Better stack traces

Signed-off-by: Nicolás Ojeda Bär <n.oje.bar@gmail.com>

src/dune_lang/ordered_set_lang.ml

@@ -411,7 +411,13 @@ module Unexpanded = struct
             let* sexp =
               let* path = expand_template fn ~mode:Single in
               let path = Value.to_path path ?error_loc:(Some loc) ~dir in
-              Action_builder.read_sexp path
+              Action_builder.push_stack_frame
+                ~human_readable_description:(fun () ->
+                  Pp.textf
+                    "(:include %s) at %s"
+                    (Path.to_string path)
+                    (Loc.to_file_colon_line loc))
+                (fun () -> Action_builder.read_sexp path)
             in
             let t = Decoder.parse decode context sexp in
             expand t.ast ~allow_include:false

src/dune_lang/ordered_set_lang_intf.ml

@@ -46,6 +46,11 @@ module type Action_builder = sig
   val all : 'a t list -> 'a list t
   val read_sexp : Path.t -> Dune_sexp.Ast.t t
 
+  val push_stack_frame
+    :  human_readable_description:(unit -> User_message.Style.t Pp.t)
+    -> (unit -> 'a t)
+    -> 'a t
+
   module O : sig
     val ( let+ ) : 'a t -> ('a -> 'b) -> 'b t
     val ( and+ ) : 'a t -> 'b t -> ('a * 'b) t

src/dune_rules/ml_sources.ml

@@ -469,9 +469,6 @@ let make
   ~include_subdirs:(loc_include_subdirs, (include_subdirs : Dune_file.Include_subdirs.t))
   ~dirs
   =
-  Memo.push_stack_frame ~human_readable_description:(fun () ->
-    Pp.textf "Finding source files in directory %s" (Path.Build.to_string dir))
-  @@ fun () ->
   let+ modules_of_stanzas =
     let modules =
       let dialects = Dune_project.dialects project in

src/dune_rules/modules_field_evaluator.ml

@@ -405,7 +405,7 @@ let eval
   =
   let open Memo.O in
   Memo.push_stack_frame ~human_readable_description:(fun () ->
-    Pp.textf "Evaluating modules field in directory %s" (Path.Build.to_string src_dir))
+    Pp.textf "(modules) field at %s" (Loc.to_file_colon_line stanza_loc))
   @@ fun () ->
   let* modules0 =
     eval0 ~expander ~loc:stanza_loc ~all_modules ~standard:all_modules settings.modules

test/blackbox-tests/test-cases/modules-expansion.t

@@ -151,10 +151,9 @@ Interaction with `(include_subdirs)` when the dependencies are in the subtree:
 
   $ dune build --display short
   Error: Dependency cycle between:
-     Finding source files in directory _build/default
+     (modules) field at dune:2
   -> %{read-lines:gen/lst} at dune:4
-  -> Evaluating modules field in directory _build/default
-  -> Finding source files in directory _build/default
+  -> (modules) field at dune:2
   [1]
 
 Let's move the gen subdirectory out of the hierarchy:
@@ -197,9 +196,9 @@ appears. We need to handle this cycle gracefully and report it to the user.
 
   $ dune exec ./mod.exe
   Error: Dependency cycle between:
-     Finding source files in directory _build/default
-  -> Evaluating modules field in directory _build/default
-  -> Finding source files in directory _build/default
+     (modules) field at dune:2
+  -> (:include _build/default/lst) at dune:2
+  -> (modules) field at dune:2
   [1]
 
 Let's do one example with a generated source file: