Emacs: Add address completion based on company-mode

When company-mode is available (Emacs >= 24), address completion
candidates are shown in a nice popup box. This is triggered either by
pressing TAB or by waiting a while during typing an address. The
completion is based entirely on the asynchronous address harvesting
from notmuch-address.el so the GUI is theoretically not blocked for
long time.

The completion works similarly as the TAB-initiated completion from
notmuch-address.el, i.e. quick harvest based on user input is executed
first and only after full harvesting is finished, in-memory cached data
is used.

[Improved by David Bremner]

emacs/Makefile.local

@@ -20,6 +20,7 @@ emacs_sources := \
 	$(dir)/notmuch-print.el \
 	$(dir)/notmuch-version.el \
 	$(dir)/notmuch-jump.el \
+	$(dir)/notmuch-company.el
 
 $(dir)/notmuch-version.el: $(dir)/Makefile.local version.stamp
 $(dir)/notmuch-version.el: $(srcdir)/$(dir)/notmuch-version.el.tmpl

emacs/notmuch-address.el

@@ -22,7 +22,9 @@
 (require 'message)
 (require 'notmuch-parser)
 (require 'notmuch-lib)
+(require 'notmuch-company)
 ;;
+(declare-function company-manual-begin "company")
 
 (defcustom notmuch-address-command 'internal
   "The command which generates possible addresses. It must take a
@@ -72,9 +74,21 @@ finished")
 (defun notmuch-address-message-insinuate ()
   (message "calling notmuch-address-message-insinuate is no longer needed"))
 
+(defcustom notmuch-address-use-company t
+  "If available, use company mode for address completion"
+  :type 'boolean
+  :group 'notmuch-send)
+
 (defun notmuch-address-setup ()
-  (let ((pair (cons notmuch-address-completion-headers-regexp
-		    #'notmuch-address-expand-name)))
+  (let* ((use-company (and notmuch-address-use-company
+			   (eq notmuch-address-command 'internal)
+			   (require 'company nil t)))
+	 (pair (cons notmuch-address-completion-headers-regexp
+		     (if use-company
+			 #'company-manual-begin
+		       #'notmuch-address-expand-name))))
+      (when use-company
+	(notmuch-company-setup))
       (unless (memq pair message-completion-alist)
 	(setq message-completion-alist
 	      (push pair message-completion-alist)))))

emacs/notmuch-company.el

@@ -0,0 +1,86 @@
+;; notmuch-company.el --- Mail address completion for notmuch via company-mode  -*- lexical-binding: t -*-
+
+;; Authors: Trevor Jim <tjim@mac.com>
+;; 	    Michal Sojka <sojkam1@fel.cvut.cz>
+;;
+;; Keywords: mail, completion
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; To enable this, install company mode (https://company-mode.github.io/)
+;;
+;; NB company-minimum-prefix-length defaults to 3 so you don't get
+;; completion unless you type 3 characters
+
+;;; Code:
+
+(eval-when-compile (require 'cl))
+
+(defvar notmuch-company-last-prefix nil)
+(make-variable-buffer-local 'notmuch-company-last-prefix)
+(declare-function company-begin-backend "company")
+(declare-function company-grab "company")
+(declare-function company-mode "company")
+(declare-function company-manual-begin "company")
+(defvar company-backends)
+
+(declare-function notmuch-address-harvest "notmuch-address")
+(declare-function notmuch-address-harvest-trigger "notmuch-address")
+(declare-function notmuch-address-matching "notmuch-address")
+(defvar notmuch-address-full-harvest-finished)
+(defvar notmuch-address-completion-headers-regexp)
+
+;;;###autoload
+(defun notmuch-company-setup ()
+  (company-mode)
+  (make-local-variable 'company-backends)
+  (setq company-backends '(notmuch-company)))
+
+;;;###autoload
+(defun notmuch-company (command &optional arg &rest _ignore)
+  "`company-mode' completion back-end for `notmuch'."
+  (interactive (list 'interactive))
+  (require 'company)
+  (let ((case-fold-search t)
+	(completion-ignore-case t))
+    (case command
+      (interactive (company-begin-backend 'notmuch-company))
+      (prefix (and (derived-mode-p 'message-mode)
+		   (looking-back (concat notmuch-address-completion-headers-regexp ".*")
+				 (line-beginning-position))
+		   (setq notmuch-company-last-prefix (company-grab "[:,][ \t]*\\(.*\\)" 1 (point-at-bol)))))
+      (candidates (cond
+		   (notmuch-address-full-harvest-finished
+		    ;; Update harvested addressed from time to time
+		    (notmuch-address-harvest-trigger)
+		    (notmuch-address-matching arg))
+		   (t
+		    (cons :async
+			  (lambda (callback)
+			    ;; First run quick asynchronous harvest based on what the user entered so far
+			    (notmuch-address-harvest
+			     (format "to:%s*" arg) nil
+			     (lambda (_proc _event)
+			       (funcall callback (notmuch-address-matching arg))
+			       ;; Then start the (potentially long-running) full asynchronous harvest if necessary
+			       (notmuch-address-harvest-trigger))))))))
+      (match (if (string-match notmuch-company-last-prefix arg)
+		 (match-end 0)
+	       0))
+      (no-cache t))))
+
+
+(provide 'notmuch-company)