Resolves third bullet of #4691, and adds tests for it. Fix #4691.

src/librustc/middle/moves.rs

@@ -134,6 +134,7 @@ use middle::typeck::{method_map};
 use util::ppaux;
 use util::ppaux::Repr;
 use util::common::indenter;
+use util::ppaux::UserString;
 
 use std::at_vec;
 use std::hashmap::{HashSet, HashMap};
@@ -433,7 +434,21 @@ impl VisitContext {
                             ty::type_moves_by_default(self.tcx, tf.mt.ty)
                     });
 
+                    fn has_dtor(tcx: ty::ctxt, ty: ty::t) -> bool {
+                        use middle::ty::{get,ty_struct,ty_enum};
+                        match get(ty).sty {
+                            ty_struct(did, _) | ty_enum(did, _) => ty::has_dtor(tcx, did),
+                            _ => false,
+                        }
+                    }
+
                     if consume_with {
+                        if has_dtor(self.tcx, with_ty) {
+                            self.tcx.sess.span_err(with_expr.span,
+                                                   fmt!("cannot move out of type `%s`, \
+                                                         which defines the `Drop` trait",
+                                                        with_ty.user_string(self.tcx)));
+                        }
                         self.consume_expr(*with_expr, visitor);
                     } else {
                         self.use_expr(*with_expr, Read, visitor);

src/test/compile-fail/borrowck-struct-update-with-dtor.rs

@@ -0,0 +1,29 @@
+// Copyright 2012-2013 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.
+
+// Issue 4691: Ensure that functional-struct-update can only copy, not
+// move, when the struct implements Drop.
+
+use NC = std::util::NonCopyable;
+struct S { a: int, nc: NC }
+impl Drop for S { fn drop(&mut self) { } }
+
+struct T { a: int, mv: ~int }
+impl Drop for T { fn drop(&mut self) { } }
+
+fn f(s0:S) {
+    let _s2 = S{a: 2, ..s0}; //~error: cannot move out of type `S`, which defines the `Drop` trait
+}
+
+fn g(s0:T) {
+    let _s2 = T{a: 2, ..s0}; //~error: cannot move out of type `T`, which defines the `Drop` trait
+}
+
+fn main() { }

src/test/run-pass/struct-update-moves-and-copies.rs

@@ -0,0 +1,101 @@
+// Copyright 2012-2013 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.
+
+// Issue 4691: Ensure that functional-struct-updates operates
+// correctly and moves rather than copy when appropriate.
+
+use NC = std::util::NonCopyable;
+
+struct ncint { nc: NC, v: int }
+fn ncint(v: int) -> ncint { ncint { nc: NC, v: v } }
+
+struct NoFoo { copied: int, noncopy: ncint, }
+impl NoFoo {
+    fn new(x:int,y:int) -> NoFoo { NoFoo { copied: x, noncopy: ncint(y) } }
+}
+
+struct MoveFoo { copied: int, moved: ~int, }
+impl MoveFoo {
+    fn new(x:int,y:int) -> MoveFoo { MoveFoo { copied: x, moved: ~y } }
+}
+
+struct DropNoFoo { inner: NoFoo }
+impl DropNoFoo {
+    fn new(x:int,y:int) -> DropNoFoo { DropNoFoo { inner: NoFoo::new(x,y) } }
+}
+impl Drop for DropNoFoo { fn drop(&mut self) { } }
+
+struct DropMoveFoo { inner: MoveFoo }
+impl DropMoveFoo {
+    fn new(x:int,y:int) -> DropMoveFoo { DropMoveFoo { inner: MoveFoo::new(x,y) } }
+}
+impl Drop for DropMoveFoo { fn drop(&mut self) { } }
+
+
+fn test0() {
+    // just copy implicitly copyable fields from `f`, no moves
+    // (and thus it is okay that these are Drop; compare against
+    // compile-fail test: borrowck-struct-update-with-dtor.rs).
+
+    // Case 1: NonCopyable
+    let f = DropNoFoo::new(1, 2);
+    let b = DropNoFoo { inner: NoFoo { noncopy: ncint(3), ..f.inner }};
+    let c = DropNoFoo { inner: NoFoo { noncopy: ncint(4), ..f.inner }};
+    assert_eq!(f.inner.copied,    1);
+    assert_eq!(f.inner.noncopy.v, 2);
+
+    assert_eq!(b.inner.copied,    1);
+    assert_eq!(b.inner.noncopy.v, 3);
+
+    assert_eq!(c.inner.copied,    1);
+    assert_eq!(c.inner.noncopy.v, 4);
+
+    // Case 2: Owned
+    let f = DropMoveFoo::new(5, 6);
+    let b = DropMoveFoo { inner: MoveFoo { moved: ~7, ..f.inner }};
+    let c = DropMoveFoo { inner: MoveFoo { moved: ~8, ..f.inner }};
+    assert_eq!(f.inner.copied,    5);
+    assert_eq!(*f.inner.moved,    6);
+
+    assert_eq!(b.inner.copied,    1);
+    assert_eq!(*b.inner.moved,    7);
+
+    assert_eq!(c.inner.copied,    1);
+    assert_eq!(*c.inner.moved,    8);
+}
+
+fn test1() {
+    // copying move-by-default fields from `f`, so it moves:
+    let f = MoveFoo::new(11, 12);
+
+    let b = MoveFoo {moved: ~13, ..f};
+    let c = MoveFoo {copied: 14, ..f};
+    assert_eq!(b.copied,    11);
+    assert_eq!(*b.moved,    13);
+    assert_eq!(c.copied,    14);
+    assert_eq!(*c.moved,    12);
+}
+
+fn test2() {
+    // move non-copyable field
+    let f = NoFoo::new(21, 22);
+    let b = NoFoo {noncopy: ncint(23), ..f};
+    let c = NoFoo {copied: 24, ..f};
+    assert_eq!(b.copied,    21);
+    assert_eq!(b.noncopy.v, 23);
+    assert_eq!(c.copied,    24);
+    assert_eq!(c.noncopy.v, 22);
+}
+
+fn main() {
+    test0();
+    test1();
+    test2();
+}