(describe-variable-custom-version-info): New function to return

variable's version or package version note.
(describe-variable): Use it, display result.

1 files changed, 37 insertions, 8 deletions

diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index f62fadc22b5..bf57824dcf0 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -456,6 +456,28 @@ If ANY-SYMBOL is non-nil, don't insist the symbol be bound."
               (and (or any-symbol (boundp sym)) sym)))))
       0))
 
+(defun describe-variable-custom-version-info (variable)
+  (let ((custom-version (get variable 'custom-version))
+        (cpv (get variable 'custom-package-version))
+        (output nil))
+    (if custom-version
+        (setq output
+              (format "This variable was introduced, or its default value was changed, in\nversion %s of Emacs.\n"
+                      custom-version))
+      (when cpv
+        (let* ((package (car-safe cpv))
+               (version (car (cdr-safe cpv)))
+               (pkg-versions (assq package customize-package-emacs-version-alist))
+               (emacsv (cdr (assoc version pkg-versions))))
+          (if (and package version)
+              (setq output
+                    (format (concat "This variable was introduced, or its default value was changed, in\nversion %s of the %s package"
+                                    (if emacsv
+                                        (format " that is part of Emacs %s" emacsv))
+                                    ".\n")
+                            version package))))))
+    output))
+
 ;;;###autoload
 (defun describe-variable (variable &optional buffer frame)
   "Display the full documentation of VARIABLE (a symbol).
@@ -646,16 +668,23 @@ it is displayed along with the global value."
               (with-current-buffer standard-output
                 (insert (or doc "Not documented as a variable."))))
             ;; Make a link to customize if this variable can be customized.
-            (if (custom-variable-p variable)
-                (let ((customize-label "customize"))
+            (when (custom-variable-p variable)
+              (let ((customize-label "customize"))
+                (terpri)
+                (terpri)
+                (princ (concat "You can " customize-label " this variable."))
+                (with-current-buffer standard-output
+                  (save-excursion
+                    (re-search-backward
+                     (concat "\\(" customize-label "\\)") nil t)
+                    (help-xref-button 1 'help-customize-variable variable))))
+              ;; Note variable's version or package version
+              (let ((output (describe-variable-custom-version-info variable)))
+                (when output
                   (terpri)
                   (terpri)
-                  (princ (concat "You can " customize-label " this variable."))
-                  (with-current-buffer standard-output
-                    (save-excursion
-                      (re-search-backward
-                       (concat "\\(" customize-label "\\)") nil t)
-                      (help-xref-button 1 'help-customize-variable variable)))))
+                  (princ output))))
+
             (print-help-return-message)
             (save-excursion
               (set-buffer standard-output)