Auto merge of #37860 - giannicic:defaultimpl, r=nagisa

#37653 support `default impl` for specialization

this commit implements the first step of the `default impl` feature:

> all items in a `default impl` are (implicitly) `default` and hence
> specializable.

In order to test this feature I've copied all the tests provided for the
`default` method implementation (in run-pass/specialization and
compile-fail/specialization directories) and moved the `default` keyword
from the item to the impl.
See [referenced](#37653) issue for further info

r? @aturon

src/grammar/parser-lalr.y

@@ -89,6 +89,7 @@ extern char *yytext;
 %token TRAIT
 %token TYPE
 %token UNSAFE
+%token DEFAULT
 %token USE
 %token WHILE
 %token CONTINUE
@@ -534,6 +535,12 @@ maybe_unsafe
 | %empty { $$ = mk_none(); }
 ;
 
+maybe_default_maybe_unsafe
+: DEFAULT UNSAFE { $$ = mk_atom("DefaultUnsafe"); }
+| DEFAULT        { $$ = mk_atom("Default"); }
+|         UNSAFE { $$ = mk_atom("Unsafe"); }
+| %empty { $$ = mk_none(); }
+
 trait_method
 : type_method { $$ = mk_node("Required", 1, $1); }
 | method      { $$ = mk_node("Provided", 1, $1); }
@@ -588,27 +595,27 @@ impl_method
 // they are ambiguous with traits. We do the same here, regrettably,
 // by splitting ty into ty and ty_prim.
 item_impl
-: maybe_unsafe IMPL generic_params ty_prim_sum maybe_where_clause '{' maybe_inner_attrs maybe_impl_items '}'
+: maybe_default_maybe_unsafe IMPL generic_params ty_prim_sum maybe_where_clause '{' maybe_inner_attrs maybe_impl_items '}'
 {
   $$ = mk_node("ItemImpl", 6, $1, $3, $4, $5, $7, $8);
 }
-| maybe_unsafe IMPL generic_params '(' ty ')' maybe_where_clause '{' maybe_inner_attrs maybe_impl_items '}'
+| maybe_default_maybe_unsafe IMPL generic_params '(' ty ')' maybe_where_clause '{' maybe_inner_attrs maybe_impl_items '}'
 {
   $$ = mk_node("ItemImpl", 6, $1, $3, 5, $6, $9, $10);
 }
-| maybe_unsafe IMPL generic_params trait_ref FOR ty_sum maybe_where_clause '{' maybe_inner_attrs maybe_impl_items '}'
+| maybe_default_maybe_unsafe IMPL generic_params trait_ref FOR ty_sum maybe_where_clause '{' maybe_inner_attrs maybe_impl_items '}'
 {
   $$ = mk_node("ItemImpl", 6, $3, $4, $6, $7, $9, $10);
 }
-| maybe_unsafe IMPL generic_params '!' trait_ref FOR ty_sum maybe_where_clause '{' maybe_inner_attrs maybe_impl_items '}'
+| maybe_default_maybe_unsafe IMPL generic_params '!' trait_ref FOR ty_sum maybe_where_clause '{' maybe_inner_attrs maybe_impl_items '}'
 {
   $$ = mk_node("ItemImplNeg", 7, $1, $3, $5, $7, $8, $10, $11);
 }
-| maybe_unsafe IMPL generic_params trait_ref FOR DOTDOT '{' '}'
+| maybe_default_maybe_unsafe IMPL generic_params trait_ref FOR DOTDOT '{' '}'
 {
   $$ = mk_node("ItemImplDefault", 3, $1, $3, $4);
 }
-| maybe_unsafe IMPL generic_params '!' trait_ref FOR DOTDOT '{' '}'
+| maybe_default_maybe_unsafe IMPL generic_params '!' trait_ref FOR DOTDOT '{' '}'
 {
   $$ = mk_node("ItemImplDefaultNeg", 3, $1, $3, $4);
 }
@@ -1935,4 +1942,4 @@ brackets_delimited_token_trees
                $2,
                mk_node("TTTok", 1, mk_atom("]")));
 }
-;
+;

