deriving should give expn_info

src/libsyntax/ext/deriving/clone.rs

@@ -19,6 +19,7 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt,
                              mitem: @MetaItem,
                              item: @Item,
                              push: |@Item|) {
+    assert!(span.expn_info.is_some(), "derived trait should have expn_info set");
     let trait_def = TraitDef {
         span: span,
         attributes: Vec::new(),

src/libsyntax/ext/deriving/generic.rs

@@ -408,6 +408,7 @@ impl<'a> TraitDef<'a> {
                          InternedString::new("automatically_derived")));
         let opt_trait_ref = Some(trait_ref);
         let ident = ast_util::impl_pretty_name(&opt_trait_ref, self_type);
+        assert!(self.span.expn_info.is_some(), "Should have expansion info")
         cx.item(
             self.span,
             ident,
@@ -613,6 +614,7 @@ impl<'a> MethodDef<'a> {
             Vec::new()
         };
 
+        assert!(trait_.span.expn_info.is_some(), "Should have expansion info")
         // Create the method.
         @ast::Method {
             ident: method_ident,

src/libsyntax/ext/deriving/mod.rs

@@ -20,6 +20,7 @@ library.
 
 use ast::{Item, MetaItem, MetaList, MetaNameValue, MetaWord};
 use ext::base::ExtCtxt;
+use codemap;
 use codemap::Span;
 
 pub mod clone;
@@ -65,7 +66,17 @@ pub fn expand_meta_deriving(cx: &mut ExtCtxt,
                     MetaNameValue(ref tname, _) |
                     MetaList(ref tname, _) |
                     MetaWord(ref tname) => {
-                        macro_rules! expand(($func:path) => ($func(cx, titem.span,
+                        let mut span = titem.span;
+                        span.expn_info = Some(@codemap::ExpnInfo {
+                            call_site: span,
+                            callee: codemap::NameAndSpan {
+                                name: format!("deriving({})", tname.get()),
+                                format: codemap::MacroAttribute,
+                                span: None,
+                            }
+                        });
+
+                        macro_rules! expand(($func:path) => ($func(cx, span,
                                                                    titem, item,
                                                                    |i| push(i))));
                         match tname.get() {