bug#38179: 26.1; clone-buffer globally unsets locally void variable

[Braun Gábor]

Hi,

* Idea:

Let's create a test, which sets the default value of a variable but
undefines it locally in some buffer.  Then clone the buffer and check
that the default value of the variable is unchanged, and it is locally
undefined in both the original buffer and the clone.

* Recipe to reproduce the bug:

Create test.el with the following content
(there is no empty line in the file):

(ert-deftest clone-buffer-unbound-local-variable ()
  "Test `clone-buffer' on locally unbound variables."
  (let ((var (make-symbol "test")))
    (set-default var 1)
    (with-temp-buffer
      (makunbound (make-local-variable var))
      (let ((buffer (current-buffer))
            (clone (clone-buffer)))
        (unwind-protect
            (progn
              (should (eq (default-value var) 1))
              (should-not (boundp var))
              (with-current-buffer clone
                (should-not (boundp var))))
          (when (buffer-live-p clone)
            (kill-buffer clone)))))))

Run the test:

$ emacs -Q -batch -l ert -l test.el -f ert-run-tests-batch-and-exit

Running 1 tests (2019-11-12 15:55:39+0100)
Test clone-buffer-unbound-local-variable backtrace:
  signal(void-variable (test))
  apply(signal (void-variable (test)))
  (setq value-2 (apply fn-0 args-1))
  (unwind-protect (setq value-2 (apply fn-0 args-1)) (setq form-descri
  (if (unwind-protect (setq value-2 (apply fn-0 args-1)) (setq form-de
  (let (form-description-4) (if (unwind-protect (setq value-2 (apply f
  (let ((value-2 'ert-form-evaluation-aborted-3)) (let (form-descripti
  (let* ((fn-0 (function eq)) (args-1 (condition-case err (let ((signa
  (progn (let* ((fn-0 (function eq)) (args-1 (condition-case err (let
  (unwind-protect (progn (let* ((fn-0 (function eq)) (args-1 (conditio
  (let ((buffer (current-buffer)) (clone (clone-buffer))) (unwind-prot
  (progn (makunbound (make-local-variable var)) (let ((buffer (current
  (unwind-protect (progn (makunbound (make-local-variable var)) (let (
  (save-current-buffer (set-buffer temp-buffer) (unwind-protect (progn
  (let ((temp-buffer (generate-new-buffer " *temp*"))) (save-current-b
  (let ((var (make-symbol "test"))) (set-default var 1) (let ((temp-bu
  (lambda nil (let ((var (make-symbol "test"))) (set-default var 1) (l
  ert--run-test-internal(#s(ert--test-execution-info :test #s(ert-test
  ert-run-test(#s(ert-test :name clone-buffer-unbound-local-variable :
  ert-run-or-rerun-test(#s(ert--stats :selector t :tests [#s(ert-test
  ert-run-tests(t #f(compiled-function (event-type &rest event-args) #
  ert-run-tests-batch(nil)
  ert-run-tests-batch-and-exit()
  command-line-1(("-l" "ert" "-l" "test.el" "-f" "ert-run-tests-batch-
  command-line()
  normal-top-level()
Test clone-buffer-unbound-local-variable condition:
    (void-variable test)
   FAILED  1/1  clone-buffer-unbound-local-variable

Ran 1 tests, 0 results as expected, 1 unexpected (2019-11-12 15:55:40+0100)

1 unexpected results:
   FAILED  clone-buffer-unbound-local-variable


The test failed but it should pass.

* Patch to fix the problem

When copying buffer local variables, make even undefined variables
buffer local before undefining them:

--- lisp/simple.el
+++ lisp/simple.el
@@ -8535,7 +8535,7 @@
       (mapc (lambda (v)
              (condition-case ()        ;in case var is read-only
                  (if (symbolp v)
-                     (makunbound v)
+                     (makunbound (make-local-variable v))
                    (set (make-local-variable (car v)) (cdr v)))
                (error nil)))
            lvars)

Best wishes,

     Gábor


In GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.4)
 of 2019-02-03, modified by Debian built on zam904
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description:     Debian GNU/Linux 10 (buster)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Ran 1 tests, 0 results were as expected, 1 unexpected
scroll-up-command: End of buffer

Configured using:
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