src/librustc/hir/lowering.rs

@@ -1326,7 +1326,13 @@ impl<'a> LoweringContext<'a> {
                 hir::ItemDefaultImpl(self.lower_unsafety(unsafety),
                                      trait_ref)
             }
-            ItemKind::Impl(unsafety, polarity, ref generics, ref ifce, ref ty, ref impl_items) => {
+            ItemKind::Impl(unsafety,
+                           polarity,
+                           defaultness,
+                           ref generics,
+                           ref ifce,
+                           ref ty,
+                           ref impl_items) => {
                 let new_impl_items = impl_items.iter()
                                                .map(|item| self.lower_impl_item_ref(item))
                                                .collect();
@@ -1340,6 +1346,7 @@ impl<'a> LoweringContext<'a> {
 
                 hir::ItemImpl(self.lower_unsafety(unsafety),
                               self.lower_impl_polarity(polarity),
+                              self.lower_defaultness(defaultness, true /* [1] */),
                               self.lower_generics(generics),
                               ifce,
                               self.lower_ty(ty),
@@ -1355,6 +1362,9 @@ impl<'a> LoweringContext<'a> {
             }
             ItemKind::MacroDef(..) | ItemKind::Mac(..) => panic!("Shouldn't still be around"),
         }
+
+        // [1] `defaultness.has_value()` is never called for an `impl`, always `true` in order to
+        //     not cause an assertion failure inside the `lower_defaultness` function
     }
 
     fn lower_trait_item(&mut self, i: &TraitItem) -> hir::TraitItem {

src/librustc/hir/mod.rs

@@ -1712,6 +1712,7 @@ pub enum Item_ {
     /// An implementation, eg `impl<A> Trait for Foo { .. }`
     ItemImpl(Unsafety,
              ImplPolarity,
+             Defaultness,
              Generics,
              Option<TraitRef>, // (optional) trait this impl implements
              P<Ty>, // self

src/librustc/hir/print.rs

@@ -678,12 +678,14 @@ impl<'a> State<'a> {
             }
             hir::ItemImpl(unsafety,
                           polarity,
+                          defaultness,
                           ref generics,
                           ref opt_trait,
                           ref ty,
                           ref impl_items) => {
                 self.head("")?;
                 self.print_visibility(&item.vis)?;
+                self.print_defaultness(defaultness)?;
                 self.print_unsafety(unsafety)?;
                 self.word_nbsp("impl")?;
 
@@ -820,6 +822,14 @@ impl<'a> State<'a> {
         }
     }
 
+    pub fn print_defaultness(&mut self, defaultness: hir::Defaultness) -> io::Result<()> {
+        match defaultness {
+            hir::Defaultness::Default { .. } => self.word_nbsp("default")?,
+            hir::Defaultness::Final => (),
+        }
+        Ok(())
+    }
+
     pub fn print_struct(&mut self,
                         struct_def: &hir::VariantData,
                         generics: &hir::Generics,
@@ -931,11 +941,7 @@ impl<'a> State<'a> {
         self.hardbreak_if_not_bol()?;
         self.maybe_print_comment(ii.span.lo)?;
         self.print_outer_attributes(&ii.attrs)?;
-
-        match ii.defaultness {
-            hir::Defaultness::Default { .. } => self.word_nbsp("default")?,
-            hir::Defaultness::Final => (),
-        }
+        self.print_defaultness(ii.defaultness)?;
 
         match ii.node {
             hir::ImplItemKind::Const(ref ty, expr) => {

src/librustc/ich/impls_hir.rs

@@ -933,7 +933,7 @@ impl_stable_hash_for!(enum hir::Item_ {
     ItemUnion(variant_data, generics),
     ItemTrait(unsafety, generics, bounds, item_refs),
     ItemDefaultImpl(unsafety, trait_ref),
-    ItemImpl(unsafety, impl_polarity, generics, trait_ref, ty, impl_item_refs)
+    ItemImpl(unsafety, impl_polarity, impl_defaultness, generics, trait_ref, ty, impl_item_refs)
 });
 
 impl_stable_hash_for!(struct hir::TraitItemRef {

src/librustc/middle/cstore.rs

@@ -195,6 +195,7 @@ pub trait CrateStore {
     fn implementations_of_trait(&self, filter: Option<DefId>) -> Vec<DefId>;
 
