auto merge of #18752 : jakub-/rust/remove-unit, r=eddyb

Closes #18614.

Author: bors

src/doc/reference.md

@@ -458,10 +458,9 @@ Examples of floating-point literals of various forms:
 12E+99_f64;                        // type f64
 ```
 
-##### Unit and boolean literals
+##### Boolean literals
 
-The _unit value_, the only value of the type that has the same name, is written
-as `()`. The two values of the boolean type are written `true` and `false`.
+The two values of the boolean type are written `true` and `false`.
 
 ### Symbols
 
@@ -2717,7 +2716,7 @@ or an item. Path expressions are [lvalues](#lvalues,-rvalues-and-temporaries).
 
 ### Tuple expressions
 
-Tuples are written by enclosing one or more comma-separated expressions in
+Tuples are written by enclosing zero or more comma-separated expressions in
 parentheses. They are used to create [tuple-typed](#tuple-types) values.
 
 ```{.tuple}
@@ -2726,6 +2725,11 @@ parentheses. They are used to create [tuple-typed](#tuple-types) values.
 ("a", 4u, true);
 ```
 
+### Unit expressions
+
+The expression `()` denotes the _unit value_, the only value of the type with
+the same name.
+
 ### Structure expressions
 
 ```{.ebnf .gram}

src/librustc/diagnostics.rs

@@ -66,7 +66,6 @@ register_diagnostics!(
     E0055,
     E0056,
     E0057,
-    E0058,
     E0059,
     E0060,
     E0061,

src/librustc/lint/builtin.rs

@@ -447,7 +447,9 @@ impl LintPass for ImproperCTypes {
             for input in decl.inputs.iter() {
                 check_ty(cx, &*input.ty);
             }
-            check_ty(cx, &*decl.output)
+            if let ast::Return(ref ret_ty) = decl.output {
+                check_ty(cx, &**ret_ty);
+            }
         }
 
         match it.node {
@@ -735,7 +737,8 @@ impl LintPass for UnusedResults {
         let t = ty::expr_ty(cx.tcx, expr);
         let mut warned = false;
         match ty::get(t).sty {
-            ty::ty_nil | ty::ty_bool => return,
+            ty::ty_tup(ref tys) if tys.is_empty() => return,
+            ty::ty_bool => return,
             ty::ty_struct(did, _) |
             ty::ty_enum(did, _) => {
                 if ast_util::is_local(did) {

src/librustc/metadata/tydecode.rs

@@ -360,7 +360,6 @@ fn parse_trait_ref(st: &mut PState, conv: conv_did) -> ty::TraitRef {
 
 fn parse_ty(st: &mut PState, conv: conv_did) -> ty::t {
     match next(st) {
-      'n' => return ty::mk_nil(),
       'b' => return ty::mk_bool(),
       'i' => return ty::mk_int(),
       'u' => return ty::mk_uint(),

src/librustc/metadata/tyencode.rs

@@ -199,7 +199,6 @@ pub fn enc_trait_store(w: &mut SeekableMemWriter, cx: &ctxt, s: ty::TraitStore)
 
 fn enc_sty(w: &mut SeekableMemWriter, cx: &ctxt, st: &ty::sty) {
     match *st {
-        ty::ty_nil => mywrite!(w, "n"),
         ty::ty_bool => mywrite!(w, "b"),
         ty::ty_char => mywrite!(w, "c"),
         ty::ty_int(t) => {

src/librustc/middle/check_match.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use middle::const_eval::{compare_const_vals, const_bool, const_float, const_nil, const_val};
+use middle::const_eval::{compare_const_vals, const_bool, const_float, const_val};
 use middle::const_eval::{const_expr_to_pat, eval_const_expr, lookup_const_by_id};
 use middle::def::*;
 use middle::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Init};
@@ -332,7 +332,6 @@ fn check_exhaustive(cx: &MatchCheckCtxt, sp: Span, matrix: &Matrix) {
 fn const_val_to_expr(value: &const_val) -> P<Expr> {
     let node = match value {
         &const_bool(b) => LitBool(b),
-        &const_nil => LitNil,
         _ => unreachable!()
     };
     P(Expr {
@@ -497,9 +496,6 @@ fn all_constructors(cx: &MatchCheckCtxt, left_ty: ty::t,
         ty::ty_bool =>
             [true, false].iter().map(|b| ConstantValue(const_bool(*b))).collect(),
 
