Avoid creating malformed location in Camlp4 when no token is consumed

When no token was consumed, Camlp4 created a location with start-pos > stop-pos.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@11902 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

1 files changed, 10 insertions, 2 deletions

diff --git a/camlp4/Camlp4/Struct/Grammar/Parser.ml b/camlp4/Camlp4/Struct/Grammar/Parser.ml
index d97eb28755..2c639b2a1c 100644
--- a/camlp4/Camlp4/Struct/Grammar/Parser.ml
+++ b/camlp4/Camlp4/Struct/Grammar/Parser.ml
@@ -34,9 +34,17 @@ module Make (Structure : Structure.S) = struct
   value drop_prev_loc = Tools.drop_prev_loc;
 
   value add_loc bp parse_fun strm =
+    let count1 = Stream.count strm in
     let x = parse_fun strm in
-    let ep = loc_ep strm in
-    let loc = Loc.merge bp ep in
+    let count2 = Stream.count strm in
+    let loc =
+      if count1 < count2 then
+        let ep = loc_ep strm in
+        Loc.merge bp ep
+      else
+        (* If nothing has been consumed, create a 0-length location. *)
+        Loc.join bp
+    in
     (x, loc);
 
   value stream_peek_nth strm n =