Implement Duration - Duration

sharksforarms · sharksforarms · commit f296de4665ce · 2025-09-17T09:30:22.000-04:00
Renames InstantSubtraction to UncheckedTimeSubtraction
diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs
@@ -226,8 +226,6 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::inherent_to_string::INHERENT_TO_STRING_SHADOW_DISPLAY_INFO,
     crate::init_numbered_fields::INIT_NUMBERED_FIELDS_INFO,
     crate::inline_fn_without_body::INLINE_FN_WITHOUT_BODY_INFO,
-    crate::time_subtraction::MANUAL_INSTANT_ELAPSED_INFO,
-    crate::time_subtraction::UNCHECKED_TIME_SUBTRACTION_INFO,
     crate::int_plus_one::INT_PLUS_ONE_INFO,
     crate::integer_division_remainder_used::INTEGER_DIVISION_REMAINDER_USED_INFO,
     crate::invalid_upcast_comparisons::INVALID_UPCAST_COMPARISONS_INFO,
@@ -703,6 +701,8 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::tabs_in_doc_comments::TABS_IN_DOC_COMMENTS_INFO,
     crate::temporary_assignment::TEMPORARY_ASSIGNMENT_INFO,
     crate::tests_outside_test_module::TESTS_OUTSIDE_TEST_MODULE_INFO,
+    crate::time_subtraction::MANUAL_INSTANT_ELAPSED_INFO,
+    crate::time_subtraction::UNCHECKED_TIME_SUBTRACTION_INFO,
     crate::to_digit_is_some::TO_DIGIT_IS_SOME_INFO,
     crate::to_string_trait_impl::TO_STRING_TRAIT_IMPL_INFO,
     crate::toplevel_ref_arg::TOPLEVEL_REF_ARG_INFO,
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
@@ -718,7 +718,7 @@ pub fn register_lint_passes(store: &mut rustc_lint::LintStore, conf: &'static Co
     store.register_late_pass(move |_| Box::new(manual_rotate::ManualRotate));
     store.register_late_pass(move |_| Box::new(operators::Operators::new(conf)));
     store.register_late_pass(move |_| Box::new(std_instead_of_core::StdReexports::new(conf)));
-    store.register_late_pass(move |_| Box::new(time_subtraction::InstantSubtraction::new(conf)));
+    store.register_late_pass(move |_| Box::new(time_subtraction::UncheckedTimeSubtraction::new(conf)));
     store.register_late_pass(|_| Box::new(partialeq_to_none::PartialeqToNone));
     store.register_late_pass(move |_| Box::new(manual_abs_diff::ManualAbsDiff::new(conf)));
     store.register_late_pass(move |_| Box::new(manual_clamp::ManualClamp::new(conf)));
diff --git a/clippy_lints/src/time_subtraction.rs b/clippy_lints/src/time_subtraction.rs
@@ -1,12 +1,12 @@
 use clippy_config::Conf;
-use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
 use clippy_utils::msrvs::{self, Msrv};
-use clippy_utils::source::snippet_with_context;
 use clippy_utils::sugg::Sugg;
 use clippy_utils::{is_path_diagnostic_item, ty};
 use rustc_errors::Applicability;
 use rustc_hir::{BinOpKind, Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty::Ty;
 use rustc_session::impl_lint_pass;
 use rustc_span::source_map::Spanned;
 use rustc_span::sym;
@@ -41,7 +41,7 @@ declare_clippy_lint! {
 
 declare_clippy_lint! {
     /// ### What it does
-    /// Lints subtraction between an `Instant` and a `Duration`.
+    /// Lints subtraction between an `Instant` and a `Duration`, or between two `Duration` values.
     ///
     /// ### Why is this bad?
     /// Unchecked subtraction could cause underflow on certain platforms, leading to
@@ -51,32 +51,38 @@ declare_clippy_lint! {
     /// ```no_run
     /// # use std::time::{Instant, Duration};
     /// let time_passed = Instant::now() - Duration::from_secs(5);
+    /// let dur1 = Duration::from_secs(3);
+    /// let dur2 = Duration::from_secs(5);
+    /// let diff = dur1 - dur2;
     /// ```
     ///
     /// Use instead:
     /// ```no_run
     /// # use std::time::{Instant, Duration};
     /// let time_passed = Instant::now().checked_sub(Duration::from_secs(5));
+    /// let dur1 = Duration::from_secs(3);
+    /// let dur2 = Duration::from_secs(5);
+    /// let diff = dur1.checked_sub(dur2);
     /// ```
     #[clippy::version = "1.67.0"]
     pub UNCHECKED_TIME_SUBTRACTION,
     pedantic,
-    "finds unchecked subtraction of a 'Duration' from an 'Instant'"
+    "finds unchecked subtraction involving 'Duration' or 'Instant'"
 }
 
