Make print_macro_backtrace non-recursive

src/libsyntax/diagnostic.rs

@@ -727,7 +727,9 @@ impl EmitterWriter {
                              cm: &codemap::CodeMap,
                              sp: Span)
                              -> io::Result<()> {
-        let cs = try!(cm.with_expn_info(sp.expn_id, |expn_info| -> io::Result<_> {
+        let mut sp_opt = Some(sp);
+        while let Some(sp) = sp_opt {
+            sp_opt = try!(cm.with_expn_info(sp.expn_id, |expn_info| -> io::Result<_> {
                 match expn_info {
                     Some(ei) => {
                         let ss = ei.callee.span.map_or(String::new(),
@@ -750,7 +752,9 @@ impl EmitterWriter {
                     None => Ok(None)
                 }
             }));
-        cs.map_or(Ok(()), |call_site| self.print_macro_backtrace(cm, call_site))
+        }
+
+        Ok(())
     }
 }