auto merge of rust-lang#12491 : eddyb/rust/deref, r=nikomatsakis

Add the `Deref` and `DerefMut` traits and implement overloading explicit dereferences.

src/doc/rust.md

@@ -2485,8 +2485,11 @@ before the expression they apply to.
 `*`
   : Dereference. When applied to a [pointer](#pointer-types) it denotes the pointed-to location.
     For pointers to mutable locations, the resulting [lvalue](#lvalues-rvalues-and-temporaries) can be assigned to.
-    For [enums](#enumerated-types) that have only a single variant, containing a single parameter,
-    the dereference operator accesses this parameter.
+    On non-pointer types, it calls calls the `deref` method of the `std::ops::Deref` trait, or the
+    `deref_mut` method of the `std::ops::DerefMut` trait (if implemented by the type and required
+    for an outer expression that will or could mutate the dereference), and produces the
+    result of dereferencing the `&` or `&mut` borrowed pointer returned from the overload method.
+
 `!`
   : Logical negation. On the boolean type, this flips between `true` and
     `false`. On integer types, this inverts the individual bits in the

src/librustc/middle/borrowck/mod.rs

@@ -921,14 +921,17 @@ impl mc::Typer for TcxTyper {
         Ok(ty::node_id_to_type(self.tcx, id))
     }
 
+    fn node_method_ty(&mut self, id: ast::NodeId) -> Option<ty::t> {
+        self.method_map.borrow().get().find(&id).map(|method| method.ty)
+    }
+
     fn adjustment(&mut self, id: ast::NodeId) -> Option<@ty::AutoAdjustment> {
         let adjustments = self.tcx.adjustments.borrow();
         adjustments.get().find_copy(&id)
     }
 
     fn is_method_call(&mut self, id: ast::NodeId) -> bool {
-        let method_map = self.method_map.borrow();
-        method_map.get().contains_key(&id)
+        self.method_map.borrow().get().contains_key(&id)
     }
 
     fn temporary_scope(&mut self, id: ast::NodeId) -> Option<ast::NodeId> {

src/librustc/middle/lang_items.rs

@@ -232,6 +232,9 @@ lets_do_this! {
     ShrTraitLangItem,                "shr",                     shr_trait;
     IndexTraitLangItem,              "index",                   index_trait;
 
+    DerefTraitLangItem,              "deref",                   deref_trait;
+    DerefMutTraitLangItem,           "deref_mut",               deref_mut_trait;
+
     EqTraitLangItem,                 "eq",                      eq_trait;
     OrdTraitLangItem,                "ord",                     ord_trait;
 

src/librustc/middle/mem_categorization.rs

@@ -267,6 +267,7 @@ pub type McResult<T> = Result<T, ()>;
 pub trait Typer {
     fn tcx(&self) -> ty::ctxt;
     fn node_ty(&mut self, id: ast::NodeId) -> McResult<ty::t>;
+    fn node_method_ty(&mut self, id: ast::NodeId) -> Option<ty::t>;
     fn adjustment(&mut self, node_id: ast::NodeId) -> Option<@ty::AutoAdjustment>;
     fn is_method_call(&mut self, id: ast::NodeId) -> bool;
     fn temporary_scope(&mut self, rvalue_id: ast::NodeId) -> Option<ast::NodeId>;
@@ -433,11 +434,13 @@ impl<TYPER:Typer> MemCategorizationContext<TYPER> {
         let expr_ty = if_ok!(self.expr_ty(expr));
         match expr.node {
           ast::ExprUnary(ast::UnDeref, e_base) => {
-            if self.typer.is_method_call(expr.id) {
-                return Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty));
-            }
-
-            let base_cmt = if_ok!(self.cat_expr(e_base));
+            let base_cmt = match self.typer.node_method_ty(expr.id) {
+                Some(method_ty) => {
+                    let ref_ty = ty::ty_fn_ret(method_ty);
+                    self.cat_rvalue_node(expr.id(), expr.span(), ref_ty)
+                }
+                None => if_ok!(self.cat_expr(e_base))
+            };
             Ok(self.cat_deref(expr, base_cmt, 0))
           }
 

