kill the fake provided method stubs

this simplifies the code while reducing the size of libcore.rlib by
3.3 MiB (~1M of which is bloat a separate patch of mine removes
too), while reducing rustc memory usage on small crates by 18MiB.

This also simplifies the code considerably.

src/librustc/metadata/common.rs

@@ -180,7 +180,7 @@ pub const tag_mod_child: usize = 0x7b;
 pub const tag_misc_info: usize = 0x108; // top-level only
 pub const tag_misc_info_crate_items: usize = 0x7c;
 
-pub const tag_item_method_provided_source: usize = 0x7d;
+// GAP 0x7d
 pub const tag_item_impl_vtables: usize = 0x7e;
 
 pub const tag_impls: usize = 0x109; // top-level only

src/librustc/metadata/decoder.rs

@@ -187,12 +187,6 @@ fn item_def_id(d: rbml::Doc, cdata: Cmd) -> DefId {
     translated_def_id(cdata, reader::get_doc(d, tag_def_id))
 }
 
-fn get_provided_source(d: rbml::Doc, cdata: Cmd) -> Option<DefId> {
-    reader::maybe_get_doc(d, tag_item_method_provided_source).map(|doc| {
-        translated_def_id(cdata, doc)
-    })
-}
-
 fn reexports<'a>(d: rbml::Doc<'a>) -> reader::TaggedDocsIterator<'a> {
     reader::tagged_docs(d, tag_items_data_item_reexport)
 }
@@ -276,11 +270,14 @@ fn item_to_def_like(cdata: Cmd, item: rbml::Doc, did: DefId) -> DefLike {
     match fam {
         Constant  => {
             // Check whether we have an associated const item.
-            if item_sort(item) == Some('C') {
-                DlDef(def::DefAssociatedConst(did))
-            } else {
-                // Regular const item.
-                DlDef(def::DefConst(did))
+            match item_sort(item) {
+                Some('C') | Some('c') => {
+                    DlDef(def::DefAssociatedConst(did))
+                }
+                _ => {
+                    // Regular const item.
+                    DlDef(def::DefConst(did))
+                }
             }
         }
         ImmStatic => DlDef(def::DefStatic(did, false)),
@@ -818,7 +815,7 @@ pub fn get_impl_items(cdata: Cmd, impl_id: ast::NodeId)
     reader::tagged_docs(cdata.lookup_item(impl_id), tag_item_impl_item).map(|doc| {
         let def_id = item_def_id(doc, cdata);
         match item_sort(doc) {
-            Some('C') => ty::ConstTraitItemId(def_id),
+            Some('C') | Some('c') => ty::ConstTraitItemId(def_id),
             Some('r') | Some('p') => ty::MethodTraitItemId(def_id),
             Some('t') => ty::TypeTraitItemId(def_id),
             _ => panic!("unknown impl item sort"),
@@ -864,24 +861,22 @@ pub fn get_impl_or_trait_item<'tcx>(intr: Rc<IdentInterner>,
     let vis = item_visibility(item_doc);
 
     match item_sort(item_doc) {
-        Some('C') => {
+        sort @ Some('C') | sort @ Some('c') => {
             let ty = doc_type(item_doc, tcx, cdata);
-            let default = get_provided_source(item_doc, cdata);
             ty::ConstTraitItem(Rc::new(ty::AssociatedConst {
                 name: name,
                 ty: ty,
                 vis: vis,
                 def_id: def_id,
                 container: container,
-                default: default,
+                has_value: sort == Some('C')
             }))
         }
         Some('r') | Some('p') => {
             let generics = doc_generics(item_doc, tcx, cdata, tag_method_ty_generics);
             let predicates = doc_predicates(item_doc, tcx, cdata, tag_method_ty_generics);
             let fty = doc_method_fty(item_doc, tcx, cdata);
             let explicit_self = get_explicit_self(item_doc);
-            let provided_source = get_provided_source(item_doc, cdata);
 
