add lang items, feature gate, tests; update typeck/trans

src/librustc/middle/expr_use_visitor.rs

@@ -584,10 +584,15 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
             }
 
             ast::ExprAssignOp(_, ref lhs, ref rhs) => {
-                // This will have to change if/when we support
-                // overloaded operators for `+=` and so forth.
                 self.mutate_expr(expr, &**lhs, WriteAndRead);
-                self.consume_expr(&**rhs);
+
+                if self.typer.is_method_call(expr.id) {
+                    let r = ty::ReScope(region::CodeExtent::from_node_id(expr.id));
+                    self.borrow_expr(rhs, r, ty::ImmBorrow, OverloadedOperator);
+                } else {
+                    // built-in assignment operations consume the RHS
+                    self.consume_expr(&**rhs);
+                }
             }
 
             ast::ExprRepeat(ref base, ref count) => {

src/librustc/middle/lang_items.rs

@@ -283,6 +283,17 @@ lets_do_this! {
     RangeToStructLangItem,           "range_to",                range_to_struct;
     RangeFullStructLangItem,         "range_full",              range_full_struct;
 
+    AddAssignTraitLangItem,          "add_assign",              add_assign_trait;
+    BitAndAssignTraitLangItem,       "bitand_assign",           bitand_assign_trait;
+    BitOrAssignTraitLangItem,        "bitor_assign",            bitor_assign_trait;
+    BitXorAssignTraitLangItem,       "bitxor_assign",           bitxor_assign_trait;
+    DivAssignTraitLangItem,          "div_assign",              div_assign_trait;
+    MulAssignTraitLangItem,          "mul_assign",              mul_assign_trait;
+    RemAssignTraitLangItem,          "rem_assign",              rem_assign_trait;
+    ShlAssignTraitLangItem,          "shl_assign",              shl_assign_trait;
+    ShrAssignTraitLangItem,          "shr_assign",              shr_assign_trait;
+    SubAssignTraitLangItem,          "sub_assign",              sub_assign_trait;
+
     UnsafeCellTypeLangItem,          "unsafe_cell",             unsafe_cell_type;
 
     DerefTraitLangItem,              "deref",                   deref_trait;

src/librustc_trans/trans/expr.rs

@@ -1041,7 +1041,15 @@ fn trans_rvalue_stmt_unadjusted<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
             }
         }
         ast::ExprAssignOp(op, ref dst, ref src) => {
-            trans_assign_op(bcx, expr, op, &**dst, &**src)
+            if ty::is_binopable(bcx.tcx(), node_id_type(bcx, dst.id), op) {
+                trans_assign_op(bcx, expr, op, &**dst, &**src)
+            } else {
+                let dst = unpack_datum!(bcx, trans(bcx, &**dst));
+                let src_datum = unpack_datum!(bcx, trans(bcx, &**src));
+                trans_overloaded_op(bcx, expr, MethodCall::expr(expr.id), dst,
+                                    vec![(src_datum, src.id)], None,
+                                    true).bcx
+            }
         }
         ast::ExprInlineAsm(ref a) => {
             asm::trans_inline_asm(bcx, a)
@@ -1239,8 +1247,9 @@ fn trans_rvalue_dps_unadjusted<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                                         "expr_cast of non-trait");
             }
         }
-        ast::ExprAssignOp(op, ref dst, ref src) => {
-            trans_assign_op(bcx, expr, op, &**dst, &**src)
+        ast::ExprAssignOp(..) => {
+            bcx.tcx().sess.span_bug(expr.span,
+                                    "operator assignment (`+=`) should always be an rvalue_stmt");
         }
         _ => {
             bcx.tcx().sess.span_bug(

src/librustc_typeck/check/mod.rs

@@ -2992,19 +2992,20 @@ fn check_expr_with_unifier<'a, 'tcx, F>(fcx: &FnCtxt<'a, 'tcx>,
         let result_t = if is_binop_assignment == SimpleBinop {
             check_user_binop(fcx, expr, lhs, lhs_t, op, rhs)
         } else {
-            fcx.type_error_message(expr.span,
-                                   |actual| {
-                                        format!("binary assignment \
-                                                 operation `{}=` \
-                                                 cannot be applied to \
-                                                 type `{}`",
-                                                ast_util::binop_to_string(op.node),
-                                                actual)
-                                   },
-                                   lhs_t,
-                                   None);
-            check_expr(fcx, &**rhs);
-            fcx.tcx().types.err
+            if fcx.tcx().sess.features.borrow().op_assign {
+                check_user_binop_assign(fcx, expr, lhs, lhs_t, op, rhs)
+            } else {
+                fcx.tcx().sess.span_err(
+                    expr.span,
+                    "overloaded augmented assignment is not stable",
+                );
+                fileline_help!(
+                    fcx.tcx().sess,
+                    expr.span,
+                    "add `#![feature(op_assign)]` to the crate attributes to enable");
+
+                fcx.tcx().types.err
+            }
         };
 
