Feature.enabled should not raise Not_found

Checking unregistered features triggered Not_found.
CIL checks for "epicenter" by default, in particular.

Author: kerneis

src/feature.ml

@@ -64,9 +64,13 @@ let registered s =
   try ignore(find s); true
   with Not_found -> false
 
-let enabled s = (find s).fd_enabled
+let enabled s = try (find s).fd_enabled with Not_found -> false
 
-let enable s = let f = find s in f.fd_enabled <- true
+let enable s =
+  try
+    let f = find s in f.fd_enabled <- true
+  with Not_found ->
+    E.s (E.error "cannot enable feature %s: not found" s)
 
 (** Dynamic linking *)
 

src/feature.mli

@@ -72,11 +72,11 @@ val registered : string -> bool
 (** Find a feature by name. Raise Not_found if the feature is not registered. *)
 val find : string -> t
 
-(** Enable a given feature, by name. Raise Not_found if the feature is not
+(** Enable a given feature, by name. Raise {!Errormsg.Error} if the feature is not
  *  registered. *)
 val enable : string -> unit
 
-(** Check if a given feature is enabled. Raise Not_found if the feature is not
+(** Check if a given feature is enabled. Return false if the feature is not
  * registered. *)
 val enabled : string -> bool