mu4e - better defaults, async and utility functions

This PR does a few things:

- supports async mode for sending mails
- registers imagemagick as handler for images if it exists
- sets default downloads directory if it exists
- sets a few (more) sane defaults
- supports format=flowed in messages

layers/+email/mu4e/README.org

@@ -11,6 +11,8 @@
 - [[#configuration][Configuration]]
   - [[#maildirs-extension][Maildirs extension]]
   - [[#multiple-accounts][Multiple Accounts]]
+  - [[#async-mode][Async mode]]
+  - [[#attachment-directory][Attachment directory]]
   - [[#example-configuration][Example configuration]]
   - [[#notifications][Notifications]]
     - [[#os-notifications][OS notifications]]
@@ -60,6 +62,7 @@ existing =dotspacemacs-configuration-layers= list in this file.
 | ~SPC a M~              | Start mu4e                      |
 | ~SPC m S~ or ~SPC m /~ | Search emails (requires helm)   |
 | ~SPC m C~              | Search contacts (requires helm) |
+| C-x m                  | Compose new message             |
 
 ** Headers mode
 
@@ -144,6 +147,26 @@ Note: We used to have a hack to support multiple accounts with older version of
 `mu` but we removed it to encourage people to update their version and use the
 new contexts feature.
 
+** Async mode
+mu4e can send mails in async mode, which speeds up sending as you do not have
+to wait for the email to be sent. This is off by default but you can enable
+it by setting the ~mu4e-enable-async-operations~ variable when including the
+layer.
+
+#+BEGIN_SRC emacs-lisp
+  (setq-default dotspacemacs-configuration-layers
+                '((mu4e :variables
+                        mu4e-enable-async-operations t)))
+#+END_SRC
+
+** Attachment directory
+By default mu4e will save attachment files to $HOME, but this layer changes
+that to $HOME/Downloads if it exists. You can override this in your user-config:
+
+#+BEGIN_SRC emacs-lisp
+  (setq mu4e-attachment-dir "~/files")
+#+END_SRC
+
 ** Example configuration
 #+BEGIN_SRC emacs-lisp
   ;;; Set up some common mu4e variables

layers/+email/mu4e/config.el

@@ -18,6 +18,9 @@
 (defvar mu4e-spacemacs-layout-binding "m"
   "Binding used in the setup for `spacemacs-layouts' micro-state")
 
+(defvar mu4e-enable-async-operations nil
+  "Prefer async operations when sending emails.")
+
 (defvar mu4e-enable-notifications nil
   "If non-nil, enable desktop notifications for unread emails.")
 

layers/+email/mu4e/funcs.el

@@ -0,0 +1,25 @@
+;;; funcs.el --- mu4e Layer functions File for Spacemacs
+;;
+;; Copyright (c) 2012-2018 Sylvain Benner & Contributors
+;;
+;; Author: Sylvain Benner <sylvain.benner@gmail.com>
+;; URL: https://github.com/syl20bnr/spacemacs
+;;
+;; This file is not part of GNU Emacs.
+;;
+;;; License: GPLv3
+
+(defun mu4e/load-signature-from-file (file)
+  "Load signature from FILE and strip separator if needed."
+  (setq mu4e-compose-signature
+        (with-temp-buffer
+          (insert-file-contents file)
+          (flush-lines message-signature-separator)
+          (buffer-string))))
+
+(defun mu4e/message-is-for-p (msg rx)
+  "Check if to, cc or bcc field in MSG has any address in RX."
+  (when (and msg rx)
+    (or (mu4e-message-contact-field-matches msg :to rx)
+        (mu4e-message-contact-field-matches msg :cc rx)
+        (mu4e-message-contact-field-matches msg :bcc rx))))

layers/+email/mu4e/packages.el

@@ -42,7 +42,15 @@
     :init
     (progn
       (spacemacs/set-leader-keys "a M" 'mu4e)
-      (global-set-key (kbd "C-x m") 'mu4e-compose-new))
+      (global-set-key (kbd "C-x m") 'mu4e-compose-new)
+      (setq mu4e-completing-read-function 'completing-read
+            mu4e-use-fancy-chars 't
+            mu4e-view-show-images 't
+            message-kill-buffer-on-exit 't)
+      (let ((dir "~/Downloads"))
+        (when (file-directory-p dir)
+          (setq mu4e-attachment-dir dir))))
+
     :config
     (progn
       (evilified-state-evilify-map mu4e-main-mode-map
@@ -78,10 +86,19 @@
         "s" 'message-dont-send         ; saves as draft
         "f" 'mml-attach-file)
 
-      (setq mu4e-completing-read-function 'completing-read)
+      (when mu4e-enable-async-operations
+        (require 'smtpmail-async)
+        (setq send-mail-function         'async-smtpmail-send-it
+              message-send-mail-function 'async-smtpmail-send-it))
+
+      (when (fboundp 'imagemagick-register-types)
+        (imagemagick-register-types))
 
       (add-to-list 'mu4e-view-actions
-                   '("View in browser" . mu4e-action-view-in-browser) t))))
+                   '("View in browser" . mu4e-action-view-in-browser) t)
+
+      (add-hook 'mu4e-compose-mode-hook
+                (lambda () (use-hard-newlines t 'guess))))))
 
 (defun mu4e/init-mu4e-alert ()
   (use-package mu4e-alert
@@ -111,6 +128,4 @@
 
 (defun mu4e/pre-init-org ()
   ;; load org-mu4e when org is actually loaded
-  (with-eval-after-load 'org
-    (require 'org-mu4e nil 'noerror)
-    (require 'org-notmuch nil 'noerror)))
+  (with-eval-after-load 'org (require 'org-mu4e nil 'noerror)))