extend UNCHECKED_DURATION_SUBTRACTION to check for Duration

Duration - Duration could panic in the same way as Instant - Duration

Author: sharksforarms

clippy_lints/src/instant_subtraction.rs

@@ -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` or `Duration` and a `Duration`.
     ///
     /// ### Why is this bad?
     /// Unchecked subtraction could cause underflow on certain platforms, leading to
@@ -51,17 +51,19 @@ declare_clippy_lint! {
     /// ```no_run
     /// # use std::time::{Instant, Duration};
     /// let time_passed = Instant::now() - Duration::from_secs(5);
+    /// let time_delta = Duration::from_secs(1) - Duration::from_secs(5);
     /// ```
     ///
     /// Use instead:
     /// ```no_run
     /// # use std::time::{Instant, Duration};
     /// let time_passed = Instant::now().checked_sub(Duration::from_secs(5));
+    /// let time_delta = Duration::from_secs(1).checked_sub(Duration::from_secs(5));
     /// ```
     #[clippy::version = "1.67.0"]
     pub UNCHECKED_DURATION_SUBTRACTION,
     pedantic,
-    "finds unchecked subtraction of a 'Duration' from an 'Instant'"
+    "finds unchecked subtraction of a 'Duration' from an 'Instant' or 'Duration'"
 }
 
 pub struct InstantSubtraction {
@@ -88,7 +90,8 @@ impl LateLintPass<'_> for InstantSubtraction {
             rhs,
         ) = expr.kind
             && let typeck = cx.typeck_results()
-            && ty::is_type_diagnostic_item(cx, typeck.expr_ty(lhs), sym::Instant)
+            && (ty::is_type_diagnostic_item(cx, typeck.expr_ty(lhs), sym::Instant)
+                || ty::is_type_diagnostic_item(cx, typeck.expr_ty(lhs), sym::Duration))
         {
             let rhs_ty = typeck.expr_ty(rhs);
 
@@ -139,16 +142,23 @@ fn print_unchecked_duration_subtraction_sugg(
     expr: &Expr<'_>,
 ) {
     let mut applicability = Applicability::MachineApplicable;
+    let ty = cx.typeck_results().expr_ty(expr).peel_refs();
+    let (left_default, left_ty) = match ty::get_type_diagnostic_name(cx, ty) {
+        Some(v) => (format!("<{}>", v.as_str().to_lowercase()), v.as_str().to_string()),
+        None => {
+            return;
+        },
+    };
 
     let ctxt = expr.span.ctxt();
-    let left_expr = snippet_with_context(cx, left_expr.span, ctxt, "<instant>", &mut applicability).0;
+    let left_expr = snippet_with_context(cx, left_expr.span, ctxt, &left_default, &mut applicability).0;
     let right_expr = snippet_with_context(cx, right_expr.span, ctxt, "<duration>", &mut applicability).0;
 
     span_lint_and_sugg(
         cx,
         UNCHECKED_DURATION_SUBTRACTION,
         expr.span,
-        "unchecked subtraction of a 'Duration' from an 'Instant'",
+        format!("unchecked subtraction of 'Duration' from '{left_ty}'"),
         "try",
         format!("{left_expr}.checked_sub({right_expr}).unwrap()"),
         applicability,

tests/ui/unchecked_duration_subtraction.fixed

@@ -3,14 +3,21 @@
 use std::time::{Duration, Instant};
 
 fn main() {
-    let _first = Instant::now();
-    let second = Duration::from_secs(3);
+    let instant = Instant::now();
+    let duration = Duration::from_secs(3);
+    let duration2 = Duration::from_secs(1);
 
-    let _ = _first.checked_sub(second).unwrap();
+    let _ = instant.checked_sub(duration).unwrap();
 
     let _ = Instant::now().checked_sub(Duration::from_secs(5)).unwrap();
 
-    let _ = _first.checked_sub(Duration::from_secs(5)).unwrap();
+    let _ = instant.checked_sub(Duration::from_secs(5)).unwrap();
 
