Add method `visible_item_path` to `CStore`

src/librustc/middle/cstore.rs

@@ -32,7 +32,7 @@ use mir::repr::Mir;
 use mir::mir_map::MirMap;
 use session::Session;
 use session::search_paths::PathKind;
-use util::nodemap::{FnvHashMap, NodeMap, NodeSet};
+use util::nodemap::{FnvHashMap, NodeMap, NodeSet, DefIdMap};
 use std::any::Any;
 use std::cell::RefCell;
 use std::rc::Rc;
@@ -169,6 +169,7 @@ pub trait CrateStore<'tcx> : Any {
     fn item_type(&self, tcx: &TyCtxt<'tcx>, def: DefId)
                  -> ty::TypeScheme<'tcx>;
     fn relative_item_path(&self, def: DefId) -> Vec<hir_map::PathElem>;
+    fn visible_parent_map<'a>(&'a self) -> ::std::cell::RefMut<'a, DefIdMap<DefId>>;
     fn extern_item_path(&self, def: DefId) -> Vec<hir_map::PathElem>;
     fn item_name(&self, def: DefId) -> ast::Name;
     fn item_predicates(&self, tcx: &TyCtxt<'tcx>, def: DefId)
@@ -347,6 +348,9 @@ impl<'tcx> CrateStore<'tcx> for DummyCrateStore {
     fn item_type(&self, tcx: &TyCtxt<'tcx>, def: DefId)
                  -> ty::TypeScheme<'tcx> { unimplemented!() }
     fn relative_item_path(&self, def: DefId) -> Vec<hir_map::PathElem> { unimplemented!() }
+    fn visible_parent_map<'a>(&'a self) -> ::std::cell::RefMut<'a, DefIdMap<DefId>> {
+        unimplemented!()
+    }
     fn extern_item_path(&self, def: DefId) -> Vec<hir_map::PathElem> { unimplemented!() }
     fn item_name(&self, def: DefId) -> ast::Name { unimplemented!() }
     fn item_predicates(&self, tcx: &TyCtxt<'tcx>, def: DefId)

src/librustc/ty/item_path.rs

@@ -10,7 +10,7 @@
 
 use front::map::DefPathData;
 use middle::cstore::LOCAL_CRATE;
-use middle::def_id::DefId;
+use middle::def_id::{DefId, CRATE_DEF_INDEX};
 use ty::{self, Ty, TyCtxt};
 use syntax::ast;
 
@@ -75,9 +75,51 @@ impl<'tcx> TyCtxt<'tcx> {
         }
     }
 
+    /// If possible, this pushes a global path resolving to `external_def_id` that is visible
+    /// from at least one local module and returns true. If the crate defining `external_def_id` is
+    /// declared with an `extern crate`, the path is guarenteed to use the `extern crate`.
+    pub fn try_push_visible_item_path<T>(&self, buffer: &mut T, external_def_id: DefId) -> bool
+        where T: ItemPathBuffer
+    {
+        let visible_parent_map = self.sess.cstore.visible_parent_map();
+
+        let (mut cur_def, mut cur_path) = (external_def_id, Vec::<ast::Name>::new());
+        loop {
+            // If `cur_def` is a direct or injected extern crate, push the path to the crate
+            // followed by the path to the item within the crate and return.
+            if cur_def.index == CRATE_DEF_INDEX {
+                match self.sess.cstore.extern_crate(cur_def.krate) {
+                    Some(extern_crate) if extern_crate.direct => {
+                        self.push_item_path(buffer, extern_crate.def_id);
+                        cur_path.iter().rev().map(|segment| buffer.push(&segment.as_str())).count();
+                        return true;
+                    }
+                    None => {
+                        buffer.push(&self.crate_name(cur_def.krate));
+                        cur_path.iter().rev().map(|segment| buffer.push(&segment.as_str())).count();
+                        return true;
+                    }
+                    _ => {},
+                }
+            }
+
+            cur_path.push(self.sess.cstore.item_name(cur_def));
+            match visible_parent_map.get(&cur_def) {
+                Some(&def) => cur_def = def,
+                None => return false,
+            };
+        }
+    }
+
     pub fn push_item_path<T>(&self, buffer: &mut T, def_id: DefId)
         where T: ItemPathBuffer
     {
+        match *buffer.root_mode() {
+            RootMode::Local if !def_id.is_local() =>
+                if self.try_push_visible_item_path(buffer, def_id) { return },
+            _ => {}
+        }
+
         let key = self.def_key(def_id);
         match key.disambiguated_data.data {
             DefPathData::CrateRoot => {

src/librustc_metadata/csearch.rs

@@ -13,17 +13,17 @@ use decoder;
 use encoder;
 use loader;
 
