A new infrastructure for warnings.

On the user side, coqtop and coqc take a list of warning names or categories
after -w. No prefix means activate the warning, a "-" prefix means deactivate
it, and "+" means turn the warning into an error. Special categories include
"all", and "default" which contains the warnings enabled by default.

We also provide a vernacular Set Warnings which takes the same flags as argument.

Note that coqc now prints warnings.

The name and category of a warning are printed with the warning itself.

On the developer side, Feedback.msg_warning is still accessible, but the
recommended way to print a warning is in two steps:

1) create it by:

let warn_my_warning =
  CWarnings.create ~name:"my-warning" ~category:"my-category"
    (fun args -> Pp.strbrk ...)

2) print it by:

warn_my_warning args

1 files changed, 4 insertions, 3 deletions

diff --git a/lib/ppstyle.ml b/lib/ppstyle.ml
index b068788c92..ecfaa822c7 100644
--- a/lib/ppstyle.ml
+++ b/lib/ppstyle.ml
@@ -124,15 +124,16 @@ let init_color_output () =
   Format.pp_set_formatter_tag_functions !std_ft tag_handler;
   Format.pp_set_formatter_tag_functions !err_ft tag_handler
 
-let color_msg ?header ft strm =
+let color_msg ?loc ?header ft strm =
   let pptag = tag in
   let open Pp in
+  let ploc = Option.cata Pp.pr_loc (Pp.mt ()) loc in
   let strm = match header with
-    | None -> hov 0 strm
+    | None -> hov 0 (ploc ++ strm)
     | Some (h, t) ->
       let tag = Pp.Tag.inj t pptag in
       let h = Pp.tag tag (str h ++ str ":") in
-      hov 0 (h ++ spc () ++ strm)
+      hov 0 (ploc ++ h ++ spc () ++ strm)
   in
   pp_with ~pp_tag ft strm;
   Format.pp_print_newline ft ();