1 files changed, 182 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/instant_subtraction.rs b/src/tools/clippy/clippy_lints/src/instant_subtraction.rs
new file mode 100644
index 000000000..dd1b23e7d
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/instant_subtraction.rs
@@ -0,0 +1,182 @@
+use clippy_utils::diagnostics::{self, span_lint_and_sugg};
+use clippy_utils::msrvs::{self, Msrv};
+use clippy_utils::source;
+use clippy_utils::sugg::Sugg;
+use clippy_utils::ty;
+use rustc_errors::Applicability;
+use rustc_hir::{BinOpKind, Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+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 = "1.65.0"]
+    pub MANUAL_INSTANT_ELAPSED,
+    pedantic,
+    "subtraction between `Instant::now()` and previous `Instant`"
+}
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Lints subtraction between an [`Instant`] and a [`Duration`].
+    ///
+    /// ### Why is this bad?
+    /// Unchecked subtraction could cause underflow on certain platforms, leading to
+    /// unintentional panics.
+    ///
+    /// ### Example
+    /// ```rust
+    /// # use std::time::{Instant, Duration};
+    /// let time_passed = Instant::now() - Duration::from_secs(5);
+    /// ```
+    ///
+    /// Use instead:
+    /// ```rust
+    /// # use std::time::{Instant, Duration};
+    /// 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: Msrv,
+}
+
+impl InstantSubtraction {
+    #[must_use]
+    pub fn new(msrv: Msrv) -> 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
+        {
+            if_chain! {
+                if is_instant_now_call(cx, lhs);
+
+                if is_an_instant(cx, rhs);
+                if let Some(sugg) = Sugg::hir_opt(cx, rhs);
+
+                then {
+                    print_manual_instant_elapsed_sugg(cx, expr, sugg)
+                } else {
+                    if_chain! {
+                        if !expr.span.from_expansion();
+                        if self.msrv.meets(msrvs::TRY_FROM);
+
+                        if is_an_instant(cx, lhs);
+                        if is_a_duration(cx, rhs);
+
+                        then {
+                            print_unchecked_duration_subtraction_sugg(cx, lhs, rhs, expr)
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    extract_msrv_attr!(LateContext);
+}
+
+fn is_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_manual_instant_elapsed_sugg(cx: &LateContext<'_>, expr: &Expr<'_>, sugg: Sugg<'_>) {
+    span_lint_and_sugg(
+        cx,
+        MANUAL_INSTANT_ELAPSED,
+        expr.span,
+        "manual implementation of `Instant::elapsed`",
+        "try",
+        format!("{}.elapsed()", sugg.maybe_par()),
+        Applicability::MachineApplicable,
+    );
+}
+
+fn print_unchecked_duration_subtraction_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!("{left_expr}.checked_sub({right_expr}).unwrap()"),
+        applicability,
+    );
+}