Re: [PATCH] EUDC email addresses via completion-at-point in message-mode

[Alexander Adolf <alexander.adolf@condition-alpha.com>]

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Hello,

Alexander Adolf <alexander.adolf@condition-alpha.com> writes:

> [...]
> Browsing through message.el quickly brought me to the sixth of the 21
> FIXMEs in that file, which reads on line 3183:
>
>   ;; FIXME: merge the completion tables from ecomplete/bbdb/...?
>   ;;(add-hook 'completion-at-point-functions #'message-ecomplete-capf nil t)
>   (add-hook 'completion-at-point-functions #'message-completion-function nil t)
> [...]

Thanks to all who cared to share their views, and their suggestions on
my proposed patch. I am attaching an updated version that includes the
improvements that were suggested:

 - remove override, and thus respect user's setting of
   completion-ignore-case (Thomas Fitzsimmons's comment)

 - do not use ":exclusive 'no" in the completion table (Stefan Monnier's
   comment)

Thanks for pointing these out, and for helping to improve the proposed
patch!

Then there was a wider discussion on potential, architectural
improvements of completion handling in message.el.

Before diving into this wider discussion, it would seem worthwhile to me
trying to get to a conclusion on the proposed patch.

Do we have a consensus, that the proposed, updated patch does not solve
all potential issues around email address completion in message mode
once and for all, but that it still provides a useful improvement for
some users without disturbing others, thus making it seem worthwhile to
include the patch?


Many thanks and looking forward to your thoughts,

  --alexander


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From 0954a5be3e01283eeb0e56059c6210f0c22037ff Mon Sep 17 00:00:00 2001
From: Alexander Adolf <alexander.adolf@condition-alpha.com>
Date: Tue, 26 Apr 2022 15:38:12 +0200
Subject: [PATCH] EUDC email addresses via completion-at-point in message-mode

* lisp/net/eudc-capf.el (new file): Add new 'eudc-capf-complete'
function.
* lisp/gnus/message.el (message-mode): Add 'eudc-capf-complete' to
'completion-at-point-functions' when a 'message-mode' buffer is
created, removing the FIXME.
* doc/misc/eudc.texi (Inline Query Expansion): Add a new subsection,
describing the new 'completion-at-point' mechanism in 'message-mode'.
* etc/NEWS (EUDC): Describe the new 'completion-at-point' method.
---
 doc/misc/eudc.texi    |  23 ++++++++
 etc/NEWS              |   6 ++
 lisp/gnus/message.el  |   4 +-
 lisp/net/eudc-capf.el | 127 ++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 158 insertions(+), 2 deletions(-)
 create mode 100644 lisp/net/eudc-capf.el

diff --git a/doc/misc/eudc.texi b/doc/misc/eudc.texi
index d2850282fe..d2a1efeed0 100644
--- a/doc/misc/eudc.texi
+++ b/doc/misc/eudc.texi
@@ -713,6 +713,7 @@ be passed to the program.
 
 @node Inline Query Expansion
 @section Inline Query Expansion
+@subsection Inline Query Expansion Using a Key Binding
 
 Inline query expansion is a powerful method to get completion from
 your directory servers.  The most common usage is for expanding names
@@ -885,6 +886,28 @@ An error is signaled.  The expansion aborts.
 Default is @code{select}
 @end defvar
 
+@subsection Inline Query Expansion Using completion-at-point
+
+In addition to providing a dedicated EUDC function for binding to a
+key shortcut (@pxref{Inline Query Expansion Using a Key Binding}),
+EUDC also provides a function to contribute search results to the
+Emacs in-buffer completion system available via the function
+@code{completion-at-point} (@pxref{Identifier
+Inquiries,,,maintaining}) in @code{message-mode} buffers
+(@pxref{Message}).  When using this mechanism, queries are made in the
+multi-server query mode of operation (@pxref{Multi-server Queries}).
+
+When a buffer in @code{message-mode} is created, EUDC's inline
+expansion function is automatically added to the variable
+@code{completion-at-point-functions}.  As a result, whenever
+@code{completion-at-point} is invoked in a @code{message-mode} buffer,
+EUDC will be queried for email addresses matching the words before
+point.  Since this will be useful only when editing specific message
+header fields that require specifying one or more email addresses, an
+additional check is performed whether point is actually in one of
+those header fields.  Thus, any matching email addresses will be
+offered for completion in suitable message header fields only, and not
+in other places, like for example the body of the message.
 
 
 @node The Server Hotlist
diff --git a/etc/NEWS b/etc/NEWS
index dc2e7c616a..1ebbaa76e8 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -882,6 +882,12 @@ is called, and the returned values are used to populate the phrase and
 comment parts (see RFC 5322 for definitions).  In both cases, the
 phrase part will be automatically quoted if necessary.
 
