bug#52810: 29.0.50; diff-font-lock-prettify broken on new and deleted files

[Matthias Meulien]

1. Configure Diff mode to enable font lock prettify:

(add-hook 'diff-mode-hook #'(lambda ()
                              (setq diff-font-lock-prettify t)))

2. Visit the recent change log of emacs sources (eg C-x v L when
visiting one of emacs source file)

3. Find commit 3d38d1d134 and call log-view-diff

4. Jump to line 245 for the chunk applying to lisp/sqlite.el

5. Observe the strange line:

new file   lisp/sqlite.ellisp/sqlite.el

where "new file   lisp/sqlite.el" is expected.

A similar problem can be observed for deleted files.

Proposed fixed (but I must confess I've no idea why the original code
tried to set two distinct overlays):

>From 0f9a40a1514fc5cf4e04bcdb69db7eb30dd0c6ba Mon Sep 17 00:00:00 2001
From: Matthias Meulien <orontee@gmail.com>
Date: Sun, 26 Dec 2021 18:39:57 +0100
Subject: [PATCH] Fix diff--font-lock-prettify broken on created or deleted
 files

---
 lisp/vc/diff-mode.el | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index 8f83aa580e..60d210ca22 100644
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -2612,19 +2612,17 @@ diff--font-lock-prettify
                          "\\(?:index.*\n\\)?"
                          "--- \\(?:" null-device "\\|a/\\(.*\\)\\)\n"
                          "\\+\\+\\+ \\(?:" null-device "\\|b/\\(.*\\)\\)\n"))))
-        (put-text-property (match-beginning 0)
-                           (or (match-beginning 2) (match-beginning 1))
-                           'display (propertize
-                                     (cond
-                                      ((null (match-beginning 1))
-                                       (concat "new file  " (match-string 2)))
-                                      ((null (match-beginning 2))
-                                       (concat "deleted   " (match-string 1)))
-                                      (t
-                                       (concat "modified  " (match-string 1))))
-                                     'face '(diff-file-header diff-header)))
-        (put-text-property (match-end 1) (1- (match-end 0))
-                           'display ""))))
+        (put-text-property (match-beginning 0) (1- (match-end 0))
+                           'display
+                           (propertize
+                            (cond
+                             ((null (match-string 1))
+                              (concat "new file  " (match-string 2)))
+                             ((null (match-string 2))
+                              (concat "deleted  " (match-string 1)))
+                             (t
+                              (concat "modified  " (match-string 1))))
+                            'face '(diff-file-header diff-header))))))
   nil)
 
 ;;; Syntax highlighting from font-lock
-- 
2.30.2



In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.24, cairo 
version 1.16.0)
 of 2021-12-11 built on carbon
Repository revision: 15553f936abcc9c0bc85a2cd245319de273ee523
Repository branch: temp
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Debian GNU/Linux 11 (bullseye)

Configured using:
 'configure --with-native-compilation'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBXML2 M17N_FLT MODULES NATIVE_COMP NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM XPM GTK3 ZLIB

Important settings:
  value of $LANG: fr_FR.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Apropos

Minor modes in effect:
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  shell-dirtrack-mode: t
  minions-mode: t
  global-company-mode: t
  company-mode: t
  desktop-save-mode: t
  save-place-mode: t
  electric-pair-mode: t
  icomplete-mode: t
  global-so-long-mode: t
  global-auto-revert-mode: t
  auto-insert-mode: t
  text-scale-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-layout-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tab-bar-mode: t
  file-name-shadow-mode: t
  context-menu-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  window-divider-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
/home/matthias/.config/emacs/elpa/transient-20211105.100/transient hides 
/usr/local/share/emacs/29.0.50/lisp/transient
/home/matthias/.config/emacs/elpa/dictionary-20201001.1727/dictionary hides 
/usr/local/share/emacs/29.0.50/lisp/net/dictionary

Features:
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cl-preloaded nadvice button loaddefs faces cus-face macroexp files
window text-properties overlay sha1 md5 base64 format env code-pages
mule custom widget keymap hashtable-print-readable backquote threads
dbusbind inotify lcms2 dynamic-setting system-font-setting
font-render-setting cairo move-toolbar gtk x-toolkit x multi-tty
make-network-process native-compile emacs)

Memory information:
((conses 16 1292883 149347)
 (symbols 48 43725 5)
 (strings 32 217988 10513)
 (string-bytes 1 9128224)
 (vectors 16 95840)
 (vector-slots 8 2474388 186797)
 (floats 8 754 1282)
 (intervals 56 118271 611)
 (buffers 992 242))

-- 
Matthias