Lib: expose API to attached and retrieve js errors to/from ocaml exce…

…ptions (#1071)

CHANGES.md

@@ -1,6 +1,7 @@
 # ??? (??) - ??
 ## Features/Changes
 * Compiler: complete support for OCaml 4.12
+* Lib: expose API to attached and retrieve js errors to/from ocaml exceptions
 
 # 3.8.0 (2020-10-21) - London
 ## Features/Changes

lib/js_of_ocaml/js.ml

@@ -673,6 +673,10 @@ let _ = Callback.register_exception "jsError" (Error (Unsafe.obj [||]))
 
 let raise_js_error : error t -> 'a = Unsafe.js_expr "(function (exn) { throw exn })"
 
+external exn_with_js_backtrace : exn -> force:bool -> exn = "caml_exn_with_js_backtrace"
+
+external js_error_of_exn : exn -> error t opt = "caml_js_error_of_exception"
+
 class type json =
   object
     method parse : js_string t -> 'a meth

lib/js_of_ocaml/js.mli

@@ -685,6 +685,19 @@ val string_of_error : error t -> string
 
 val raise_js_error : error t -> 'a
 
+val exn_with_js_backtrace : exn -> force:bool -> exn
+(** Attach a JavasScript error to an OCaml exception.  if [force = false] and a
+    JavasScript error is already attached, it will do nothing. This function is useful to
+    store and retrieve information about JavaScript stack traces.
+
+    Attaching JavasScript errors will happen automatically when compiling with
+    [--enable with-js-error].
+*)
+
+val js_error_of_exn : exn -> error t opt
+(** Extract a JavaScript error attached to an OCaml exception, if any.  This is useful to
+    inspect an eventual stack strace, especially when sourcemap is enabled. *)
+
 exception Error of error t
 (** The [Error] exception wrap javascript exceptions when caught by OCaml code.
       In case the javascript exception is not an instance of javascript [Error],

lib/js_of_ocaml/js_of_ocaml_stubs.c

@@ -32,6 +32,10 @@ void caml_create_file () {
   fprintf(stderr, "Unimplemented Javascript primitive caml_create_file!\n");
   exit(1);
 }
+void caml_exn_with_js_backtrace () {
+  fprintf(stderr, "Unimplemented Javascript primitive caml_exn_with_js_backtrace!\n");
+  exit(1);
+}
 void caml_int64_create_lo_mi_hi () {
   fprintf(stderr, "Unimplemented Javascript primitive caml_int64_create_lo_mi_hi!\n");
   exit(1);
@@ -48,6 +52,10 @@ void caml_js_equals () {
   fprintf(stderr, "Unimplemented Javascript primitive caml_js_equals!\n");
   exit(1);
 }
+void caml_js_error_of_exception () {
+  fprintf(stderr, "Unimplemented Javascript primitive caml_js_error_of_exception!\n");
+  exit(1);
+}
 void caml_js_eval_string () {
   fprintf(stderr, "Unimplemented Javascript primitive caml_js_eval_string!\n");
   exit(1);