Add lint for comparing floats in an array

clippy_lints/src/misc.rs

@@ -489,7 +489,13 @@ fn is_signum(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
 }
 
 fn is_float(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
-    matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).sty, ty::Float(_))
+    let value = &walk_ptrs_ty(cx.tables.expr_ty(expr)).sty;
+
+    if let ty::Array(arr_ty, _) = value {
+        return matches!(arr_ty.sty, ty::Float(_));
+    };
+
+    matches!(value, ty::Float(_))
 }
 
 fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr, other: &Expr) {

tests/ui/float_cmp.rs

@@ -77,6 +77,13 @@ fn main() {
 
     assert_eq!(a, b); // no errors
 
+    let a1: [f32; 1] = [0.0];
+    let a2: [f32; 1] = [1.1];
+
+    assert_eq!(a1[0], a2[0]);
+
+    assert_eq!(&a1[0], &a2[0]);
+
     // no errors - comparing signums is ok
     let x32 = 3.21f32;
     1.23f32.signum() == x32.signum();

tests/ui/float_cmp.stderr

@@ -35,5 +35,31 @@ note: std::f32::EPSILON and std::f64::EPSILON are available.
 LL |     twice(x) != twice(ONE as f64);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 3 previous errors
+error: strict comparison of f32 or f64
+  --> $DIR/float_cmp.rs:83:5
+   |
+LL |     assert_eq!(a1[0], a2[0]);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: std::f32::EPSILON and std::f64::EPSILON are available.
+  --> $DIR/float_cmp.rs:83:5
+   |
+LL |     assert_eq!(a1[0], a2[0]);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+
+error: strict comparison of f32 or f64
+  --> $DIR/float_cmp.rs:85:5
+   |
+LL |     assert_eq!(&a1[0], &a2[0]);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: std::f32::EPSILON and std::f64::EPSILON are available.
+  --> $DIR/float_cmp.rs:85:5
+   |
+LL |     assert_eq!(&a1[0], &a2[0]);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+
+error: aborting due to 5 previous errors