Mu4e: More contextual +mu4e-set-from-address-h

This hook should only be used when users define email aliases, or no
contexts are defined (in which case the list of personal addresses
should be used). Otherwise, the `:match-func` contexts feature is
sufficient.

modules/email/mu4e/README.org

@@ -169,6 +169,22 @@ Then configure Emacs to use your email address:
   t)
 #+END_SRC
 
+If you use multiple email accounts, defining them with ~set-email-account!~ will
+automatically set the appropriate account context when replying to emails in
+that account's maildir. ~mu4e-context-policy~ and ~mu4e-compose-context-policy~
+can be modified to change context behavior when opening mu4e and composing
+email:
+
+#+begin_src emacs-lisp
+(setq mu4e-context-policy 'ask-if-none
+      mu4e-compose-context-policy 'always-ask)
+#+end_src
+
+If you send mail from various email aliases for different services,
+~+mu4e-personal-addresses~ can be set per-context with ~set-email-account!~. If
+you are not replying to an email to or from one of the specified aliases, you
+will be prompted for an alias to send from.
+
 *** Gmail
 With the =+gmail= flag, integrations are applied which account for the different
 behaviour of Gmail.

modules/email/mu4e/autoload/email.el

@@ -30,8 +30,11 @@ default/fallback account."
                    collect context))
     (let ((context (make-mu4e-context
                     :name label
-                    :enter-func (lambda () (mu4e-message "Switched to %s" label))
+                    :enter-func
-                    :leave-func #'mu4e-clear-caches
+                    (lambda () (mu4e-message "Switched to %s" label))
+                    :leave-func
+                    (lambda () (progn (setq +mu4e-personal-addresses nil)
+                                      (mu4e-clear-caches)))
                     :match-func
                     (lambda (msg)
                       (when msg
@@ -328,26 +331,20 @@ When otherwise called, open a dired buffer and enable `dired-mu4e-attach-ctrl-c-
 
 ;;;###autoload
 (defun +mu4e-set-from-address-h ()
-  "Set the account for composing a message. If a 'To' header is present,
+  "If the user defines multiple `+mu4e-personal-addresses' for email aliases
-and correspands to an email address, this address will be selected.
+within a context, set `user-mail-address' to an alias found in the 'To' or
-Otherwise, the user is prompted for the address they wish to use. Possible
+'From' headers of the parent message if present, or prompt the user for a
-selections come from the mu database or a list of email addresses associated
+preferred alias"
-with the current context."
+  (when-let ((addresses (if (or mu4e-contexts+mu4e-personal-addresses)
-  (unless (and mu4e-compose-parent-message
+                            (and (> (length +mu4e-personal-addresses) 1)
+                                 +mu4e-personal-addresses)
+                          (mu4e-personal-addresses))))
+    (setq user-mail-address
+          (if mu4e-compose-parent-message
               (let ((to (cdr (car (mu4e-message-field mu4e-compose-parent-message :to))))
                     (from (cdr (car (mu4e-message-field mu4e-compose-parent-message :from)))))
-                 (if (member to (mu4e-personal-addresses))
+                (cond
-                     (setq user-mail-address to)
+                 ((member to addresses) to)
-                   (if (member from (mu4e-personal-addresses))
+                 ((member from addresses) from)
-                       (setq user-mail-address from)
+                 (t (completing-read "From: " addresses))))
-                     nil))))
+            (completing-read "From: " addresses)))))
-    (setq user-mail-address
-          (if (= (length +mu4e-personal-addresses) 1)
-              (car +mu4e-personal-addresses)
-            (completing-read
-             "From: "
-             (if-let ((context-addresses
-                       (when mu4e~context-current
-                         (alist-get '+mu4e-personal-addresses (mu4e-context-vars mu4e~context-current)))))
-                 context-addresses
-               (mu4e-personal-addresses)))))))