     // impl info
+    fn impl_defaultness(&self, def: DefId) -> hir::Defaultness;
     fn impl_parent(&self, impl_def_id: DefId) -> Option<DefId>;
 
     // trait/impl-item info
@@ -329,6 +330,7 @@ impl CrateStore for DummyCrateStore {
     fn implementations_of_trait(&self, filter: Option<DefId>) -> Vec<DefId> { vec![] }
 
     // impl info
+    fn impl_defaultness(&self, def: DefId) -> hir::Defaultness { bug!("impl_defaultness") }
     fn impl_parent(&self, def: DefId) -> Option<DefId> { bug!("impl_parent") }
 
     // trait/impl-item info

src/librustc/middle/reachable.rs

@@ -49,7 +49,7 @@ fn item_might_be_inlined(item: &hir::Item) -> bool {
     }
 
     match item.node {
-        hir::ItemImpl(_, _, ref generics, ..) |
+        hir::ItemImpl(_, _, _, ref generics, ..) |
         hir::ItemFn(.., ref generics, _) => {
             generics_require_inlining(generics)
         }
@@ -185,7 +185,7 @@ impl<'a, 'tcx> ReachableContext<'a, 'tcx> {
                             // does too.
                             let impl_node_id = self.tcx.hir.as_local_node_id(impl_did).unwrap();
                             match self.tcx.hir.expect_item(impl_node_id).node {
-                                hir::ItemImpl(_, _, ref generics, ..) => {
+                                hir::ItemImpl(_, _, _, ref generics, ..) => {
                                     generics_require_inlining(generics)
                                 }
                                 _ => false

src/librustc/middle/resolve_lifetime.rs

@@ -331,7 +331,7 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
             hir::ItemStruct(_, ref generics) |
             hir::ItemUnion(_, ref generics) |
             hir::ItemTrait(_, ref generics, ..) |
-            hir::ItemImpl(_, _, ref generics, ..) => {
+            hir::ItemImpl(_, _, _, ref generics, ..) => {
                 // These kinds of items have only early bound lifetime parameters.
                 let mut index = if let hir::ItemTrait(..) = item.node {
                     1 // Self comes before lifetimes
@@ -834,7 +834,7 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
             }
             match parent.node {
                 hir::ItemTrait(_, ref generics, ..) |
-                hir::ItemImpl(_, _, ref generics, ..) => {
+                hir::ItemImpl(_, _, _, ref generics, ..) => {
                     index += (generics.lifetimes.len() + generics.ty_params.len()) as u32;
                 }
                 _ => {}

src/librustc/traits/project.rs

@@ -923,7 +923,8 @@ fn assemble_candidates_from_impls<'cx, 'gcx, 'tcx>(
                         // being invoked).
                         node_item.item.defaultness.has_value()
                     } else {
-                        node_item.item.defaultness.is_default()
+                        node_item.item.defaultness.is_default() ||
+                        selcx.tcx().impl_is_default(node_item.node.def_id())
                     };
 
                     // Only reveal a specializable default if we're past type-checking

src/librustc/traits/util.rs

@@ -13,6 +13,8 @@ use ty::subst::{Subst, Substs};
 use ty::{self, Ty, TyCtxt, ToPredicate, ToPolyTraitRef};
 use ty::outlives::Component;
 use util::nodemap::FxHashSet;
+use hir::{self};
+use traits::specialize::specialization_graph::NodeItem;
 
 use super::{Obligation, ObligationCause, PredicateObligation, SelectionContext, Normalized};
 
