feat: add and implement unchecked_duration_subtraction lint

Author: nfejzic

CHANGELOG.md

@@ -4428,6 +4428,7 @@ Released 2018-09-13
 [`try_err`]: https://rust-lang.github.io/rust-clippy/master/index.html#try_err
 [`type_complexity`]: https://rust-lang.github.io/rust-clippy/master/index.html#type_complexity
 [`type_repetition_in_bounds`]: https://rust-lang.github.io/rust-clippy/master/index.html#type_repetition_in_bounds
+[`unchecked_duration_subtraction`]: https://rust-lang.github.io/rust-clippy/master/index.html#unchecked_duration_subtraction
 [`undocumented_unsafe_blocks`]: https://rust-lang.github.io/rust-clippy/master/index.html#undocumented_unsafe_blocks
 [`undropped_manually_drops`]: https://rust-lang.github.io/rust-clippy/master/index.html#undropped_manually_drops
 [`unicode_not_nfc`]: https://rust-lang.github.io/rust-clippy/master/index.html#unicode_not_nfc

clippy_lints/src/lib.rs

@@ -279,6 +279,7 @@ mod trailing_empty_array;
 mod trait_bounds;
 mod transmute;
 mod types;
+mod unchecked_duration_subtraction;
 mod undocumented_unsafe_blocks;
 mod unicode;
 mod uninit_vec;
@@ -921,6 +922,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|_| Box::new(from_raw_with_void_ptr::FromRawWithVoidPtr));
     store.register_late_pass(|_| Box::new(suspicious_xor_used_as_pow::ConfusingXorAndPow));
     store.register_late_pass(move |_| Box::new(manual_is_ascii_check::ManualIsAsciiCheck::new(msrv)));
+    store.register_late_pass(move || Box::new(unchecked_duration_subtraction::UncheckedDurationSubtraction::new(msrv)));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/unchecked_duration_subtraction.rs

@@ -0,0 +1,107 @@
+use clippy_utils::{diagnostics, meets_msrv, msrvs, source, ty};
+use rustc_errors::Applicability;
+use rustc_hir::*;
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_semver::RustcVersion;
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::symbol::sym;
+
+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 bugs and/or
+    /// 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 UncheckedDurationSubtraction {
+    msrv: Option<RustcVersion>,
+}
+
+impl UncheckedDurationSubtraction {
+    #[must_use]
+    pub fn new(msrv: Option<RustcVersion>) -> Self {
+        Self { msrv }
+    }
+}
+
+impl_lint_pass!(UncheckedDurationSubtraction => [UNCHECKED_DURATION_SUBTRACTION]);
+
+impl<'tcx> LateLintPass<'tcx> for UncheckedDurationSubtraction {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
+        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 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, dbg!(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,
+    );
+}

clippy_lints/src/utils/conf.rs

@@ -213,7 +213,7 @@ define_Conf! {
     ///
     /// Suppress lints whenever the suggested change would cause breakage for other crates.
     (avoid_breaking_exported_api: bool = true),
-    /// Lint: MANUAL_SPLIT_ONCE, MANUAL_STR_REPEAT, CLONED_INSTEAD_OF_COPIED, REDUNDANT_FIELD_NAMES, REDUNDANT_STATIC_LIFETIMES, FILTER_MAP_NEXT, CHECKED_CONVERSIONS, MANUAL_RANGE_CONTAINS, USE_SELF, MEM_REPLACE_WITH_DEFAULT, MANUAL_NON_EXHAUSTIVE, OPTION_AS_REF_DEREF, MAP_UNWRAP_OR, MATCH_LIKE_MATCHES_MACRO, MANUAL_STRIP, MISSING_CONST_FOR_FN, UNNESTED_OR_PATTERNS, FROM_OVER_INTO, PTR_AS_PTR, IF_THEN_SOME_ELSE_NONE, APPROX_CONSTANT, DEPRECATED_CFG_ATTR, INDEX_REFUTABLE_SLICE, MAP_CLONE, BORROW_AS_PTR, MANUAL_BITS, ERR_EXPECT, CAST_ABS_TO_UNSIGNED, UNINLINED_FORMAT_ARGS, MANUAL_CLAMP, MANUAL_LET_ELSE.
+    /// Lint: MANUAL_SPLIT_ONCE, MANUAL_STR_REPEAT, CLONED_INSTEAD_OF_COPIED, REDUNDANT_FIELD_NAMES, REDUNDANT_STATIC_LIFETIMES, FILTER_MAP_NEXT, CHECKED_CONVERSIONS, MANUAL_RANGE_CONTAINS, USE_SELF, MEM_REPLACE_WITH_DEFAULT, MANUAL_NON_EXHAUSTIVE, OPTION_AS_REF_DEREF, MAP_UNWRAP_OR, MATCH_LIKE_MATCHES_MACRO, MANUAL_STRIP, MISSING_CONST_FOR_FN, UNNESTED_OR_PATTERNS, FROM_OVER_INTO, PTR_AS_PTR, IF_THEN_SOME_ELSE_NONE, APPROX_CONSTANT, DEPRECATED_CFG_ATTR, INDEX_REFUTABLE_SLICE, MAP_CLONE, BORROW_AS_PTR, MANUAL_BITS, ERR_EXPECT, CAST_ABS_TO_UNSIGNED, UNINLINED_FORMAT_ARGS, MANUAL_CLAMP, MANUAL_LET_ELSE, UNCHECKED_DURATION_SUBTRACTION.
     ///
     /// The minimum rust version that the project supports
     (msrv: Option<String> = None),