Record expansion info

serde_codegen/src/de.rs

@@ -8,6 +8,7 @@ use syntax::ptr::P;
 use syntax::tokenstream::TokenTree;
 
 use bound;
+use span;
 use internals::ast::{Body, Field, Item, Style, Variant};
 use internals::{attr, Error};
 
@@ -44,7 +45,7 @@ pub fn expand_derive_deserialize(
     let builder = aster::AstBuilder::new().span(span);
 
     let impl_item = deserialize_item(cx, &builder, &item);
-    push(Annotatable::Item(impl_item))
+    push(span::record_expansion(cx, impl_item, "Deserialize"))
 }
 
 fn deserialize_item(

serde_codegen/src/lib.rs.in

@@ -1,3 +1,4 @@
 mod bound;
 mod de;
 mod ser;
+mod span;

serde_codegen/src/ser.rs

@@ -6,6 +6,7 @@ use syntax::ext::base::{Annotatable, ExtCtxt};
 use syntax::ptr::P;
 
 use bound;
+use span;
 use internals::ast::{Body, Field, Item, Style, Variant};
 use internals::{attr, Error};
 
@@ -38,7 +39,7 @@ pub fn expand_derive_serialize(
     let builder = aster::AstBuilder::new().span(span);
 
     let impl_item = serialize_item(cx, &builder, &item);
-    push(Annotatable::Item(impl_item))
+    push(span::record_expansion(cx, impl_item, "Serialize"))
 }
 
 fn serialize_item(

serde_codegen/src/span.rs

@@ -0,0 +1,43 @@
+use syntax::ast;
+use syntax::codemap::{self, ExpnId, Span};
+use syntax::ext::base::{Annotatable, ExtCtxt};
+use syntax::fold::{self, Folder};
+use syntax::parse::token::intern;
+use syntax::ptr::P;
+
+pub fn record_expansion(
+    cx: &ExtCtxt,
+    item: P<ast::Item>,
+    derive: &str,
+) -> Annotatable {
+    let info = codemap::ExpnInfo {
+        call_site: codemap::DUMMY_SP,
+        callee: codemap::NameAndSpan {
+            format: codemap::MacroAttribute(intern(&format!("derive({})", derive))),
+            span: None,
+            allow_internal_unstable: false,
+        },
+    };
+    let expn_id = cx.codemap().record_expansion(info);
+
+    let mut respanner = Respanner { expn_id: expn_id };
+    let item = item.map(|item| respanner.fold_item_simple(item));
+    Annotatable::Item(item)
+}
+
+struct Respanner {
+    expn_id: ExpnId,
+}
+
+impl Folder for Respanner {
+    fn new_span(&mut self, span: Span) -> Span {
+        Span {
+            expn_id: self.expn_id,
+            .. span
+        }
+    }
+
+    fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
+        fold::noop_fold_mac(mac, self)
+    }
+}