@@ -504,6 +506,30 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         };
         ty::Binder((trait_ref, sig.skip_binder().output()))
     }
+
+    pub fn impl_is_default(self, node_item_def_id: DefId) -> bool {
+        match self.hir.as_local_node_id(node_item_def_id) {
+            Some(node_id) => {
+                let item = self.hir.expect_item(node_id);
+                if let hir::ItemImpl(_, _, defaultness, ..) = item.node {
+                    defaultness.is_default()
+                } else {
+                    false
+                }
+            }
+            None => {
+                self.global_tcx()
+                    .sess
+                    .cstore
+                    .impl_defaultness(node_item_def_id)
+                    .is_default()
+            }
+        }
+    }
+
+    pub fn impl_item_is_final(self, node_item: &NodeItem<hir::Defaultness>) -> bool {
+        node_item.item.is_final() && !self.impl_is_default(node_item.node.def_id())
+    }
 }
 
 pub enum TupleArgumentsFlag { Yes, No }

src/librustc_metadata/cstore_impl.rs

@@ -178,6 +178,12 @@ impl CrateStore for cstore::CStore {
         result
     }
 
+    fn impl_defaultness(&self, def: DefId) -> hir::Defaultness
+    {
+        self.dep_graph.read(DepNode::MetaData(def));
+        self.get_crate_data(def.krate).get_impl_defaultness(def.index)
+    }
+
     fn impl_parent(&self, impl_def: DefId) -> Option<DefId> {
         self.dep_graph.read(DepNode::MetaData(impl_def));
         self.get_crate_data(impl_def.krate).get_parent_impl(impl_def.index)

src/librustc_metadata/decoder.rs

@@ -629,6 +629,10 @@ impl<'a, 'tcx> CrateMetadata {
         self.get_impl_data(id).polarity
     }
 
+    pub fn get_impl_defaultness(&self, id: DefIndex) -> hir::Defaultness {
+        self.get_impl_data(id).defaultness
+    }
+
     pub fn get_coerce_unsized_info(&self,
                                    id: DefIndex)
                                    -> Option<ty::adjustment::CoerceUnsizedInfo> {

src/librustc_metadata/encoder.rs

@@ -706,14 +706,15 @@ impl<'a, 'b: 'a, 'tcx: 'b> EntryBuilder<'a, 'b, 'tcx> {
             hir::ItemDefaultImpl(..) => {
                 let data = ImplData {
                     polarity: hir::ImplPolarity::Positive,
+                    defaultness: hir::Defaultness::Final,
                     parent_impl: None,
                     coerce_unsized_info: None,
                     trait_ref: tcx.impl_trait_ref(def_id).map(|trait_ref| self.lazy(&trait_ref)),
                 };
 
                 EntryKind::DefaultImpl(self.lazy(&data))
             }
-            hir::ItemImpl(_, polarity, ..) => {
+            hir::ItemImpl(_, polarity, defaultness, ..) => {
                 let trait_ref = tcx.impl_trait_ref(def_id);
                 let parent = if let Some(trait_ref) = trait_ref {
                     let trait_def = tcx.trait_def(trait_ref.def_id);
@@ -740,6 +741,7 @@ impl<'a, 'b: 'a, 'tcx: 'b> EntryBuilder<'a, 'b, 'tcx> {
 
                 let data = ImplData {
                     polarity: polarity,
+                    defaultness: defaultness,
                     parent_impl: parent,
                     coerce_unsized_info: coerce_unsized_info,
                     trait_ref: trait_ref.map(|trait_ref| self.lazy(&trait_ref)),

src/librustc_metadata/schema.rs

@@ -406,6 +406,7 @@ impl_stable_hash_for!(struct TraitData<'tcx> {
 #[derive(RustcEncodable, RustcDecodable)]
 pub struct ImplData<'tcx> {
     pub polarity: hir::ImplPolarity,
+    pub defaultness: hir::Defaultness,
     pub parent_impl: Option<DefId>,
 