++++
+*** New function 'eudc-capf-complete' with message-mode integration
+EUDC can now contribute email addresses to 'completion-at-point' by
+adding the new function 'eudc-capf-complete' to
+'completion-at-point-functions' in message-mode.
+
 ** eww/shr
 
 +++
diff --git a/lisp/gnus/message.el b/lisp/gnus/message.el
index cc994d3ba5..b59ab2c31d 100644
--- a/lisp/gnus/message.el
+++ b/lisp/gnus/message.el
@@ -51,6 +51,7 @@
 (require 'yank-media)
 (require 'mailcap)
 (require 'sendmail)
+(require 'eudc-capf)
 
 (autoload 'mailclient-send-it "mailclient")
 
@@ -3180,8 +3181,7 @@ Like `text-mode', but with these additional commands:
     (mail-abbrevs-setup))
    ((message-mail-alias-type-p 'ecomplete)
     (ecomplete-setup)))
-  ;; FIXME: merge the completion tables from ecomplete/bbdb/...?
-  ;;(add-hook 'completion-at-point-functions #'message-ecomplete-capf nil t)
+  (add-hook 'completion-at-point-functions #'eudc-capf-complete -1 t)
   (add-hook 'completion-at-point-functions #'message-completion-function nil t)
   (unless buffer-file-name
     (message-set-auto-save-file-name))
diff --git a/lisp/net/eudc-capf.el b/lisp/net/eudc-capf.el
new file mode 100644
index 0000000000..b11ef8776b
--- /dev/null
+++ b/lisp/net/eudc-capf.el
@@ -0,0 +1,127 @@
+;;; eudc-capf.el --- EUDC - completion-at-point bindings  -*- lexical-binding:t -*-
+
+;; Copyright (C) 2022 Free Software Foundation, Inc.
+;;
+;; Author: Alexander Adolf
+;;
+;; This file is part of GNU Emacs.
+;;
+;; GNU Emacs 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.
+;;
+;; GNU Emacs 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 GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;    This library provides functions to deliver email addresses from
+;;    EUDC search results to `completion-at-point'.
+;;
+;;    Email address completion will likely be desirable only in
+;;    situations where designating email recipients plays a role, such
+;;    as when composing or replying to email messages, or when posting
+;;    to newsgroups, possibly with copies of the post being emailed.
+;;    Hence, modes relevant in such contexts, such as for example
+;;    `message-mode' and `mail-mode', often at least to some extent
+;;    provide infrastructure for different functions to be called when
+;;    completing in certain message header fields, or in the body of
+;;    the message.  In other modes for editing email messages or
+;;    newsgroup posts, which do not provide such infrastructure, any
+;;    completion function providing email addresses will need to check
+;;    whether the completion attempt occurs in an appropriate context
+;;    (that is, in a relevant message header field) before providing
+;;    completion candidates.  Two mechanisms are thus provided by this
+;;    library.
+;;
+;;    The first mechanism is intended for use by the modes listed in
+;;    `eudc-capf-modes', and relies on these modes adding
+;;    `eudc-capf-complete' to `completion-at-point-functions', as
+;;    would be usually done for any general-purpose completion
+;;    function.  In this mode of operation, and in order to offer
+;;    email addresses only in contexts where the user would expect
+;;    them, a check is performed whether point is on a line that is a
+;;    message header field suitable for email addresses, such as for
+;;    example "To:", "Cc:", etc.
+;;
+;;    The second mechanism is intended for when the user modifies
+;;    `message-completion-alist' to replace `message-expand-name' with
+;;    the function `eudc-capf-message-expand-name'.  As a result,
+;;    minibuffer completion (`completing-read') for email addresses
+;;    would no longer enabled in `message-mode', but
+;;    `completion-at-point' (in-buffer completion) only.
+
+;;; Usage:
+
+;;    (require 'eudc-capf)
+;;    (add-hook 'completion-at-point-functions #'eudc-capf-complete -1 t)
+
+;;; Code:
+
+(require 'eudc)
+
+(defvar message-email-recipient-header-regexp)
+(defvar mail-abbrev-mode-regexp)
+(declare-function mail-abbrev-in-expansion-header-p "mailabbrev" ())
+
+(defconst eudc-capf-modes '(message-mode) "List of modes in which email \
+address completion is to be attempted.")
+
+;; completion functions
+
+;;;###autoload
+(defun eudc-capf-complete ()
+  "Email address completion function for `completion-at-point-functions'.
+
+This function checks whether the current major mode is one of the
+modes listed in `eudc-capf-modes', and whether point is on a line
+with a message header listing email recipients, that is, a line
+whose beginning matches `message-email-recipient-header-regexp',
+and, if the check succeeds, searches for records matching the
+words before point.
+
+The return value is either nil when no match is found, or a
+completion table as required for functions listed in
+`completion-at-point-functions'."
+  (if (and (seq-some #'derived-mode-p eudc-capf-modes)
+           (let ((mail-abbrev-mode-regexp message-email-recipient-header-regexp))
+             (mail-abbrev-in-expansion-header-p)))
+      (eudc-capf-message-expand-name)
+    nil))
+
+;;;###autoload
+(defun eudc-capf-message-expand-name ()
+  "Email address completion function for `message-completion-alist'.
+
+When this function is added to `message-completion-alist',
+replacing any existing entry for `message-expand-name' there,
+with an appropriate regular expression such as for example
+`message-email-recipient-header-regexp', then EUDC will be
+queried for email addresses, and the results delivered to
+`completion-at-point'."
+  (if (or (and (boundp 'eudc-server) eudc-server)
+          (and (boundp 'eudc-server-hotlist) eudc-server-hotlist))
+      (progn
+        (setq-local completion-styles '(substring partial-completion))
+        (let* ((beg (save-excursion
+                      (if (re-search-backward "\\([:,]\\|^\\)[ \t]*"
+                                              (point-at-bol) 'move)
+                          (goto-char (match-end 0)))
+                      (point)))
+               (end (point))
+               (prefix (save-excursion (buffer-substring-no-properties beg end))))
+          (list beg end
+                (completion-table-with-cache
+                 (lambda (_)
+                   (eudc-query-with-words (split-string prefix "[ \t]+") t))
+                 t))))
+    nil))
+
+(provide 'eudc-capf)
+;;; eudc-capf.el ends here
-- 
2.36.0