-pub struct InstantSubtraction {
+pub struct UncheckedTimeSubtraction {
     msrv: Msrv,
 }
 
-impl InstantSubtraction {
+impl UncheckedTimeSubtraction {
     pub fn new(conf: &'static Conf) -> Self {
         Self { msrv: conf.msrv }
     }
 }
 
-impl_lint_pass!(InstantSubtraction => [MANUAL_INSTANT_ELAPSED, UNCHECKED_TIME_SUBTRACTION]);
+impl_lint_pass!(UncheckedTimeSubtraction => [MANUAL_INSTANT_ELAPSED, UNCHECKED_TIME_SUBTRACTION]);
 
-impl LateLintPass<'_> for InstantSubtraction {
+impl LateLintPass<'_> for UncheckedTimeSubtraction {
     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'_ Expr<'_>) {
         if let ExprKind::Binary(
             Spanned {
@@ -85,21 +91,54 @@ impl LateLintPass<'_> for InstantSubtraction {
             lhs,
             rhs,
         ) = expr.kind
-            && let typeck = cx.typeck_results()
-            && ty::is_type_diagnostic_item(cx, typeck.expr_ty(lhs), sym::Instant)
         {
+            let typeck = cx.typeck_results();
+            let lhs_ty = typeck.expr_ty(lhs);
             let rhs_ty = typeck.expr_ty(rhs);
 
-            if is_instant_now_call(cx, lhs)
-                && ty::is_type_diagnostic_item(cx, rhs_ty, sym::Instant)
-                && let Some(sugg) = Sugg::hir_opt(cx, rhs)
-            {
-                print_manual_instant_elapsed_sugg(cx, expr, sugg);
-            } else if ty::is_type_diagnostic_item(cx, rhs_ty, sym::Duration)
+            if ty::is_type_diagnostic_item(cx, lhs_ty, sym::Instant) {
+                // Instant::now() - instant
+                if is_instant_now_call(cx, lhs)
+                    && ty::is_type_diagnostic_item(cx, rhs_ty, sym::Instant)
+                    && let Some(sugg) = Sugg::hir_opt(cx, rhs)
+                {
+                    print_manual_instant_elapsed_sugg(cx, expr, sugg);
+                }
+                // instant - duration
+                else if ty::is_type_diagnostic_item(cx, rhs_ty, sym::Duration)
+                    && !expr.span.from_expansion()
+                    && self.msrv.meets(cx, msrvs::TRY_FROM)
+                {
+                    // For chained subtraction like (instant - dur1) - dur2, avoid suggestions
+                    if is_chained_time_subtraction(cx, lhs) {
+                        span_lint(
+                            cx,
+                            UNCHECKED_TIME_SUBTRACTION,
+                            expr.span,
+                            "unchecked subtraction of a 'Duration' from an 'Instant'",
+                        );
+                    } else {
+                        // instant - duration
+                        print_unchecked_duration_subtraction_sugg(cx, lhs, rhs, expr);
+                    }
+                }
+            } else if ty::is_type_diagnostic_item(cx, lhs_ty, sym::Duration)
+                && ty::is_type_diagnostic_item(cx, rhs_ty, sym::Duration)
                 && !expr.span.from_expansion()
                 && self.msrv.meets(cx, msrvs::TRY_FROM)
             {
-                print_unchecked_duration_subtraction_sugg(cx, lhs, rhs, expr);
+                // For chained subtraction like (dur1 - dur2) - dur3, avoid suggestions
+                if is_chained_time_subtraction(cx, lhs) {
+                    span_lint(
+                        cx,
+                        UNCHECKED_TIME_SUBTRACTION,
+                        expr.span,
+                        "unchecked subtraction between 'Duration' values",
+                    );
+                } else {
+                    // duration - duration
+                    print_unchecked_duration_subtraction_sugg(cx, lhs, rhs, expr);
+                }
             }
         }
     }
@@ -115,6 +154,25 @@ fn is_instant_now_call(cx: &LateContext<'_>, expr_block: &'_ Expr<'_>) -> bool {
     }
 }
 