     /// This is `Some` only for impls of `CoerceUnsized`.
@@ -415,6 +416,7 @@ pub struct ImplData<'tcx> {
 
 impl_stable_hash_for!(struct ImplData<'tcx> {
     polarity,
+    defaultness,
     parent_impl,
     coerce_unsized_info,
     trait_ref

src/librustc_save_analysis/dump_visitor.rs

@@ -430,7 +430,7 @@ impl<'l, 'tcx: 'l, 'll, D: Dump + 'll> DumpVisitor<'l, 'tcx, 'll, D> {
                             }
                             None => {
                                 if let Some(NodeItem(item)) = self.tcx.hir.get_if_local(id) {
-                                    if let hir::ItemImpl(_, _, _, _, ref ty, _) = item.node {
+                                    if let hir::ItemImpl(_, _, _, _, _, ref ty, _) = item.node {
                                         trait_id = self.lookup_def_id(ty.id);
                                     }
                                 }

src/librustc_trans/collector.rs

@@ -880,7 +880,7 @@ impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
                 let parent_node_id = hir_map.get_parent_node(ii.id);
                 let is_impl_generic = match hir_map.expect_item(parent_node_id) {
                     &hir::Item {
-                        node: hir::ItemImpl(_, _, ref generics, ..),
+                        node: hir::ItemImpl(_, _, _, ref generics, ..),
                         ..
                     } => {
                         generics.is_type_parameterized()
@@ -911,6 +911,7 @@ fn create_trans_items_for_default_impls<'a, 'tcx>(scx: &SharedCrateContext<'a, '
     let tcx = scx.tcx();
     match item.node {
         hir::ItemImpl(_,
+                      _,
                       _,
                       ref generics,
                       ..,

src/librustc_typeck/check/mod.rs

@@ -1141,7 +1141,7 @@ fn check_specialization_validity<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         .map(|node_item| node_item.map(|parent| parent.defaultness));
 
     if let Some(parent) = parent {
-        if parent.item.is_final() {
+        if tcx.impl_item_is_final(&parent) {
             report_forbidden_specialization(tcx, impl_item, parent.node.def_id());
         }
     }

src/librustc_typeck/check/wfcheck.rs

@@ -105,11 +105,11 @@ impl<'a, 'gcx> CheckTypeWellFormedVisitor<'a, 'gcx> {
             ///
             /// won't be allowed unless there's an *explicit* implementation of `Send`
             /// for `T`
-            hir::ItemImpl(_, hir::ImplPolarity::Positive, _,
+            hir::ItemImpl(_, hir::ImplPolarity::Positive, _, _,
                           ref trait_ref, ref self_ty, _) => {
                 self.check_impl(item, self_ty, trait_ref);
             }
-            hir::ItemImpl(_, hir::ImplPolarity::Negative, _, Some(_), ..) => {
+            hir::ItemImpl(_, hir::ImplPolarity::Negative, _, _, Some(_), ..) => {
                 // FIXME(#27579) what amount of WF checking do we need for neg impls?
 
                 let trait_ref = tcx.impl_trait_ref(tcx.hir.local_def_id(item.id)).unwrap();

src/librustc_typeck/coherence/unsafety.rs

@@ -87,7 +87,7 @@ impl<'cx, 'tcx, 'v> ItemLikeVisitor<'v> for UnsafetyChecker<'cx, 'tcx> {
             hir::ItemDefaultImpl(unsafety, _) => {
                 self.check_unsafety_coherence(item, None, unsafety, hir::ImplPolarity::Positive);
             }
-            hir::ItemImpl(unsafety, polarity, ref generics, Some(_), _, _) => {
+            hir::ItemImpl(unsafety, polarity, _, ref generics, ..) => {
                 self.check_unsafety_coherence(item, Some(generics), unsafety, polarity);
             }
             _ => {}