             ty::MethodTraitItem(Rc::new(ty::Method::new(name,
                                                         generics,
@@ -890,8 +885,7 @@ pub fn get_impl_or_trait_item<'tcx>(intr: Rc<IdentInterner>,
                                                         explicit_self,
                                                         vis,
                                                         def_id,
-                                                        container,
-                                                        provided_source)))
+                                                        container)))
         }
         Some('t') => {
             let ty = maybe_doc_type(item_doc, tcx, cdata);
@@ -913,7 +907,7 @@ pub fn get_trait_item_def_ids(cdata: Cmd, id: ast::NodeId)
     reader::tagged_docs(item, tag_item_trait_item).map(|mth| {
         let def_id = item_def_id(mth, cdata);
         match item_sort(mth) {
-            Some('C') => ty::ConstTraitItemId(def_id),
+            Some('C') | Some('c') => ty::ConstTraitItemId(def_id),
             Some('r') | Some('p') => ty::MethodTraitItemId(def_id),
             Some('t') => ty::TypeTraitItemId(def_id),
             _ => panic!("unknown trait item sort"),
@@ -967,18 +961,19 @@ pub fn get_associated_consts<'tcx>(intr: Rc<IdentInterner>,
             let did = item_def_id(ac_id, cdata);
             let ac_doc = cdata.lookup_item(did.node);
 
-            if item_sort(ac_doc) == Some('C') {
-                let trait_item = get_impl_or_trait_item(intr.clone(),
-                                                        cdata,
-                                                        did.node,
-                                                        tcx);
-                if let ty::ConstTraitItem(ref ac) = trait_item {
-                    Some((*ac).clone())
-                } else {
-                    None
+            match item_sort(ac_doc) {
+                Some('C') | Some('c') => {
+                    let trait_item = get_impl_or_trait_item(intr.clone(),
+                                                            cdata,
+                                                            did.node,
+                                                            tcx);
+                    if let ty::ConstTraitItem(ref ac) = trait_item {
+                        Some((*ac).clone())
+                    } else {
+                        None
+                    }
                 }
-            } else {
-                None
+                _ => None
             }
         })
     }).collect()

src/librustc/metadata/encoder.rs

@@ -609,13 +609,6 @@ fn encode_parent_sort(rbml_w: &mut Encoder, sort: char) {
     rbml_w.wr_tagged_u8(tag_item_trait_parent_sort, sort as u8);
 }
 
-fn encode_provided_source(rbml_w: &mut Encoder,
-                          source_opt: Option<DefId>) {
-    if let Some(source) = source_opt {
-        rbml_w.wr_tagged_u64(tag_item_method_provided_source, def_to_u64(source));
-    }
-}
-
 fn encode_field<'a, 'tcx>(ecx: &EncodeContext<'a, 'tcx>,
                           rbml_w: &mut Encoder,
                           field: ty::FieldDef<'tcx>,
@@ -776,7 +769,6 @@ fn encode_method_ty_fields<'a, 'tcx>(ecx: &EncodeContext<'a, 'tcx>,
         }
         _ => encode_family(rbml_w, METHOD_FAMILY)
     }
-    encode_provided_source(rbml_w, method_ty.provided_source);
 }
 
 fn encode_info_for_associated_const(ecx: &EncodeContext,
@@ -795,7 +787,6 @@ fn encode_info_for_associated_const(ecx: &EncodeContext,
     encode_name(rbml_w, associated_const.name);
     encode_visibility(rbml_w, associated_const.vis);
     encode_family(rbml_w, 'C');
-    encode_provided_source(rbml_w, associated_const.default);
 
     encode_parent_item(rbml_w, DefId::local(parent_id));
     encode_item_sort(rbml_w, 'C');
@@ -1367,13 +1358,10 @@ fn encode_info_for_item(ecx: &EncodeContext,
                     encode_def_id(rbml_w, associated_const.def_id);
                     encode_visibility(rbml_w, associated_const.vis);
 
-                    encode_provided_source(rbml_w, associated_const.default);
-
                     let elem = ast_map::PathName(associated_const.name);
                     encode_path(rbml_w,
                                 path.clone().chain(Some(elem)));
 
