bug#21355: 24.4; Loading a theme causes session customizations to be saved

[Mauro Aranda <maurooaranda@gmail.com>]

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I attach a patch with three tests that demonstrate the bug.

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From cd0266909efd6c2f6763ef9aff18f26149651a8a Mon Sep 17 00:00:00 2001
From: Mauro Aranda <maurooaranda@gmail.com>
Date: Tue, 8 Sep 2020 09:23:40 -0300
Subject: [PATCH] Add tests demonstrating Bug#21355

* test/lisp/custom-resources/custom--test-saved-value-theme.el: A new
theme.
* test/lisp/custom-tests.el
(custom-test-no-saved-value-after-enabling-theme)
(custom-test-no-saved-value-after-enabling-theme-2)
(custom-test-no-saved-value-after-customizing-option): New tests.
---
 .../custom--test-saved-value-theme.el         |  11 ++
 test/lisp/custom-tests.el                     | 111 ++++++++++++++++++
 2 files changed, 122 insertions(+)
 create mode 100644 test/lisp/custom-resources/custom--test-saved-value-theme.el

diff --git a/test/lisp/custom-resources/custom--test-saved-value-theme.el b/test/lisp/custom-resources/custom--test-saved-value-theme.el
new file mode 100644
index 0000000000..eea1547916
--- /dev/null
+++ b/test/lisp/custom-resources/custom--test-saved-value-theme.el
@@ -0,0 +1,11 @@
+;;; custom--test-saved-value-theme.el -- A test theme to test Bug#21355.  -*- lexical-binding:t -*-
+
+(deftheme custom--test-saved-value
+  "A test theme to test against saving session customizations by mistake.")
+
+(custom-theme-set-variables
+ 'custom--test-saved-value
+ '(custom--test-bug-21355-before 'before)
+ '(custom--test-bug-21355-after 'after))
+
+(provide-theme 'custom--test-saved-value)
diff --git a/test/lisp/custom-tests.el b/test/lisp/custom-tests.el
index cabbf861f1..9cf25be87a 100644
--- a/test/lisp/custom-tests.el
+++ b/test/lisp/custom-tests.el
@@ -147,4 +147,115 @@ custom-test-show-comment-preserves-changes
                                (widget-apply field :value-to-internal origvalue)
                                "bar"))))))
 
