Merge from origin/emacs-26

b0da915 (origin/emacs-26, emacs-26) Fix a typo in ELisp manual
400907b Add option to disable help completion autoloading (Bug#28607)
122ba16 Don't segfault on force-window-update of deleted window
015b12e Fix typo in ELisp manual
eadf044 Remove repeated function call in picture.el
1228a90 ; Fix mm-destroy-parts docstring typo
6cfd68d Fix Hideshow key binding typo in Emacs manual

10 files changed, 57 insertions, 10 deletions

diff --git a/doc/emacs/building.texi b/doc/emacs/building.texi
index 518d157e4ee..6e16588861e 100644
--- a/doc/emacs/building.texi
+++ b/doc/emacs/building.texi
@@ -1521,6 +1521,12 @@ library lets Emacs properly set up the hyperlinks in the @file{*Help*}
 buffer).  To disable this feature, change the variable
 @code{help-enable-auto-load} to @code{nil}.
 
+@vindex help-enable-completion-auto-load
+Automatic loading also occurs when completing names for
+@code{describe-variable} and @code{describe-function}, based on the
+prefix being completed.  To disable this feature, change the variable
+@code{help-enable-completion-auto-load} to @code{nil}.
+
 @vindex load-dangerous-libraries
 @cindex Lisp files byte-compiled by XEmacs
   By default, Emacs refuses to load compiled Lisp files which were
diff --git a/doc/emacs/programs.texi b/doc/emacs/programs.texi
index c1ad5b57023..28bfa5b578f 100644
--- a/doc/emacs/programs.texi
+++ b/doc/emacs/programs.texi
@@ -1298,8 +1298,11 @@ count as blocks.
 @findex hs-show-block
 @findex hs-show-region
 @findex hs-hide-level
+@findex hs-toggle-hiding
+@findex hs-mouse-toggle-hiding
 @kindex C-c @@ C-h
 @kindex C-c @@ C-s
+@kindex C-c @@ C-c
 @kindex C-c @@ C-M-h
 @kindex C-c @@ C-M-s
 @kindex C-c @@ C-r
@@ -1312,7 +1315,7 @@ Hide the current block (@code{hs-hide-block}).
 @item C-c @@ C-s
 Show the current block (@code{hs-show-block}).
 @item C-c @@ C-c
-@itemx C-x @@ C-e
+@itemx C-c @@ C-e
 Either hide or show the current block (@code{hs-toggle-hiding}).
 @item S-mouse-2
 Toggle hiding for the block you click on (@code{hs-mouse-toggle-hiding}).
diff --git a/doc/lispref/loading.texi b/doc/lispref/loading.texi
index 6f1213f097b..3261e6d1888 100644
--- a/doc/lispref/loading.texi
+++ b/doc/lispref/loading.texi
@@ -466,9 +466,11 @@ first call to the function automatically loads the proper library, in
 order to install the real definition and other associated code, then
 runs the real definition as if it had been loaded all along.
 Autoloading can also be triggered by looking up the documentation of
-the function or macro (@pxref{Documentation Basics}).
+the function or macro (@pxref{Documentation Basics}), and completion
+of variable and function names (@pxref{Autoload by Prefix} below).
 
 @menu
+* Autoload by Prefix:: Autoload by Prefix.
 * When to Autoload::   When to Use Autoload.
 @end menu
 
@@ -703,6 +705,25 @@ symbol's new function value.  If the value of the optional argument
 function, only a macro.
 @end defun
 
