Auto merge of #9617 - llogiq:cast-nan-to-int, r=Alexendoo

add `cast-nan-to-int` lint

This fixes #371.

r? `@Alexendoo`

---

changelog: add [`cast-nan-to-int`] lint

2 files changed, 69 insertions, 0 deletions

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
+