convert the creepy case to just return None -- in practice, it would

have always been returning None anyway, since it was comparing node-ids
across crates incorrectly -- and remove the now unused map
`extern_const_variants`

Author: nikomatsakis

src/librustc/middle/const_eval.rs

@@ -82,32 +82,7 @@ fn lookup_variant_by_id<'a>(tcx: &'a ty::ctxt,
             Some(_) => None
         }
     } else {
-        match tcx.extern_const_variants.borrow().get(&variant_def) {
-            Some(&ast::DUMMY_NODE_ID) => return None,
-            Some(&expr_id) => {
-                return Some(tcx.map.expect_expr(expr_id));
-            }
-            None => {}
-        }
-        let expr_id = match
-            csearch::maybe_get_item_ast(
-                tcx, enum_def,
-                Box::new(|a, b, c, d, e| astencode::decode_inlined_item(a, b, c, d, e)))
-        {
-            csearch::FoundAst::Found(&InlinedItem::Item(ref item)) => match item.node {
-                hir::ItemEnum(hir::EnumDef { .. }, _) => {
-                    tcx.sess.span_bug(
-                        item.span,
-                        &format!("cross-crate enum discr constant with enum {:?} variant {:?}",
-                                 enum_def, variant_def));
-                }
-                _ => None
-            },
-            _ => None
-        };
-        tcx.extern_const_variants.borrow_mut().insert(variant_def,
-                                                      expr_id.unwrap_or(ast::DUMMY_NODE_ID));
-        expr_id.map(|id| tcx.map.expect_expr(id))
+        None
     }
 }
 

src/librustc/middle/ty/context.rs

@@ -307,7 +307,6 @@ pub struct ctxt<'tcx> {
 
     /// These caches are used by const_eval when decoding external constants.
     pub extern_const_statics: RefCell<DefIdMap<NodeId>>,
-    pub extern_const_variants: RefCell<DefIdMap<NodeId>>,
     pub extern_const_fns: RefCell<DefIdMap<NodeId>>,
 
     pub node_lint_levels: RefCell<FnvHashMap<(NodeId, lint::LintId),
@@ -500,7 +499,6 @@ impl<'tcx> ctxt<'tcx> {
             populated_external_types: RefCell::new(DefIdSet()),
             populated_external_primitive_impls: RefCell::new(DefIdSet()),
             extern_const_statics: RefCell::new(DefIdMap()),
-            extern_const_variants: RefCell::new(DefIdMap()),
             extern_const_fns: RefCell::new(DefIdMap()),
             node_lint_levels: RefCell::new(FnvHashMap()),
             transmute_restrictions: RefCell::new(Vec::new()),