         fcx.write_ty(expr.id, result_t);
@@ -3053,6 +3054,42 @@ fn check_expr_with_unifier<'a, 'tcx, F>(fcx: &FnCtxt<'a, 'tcx>,
         }, if ast_util::is_by_value_binop(op.node) { AutorefArgs::No } else { AutorefArgs::Yes })
     }
 
+    fn check_user_binop_assign<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
+                                         ex: &'tcx ast::Expr,
+                                         lhs_expr: &'tcx ast::Expr,
+                                         lhs_resolved_t: Ty<'tcx>,
+                                         op: ast::BinOp,
+                                         rhs: &'tcx P<ast::Expr>) -> Ty<'tcx> {
+        let tcx = fcx.ccx.tcx;
+        let lang = &tcx.lang_items;
+        let (name, trait_did) = match op.node {
+            ast::BiAdd => ("add_assign", lang.add_assign_trait()),
+            ast::BiSub => ("sub_assign", lang.sub_assign_trait()),
+            ast::BiMul => ("mul_assign", lang.mul_assign_trait()),
+            ast::BiDiv => ("div_assign", lang.div_assign_trait()),
+            ast::BiRem => ("rem_assign", lang.rem_assign_trait()),
+            ast::BiBitXor => ("bitxor_assign", lang.bitxor_assign_trait()),
+            ast::BiBitAnd => ("bitand_assign", lang.bitand_assign_trait()),
+            ast::BiBitOr => ("bitor_assign", lang.bitor_assign_trait()),
+            ast::BiShl => ("shl_assign", lang.shl_assign_trait()),
+            ast::BiShr => ("shr_assign", lang.shr_assign_trait()),
+            ast::BiLt | ast::BiLe | ast::BiGe | ast::BiGt | ast::BiEq | ast::BiNe | ast::BiAnd |
+                ast::BiOr =>
+            {
+                check_expr(fcx, &**rhs);
+                return tcx.types.err;
+            }
+        };
+        lookup_op_method(fcx, ex, lhs_resolved_t, token::intern(name),
+                         trait_did, lhs_expr, Some(rhs), || {
+            fcx.type_error_message(ex.span, |actual| {
+                format!("binary operation `{}=` cannot be applied to type `{}`",
+                        ast_util::binop_to_string(op.node),
+                        actual)
+            }, lhs_resolved_t, None)
+        }, AutorefArgs::Yes)
+    }
+
     fn check_user_unop<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                                  op_str: &str,
                                  mname: &str,
@@ -3484,10 +3521,6 @@ fn check_expr_with_unifier<'a, 'tcx, F>(fcx: &FnCtxt<'a, 'tcx>,
       ast::ExprAssignOp(op, ref lhs, ref rhs) => {
         check_binop(fcx, expr, op, &**lhs, rhs, BinopAssignment);
 
-        let lhs_t = fcx.expr_ty(&**lhs);
-        let result_t = fcx.expr_ty(expr);
-        demand::suptype(fcx, expr.span, result_t, lhs_t);
-
         let tcx = fcx.tcx();
         if !ty::expr_is_lval(tcx, &**lhs) {
             span_err!(tcx.sess, lhs.span, E0067, "illegal left-hand side expression");
@@ -3498,7 +3531,7 @@ fn check_expr_with_unifier<'a, 'tcx, F>(fcx: &FnCtxt<'a, 'tcx>,
         // Overwrite result of check_binop...this preserves existing behavior
         // but seems quite dubious with regard to user-defined methods
         // and so forth. - Niko
-        if !ty::type_is_error(result_t) {
+        if !ty::type_is_error(fcx.expr_ty(expr)) {
             fcx.write_nil(expr.id);
         }
       }

src/libsyntax/feature_gate.rs

@@ -153,6 +153,9 @@ const KNOWN_FEATURES: &'static [(&'static str, &'static str, Status)] = &[
     // below (it has to be checked before expansion possibly makes
     // macros disappear).
     ("allow_internal_unstable", "1.0.0", Active),
+
+    // Augmented assignment `a += b`; RFC 953
+    ("op_assign", "1.0.0", Active),
 ];
 // (changing above list without updating src/doc/reference.md makes @cmr sad)
 
