Implement tuple and tuple struct indexing

This allows code to access the fields of tuples and tuple structs:

    let x = (1i, 2i);
    assert_eq!(x.1, 2);

    struct Point(int, int);
    let origin = Point(0, 0);
    assert_eq!(origin.0, 0);
    assert_eq!(origin.1, 0);

src/doc/rust.md

@@ -2555,6 +2555,8 @@ The currently implemented features of the reference compiler are:
                         which is considered wildly unsafe and will be
                         obsoleted by language improvements.
 
+* `tuple_indexing` - Allows use of tuple indexing (expressions like `expr.0`)
+
 If a feature is promoted to a language feature, then all existing programs will
 start to receive compilation warnings about #[feature] directives which enabled
 the new feature (because the directive is no longer necessary). However, if

src/librustc/front/feature_gate.rs

@@ -70,6 +70,7 @@ static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
     ("unboxed_closures", Active),
     ("import_shadowing", Active),
     ("advanced_slice_patterns", Active),
+    ("tuple_indexing", Active),
 
     // if you change this list without updating src/doc/rust.md, cmr will be sad
 
@@ -338,6 +339,11 @@ impl<'a> Visitor<()> for Context<'a> {
                                   "unboxed closures are a work-in-progress \
                                    feature with known bugs");
             }
+            ast::ExprTupField(..) => {
+                self.gate_feature("tuple_indexing",
+                                  e.span,
+                                  "tuple indexing is experimental");
+            }
             _ => {}
         }
         visit::walk_expr(self, e, ());

src/librustc/lint/builtin.rs

@@ -1056,6 +1056,7 @@ impl UnnecessaryParens {
                 ast::ExprUnary(_, ref x) |
                 ast::ExprCast(ref x, _) |
                 ast::ExprField(ref x, _, _) |
+                ast::ExprTupField(ref x, _, _) |
                 ast::ExprIndex(ref x, _) => {
                     // &X { y: 1 }, X { y: 1 }.y
                     contains_exterior_struct_lit(&**x)

src/librustc/middle/borrowck/mod.rs

@@ -807,7 +807,7 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
                         out.push_str(token::get_name(fname).get());
                     }
                     mc::PositionalField(idx) => {
-                        out.push_char('#'); // invent a notation here
+                        out.push_char('.');
                         out.push_str(idx.to_string().as_slice());
                     }
                 }

src/librustc/middle/cfg/construct.rs

@@ -467,7 +467,8 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
             ast::ExprCast(e, _) |
             ast::ExprUnary(_, e) |
             ast::ExprParen(e) |
-            ast::ExprField(e, _, _) => {
+            ast::ExprField(e, _, _) |
+            ast::ExprTupField(e, _, _) => {
                 self.straightline(expr, pred, [e])
             }
 

src/librustc/middle/check_const.rs

@@ -173,6 +173,7 @@ fn check_expr(v: &mut CheckCrateVisitor, e: &Expr, is_const: bool) {
           ExprAddrOf(MutImmutable, _) |
           ExprParen(..) |
           ExprField(..) |
+          ExprTupField(..) |
           ExprIndex(..) |
           ExprTup(..) |
           ExprRepeat(..) |

src/librustc/middle/check_static.rs

@@ -106,7 +106,7 @@ impl<'a, 'tcx> Visitor<bool> for CheckStaticVisitor<'a, 'tcx> {
         }
 
         match e.node {
-            ast::ExprField(..) | ast::ExprVec(..) |
+            ast::ExprField(..) | ast::ExprTupField(..) | ast::ExprVec(..) |
             ast::ExprBlock(..) | ast::ExprTup(..)  => {
                 visit::walk_expr(self, e, is_const);
             }

src/librustc/middle/const_eval.rs

@@ -225,6 +225,8 @@ impl<'a, 'tcx> ConstEvalVisitor<'a, 'tcx> {
 
             ast::ExprField(ref base, _, _) => self.classify(&**base),
 
+            ast::ExprTupField(ref base, _, _) => self.classify(&**base),
+
             ast::ExprIndex(ref base, ref idx) =>
                 join(self.classify(&**base), self.classify(&**idx)),
 

src/librustc/middle/dead.rs

@@ -145,6 +145,17 @@ impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
         }
     }
 
