Re-add old tests for empty range loops

tests/ui/reversed_empty_ranges_loops_fixable.fixed

@@ -0,0 +1,57 @@
+// run-rustfix
+#![warn(clippy::reversed_empty_ranges)]
+
+fn main() {
+    const MAX_LEN: usize = 42;
+
+    for i in (0..10).rev() {
+        println!("{}", i);
+    }
+
+    for i in (0..=10).rev() {
+        println!("{}", i);
+    }
+
+    for i in (0..MAX_LEN).rev() {
+        println!("{}", i);
+    }
+
+    for i in 5..=5 {
+        // not an error, this is the range with only one element “5”
+        println!("{}", i);
+    }
+
+    for i in 0..10 {
+        // not an error, the start index is less than the end index
+        println!("{}", i);
+    }
+
+    for i in -10..0 {
+        // not an error
+        println!("{}", i);
+    }
+
+    for i in (0..10).rev().map(|x| x * 2) {
+        println!("{}", i);
+    }
+
+    // testing that the empty range lint folds constants
+    for i in (5 + 4..10).rev() {
+        println!("{}", i);
+    }
+
+    for i in ((3 - 1)..(5 + 2)).rev() {
+        println!("{}", i);
+    }
+
+    for i in (2 * 2)..(2 * 3) {
+        // no error, 4..6 is fine
+        println!("{}", i);
+    }
+
+    let x = 42;
+    for i in x..10 {
+        // no error, not constant-foldable
+        println!("{}", i);
+    }
+}

tests/ui/reversed_empty_ranges_loops_fixable.rs

@@ -0,0 +1,57 @@
+// run-rustfix
+#![warn(clippy::reversed_empty_ranges)]
+
+fn main() {
+    const MAX_LEN: usize = 42;
+
+    for i in 10..0 {
+        println!("{}", i);
+    }
+
+    for i in 10..=0 {
+        println!("{}", i);
+    }
+
+    for i in MAX_LEN..0 {
+        println!("{}", i);
+    }
+
+    for i in 5..=5 {
+        // not an error, this is the range with only one element “5”
+        println!("{}", i);
+    }
+
+    for i in 0..10 {
+        // not an error, the start index is less than the end index
+        println!("{}", i);
+    }
+
+    for i in -10..0 {
+        // not an error
+        println!("{}", i);
+    }
+
+    for i in (10..0).map(|x| x * 2) {
+        println!("{}", i);
+    }
+
+    // testing that the empty range lint folds constants
+    for i in 10..5 + 4 {
+        println!("{}", i);
+    }
+
+    for i in (5 + 2)..(3 - 1) {
+        println!("{}", i);
+    }
+
+    for i in (2 * 2)..(2 * 3) {
+        // no error, 4..6 is fine
+        println!("{}", i);
+    }
+
+    let x = 42;
+    for i in x..10 {
+        // no error, not constant-foldable
+        println!("{}", i);
+    }
+}

tests/ui/reversed_empty_ranges_loops_fixable.stderr

@@ -0,0 +1,69 @@
+error: this range is empty so it will yield no values
+  --> $DIR/reversed_empty_ranges_loops_fixable.rs:7:14
+   |
+LL |     for i in 10..0 {
+   |              ^^^^^
+   |
+   = note: `-D clippy::reversed-empty-ranges` implied by `-D warnings`
+help: consider using the following if you are attempting to iterate over this range in reverse
+   |
+LL |     for i in (0..10).rev() {
+   |              ^^^^^^^^^^^^^
+
+error: this range is empty so it will yield no values
+  --> $DIR/reversed_empty_ranges_loops_fixable.rs:11:14
+   |
+LL |     for i in 10..=0 {
+   |              ^^^^^^
+   |
+help: consider using the following if you are attempting to iterate over this range in reverse
+   |
+LL |     for i in (0..=10).rev() {
+   |              ^^^^^^^^^^^^^^
+
+error: this range is empty so it will yield no values
+  --> $DIR/reversed_empty_ranges_loops_fixable.rs:15:14
+   |
+LL |     for i in MAX_LEN..0 {
+   |              ^^^^^^^^^^
+   |
+help: consider using the following if you are attempting to iterate over this range in reverse
+   |
+LL |     for i in (0..MAX_LEN).rev() {
+   |              ^^^^^^^^^^^^^^^^^^
+
+error: this range is empty so it will yield no values
+  --> $DIR/reversed_empty_ranges_loops_fixable.rs:34:14
+   |
+LL |     for i in (10..0).map(|x| x * 2) {
+   |              ^^^^^^^
+   |
+help: consider using the following if you are attempting to iterate over this range in reverse
+   |
+LL |     for i in (0..10).rev().map(|x| x * 2) {
+   |              ^^^^^^^^^^^^^
+
+error: this range is empty so it will yield no values
+  --> $DIR/reversed_empty_ranges_loops_fixable.rs:39:14
+   |
+LL |     for i in 10..5 + 4 {
+   |              ^^^^^^^^^
+   |
+help: consider using the following if you are attempting to iterate over this range in reverse
+   |
+LL |     for i in (5 + 4..10).rev() {
+   |              ^^^^^^^^^^^^^^^^^
+
+error: this range is empty so it will yield no values
+  --> $DIR/reversed_empty_ranges_loops_fixable.rs:43:14
+   |
+LL |     for i in (5 + 2)..(3 - 1) {
+   |              ^^^^^^^^^^^^^^^^
+   |
+help: consider using the following if you are attempting to iterate over this range in reverse
+   |
+LL |     for i in ((3 - 1)..(5 + 2)).rev() {
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 6 previous errors
+

tests/ui/reversed_empty_ranges_loops_unfixable.rs

@@ -0,0 +1,11 @@
+#![warn(clippy::reversed_empty_ranges)]
+
+fn main() {
+    for i in 5..5 {
+        println!("{}", i);
+    }
+
+    for i in (5 + 2)..(8 - 1) {
+        println!("{}", i);
+    }
+}

tests/ui/reversed_empty_ranges_loops_unfixable.stderr

@@ -0,0 +1,16 @@
+error: this range is empty so it will yield no values
+  --> $DIR/reversed_empty_ranges_loops_unfixable.rs:4:14
+   |
+LL |     for i in 5..5 {
+   |              ^^^^
+   |
+   = note: `-D clippy::reversed-empty-ranges` implied by `-D warnings`
+
+error: this range is empty so it will yield no values
+  --> $DIR/reversed_empty_ranges_loops_unfixable.rs:8:14
+   |
+LL |     for i in (5 + 2)..(8 - 1) {
+   |              ^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+