-use middle::cstore::{CrateStore, CrateSource, ChildItem, ExternCrate, FoundAst};
+use middle::cstore::{CrateStore, CrateSource, ChildItem, ExternCrate, FoundAst, DefLike};
 use middle::cstore::{NativeLibraryKind, LinkMeta, LinkagePreference};
 use middle::def;
 use middle::lang_items;
 use rustc::ty::{self, Ty, TyCtxt, VariantKind};
-use middle::def_id::{DefId, DefIndex};
+use middle::def_id::{DefId, DefIndex, CRATE_DEF_INDEX};
 
 use rustc::front::map as hir_map;
 use rustc::mir::repr::Mir;
 use rustc::mir::mir_map::MirMap;
-use rustc::util::nodemap::{FnvHashMap, NodeMap, NodeSet};
+use rustc::util::nodemap::{FnvHashMap, NodeMap, NodeSet, DefIdMap};
 
 use std::cell::RefCell;
 use std::rc::Rc;
@@ -544,4 +544,60 @@ impl<'tcx> CrateStore<'tcx> for cstore::CStore {
     {
         encoder::metadata_encoding_version
     }
+
+    /// Returns a map from a sufficiently visible external item (i.e. an external item that is
+    /// visible from at least one local module) to a sufficiently visible parent (considering
+    /// modules that re-export the external item to be parents).
+    fn visible_parent_map<'a>(&'a self) -> ::std::cell::RefMut<'a, DefIdMap<DefId>> {
+        let mut visible_parent_map = self.visible_parent_map.borrow_mut();
+        if !visible_parent_map.is_empty() { return visible_parent_map; }
+
+        use rustc_front::hir;
+        use rustc::middle::cstore::{CrateStore, ChildItem};
+        use std::collections::vec_deque::VecDeque;
+        use std::collections::hash_map::Entry;
+        for cnum in 1 .. self.next_crate_num() {
+            let cdata = self.get_crate_data(cnum);
+
+            match cdata.extern_crate.get() {
+                // Ignore crates without a corresponding local `extern crate` item.
+                Some(extern_crate) if !extern_crate.direct => continue,
+                _ => {},
+            }
+
+            let mut bfs_queue = &mut VecDeque::new();
+            let mut add_child = |bfs_queue: &mut VecDeque<_>, child: ChildItem, parent: DefId| {
+                let child = match child.def {
+                    DefLike::DlDef(def) if child.vis == hir::Public => def.def_id(),
+                    _ => return,
+                };
+
+                match visible_parent_map.entry(child) {
+                    Entry::Occupied(mut entry) => {
+                        // If `child` is defined in crate `cnum`, ensure
+                        // that it is mapped to a parent in `cnum`.
+                        if child.krate == cnum && entry.get().krate != cnum {
+                            entry.insert(parent);
+                        }
+                    }
+                    Entry::Vacant(entry) => {
+                        entry.insert(parent);
+                        bfs_queue.push_back(child);
+                    }
+                }
+            };
+
+            let croot = DefId { krate: cnum, index: CRATE_DEF_INDEX };
+            for child in self.crate_top_level_items(cnum) {
+                add_child(bfs_queue, child, croot);
+            }
+            while let Some(def) = bfs_queue.pop_front() {
+                for child in self.item_children(def) {
+                    add_child(bfs_queue, child, def);
+                }
+            }
+        }
+
+        visible_parent_map
+    }
 }

src/librustc_metadata/cstore.rs

@@ -22,7 +22,8 @@ use loader;
 
 use rustc::back::svh::Svh;
 use rustc::middle::cstore::{ExternCrate};
-use rustc::util::nodemap::{FnvHashMap, NodeMap, NodeSet};
+use rustc::util::nodemap::{FnvHashMap, NodeMap, NodeSet, DefIdMap};
+use rustc::middle::def_id::DefId;
 
 use std::cell::{RefCell, Ref, Cell};
 use std::rc::Rc;
@@ -92,6 +93,7 @@ pub struct CStore {
     used_link_args: RefCell<Vec<String>>,
     statically_included_foreign_items: RefCell<NodeSet>,
     pub intr: Rc<IdentInterner>,
+    pub visible_parent_map: RefCell<DefIdMap<DefId>>,
 }
 
 impl CStore {
@@ -104,6 +106,7 @@ impl CStore {
             used_link_args: RefCell::new(Vec::new()),
             intr: intr,
             statically_included_foreign_items: RefCell::new(NodeSet()),
+            visible_parent_map: RefCell::new(FnvHashMap()),
         }
     }