Add an optional parameter to kill-all-local-variables

* doc/lispref/variables.texi (Creating Buffer-Local): Document it
(bug#30204).

* src/buffer.c (Fkill_all_local_variables): Allow killing
permanent local variables, too.

* src/print.c (temp_output_buffer_setup):
* src/minibuf.c (set_minibuffer_mode): Adjust callers.

1 files changed, 7 insertions, 5 deletions

diff --git a/src/buffer.c b/src/buffer.c
index 4eb7ab6d6ba..c5b2736ae3a 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -2805,7 +2805,7 @@ current buffer is cleared.  */)
 }
 
 DEFUN ("kill-all-local-variables", Fkill_all_local_variables,
-       Skill_all_local_variables, 0, 0, 0,
+       Skill_all_local_variables, 0, 1, 0,
        doc: /* Switch to Fundamental mode by killing current buffer's local variables.
 Most local variable bindings are eliminated so that the default values
 become effective once more.  Also, the syntax table is set from
@@ -2816,18 +2816,20 @@ This function also forces redisplay of the mode line.
 Every function to select a new major mode starts by
 calling this function.
 
-As a special exception, local variables whose names have
-a non-nil `permanent-local' property are not eliminated by this function.
+As a special exception, local variables whose names have a non-nil
+`permanent-local' property are not eliminated by this function.  If
+the optional KILL-PERMANENT argument is non-nil, clear out these local
+variables, too.
 
 The first thing this function does is run
 the normal hook `change-major-mode-hook'.  */)
-  (void)
+  (Lisp_Object kill_permanent)
 {
   run_hook (Qchange_major_mode_hook);
 
   /* Actually eliminate all local bindings of this buffer.  */
 
-  reset_buffer_local_variables (current_buffer, 0);
+  reset_buffer_local_variables (current_buffer, !NILP (kill_permanent));
 
   /* Force mode-line redisplay.  Useful here because all major mode
      commands call this function.  */