feat: `caml_fatal_error` on misuse of serialize functions

These should only be called from within a `caml_output_*` entrypoint context.

Signed-off-by: Alexander Skvortsov <sasha.skvortsov109@gmail.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/runtime/extern.c b/runtime/extern.c
index 7ca8d18a89..fe0e5a1cee 100644
--- a/runtime/extern.c
+++ b/runtime/extern.c
@@ -145,6 +145,13 @@ static struct caml_extern_state* prepare_extern_state (void)
 static struct caml_extern_state* get_extern_state (void)
 {
   Caml_check_caml_state();
+
+  if (Caml_state->extern_state == NULL)
+    caml_fatal_error (
+      "extern_state not initialized:"
+      "this function can only be called from a `caml_output_*` entrypoint."
+    );
+
   return Caml_state->extern_state;
 }