remove defaulting to unit

Types will no longer default to `()`, instead always defaulting to `!`.
This disables the associated warning and removes the flag from TyTuple

Author: canndrew

src/librustc/ich/impls_ty.rs

@@ -635,9 +635,8 @@ for ty::TypeVariants<'gcx>
                 closure_substs.hash_stable(hcx, hasher);
                 interior.hash_stable(hcx, hasher);
             }
-            TyTuple(inner_tys, from_diverging_type_var) => {
+            TyTuple(inner_tys) => {
                 inner_tys.hash_stable(hcx, hasher);
-                from_diverging_type_var.hash_stable(hcx, hasher);
             }
             TyProjection(ref projection_ty) => {
                 projection_ty.hash_stable(hcx, hasher);

src/librustc/infer/resolve.rs

@@ -173,12 +173,6 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for FullTypeResolver<'a, 'gcx, 'tcx>
                 ty::TyInfer(_) => {
                     bug!("Unexpected type in full type resolver: {:?}", t);
                 }
-                ty::TyTuple(tys, true) => {
-                    // Un-default defaulted tuples - we are going to a
-                    // different infcx, and the default will just cause
-                    // pollution.
-                    self.tcx().intern_tup(tys, false)
-                }
                 _ => {
                     t.super_fold_with(self)
                 }

src/librustc/lint/builtin.rs

@@ -142,13 +142,6 @@ declare_lint! {
     "lints that have been renamed or removed"
 }
 
-declare_lint! {
-    pub RESOLVE_TRAIT_ON_DEFAULTED_UNIT,
-    Deny,
-    "attempt to resolve a trait on an expression whose type cannot be inferred but which \
-     currently defaults to ()"
-}
-
 declare_lint! {
     pub SAFE_EXTERN_STATICS,
     Deny,
@@ -275,7 +268,6 @@ impl LintPass for HardwiredLints {
             INVALID_TYPE_PARAM_DEFAULT,
             CONST_ERR,
             RENAMED_AND_REMOVED_LINTS,
-            RESOLVE_TRAIT_ON_DEFAULTED_UNIT,
             SAFE_EXTERN_STATICS,
             SAFE_PACKED_BORROWS,
             PATTERNS_IN_FNS_WITHOUT_BODY,

src/librustc/middle/mem_categorization.rs

@@ -1298,7 +1298,7 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
           PatKind::Tuple(ref subpats, ddpos) => {
             // (p1, ..., pN)
             let expected_len = match self.pat_ty(&pat)?.sty {
-                ty::TyTuple(ref tys, _) => tys.len(),
+                ty::TyTuple(ref tys) => tys.len(),
                 ref ty => span_bug!(pat.span, "tuple pattern unexpected type {:?}", ty),
             };
             for (i, subpat) in subpats.iter().enumerate_and_adjust(expected_len, ddpos) {

src/librustc/mir/tcx.rs

@@ -171,7 +171,7 @@ impl<'tcx> Rvalue<'tcx> {
                 let lhs_ty = lhs.ty(local_decls, tcx);
                 let rhs_ty = rhs.ty(local_decls, tcx);
                 let ty = op.ty(tcx, lhs_ty, rhs_ty);
-                tcx.intern_tup(&[ty, tcx.types.bool], false)
+                tcx.intern_tup(&[ty, tcx.types.bool])
             }
             Rvalue::UnaryOp(UnOp::Not, ref operand) |
             Rvalue::UnaryOp(UnOp::Neg, ref operand) => {
@@ -195,10 +195,7 @@ impl<'tcx> Rvalue<'tcx> {
                         tcx.mk_array(ty, ops.len() as u64)
                     }
                     AggregateKind::Tuple => {
-                        tcx.mk_tup(
-                            ops.iter().map(|op| op.ty(local_decls, tcx)),
-                            false
-                        )
+                        tcx.mk_tup(ops.iter().map(|op| op.ty(local_decls, tcx)))
                     }
                     AggregateKind::Adt(def, _, substs, _) => {
                         tcx.type_of(def.did).subst(tcx, substs)

src/librustc/traits/error_reporting.rs

@@ -718,14 +718,14 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 }).map(|sp| self.tcx.sess.codemap().def_span(sp)); // the sp could be an fn def
 
