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refactor(time_subtraction): give the same message for Instant - Duration and Duration - Duration #16097

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Merged
merged 2 commits into from
Nov 16, 2025
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refactor(time_subtraction): give the same message for Instant - Duration and Duration - Duration #16097

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e1344da
Handle the suggestion-less case inside `print_unchecked_duration_subt…
ada4a Nov 15, 2025
32f5ae1
Give the same message for `Instant - Duration` and `Duration - Duration`
ada4a Nov 15, 2025
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68 changes: 24 additions & 44 deletions clippy_lints/src/time_subtraction.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
use clippy_config::Conf;
use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
use clippy_utils::msrvs::{self, Msrv};
use clippy_utils::res::{MaybeDef, MaybeTypeckRes};
use clippy_utils::sugg::Sugg;
Expand Down Expand Up @@ -109,36 +109,16 @@ impl LateLintPass<'_> for UncheckedTimeSubtraction {
&& !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);
}
print_unchecked_duration_subtraction_sugg(cx, lhs, rhs, expr);
}
} else if lhs_ty.is_diag_item(cx, sym::Duration)
}
// duration - duration
else if lhs_ty.is_diag_item(cx, sym::Duration)
&& rhs_ty.is_diag_item(cx, sym::Duration)
&& !expr.span.from_expansion()
&& self.msrv.meets(cx, msrvs::TRY_FROM)
{
// 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);
}
print_unchecked_duration_subtraction_sugg(cx, lhs, rhs, expr);
}
}
}
Expand Down Expand Up @@ -191,26 +171,26 @@ fn print_unchecked_duration_subtraction_sugg(
right_expr: &Expr<'_>,
expr: &Expr<'_>,
) {
let typeck = cx.typeck_results();
let left_ty = typeck.expr_ty(left_expr);

let lint_msg = if left_ty.is_diag_item(cx, 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(
span_lint_and_then(
cx,
UNCHECKED_TIME_SUBTRACTION,
expr.span,
lint_msg,
"try",
format!("{}.checked_sub({}).unwrap()", left_sugg.maybe_paren(), right_sugg),
applicability,
"unchecked subtraction of a `Duration`",
|diag| {
// For chained subtraction, like `(dur1 - dur2) - dur3` or `(instant - dur1) - dur2`,
// avoid suggestions
if !is_chained_time_subtraction(cx, left_expr) {
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);

diag.span_suggestion(
expr.span,
"try",
format!("{}.checked_sub({}).unwrap()", left_sugg.maybe_paren(), right_sugg),
applicability,
);
}
},
);
}
16 changes: 8 additions & 8 deletions tests/ui/unchecked_time_subtraction.stderr
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
error: unchecked subtraction of a 'Duration' from an 'Instant'
error: unchecked subtraction of a `Duration`
--> tests/ui/unchecked_time_subtraction.rs:9:13
|
LL | let _ = _first - second;
Expand All @@ -7,43 +7,43 @@ LL | let _ = _first - second;
= note: `-D clippy::unchecked-time-subtraction` implied by `-D warnings`
= help: to override `-D warnings` add `#[allow(clippy::unchecked_time_subtraction)]`

error: unchecked subtraction of a 'Duration' from an 'Instant'
error: unchecked subtraction of a `Duration`
--> tests/ui/unchecked_time_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'
error: unchecked subtraction of a `Duration`
--> tests/ui/unchecked_time_subtraction.rs:15:13
|
LL | let _ = _first - Duration::from_secs(5);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `_first.checked_sub(Duration::from_secs(5)).unwrap()`

error: unchecked subtraction of a 'Duration' from an 'Instant'
error: unchecked subtraction of a `Duration`
--> tests/ui/unchecked_time_subtraction.rs:18:13
|
LL | let _ = Instant::now() - second;
| ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Instant::now().checked_sub(second).unwrap()`

error: unchecked subtraction between 'Duration' values
error: unchecked subtraction of a `Duration`
--> 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
error: unchecked subtraction of a `Duration`
--> 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
error: unchecked subtraction of a `Duration`
--> 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
error: unchecked subtraction of a `Duration`
--> tests/ui/unchecked_time_subtraction.rs:35:13
|
LL | let _ = 2 * dur1 - dur2;
Expand Down
8 changes: 4 additions & 4 deletions tests/ui/unchecked_time_subtraction_unfixable.stderr
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
error: unchecked subtraction between 'Duration' values
error: unchecked subtraction of a `Duration`
--> tests/ui/unchecked_time_subtraction_unfixable.rs:12:13
|
LL | let _ = dur1 - dur2 - dur3;
Expand All @@ -7,19 +7,19 @@ 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
error: unchecked subtraction of a `Duration`
--> 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'
error: unchecked subtraction of a `Duration`
--> tests/ui/unchecked_time_subtraction_unfixable.rs:19:13
|
LL | let _ = instant1 - dur2 - dur3;
| ^^^^^^^^^^^^^^^^^^^^^^

error: unchecked subtraction of a 'Duration' from an 'Instant'
error: unchecked subtraction of a `Duration`
--> tests/ui/unchecked_time_subtraction_unfixable.rs:19:13
|
LL | let _ = instant1 - dur2 - dur3;
Expand Down