diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8babfc8d63c..f593966c045 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3773,6 +3773,7 @@ Released 2018-09-13
[`cast_enum_constructor`]: https://rust-lang.github.io/rust-clippy/master/index.html#cast_enum_constructor
[`cast_enum_truncation`]: https://rust-lang.github.io/rust-clippy/master/index.html#cast_enum_truncation
[`cast_lossless`]: https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
+[`cast_nan_to_int`]: https://rust-lang.github.io/rust-clippy/master/index.html#cast_nan_to_int
[`cast_possible_truncation`]: https://rust-lang.github.io/rust-clippy/master/index.html#cast_possible_truncation
[`cast_possible_wrap`]: https://rust-lang.github.io/rust-clippy/master/index.html#cast_possible_wrap
[`cast_precision_loss`]: https://rust-lang.github.io/rust-clippy/master/index.html#cast_precision_loss
diff --git a/clippy_lints/src/casts/cast_nan_to_int.rs b/clippy_lints/src/casts/cast_nan_to_int.rs
new file mode 100644
index 00000000000..322dc41b3a1
--- /dev/null
+++ b/clippy_lints/src/casts/cast_nan_to_int.rs
@@ -0,0 +1,28 @@
+use super::CAST_NAN_TO_INT;
+
+use clippy_utils::consts::{constant, Constant};
+use clippy_utils::diagnostics::span_lint_and_note;
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_middle::ty::Ty;
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, from_ty: Ty<'_>, to_ty: Ty<'_>) {
+ if from_ty.is_floating_point() && to_ty.is_integral() && is_known_nan(cx, cast_expr) {
+ span_lint_and_note(
+ cx,
+ CAST_NAN_TO_INT,
+ expr.span,
+ &format!("casting a known NaN to {to_ty}"),
+ None,
+ "this always evaluates to 0",
+ );
+ }
+}
+
+fn is_known_nan(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
+ match constant(cx, cx.typeck_results(), e) {
+ Some((Constant::F64(n), _)) => n.is_nan(),
+ Some((Constant::F32(n), _)) => n.is_nan(),
+ _ => false,
+ }
+}
diff --git a/clippy_lints/src/casts/mod.rs b/clippy_lints/src/casts/mod.rs
index b8f0dedf5ed..b72c4c772f1 100644
--- a/clippy_lints/src/casts/mod.rs
+++ b/clippy_lints/src/casts/mod.rs
@@ -4,6 +4,7 @@ mod borrow_as_ptr;
mod cast_abs_to_unsigned;
mod cast_enum_constructor;
mod cast_lossless;
+mod cast_nan_to_int;
mod cast_possible_truncation;
mod cast_possible_wrap;
mod cast_precision_loss;
@@ -570,6 +571,7 @@ declare_clippy_lint! {
pedantic,
"borrowing just to cast to a raw pointer"
}
+
declare_clippy_lint! {
/// ### What it does
/// Checks for a raw slice being cast to a slice pointer
@@ -623,6 +625,28 @@ declare_clippy_lint! {
"casting the result of the `&self`-taking `as_ptr` to a mutabe pointer"
}
+declare_clippy_lint! {
+ /// ### What it does
+ /// Checks for a known NaN float being cast to an integer
+ ///
+ /// ### Why is this bad?
+ /// NaNs are cast into zero, so one could simply use this and make the
+ /// code more readable. The lint could also hint at a programmer error.
+ ///
+ /// ### Example
+ /// ```rust,ignore
+ /// let _: (0.0_f32 / 0.0) as u64;
+ /// ```
+ /// Use instead:
+ /// ```rust,ignore
+ /// let _: = 0_u64;
+ /// ```
+ #[clippy::version = "1.64.0"]
+ pub CAST_NAN_TO_INT,
+ suspicious,
+ "casting a known floating-point NaN into an integer"
+}
+
pub struct Casts {
msrv: Option<RustcVersion>,
}
@@ -656,6 +680,7 @@ impl_lint_pass!(Casts => [
BORROW_AS_PTR,
CAST_SLICE_FROM_RAW_PARTS,
AS_PTR_CAST_MUT,
+ CAST_NAN_TO_INT,
]);
impl<'tcx> LateLintPass<'tcx> for Casts {
@@ -693,6 +718,7 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
cast_precision_loss::check(cx, expr, cast_from, cast_to);
cast_sign_loss::check(cx, expr, cast_expr, cast_from, cast_to);
cast_abs_to_unsigned::check(cx, expr, cast_expr, cast_from, cast_to, self.msrv);
+ cast_nan_to_int::check(cx, expr, cast_expr, cast_from, cast_to);
}
cast_lossless::check(cx, expr, cast_expr, cast_from, cast_to, self.msrv);
cast_enum_constructor::check(cx, expr, cast_expr, cast_from);
diff --git a/clippy_lints/src/lib.register_all.rs b/clippy_lints/src/lib.register_all.rs
index 758f9936064..a2f54c74d72 100644
--- a/clippy_lints/src/lib.register_all.rs
+++ b/clippy_lints/src/lib.register_all.rs
@@ -25,6 +25,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
LintId::of(casts::CAST_ABS_TO_UNSIGNED),
LintId::of(casts::CAST_ENUM_CONSTRUCTOR),
LintId::of(casts::CAST_ENUM_TRUNCATION),
+ LintId::of(casts::CAST_NAN_TO_INT),
LintId::of(casts::CAST_REF_TO_MUT),
LintId::of(casts::CAST_SLICE_DIFFERENT_SIZES),
LintId::of(casts::CAST_SLICE_FROM_RAW_PARTS),
diff --git a/clippy_lints/src/lib.register_lints.rs b/clippy_lints/src/lib.register_lints.rs
index 546685c8175..de1253c8510 100644
--- a/clippy_lints/src/lib.register_lints.rs
+++ b/clippy_lints/src/lib.register_lints.rs
@@ -73,6 +73,7 @@ store.register_lints(&[
casts::CAST_ENUM_CONSTRUCTOR,
casts::CAST_ENUM_TRUNCATION,
casts::CAST_LOSSLESS,
+ casts::CAST_NAN_TO_INT,
casts::CAST_POSSIBLE_TRUNCATION,
casts::CAST_POSSIBLE_WRAP,
casts::CAST_PRECISION_LOSS,
diff --git a/clippy_lints/src/lib.register_suspicious.rs b/clippy_lints/src/lib.register_suspicious.rs
index 6125d0f7a86..ef5cc9ad7f9 100644
--- a/clippy_lints/src/lib.register_suspicious.rs
+++ b/clippy_lints/src/lib.register_suspicious.rs
@@ -11,6 +11,7 @@ store.register_group(true, "clippy::suspicious", Some("clippy_suspicious"), vec!
