emacs-29 7acae22f42f: Fix auto-filling in Texinfo mode

[Eli Zaretskii]

branch: emacs-29
commit 7acae22f42f1b2df2042d5d77a0839f0ca9c02e7
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Fix auto-filling in Texinfo mode
    
    This fixes auto-filling in Texinfo buffers.  It was broken by the
    fix to bug#49558, which made M-q fill over-long @noindent lines by
    refraining from customizing 'paragraph-separate' in Texinfo mode.
    The underlying problem here is that 'auto-fill-mode' doesn't call
    mode-specific filling functions, but does its job by itself, and
    depends on 'forward-paragraph' to find the beginning of the
    paragraph as appropriate for calculation of 'fill-prefix', and a
    different value of 'paragraph-separate' broke that.  As a side
    effect, the change below also changes paragraph-movement commands
    in Texinfo back to how they behaved prior to that bugfix, but I
    don't see why the paragraph-movement behavior introduced by that
    fix made more sense.  Try to move through a series of
    @-directives, like a paragraph preceded by several @cindex
    entries, and you will see the inconsistencies.  In any case, the
    adverse effects of that fix on auto-filling is unacceptable.
    
    * lisp/textmodes/texinfo.el (fill-paragraph-separate): New
    variable.
    (texinfo-mode): Set 'fill-paragraph-separate' to the default value
    of 'paragraph-separate'.  Customize 'paragraph-separate' to the
    Texinfo-specific value, as it was before commit dde591571abf.
    (texinfo--fill-paragraph): Bind 'paragraph-separate' to the value
    of 'fill-paragraph-separate', to keep 'M-q' happy.
---
 lisp/textmodes/texinfo.el | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/lisp/textmodes/texinfo.el b/lisp/textmodes/texinfo.el
index 7416c631c9f..bedf9ec92a5 100644
--- a/lisp/textmodes/texinfo.el
+++ b/lisp/textmodes/texinfo.el
@@ -409,6 +409,8 @@ REPORT-FN is the callback function."
 
 ;;; Texinfo mode
 
+(defvar fill-paragraph-separate nil)
+
 ;;;###autoload
 (define-derived-mode texinfo-mode text-mode "Texinfo"
   "Major mode for editing Texinfo files.
@@ -482,6 +484,10 @@ value of `texinfo-mode-hook'."
                      "\\)\\>"))
   (setq-local require-final-newline mode-require-final-newline)
   (setq-local indent-tabs-mode nil)
+  ;; This is used in 'texinfo--fill-paragraph'.
+  (setq-local fill-paragraph-separate (default-value 'paragraph-separate))
+  (setq-local paragraph-separate
+              (concat "@[a-zA-Z]*[ \n]\\|" paragraph-separate))
   (setq-local paragraph-start (concat "@[a-zA-Z]*[ \n]\\|"
                                      paragraph-start))
   (setq-local fill-paragraph-function 'texinfo--fill-paragraph)
@@ -536,7 +542,13 @@ value of `texinfo-mode-hook'."
 
 (defun texinfo--fill-paragraph (justify)
   "Function to fill a paragraph in `texinfo-mode'."
-  (let ((command-re "\\(@[a-zA-Z]+\\)[ \t\n]"))
+  (let ((command-re "\\(@[a-zA-Z]+\\)[ \t\n]")
+        ;; Kludge alert: we override paragraph-separate here because
+        ;; that is needed for filling @noindent and similar lines.
+        ;; The default Texinfo-specific paragraph-separate value,
+        ;; OTOH, is needed for auto-fill-mode, which doesn't call
+        ;; mode-specific functions.
+        (paragraph-separate fill-paragraph-separate))
     (catch 'no-fill
       (save-restriction
         ;; First check whether we're on a command line that can be