warning for variables that can only match the empty sequence

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/cducetrunk@7588 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

4 files changed, 18 insertions, 2 deletions

diff --git a/README.cduce b/README.cduce
index bd7114c43c..0c25557622 100644
--- a/README.cduce
+++ b/README.cduce
@@ -108,3 +108,5 @@ CHANGE LOG:
 
 Since then
 - support line number directives within {{ ... }}
+- support non-ascii X-capture variable names
+- warning for variables that always bind to {{ [] }}
\ No newline at end of file
diff --git a/typing/typeext.ml b/typing/typeext.ml
index 22f6402009..fea131ac4a 100644
--- a/typing/typeext.ml
+++ b/typing/typeext.ml
@@ -755,8 +755,9 @@ let add_values =
 let ext_branch env loc t p a =
   let module P = Cduce_types.Patterns in
   let fv = P.fv p in
+  let id x = U.to_string (snd x) in
   let ids = 
-    List.map (fun x -> x, Ident.create (Cduce_types.Ident.to_string x)) fv in
+    List.map (fun x -> x, Ident.create (id x)) fv in
   let vars = 
     if !extmode then List.map (fun (_,x) -> x, anyext_var) ids
     else
@@ -765,7 +766,16 @@ let ext_branch env loc t p a =
 	let ta = CT.cap t ta in
 	if (CT.is_empty ta) && (loc != Location.none) then
 	  Location.prerr_warning loc Warnings.Unused_match;
-	P.filter ta p 
+	let res = P.filter ta p  in
+
+	Cduce_types.Ident.IdMap.iteri
+	  (fun x t -> 
+	     if (CT.subtype (CT.descr t) SEQ.nil_type) then
+	       Location.prerr_warning loc (Warnings.Match_epsilon (id x)))
+	  res;
+	
+	res
+
       ) in
       to_eval := (fun () -> ignore (lazy_force loc z)) :: !to_eval; 
       (* to get a warning for unused
diff --git a/utils/warnings.ml b/utils/warnings.ml
index 850dd80b85..abcae9b49f 100644
--- a/utils/warnings.ml
+++ b/utils/warnings.ml
@@ -26,6 +26,7 @@ type t =                             (* A is all *)
   | Statement_type                   (* S *)
   | Unused_match                     (* U *)
   | Unused_pat
+  | Match_epsilon of string
   | Hide_instance_variable of string (* V *)
   | Illegal_backslash                (* X *)
   | Implicit_public_methods of string list
@@ -53,6 +54,7 @@ let letter = function        (* 'a' is all *)
   | Partial_match _ ->          'p'
   | Statement_type ->           's'
   | Unused_match
+  | Match_epsilon _
   | Unused_pat ->               'u'
   | Hide_instance_variable _ -> 'v'
   | Illegal_backslash
@@ -113,6 +115,7 @@ let message = function
        Here is an example of a value that is not matched:\n" ^ s
   | Unused_match -> "this match case is unused."
   | Unused_pat   -> "this pattern is unused."
+  | Match_epsilon s -> "the variable " ^ s ^ " can only match the empty sequence."
   | Fragile_pat "" ->
       "this pattern is fragile. It would hide\n\
        the addition of new constructors to the data types it matches."
diff --git a/utils/warnings.mli b/utils/warnings.mli
index 5f22c91bea..0e467a340d 100644
--- a/utils/warnings.mli
+++ b/utils/warnings.mli
@@ -26,6 +26,7 @@ type t =                             (* A is all *)
   | Statement_type                   (* S *)
   | Unused_match                     (* U *)
   | Unused_pat
+  | Match_epsilon of string
   | Hide_instance_variable of string (* V *)
   | Illegal_backslash                (* X *)
   | Implicit_public_methods of string list