mu4e: Replace mu4e-view-use-gnus with mu4e-view-use-old

Make mu4e-view-use-gnus obsolete (it's the default now), and add a
variable mu4e-view-use-old (which must be set before starting mu4e).

Update documentation / mentions.

Load the correct view when starting mu4e, so people can customize
e.g. the keymap.

Add some sanity checking.

NEWS.org

@@ -39,16 +39,21 @@
 *** mu4e
 
     - Use the gnus-based message viewer as the default; the new viewer has quite
-      a few features compared to the old, mu4e-specific one, such as faster
-      crypto, support for S/MIME, syntax-highlighting, calendar invitations and
-      more.
+      a few extra features compared to the old, mu4e-specific one, such as
+      faster crypto, support for S/MIME, syntax-highlighting, calendar
+      invitations and more.
 
       It does not do everything the old viewer does though (e.g., attachment
-      actions), so if you depend on those, you can use:
+      actions), so if you depend on those:
       #+begin_example
-      (setq mu4e-view-use-gnus nil)
+      ;; set *before* loading mu4e; and restart emacs if you want to change it
+      ;; users of use-packag~ should can use the :init section for this.
+      (setq mu4e-view-use-old t)
       #+end_example
 
+      (The older variable ~mu4e-view-use-gnus~ with the opposite meaning is
+      obsolete now, and no longer in use).
+
     - Include maildir-shortcuts in the main-view with overall/unread counts,
       similar to bookmarks, and with the same ~:hide~ and ~:hide-unread~ properties.
       Note that for the latter, you need to update your maildir-shortcuts to the

mu4e/mu4e-contrib.el

@@ -1,6 +1,6 @@
 ;;; mu4e-contrib.el -- part of mu4e, the mu mail user agent -*- lexical-binding: t -*-
 
-;; Copyright (C) 2013-2020 Dirk-Jan C. Binnema
+;; Copyright (C) 2013-2021 Dirk-Jan C. Binnema
 
 ;; This file is not part of GNU Emacs.
 

mu4e/mu4e-headers.el

@@ -1749,7 +1749,7 @@ _not_ refresh the last search with the new setting for threading."
 
 (defun mu4e~decrypt-p (msg)
   "Should we decrypt this message?"
-  (unless mu4e-view-use-gnus ;; we don't decrypt in the gnus-view case
+  (when mu4e-view-use-old ;; we don't decrypt in the gnus-view case
     (and (member 'encrypted (mu4e-message-field msg :flags))
          (if (eq mu4e-decryption-policy 'ask)
              (yes-or-no-p (mu4e-format "Decrypt message?"))
@@ -1773,7 +1773,7 @@ window                                                      . "
               (funcall mu4e-view-auto-mark-as-read msg)
             mu4e-view-auto-mark-as-read))
          (decrypt (mu4e~decrypt-p msg))
-         (verify  (not mu4e-view-use-gnus))
+         (verify  mu4e-view-use-old)
          (viewwin (mu4e~headers-redraw-get-view-window)))
     (unless (window-live-p viewwin)
       (mu4e-error "Cannot get a message view"))

mu4e/mu4e-icalendar.el

@@ -58,6 +58,9 @@
 (require 'mu4e-view)
 (require 'mu4e-vars)
 
+(when mu4e-view-use-old
+  (mu4e-error "iCalender support is not available with the old viewer"))
+
 ;;;###autoload
 (defun mu4e-icalendar-setup ()
   "Perform the necessary initialization to use mu4e-icalendar."

mu4e/mu4e-utils.el

@@ -856,9 +856,9 @@ When successful, call FUNC (if non-nil) afterwards."
   ;; kill all mu4e buffers
   (mapc
    (lambda (buf)
-     ;; When using mu4e-view-use-gnus, the view buffer has the kill-buffer-hook
-     ;; function mu4e~view-kill-buffer-hook-fn which kills the mm-* buffers
-     ;; created by Gnus' article mode.  Those have been returned by
+     ;; When using the Gnus-based viewer, the view buffer has the
+     ;; kill-buffer-hook function mu4e~view-kill-buffer-hook-fn which kills the
+     ;; mm-* buffers created by Gnus' article mode.  Those have been returned by
      ;; `buffer-list' but might already be deleted in case the view buffer has
      ;; been killed first.  So we need a `buffer-live-p' check here.
      (when (buffer-live-p buf)

mu4e/mu4e-vars.el

@@ -69,12 +69,13 @@ Setting this to t increases the amount of information in the log."
   "Settings for the message view."
   :group 'mu4e)
 
-(defcustom mu4e-view-use-gnus t
-  "If non-nil, use the new Gnus-based viewer.
-Otherwise, use the old viewer."
+(defcustom mu4e-view-use-old nil
+  "If non-nil, use the old viewer.
+Otherwise, use the new, Gnus-based viewer."
   :type 'boolean
   :group 'mu4e-view)
 
+(make-obsolete-variable 'mu4e-view-use-gnus 'mu4e-view-use-old "1.5.10")
 
 (defcustom mu4e-speedbar-support nil
   "Support having a speedbar to navigate folders/bookmarks."
@@ -421,7 +422,7 @@ The setting is a symbol:
  * `ask': ask before decrypting anything
  * nil:   don't try to decrypt anything.
 
