fix(fsevents): correctly handle unknown events

CHANGES.md

@@ -1,6 +1,8 @@
 3.5.0 (unreleased)
 ------------------
 
+- macOS: Handle unknown fsevents without crashing (#6217, @rgrinberg)
+
 - Enable file watching on MacOS SDK < 10.13. (#6218, @rgrinberg)
 
 - Sandbox running cinaps actions starting from cinaps 1.1 (#6176, @rgrinberg)

src/dune_file_watcher/dune_file_watcher.ml

@@ -514,10 +514,9 @@ let fsevents ?exclusion_paths ~latency ~paths scheduler f =
   fsevents
 
 let fsevents_standard_event event path =
-  let action = Fsevents.Event.action event in
   let kind =
-    match action with
-    | Unknown -> Fs_memo_event.Unknown
+    match Fsevents.Event.action event with
+    | Rename | Unknown -> Fs_memo_event.Unknown
     | Create -> Created
     | Remove -> Deleted
     | Modify ->
@@ -540,7 +539,7 @@ let create_fsevents ?(latency = 0.2) ~(scheduler : Scheduler.t) () =
         else
           match Fsevents.Event.action event with
           | Remove -> None
-          | Unknown | Create | Modify ->
+          | Rename | Unknown | Create | Modify ->
             Option.map (Fs_sync.consume_event sync_table path) ~f:(fun id ->
                 Event.Sync id))
   in

src/fsevents/fsevents.ml

@@ -194,10 +194,11 @@ module Event = struct
   let kind t = kind t.flags
 
   type action =
-    | Unknown
     | Create
     | Remove
     | Modify
+    | Rename
+    | Unknown
 
   external action : Int32.t -> action = "dune_fsevents_action"
 
@@ -209,7 +210,8 @@ module Event = struct
       | Create -> "Create"
       | Remove -> "Remove"
       | Modify -> "Modify"
-      | Unknown -> "Unknown")
+      | Unknown -> "Unknown"
+      | Rename -> "Rename")
 
   let to_dyn t =
     let open Dyn in

src/fsevents/fsevents.mli

@@ -44,13 +44,13 @@ module Event : sig
   val kind : t -> kind
 
   type action =
+    | Create (* [path t] guaranteed to exist *)
+    | Remove (* [path t] guaranteed to be absent *)
+    | Modify (* [path t] guaranteed to exist *)
+    | Rename
     | Unknown
         (** multiple actions merged into one by debouncing or an uninformative
             "rename". inspect the FS to see what happened *)
-    | Create (* [path t] guaranteed to exist *)
-    | Remove (* [path t] guaranteed to be absent *)
-    | Modify
-  (* [path t] guaranteed to exist *)
 
   val dyn_of_action : action -> Dyn.t
 

src/fsevents/fsevents_stubs.c

@@ -270,24 +270,16 @@ CAMLprim value dune_fsevents_action(value v_flags) {
   CAMLlocal1(v_action);
 
   uint32_t flags = Int32_val(v_flags) & action_mask;
-  int count = __builtin_popcount(flags);
-
-  flags = Int32_val(v_flags);
-  if (count >= 2 || flags & kFSEventStreamEventFlagItemRenamed) {
-    // we don't bother tracking renamed acurately for now. macos makes it
-    // tricky by not telling is which path is created and which one is deleted.
-    // it is possible to reverse engineer this from the chain of inodes in the
-    // events, but it's also error prone as inodes can be reused. so for now, we
-    // avoid this is and treat renamed as unknown
+  if (flags & kFSEventStreamEventFlagItemCreated) {
     v_action = Val_int(0);
-  } else if (flags & kFSEventStreamEventFlagItemCreated) {
-    v_action = Val_int(1);
   } else if (flags & kFSEventStreamEventFlagItemRemoved) {
-    v_action = Val_int(2);
+    v_action = Val_int(1);
   } else if (flags & kFSEventStreamEventFlagItemModified) {
+    v_action = Val_int(2);
+  } else if (flags & kFSEventStreamEventFlagItemRenamed) {
     v_action = Val_int(3);
   } else {
-    caml_failwith("fsevents: unexpected event action");
+    v_action = Val_int(4);
   }
 
   CAMLreturn(v_action);