From 2e3d84fc1d8457046a0aceed7e1f9837330a4365 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Wed, 15 May 2019 20:29:38 -0400
Subject: [PATCH] Add option to disable help completion autoloading (Bug#28607)

* lisp/help-fns.el (help-enable-completion-auto-load): New option.
(help--symbol-completion-table): Consult it.
* etc/NEWS: Announce it.
---
 etc/NEWS         |  6 ++++++
 lisp/help-fns.el | 18 +++++++++++++++---
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 573c8236b2..286f9ee275 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -24,6 +24,12 @@ with a prefix argument or by typing 'C-u C-h C-n'.
 
 * Changes in Emacs 26.3
 
+---
+** New option 'help-enable-completion-auto-load'.
+This allows disabling the new feature introduced in Emacs 26.1 which
+loads files during completion of 'C-h f' and 'C-h v' according to
+'definition-prefixes'.
+
 
 * Editing Changes in Emacs 26.3
 
diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index a7812e3b4b..8684a853af 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -89,11 +89,23 @@ help--load-prefixes
       (unless (help--loaded-p file)
         (load file 'noerror 'nomessage)))))
 
+(defcustom help-enable-completion-auto-load t
+  "Whether completion for Help commands can perform autoloading.
+If non-nil, whenever invoking completion for `describe-function'
+or `describe-variable' load files that might contain definitions
+with the current prefix.  The files are chosen according to
+`definition-prefixes'."
+  :type 'boolean
+  :group 'help
+  :version "26.3")
+
 (defun help--symbol-completion-table (string pred action)
-  (let ((prefixes (radix-tree-prefixes (help-definition-prefixes) string)))
-    (help--load-prefixes prefixes))
+  (when help-enable-completion-auto-load
+    (let ((prefixes (radix-tree-prefixes (help-definition-prefixes) string)))
+      (help--load-prefixes prefixes)))
   (let ((prefix-completions
-         (mapcar #'intern (all-completions string definition-prefixes))))
+         (and help-enable-completion-auto-load
+              (mapcar #'intern (all-completions string definition-prefixes)))))
     (complete-with-action action obarray string
                           (if pred (lambda (sym)
                                      (or (funcall pred sym)
-- 
2.11.0