dune_trace: Dune trace abstract event (#12864)

* refactor(trace): make event module abstract

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

Author: rgrinberg

src/dune_engine/sandbox.ml

@@ -185,8 +185,7 @@ let create ~mode ~dune_stats ~rule_loc ~dirs ~deps ~rule_dir ~rule_digest =
     Dune_trace.start dune_stats (fun () ->
       let cat = Some [ "create-sandbox" ] in
       let name = Loc.to_file_colon_line rule_loc in
-      let args = None in
-      { cat; name; args })
+      Dune_trace.Event.data ~cat ~name ~args:None)
   in
   init ();
   let sandbox_dir =

src/dune_pkg/fetch.ml

@@ -253,9 +253,10 @@ let fetch ~unpack ~checksum ~target ~url:(url_loc, url) =
   let event =
     Dune_trace.(
       start (global ()) (fun () ->
-        { cat = None
-        ; name = label
-        ; args =
+        Dune_trace.Event.data
+          ~cat:None
+          ~name:label
+          ~args:
             (let args =
                [ "url", `String (OpamUrl.to_string url)
                ; "target", `String (Path.to_string target)
@@ -265,8 +266,7 @@ let fetch ~unpack ~checksum ~target ~url:(url_loc, url) =
                (match checksum with
                 | None -> args
                 | Some checksum ->
-                  ("checksum", `String (Checksum.to_string checksum)) :: args))
-        }))
+                  ("checksum", `String (Checksum.to_string checksum)) :: args))))
   in
   let unsupported_backend s =
     User_error.raise ~loc:url_loc [ Pp.textf "Unsupported backend: %s" s ]

src/dune_trace/dune_trace.ml

@@ -95,6 +95,8 @@ module Event = struct
     ; event_data : data
     ; start : float
     }
+
+  let data ~args ~cat ~name = { args; cat; name }
 end
 
 let start t k : Event.t option =

src/dune_trace/dune_trace.mli

@@ -1,6 +1,8 @@
 type t
 
 module Json : sig
+  type t = Chrome_trace.Json.t
+
   val to_string : Chrome_trace.Json.t -> string
 end
 
@@ -22,12 +24,13 @@ val extended_build_job_info : t -> bool
 
 module Event : sig
   type t
+  type data
 
-  type data =
-    { args : Chrome_trace.Event.args option
-    ; cat : string list option
-    ; name : string
-    }
+  val data
+    :  args:(string * Json.t) list option
+    -> cat:string list option
+    -> name:string
+    -> data
 end
 
 val start : t option -> (unit -> Event.data) -> Event.t option