+;; The following three tests demonstrate Bug#21355.
+;; In this one, we set an user option for the current session,
+;; then we enable a theme that doesn't have a setting for it, and we end up
+;; with a 'saved-value property, and the caar of the 'theme-value property
+;; is 'user, which means we would end up saving a setting that was meant
+;; for the current session only.
+(ert-deftest custom-test-no-saved-value-after-enabling-theme ()
+  "Test that we don't record a saved-value property when we shouldn't."
+  :expected-result :failed
+  (let ((custom-theme-load-path
+         `(,(expand-file-name
+	     "custom-resources"
+	     (expand-file-name "lisp" (getenv "EMACS_TEST_DIRECTORY"))))))
+    (customize-option 'mark-ring-max)
+    (let* ((field (seq-find (lambda (widget)
+                              (eq mark-ring-max (widget-value widget)))
+                            widget-field-list))
+           (parent (widget-get field :parent)))
+      ;; We move to the editable widget, modify the value and save it.
+      (goto-char (widget-field-text-end field))
+      (insert "0")
+      (widget-apply parent :custom-set)
+      ;; Just setting for the current session should not store a 'saved-value
+      ;; property.
+      (should-not (get 'mark-ring-max 'saved-value))
+      ;; Now we enable and disable our test theme.
+      (load-theme 'custom--test 'no-confirm)
+      (disable-theme 'custom--test)
+      ;; Since the user customized the option, this happens.
+      (should (eq (caar (get 'mark-ring-max 'theme-value)) 'user))
+      ;; But this should not happen: the 'saved-value property should still
+      ;; be nil.
+      (should-not (get 'mark-ring-max 'saved-value)))))
+
+;; In this second test, we load a theme that has a setting for the user option
+;; above.  Regardless, the same happens: we end up with a non-nil saved-value
+;; property, and a user setting active in the 'theme-value property, which
+;; means we could inadvertently save the session setting in the custom-file.
+(defcustom custom--test-bug-21355-before 'foo
+  "User option for `custom-test-no-saved-value-after-enabling-theme-2'."
+  :type 'symbol :group 'emacs)
+
+(ert-deftest custom-test-no-saved-value-after-enabling-theme-2 ()
+  "Test that we don't record a saved-value property when we shouldn't."
+  :expected-result :failed
+  (let ((custom-theme-load-path
+         `(,(file-name-as-directory (expand-file-name
+	     "custom-resources"
+	     (expand-file-name "lisp" (getenv "EMACS_TEST_DIRECTORY")))))))
+    (customize-option 'custom--test-bug-21355-before)
+    (let* ((field (seq-find (lambda (widget)
+                              (eq custom--test-bug-21355-before (widget-value widget)))
+                            widget-field-list))
+           (parent (widget-get field :parent)))
+      ;; We move to the editable widget, modify the value and save it.
+      (goto-char (widget-field-text-end field))
+      ;; Modify the value and save it.
+      (insert "bar")
+      (widget-apply parent :custom-set)
+      ;; Just setting for the current session should not store a 'saved-value
+      ;; property.
+      (should-not (get 'custom--test-bug-21355-before 'saved-value))
+      ;; Now we load our test theme, which has a setting for
+      ;; `custom--test-user-option'.
+      (load-theme 'custom--test-saved-value 'no-confirm)
+      (enable-theme 'custom--test-saved-value)
+      ;; We still shouldn't have a non-nil 'saved-value property, even if
+      ;; the theme has a setting for the variable.
+      ;; Since the user customized the option, this happens.
+      (should (eq (caar (get 'custom--test-bug-21355-before 'theme-value))
+                  'user))
+      ;; But this should not happen.
+      (should-not (get 'custom--test-bug-21355-before 'saved-value)))))
+
+;; And in this test we check that stashing a theme value for a not yet defined
+;; option works, but that later on if the user customizes the option for the
+;; current session, we might save the theme setting in the custom file.
+(ert-deftest custom-test-no-saved-value-after-customizing-option ()
+  "Test that we don't have a non-nil saved-value after customizing an option."
+  :expected-result :failed
+  (let ((custom-theme-load-path
+         `(,(file-name-as-directory (expand-file-name
+	     "custom-resources"
+	     (expand-file-name "lisp" (getenv "EMACS_TEST_DIRECTORY")))))))
+    ;; Check that we correctly stashed the value.
+    (should (and (not (boundp 'custom--test-bug-21355-after))
+                 (eq (eval
+                      (car (get 'custom--test-bug-21355-after 'saved-value)))
+                     'after)))
+    ;; Now Emacs finds the defcustom.
+    (defcustom custom--test-bug-21355-after 'initially "..."
+      :type 'symbol :group 'emacs)
+    ;; And we used the stashed value correctly.
+    (should (and (boundp 'custom--test-bug-21355-after)
+                 (eq custom--test-bug-21355-after 'after)))
+    ;; Now we customize it.
+    (customize-option 'custom--test-bug-21355-after)
+    (let* ((field (seq-find (lambda (widget)
+                              (eq custom--test-bug-21355-after (widget-value widget)))
+                            widget-field-list))
+           (parent (widget-get field :parent)))
+      ;; We move to the editable widget, modify the value and save it.
+      (goto-char (widget-field-text-end field))
+      (insert "bar")
+      (widget-apply parent :custom-set)
+      ;; The user customized the variable, so this should happen.
+      (should (eq (caar (get 'custom--test-bug-21355-after 'theme-value))
+                  'user))
+      ;; But it was only for the current session, so this should not happen.
+      (should-not (get 'custom--test-bug-21355-after 'saved-value)))))
+
 ;;; custom-tests.el ends here
-- 
2.28.0