From 5bacde1f77c96318a9d36e82d3d6646e91094228 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20Ankarstr=C3=B6m?= <john@ankarstrom.se>
Date: Mon, 13 Jun 2022 23:24:28 +0200
Subject: xroff.el: Improve highlighting of troff escapes.

---
 xroff.el | 50 ++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 40 insertions(+), 10 deletions(-)

diff --git a/xroff.el b/xroff.el
index 48ba533..54ae981 100644
--- a/xroff.el
+++ b/xroff.el
@@ -6,20 +6,50 @@
 		       (not ?>))))
 	 ">"))
 
+(defvar xroff--single-escape-regexp
+  (rx "\\" any))
+
+(defvar xroff--identifier-escape-regexp
+  (rx "\\"
+      (any "FfgkmnOsYZ*$")
+      (? (any "+-"))
+      (or (not (any "([+-"))
+	  (seq "(" any any)
+	  (seq "[" (* (not "]")) "]"))))
+
+(defvar xroff--parameter-escape-regexp
+  (rx "\\"
+      (any "ABbCDHhLlMNoRSVvwXxz")
+      "'" (* (not "'")) "'"))
+
 (defconst xroff-font-lock-keywords
   `(("<!--.*-->"
      (0 font-lock-comment-face))
-    ("\\\\\\(.\\)"
-     (1 font-lock-builtin-face))
     (,(concat xroff--request-regexp)
      (1 font-lock-keyword-face)
      (2 font-lock-string-face))
     (,(concat "\\\\" xroff--request-regexp)
      (1 nil t)
      (2 nil t))
-    ;; ("<FS\\(?: \\(?:\\\\>\\|[^>]\\)*\\)?>\\(.*?\\)<FE\\(?: \\(?:\\\\>\\|[^>]\\)*\\)?>"
-    ;;  1 font-lock-doc-string)
-    ))
+    (,xroff--parameter-escape-regexp
+     (0 xroff-escape-face))
+    (,(concat "\\\\" xroff--parameter-escape-regexp)
+     (0 nil t))
+    (,xroff--identifier-escape-regexp
+     (0 xroff-escape-face))
+    (,(concat "\\\\" xroff--identifier-escape-regexp)
+     (0 nil t))
+    (,xroff--single-escape-regexp
+     (0 xroff-escape-face))
+    (,(concat "\\\\" xroff--single-escape-regexp)
+     (0 nil t))
+    (,"\\\\\\\\"
+     (0 xroff-escape-face t))))
+
+(defface xroff-escape
+  '((t (:foreground "gray")))
+  "`xroff-mode' face used to highlight backslash escapes.")
+(defvar xroff-escape-face 'xroff-escape)
 
 (define-derived-mode xroff-mode text-mode "Xroff"
   "Major mode for editing documents with xroff syntax."
@@ -29,19 +59,19 @@
   (setq-local paragraph-start "<\\([^>]\\)+>")
   (setq-local paragraph-separate "$\\|\\]>")
   (setq-local adaptive-fill-regexp "[ \t]*")
-  (add-hook 'fill-nobreak-predicate 'sgml-fill-nobreak nil t)
-  (setq-local indent-line-function 'sgml-indent-line)
+  ;; (add-hook 'fill-nobreak-predicate 'sgml-fill-nobreak nil t)
+  ;; (setq-local indent-line-function 'sgml-indent-line)
   (setq-local comment-start "<!-- ")
   (setq-local comment-end " -->")
-  (setq-local comment-indent-function 'sgml-comment-indent)
-  (setq-local comment-line-break-function 'sgml-comment-indent-new-line)
+  ;; (setq-local comment-indent-function 'sgml-comment-indent)
+  ;; (setq-local comment-line-break-function 'sgml-comment-indent-new-line)
   (setq-local skeleton-further-elements '((completion-ignore-case t)))
   (setq-local skeleton-end-hook
 	      (lambda ()
 		(or (eolp)
 		    (not (or (eq v2 '\n) (eq (car-safe v2) '\n)))
 		    (newline-and-indent))))
-  (setq-local font-lock-defaults '((xroff-font-lock-keywords) nil t nil))
+  (setq-local font-lock-defaults '((xroff-font-lock-keywords)))
   ;; (setq-local font-lock-multiline t)
   (setq-local comment-start-skip "<!--[ \t]*")
   (setq-local comment-end-skip "[ \t]*--[ \t\n]*>")
-- 
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