auto merge of #8497 : nikomatsakis/rust/improvements-to-object-coercion, r=pcwalton

While looking over the code for object coercion, I realized that it wasn't quite handling freezing and reborrowing correctly. Tweak the code, adding tests for the relevant cases. 

r? @pcwalton

Author: bors

src/librustc/middle/typeck/check/regionck.rs

@@ -391,7 +391,7 @@ fn visit_expr(expr: @ast::expr, (rcx, v): (@mut Rcx, rvt)) {
             let target_ty = rcx.resolve_node_type(expr.id);
             match ty::get(target_ty).sty {
                 ty::ty_trait(_, _, ty::RegionTraitStore(trait_region), _, _) => {
-                    let source_ty = rcx.fcx.expr_ty(source);
+                    let source_ty = rcx.resolve_expr_type_adjusted(source);
                     constrain_regions_in_type(
                         rcx,
                         trait_region,
@@ -1153,17 +1153,20 @@ pub mod guarantor {
         match ty::get(ty).sty {
             ty::ty_rptr(r, _) |
             ty::ty_evec(_, ty::vstore_slice(r)) |
+            ty::ty_trait(_, _, ty::RegionTraitStore(r), _, _) |
             ty::ty_estr(ty::vstore_slice(r)) => {
                 BorrowedPointer(r)
             }
             ty::ty_uniq(*) |
             ty::ty_estr(ty::vstore_uniq) |
+            ty::ty_trait(_, _, ty::UniqTraitStore, _, _) |
             ty::ty_evec(_, ty::vstore_uniq) => {
                 OwnedPointer
             }
             ty::ty_box(*) |
             ty::ty_ptr(*) |
             ty::ty_evec(_, ty::vstore_box) |
+            ty::ty_trait(_, _, ty::BoxTraitStore, _, _) |
             ty::ty_estr(ty::vstore_box) => {
                 OtherPointer
             }

src/librustc/middle/typeck/infer/coercion.rs

@@ -121,9 +121,9 @@ impl Coerce {
                 };
             }
 
-            ty::ty_trait(_, _, ty::RegionTraitStore(*), _, _) => {
+            ty::ty_trait(_, _, ty::RegionTraitStore(*), m, _) => {
                 return do self.unpack_actual_value(a) |sty_a| {
-                    self.coerce_borrowed_object(a, sty_a, b)
+                    self.coerce_borrowed_object(a, sty_a, b, m)
                 };
             }
 
@@ -274,34 +274,30 @@ impl Coerce {
     fn coerce_borrowed_object(&self,
                               a: ty::t,
                               sty_a: &ty::sty,
-                              b: ty::t) -> CoerceResult
+                              b: ty::t,
+                              b_mutbl: ast::mutability) -> CoerceResult
     {
         debug!("coerce_borrowed_object(a=%s, sty_a=%?, b=%s)",
                a.inf_str(self.infcx), sty_a,
                b.inf_str(self.infcx));
 
         let tcx = self.infcx.tcx;
         let r_a = self.infcx.next_region_var(Coercion(self.trace));
-        let trt_mut;
 
         let a_borrowed = match *sty_a {
-            ty::ty_trait(_, _, ty::RegionTraitStore(_), _, _) => {
-                return self.subtype(a, b);
-            }
-            ty::ty_trait(did, ref substs, _, m, b) => {
-                trt_mut = m;
+            ty::ty_trait(did, ref substs, _, _, b) => {
                 ty::mk_trait(tcx, did, substs.clone(),
-                             ty::RegionTraitStore(r_a), m, b)
+                             ty::RegionTraitStore(r_a), b_mutbl, b)
             }
             _ => {
                 return self.subtype(a, b);
             }
         };
 
-        if_ok!(self.tys(a_borrowed, b));
+        if_ok!(self.subtype(a_borrowed, b));
         Ok(Some(@AutoDerefRef(AutoDerefRef {
             autoderefs: 0,
-            autoref: Some(AutoBorrowObj(r_a, trt_mut))
+            autoref: Some(AutoBorrowObj(r_a, b_mutbl))
         })))
     }
 

src/test/run-fail/borrowck-wg-fail-object-arg.rs

@@ -0,0 +1,22 @@
+// error-pattern:borrowed
+
+trait Foo {
+    fn foo(&self, @mut int);
+}
+
+impl Foo for int {
+    fn foo(&self, x: @mut int) {
+        *x += *self;
+    }
+}
+
+fn it_takes_two(f: &Foo, g: &mut Foo) {
+}
+
+fn main() {
+    let x = @mut 3_i;
+    let y = x as @mut Foo;
+    let z = y;
+
+    it_takes_two(y, z);
+}

src/test/run-pass/objects-coerce-freeze-borrored.rs

@@ -0,0 +1,48 @@
+// Copyright 2012 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.
+
+// Test that we can coerce an `@Object` to an `&Object`
+
+trait Foo {
+    fn foo(&self) -> uint;
+    fn bar(&mut self) -> uint;
+}
+
+impl Foo for uint {
+    fn foo(&self) -> uint {
+        *self
+    }
+
+    fn bar(&mut self) -> uint {
+        *self += 1;
+        *self
+    }
+}
+
+fn do_it_mut(obj: &mut Foo) {
+    let x = obj.bar();
+    let y = obj.foo();
+    assert_eq!(x, y);
+
+    do_it_imm(obj, y);
+}
+
+fn do_it_imm(obj: &Foo, v: uint) {
+    let y = obj.foo();
+    assert_eq!(v, y);
+}
+
+fn main() {
+    let mut x = 22_u;
+    let obj = &mut x as &mut Foo;
+    do_it_mut(obj);
+    do_it_imm(obj, 23u);
+    do_it_mut(obj);
+}

src/test/run-pass/objects-coerce-from-managed-to-borrowed.rs

@@ -0,0 +1,44 @@
+// Copyright 2012 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.
+
+// Test that we can coerce an `@Object` to an `&Object`
+
+trait Foo {
+    fn foo(&self) -> uint;
+    fn bar(&mut self) -> uint;
+}
+
+impl Foo for uint {
+    fn foo(&self) -> uint {
+        *self
+    }
+
+    fn bar(&mut self) -> uint {
+        *self += 1;
+        *self
+    }
+}
+
+fn do_it_mut(obj: &mut Foo) {
+    let x = obj.bar();
+    let y = obj.foo();
+    assert_eq!(x, y);
+}
+
+fn do_it_imm(obj: &Foo, v: uint) {
+    let y = obj.foo();
+    assert_eq!(v, y);
+}
+
+fn main() {
+    let x = @mut 22u as @mut Foo;
+    do_it_mut(x);
+    do_it_imm(x, 23u);
+}