note: `-D clippy::allow-attribute` implied by `-D warnings`
+
+error: aborting due to previous error
+