From 1ead480ca1f49b6759bb30353ee78656490149ae Mon Sep 17 00:00:00 2001
From: Lars Ingebrigtsen <larsi@gnus.org>
Date: Wed, 15 Jun 2022 18:29:42 +0200
Subject: [PATCH] Allow completing tags, parameters and values in html-mode

* lisp/textmodes/sgml-mode.el (html-mode--complete-at-point):
Allow completing tags, parameters and values (bug#29057).
---
 lisp/textmodes/sgml-mode.el | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/lisp/textmodes/sgml-mode.el b/lisp/textmodes/sgml-mode.el
index b49541f47d4..ff881377a7e 100644
--- a/lisp/textmodes/sgml-mode.el
+++ b/lisp/textmodes/sgml-mode.el
@@ -2409,6 +2409,7 @@ To work around that, do:
 	      (lambda () (char-before (match-end 0))))
   (setq-local add-log-current-defun-function #'html-current-defun-name)
   (setq-local sentence-end-base "[.?!][]\"'”)}]*\\(<[^>]*>\\)*")
+  (add-hook 'completion-at-point-functions 'html-mode--complete-at-point nil t)
 
   (when (fboundp 'libxml-parse-html-region)
     (defvar css-class-list-function)
@@ -2434,6 +2435,36 @@ To work around that, do:
   ;; (setq imenu-sort-function nil) ; sorting the menu defeats the purpose
   )
 
+(defun html-mode--complete-at-point ()
+  ;; Complete a tag like <colg etc.
+  (or
+   (when-let ((tag (save-excursion
+                     (and (looking-back "<\\([^ \t\n]*\\)"
+                                        (line-beginning-position))
+                          (match-string 1)))))
+     (list (match-beginning 1) (point)
+           (mapcar #'car html-tag-alist)))
+   ;; Complete params like <colgroup ali etc.
+   (when-let ((tag (save-excursion (sgml-beginning-of-tag)))
+              (params (seq-filter #'consp (cdr (assoc tag html-tag-alist))))
+              (param (save-excursion
+                       (and (looking-back "[ \t\n]\\([^= \t\n]*\\)"
+                                          (line-beginning-position))
+                            (match-string 1)))))
+     (list (match-beginning 1) (point)
+           (mapcar #'car params)))
+   ;; Complete param values like <colgroup align=mi etc.
+   (when-let ((tag (save-excursion (sgml-beginning-of-tag)))
+              (params (seq-filter #'consp (cdr (assoc tag html-tag-alist))))
+              (param (save-excursion
+                       (and (looking-back
+                             "[ \t\n]\\([^= \t\n]+\\)=\\([^= \t\n]*\\)"
+                             (line-beginning-position))
+                            (match-string 1))))
+              (values (cdr (assoc param params))))
+     (list (match-beginning 2) (point)
+           (mapcar #'car values)))))
+
 (defun html-mode--html-yank-handler (_type html)
   (save-restriction
     (insert html)
-- 
2.39.2