mu4e: make eldoc support configurable

Add new defcustom, mu4e-eldoc-support, turn it off by default.

NEWS.org

@@ -92,6 +92,9 @@
     - When searching, the number of hidden messages is now shown in the
       message footer along with the number of Found messages
 
+    - The ~eldoc~ support in header-mode is now optional and disabled by default;
+      set ~mu4e-eldoc-support~ to non-nil to enable it.
+
     - all the obsolete function and variable aliases have been moved to
  ~mu4e-obsolete.el~ so we can unclutter the non-obsolete code a bit.
 

mu4e/mu4e-headers.el

@@ -1121,15 +1121,14 @@ The following specs are supported:
   (set (make-local-variable 'hl-line-face) 'mu4e-header-highlight-face)
 
   ;; Eldoc support
-  (when (featurep 'eldoc)
+  (when (and (featurep 'eldoc) mu4e-eldoc-support)
     (if (boundp 'eldoc-documentation-functions)
         ;; Emacs 28 or newer
         (add-hook 'eldoc-documentation-functions
                   #'mu4e-headers-eldoc-function nil t)
       ;; Emacs 27 or older
-      (when (fboundp 'add-function) ;; add-function was added in 24.4.
-        (add-function :before-until (local 'eldoc-documentation-function)
-                      #'mu4e-headers-eldoc-function))))
+      (add-function :before-until (local 'eldoc-documentation-function)
+                    #'mu4e-headers-eldoc-function)))
 
   ;; support bookmarks.
   (set (make-local-variable 'bookmark-make-record-function)

mu4e/mu4e.el

@@ -69,6 +69,12 @@
   :type 'boolean
   :group 'mu4e)
 
+(defcustom mu4e-eldoc-support nil
+  "Support eldoc help in the headers-view."
+  :type 'boolean
+  :group 'mu4e)
+
+
 (when mu4e-speedbar-support
   (require 'mu4e-speedbar)) ;; support for speedbar
 (when mu4e-org-support

mu4e/mu4e.texi

@@ -3087,6 +3087,7 @@ ways. Here we focus on Emacs built-ins; for dealing with external tools,
 * Modeline::Showing mu4e's status in the modeline
 * Desktop notifications::Get desktop notifications for new mail
 * Emacs bookmarks::Using Emacs' bookmark system
+* Eldoc::Information about the current header in the echo area
 * Org-mode links::Adding mu4e to your organized life
 * iCalendar::Enabling iCalendar invite processing
 * Speedbar::A special frame with your folders
@@ -3206,13 +3207,21 @@ want tweak the details, have a look at @code{mu4e-notification-filter} and
 @section Emacs bookmarks
 @cindex Emacs bookmarks
 
-Note, emacs bookmarks are not to be confused with mu4e's bookmarks; the former
-are a generic linking system, while the latter are remember stored queries.
+Note, Emacs bookmarks are not to be confused with mu4e's bookmarks; the former
+are a generic linking system across Emacs, while the latter are stored queries
+within @t{mu4e}.
 
 @t{mu4e} supports linking to the message-at-point through the normal Emacs
 built-in bookmark system. The links are based on the message's message-id, and
 thus the bookmarks stay valid even if you move the message around.
 
+@node Eldoc
+@section Eldoc
+@cindex eldoc
+
+It is possible to get information about the current header in the echo-area.
+You can enable this by setting @t{mu4e-eldoc-support} to non-@t{nil}.
+
 @node Org-mode links
 @section Org-mode links
 
@@ -3366,7 +3375,6 @@ functions use that to set the @code{datetree} location:
 If you do this, you'll want to omit the @code{:timeprompt t} setting
 from your capture template.
 
-
 @node Speedbar
 @section Speedbar
 @cindex speedbar