Add a command flag for word diff textual diff output

bin/api_diff.ml

@@ -40,7 +40,8 @@ let mode ~reference ~current ~main_module ~unwrapped =
         "Either --main-module or --unwrapped must be provided when diffing \
          entire libraries."
 
-let run (`Main_module main_module) (`Unwrapped_library unwrapped)
+let run (`Word_diff word_diff) (`Main_module main_module)
+    (`Unwrapped_library unwrapped)
     (`Ref_cmi reference) (`Current_cmi current) =
   let open CCResult.Infix in
   let* reference_map, current_map =
@@ -75,12 +76,23 @@ let run (`Main_module main_module) (`Unwrapped_library unwrapped)
   List.iter
     (fun diff ->
       let text_diff = Api_watch.Text_diff.from_diff diff in
-      Api_watch.Text_diff.With_colors.pp Format.std_formatter text_diff)
+      if word_diff
+      then Api_watch.Text_diff.With_colors.pp Format.std_formatter text_diff
+      else Api_watch.Text_diff.Word.pp Format.std_formatter text_diff)
     diff_map;
   if has_changes then Ok 1 else Ok 0
 
 let named f = Cmdliner.Term.(app (const f))
 
+let word_diff =
+  let doc =
+    "Show changes in a signature item inline, where a removed part of an item is wrapped in
+      $(b,[-removed-]) and an added one is wrapped in $(b,{+added+})"
+  in
+  named
+    (fun x -> `Word_diff x)
+    Cmdliner.Arg.(value & flag & info ~doc [ "word-diff" ])
+
 let main_module =
   let docv = "MAIN_MODULE_NAME" in
   let doc =
@@ -128,7 +140,7 @@ let info =
 
 let term =
   Cmdliner.Term.(
-    const run $ main_module $ unwrapped_library $ ref_cmi $ current_cmi)
+    const run $ word_diff $ main_module $ unwrapped_library $ ref_cmi $ current_cmi)
 
 let () =
   Fmt_tty.setup_std_outputs ();

lib/text_diff.ml

@@ -630,3 +630,7 @@ module With_colors = struct
   let pp_diff fmt diff = pp_ printer fmt diff
   let pp fmt t = gen_pp pp_diff fmt t
 end
+
+module Word = struct
+  let pp _fmt _t = assert false
+end

lib/text_diff.mli

@@ -23,3 +23,7 @@ module With_colors : sig
   (** Same as regular [pp] but prints added lines in green and removed lines in
       red. *)
 end
+
+module Word : sig
+  val pp : Format.formatter -> t -> unit
+end