* src/data.c (Fmake_local_variable): Fix bug#34318

Revert part of ed962f2b8a.

* test/src/data-tests.el (data-tests-make-local-forwarded-var):
Add corresponding test.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/data.c b/src/data.c
index 571114802a1..ed6dedbe243 100644
--- a/src/data.c
+++ b/src/data.c
@@ -1954,6 +1954,16 @@ Instead, use `add-hook' and specify t for the LOCAL argument.  */)
 	(current_buffer,
 	 Fcons (Fcons (variable, XCDR (blv->defcell)),
 		BVAR (current_buffer, local_var_alist)));
+
+      /* If the symbol forwards into a C variable, then load the binding
+         for this buffer now, to preserve the invariant that forwarded
+         variables must always hold the value corresponding to the
+         current buffer (they are swapped eagerly).
+         Otherwise, if C code modifies the variable before we load the
+         binding in, then that new value would clobber the default binding
+         the next time we unload it.  See bug#34318.  */
+      if (blv->fwd)
+        swap_in_symval_forwarding (sym, blv);
     }
 
   return variable;