src/librustc/middle/trans/callee.rs

@@ -444,14 +444,12 @@ pub fn trans_call<'a>(
                   call_ex: &ast::Expr,
                   f: &ast::Expr,
                   args: CallArgs,
-                  id: ast::NodeId,
                   dest: expr::Dest)
                   -> &'a Block<'a> {
     let _icx = push_ctxt("trans_call");
     trans_call_inner(in_cx,
                      Some(common::expr_info(call_ex)),
                      expr_ty(in_cx, f),
-                     node_id_type(in_cx, id),
                      |cx, _| trans(cx, f),
                      args,
                      Some(dest)).bcx
@@ -471,7 +469,6 @@ pub fn trans_method_call<'a>(
         bcx,
         Some(common::expr_info(call_ex)),
         monomorphize_type(bcx, method_ty),
-        expr_ty(bcx, call_ex),
         |cx, arg_cleanup_scope| {
             meth::trans_method_callee(cx, call_ex.id, rcvr, arg_cleanup_scope)
         },
@@ -490,11 +487,9 @@ pub fn trans_lang_call<'a>(
     } else {
         csearch::get_type(bcx.ccx().tcx, did).ty
     };
-    let rty = ty::ty_fn_ret(fty);
     callee::trans_call_inner(bcx,
                              None,
                              fty,
-                             rty,
                              |bcx, _| {
                                 trans_fn_ref_with_vtables_to_callee(bcx,
                                                                     did,
@@ -520,12 +515,10 @@ pub fn trans_lang_call_with_type_params<'a>(
         fty = csearch::get_type(bcx.tcx(), did).ty;
     }
 
-    let rty = ty::ty_fn_ret(fty);
     return callee::trans_call_inner(
         bcx,
         None,
         fty,
-        rty,
         |bcx, _| {
             let callee =
                 trans_fn_ref_with_vtables_to_callee(bcx, did, 0,
@@ -554,7 +547,6 @@ pub fn trans_call_inner<'a>(
                         bcx: &'a Block<'a>,
                         call_info: Option<NodeInfo>,
                         callee_ty: ty::t,
-                        ret_ty: ty::t,
                         get_callee: |bcx: &'a Block<'a>,
                                      arg_cleanup_scope: cleanup::ScopeId|
                                      -> Callee<'a>,
@@ -610,9 +602,10 @@ pub fn trans_call_inner<'a>(
         }
     };
 
-    let abi = match ty::get(callee_ty).sty {
-        ty::ty_bare_fn(ref f) => f.abis,
-        _ => AbiSet::Rust()
+    let (abi, ret_ty) = match ty::get(callee_ty).sty {
+        ty::ty_bare_fn(ref f) => (f.abis, f.sig.output),
+        ty::ty_closure(ref f) => (AbiSet::Rust(), f.sig.output),
+        _ => fail!("expected bare rust fn or closure in trans_call_inner")
     };
     let is_rust_fn =
         abi.is_rust() ||

src/librustc/middle/trans/expr.rs

@@ -467,10 +467,6 @@ fn trans_datum_unadjusted<'a>(bcx: &'a Block<'a>,
 
             trans_binary(bcx, expr, op, lhs, rhs)
         }
-        ast::ExprUnary(ast::UnDeref, base) => {
-            let basedatum = unpack_datum!(bcx, trans(bcx, base));
-            deref_once(bcx, expr, basedatum, 0)
-        }
         ast::ExprUnary(op, x) => {
             trans_unary_datum(bcx, expr, op, x)
         }
@@ -782,12 +778,7 @@ fn trans_rvalue_dps_unadjusted<'a>(bcx: &'a Block<'a>,
             closure::trans_expr_fn(bcx, sigil, decl, body, expr.id, dest)
         }
         ast::ExprCall(f, ref args) => {
-            callee::trans_call(bcx,
-                               expr,
-                               f,
-                               callee::ArgExprs(args.as_slice()),
-                               expr.id,
-                               dest)
+            callee::trans_call(bcx, expr, f, callee::ArgExprs(args.as_slice()), dest)
         }
         ast::ExprMethodCall(_, _, ref args) => {
             callee::trans_method_call(bcx,
@@ -798,18 +789,15 @@ fn trans_rvalue_dps_unadjusted<'a>(bcx: &'a Block<'a>,
         }
         ast::ExprBinary(_, lhs, rhs) => {
             // if not overloaded, would be RvalueDatumExpr
-            trans_overloaded_op(bcx, expr, lhs,
-                                Some(&*rhs), expr_ty(bcx, expr), dest)
+            trans_overloaded_op(bcx, expr, lhs, Some(&*rhs), Some(dest)).bcx
         }
         ast::ExprUnary(_, subexpr) => {
             // if not overloaded, would be RvalueDatumExpr
-            trans_overloaded_op(bcx, expr, subexpr,
-                                None, expr_ty(bcx, expr), dest)
+            trans_overloaded_op(bcx, expr, subexpr, None, Some(dest)).bcx
         }
         ast::ExprIndex(base, idx) => {
             // if not overloaded, would be RvalueDatumExpr
-            trans_overloaded_op(bcx, expr, base,
-                                Some(&*idx), expr_ty(bcx, expr), dest)
+            trans_overloaded_op(bcx, expr, base, Some(&*idx), Some(dest)).bcx
         }
         ast::ExprCast(val, _) => {
             // DPS output mode means this is a trait cast:
@@ -1185,17 +1173,14 @@ fn trans_unary_datum<'a>(
     let mut bcx = bcx;
     let _icx = push_ctxt("trans_unary_datum");
 