+/// Returns true if this subtraction is part of a chain like `(a - b) - c`
+fn is_chained_time_subtraction(cx: &LateContext<'_>, lhs: &Expr<'_>) -> bool {
+    if let ExprKind::Binary(op, inner_lhs, inner_rhs) = &lhs.kind
+        && matches!(op.node, BinOpKind::Sub)
+    {
+        let typeck = cx.typeck_results();
+        let left_ty = typeck.expr_ty(inner_lhs);
+        let right_ty = typeck.expr_ty(inner_rhs);
+        is_time_type(cx, left_ty) && is_time_type(cx, right_ty)
+    } else {
+        false
+    }
+}
+
+/// Returns true if the type is Duration or Instant
+fn is_time_type(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
+    ty::is_type_diagnostic_item(cx, ty, sym::Duration) || ty::is_type_diagnostic_item(cx, ty, sym::Instant)
+}
+
 fn print_manual_instant_elapsed_sugg(cx: &LateContext<'_>, expr: &Expr<'_>, sugg: Sugg<'_>) {
     span_lint_and_sugg(
         cx,
@@ -133,19 +191,26 @@ fn print_unchecked_duration_subtraction_sugg(
     right_expr: &Expr<'_>,
     expr: &Expr<'_>,
 ) {
-    let mut applicability = Applicability::MachineApplicable;
+    let typeck = cx.typeck_results();
+    let left_ty = typeck.expr_ty(left_expr);
 
-    let ctxt = expr.span.ctxt();
-    let left_expr = snippet_with_context(cx, left_expr.span, ctxt, "<instant>", &mut applicability).0;
-    let right_expr = snippet_with_context(cx, right_expr.span, ctxt, "<duration>", &mut applicability).0;
+    let lint_msg = if ty::is_type_diagnostic_item(cx, left_ty, sym::Instant) {
+        "unchecked subtraction of a 'Duration' from an 'Instant'"
+    } else {
+        "unchecked subtraction between 'Duration' values"
+    };
+
+    let mut applicability = Applicability::MachineApplicable;
+    let left_sugg = Sugg::hir_with_applicability(cx, left_expr, "<left>", &mut applicability);
+    let right_sugg = Sugg::hir_with_applicability(cx, right_expr, "<right>", &mut applicability);
 
     span_lint_and_sugg(
         cx,
         UNCHECKED_TIME_SUBTRACTION,
         expr.span,
-        "unchecked subtraction of a 'Duration' from an 'Instant'",
+        lint_msg,
         "try",
-        format!("{left_expr}.checked_sub({right_expr}).unwrap()"),
+        format!("{}.checked_sub({}).unwrap()", left_sugg.maybe_paren(), right_sugg),
         applicability,
     );
 }
diff --git a/tests/ui/unchecked_time_subtraction.fixed b/tests/ui/unchecked_time_subtraction.fixed
@@ -17,4 +17,21 @@ fn main() {
 
     let _ = Instant::now().checked_sub(second).unwrap();
     //~^ unchecked_time_subtraction
+
+    // Duration - Duration cases
+    let dur1 = Duration::from_secs(5);
+    let dur2 = Duration::from_secs(3);
+
+    let _ = dur1.checked_sub(dur2).unwrap();
+    //~^ unchecked_time_subtraction
+
+    let _ = Duration::from_secs(10).checked_sub(Duration::from_secs(5)).unwrap();
+    //~^ unchecked_time_subtraction
+
+    let _ = second.checked_sub(dur1).unwrap();
+    //~^ unchecked_time_subtraction
+
+    // Duration multiplication and subtraction
+    let _ = (2 * dur1).checked_sub(dur2).unwrap();
+    //~^ unchecked_time_subtraction
 }
diff --git a/tests/ui/unchecked_time_subtraction.rs b/tests/ui/unchecked_time_subtraction.rs
@@ -17,4 +17,21 @@ fn main() {
 
     let _ = Instant::now() - second;
     //~^ unchecked_time_subtraction
+
+    // Duration - Duration cases
+    let dur1 = Duration::from_secs(5);
+    let dur2 = Duration::from_secs(3);
+
+    let _ = dur1 - dur2;
+    //~^ unchecked_time_subtraction
+
+    let _ = Duration::from_secs(10) - Duration::from_secs(5);
+    //~^ unchecked_time_subtraction
+
+    let _ = second - dur1;
+    //~^ unchecked_time_subtraction
+
+    // Duration multiplication and subtraction
+    let _ = 2 * dur1 - dur2;
+    //~^ unchecked_time_subtraction
 }
diff --git a/tests/ui/unchecked_time_subtraction.stderr b/tests/ui/unchecked_time_subtraction.stderr
@@ -25,5 +25,29 @@ error: unchecked subtraction of a 'Duration' from an 'Instant'
 LL |     let _ = Instant::now() - second;
    |             ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Instant::now().checked_sub(second).unwrap()`
 
