Fix: (activities-tabs-mode) When re-enabled without being disabled

Fixes #7.

README.org

@@ -120,7 +120,8 @@ When option ~activities-bookmark-store~ is enabled, an Emacs bookmark is stored
 
 ** v0.3.1-pre
 
-Nothing new yet.
+*Fixes*
++ Handle case in which ~activities-tabs-mode~ is enabled again without having been disabled (which caused an error in ~tab-bar-mode~). ([[https://github.com/alphapapa/activities.el/issues/7][#7]])
 
 ** v0.3
 

activities-tabs.el

@@ -76,13 +76,21 @@ accordingly."
           (advice-add #'activities-resume :before #'activities-tabs-before-resume)
           (pcase-dolist (`(,symbol . ,function) override-map)
             (advice-add symbol :override function))
-          (setf activities-tabs-tab-bar-tab-face-function-original tab-bar-tab-face-function
-                tab-bar-tab-face-function #'activities-tabs--tab-bar-tab-face-function))
+          ;; The mode command could be called to activate the mode
+          ;; when it already is, in which case we must not swap the
+          ;; tab-face-function again, which would discard the actual,
+          ;; original value.  (IOW, this must be idempotent.)
+          ;; TODO: A way to prevent modes' body forms from being
+          ;; reevaluated when they are already active.
+          (unless activities-tabs-tab-bar-tab-face-function-original
+            (setf activities-tabs-tab-bar-tab-face-function-original tab-bar-tab-face-function
+                  tab-bar-tab-face-function #'activities-tabs--tab-bar-tab-face-function)))
       (advice-remove #'activities-resume #'activities-tabs-before-resume)
       (pcase-dolist (`(,symbol . ,function) override-map)
         (advice-remove symbol function))
-      (setf tab-bar-tab-face-function activities-tabs-tab-bar-tab-face-function-original
-            activities-tabs-tab-bar-tab-face-function-original nil))))
+      (when activities-tabs-tab-bar-tab-face-function-original
+        (setf tab-bar-tab-face-function activities-tabs-tab-bar-tab-face-function-original
+              activities-tabs-tab-bar-tab-face-function-original nil)))))
 
 ;;;; Functions
 

activities.info

@@ -327,7 +327,11 @@ File: README.info,  Node: v031-pre,  Next: v03,  Up: Changelog
 4.1 v0.3.1-pre
 ==============
 
-Nothing new yet.
+*Fixes*
+   • Handle case in which ‘activities-tabs-mode’ is enabled again
+     without having been disabled (which caused an error in
+     ‘tab-bar-mode’).  (#7
+     (https://github.com/alphapapa/activities.el/issues/7))
 
 
 File: README.info,  Node: v03,  Next: v02,  Prev: v031-pre,  Up: Changelog
@@ -409,12 +413,12 @@ Node: Bookmarks8500
 Node: FAQ8852
 Node: Changelog11928
 Node: v031-pre12135
-Node: v0312250
-Node: v0212644
-Node: v01313136
-Node: v01213285
-Node: v01113462
-Node: v0113625
+Node: v0312464
+Node: v0212858
+Node: v01313350
+Node: v01213499
+Node: v01113676
+Node: v0113839
 
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