Emit dummy open drop for unsafe binder

Author: compiler-errors

compiler/rustc_mir_transform/src/elaborate_drop.rs

@@ -1278,6 +1278,23 @@ where
             }
             ty::Slice(ety) => self.drop_loop_trio_for_slice(*ety),
 
+            ty::UnsafeBinder(_) => {
+                // Unsafe binders may elaborate drops if their inner type isn't copy.
+                // This is enforced in typeck, so this should never happen.
+                self.tcx().dcx().span_delayed_bug(
+                    self.source_info.span,
+                    "open drop for unsafe binder shouldn't be encountered",
+                );
+                self.elaborator.patch().new_block(BasicBlockData {
+                    statements: vec![],
+                    terminator: Some(Terminator {
+                        source_info: self.source_info,
+                        kind: TerminatorKind::Unreachable,
+                    }),
+                    is_cleanup: self.unwind.is_cleanup(),
+                })
+            }
+
             _ => span_bug!(self.source_info.span, "open drop from non-ADT `{:?}`", ty),
         }
     }

tests/ui/unsafe/move-out-of-non-copy.rs

@@ -0,0 +1,15 @@
+//@ compile-flags: -Zvalidate-mir
+
+// Regression test for <https://github.com/rust-lang/rust/issues/141394>.
+
+#![feature(unsafe_binders)]
+#![allow(incomplete_features)]
+
+use std::unsafe_binder::unwrap_binder;
+
+fn id<T>(x: unsafe<> T) -> T {
+    //~^ ERROR the trait bound `T: Copy` is not satisfied
+    unsafe { unwrap_binder!(x) }
+}
+
+fn main() {}

tests/ui/unsafe/move-out-of-non-copy.stderr

@@ -0,0 +1,14 @@
+error[E0277]: the trait bound `T: Copy` is not satisfied
+  --> $DIR/move-out-of-non-copy.rs:10:13
+   |
+LL | fn id<T>(x: unsafe<> T) -> T {
+   |             ^^^^^^^^^^ the trait `Copy` is not implemented for `T`
+   |
+help: consider restricting type parameter `T` with trait `Copy`
+   |
+LL | fn id<T: std::marker::Copy>(x: unsafe<> T) -> T {
+   |        +++++++++++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.