+use clippy_utils::{
+ diagnostics::{self, span_lint_and_sugg},
+ meets_msrv, msrvs, source, ty,
+};
+use rustc_errors::Applicability;
+use rustc_hir::{BinOpKind, Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_semver::RustcVersion;
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::{source_map::Spanned, sym};
+
+declare_clippy_lint! {
+ /// ### What it does
+ /// Lints subtraction between `Instant::now()` and another `Instant`.
+ ///
+ /// ### Why is this bad?
+ /// It is easy to accidentally write `prev_instant - Instant::now()`, which will always be 0ns
+ /// as `Instant` subtraction saturates.
+ ///
+ /// `prev_instant.elapsed()` also more clearly signals intention.
+ ///
+ /// ### Example
+ /// ```rust
+ /// use std::time::Instant;
+ /// let prev_instant = Instant::now();
+ /// let duration = Instant::now() - prev_instant;
+ /// ```
+ /// Use instead:
+ /// ```rust
+ /// use std::time::Instant;
+ /// let prev_instant = Instant::now();
+ /// let duration = prev_instant.elapsed();
+ /// ```
+ #[clippy::version = "1.64.0"]
+ pub MANUAL_INSTANT_ELAPSED,
+ pedantic,
+ "subtraction between `Instant::now()` and previous `Instant`"
+}
+
+declare_clippy_lint! {
+ /// ### What it does
+ /// Finds patterns of unchecked subtraction of [`Duration`] from [`Instant::now()`].
+ ///
+ /// ### Why is this bad?
+ /// Unchecked subtraction could cause underflow on certain platforms, leading to
+ /// unintentional panics.
+ ///
+ /// ### Example
+ /// ```rust
+ /// let time_passed = Instant::now() - Duration::from_secs(5);
+ /// ```
+ ///
+ /// Use instead:
+ /// ```rust
+ /// let time_passed = Instant::now().checked_sub(Duration::from_secs(5));
+ /// ```
+ ///
+ /// [`Duration`]: std::time::Duration
+ /// [`Instant::now()`]: std::time::Instant::now;
+ #[clippy::version = "1.65.0"]
+ pub UNCHECKED_DURATION_SUBTRACTION,
+ suspicious,
+ "finds unchecked subtraction of a 'Duration' from an 'Instant'"
+}
+
+pub struct InstantSubtraction {
+ msrv: Option<RustcVersion>,
+}
+
+impl InstantSubtraction {
+ #[must_use]
+ pub fn new(msrv: Option<RustcVersion>) -> Self {
+ Self { msrv }
+ }
+}
+
+impl_lint_pass!(InstantSubtraction => [MANUAL_INSTANT_ELAPSED, UNCHECKED_DURATION_SUBTRACTION]);
+
+impl LateLintPass<'_> for InstantSubtraction {
+ fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'_ Expr<'_>) {
+ if let ExprKind::Binary(Spanned {node: BinOpKind::Sub, ..}, lhs, rhs) = expr.kind
+ && check_instant_now_call(cx, lhs)
+ && let ty_resolved = cx.typeck_results().expr_ty(rhs)
+ && let rustc_middle::ty::Adt(def, _) = ty_resolved.kind()
+ && clippy_utils::match_def_path(cx, def.did(), &clippy_utils::paths::INSTANT)
+ && let Some(sugg) = clippy_utils::sugg::Sugg::hir_opt(cx, rhs)
+ {
+ span_lint_and_sugg(
+ cx,
+ MANUAL_INSTANT_ELAPSED,
+ expr.span,
+ "manual implementation of `Instant::elapsed`",
+ "try",
+ format!("{}.elapsed()", sugg.maybe_par()),
+ Applicability::MachineApplicable,
+ );
+ }
+
+ if expr.span.from_expansion() || !meets_msrv(self.msrv, msrvs::TRY_FROM) {
+ return;
+ }
+
+ if_chain! {
+ if let ExprKind::Binary(op, lhs, rhs) = expr.kind;
+
+ if let BinOpKind::Sub = op.node;
+
+ // get types of left and right side
+ if is_an_instant(cx, lhs);
+ if is_a_duration(cx, rhs);
+
+ then {
+ print_lint_and_sugg(cx, lhs, rhs, expr)
+ }
+ }
+ }
+}
+
+fn check_instant_now_call(cx: &LateContext<'_>, expr_block: &'_ Expr<'_>) -> bool {
+ if let ExprKind::Call(fn_expr, []) = expr_block.kind
+ && let Some(fn_id) = clippy_utils::path_def_id(cx, fn_expr)
+ && clippy_utils::match_def_path(cx, fn_id, &clippy_utils::paths::INSTANT_NOW)
+ {
+ true
+ } else {
+ false
+ }
+}
+
+fn is_an_instant(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+ let expr_ty = cx.typeck_results().expr_ty(expr);
+
+ match expr_ty.kind() {
+ rustc_middle::ty::Adt(def, _) => clippy_utils::match_def_path(cx, def.did(), &clippy_utils::paths::INSTANT),
+ _ => false,
+ }
+}
+
+fn is_a_duration(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+ let expr_ty = cx.typeck_results().expr_ty(expr);
+ ty::is_type_diagnostic_item(cx, expr_ty, sym::Duration)
+}
+
+fn print_lint_and_sugg(cx: &LateContext<'_>, left_expr: &Expr<'_>, right_expr: &Expr<'_>, expr: &Expr<'_>) {
+ let mut applicability = Applicability::MachineApplicable;
+
+ let left_expr =
+ source::snippet_with_applicability(cx, left_expr.span, "std::time::Instant::now()", &mut applicability);
+ let right_expr = source::snippet_with_applicability(
+ cx,
+ right_expr.span,
+ "std::time::Duration::from_secs(1)",
+ &mut applicability,
+ );
+
+ diagnostics::span_lint_and_sugg(
+ cx,
+ UNCHECKED_DURATION_SUBTRACTION,
+ expr.span,
+ "unchecked subtraction of a 'Duration' from an 'Instant'",
+ "try",
+ format!("{}.checked_sub({}).unwrap();", left_expr, right_expr),
+ applicability,
+ );
+}