Rollup merge of #37688 - eddyb:lazy-8, r=petrochenkov

[8/n] rustc: clean up lookup_item_type and remove TypeScheme.

_This is part of a series ([prev](https://github.com/rust-lang/rust/pull/37676) | [next]()) of patches designed to rework rustc into an out-of-order on-demand pipeline model for both better feature support (e.g. [MIR-based](https://github.com/solson/miri) early constant evaluation) and incremental execution of compiler passes (e.g. type-checking), with beneficial consequences to IDE support as well.
If any motivation is unclear, please ask for additional PR description clarifications or code comments._

<hr>

* `tcx.tcache` -> `tcx.item_types`
* `TypeScheme` (grouping `Ty` and `ty::Generics`) is removed
* `tcx.item_types` entries no longer duplicated in `tcx.tables.node_types`
* `tcx.lookup_item_type(def_id).ty` -> `tcx.item_type(def_id)`
* `tcx.lookup_item_type(def_id).generics` -> `tcx.item_generics(def_id)`
* `tcx.lookup_generics(def_id)` -> `tcx.item_generics(def_id)`
* `tcx.lookup_{super_,}predicates(def_id)` -> `tcx.item_{super_,}predicates(def_id)`

3 files changed, 11 insertions, 8 deletions

diff --git a/src/librustc_metadata/astencode.rs b/src/librustc_metadata/astencode.rs
index e009955b92e..e2fa535bb44 100644
--- a/src/librustc_metadata/astencode.rs
+++ b/src/librustc_metadata/astencode.rs
@@ -133,7 +133,10 @@ pub fn decode_inlined_item<'a, 'tcx>(cdata: &CrateMetadata,
         &InlinedItem::ImplItem(_, ref ii) => ii.id,
     };
     let inlined_did = tcx.map.local_def_id(item_node_id);
-    tcx.register_item_type(inlined_did, tcx.lookup_item_type(orig_did));
+    let ty = tcx.item_type(orig_did);
+    let generics = tcx.item_generics(orig_did);
+    tcx.item_types.borrow_mut().insert(inlined_did, ty);
+    tcx.generics.borrow_mut().insert(inlined_did, generics);
 
     for (id, entry) in ast.side_tables.decode((cdata, tcx, id_ranges)) {
         match entry {
@@ -141,7 +144,7 @@ pub fn decode_inlined_item<'a, 'tcx>(cdata: &CrateMetadata,
                 tcx.def_map.borrow_mut().insert(id, def::PathResolution::new(def));
             }
             TableEntry::NodeType(ty) => {
-                tcx.node_type_insert(id, ty);
+                tcx.tables.borrow_mut().node_types.insert(id, ty);
             }
             TableEntry::ItemSubsts(item_substs) => {
                 tcx.tables.borrow_mut().item_substs.insert(id, item_substs);
diff --git a/src/librustc_metadata/decoder.rs b/src/librustc_metadata/decoder.rs
index 78cde4c2fcb..ba85544326f 100644
--- a/src/librustc_metadata/decoder.rs
+++ b/src/librustc_metadata/decoder.rs
@@ -527,7 +527,7 @@ impl<'a, 'tcx> CrateMetadata {
 
         ty::TraitDef::new(data.unsafety,
                           data.paren_sugar,
-                          tcx.lookup_generics(self.local_def_id(item_id)),
+                          tcx.item_generics(self.local_def_id(item_id)),
                           data.trait_ref.decode((self, tcx)),
                           self.def_path(item_id).unwrap().deterministic_hash(tcx))
     }
diff --git a/src/librustc_metadata/encoder.rs b/src/librustc_metadata/encoder.rs
index ac1f2afcb2a..f169ad66480 100644
--- a/src/librustc_metadata/encoder.rs
+++ b/src/librustc_metadata/encoder.rs
@@ -246,7 +246,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 
     fn encode_item_type(&mut self, def_id: DefId) -> Lazy<Ty<'tcx>> {
         let tcx = self.tcx;
-        self.lazy(&tcx.lookup_item_type(def_id).ty)
+        self.lazy(&tcx.item_type(def_id))
     }
 
     /// Encode data for the given variant of the given ADT. The
@@ -444,12 +444,12 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 
     fn encode_generics(&mut self, def_id: DefId) -> Lazy<ty::Generics<'tcx>> {
         let tcx = self.tcx;
-        self.lazy(tcx.lookup_generics(def_id))
+        self.lazy(tcx.item_generics(def_id))
     }
 
     fn encode_predicates(&mut self, def_id: DefId) -> Lazy<ty::GenericPredicates<'tcx>> {
         let tcx = self.tcx;
-        self.lazy(&tcx.lookup_predicates(def_id))
+        self.lazy(&tcx.item_predicates(def_id))
     }
 
     fn encode_info_for_trait_item(&mut self, def_id: DefId) -> Entry<'tcx> {
@@ -556,7 +556,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         let (ast, mir) = if impl_item.kind == ty::AssociatedKind::Const {
             (true, true)
         } else if let hir::ImplItemKind::Method(ref sig, _) = ast_item.node {
-            let generics = self.tcx.lookup_generics(def_id);
+            let generics = self.tcx.item_generics(def_id);
             let types = generics.parent_types as usize + generics.types.len();
             let needs_inline = types > 0 || attr::requests_inline(&ast_item.attrs);
             let is_const_fn = sig.constness == hir::Constness::Const;
@@ -717,7 +717,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                     paren_sugar: trait_def.paren_sugar,
                     has_default_impl: tcx.trait_has_default_impl(def_id),
                     trait_ref: self.lazy(&trait_def.trait_ref),
-                    super_predicates: self.lazy(&tcx.lookup_super_predicates(def_id)),
+                    super_predicates: self.lazy(&tcx.item_super_predicates(def_id)),
                 };
 
                 EntryKind::Trait(self.lazy(&data))