Add a map from external cnums to local cnums in cstore::crate_metadata

Once populated, this will allow us to load type info for types defined in
external crates referenced by other external crates.

src/comp/metadata/creader.rs

@@ -22,6 +22,7 @@ import std::option;
 import std::option::none;
 import std::option::some;
 import std::map::hashmap;
+import std::map::new_int_hash;
 import syntax::print::pprust;
 import common::*;
 
@@ -225,8 +226,10 @@ fn load_library_crate(&session::session sess, span span, ast::crate_num cnum,
     alt (find_library_crate(sess, ident, metas, library_search_paths)) {
         case (some(?t)) {
             auto cstore = sess.get_cstore();
-            cstore::set_crate_data(cstore, cnum,
-                                   rec(name=ident, data=t._1));
+            auto cmeta = rec(name=ident,
+                             data=t._1,
+                             cnum_map = new_int_hash[ast::crate_num]());
+            cstore::set_crate_data(cstore, cnum, cmeta);
             cstore::add_used_crate_file(cstore, t._0);
             ret;
         }

src/comp/metadata/cstore.rs

@@ -6,7 +6,15 @@ import std::vec;
 import std::str;
 import syntax::ast;
 
-type crate_metadata = rec(str name, vec[u8] data);
+// A map from external crate numbers (as decoded from some crate file) to
+// local crate numbers (as generated during this session). Each external
+// crate may refer to types in other external crates, and each has their
+// own crate numbers.
+type cnum_map = map::hashmap[ast::crate_num, ast::crate_num];
+
+type crate_metadata = rec(str name,
+                          vec[u8] data,
+                          cnum_map cnum_map);
 
 // Map from node_id's of local use statements to crate numbers
 type use_crate_map = map::hashmap[ast::node_id, ast::crate_num];