docs: add docs for `unchecked_duration_subtraction` lint

1 files changed, 19 insertions, 0 deletions

diff --git a/src/docs/unchecked_duration_subtraction.txt b/src/docs/unchecked_duration_subtraction.txt
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+++ b/src/docs/unchecked_duration_subtraction.txt
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+### 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
+```
+let time_passed = Instant::now() - Duration::from_secs(5);
+```
+
+Use instead:
+```
+let time_passed = Instant::now().checked_sub(Duration::from_secs(5));
+```
+
+[`Duration`]: std::time::Duration
+[`Instant::now()`]: std::time::Instant::now;
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