fix: ignore insignificant_changes by default

but introduce a --react-insignificant-changes to restore the old
behavior for anyone that needs it (to benchmark)

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

CHANGES.md

@@ -21,6 +21,10 @@
 - Fix handling of the `(deps)` field in `(test)` stanzas when there is an
   `.expected` file. (#5952, #5951, fixes #5950, @emillon)
 
+- Ignore insignificant filesystem events. This stops RPC in watch mode from
+  flashing errors when file system events such as changes in the `.git/`
+  directory occur. (#5953, @rgrinberg)
+
 3.3.1 (19-06-2022)
 ------------------
 

bin/common.ml

@@ -49,6 +49,7 @@ type t =
   ; cache_debug_flags : Dune_engine.Cache_debug_flags.t
   ; report_errors_config : Dune_engine.Report_errors_config.t
   ; require_dune_project_file : bool
+  ; insignificant_changes : [ `React | `Ignore ]
   }
 
 let capture_outputs t = t.capture_outputs
@@ -75,6 +76,8 @@ let rpc t = Lazy.force t.rpc
 
 let stats t = t.stats
 
+let insignificant_changes t = t.insignificant_changes
+
 let set_print_directory t b = { t with no_print_directory = not b }
 
 let set_promote t v = { t with promote = Some v }
@@ -977,6 +980,17 @@ let term ~default_root_is_cwd =
              $(b,twice) - report each error twice: once as soon as the error \
              is discovered and then again at the end of the build, in a \
              deterministic order.")
+  and+ react_to_insignificant_changes =
+    Arg.(
+      value & flag
+      & info
+          [ "react-to-insignificant-changes" ]
+          ~doc:
+            "react to insignificant file system changes; this is only useful \
+             for benchmarking dune")
+  in
+  let insignificant_changes =
+    if react_to_insignificant_changes then `React else `Ignore
   in
   let build_dir = Option.value ~default:default_build_dir build_dir in
   let root =
@@ -1032,6 +1046,7 @@ let term ~default_root_is_cwd =
   ; cache_debug_flags
   ; report_errors_config
   ; require_dune_project_file
+  ; insignificant_changes
   }
 
 let term_with_default_root_is_cwd = term ~default_root_is_cwd:true

bin/common.mli

@@ -24,6 +24,8 @@ val default_target : t -> Arg.Dep.t
 
 val prefix_target : t -> string -> string
 
+val insignificant_changes : t -> [ `React | `Ignore ]
+
 (** [init] executes sequence of side-effecting actions to initialize Dune's
     working environment based on the options determined in a [Common.t]
     record.contents.

bin/import.ml

@@ -128,15 +128,17 @@ module Scheduler = struct
   let go ~(common : Common.t) ~config:dune_config f =
     let stats = Common.stats common in
     let config =
-      Dune_config.for_scheduler dune_config stats ~insignificant_changes:`React
+      let insignificant_changes = Common.insignificant_changes common in
+      Dune_config.for_scheduler dune_config stats ~insignificant_changes
     in
     Scheduler.Run.go config ~on_event:(on_event dune_config) f
 
   let go_with_rpc_server_and_console_status_reporting ~(common : Common.t)
       ~config:dune_config run =
     let stats = Common.stats common in
     let config =
-      Dune_config.for_scheduler dune_config stats ~insignificant_changes:`React
+      let insignificant_changes = Common.insignificant_changes common in
+      Dune_config.for_scheduler dune_config stats ~insignificant_changes
     in
     let file_watcher = Common.file_watcher common in
     let rpc = Common.rpc common in