-Note that this is not used when `mu4e-view-use-gnus' is enabled."
+Note that this is not used unless `mu4e-view-use-old' is enabled."
   :type '(choice (const :tag "Try to decrypt automatically" t)
                  (const :tag "Ask before decrypting anything" ask)
                  (const :tag "Don't try to decrypt anything" nil))
@@ -1019,10 +1020,9 @@ property, which should point to a function that takes a message
 plist as argument, and returns a string. See the default value of
 `mu4e-header-info-custom for an example.
 
-Note that when using the gnus-based view (see
-`mu4e-view-use-gnus'), you only have access to a limited set of
-message fields: only the ones used in the header-view, not
-including, for instance, the message body.")
+Note that when using the gnus-based view, you only have access to
+a limited set of message fields: only the ones used in the
+header-view, not including, for instance, the message body.")
 
 ;;; Run-time variables / constants
 

mu4e/mu4e-view.el

@@ -33,6 +33,7 @@
 (declare-function mu4e-error   "mu4e-utils")
 
 (require 'mu4e-view-common)
+(require (if mu4e-view-use-old 'mu4e-view-old 'mu4e-view-gnus))
 
 (defun mu4e-view (msg)
   "Display the message MSG in a new buffer, and keep in sync with HDRSBUF.
@@ -42,23 +43,21 @@ the the message view affects HDRSBUF, as does marking etc.
 As a side-effect, a message that is being viewed loses its 'unread'
 marking if it still had that.
 
-Depending on the value of `mu4e-view-use-gnus', either use mu4e's
-internal display mode, or a display mode based on Gnus'
-article-mode."
+Depending on the value of `mu4e-view-use-old', either use mu4e's
+internal display mode, or a (by default) display mode based on
+Gnus' article-mode."
+
+  ;; sanity checks.
+  (if (and mu4e-view-use-old (featurep 'mu4e-view-gnus))
+    (error "Cannot use old view when gnus-view is loaded; restart emacs")
+    (if (and (not mu4e-view-use-old) (featurep 'mu4e-view-old))
+        (error "Cannot use gnus-based view with old view loaded; restart emacs")))
+
   (mu4e~headers-update-handler msg nil nil);; update headers, if necessary.
 
-  ;; sanity check; only one can be active.
-  (if mu4e-view-use-gnus
-      (progn
-        (when (featurep 'mu4e-view-old)
-          (mu4e-error "Cannot load gnus-based view with old one loaded. Restart emacs"))
-        (require 'mu4e-view-gnus)
-        (mu4e~view-gnus msg))
-    (progn
-      (when (featurep 'mu4e-view-gnus)
-        (mu4e-error "Cannot load old view with gnus-based view loaded. Restart emacs"))
-      (require 'mu4e-view-old)
-      (mu4e~view-old msg))))
+  (if mu4e-view-use-old
+      (mu4e~view-old msg)
+    (mu4e~view-gnus msg)))
 
 (defun mu4e-view-message-with-message-id (msgid)
   "View message with message-id MSGID. This (re)creates a

mu4e/mu4e.texi

@@ -1329,7 +1329,6 @@ q            leave the message view
 
 For the marking commands, please refer to @ref{Marking messages}.
 
-
 @node MSGV Custom headers
 @section Custom headers
 
@@ -1361,11 +1360,18 @@ Since version 1.6 @t{mu4e} defaults to the new, Gnus-based, message view.
 
 However, the older view is still available, and this chapter is about
 that one. While we recommend using the default one, you can still use
-the old one by configuring it:
+the old one by configuring it @emph{before} @t{require}'ing @t{mu4e}:
 @lisp
-(setq mu4e-view-use-gnus nil)
+(setq mu4e-view-use-old t)
 @end lisp
 
+Users of
+@t{use-package}@footnote{@url{https://jwiegley.github.io/use-package/}}
+can use the @t{:init} section for this.
+
+If you want to change this, you need to fully restart @t{mu4e} (in
+practice, this means you need to restart @t{emacs}.
+
 After selecting a message in the @ref{Headers view}, it appears in a message
 view window, which shows the message headers, followed by the message
 body. Its major mode is @code{mu4e-view-mode}.
@@ -3805,13 +3811,8 @@ Now, you can bind a convenient key to my-mu4e-bookmarks/body.
 By default, mu4e presents iCalendar invitations as .vcs file
 attachments. Experimental support is available to parse these
 attachments in order to add the expected ``Accept'', ``Reject'', ``Add
-to Calendar'' buttons. This requires using Gnus' article view, instead
-of mu4e's internal viewer. We do this by setting the value of
-mu4e-view-use-gnus:
-
-@lisp
-(setq mu4e-view-use-gnus t)
-@end lisp
+to Calendar'' buttons. This requires using Gnus' article view, which
+is the default since @t{mu4e} version 1.6.
 
 The minimal setup is:
 
@@ -3838,22 +3839,6 @@ To enable optional functionality to capture iCalendar events to your org files:
 NOTE: both the capture file and the headline(s) inside must already
 exist.
 
-These features require the Gnus article viewer. This is currently
-experimental, and doesn't yet support all the features available with
-mu4e's internal viewer. Consequently, you may want a way to toggle
-between the two modes. You can do this with the following:
-
-@lisp
-(defun mu4e-toggle-gnus-view ()
-  (interactive)
-  (mu4e~view-quit-buffer)
-  (setq mu4e-view-use-gnus
-        (not mu4e-view-use-gnus))
-  (mu4e-headers-view-message))
-
-(define-key mu4e-view-mode-map "i" 'mu4e-toggle-gnus-view)
-@end lisp
-
 @node Example configs
 @appendix Example configs