clippy_lints/src/unchecked_duration_subtraction.rs

   1 use clippy_utils::{diagnostics, meets_msrv, msrvs, source, ty};
   2 use rustc_errors::Applicability;
   3 use rustc_hir::*;
   4 use rustc_lint::{LateContext, LateLintPass};
   5 use rustc_semver::RustcVersion;
   6 use rustc_session::{declare_tool_lint, impl_lint_pass};
   7 use rustc_span::symbol::sym;
   8
   9 declare_clippy_lint! {
  10     /// ### What it does
  11     /// Finds patterns of unchecked subtraction of [`Duration`] from [`Instant::now()`].
  12     ///
  13     /// ### Why is this bad?
  14     /// Unchecked subtraction could cause underflow on certain platforms, leading to bugs and/or
  15     /// unintentional panics.
  16     ///
  17     /// ### Example
  18     /// ```rust
  19     /// let time_passed = Instant::now() - Duration::from_secs(5);
  20     /// ```
  21     ///
  22     /// Use instead:
  23     /// ```rust
  24     /// let time_passed = Instant::now().checked_sub(Duration::from_secs(5));
  25     /// ```
  26     ///
  27     /// [`Duration`]: std::time::Duration
  28     /// [`Instant::now()`]: std::time::Instant::now;
  29     #[clippy::version = "1.65.0"]
  30     pub UNCHECKED_DURATION_SUBTRACTION,
  31     suspicious,
  32     "finds unchecked subtraction of a 'Duration' from an 'Instant'"
  33 }
  34
  35 pub struct UncheckedDurationSubtraction {
  36     msrv: Option<RustcVersion>,
  37 }
  38
  39 impl UncheckedDurationSubtraction {
  40     #[must_use]
  41     pub fn new(msrv: Option<RustcVersion>) -> Self {
  42         Self { msrv }
  43     }
  44 }
  45
  46 impl_lint_pass!(UncheckedDurationSubtraction => [UNCHECKED_DURATION_SUBTRACTION]);
  47
  48 impl<'tcx> LateLintPass<'tcx> for UncheckedDurationSubtraction {
  49     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  50         if expr.span.from_expansion() || !meets_msrv(self.msrv, msrvs::TRY_FROM) {
  51             return;
  52         }
  53
  54         if_chain! {
  55             if let ExprKind::Binary(op, lhs, rhs) = expr.kind;
  56
  57             if let BinOpKind::Sub = op.node;
  58
  59             // get types of left and right side
  60             if is_an_instant(cx, lhs);
  61             if is_a_duration(cx, rhs);
  62
  63             then {
  64                 print_lint_and_sugg(cx, lhs, rhs, expr)
  65             }
  66         }
  67     }
  68 }
  69
  70 fn is_an_instant(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
  71     let expr_ty = cx.typeck_results().expr_ty(expr);
  72
  73     match expr_ty.kind() {
  74         rustc_middle::ty::Adt(def, _) => {
  75             clippy_utils::match_def_path(cx, dbg!(def).did(), &clippy_utils::paths::INSTANT)
  76         },
  77         _ => false,
  78     }
  79 }
  80
  81 fn is_a_duration(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
  82     let expr_ty = cx.typeck_results().expr_ty(expr);
  83     ty::is_type_diagnostic_item(cx, expr_ty, sym::Duration)
  84 }
  85
  86 fn print_lint_and_sugg(cx: &LateContext<'_>, left_expr: &Expr<'_>, right_expr: &Expr<'_>, expr: &Expr<'_>) {
  87     let mut applicability = Applicability::MachineApplicable;
  88
  89     let left_expr =
  90         source::snippet_with_applicability(cx, left_expr.span, "std::time::Instant::now()", &mut applicability);
  91     let right_expr = source::snippet_with_applicability(
  92         cx,
  93         right_expr.span,
  94         "std::time::Duration::from_secs(1)",
  95         &mut applicability,
  96     );
  97
  98     diagnostics::span_lint_and_sugg(
  99         cx,
 100         UNCHECKED_DURATION_SUBTRACTION,
 101         expr.span,
 102         "unchecked subtraction of a 'Duration' from an 'Instant'",
 103         "try",
 104         format!("{}.checked_sub({}).unwrap();", left_expr, right_expr),
 105         applicability,
 106     );
 107 }