-error: aborting due to 4 previous errors
+error: unchecked subtraction between 'Duration' values
+  --> tests/ui/unchecked_time_subtraction.rs:25:13
+   |
+LL |     let _ = dur1 - dur2;
+   |             ^^^^^^^^^^^ help: try: `dur1.checked_sub(dur2).unwrap()`
+
+error: unchecked subtraction between 'Duration' values
+  --> tests/ui/unchecked_time_subtraction.rs:28:13
+   |
+LL |     let _ = Duration::from_secs(10) - Duration::from_secs(5);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Duration::from_secs(10).checked_sub(Duration::from_secs(5)).unwrap()`
+
+error: unchecked subtraction between 'Duration' values
+  --> tests/ui/unchecked_time_subtraction.rs:31:13
+   |
+LL |     let _ = second - dur1;
+   |             ^^^^^^^^^^^^^ help: try: `second.checked_sub(dur1).unwrap()`
+
+error: unchecked subtraction between 'Duration' values
+  --> tests/ui/unchecked_time_subtraction.rs:35:13
+   |
+LL |     let _ = 2 * dur1 - dur2;
+   |             ^^^^^^^^^^^^^^^ help: try: `(2 * dur1).checked_sub(dur2).unwrap()`
+
+error: aborting due to 8 previous errors
 
diff --git a/tests/ui/unchecked_time_subtraction_unfixable.rs b/tests/ui/unchecked_time_subtraction_unfixable.rs
@@ -0,0 +1,22 @@
+#![warn(clippy::unchecked_time_subtraction)]
+//@no-rustfix
+
+use std::time::{Duration, Instant};
+
+fn main() {
+    let dur1 = Duration::from_secs(5);
+    let dur2 = Duration::from_secs(3);
+    let dur3 = Duration::from_secs(1);
+
+    // Chained Duration subtraction - should lint without suggestion due to complexity
+    let _ = dur1 - dur2 - dur3;
+    //~^ unchecked_time_subtraction
+    //~| unchecked_time_subtraction
+
+    // Chained Instant - Duration subtraction - should lint without suggestion due to complexity
+    let instant1 = Instant::now();
+
+    let _ = instant1 - dur2 - dur3;
+    //~^ unchecked_time_subtraction
+    //~| unchecked_time_subtraction
+}
diff --git a/tests/ui/unchecked_time_subtraction_unfixable.stderr b/tests/ui/unchecked_time_subtraction_unfixable.stderr
@@ -0,0 +1,29 @@
+error: unchecked subtraction between 'Duration' values
+  --> tests/ui/unchecked_time_subtraction_unfixable.rs:12:13
+   |
+LL |     let _ = dur1 - dur2 - dur3;
+   |             ^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::unchecked-time-subtraction` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::unchecked_time_subtraction)]`
+
+error: unchecked subtraction between 'Duration' values
+  --> tests/ui/unchecked_time_subtraction_unfixable.rs:12:13
+   |
+LL |     let _ = dur1 - dur2 - dur3;
+   |             ^^^^^^^^^^^ help: try: `dur1.checked_sub(dur2).unwrap()`
+
+error: unchecked subtraction of a 'Duration' from an 'Instant'
+  --> tests/ui/unchecked_time_subtraction_unfixable.rs:19:13
+   |
+LL |     let _ = instant1 - dur2 - dur3;
+   |             ^^^^^^^^^^^^^^^^^^^^^^
+
+error: unchecked subtraction of a 'Duration' from an 'Instant'
+  --> tests/ui/unchecked_time_subtraction_unfixable.rs:19:13
+   |
+LL |     let _ = instant1 - dur2 - dur3;
+   |             ^^^^^^^^^^^^^^^ help: try: `instant1.checked_sub(dur2).unwrap()`
+
+error: aborting due to 4 previous errors
+
