Add test for issue-67166

Author: JohnTitor

src/test/ui/impl-trait/issue-67166.rs

@@ -0,0 +1,11 @@
+// Regression test for #67166
+
+#![feature(impl_trait_in_bindings)]
+#![allow(incomplete_features)]
+
+pub fn run() {
+    let _foo: Box<impl Copy + '_> = Box::new(());
+    //~^ ERROR: opaque type expands to a recursive type
+}
+
+fn main() {}

src/test/ui/impl-trait/issue-67166.stderr

@@ -0,0 +1,11 @@
+error[E0720]: opaque type expands to a recursive type
+  --> $DIR/issue-67166.rs:7:19
+   |
+LL |     let _foo: Box<impl Copy + '_> = Box::new(());
+   |                   ^^^^^^^^^^^^^^ expands to a recursive type
+   |
+   = note: type resolves to itself
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0720`.