+    fn handle_tup_field_access(&mut self, lhs: &ast::Expr, idx: uint) {
+        match ty::get(ty::expr_ty_adjusted(self.tcx, lhs)).sty {
+            ty::ty_struct(id, _) => {
+                let fields = ty::lookup_struct_fields(self.tcx, id);
+                let field_id = fields[idx].id;
+                self.live_symbols.insert(field_id.node);
+            },
+            _ => ()
+        }
+    }
+
     fn handle_field_pattern_match(&mut self, lhs: &ast::Pat, pats: &[ast::FieldPat]) {
         let id = match self.tcx.def_map.borrow().get(&lhs.id) {
             &def::DefVariant(_, id, _) => id,
@@ -255,6 +266,9 @@ impl<'a, 'tcx> Visitor<MarkSymbolVisitorContext> for MarkSymbolVisitor<'a, 'tcx>
             ast::ExprField(ref lhs, ref ident, _) => {
                 self.handle_field_access(&**lhs, &ident.node);
             }
+            ast::ExprTupField(ref lhs, idx, _) => {
+                self.handle_tup_field_access(&**lhs, idx.node);
+            }
             _ => ()
         }
 

src/librustc/middle/expr_use_visitor.rs

@@ -324,6 +324,10 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,TYPER> {
                 self.select_from_expr(&**base);
             }
 
+            ast::ExprTupField(ref base, _, _) => {         // base.<n>
+                self.select_from_expr(&**base);
+            }
+
             ast::ExprIndex(ref lhs, ref rhs) => {           // lhs[rhs]
                 if !self.walk_overloaded_operator(expr, &**lhs, [rhs.clone()]) {
                     self.select_from_expr(&**lhs);

src/librustc/middle/liveness.rs

@@ -511,7 +511,7 @@ fn visit_expr(ir: &mut IrMaps, expr: &Expr) {
       }
 
       // otherwise, live nodes are not required:
-      ExprIndex(..) | ExprField(..) | ExprVec(..) |
+      ExprIndex(..) | ExprField(..) | ExprTupField(..) | ExprVec(..) |
       ExprCall(..) | ExprMethodCall(..) | ExprTup(..) |
       ExprBinary(..) | ExprAddrOf(..) |
       ExprCast(..) | ExprUnary(..) | ExprBreak(_) |
@@ -965,6 +965,10 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
               self.propagate_through_expr(&**e, succ)
           }
 
+          ExprTupField(ref e, _, _) => {
+              self.propagate_through_expr(&**e, succ)
+          }
+
           ExprFnBlock(_, _, ref blk) |
           ExprProc(_, ref blk) |
           ExprUnboxedFn(_, _, _, ref blk) => {
@@ -1271,6 +1275,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
         match expr.node {
             ExprPath(_) => succ,
             ExprField(ref e, _, _) => self.propagate_through_expr(&**e, succ),
+            ExprTupField(ref e, _, _) => self.propagate_through_expr(&**e, succ),
             _ => self.propagate_through_expr(expr, succ)
         }
     }
@@ -1445,7 +1450,7 @@ fn check_expr(this: &mut Liveness, expr: &Expr) {
       // no correctness conditions related to liveness
       ExprCall(..) | ExprMethodCall(..) | ExprIf(..) | ExprMatch(..) |
       ExprWhile(..) | ExprLoop(..) | ExprIndex(..) | ExprField(..) |
-      ExprVec(..) | ExprTup(..) | ExprBinary(..) |
+      ExprTupField(..) | ExprVec(..) | ExprTup(..) | ExprBinary(..) |
       ExprCast(..) | ExprUnary(..) | ExprRet(..) | ExprBreak(..) |
       ExprAgain(..) | ExprLit(_) | ExprBlock(..) |
       ExprMac(..) | ExprAddrOf(..) | ExprStruct(..) | ExprRepeat(..) |

src/librustc/middle/mem_categorization.rs

@@ -465,6 +465,11 @@ impl<'t,'tcx,TYPER:Typer<'tcx>> MemCategorizationContext<'t,TYPER> {
             Ok(self.cat_field(expr, base_cmt, f_name.node, expr_ty))
           }
 
+          ast::ExprTupField(ref base, idx, _) => {
+            let base_cmt = if_ok!(self.cat_expr(&**base));
+            Ok(self.cat_tup_field(expr, base_cmt, idx.node, expr_ty))
+          }
+
           ast::ExprIndex(ref base, _) => {
             let method_call = typeck::MethodCall::expr(expr.id());
             match self.typer.node_method_ty(method_call) {
@@ -737,6 +742,21 @@ impl<'t,'tcx,TYPER:Typer<'tcx>> MemCategorizationContext<'t,TYPER> {
         })
     }
 