LintId::of(casts::CAST_ABS_TO_UNSIGNED),
LintId::of(casts::CAST_ENUM_CONSTRUCTOR),
LintId::of(casts::CAST_ENUM_TRUNCATION),
+ LintId::of(casts::CAST_NAN_TO_INT),
LintId::of(casts::CAST_SLICE_FROM_RAW_PARTS),
LintId::of(crate_in_macro_def::CRATE_IN_MACRO_DEF),
LintId::of(drop_forget_ref::DROP_NON_DROP),
diff --git a/src/docs.rs b/src/docs.rs
index 971d57ccb6f..41c31f91bca 100644
--- a/src/docs.rs
+++ b/src/docs.rs
@@ -61,6 +61,7 @@ docs! {
"cast_enum_constructor",
"cast_enum_truncation",
"cast_lossless",
+ "cast_nan_to_int",
"cast_possible_truncation",
"cast_possible_wrap",
"cast_precision_loss",
diff --git a/src/docs/cast_nan_to_int.txt b/src/docs/cast_nan_to_int.txt
new file mode 100644
index 00000000000..122f5da0c92
--- /dev/null
+++ b/src/docs/cast_nan_to_int.txt
@@ -0,0 +1,15 @@
+### What it does
+Checks for a known NaN float being cast to an integer
+
+### Why is this bad?
+NaNs are cast into zero, so one could simply use this and make the
+code more readable. The lint could also hint at a programmer error.
+
+### Example
+```
+let _: (0.0_f32 / 0.0) as u64;
+```
+Use instead:
+```
+let _: = 0_u64;
+```
\ No newline at end of file
diff --git a/tests/ui/cast_nan_to_int.rs b/tests/ui/cast_nan_to_int.rs
new file mode 100644
index 00000000000..287c5aa216b
--- /dev/null
+++ b/tests/ui/cast_nan_to_int.rs
@@ -0,0 +1,18 @@
+#![warn(clippy::cast_nan_to_int)]
+#![allow(clippy::eq_op)]
+
+fn main() {
+ let _ = (0.0_f32 / -0.0) as usize;
+ let _ = (f64::INFINITY * -0.0) as usize;
+ let _ = (0.0 * f32::INFINITY) as usize;
+
+ let _ = (f64::INFINITY + f64::NEG_INFINITY) as usize;
+ let _ = (f32::INFINITY - f32::INFINITY) as usize;
+ let _ = (f32::INFINITY / f32::NEG_INFINITY) as usize;
+
+ // those won't be linted:
+ let _ = (1.0_f32 / 0.0) as usize;
+ let _ = (f32::INFINITY * f32::NEG_INFINITY) as usize;
+ let _ = (f32::INFINITY - f32::NEG_INFINITY) as usize;
+ let _ = (f64::INFINITY - 0.0) as usize;
+}
diff --git a/tests/ui/cast_nan_to_int.stderr b/tests/ui/cast_nan_to_int.stderr
new file mode 100644
index 00000000000..3539be75a19
--- /dev/null
+++ b/tests/ui/cast_nan_to_int.stderr
@@ -0,0 +1,51 @@
+error: casting a known NaN to usize
+ --> $DIR/cast_nan_to_int.rs:5:13
+ |
+LL | let _ = (0.0_f32 / -0.0) as usize;
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+ = note: this always evaluates to 0
+ = note: `-D clippy::cast-nan-to-int` implied by `-D warnings`
+
+error: casting a known NaN to usize
+ --> $DIR/cast_nan_to_int.rs:6:13
+ |
+LL | let _ = (f64::INFINITY * -0.0) as usize;
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+ = note: this always evaluates to 0
+
+error: casting a known NaN to usize
+ --> $DIR/cast_nan_to_int.rs:7:13
+ |
+LL | let _ = (0.0 * f32::INFINITY) as usize;
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+ = note: this always evaluates to 0
+
+error: casting a known NaN to usize
+ --> $DIR/cast_nan_to_int.rs:9:13
+ |
+LL | let _ = (f64::INFINITY + f64::NEG_INFINITY) as usize;
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+ = note: this always evaluates to 0
+
+error: casting a known NaN to usize
+ --> $DIR/cast_nan_to_int.rs:10:13
+ |
+LL | let _ = (f32::INFINITY - f32::INFINITY) as usize;
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+ = note: this always evaluates to 0
+
+error: casting a known NaN to usize
+ --> $DIR/cast_nan_to_int.rs:11:13
+ |
+LL | let _ = (f32::INFINITY / f32::NEG_INFINITY) as usize;
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+ = note: this always evaluates to 0
+
+error: aborting due to 6 previous errors
+