feature: trace some custom actions

bin/common.ml

@@ -1312,6 +1312,7 @@ let init_with_root ~(root : Workspace_root.t) (builder : Builder.t) =
             ; File_watcher
             ; Diagnostics
             ; Cram
+            ; Action
             ]
         | Some s ->
           String.split ~on:',' s

doc/changes/added/13265.md

@@ -0,0 +1 @@
+- Add trace events for custom actions (#13265, @rgrinberg)

src/action_ext/action_ext.ml

@@ -31,7 +31,10 @@ struct
 
     let action a ~ectx ~eenv =
       let open Fiber.O in
+      let start = Time.now () in
+      Dune_trace.emit Action (fun () -> Dune_trace.Event.Action.start ~name ~start);
       let+ () = action a ~ectx ~eenv in
+      Dune_trace.emit Action (fun () -> Dune_trace.Event.Action.finish ~name ~start);
       Done_or_more_deps.Done
     ;;
   end

src/action_ext/dune

@@ -1,3 +1,3 @@
 (library
  (name action_ext)
- (libraries dune_engine fiber stdune))
+ (libraries dune_engine dune_trace fiber stdune))

src/dune_trace/category.ml

@@ -18,6 +18,7 @@ type t =
   | Diagnostics
   | Log
   | Cram
+  | Action
 
 let all =
   [ Rpc
@@ -37,6 +38,7 @@ let all =
   ; Diagnostics
   ; Log
   ; Cram
+  ; Action
   ]
 ;;
 
@@ -58,6 +60,7 @@ let to_string = function
   | Diagnostics -> "diagnostics"
   | Log -> "log"
   | Cram -> "cram"
+  | Action -> "action"
 ;;
 
 let of_string =
@@ -91,5 +94,6 @@ module Set = Bit_set.Make (struct
       | Diagnostics -> 14
       | Log -> 15
       | Cram -> 16
+      | Action -> 17
     ;;
   end)

src/dune_trace/category.mli

@@ -16,6 +16,7 @@ type t =
   | Diagnostics
   | Log
   | Cram
+  | Action
 
 val to_string : t -> string
 val of_string : string -> t option

src/dune_trace/dune_trace.mli

@@ -19,6 +19,7 @@ module Category : sig
     | Diagnostics
     | Log
     | Cram
+    | Action
 
   val of_string : string -> t option
 end
@@ -165,6 +166,11 @@ module Event : sig
 
     val test : test:Path.t -> command list -> t
   end
+
+  module Action : sig
+    val start : name:string -> start:Time.t -> t
+    val finish : name:string -> start:Time.t -> t
+  end
 end
 
 module Out : sig

src/dune_trace/event.ml

@@ -569,3 +569,14 @@ module Cram = struct
     Event.instant ~args ~name:"cram" now Cram
   ;;
 end
+
+module Action = struct
+  let start ~name ~start =
+    Event.instant ~args:[ "name", Arg.string name ] ~name:"start" start Action
+  ;;
+
+  let finish ~name ~start =
+    let dur = Time.diff (Time.now ()) start in
+    Event.complete ~args:[ "name", Arg.string name ] ~name:"finish" ~start ~dur Action
+  ;;
+end