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

   1 use ast::AttrStyle;
   2 use clippy_utils::diagnostics::span_lint_and_sugg;
   3 use rustc_ast as ast;
   4 use rustc_errors::Applicability;
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7
   8 declare_clippy_lint! {
   9     /// Detects uses of the `#[allow]` attribute and suggests replacing it with
  10     /// the `#[expect]` (See [RFC 2383](https://rust-lang.github.io/rfcs/2383-lint-reasons.html))
  11     ///
  12     /// The expect attribute is still unstable and requires the `lint_reasons`
  13     /// on nightly. It can be enabled by adding `#![feature(lint_reasons)]` to
  14     /// the crate root.
  15     ///
  16     /// This lint only warns outer attributes (`#[allow]`), as inner attributes
  17     /// (`#![allow]`) are usually used to enable or disable lints on a global scale.
  18     ///
  19     /// ### Why is this bad?
  20     ///
  21     /// `#[expect]` attributes suppress the lint emission, but emit a warning, if
  22     /// the expectation is unfulfilled. This can be useful to be notified when the
  23     /// lint is no longer triggered.
  24     ///
  25     /// ### Example
  26     /// ```rust,ignore
  27     /// #[allow(unused_mut)]
  28     /// fn foo() -> usize {
  29     ///    let mut a = Vec::new();
  30     ///    a.len()
  31     /// }
  32     /// ```
  33     /// Use instead:
  34     /// ```rust,ignore
  35     /// #![feature(lint_reasons)]
  36     /// #[expect(unused_mut)]
  37     /// fn foo() -> usize {
  38     ///     let mut a = Vec::new();
  39     ///     a.len()
  40     /// }
  41     /// ```
  42     #[clippy::version = "1.69.0"]
  43     pub ALLOW_ATTRIBUTES,
  44     restriction,
  45     "`#[allow]` will not trigger if a warning isn't found. `#[expect]` triggers if there are no warnings."
  46 }
  47
  48 declare_lint_pass!(AllowAttribute => [ALLOW_ATTRIBUTES]);
  49
  50 impl LateLintPass<'_> for AllowAttribute {
  51     // Separate each crate's features.
  52     fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
  53         if_chain! {
  54             if cx.tcx.features().lint_reasons;
  55             if let AttrStyle::Outer = attr.style;
  56             if let Some(ident) = attr.ident();
  57             if ident.name == rustc_span::symbol::sym::allow;
  58             then {
  59                 span_lint_and_sugg(
  60                     cx,
  61                     ALLOW_ATTRIBUTES,
  62                     ident.span,
  63                     "#[allow] attribute found",
  64                     "replace it with",
  65                     "expect".into(),
  66                     Applicability::MachineApplicable,
  67                 );
  68             }
  69         }
  70     }
  71 }