1 files changed, 99 insertions, 0 deletions
diff --git a/tests/ui/lint/drop_ref.rs b/tests/ui/lint/drop_ref.rs
new file mode 100644
index 00000000000..db4f7569f6f
--- /dev/null
+++ b/tests/ui/lint/drop_ref.rs
@@ -0,0 +1,99 @@
+// check-pass
+
+#![warn(drop_ref)]
+
+struct SomeStruct;
+
+fn main() {
+    drop(&SomeStruct); //~ WARN calls to `std::mem::drop`
+
+    let mut owned1 = SomeStruct;
+    drop(&owned1); //~ WARN calls to `std::mem::drop`
+    drop(&&owned1); //~ WARN calls to `std::mem::drop`
+    drop(&mut owned1); //~ WARN calls to `std::mem::drop`
+    drop(owned1);
+
+    let reference1 = &SomeStruct;
+    drop(reference1); //~ WARN calls to `std::mem::drop`
+
+    let reference2 = &mut SomeStruct;
+    drop(reference2); //~ WARN calls to `std::mem::drop`
+
+    let ref reference3 = SomeStruct;
+    drop(reference3); //~ WARN calls to `std::mem::drop`
+}
+
+#[allow(dead_code)]
+fn test_generic_fn_drop<T>(val: T) {
+    drop(&val); //~ WARN calls to `std::mem::drop`
+    drop(val);
+}
+
+#[allow(dead_code)]
+fn test_similarly_named_function() {
+    fn drop<T>(_val: T) {}
+    drop(&SomeStruct); //OK; call to unrelated function which happens to have the same name
+    std::mem::drop(&SomeStruct); //~ WARN calls to `std::mem::drop`
+}
+
+#[derive(Copy, Clone)]
+pub struct Error;
+fn produce_half_owl_error() -> Result<(), Error> {
+    Ok(())
+}
+
+fn produce_half_owl_ok() -> Result<bool, ()> {
+    Ok(true)
+}
+
+#[allow(dead_code)]
+fn test_owl_result() -> Result<(), ()> {
+    produce_half_owl_error().map_err(|_| ())?;
+    produce_half_owl_ok().map(|_| ())?;
+    // the following should not be linted,
+    // we should not force users to use toilet closures
+    // to produce owl results when drop is more convenient
+    produce_half_owl_error().map_err(drop)?;
+    produce_half_owl_ok().map_err(drop)?;
+    Ok(())
+}
+
+#[allow(dead_code)]
+fn test_owl_result_2() -> Result<u8, ()> {
+    produce_half_owl_error().map_err(|_| ())?;
+    produce_half_owl_ok().map(|_| ())?;
+    // the following should not be linted,
+    // we should not force users to use toilet closures
+    // to produce owl results when drop is more convenient
+    produce_half_owl_error().map_err(drop)?;
+    produce_half_owl_ok().map(drop)?;
+    Ok(1)
+}
+
+#[allow(unused)]
+#[allow(clippy::unit_cmp)]
+fn issue10122(x: u8) {
+    // This is a function which returns a reference and has a side-effect, which means
+    // that calling drop() on the function is considered an idiomatic way of achieving
+    // the side-effect in a match arm.
+    fn println_and<T>(t: &T) -> &T {
+        println!("foo");
+        t
+    }
+
+    match x {
+        // Don't lint (copy type), we only care about side-effects
+        0 => drop(println_and(&12)),
+        // Don't lint (no copy type), we only care about side-effects
+        1 => drop(println_and(&String::new())),
+        2 => {
+            // Lint, even if we only care about the side-effect, it's already in a block
+            drop(println_and(&13)); //~ WARN calls to `std::mem::drop`
+        },
+        // Lint, idiomatic use is only in body of `Arm`
+        3 if drop(println_and(&14)) == () => (), //~ WARN calls to `std::mem::drop`
+         // Lint, not a fn/method call
+        4 => drop(&2), //~ WARN calls to `std::mem::drop`
+        _ => (),
+    }
+}