+    pub fn cat_tup_field<N:ast_node>(&self,
+                                     node: &N,
+                                     base_cmt: cmt,
+                                     f_idx: uint,
+                                     f_ty: ty::t)
+                                     -> cmt {
+        Rc::new(cmt_ {
+            id: node.id(),
+            span: node.span(),
+            mutbl: base_cmt.mutbl.inherit(),
+            cat: cat_interior(base_cmt, InteriorField(PositionalField(f_idx))),
+            ty: f_ty
+        })
+    }
+
     pub fn cat_deref_obj<N:ast_node>(&self, node: &N, base_cmt: cmt) -> cmt {
         self.cat_deref_common(node, base_cmt, 0, ty::mk_nil(), false)
     }

src/librustc/middle/privacy.rs

@@ -819,6 +819,14 @@ impl<'a, 'tcx> Visitor<()> for PrivacyVisitor<'a, 'tcx> {
                     _ => {}
                 }
             }
+            ast::ExprTupField(ref base, idx, _) => {
+                match ty::get(ty::expr_ty_adjusted(self.tcx, &**base)).sty {
+                    ty::ty_struct(id, _) => {
+                        self.check_field(expr.span, id, UnnamedField(idx.node));
+                    }
+                    _ => {}
+                }
+            }
             ast::ExprMethodCall(ident, _, _) => {
                 let method_call = MethodCall::expr(expr.id);
                 match self.tcx.method_map.borrow().find(&method_call) {

src/librustc/middle/region.rs

@@ -779,6 +779,7 @@ fn resolve_local(visitor: &mut RegionResolutionVisitor,
                 ast::ExprAddrOf(_, ref subexpr) |
                 ast::ExprUnary(ast::UnDeref, ref subexpr) |
                 ast::ExprField(ref subexpr, _, _) |
+                ast::ExprTupField(ref subexpr, _, _) |
                 ast::ExprIndex(ref subexpr, _) |
                 ast::ExprParen(ref subexpr) => {
                     let subexpr: &'a Gc<Expr> = subexpr; // FIXME(#11586)

src/librustc/middle/save/mod.rs

@@ -1314,6 +1314,34 @@ impl<'l, 'tcx> Visitor<DxrVisitorEnv> for DxrVisitor<'l, 'tcx> {
                                             "Expected struct type, but not ty_struct"),
                 }
             },
+            ast::ExprTupField(sub_ex, idx, _) => {
+                if generated_code(sub_ex.span) {
+                    return
+                }
+
+                self.visit_expr(&*sub_ex, e);
+
+                let t = ty::expr_ty_adjusted(&self.analysis.ty_cx, &*sub_ex);
+                let t_box = ty::get(t);
+                match t_box.sty {
+                    ty::ty_struct(def_id, _) => {
+                        let fields = ty::lookup_struct_fields(&self.analysis.ty_cx, def_id);
+                        for (i, f) in fields.iter().enumerate() {
+                            if i == idx.node {
+                                let sub_span = self.span.span_for_last_ident(ex.span);
+                                self.fmt.ref_str(recorder::VarRef,
+                                                 ex.span,
+                                                 sub_span,
+                                                 f.id,
+                                                 e.cur_scope);
+                                break;
+                            }
+                        }
+                    },
+                    _ => self.sess.span_bug(ex.span,
+                                            "Expected struct type, but not ty_struct"),
+                }
+            },
             ast::ExprFnBlock(_, decl, body) => {
                 if generated_code(body.span) {
                     return

src/librustc/middle/trans/consts.rs

@@ -440,6 +440,13 @@ fn const_expr_unadjusted(cx: &CrateContext, e: &ast::Expr,
                   (adt::const_get_field(cx, &*brepr, bv, discr, ix), inlineable)
               })
           }
+          ast::ExprTupField(ref base, idx, _) => {
+              let (bv, inlineable, bt) = const_expr(cx, &**base, is_local);
+              let brepr = adt::represent_type(cx, bt);
+              expr::with_field_tys(cx.tcx(), bt, None, |discr, _| {
+                  (adt::const_get_field(cx, &*brepr, bv, discr, idx.node), inlineable)
+              })
+          }
 
           ast::ExprIndex(ref base, ref index) => {
               let (bv, inlineable, bt) = const_expr(cx, &**base, is_local);

src/librustc/middle/trans/debuginfo.rs

@@ -3457,6 +3457,7 @@ fn populate_scope_map(cx: &CrateContext,
             ast::ExprCast(ref sub_exp, _)     |
             ast::ExprAddrOf(_, ref sub_exp)  |
             ast::ExprField(ref sub_exp, _, _) |
+            ast::ExprTupField(ref sub_exp, _, _) |
             ast::ExprParen(ref sub_exp) =>
                 walk_expr(cx, &**sub_exp, scope_stack, scope_map),
 

src/librustc/middle/trans/expr.rs

@@ -62,7 +62,7 @@ use middle::trans::meth;
 use middle::trans::inline;
 use middle::trans::tvec;
 use middle::trans::type_of;
-use middle::ty::struct_fields;
+use middle::ty::{struct_fields, tup_fields};
 use middle::ty::{AutoDerefRef, AutoAddEnv, AutoUnsafe};
 use middle::ty::{AutoPtr};
 use middle::ty;
@@ -593,6 +593,9 @@ fn trans_datum_unadjusted<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
         ast::ExprField(ref base, ident, _) => {
             trans_rec_field(bcx, &**base, ident.node)
         }
+        ast::ExprTupField(ref base, idx, _) => {
+            trans_rec_tup_field(bcx, &**base, idx.node)
+        }
         ast::ExprIndex(ref base, ref idx) => {
             trans_index(bcx, expr, &**base, &**idx, MethodCall::expr(expr.id))
         }
@@ -666,20 +669,18 @@ fn trans_datum_unadjusted<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
     }
 }
 
