fix a bug in drop code of structs with unsized fields

src/terminator/drop.rs

@@ -94,10 +94,7 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
             ty::TyAdt(adt_def, substs) => {
                 // FIXME: some structs are represented as ByValPair
                 let mut lval = self.force_allocation(lval)?;
-                let adt_ptr = match lval {
-                    Lvalue::Ptr { ptr, .. } => ptr,
-                    _ => bug!("force allocation can only yield Lvalue::Ptr"),
-                };
+                let (adt_ptr, extra) = lval.to_ptr_and_extra();
 
                 // run drop impl before the fields' drop impls
                 if let Some(drop_def_id) = adt_def.destructor() {
@@ -109,7 +106,13 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
                         traits::VtableImpl(data) => data,
                         _ => bug!("dtor for {:?} is not an impl???", ty)
                     };
-                    drop.push((drop_def_id, Value::ByVal(PrimVal::Ptr(adt_ptr)), vtable.substs));
+                    let val = match extra {
+                        LvalueExtra::None => Value::ByVal(PrimVal::Ptr(adt_ptr)),
+                        LvalueExtra::DowncastVariant(_) => bug!("downcast variant in drop"),
+                        LvalueExtra::Length(n) => Value::ByValPair(PrimVal::Ptr(adt_ptr), PrimVal::from_u128(n as u128)),
+                        LvalueExtra::Vtable(vtable) => Value::ByValPair(PrimVal::Ptr(adt_ptr), PrimVal::Ptr(vtable)),
+                    };
+                    drop.push((drop_def_id, val, vtable.substs));
                 }
 
                 let layout = self.type_layout(ty)?;

tests/run-pass/issue-26709.rs

@@ -0,0 +1,26 @@
+// Copyright 2015 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.
+
+struct Wrapper<'a, T: ?Sized>(&'a mut i32, T);
+
+impl<'a, T: ?Sized> Drop for Wrapper<'a, T> {
+    fn drop(&mut self) {
+        *self.0 = 432;
+    }
+}
+
+fn main() {
+    let mut x = 0;
+    {
+        let wrapper = Box::new(Wrapper(&mut x, 123));
+        let _: Box<Wrapper<Send>> = wrapper;
+    }
+    assert_eq!(432, x)
+}