-    let _ = Instant::now().checked_sub(second).unwrap();
+    let _ = Instant::now().checked_sub(duration).unwrap();
+
+    let _ = Duration::from_secs(1).checked_sub(duration).unwrap();
+
+    let _ = duration2.checked_sub(duration).unwrap();
+
+    let _ = Instant::now().elapsed().checked_sub(duration).unwrap();
 }

tests/ui/unchecked_duration_subtraction.rs

@@ -3,14 +3,21 @@
 use std::time::{Duration, Instant};
 
 fn main() {
-    let _first = Instant::now();
-    let second = Duration::from_secs(3);
+    let instant = Instant::now();
+    let duration = Duration::from_secs(3);
+    let duration2 = Duration::from_secs(1);
 
-    let _ = _first - second;
+    let _ = instant - duration;
 
     let _ = Instant::now() - Duration::from_secs(5);
 
-    let _ = _first - Duration::from_secs(5);
+    let _ = instant - Duration::from_secs(5);
 
-    let _ = Instant::now() - second;
+    let _ = Instant::now() - duration;
+
+    let _ = Duration::from_secs(1) - duration;
+
+    let _ = duration2 - duration;
+
+    let _ = Instant::now().elapsed() - duration;
 }

tests/ui/unchecked_duration_subtraction.stderr

@@ -1,29 +1,47 @@
 error: unchecked subtraction of a 'Duration' from an 'Instant'
-  --> tests/ui/unchecked_duration_subtraction.rs:9:13
+  --> tests/ui/unchecked_duration_subtraction.rs:10:13
    |
-LL |     let _ = _first - second;
-   |             ^^^^^^^^^^^^^^^ help: try: `_first.checked_sub(second).unwrap()`
+LL |     let _ = instant - duration;
+   |             ^^^^^^^^^^^^^^^^^^ help: try: `instant.checked_sub(duration).unwrap()`
    |
    = note: `-D clippy::unchecked-duration-subtraction` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::unchecked_duration_subtraction)]`
 
 error: unchecked subtraction of a 'Duration' from an 'Instant'
-  --> tests/ui/unchecked_duration_subtraction.rs:11:13
+  --> tests/ui/unchecked_duration_subtraction.rs:12:13
    |
 LL |     let _ = Instant::now() - Duration::from_secs(5);
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Instant::now().checked_sub(Duration::from_secs(5)).unwrap()`
 
 error: unchecked subtraction of a 'Duration' from an 'Instant'
-  --> tests/ui/unchecked_duration_subtraction.rs:13:13
+  --> tests/ui/unchecked_duration_subtraction.rs:14:13
    |
-LL |     let _ = _first - Duration::from_secs(5);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `_first.checked_sub(Duration::from_secs(5)).unwrap()`
+LL |     let _ = instant - Duration::from_secs(5);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `instant.checked_sub(Duration::from_secs(5)).unwrap()`
 
 error: unchecked subtraction of a 'Duration' from an 'Instant'
-  --> tests/ui/unchecked_duration_subtraction.rs:15:13
+  --> tests/ui/unchecked_duration_subtraction.rs:16:13
    |
-LL |     let _ = Instant::now() - second;
-   |             ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Instant::now().checked_sub(second).unwrap()`
+LL |     let _ = Instant::now() - duration;
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Instant::now().checked_sub(duration).unwrap()`
 
-error: aborting due to 4 previous errors
+error: unchecked subtraction of a 'Duration' from an 'Duration'
+  --> tests/ui/unchecked_duration_subtraction.rs:18:13
+   |
+LL |     let _ = Duration::from_secs(1) - duration;
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Duration::from_secs(1).checked_sub(duration).unwrap()`
+
+error: unchecked subtraction of a 'Duration' from an 'Duration'
+  --> tests/ui/unchecked_duration_subtraction.rs:20:13
+   |
+LL |     let _ = duration2 - duration;
+   |             ^^^^^^^^^^^^^^^^^^^^ help: try: `duration2.checked_sub(duration).unwrap()`
+
+error: unchecked subtraction of a 'Duration' from an 'Duration'
+  --> tests/ui/unchecked_duration_subtraction.rs:22:13
+   |
+LL |     let _ = Instant::now().elapsed() - duration;
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Instant::now().elapsed().checked_sub(duration).unwrap()`
+
+error: aborting due to 7 previous errors