Add more tests for empty ranges and singletons

Author: rspencer01

tests/ui/map_with_unused_argument_over_ranges.fixed

@@ -1,4 +1,4 @@
-#![allow(unused, clippy::redundant_closure)]
+#![allow(unused, clippy::redundant_closure, clippy::reversed_empty_ranges)]
 #![warn(clippy::map_with_unused_argument_over_ranges)]
 
 fn do_something() -> usize {
@@ -36,6 +36,8 @@ fn main() {
     std::iter::repeat_with(|| do_something()).take(upper_fn() - 2);
     std::iter::repeat_with(|| do_something()).take(upper_fn() - 1);
     (-3..9).map(|_| do_something());
+    std::iter::repeat_with(|| do_something()).take(0);
+    std::iter::repeat_with(|| do_something()).take(1);
     // These should not be raised
     gen!();
     let lower = 2;

tests/ui/map_with_unused_argument_over_ranges.rs

@@ -1,4 +1,4 @@
-#![allow(unused, clippy::redundant_closure)]
+#![allow(unused, clippy::redundant_closure, clippy::reversed_empty_ranges)]
 #![warn(clippy::map_with_unused_argument_over_ranges)]
 
 fn do_something() -> usize {
@@ -36,6 +36,8 @@ fn main() {
     (2..upper_fn()).map(|_| do_something());
     (2..=upper_fn()).map(|_| do_something());
     (-3..9).map(|_| do_something());
+    (9..3).map(|_| do_something());
+    (9..=9).map(|_| do_something());
     // These should not be raised
     gen!();
     let lower = 2;

tests/ui/map_with_unused_argument_over_ranges.stderr

@@ -161,7 +161,31 @@ LL +     std::iter::repeat_with(|| do_something()).take(upper_fn() - 1);
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:57:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:39:5
+   |
+LL |     (9..3).map(|_| do_something());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: remove the explicit range and use `repeat_with` and `take`
+   |
+LL -     (9..3).map(|_| do_something());
+LL +     std::iter::repeat_with(|| do_something()).take(0);
+   |
+
+error: map of a closure that does not depend on its parameter over a range
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:40:5
+   |
+LL |     (9..=9).map(|_| do_something());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: remove the explicit range and use `repeat_with` and `take`
+   |
+LL -     (9..=9).map(|_| do_something());
+LL +     std::iter::repeat_with(|| do_something()).take(1);
+   |
+
+error: map of a closure that does not depend on its parameter over a range
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:59:5
    |
 LL |     (0..10).map(|_| do_something());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -172,5 +196,5 @@ LL -     (0..10).map(|_| do_something());
 LL +     std::iter::repeat_with(|| do_something()).take(10);
    |
 
-error: aborting due to 14 previous errors
+error: aborting due to 16 previous errors