bug#54346: persist-save doesn't persist variables when the value is set to the default

[Gulshan Singh <gsingh2011@gmail.com>]

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Hi,

I cloned the upstream project [1] and created a merge request [2]
there. The fix deletes the persist file when it gets set back to the
default value, and it modifies a test to verify this behavior. I've
attached the same patch here (created with `git format-patch HEAD^`, I
haven't submitted a patch here before so let me know if this is the
correct way to do this).

I'm a little confused though, I see that on the externals/persist
branch [3] there is a commit that does not exist on the upstream
GitLab project. Why is this the case? Should I actually be making a
patch off of the externals/persist branch?

[1] https://gitlab.com/phillord/persist/
[2] https://gitlab.com/phillord/persist/-/merge_requests/1
[3] https://git.savannah.gnu.org/cgit/emacs/elpa.git/log/?h=externals/persist

On Sun, Apr 10, 2022 at 5:17 AM Lars Ingebrigtsen <larsi@gnus.org> wrote:
>
> Gulshan Singh <gsingh2011@gmail.com> writes:
>
> > If either of these solutions make sense, or if Phillip has any other
> > suggestions, I'd be happy to make the fix myself if that would be
> > easier.
>
> Yes, that'd be great (and post the patch here).
>
> --
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no

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From b0496a5a8848d11233f241f6b78f00f1536410d6 Mon Sep 17 00:00:00 2001
From: Gulshan Singh <gsingh2011@gmail.com>
Date: Sun, 10 Apr 2022 12:13:31 -0700
Subject: [PATCH] Delete persist file when symbol is set to default value

---
 persist.el            | 26 ++++++++++++++------------
 test/persist-tests.el |  3 +++
 2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/persist.el b/persist.el
index 091e428..8b645ea 100644
--- a/persist.el
+++ b/persist.el
@@ -132,18 +132,20 @@ variables persist automatically when Emacs exits."
   (unless (persist--persistant-p symbol)
     (error (format
             "Symbol %s is not persistant" symbol)))
-  (unless (equal (symbol-value symbol)
-                 (persist-default symbol))
-    (let ((dir-loc
-           (file-name-directory
-            (persist--file-location symbol))))
-      (unless (file-exists-p dir-loc)
-        (mkdir dir-loc)))
-    (with-temp-buffer
-      (print (symbol-value symbol) (current-buffer))
-      (write-region (point-min) (point-max)
-                    (persist--file-location symbol)
-                    nil 'quiet))))
+  (let ((symbol-file-loc (persist--file-location symbol)))
+    (if (equal (symbol-value symbol)
+               (persist-default symbol))
+        (when (file-exists-p symbol-file-loc)
+          (delete-file symbol-file-loc))
+      (let ((dir-loc
+             (file-name-directory symbol-file-loc)))
+        (unless (file-exists-p dir-loc)
+          (mkdir dir-loc))
+        (with-temp-buffer
+          (print (symbol-value symbol) (current-buffer))
+          (write-region (point-min) (point-max)
+                        symbol-file-loc
+                        nil 'quiet))))))
 
 (defun persist-default (symbol)
   "Return the default value for SYMBOL."
diff --git a/test/persist-tests.el b/test/persist-tests.el
index 9fa406f..b6645a9 100644
--- a/test/persist-tests.el
+++ b/test/persist-tests.el
@@ -44,6 +44,9 @@
        (with-temp-buffer
          (insert-file-contents (persist--file-location sym))
          (buffer-string))))
+     (set sym 10)
+     (persist-save sym)
+     (should-not (file-exists-p (persist--file-location sym)))
      (should-error
       (persist-save 'fred)))))
 
-- 
2.35.1.1178.g4f1659d476-goog