-                    encode_item_sort(rbml_w, 'C');
                     encode_family(rbml_w, 'C');
 
                     encode_bounds_and_type_for_item(rbml_w, ecx,
@@ -1429,7 +1417,13 @@ fn encode_info_for_item(ecx: &EncodeContext,
             let trait_item = &*ms[i];
             encode_attributes(rbml_w, &trait_item.attrs);
             match trait_item.node {
-                hir::ConstTraitItem(_, _) => {
+                hir::ConstTraitItem(_, ref default) => {
+                    if default.is_some() {
+                        encode_item_sort(rbml_w, 'C');
+                    } else {
+                        encode_item_sort(rbml_w, 'c');
+                    }
+
                     encode_inlined_item(ecx, rbml_w,
                                         InlinedItemRef::TraitItem(def_id, trait_item));
                 }

src/librustc/middle/ty/context.rs

@@ -235,8 +235,6 @@ pub struct ctxt<'tcx> {
     pub ty_param_defs: RefCell<NodeMap<ty::TypeParameterDef<'tcx>>>,
     pub normalized_cache: RefCell<FnvHashMap<Ty<'tcx>, Ty<'tcx>>>,
     pub lang_items: middle::lang_items::LanguageItems,
-    /// A mapping of fake provided method def_ids to the default implementation
-    pub provided_method_sources: RefCell<DefIdMap<DefId>>,
 
     /// Maps from def-id of a type or region parameter to its
     /// (inferred) variance.
@@ -471,7 +469,6 @@ impl<'tcx> ctxt<'tcx> {
             ty_param_defs: RefCell::new(NodeMap()),
             normalized_cache: RefCell::new(FnvHashMap()),
             lang_items: lang_items,
-            provided_method_sources: RefCell::new(DefIdMap()),
             inherent_impls: RefCell::new(DefIdMap()),
             impl_items: RefCell::new(DefIdMap()),
             used_unsafe: RefCell::new(NodeSet()),

src/librustc/middle/ty/mod.rs

@@ -235,9 +235,6 @@ pub struct Method<'tcx> {
     pub vis: hir::Visibility,
     pub def_id: DefId,
     pub container: ImplOrTraitItemContainer,
-
-    // If this method is provided, we need to know where it came from
-    pub provided_source: Option<DefId>
 }
 
 impl<'tcx> Method<'tcx> {
@@ -248,8 +245,7 @@ impl<'tcx> Method<'tcx> {
                explicit_self: ExplicitSelfCategory,
                vis: hir::Visibility,
                def_id: DefId,
-               container: ImplOrTraitItemContainer,
-               provided_source: Option<DefId>)
+               container: ImplOrTraitItemContainer)
                -> Method<'tcx> {
        Method {
             name: name,
@@ -260,7 +256,6 @@ impl<'tcx> Method<'tcx> {
             vis: vis,
             def_id: def_id,
             container: container,
-            provided_source: provided_source
         }
     }
 
@@ -293,7 +288,7 @@ pub struct AssociatedConst<'tcx> {
     pub vis: hir::Visibility,
     pub def_id: DefId,
     pub container: ImplOrTraitItemContainer,
-    pub default: Option<DefId>,
+    pub has_value: bool
 }
 
 #[derive(Clone, Copy, Debug)]
@@ -2105,10 +2100,6 @@ impl<'tcx> ctxt<'tcx> {
         }
     }
 
-    pub fn provided_source(&self, id: DefId) -> Option<DefId> {
-        self.provided_method_sources.borrow().get(&id).cloned()
-    }
-
     pub fn provided_trait_methods(&self, id: DefId) -> Vec<Rc<Method<'tcx>>> {
         if id.is_local() {
             if let ItemTrait(_, _, _, ref ms) = self.map.expect_item(id.node).node {
@@ -2477,16 +2468,9 @@ impl<'tcx> ctxt<'tcx> {
             // the map. This is a bit unfortunate.
             for impl_item_def_id in &impl_items {
                 let method_def_id = impl_item_def_id.def_id();
-                match self.impl_or_trait_item(method_def_id) {
-                    MethodTraitItem(method) => {
-                        if let Some(source) = method.provided_source {
-                            self.provided_method_sources
-                                .borrow_mut()
-                                .insert(method_def_id, source);
-                        }
-                    }
-                    _ => {}
-                }
+                // load impl items eagerly for convenience
+                // FIXME: we may want to load these lazily
+                self.impl_or_trait_item(method_def_id);
             }
 
