>From f464242eab092e610dda6b654e6fd197ef649d3e Mon Sep 17 00:00:00 2001
From: Ikumi Keita <ikumi@ikumi.que.jp>
Date: Sat, 5 Mar 2022 00:29:08 +0900
Subject: [PATCH] Enable indent by square bracket

* tex.el (TeX-indent-open-delimiters):
(TeX-indent-close-delimiters): New options regarded as additional
open/close delimiters at indentation.
* tex.el (TeX-brace-count-line): Increase indentation inside those
options in addition to "{", "}".  In comments, don't ignore those
additional characters.
* latex.el (LaTeX-indent-calculate):
(LaTeX-indent-calculate-last):
Treat chars in `TeX-indent-close-delimiters' in the same way as "}".
---
 latex.el |  7 +++++--
 tex.el   | 41 +++++++++++++++++++++++++++++++++++------
 2 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/latex.el b/latex.el
index 4de97600..142d075c 100644
--- a/latex.el
+++ b/latex.el
@@ -3899,7 +3899,8 @@ outer indentation in case of a commented line.  The symbols
                                  "\\)"))
              ;; Items.
              (+ (LaTeX-indent-calculate-last force-type) LaTeX-item-indent))
-            ((looking-at "}")
+            ((memq (char-after) (append
+                                 TeX-indent-close-delimiters '(?\})))
              ;; End brace in the start of the line.
              (- (LaTeX-indent-calculate-last force-type)
                 TeX-brace-indent-level))
@@ -4041,7 +4042,9 @@ outer indentation in case of a commented line.  The symbols
                                            LaTeX-item-regexp
                                            "\\)"))
                        (- LaTeX-item-indent))
-                      ((looking-at "}")
+                      ((memq (char-after) (append
+                                           TeX-indent-close-delimiters
+                                           '(?\})))
                        TeX-brace-indent-level)
                       (t 0)))))))
 
diff --git a/tex.el b/tex.el
index 4876ae55..eb32a379 100644
--- a/tex.el
+++ b/tex.el
@@ -5410,6 +5410,20 @@ regardless of its data type."
   :group 'TeX-indentation
   :type 'integer)
 
+(defcustom TeX-indent-open-delimiters ""
+  "Additional open delimiters to increase indentation.
+Include \"[\" to indent inside square brackets.
+See `TeX-brace-count-line' and `TeX-indent-close-delimiters'."
+  :group  'TeX-indentation
+  :type '(string :tag "Open delimiters"))
+
+(defcustom TeX-indent-close-delimiters ""
+  "Additional close delimiters to increase indentation.
+Include \"]\" to indent inside square brackets.
+See `TeX-brace-count-line' and `TeX-indent-open-delimiters'."
+  :group  'TeX-indentation
+  :type '(string :tag "Close delimiters"))
+
 (defun TeX-comment-indent ()
   "Determine the indentation of a comment."
   (if (looking-at "%%%")
@@ -5419,17 +5433,32 @@ regardless of its data type."
          comment-column)))
 
 (defun TeX-brace-count-line ()
-  "Count number of open/closed braces."
+  "Count indent caused by open/closed braces.
+In addition to \"{\" and \"}\", characters in
+`TeX-indent-open-delimiters' and `TeX-indent-close-delimiters'
+are also taken into account.  Ignore them when they are escaped
+by \"\\\".  In comments, ignore \"{\" and \"}\" but don't ignore
+additional characters."
   (save-excursion
     (let ((count 0) (limit (line-end-position)) char)
       (while (progn
-               (skip-chars-forward "^{}\\\\" limit)
-               (when (and (< (point) limit) (not (TeX-in-comment)))
-                 (setq char (char-after))
+               (skip-chars-forward
+                (concat "^{}\\\\"
+                        TeX-indent-open-delimiters
+                        TeX-indent-close-delimiters)
+                limit)
+               (when (and (< (point) limit)
+                          (not (and (memq (setq char (char-after))
+                                          '(?\{ ?\} ?\\))
+                                    (TeX-in-comment))))
                  (forward-char)
-                 (cond ((eq char ?\{)
+                 (cond ((memq char (append
+                                    TeX-indent-open-delimiters
+                                    '(?\{)))
                         (setq count (+ count TeX-brace-indent-level)))
-                       ((eq char ?\})
+                       ((memq char (append
+                                    TeX-indent-close-delimiters
+                                    '(?\})))
                         (setq count (- count TeX-brace-indent-level)))
                        ((eq char ?\\)
                         (when (< (point) limit)
-- 
2.34.1