                 let found = match found_trait_ref.skip_binder().substs.type_at(1).sty {
-                    ty::TyTuple(ref tys, _) => tys.iter()
+                    ty::TyTuple(ref tys) => tys.iter()
                         .map(|_| ArgKind::empty()).collect::<Vec<_>>(),
                     _ => vec![ArgKind::empty()],
                 };
                 let expected = match expected_trait_ref.skip_binder().substs.type_at(1).sty {
-                    ty::TyTuple(ref tys, _) => tys.iter()
+                    ty::TyTuple(ref tys) => tys.iter()
                         .map(|t| match t.sty {
-                            ty::TypeVariants::TyTuple(ref tys, _) => ArgKind::Tuple(
+                            ty::TypeVariants::TyTuple(ref tys) => ArgKind::Tuple(
                                 span,
                                 tys.iter()
                                     .map(|ty| ("_".to_owned(), format!("{}", ty.sty)))
@@ -937,7 +937,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         fn build_fn_sig_string<'a, 'gcx, 'tcx>(tcx: ty::TyCtxt<'a, 'gcx, 'tcx>,
                                                trait_ref: &ty::TraitRef<'tcx>) -> String {
             let inputs = trait_ref.substs.type_at(1);
-            let sig = if let ty::TyTuple(inputs, _) = inputs.sty {
+            let sig = if let ty::TyTuple(inputs) = inputs.sty {
                 tcx.mk_fn_sig(
                     inputs.iter().map(|&x| x),
                     tcx.mk_infer(ty::TyVar(ty::TyVid { index: 0 })),

src/librustc/traits/fulfill.rs

@@ -328,11 +328,7 @@ fn process_predicate<'a, 'gcx, 'tcx>(
             if data.is_global() {
                 // no type variables present, can use evaluation for better caching.
                 // FIXME: consider caching errors too.
-                if
-                    // make defaulted unit go through the slow path for better warnings,
-                    // please remove this when the warnings are removed.
-                    !trait_obligation.predicate.skip_binder().self_ty().is_defaulted_unit() &&
-                    selcx.evaluate_obligation_conservatively(&obligation) {
+                if selcx.evaluate_obligation_conservatively(&obligation) {
                     debug!("selecting trait `{:?}` at depth {} evaluated to holds",
                            data, obligation.recursion_depth);
                     return Ok(Some(vec![]))

src/librustc/traits/select.rs

@@ -52,7 +52,6 @@ use std::mem;
 use std::rc::Rc;
 use syntax::abi::Abi;
 use hir;
-use lint;
 use util::nodemap::FxHashMap;
 
 struct InferredObligationsSnapshotVecDelegate<'tcx> {
@@ -517,8 +516,6 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
         debug!("select({:?})", obligation);
         assert!(!obligation.predicate.has_escaping_regions());
 
-        let tcx = self.tcx();
-
         let stack = self.push_stack(TraitObligationStackList::empty(), obligation);
         let ret = match self.candidate_from_obligation(&stack)? {
             None => None,
@@ -530,46 +527,6 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             },
         };
 
-        // Test whether this is a `()` which was produced by defaulting a
-        // diverging type variable with `!` disabled. If so, we may need
-        // to raise a warning.
-        if obligation.predicate.skip_binder().self_ty().is_defaulted_unit() {
-            let mut raise_warning = true;
-            // Don't raise a warning if the trait is implemented for ! and only
-            // permits a trivial implementation for !. This stops us warning
-            // about (for example) `(): Clone` becoming `!: Clone` because such
-            // a switch can't cause code to stop compiling or execute
-            // differently.
-            let mut never_obligation = obligation.clone();
-            let def_id = never_obligation.predicate.skip_binder().trait_ref.def_id;
-            never_obligation.predicate = never_obligation.predicate.map_bound(|mut trait_pred| {
-                // Swap out () with ! so we can check if the trait is impld for !
-                {
-                    let trait_ref = &mut trait_pred.trait_ref;
-                    let unit_substs = trait_ref.substs;
-                    let mut never_substs = Vec::with_capacity(unit_substs.len());
-                    never_substs.push(From::from(tcx.types.never));
-                    never_substs.extend(&unit_substs[1..]);
-                    trait_ref.substs = tcx.intern_substs(&never_substs);
-                }
-                trait_pred
-            });
-            if let Ok(Some(..)) = self.select(&never_obligation) {
-                if !tcx.trait_relevant_for_never(def_id) {
-                    // The trait is also implemented for ! and the resulting
-                    // implementation cannot actually be invoked in any way.
-                    raise_warning = false;
-                }
-            }
-
-            if raise_warning {
-                tcx.lint_node(lint::builtin::RESOLVE_TRAIT_ON_DEFAULTED_UNIT,
-                              obligation.cause.body_id,
-                              obligation.cause.span,
-                              &format!("code relies on type inference rules which are likely \
-                                        to change"));
-            }
-        }
         Ok(ret)
     }
 
