mu4e: centralize mode-line context setting code

Add mu4e-context-in-modeline to handle all setting of context in the
mode-line, to address some corner-cases with the current setup.

mu4e/mu4e-compose.el

@@ -443,8 +443,7 @@ buffers; lets remap its faces so it uses the ones for mu4e."
 \\{message-mode-map}."
   (progn
     (use-local-map mu4e-compose-mode-map)
-    (make-local-variable 'global-mode-string)
-    (add-to-list 'global-mode-string '(:eval (mu4e-context-label)))
+    (mu4e-context-in-modeline)
     (set (make-local-variable 'message-signature) mu4e-compose-signature)
     ;; set this to allow mu4e to work when gnus-agent is unplugged in gnus
     (set (make-local-variable 'message-send-mail-real-function) nil)

mu4e/mu4e-context.el

@@ -284,6 +284,13 @@ match, POLICY determines what to do:
                           (mu4e~context-ask-user "Select context: ")))
          (otherwise nil))))))
 
+(defun mu4e-context-in-modeline ()
+  "Display the mu4e-context (if any) in a (buffer-specific)
+global-mode-line."
+  (add-to-list
+   (make-local-variable 'global-mode-string)
+   '(:eval (mu4e-context-label))))
+
 ;;; _
 (provide 'mu4e-context)
 ;;; mu4e-context.el ends here

mu4e/mu4e-headers.el

@@ -1086,9 +1086,10 @@ no user-interaction ongoing."
   (use-local-map mu4e-headers-mode-map)
   (make-local-variable 'mu4e~headers-proc)
   (make-local-variable 'mu4e~highlighted-docid)
-  (make-local-variable 'global-mode-string)
   (set (make-local-variable 'hl-line-face) 'mu4e-header-highlight-face)
 
+  (mu4e-context-in-modeline)
+
   ;; maybe update the current headers upon indexing changes
   (add-hook 'mu4e-index-updated-hook 'mu4e~headers-maybe-auto-update)
   (add-hook 'mu4e-index-updated-hook
@@ -1233,6 +1234,7 @@ the query history stack."
       (setq
        mode-name "mu4e-headers"
        mu4e~headers-last-query rewritten-expr)
+      (make-local-variable 'global-mode-string)
       (add-to-list 'global-mode-string
                    '(:eval
                      (concat
@@ -1240,7 +1242,6 @@ the query history stack."
                        (mu4e~quote-for-modeline mu4e~headers-last-query)
                        'face 'mu4e-modeline-face)
                       " "
-                      (mu4e-context-label)
                       (if (and mu4e-display-update-status-in-modeline
                                (buffer-live-p mu4e~update-buffer)
                                (process-live-p (get-buffer-process

mu4e/mu4e-main.el

@@ -80,10 +80,7 @@ with SPC and therefore is not visible in buffer list.")
 \\{mu4e-main-mode-map}."
   (setq truncate-lines t
         overwrite-mode 'overwrite-mode-binary)
-
-  ;; show context in mode-string
-  (make-local-variable 'global-mode-string)
-  (add-to-list 'global-mode-string '(:eval (mu4e-context-label)))
+  (mu4e-context-in-modeline)
   (set (make-local-variable 'revert-buffer-function) #'mu4e~main-view-real))
 
 
@@ -225,7 +222,7 @@ When REFRESH is non nil refresh infos from server."
          (mu4e~key-val "personal addresses" (if addrs (mapconcat #'identity addrs ", "  ) "none"))))
 
       (if mu4e-main-buffer-hide-personal-addresses ""
-        (when (and addrs user-mail-address (not (member user-mail-address addrs)))
+        (when (and user-mail-address (not (member user-mail-address addrs)))
           (mu4e-message (concat
                          "Note: `user-mail-address' ('%s') is not part "
                          "of mu's addresses; add it with 'mu init --my-address='")
@@ -276,8 +273,7 @@ When REFRESH is non nil refresh infos from server."
       (switch-to-buffer buf)
       (with-current-buffer buf
         (mu4e~main-view-real-1 refresh))
-      (goto-char (point-min)))
-  (add-to-list 'global-mode-string '(:eval (mu4e-context-label)))))
+      (goto-char (point-min)))))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Interactive functions

mu4e/mu4e-view.el

@@ -989,9 +989,7 @@ FUNC should be a function taking two arguments:
 (defun mu4e~view-mode-body ()
   "Body of the mode-function."
   (use-local-map mu4e-view-mode-map)
-  ;; show context in mode-string
-  (make-local-variable 'global-mode-string)
-  (add-to-list 'global-mode-string '(:eval (mu4e-context-label)))
+  (mu4e-context-in-modeline)
   (setq buffer-undo-list t);; don't record undo info
   ;; autopair mode gives error when pressing RET
   ;; turn it off
@@ -1840,7 +1838,6 @@ other windows."
 (define-derived-mode mu4e-loading-mode special-mode
   "mu4e:loading"
   (use-local-map mu4e-loading-mode-map)
-  (make-local-variable 'global-mode-string)
   (let ((inhibit-read-only t))
     (erase-buffer)
     (insert (propertize "Loading message..."