[exn] Forbid raising in exn printers, make them return Pp.t option

Raising inside exception printers is quite tricky as the order of
registration for printers will indeed depend on the linking order.

We thus forbid this, and make our API closer to the upstream
`Printexn` by having printers return an option type.

2 files changed, 6 insertions, 5 deletions

diff --git a/tactics/declare.ml b/tactics/declare.ml
index ce2f3ec2c5..5655bdfd4d 100644
--- a/tactics/declare.ml
+++ b/tactics/declare.ml
@@ -24,10 +24,11 @@ exception AlreadyDeclared of (string option * Id.t)
 
 let _ = CErrors.register_handler (function
     | AlreadyDeclared (kind, id) ->
-      seq [ Pp.pr_opt_no_spc (fun s -> str s ++ spc ()) kind
-          ; Id.print id; str " already exists."]
+      Some
+        (seq [ Pp.pr_opt_no_spc (fun s -> str s ++ spc ()) kind
+             ; Id.print id; str " already exists."])
     | _ ->
-      raise CErrors.Unhandled)
+      None)
 
 module NamedDecl = Context.Named.Declaration
 
diff --git a/tactics/pfedit.ml b/tactics/pfedit.ml
index 72204e1d24..dbabc4e4e0 100644
--- a/tactics/pfedit.ml
+++ b/tactics/pfedit.ml
@@ -26,8 +26,8 @@ let use_unification_heuristics () = !use_unification_heuristics_ref
 
 exception NoSuchGoal
 let () = CErrors.register_handler begin function
-  | NoSuchGoal -> Pp.(str "No such goal.")
-  | _ -> raise CErrors.Unhandled
+  | NoSuchGoal -> Some Pp.(str "No such goal.")
+  | _ -> None
 end
 
 let get_nth_V82_goal p i =