Extraction: nicer error when a toplevel module has no body (#2525)

 I thought this situation wasn't possible, hence the Option.get.
 But it's apparently legal to use Declare Module anywhere, even
 outside a Module Type. No idea on how to handle that at extraction
 for the moment, hence a proper "unsupported" error message.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@14013 85f007b7-540e-0410-9357-904b9bb8a0f7

3 files changed, 18 insertions, 4 deletions

diff --git a/plugins/extraction/extract_env.ml b/plugins/extraction/extract_env.ml
index 126305566..bc9047c0a 100644
--- a/plugins/extraction/extract_env.ml
+++ b/plugins/extraction/extract_env.ml
@@ -339,10 +339,17 @@ and extract_seb env mp all = function
   | SEBwith (_,_) -> anomaly "Not available yet"
 
 and extract_module env mp all mb =
-  (* [mb.mod_expr <> None ], since we look at modules from outside. *)
-  (* Example of module with empty [mod_expr] is X inside a Module F [X:SIG]. *)
-  { ml_mod_expr = extract_seb env mp all (Option.get mb.mod_expr);
-    ml_mod_type = extract_seb_spec env mp (my_type_of_mb mb) }
+  (* A module has an empty [mod_expr] when :
+     - it is a module variable (for instance X inside a Module F [X:SIG])
+     - it is a module assumption (Declare Module).
+     Since we look at modules from outside, we shouldn't have variables.
+     But a Declare Module at toplevel seems legal (cf #2525). For the
+     moment we don't support this situation. *)
+  match mb.mod_expr with
+    | None -> error_no_module_expr mp
+    | Some me ->
+      { ml_mod_expr = extract_seb env mp all me;
+	ml_mod_type = extract_seb_spec env mp (my_type_of_mb mb) }
 
 
 let unpack = function MEstruct (_,sel) -> sel | _ -> assert false
diff --git a/plugins/extraction/table.ml b/plugins/extraction/table.ml
index 4e08079a3..3dbfa7c02 100644
--- a/plugins/extraction/table.ml
+++ b/plugins/extraction/table.ml
@@ -329,6 +329,12 @@ let error_module_clash mp1 mp2 =
        pr_long_mp mp2 ++ str " have the same ML name.\n" ++
        str "This is not supported yet. Please do some renaming first.")
 
+let error_no_module_expr mp =
+  err (str "The module " ++ pr_long_mp mp
+       ++ str " has no body, it probably comes from\n"
+       ++ str "some Declare Module outside any Module Type.\n"
+       ++ str "This situation is currently unsupported by the extraction.")
+
 let error_unknown_module m =
   err (str "Module" ++ spc () ++ pr_qualid m ++ spc () ++ str "not found.")
 
diff --git a/plugins/extraction/table.mli b/plugins/extraction/table.mli
index dc07349ca..ce57a7840 100644
--- a/plugins/extraction/table.mli
+++ b/plugins/extraction/table.mli
@@ -28,6 +28,7 @@ val error_constant : global_reference -> 'a
 val error_inductive : global_reference -> 'a
 val error_nb_cons : unit -> 'a
 val error_module_clash : module_path -> module_path -> 'a
+val error_no_module_expr : module_path -> 'a
 val error_unknown_module : qualid -> 'a
 val error_scheme : unit -> 'a
 val error_not_visible : global_reference -> 'a