incr.comp.: Provide session to some more decoding contexts.

src/librustc_metadata/creader.rs

@@ -258,14 +258,15 @@ impl<'a> CrateLoader<'a> {
         let cnum_map = self.resolve_crate_deps(root, &crate_root, &metadata, cnum, span, dep_kind);
 
         let def_path_table = record_time(&self.sess.perf_stats.decode_def_path_tables_time, || {
-            crate_root.def_path_table.decode(&metadata)
+            crate_root.def_path_table.decode((&metadata, self.sess))
         });
 
-        let exported_symbols = crate_root.exported_symbols.decode(&metadata).collect();
-
+        let exported_symbols = crate_root.exported_symbols
+                                         .decode((&metadata, self.sess))
+                                         .collect();
         let trait_impls = crate_root
             .impls
-            .decode(&metadata)
+            .decode((&metadata, self.sess))
             .map(|trait_impls| (trait_impls.trait_id, trait_impls.impls))
             .collect();
 
@@ -298,7 +299,7 @@ impl<'a> CrateLoader<'a> {
         let dllimports: FxHashSet<_> = cmeta
             .root
             .native_libraries
-            .decode(&cmeta)
+            .decode((&cmeta, self.sess))
             .filter(|lib| relevant_lib(self.sess, lib) &&
                           lib.kind == cstore::NativeLibraryKind::NativeUnknown)
             .flat_map(|lib| {

src/librustc_metadata/cstore_impl.rs

@@ -183,7 +183,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     is_no_builtins => { cdata.is_no_builtins(tcx.sess) }
     impl_defaultness => { cdata.get_impl_defaultness(def_id.index) }
     exported_symbol_ids => { Rc::new(cdata.get_exported_symbols()) }
-    native_libraries => { Rc::new(cdata.get_native_libraries()) }
+    native_libraries => { Rc::new(cdata.get_native_libraries(tcx.sess)) }
     plugin_registrar_fn => {
         cdata.root.plugin_registrar_fn.map(|index| {
             DefId { krate: def_id.krate, index }

src/librustc_metadata/decoder.rs

@@ -87,6 +87,20 @@ impl<'a, 'tcx> Metadata<'a, 'tcx> for &'a MetadataBlob {
     }
 }
 
+
+impl<'a, 'tcx> Metadata<'a, 'tcx> for (&'a MetadataBlob, &'a Session) {
+    fn raw_bytes(self) -> &'a [u8] {
+        let (blob, _) = self;
+        &blob.0
+    }
+
+    fn sess(self) -> Option<&'a Session> {
+        let (_, sess) = self;
+        Some(sess)
+    }
+}
+
+
 impl<'a, 'tcx> Metadata<'a, 'tcx> for &'a CrateMetadata {
     fn raw_bytes(self) -> &'a [u8] {
         self.blob.raw_bytes()
@@ -1017,8 +1031,8 @@ impl<'a, 'tcx> CrateMetadata {
     }
 
 
-    pub fn get_native_libraries(&self) -> Vec<NativeLibrary> {
-        self.root.native_libraries.decode(self).collect()
+    pub fn get_native_libraries(&self, sess: &Session) -> Vec<NativeLibrary> {
+        self.root.native_libraries.decode((self, sess)).collect()
     }
 
     pub fn get_dylib_dependency_formats(&self) -> Vec<(CrateNum, LinkagePreference)> {