[minor] Format: factorize check_geometry to avoid invariant duplication

stdlib/format.ml

@@ -815,32 +815,44 @@ let pp_set_margin state n =
 (** Geometry functions and types *)
 type geometry = { max_indent:int; margin: int}
 
+let validate_geometry {margin; max_indent} =
+  if max_indent < 2 then
+    Error "max_indent < 2"
+  else if margin <= max_indent then
+    Error "margin <= max_indent"
+  else Ok ()
+
 let check_geometry geometry =
-  geometry.max_indent > 1
-  &&  geometry.margin > geometry.max_indent
+  match validate_geometry geometry with
+  | Ok () -> true
+  | Error _ -> false
 
 let pp_get_margin state () = state.pp_margin
 
-let pp_set_geometry state ~max_indent ~margin =
-  if max_indent < 2 then
-    raise (Invalid_argument "Format.pp_set_geometry: max_indent < 2");
-  if margin <= max_indent then
-    raise (Invalid_argument "Format.pp_set_geometry: margin <= max_indent");
+let pp_set_full_geometry state {margin; max_indent} =
   pp_set_margin state margin;
-  pp_set_max_indent state max_indent
+  pp_set_max_indent state max_indent;
+  ()
+
+let pp_set_geometry state ~max_indent ~margin =
+  let geometry = { max_indent; margin } in
+  match validate_geometry geometry with
+  | Error msg ->
+    raise (Invalid_argument ("Format.pp_set_geometry: " ^ msg))
+  | Ok () ->
+    pp_set_full_geometry state geometry
 
 let pp_safe_set_geometry state ~max_indent ~margin =
-  if check_geometry {max_indent;margin} then
-    pp_set_geometry state ~max_indent ~margin
-  else
-    ()
+  let geometry = { max_indent; margin } in
+  match validate_geometry geometry with
+  | Error _msg ->
+     ()
+  | Ok () ->
+    pp_set_full_geometry state geometry
 
 let pp_get_geometry state () =
   { margin = pp_get_margin state (); max_indent = pp_get_max_indent state () }
 
-let pp_set_full_geometry state {margin; max_indent} =
-  pp_set_geometry state ~max_indent ~margin
-
 let pp_update_geometry state update =
   let geometry = pp_get_geometry state () in
   pp_set_full_geometry state (update geometry)