[PATCH 3/3] Emacs: Add address completion based on company-mode

[David Bremner]

From: Michal Sojka <sojkam1 at fel.cvut.cz>

With this patch, address completion candidates are shown automatically
after short typing delay in a nice popup box. This requires company-mode
to be installed and it works only on Emacs >= 24. 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.
---
 emacs/Makefile.local     |  1 +
 emacs/notmuch-company.el | 73 ++++++++++++++++++++++++++++++++++++++++++++++++
 emacs/notmuch-mua.el     | 13 ++++++++-
 3 files changed, 86 insertions(+), 1 deletion(-)
 create mode 100644 emacs/notmuch-company.el

diff --git a/emacs/Makefile.local b/emacs/Makefile.local
index 1109cfa..4c06c52 100644
--- a/emacs/Makefile.local
+++ b/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
diff --git a/emacs/notmuch-company.el b/emacs/notmuch-company.el
new file mode 100644
index 0000000..03c492f
--- /dev/null
+++ b/emacs/notmuch-company.el
@@ -0,0 +1,73 @@
+;; notmuch-company.el --- Mail address completion for notmuch via company-mode  -*- lexical-binding: t -*-
+
+
+;; Authors: Trevor Jim <tjim at mac.com>
+;; 	    Michal Sojka <sojkam1 at 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/)
+;; and customize notmuch-message-use-company
+;;
+;; NB company-minimum-prefix-length defaults to 3 so you don't get
+;; completion unless you type 3 characters
+
+;;; Code:
+
+(require 'notmuch-address)
+(require 'cl-lib)
+
+(defvar-local notmuch-company-last-prefix nil)
+(declare-function company-begin-backend "company")
+(declare-function company-grab "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))
+    (cl-case command
+      (interactive (company-begin-backend 'notmuch-company))
+      (prefix (and (derived-mode-p 'message-mode)
+		   (looking-back "^\\(To\\|Cc\\|Bcc\\):.*"
+				 (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 (re)start potentially long-running full asynchronous harvesting
+			       (notmuch-address-harvest-trigger))))))))
+      (match (if (string-match notmuch-company-last-prefix arg)
+		 (match-end 0)
+	       0))
+      (no-cache t))))
+
+
+(provide 'notmuch-company)
diff --git a/emacs/notmuch-mua.el b/emacs/notmuch-mua.el
index 6cc9656..c90381d 100644
--- a/emacs/notmuch-mua.el
+++ b/emacs/notmuch-mua.el
@@ -25,6 +25,7 @@
 
 (require 'notmuch-lib)
 (require 'notmuch-address)
+(require 'notmuch-company)
 
 (eval-when-compile (require 'cl))
 
@@ -268,12 +269,22 @@ Note that these functions use `mail-citation-hook' if that is non-nil."
   (message-goto-body)
   (set-buffer-modified-p nil))
 
+(defcustom notmuch-message-use-company t
+  "If available, use company mode for completion in notmuch-message-mode"
+  :type 'boolean
+  :group 'notmuch-send)
+
 (define-derived-mode notmuch-message-mode message-mode "Message[Notmuch]"
   "Notmuch message composition mode. Mostly like `message-mode'"
   (when notmuch-address-command
     (unless (memq notmuch-address-message-alist-member message-completion-alist)
       (setq message-completion-alist
-	    (push notmuch-address-message-alist-member message-completion-alist)))))
+	    (push notmuch-address-message-alist-member message-completion-alist))))
+  (when (and notmuch-message-use-company
+	     (require 'company nil t))
+    (company-mode)
+    (make-local-variable 'company-backends)
+    (setq company-backends '(notmuch-company))))
 
 (define-key notmuch-message-mode-map (kbd "C-c C-c") #'notmuch-mua-send-and-exit)
 (define-key notmuch-message-mode-map (kbd "C-c C-s") #'notmuch-mua-send)
-- 
2.6.1