Backport: Add module test for edge case.

This backports commit 6355a3ec62 from master.  Since the bug isn’t
present in emacs-27, just backport the test case.

* test/data/emacs-module/mod-test.c
(Fmod_test_invalid_store_copy): New test module function.
(emacs_module_init): Export it.

* test/src/emacs-module-tests.el
(module--test-assertions--load-non-live-object-with-global-copy):
New unit test.

2 files changed, 36 insertions, 0 deletions

diff --git a/test/data/emacs-module/mod-test.c b/test/data/emacs-module/mod-test.c
index 8dc9ff144af..f6c1c7cf3d2 100644
--- a/test/data/emacs-module/mod-test.c
+++ b/test/data/emacs-module/mod-test.c
@@ -296,6 +296,22 @@ Fmod_test_invalid_load (emacs_env *env, ptrdiff_t nargs, emacs_value *args,
   return invalid_stored_value;
 }
 
+/* The next function works in conjunction with the two previous ones.
+   It stows away a copy of the object created by
+   `Fmod_test_invalid_store' in a global reference.  Module assertions
+   should still detect the invalid load of the local reference.  */
+
+static emacs_value global_copy_of_invalid_stored_value;
+
+static emacs_value
+Fmod_test_invalid_store_copy (emacs_env *env, ptrdiff_t nargs,
+                              emacs_value *args, void *data)
+{
+  emacs_value local = Fmod_test_invalid_store (env, 0, NULL, NULL);
+  return global_copy_of_invalid_stored_value
+         = env->make_global_ref (env, local);
+}
+
 /* An invalid finalizer: Finalizers are run during garbage collection,
    where Lisp code can’t be executed.  -module-assertions tests for
    this case.  */
@@ -559,6 +575,8 @@ emacs_module_init (struct emacs_runtime *ert)
   DEFUN ("mod-test-vector-fill", Fmod_test_vector_fill, 2, 2, NULL, NULL);
   DEFUN ("mod-test-vector-eq", Fmod_test_vector_eq, 2, 2, NULL, NULL);
   DEFUN ("mod-test-invalid-store", Fmod_test_invalid_store, 0, 0, NULL, NULL);
+  DEFUN ("mod-test-invalid-store-copy", Fmod_test_invalid_store_copy, 0, 0,
+         NULL, NULL);
   DEFUN ("mod-test-invalid-load", Fmod_test_invalid_load, 0, 0, NULL, NULL);
   DEFUN ("mod-test-invalid-finalizer", Fmod_test_invalid_finalizer, 0, 0,
          NULL, NULL);
diff --git a/test/src/emacs-module-tests.el b/test/src/emacs-module-tests.el
index 6f14d4f7fa3..de707a4243a 100644
--- a/test/src/emacs-module-tests.el
+++ b/test/src/emacs-module-tests.el
@@ -270,6 +270,24 @@ must evaluate to a regular expression string."
     (mod-test-invalid-store)
     (mod-test-invalid-load)))
 
+(ert-deftest module--test-assertions--load-non-live-object-with-global-copy ()
+  "Check that -module-assertions verify that non-live objects aren't accessed.
+This differs from `module--test-assertions-load-non-live-object'
+in that it stows away a global reference.  The module assertions
+should nevertheless detect the invalid load."
+  (skip-unless (or (file-executable-p mod-test-emacs)
+                   (and (eq system-type 'windows-nt)
+                        (file-executable-p (concat mod-test-emacs ".exe")))))
+  ;; This doesn't yet cause undefined behavior.
+  (should (eq (mod-test-invalid-store-copy) 123))
+  (module--test-assertion (rx "Emacs value not found in "
+                              (+ digit) " values of "
+                              (+ digit) " environments\n")
+    ;; Storing and reloading a local value causes undefined behavior,
+    ;; which should be detected by the module assertions.
+    (mod-test-invalid-store-copy)
+    (mod-test-invalid-load)))
+
 (ert-deftest module--test-assertions--call-emacs-from-gc ()
   "Check that -module-assertions prevents calling Emacs functions
 during garbage collection."