src/tools/clippy/clippy_lints/src/as_conversions.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::is_from_proc_macro;
   3 use rustc_hir::{Expr, ExprKind};
   4 use rustc_lint::{LateContext, LateLintPass, LintContext};
   5 use rustc_middle::lint::in_external_macro;
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7
   8 declare_clippy_lint! {
   9     /// ### What it does
  10     /// Checks for usage of `as` conversions.
  11     ///
  12     /// Note that this lint is specialized in linting *every single* use of `as`
  13     /// regardless of whether good alternatives exist or not.
  14     /// If you want more precise lints for `as`, please consider using these separate lints:
  15     /// `unnecessary_cast`, `cast_lossless/cast_possible_truncation/cast_possible_wrap/cast_precision_loss/cast_sign_loss`,
  16     /// `fn_to_numeric_cast(_with_truncation)`, `char_lit_as_u8`, `ref_to_mut` and `ptr_as_ptr`.
  17     /// There is a good explanation the reason why this lint should work in this way and how it is useful
  18     /// [in this issue](https://github.com/rust-lang/rust-clippy/issues/5122).
  19     ///
  20     /// ### Why is this bad?
  21     /// `as` conversions will perform many kinds of
  22     /// conversions, including silently lossy conversions and dangerous coercions.
  23     /// There are cases when it makes sense to use `as`, so the lint is
  24     /// Allow by default.
  25     ///
  26     /// ### Example
  27     /// ```rust,ignore
  28     /// let a: u32;
  29     /// ...
  30     /// f(a as u16);
  31     /// ```
  32     ///
  33     /// Use instead:
  34     /// ```rust,ignore
  35     /// f(a.try_into()?);
  36     ///
  37     /// // or
  38     ///
  39     /// f(a.try_into().expect("Unexpected u16 overflow in f"));
  40     /// ```
  41     #[clippy::version = "1.41.0"]
  42     pub AS_CONVERSIONS,
  43     restriction,
  44     "using a potentially dangerous silent `as` conversion"
  45 }
  46
  47 declare_lint_pass!(AsConversions => [AS_CONVERSIONS]);
  48
  49 impl<'tcx> LateLintPass<'tcx> for AsConversions {
  50     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
  51         if in_external_macro(cx.sess(), expr.span) || is_from_proc_macro(cx, expr) {
  52             return;
  53         }
  54
  55         if let ExprKind::Cast(_, _) = expr.kind {
  56             span_lint_and_help(
  57                 cx,
  58                 AS_CONVERSIONS,
  59                 expr.span,
  60                 "using a potentially dangerous silent `as` conversion",
  61                 None,
  62                 "consider using a safe wrapper for this conversion",
  63             );
  64         }
  65     }
  66 }