+@node Autoload by Prefix
+@subsection Autoload by Prefix
+@cindex autoload by prefix
+
+@vindex definition-prefixes
+@findex register-definition-prefixes
+@vindex autoload-compute-prefixes
+During completion for the commands @code{describe-variable} and
+@code{describe-function}, Emacs will try to load files which may
+contain definitions matching the prefix being completed.  The variable
+@code{definition-prefixes} holds a hashtable which maps a prefix to
+the corresponding list of files to load for it.  Entries to this
+mapping are added by calls to @code{register-definition-prefixes}
+which are generated by @code{update-file-autoloads}
+(@pxref{Autoload}).  Files which don't contain any definitions worth
+loading (test files, for examples), should set
+@code{autoload-compute-prefixes} to @code{nil} as a file-local
+variable.
+
 @node When to Autoload
 @subsection When to Use Autoload
 @cindex autoload, when to use
diff --git a/doc/lispref/sequences.texi b/doc/lispref/sequences.texi
index a7f270c0680..4b67a5f9f1a 100644
--- a/doc/lispref/sequences.texi
+++ b/doc/lispref/sequences.texi
@@ -601,7 +601,7 @@ returned value is a list.
 @defun seq-mapn function &rest sequences
   This function returns the result of applying @var{function} to each
 element of @var{sequences}.  The arity (@pxref{What Is a Function,
-sub-arity}) of @var{function} must match the number of sequences.
+subr-arity}) of @var{function} must match the number of sequences.
 Mapping stops at the end of the shortest sequence, and the returned
 value is a list.
 
diff --git a/doc/lispref/variables.texi b/doc/lispref/variables.texi
index aca7d2f5e93..932b7c829b9 100644
--- a/doc/lispref/variables.texi
+++ b/doc/lispref/variables.texi
@@ -2009,7 +2009,7 @@ all files in those directories.  The list in @var{variables} can be of
 one of the two forms: @code{(@var{major-mode} . @var{alist})} or
 @code{(@var{directory} . @var{list})}.  With the first form, if the
 file's buffer turns on a mode that is derived from @var{major-mode},
-then the all the variables in the associated @var{alist} are applied;
+then all the variables in the associated @var{alist} are applied;
 @var{alist} should be of the form @code{(@var{name} . @var{value})}.
 A special value @code{nil} for @var{major-mode} means the settings are
 applicable to any mode.  In @var{alist}, you can use a special
diff --git a/etc/NEWS b/etc/NEWS
index 72702a9aaac..064143047df 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -153,6 +153,12 @@ after Emacs has finished initialization and is ready for use.
 emacs.service file to eg "~/.config/systemd/user/", you will need to copy
 the new version of the file again.)
 
++++
+** 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'.
+
 
 * Changes in Emacs 27.1
 
diff --git a/lisp/gnus/mm-decode.el b/lisp/gnus/mm-decode.el
index 5b1859e3240..0b9cdde1fa5 100644
--- a/lisp/gnus/mm-decode.el
+++ b/lisp/gnus/mm-decode.el
@@ -1111,7 +1111,7 @@ external if displayed external."
 	  (mm-remove-part handle)))))))
 
 (defun mm-destroy-parts (handles)
-  "Remove the displayed MIME parts represented by HANDLES."
+  "Destroy the displayed MIME parts represented by HANDLES."
   (if (and (listp handles)
 	   (bufferp (car handles)))
       (mm-destroy-part handles)
diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index 9d997368074..91b4104becf 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -103,11 +103,23 @@ and the output should go to `standard-output'.")
         (with-demoted-errors "while loading: %S"
           (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)
diff --git a/lisp/textmodes/picture.el b/lisp/textmodes/picture.el
index 0b508547314..79039bc1980 100644
--- a/lisp/textmodes/picture.el
+++ b/lisp/textmodes/picture.el
@@ -624,7 +624,6 @@ Leaves the region surrounding the rectangle."
 (defvar picture-mode-map
   (let ((map (make-keymap)))
     (define-key map [remap self-insert-command] 'picture-self-insert)
-    (define-key map [remap self-insert-command] 'picture-self-insert)
     (define-key map [remap completion-separator-self-insert-command]
 			  'picture-self-insert)
     (define-key map [remap completion-separator-self-insert-autofilling]
diff --git a/src/window.c b/src/window.c
index 30ffad0e513..ca7cf7a4a61 100644
--- a/src/window.c
+++ b/src/window.c
@@ -4089,7 +4089,7 @@ displaying that buffer.  */)
       return Qt;
     }
 
-  if (WINDOWP (object))
+  if (WINDOW_LIVE_P (object))
     {
       struct window *w = XWINDOW (object);
       mark_window_display_accurate (object, false);