-        ty::ty_nil =>
-            vec!(ConstantValue(const_nil)),
-
         ty::ty_rptr(_, ty::mt { ty, .. }) => match ty::get(ty).sty {
             ty::ty_vec(_, None) =>
                 range_inclusive(0, max_slice_length).map(|length| Slice(length)).collect(),
@@ -552,7 +548,7 @@ fn is_useful(cx: &MatchCheckCtxt,
         None => v[0]
     };
     let left_ty = if real_pat.id == DUMMY_NODE_ID {
-        ty::mk_nil()
+        ty::mk_nil(cx.tcx)
     } else {
         ty::pat_ty(cx.tcx, &*real_pat)
     };

src/librustc/middle/const_eval.rs

@@ -311,8 +311,7 @@ pub enum const_val {
     const_uint(u64),
     const_str(InternedString),
     const_binary(Rc<Vec<u8> >),
-    const_bool(bool),
-    const_nil
+    const_bool(bool)
 }
 
 pub fn const_expr_to_pat(tcx: &ty::ctxt, expr: &Expr) -> P<Pat> {
@@ -589,7 +588,6 @@ pub fn lit_to_const(lit: &Lit) -> const_val {
         LitFloatUnsuffixed(ref n) => {
             const_float(from_str::<f64>(n.get()).unwrap() as f64)
         }
-        LitNil => const_nil,
         LitBool(b) => const_bool(b)
     }
 }
@@ -605,7 +603,6 @@ pub fn compare_const_vals(a: &const_val, b: &const_val) -> Option<int> {
         (&const_str(ref a), &const_str(ref b)) => compare_vals(a, b),
         (&const_bool(a), &const_bool(b)) => compare_vals(a, b),
         (&const_binary(ref a), &const_binary(ref b)) => compare_vals(a, b),
-        (&const_nil, &const_nil) => compare_vals((), ()),
         _ => None
     }
 }

src/librustc/middle/resolve.rs

@@ -4285,7 +4285,9 @@ impl<'a> Resolver<'a> {
                                     _ => {}
                                 }
 
-                                this.resolve_type(&*ty_m.decl.output);
+                                if let ast::Return(ref ret_ty) = ty_m.decl.output {
+                                    this.resolve_type(&**ret_ty);
+                                }
                             });
                           }
                           ast::ProvidedMethod(ref m) => {
@@ -4467,7 +4469,9 @@ impl<'a> Resolver<'a> {
                         debug!("(resolving function) recorded argument");
                     }
 
-                    this.resolve_type(&*declaration.output);
+                    if let ast::Return(ref ret_ty) = declaration.output {
+                        this.resolve_type(&**ret_ty);
+                    }
                 }
             }
 

src/librustc/middle/save/mod.rs

@@ -383,7 +383,11 @@ impl <'l, 'tcx> DxrVisitor<'l, 'tcx> {
         for arg in method.pe_fn_decl().inputs.iter() {
             self.visit_ty(&*arg.ty);
         }
-        self.visit_ty(&*method.pe_fn_decl().output);
+
+        if let ast::Return(ref ret_ty) = method.pe_fn_decl().output {
+            self.visit_ty(&**ret_ty);
+        }
+
         // walk the fn body
         self.nest(method.id, |v| v.visit_block(&*method.pe_body()));
 
@@ -491,7 +495,10 @@ impl <'l, 'tcx> DxrVisitor<'l, 'tcx> {
         for arg in decl.inputs.iter() {
             self.visit_ty(&*arg.ty);
         }
-        self.visit_ty(&*decl.output);
+
+        if let ast::Return(ref ret_ty) = decl.output {
+            self.visit_ty(&**ret_ty);
+        }
 
         // walk the body
         self.nest(item.id, |v| v.visit_block(&*body));
@@ -1136,7 +1143,10 @@ impl<'l, 'tcx, 'v> Visitor<'v> for DxrVisitor<'l, 'tcx> {
                 for arg in method_type.decl.inputs.iter() {
                     self.visit_ty(&*arg.ty);
                 }
-                self.visit_ty(&*method_type.decl.output);
+
+                if let ast::Return(ref ret_ty) = method_type.decl.output {
+                    self.visit_ty(&**ret_ty);
+                }
 
                 self.process_generic_params(&method_type.generics,
                                             method_type.span,
@@ -1352,7 +1362,10 @@ impl<'l, 'tcx, 'v> Visitor<'v> for DxrVisitor<'l, 'tcx> {
                 for arg in decl.inputs.iter() {
                     self.visit_ty(&*arg.ty);
                 }
-                self.visit_ty(&*decl.output);
+
+                if let ast::Return(ref ret_ty) = decl.output {
+                    self.visit_ty(&**ret_ty);
+                }
 
                 // walk the body
                 self.nest(ex.id, |v| v.visit_block(&**body));

src/librustc/middle/traits/coherence.rs

@@ -79,7 +79,6 @@ pub fn ty_is_local(tcx: &ty::ctxt,
     debug!("ty_is_local({})", ty.repr(tcx));
 
     match ty::get(ty).sty {
-        ty::ty_nil |
         ty::ty_bool |
         ty::ty_char |
         ty::ty_int(..) |