             // Store the implementation info.

src/librustc/middle/ty/util.rs

@@ -14,7 +14,7 @@ use back::svh::Svh;
 use middle::const_eval::{self, ConstVal, ErrKind};
 use middle::const_eval::EvalHint::UncheckedExprHint;
 use middle::def_id::DefId;
-use middle::subst;
+use middle::subst::{self, Subst, Substs};
 use middle::infer;
 use middle::pat_util;
 use middle::traits;
@@ -26,6 +26,7 @@ use util::num::ToPrimitive;
 
 use std::cmp;
 use std::hash::{Hash, SipHasher, Hasher};
+use std::rc::Rc;
 use syntax::ast::{self, Name};
 use syntax::attr::{self, AttrMetaMethods, SignedInt, UnsignedInt};
 use syntax::codemap::Span;
@@ -646,6 +647,58 @@ impl<'tcx> ty::ctxt<'tcx> {
     }
 }
 
+#[derive(Debug)]
+pub struct ImplMethod<'tcx> {
+    pub method: Rc<ty::Method<'tcx>>,
+    pub substs: Substs<'tcx>,
+    pub is_provided: bool
+}
+
+impl<'tcx> ty::ctxt<'tcx> {
+    #[inline(never)] // is this perfy enough?
+    pub fn get_impl_method(&self,
+                           impl_def_id: DefId,
+                           substs: Substs<'tcx>,
+                           name: Name)
+                           -> ImplMethod<'tcx>
+    {
+        // there don't seem to be nicer accessors to these:
+        let impl_or_trait_items_map = self.impl_or_trait_items.borrow();
+
+        for impl_item in &self.impl_items.borrow()[&impl_def_id] {
+            if let ty::MethodTraitItem(ref meth) =
+                impl_or_trait_items_map[&impl_item.def_id()] {
+                if meth.name == name {
+                    return ImplMethod {
+                        method: meth.clone(),
+                        substs: substs,
+                        is_provided: false
+                    }
+                }
+            }
+        }
+
+        // It is not in the impl - get the default from the trait.
+        let trait_ref = self.impl_trait_ref(impl_def_id).unwrap();
+        for trait_item in self.trait_items(trait_ref.def_id).iter() {
+            if let &ty::MethodTraitItem(ref meth) = trait_item {
+                if meth.name == name {
+                    let impl_to_trait_substs = self
+                        .make_substs_for_receiver_types(&trait_ref, meth);
+                    return ImplMethod {
+                        method: meth.clone(),
+                        substs: impl_to_trait_substs.subst(self, &substs),
+                        is_provided: true
+                    }
+                }
+            }
+        }
+
+        self.sess.bug(&format!("method {:?} not found in {:?}",
+                               name, impl_def_id))
+    }
+}
+
 impl<'tcx> ty::TyS<'tcx> {
     fn impls_bound<'a>(&'tcx self, param_env: &ParameterEnvironment<'a,'tcx>,
                        bound: ty::BuiltinBound,

src/librustc_privacy/lib.rs

@@ -725,19 +725,6 @@ impl<'a, 'tcx> PrivacyVisitor<'a, 'tcx> {
                            span: Span,
                            method_id: DefId,
                            name: ast::Name) {
-        // If the method is a default method, we need to use the def_id of
-        // the default implementation.
-        let method_id = match self.tcx.impl_or_trait_item(method_id) {
-            ty::MethodTraitItem(method_type) => {
-                method_type.provided_source.unwrap_or(method_id)
-            }
-            _ => {
-                self.tcx.sess
-                    .span_bug(span,
-                              "got non-method item in check_static_method")
-            }
-        };
-
         self.report_error(self.ensure_public(span,
                                              method_id,
                                              None,