Add tests for empty_loop lint

tests/ui/auxiliary/macro_rules.rs

@@ -0,0 +1,9 @@
+#![allow(dead_code)]
+
+/// Used to test that certain lints don't trigger in imported external macros
+#[macro_export]
+macro_rules! foofoo {
+    () => {
+        loop {}
+    };
+}

tests/ui/empty_loop.rs

@@ -0,0 +1,52 @@
+// aux-build:macro_rules.rs
+
+#![warn(clippy::empty_loop)]
+#![allow(clippy::unused_label)]
+
+#[macro_use]
+extern crate macro_rules;
+
+fn should_trigger() {
+    loop {}
+    loop {
+        loop {}
+    }
+
+    'outer: loop {
+        'inner: loop {}
+    }
+}
+
+fn should_not_trigger() {
+    loop {
+        panic!("This is fine")
+    }
+    let ten_millis = std::time::Duration::from_millis(10);
+    loop {
+        std::thread::sleep(ten_millis)
+    }
+
+    #[allow(clippy::never_loop)]
+    'outer: loop {
+        'inner: loop {
+            break 'inner;
+        }
+        break 'outer;
+    }
+
+    // Make sure `allow` works for this lint
+    #[allow(clippy::empty_loop)]
+    loop {}
+
+    // We don't lint loops inside macros
+    macro_rules! foo {
+        () => {
+            loop {}
+        };
+    }
+
+    // We don't lint external macros
+    foofoo!()
+}
+
+fn main() {}

tests/ui/empty_loop.stderr

@@ -0,0 +1,22 @@
+error: empty `loop {}` detected. You may want to either use `panic!()` or add `std::thread::sleep(..);` to the loop body.
+  --> $DIR/empty_loop.rs:10:5
+   |
+LL |     loop {}
+   |     ^^^^^^^
+   |
+   = note: `-D clippy::empty-loop` implied by `-D warnings`
+
+error: empty `loop {}` detected. You may want to either use `panic!()` or add `std::thread::sleep(..);` to the loop body.
+  --> $DIR/empty_loop.rs:12:9
+   |
+LL |         loop {}
+   |         ^^^^^^^
+
+error: empty `loop {}` detected. You may want to either use `panic!()` or add `std::thread::sleep(..);` to the loop body.
+  --> $DIR/empty_loop.rs:16:9
+   |
+LL |         'inner: loop {}
+   |         ^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+