@@ -317,6 +320,7 @@ pub enum AttributeType {
 
 /// A set of features to be used by later passes.
 pub struct Features {
+    pub op_assign: bool,
     pub unboxed_closures: bool,
     pub rustc_diagnostic_macros: bool,
     pub visible_private_types: bool,
@@ -339,6 +343,7 @@ pub struct Features {
 impl Features {
     pub fn new() -> Features {
         Features {
+            op_assign: false,
             unboxed_closures: false,
             rustc_diagnostic_macros: false,
             visible_private_types: false,
@@ -787,6 +792,7 @@ fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::C
     // to a single-pass (instead of N calls to `.has_feature`).
 
     Features {
+        op_assign: cx.has_feature("op_assign"),
         unboxed_closures: cx.has_feature("unboxed_closures"),
         rustc_diagnostic_macros: cx.has_feature("rustc_diagnostic_macros"),
         visible_private_types: cx.has_feature("visible_private_types"),

src/test/compile-fail/assignment-operator-unimplemented.rs

@@ -8,10 +8,12 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(op_assign)]
+
 struct Foo;
 
 fn main() {
   let mut a = Foo;
   let ref b = Foo;
-  a += *b; //~ Error: binary assignment operation `+=` cannot be applied to type `Foo`
+  a += *b; //~ Error: binary operation `+=` cannot be applied to type `Foo`
 }

src/test/compile-fail/feature-gate-op-assign.rs

@@ -0,0 +1,29 @@
+// 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.
+
+use std::ops::AddAssign;
+
+struct MyInt(i32);
+
+impl AddAssign for MyInt {
+    fn add_assign(&mut self, rhs: &MyInt) {
+        self.0 += rhs.0
+    }
+}
+
+fn main() {
+    let mut x = MyInt(1);
+    x += MyInt(2);
+    //~^ error: overloaded augmented assignment is not stable
+    //~^^ help: add `#![feature(op_assign)]` to the crate attributes to enable
+    x -= MyInt(3);
+    //~^ error: overloaded augmented assignment is not stable
+    //~^^ help: add `#![feature(op_assign)]` to the crate attributes to enable
+}

src/test/compile-fail/issue-10401.rs

@@ -8,8 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(op_assign)]
+
 fn main() {
     let mut a = "a";
     a += { "b" };
-    //~^ ERROR: binary assignment operation `+=` cannot be applied
+    //~^ ERROR: binary operation `+=` cannot be applied to type `&str`
 }

src/test/compile-fail/issue-5239-1.rs

@@ -10,7 +10,9 @@
 
 // Regression test for issue #5239
 
+#![feature(op_assign)]
+
 fn main() {
     let x = |ref x: isize| -> isize { x += 1; };
-    //~^ ERROR binary assignment operation `+=` cannot be applied to type `&isize`
+    //~^ ERROR binary operation `+=` cannot be applied to type `&isize`
 }

src/test/compile-fail/issue-6738.rs

@@ -8,13 +8,15 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(op_assign)]
+
 struct Foo<T> {
     x: T,
 }
 impl<T> Foo<T> {
     fn add(&mut self, v: Foo<T>){
         self.x += v.x;
-        //~^ ERROR: binary assignment operation `+=` cannot be applied
+        //~^ ERROR: binary operation `+=` cannot be applied to type `T`
     }
 }
 fn main() {}

src/test/compile-fail/op-assign-borrow.rs

@@ -0,0 +1,33 @@
+// 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.
+
+#![feature(op_assign)]
+
+use std::ops::AddAssign;
+
+struct Int(i32);
+
+impl AddAssign for Int {
+    fn add_assign(&mut self, rhs: &Int) {
+        self.0 += rhs.0
+    }
+}
+
+fn main() {
+    let mut x = Int(1);
+    x  //~ error: cannot borrow `x` as mutable because it is also borrowed as immutable
+    +=
+    x;  //~ note: previous borrow of `x` occurs here
+
+    let y = Int(2);
+    y  //~ error: cannot borrow immutable local variable `y` as mutable
+    +=
+    Int(1);
+}