-    // if deref, would be LvalueExpr
-    assert!(op != ast::UnDeref);
-
-    // if overloaded, would be RvalueDpsExpr
-    {
+    let overloaded = {
         let method_map = bcx.ccx().maps.method_map.borrow();
-        assert!(!method_map.get().contains_key(&un_expr.id));
-    }
+        method_map.get().contains_key(&un_expr.id)
+    };
+    // if overloaded, would be RvalueDpsExpr
+    assert!(!overloaded || op == ast::UnDeref);
 
     let un_ty = expr_ty(bcx, un_expr);
-    let sub_ty = expr_ty(bcx, sub_expr);
 
     return match op {
         ast::UnNot => {
@@ -1226,15 +1211,19 @@ fn trans_unary_datum<'a>(
             immediate_rvalue_bcx(bcx, llneg, un_ty).to_expr_datumblock()
         }
         ast::UnBox => {
-            trans_boxed_expr(bcx, un_ty, sub_expr, sub_ty, heap_managed)
+            trans_boxed_expr(bcx, un_ty, sub_expr, expr_ty(bcx, sub_expr), heap_managed)
         }
         ast::UnUniq => {
-            trans_boxed_expr(bcx, un_ty, sub_expr, sub_ty, heap_exchange)
+            trans_boxed_expr(bcx, un_ty, sub_expr, expr_ty(bcx, sub_expr), heap_exchange)
         }
         ast::UnDeref => {
-            bcx.sess().bug("deref expressions should have been \
-                            translated using trans_lvalue(), not \
-                            trans_unary_datum()")
+            if overloaded {
+                let r = trans_overloaded_op(bcx, un_expr, sub_expr, None, None);
+                DatumBlock(r.bcx, Datum(r.val, un_ty, LvalueExpr))
+            } else {
+                let datum = unpack_datum!(bcx, trans(bcx, sub_expr));
+                deref_once(bcx, un_expr, datum, 0)
+            }
         }
     };
 }
@@ -1506,22 +1495,20 @@ fn trans_overloaded_op<'a, 'b>(
                        expr: &ast::Expr,
                        rcvr: &'b ast::Expr,
                        arg: Option<&'b ast::Expr>,
-                       ret_ty: ty::t,
-                       dest: Dest)
-                       -> &'a Block<'a> {
+                       dest: Option<Dest>)
+                       -> Result<'a> {
     let method_ty = bcx.ccx().maps.method_map.borrow().get().get(&expr.id).ty;
     callee::trans_call_inner(bcx,
                              Some(expr_info(expr)),
                              monomorphize_type(bcx, method_ty),
-                             ret_ty,
                              |bcx, arg_cleanup_scope| {
                                 meth::trans_method_callee(bcx,
                                                           expr.id,
                                                           rcvr,
                                                           arg_cleanup_scope)
                              },
                              callee::ArgAutorefSecond(rcvr, arg),
-                             Some(dest)).bcx
+                             dest)
 }
 
 fn int_cast(bcx: &Block,

src/librustc/middle/trans/reflect.rs

@@ -105,9 +105,8 @@ impl<'a> Reflector<'a> {
         for (i, a) in args.iter().enumerate() {
             debug!("arg {}: {}", i, bcx.val_to_str(*a));
         }
-        let bool_ty = ty::mk_bool();
         let result = unpack_result!(bcx, callee::trans_call_inner(
-            self.bcx, None, mth_ty, bool_ty,
+            self.bcx, None, mth_ty,
             |bcx, _| meth::trans_trait_callee_from_llval(bcx,
                                                          mth_ty,
                                                          mth_idx,

src/librustc/middle/ty.rs

@@ -3284,6 +3284,7 @@ pub fn expr_kind(tcx: ctxt,
             // exception, as its result is always unit.
             return match expr.node {
                 ast::ExprAssignOp(..) => RvalueStmtExpr,
+                ast::ExprUnary(ast::UnDeref, _) => LvalueExpr,
                 _ => RvalueDpsExpr
             };
         }