fix Elpi Typecheck program

Author: gares

_CoqProject.test

@@ -55,3 +55,4 @@ tests/test_link_order_import3.v
 tests/test_query_extra_dep.v
 tests/test_toposort.v
 tests/test_synterp.v
+tests/test_checker.v

src/coq_elpi_vernacular.ml

@@ -286,7 +286,7 @@ let set_current_program n =
   current_program := Some n
 
 let typecheck_program ?program () =
-  match !current_program with
+  match Option.append program !current_program with
   | None -> ()
   | Some program ->
       let elpi = P.ensure_initialized () in

tests/test_checker.v

@@ -0,0 +1,19 @@
+From elpi Require Import elpi.
+
+Elpi Command foo.
+Elpi Accumulate lp:{{
+pred p i:int.
+p 0 0.
+
+}}.
+Fail Elpi Typecheck.
+
+Elpi Command bar.
+Elpi Accumulate lp:{{
+pred p i:int.
+p 0.
+
+}}.
+Elpi Typecheck.
+
+Fail Elpi Typecheck foo.