tests for needless_range_loop

tests/ui/needless_range_loop.rs

@@ -0,0 +1,27 @@
+fn calc_idx(i: usize) -> usize {
+    (i + i + 20) % 4
+}
+
+fn main() {
+    let ns = [2, 3, 5, 7];
+
+    for i in 3..10 {
+        println!("{}", ns[i]);
+    }
+
+    for i in 3..10 {
+        println!("{}", ns[i % 4]);
+    }
+
+    for i in 3..10 {
+        println!("{}", ns[i % ns.len()]);
+    }
+
+    for i in 3..10 {
+        println!("{}", ns[calc_idx(i)]);
+    }
+
+    for i in 3..10 {
+        println!("{}", ns[calc_idx(i) % 4]);
+    }
+}

tests/ui/needless_range_loop.stderr

@@ -0,0 +1,14 @@
+error: the loop variable `i` is only used to index `ns`.
+  --> $DIR/needless_range_loop.rs:8:5
+   |
+8  | /     for i in 3..10 {
+9  | |         println!("{}", ns[i]);
+10 | |     }
+   | |_____^
+   |
+   = note: `-D needless-range-loop` implied by `-D warnings`
+help: consider using an iterator
+   |
+8  |     for <item> in ns.iter().take(10).skip(3) {
+   |         ^^^^^^
+