bug#18871: 24.4; nxml-mode: DTD edition breaks the file structure

[Noam Postavsky]

Vincent Lefevre <vincent@vinc17.net> writes:

> This patch makes 6 tests fail (when applied to the Debian package):

>     (void-variable beg)

Dang it, I had thought I had fixed that before posting.  Here's the
correct version.

>From b8c659dc0c6ef41adc19db3c1884f73c1a10c8d8 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Sat, 18 May 2019 14:54:36 -0400
Subject: [PATCH] Keep nxml-prolog-end up to date (Bug#18871)

The change on 2016-01-16 "lisp/nxml: Use syntax-tables for comments"
removed the update of nxml-prolog-end, although it already failed to
work correctly after 2013-10-07 "* lisp/nxml/nxml-mode.el: Use
lexical-binding and syntax-propertize."
* lisp/nxml/nxml-rap.el: New function.
* lisp/nxml/nxml-mode.el (nxml-mode): Add it to
after-change-functions.
---
 lisp/nxml/nxml-mode.el | 1 +
 lisp/nxml/nxml-rap.el  | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/lisp/nxml/nxml-mode.el b/lisp/nxml/nxml-mode.el
index 7c39c5023c..b816bba819 100644
--- a/lisp/nxml/nxml-mode.el
+++ b/lisp/nxml/nxml-mode.el
@@ -534,6 +534,7 @@ nxml-mode
   (setq-local syntax-ppss-table sgml-tag-syntax-table)
   (setq-local syntax-propertize-function #'nxml-syntax-propertize)
   (add-hook 'change-major-mode-hook #'nxml-cleanup nil t)
+  (add-hook 'after-change-functions #'nxml-maybe-rescan-prolog nil t)
 
   ;; Emacs 23 handles the encoding attribute on the xml declaration
   ;; transparently to nxml-mode, so there is no longer a need for the below
diff --git a/lisp/nxml/nxml-rap.el b/lisp/nxml/nxml-rap.el
index 21dbaded25..3be413ae00 100644
--- a/lisp/nxml/nxml-rap.el
+++ b/lisp/nxml/nxml-rap.el
@@ -108,6 +108,12 @@ nxml-scan-prolog
     (setq nxml-prolog-regions (xmltok-forward-prolog))
     (setq nxml-prolog-end (point))))
 
+(defun nxml-maybe-rescan-prolog (start _end _length)
+  "Reparse the prolog if START lies within it.
+`nxml-mode' adds this function on `after-change-functions'."
+  (when (<= start nxml-prolog-end)
+    (save-excursion
+      (nxml-scan-prolog))))
 
 ;;; Random access parsing
 
-- 
2.11.0