Add lint when comparing floats in an array

Finishes rust-lang#4277

Author: briankabiro

clippy_lints/src/misc.rs

@@ -498,8 +498,14 @@ fn is_signum(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
     false
 }
 
-fn is_float(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
-    matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).kind, ty::Float(_))
+fn is_float(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
+    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<'_>) {