-fn trans_rec_field<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
-                               base: &ast::Expr,
-                               field: ast::Ident)
-                               -> DatumBlock<'blk, 'tcx, Expr> {
-    //! Translates `base.field`.
-
+fn trans_field<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
+                           base: &ast::Expr,
+                           get_idx: |&'blk ty::ctxt<'tcx>, &[ty::field]| -> uint)
+                           -> DatumBlock<'blk, 'tcx, Expr> {
     let mut bcx = bcx;
     let _icx = push_ctxt("trans_rec_field");
 
     let base_datum = unpack_datum!(bcx, trans_to_lvalue(bcx, base, "field"));
     let bare_ty = ty::unopen_type(base_datum.ty);
     let repr = adt::represent_type(bcx.ccx(), bare_ty);
     with_field_tys(bcx.tcx(), bare_ty, None, |discr, field_tys| {
-        let ix = ty::field_idx_strict(bcx.tcx(), field.name, field_tys);
+        let ix = get_idx(bcx.tcx(), field_tys);
         let d = base_datum.get_element(
             bcx,
             field_tys[ix].mt.ty,
@@ -697,6 +698,23 @@ fn trans_rec_field<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 
         }
     })
+
+}
+
+/// Translates `base.field`.
+fn trans_rec_field<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
+                               base: &ast::Expr,
+                               field: ast::Ident)
+                               -> DatumBlock<'blk, 'tcx, Expr> {
+    trans_field(bcx, base, |tcx, field_tys| ty::field_idx_strict(tcx, field.name, field_tys))
+}
+
+/// Translates `base.<idx>`.
+fn trans_rec_tup_field<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
+                                   base: &ast::Expr,
+                                   idx: uint)
+                                   -> DatumBlock<'blk, 'tcx, Expr> {
+    trans_field(bcx, base, |_, _| idx)
 }
 
 fn trans_index<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
@@ -1238,6 +1256,10 @@ pub fn with_field_tys<R>(tcx: &ty::ctxt,
             op(0, struct_fields(tcx, did, substs).as_slice())
         }
 
+        ty::ty_tup(ref v) => {
+            op(0, tup_fields(v.as_slice()).as_slice())
+        }
+
         ty::ty_enum(_, ref substs) => {
             // We want the *variant* ID here, not the enum ID.
             match node_id_opt {

src/librustc/middle/ty.rs

@@ -3599,6 +3599,7 @@ pub fn expr_kind(tcx: &ctxt, expr: &ast::Expr) -> ExprKind {
 
         ast::ExprUnary(ast::UnDeref, _) |
         ast::ExprField(..) |
+        ast::ExprTupField(..) |
         ast::ExprIndex(..) => {
             LvalueExpr
         }
@@ -4527,6 +4528,11 @@ pub fn lookup_struct_fields(cx: &ctxt, did: ast::DefId) -> Vec<field_ty> {
     }
 }
 
+pub fn is_tuple_struct(cx: &ctxt, did: ast::DefId) -> bool {
+    let fields = lookup_struct_fields(cx, did);
+    !fields.is_empty() && fields.iter().all(|f| f.name == token::special_names::unnamed_field)
+}
+
 pub fn lookup_struct_field(cx: &ctxt,
                            parent: ast::DefId,
                            field_id: ast::DefId)
@@ -4554,6 +4560,21 @@ pub fn struct_fields(cx: &ctxt, did: ast::DefId, substs: &Substs)
     }).collect()
 }
 
+// Returns a list of fields corresponding to the tuple's items. trans uses
+// this.
+pub fn tup_fields(v: &[t]) -> Vec<field> {
+    v.iter().enumerate().map(|(i, &f)| {
+       field {
+            // FIXME #6993: change type of field to Name and get rid of new()
+            ident: ast::Ident::new(token::intern(i.to_string().as_slice())),
+            mt: mt {
+                ty: f,
+                mutbl: MutImmutable
+            }
+        }
+    }).collect()
+}
+
 pub struct UnboxedClosureUpvar {
     pub def: def::Def,
     pub span: Span,