Elimite `$crate` before invokng custom derives.

src/librustc_resolve/macros.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use {Module, Resolver};
+use {Module, ModuleKind, Resolver};
 use build_reduced_graph::BuildReducedGraphVisitor;
 use rustc::hir::def_id::{CRATE_DEF_INDEX, DefIndex};
 use rustc::hir::map::{self, DefCollector};
@@ -21,7 +21,9 @@
 use syntax::ext::expand::Expansion;
 use syntax::ext::hygiene::Mark;
 use syntax::ext::tt::macro_rules;
+use syntax::fold::Folder;
 use syntax::parse::token::intern;
+use syntax::ptr::P;
 use syntax::util::lev_distance::find_best_match_for_name;
 use syntax_pos::Span;
 
@@ -97,6 +99,31 @@ fn get_module_scope(&mut self, id: ast::NodeId) -> Mark {
         mark
     }
 
+    fn eliminate_crate_var(&mut self, item: P<ast::Item>) -> P<ast::Item> {
+        struct EliminateCrateVar<'b, 'a: 'b>(&'b mut Resolver<'a>);
+
+        impl<'a, 'b> Folder for EliminateCrateVar<'a, 'b> {
+            fn fold_path(&mut self, mut path: ast::Path) -> ast::Path {
+                let ident = path.segments[0].identifier;
+                if &ident.name.as_str() == "$crate" {
+                    path.global = true;
+                    let module = self.0.resolve_crate_var(ident.ctxt);
+                    if module.is_local() {
+                        path.segments.remove(0);
+                    } else {
+                        path.segments[0].identifier = match module.kind {
+                            ModuleKind::Def(_, name) => ast::Ident::with_empty_ctxt(name),
+                            _ => unreachable!(),
+                        };
+                    }
+                }
+                path
+            }
+        }
+
+        EliminateCrateVar(self).fold_item(item).expect_one("")
+    }
+
     fn visit_expansion(&mut self, mark: Mark, expansion: &Expansion) {
         let invocation = self.invocations[&mark];
         self.collect_def_ids(invocation, expansion);

src/libsyntax/ext/base.rs

@@ -517,6 +517,7 @@ pub enum SyntaxExtension {
 pub trait Resolver {
     fn next_node_id(&mut self) -> ast::NodeId;
     fn get_module_scope(&mut self, id: ast::NodeId) -> Mark;
+    fn eliminate_crate_var(&mut self, item: P<ast::Item>) -> P<ast::Item>;
 
     fn visit_expansion(&mut self, mark: Mark, expansion: &Expansion);
     fn add_macro(&mut self, scope: Mark, def: ast::MacroDef, export: bool);
@@ -539,6 +540,7 @@ pub enum Determinacy {
 impl Resolver for DummyResolver {
     fn next_node_id(&mut self) -> ast::NodeId { ast::DUMMY_NODE_ID }
     fn get_module_scope(&mut self, _id: ast::NodeId) -> Mark { Mark::root() }
+    fn eliminate_crate_var(&mut self, item: P<ast::Item>) -> P<ast::Item> { item }
 
     fn visit_expansion(&mut self, _invoc: Mark, _expansion: &Expansion) {}
     fn add_macro(&mut self, _scope: Mark, _def: ast::MacroDef, _export: bool) {}

src/libsyntax_ext/deriving/custom.rs

@@ -73,7 +73,7 @@ fn expand(&self,
         // Mark attributes as known, and used.
         MarkAttrs(&self.attrs).visit_item(&item);
 
-        let input = __internal::new_token_stream(item.clone());
+        let input = __internal::new_token_stream(ecx.resolver.eliminate_crate_var(item.clone()));
         let res = __internal::set_parse_sess(&ecx.parse_sess, || {
             let inner = self.inner;
             panic::catch_unwind(panic::AssertUnwindSafe(|| inner(input)))