implement drop for NonZero optimized enums

src/interpreter/terminator/mod.rs

@@ -560,6 +560,21 @@ fn drop(
                             return Ok(()); // nothing to do, this is zero sized (e.g. `None`)
                         }
                     },
+                    Layout::RawNullablePointer { nndiscr, .. } => {
+                        let discr = self.read_discriminant_value(adt_ptr, ty)?;
+                        if discr == nndiscr {
+                            assert_eq!(adt_def.variants[discr as usize].fields.len(), 1);
+                            let field_ty = &adt_def.variants[discr as usize].fields[0];
+                            let field_ty = self.monomorphize_field_ty(field_ty, substs);
+                            // FIXME: once read_discriminant_value works with lvalue, don't force
+                            // alloc in the RawNullablePointer case
+                            self.drop(Lvalue::from_ptr(adt_ptr), field_ty, drop)?;
+                            return Ok(());
+                        } else {
+                            // FIXME: the zst variant might contain zst types that impl Drop
+                            return Ok(()); // nothing to do, this is zero sized (e.g. `None`)
+                        }
+                    },
                     _ => bug!("{:?} is not an adt layout", layout),
                 };
                 for (field_ty, offset) in fields {

tests/run-pass/regions-lifetime-nonfree-late-bound.rs

+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// This is a regression test for the ICE from issue #10846.
+//
+// The original issue causing the ICE: the LUB-computations during
+// type inference were encountering late-bound lifetimes, and
+// asserting that such lifetimes should have already been substituted
+// with a concrete lifetime.
+//
+// However, those encounters were occurring within the lexical scope
+// of the binding for the late-bound lifetime; that is, the late-bound
+// lifetimes were perfectly valid.  The core problem was that the type
+// folding code was over-zealously passing back all lifetimes when
+// doing region-folding, when really all clients of the region-folding
+// case only want to see FREE lifetime variables, not bound ones.
+
+// pretty-expanded FIXME #23616
+
+#![allow(unused_features)]
+#![feature(box_syntax)]
+
+pub fn main() {
+    fn explicit() {
+        fn test<F>(_x: Option<Box<F>>) where F: FnMut(Box<for<'a> FnMut(&'a isize)>) {}
+        test(Some(box |_f: Box<for<'a> FnMut(&'a isize)>| {}));
+    }
+
+    // The code below is shorthand for the code above (and more likely
+    // to represent what one encounters in practice).
+    fn implicit() {
+        fn test<F>(_x: Option<Box<F>>) where F: FnMut(Box<        FnMut(&   isize)>) {}
+        test(Some(box |_f: Box<        FnMut(&   isize)>| {}));
+    }
+
+    explicit();
+    implicit();
+}