>From 658b5ff4dad7f392a9d09f28f6c2bb97f5ae93e8 Mon Sep 17 00:00:00 2001
From: Alexander Adolf <alexander.adolf@condition-alpha.com>
Date: Fri, 9 Dec 2022 22:15:42 +0100
Subject: [PATCH] Untangle EUDC's completion-at-point function from
 message-mode

The default completion-styles turned out to not be generous enough to
allow useful email address completion. Hence, this commit sets the
buffer-local value of completion-styles to a better suited value when
performing email completion via eudc-capf-complete, which is also no
longer added to completion-at-point-functions in message-mode.
message-mode has EUDC support already, and that would have been
duplicated functionality. Users are still free to add
eudc-capf-complete to completion-at-point-functions at their own
discretion (for example in mail-mode).

* lisp/net/eudc-capf.el (eudc-capf-complete): Set
completion-styles buffer locally to a more generous value, so that
more candidates can pass the filtering.
(eudc-capf-message-expand-name): Rename to
eudc-capf--message-expand-name to mark it as an internal use
function, and improved the doc string.
* lisp/gnus/message.el (message-mode): No longer add
eudc-capf-complete to the buffer-local value of
completion-at-point-functions.
---
 lisp/gnus/message.el  |  1 -
 lisp/net/eudc-capf.el | 46 ++++++++++++++++++++-----------------------
 2 files changed, 21 insertions(+), 26 deletions(-)

diff --git a/lisp/gnus/message.el b/lisp/gnus/message.el
index e7d11b597b3..6c10a4ae976 100644
--- a/lisp/gnus/message.el
+++ b/lisp/gnus/message.el
@@ -3191,7 +3191,6 @@ message-mode
     (mail-abbrevs-setup))
    ((message-mail-alias-type-p 'ecomplete)
     (ecomplete-setup)))
-  (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
index e2bbd5b28b6..c655c14df6d 100644
--- a/lisp/net/eudc-capf.el
+++ b/lisp/net/eudc-capf.el
@@ -101,34 +101,30 @@ eudc-capf-complete
 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)))
+  (when (and (or eudc-server eudc-server-hotlist)
+             (seq-some #'derived-mode-p eudc-capf-modes)
+             (let ((mail-abbrev-mode-regexp message-email-recipient-header-regexp))
+               (mail-abbrev-in-expansion-header-p)))
+    (setq-local completion-styles '(substring partial-completion))
+    (eudc-capf--message-expand-name)))
 
 ;;;###autoload
-(defun eudc-capf-message-expand-name ()
-  "Email address completion function for `message-completion-alist'.
+(defun eudc-capf--message-expand-name ()
+  "Helper for `eudc-capf-complete'.
 
-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 eudc-server eudc-server-hotlist)
-      (progn
-        (let* ((beg (save-excursion
-                      (re-search-backward "\\([:,]\\|^\\)[ \t]*")
-                      (match-end 0)))
-               (end (point))
-               (prefix (save-excursion (buffer-substring-no-properties beg end))))
-          (let ((result
-                 (eudc-query-with-words (split-string prefix "[ \t]+") t)))
-            (when result
-              (list beg end
-                    (completion-table-with-cache
-                     (lambda (_) result) t))))))))
+Computes a completion table as required for functions listed in
+`completion-at-point-functions'."
+  (let* ((beg (save-excursion
+                (re-search-backward "\\([:,]\\|^\\)[ \t]*")
+                (match-end 0)))
+         (end (point))
+         (prefix (save-excursion (buffer-substring-no-properties beg end))))
+    (let ((result
+           (eudc-query-with-words (split-string prefix "[ \t]+") t)))
+      (when result
+        (list beg end
+              (completion-table-with-cache
+               (lambda (_) result) t))))))
 
 (provide 'eudc-capf)
 ;;; eudc-capf.el ends here
-- 
2.33.1