@@ -1913,7 +1870,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             }
 
             // (.., T) -> (.., U).
-            (&ty::TyTuple(tys_a, _), &ty::TyTuple(tys_b, _)) => {
+            (&ty::TyTuple(tys_a), &ty::TyTuple(tys_b)) => {
                 tys_a.len() == tys_b.len()
             }
 
@@ -2052,7 +2009,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
 
             ty::TyStr | ty::TySlice(_) | ty::TyDynamic(..) | ty::TyForeign(..) => Never,
 
-            ty::TyTuple(tys, _) => {
+            ty::TyTuple(tys) => {
                 Where(ty::Binder(tys.last().into_iter().cloned().collect()))
             }
 
@@ -2105,7 +2062,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                 Where(ty::Binder(vec![element_ty]))
             }
 
-            ty::TyTuple(tys, _) => {
+            ty::TyTuple(tys) => {
                 // (*) binder moved here
                 Where(ty::Binder(tys.to_vec()))
             }
@@ -2196,7 +2153,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                 vec![element_ty]
             }
 
-            ty::TyTuple(ref tys, _) => {
+            ty::TyTuple(ref tys) => {
                 // (T1, ..., Tn) -- meets any bound that all of T1...Tn meet
                 tys.to_vec()
             }
@@ -2969,7 +2926,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             }
 
             // (.., T) -> (.., U).
-            (&ty::TyTuple(tys_a, _), &ty::TyTuple(tys_b, _)) => {
+            (&ty::TyTuple(tys_a), &ty::TyTuple(tys_b)) => {
                 assert_eq!(tys_a.len(), tys_b.len());
 
                 // The last field of the tuple has to exist.
@@ -2982,7 +2939,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
 
                 // Check that the source tuple with the target's
                 // last element is equal to the target.
-                let new_tuple = tcx.mk_tup(a_mid.iter().chain(Some(b_last)), false);
+                let new_tuple = tcx.mk_tup(a_mid.iter().chain(Some(b_last)));
                 let InferOk { obligations, .. } =
                     self.infcx.at(&obligation.cause, obligation.param_env)
                               .eq(target, new_tuple)

src/librustc/traits/util.rs

@@ -511,7 +511,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         let arguments_tuple = match tuple_arguments {
             TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
             TupleArgumentsFlag::Yes =>
-                self.intern_tup(sig.skip_binder().inputs(), false),
+                self.intern_tup(sig.skip_binder().inputs()),
         };
         let trait_ref = ty::TraitRef {
             def_id: fn_trait_def_id,

src/librustc/ty/context.rs

@@ -1880,7 +1880,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     pub fn coerce_closure_fn_ty(self, sig: PolyFnSig<'tcx>) -> Ty<'tcx> {
         let converted_sig = sig.map_bound(|s| {
             let params_iter = match s.inputs()[0].sty {
-                ty::TyTuple(params, _) => {
+                ty::TyTuple(params) => {
                     params.into_iter().cloned()
                 }
                 _ => bug!(),
@@ -2005,25 +2005,16 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         self.mk_ty(TySlice(ty))
     }
 
-    pub fn intern_tup(self, ts: &[Ty<'tcx>], defaulted: bool) -> Ty<'tcx> {
-        self.mk_ty(TyTuple(self.intern_type_list(ts), defaulted))
+    pub fn intern_tup(self, ts: &[Ty<'tcx>]) -> Ty<'tcx> {
+        self.mk_ty(TyTuple(self.intern_type_list(ts)))
     }
 
-    pub fn mk_tup<I: InternAs<[Ty<'tcx>], Ty<'tcx>>>(self, iter: I,
-                                                     defaulted: bool) -> I::Output {
-        iter.intern_with(|ts| self.mk_ty(TyTuple(self.intern_type_list(ts), defaulted)))
+    pub fn mk_tup<I: InternAs<[Ty<'tcx>], Ty<'tcx>>>(self, iter: I) -> I::Output {
+        iter.intern_with(|ts| self.mk_ty(TyTuple(self.intern_type_list(ts))))
     }
 
     pub fn mk_nil(self) -> Ty<'tcx> {
-        self.intern_tup(&[], false)
-    }
-
-    pub fn mk_diverging_default(self) -> Ty<'tcx> {
-        if self.sess.features.borrow().never_type {
-            self.types.never
-        } else {
-            self.intern_tup(&[], true)
-        }
+        self.intern_tup(&[])
     }
 
     pub fn mk_bool(self) -> Ty<'tcx> {