Make missing_copy_implementations more cautious

src/test/ui/lint/lint-missing-copy-implementations-allow.rs

@@ -0,0 +1,35 @@
+// check-pass
+#![deny(missing_copy_implementations)]
+
+// Don't recommend implementing Copy on something stateful like an iterator.
+pub struct MyIterator {
+    num: u8,
+}
+
+impl Iterator for MyIterator {
+    type Item = u8;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+pub struct Handle {
+    inner: *mut (),
+}
+
+pub struct Handle2 {
+    inner: *const (),
+}
+
+pub enum MaybeHandle {
+    Ptr(*mut ()),
+}
+
+pub union UnionHandle {
+    ptr: *mut (),
+}
+
+pub struct Array([u8; 2048]);
+
+fn main() {}