refactor: share code for formatting aligned messages (#10906)

Signed-off-by: Stephen Sherratt <[email protected]>

otherlibs/stdune/src/user_message.ml

@@ -311,3 +311,9 @@ let command cmd =
     ; Pp.verbatim "'"
     ]
 ;;
+
+let aligned_message ~left:(left_tag, left_string) ~right =
+  let open Pp.O in
+  let left_padded = Printf.sprintf "%12s" left_string in
+  Pp.tag left_tag (Pp.verbatim left_padded) ++ Pp.char ' ' ++ right
+;;

otherlibs/stdune/src/user_message.mli

@@ -124,3 +124,8 @@ val needs_stack_trace : t -> bool
 
 (** Formatting of shell commands *)
 val command : string -> Style.t Pp.t
+
+(** A message with a left and right component separated by a
+    space. The left component is padded to 12 characters so that the space
+    separating the left and right side of all messages are aligned. *)
+val aligned_message : left:Style.t * string -> right:Style.t Pp.t -> Style.t Pp.t

src/dune_engine/process.ml

@@ -425,9 +425,9 @@ end = struct
   ;;
 
   let progname_and_purpose ~tag ~prog ~purpose =
-    let open Pp.O in
-    let progname = sprintf "%12s" (Fancy.short_prog_name_of_prog prog) in
-    Pp.tag tag (Pp.verbatim progname) ++ Pp.char ' ' ++ pp_purpose purpose
+    User_message.aligned_message
+      ~left:(tag, Fancy.short_prog_name_of_prog prog)
+      ~right:(pp_purpose purpose)
   ;;
 
   let pp_ok = progname_and_purpose ~tag:Ok

src/dune_rules/pkg_build_progress.ml

@@ -15,7 +15,7 @@ end
 let format_user_message ~verb ~object_ =
   let status_tag = User_message.Style.Success in
   User_message.make
-    [ Pp.concat ~sep:Pp.space [ Pp.tag status_tag (Pp.textf "%12s" verb); object_ ] ]
+    [ User_message.aligned_message ~left:(status_tag, verb) ~right:object_ ]
 ;;
 
 module Message = struct