From: Paul Eggert <eggert@cs.ucla.edu>
Date: Fri, 18 Jul 2025 06:00:38 +0000 (-0700)
Subject: Fix insert-file-contents optimization glitch
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=9a3c35203fc2435e1a73fa0f5b8861d9ff1008de;p=emacs.git

Fix insert-file-contents optimization glitch

This improves on recent fixes to Bug#77315.
* src/fileio.c (Finsert_file_contents): When optimizing
do not seek to 0 if the initial file offset is positive,
as that causes the optimized code to behave differently
from the nonoptimized.

(cherry picked from commit 5f4b71b0c4872b6bd9f8b4ced9f4715062db1bad)
---

diff --git a/src/fileio.c b/src/fileio.c
index 248a369341a..fc5d4c27cfb 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4291,13 +4291,8 @@ by calling `format-decode', which see.  */)
       else
 	{
 	  /* Don't try looking inside a file for a coding system
-	     specification if it is not a regular, seekable file.  */
-	  bool look_inside = (regular && seekable
-			      && !NILP (Vset_auto_coding_function));
-	  if (look_inside && 0 < initial_offset
-	      && emacs_fd_lseek (fd, 0, SEEK_SET) < 0)
-	    look_inside = seekable = false;
-	  if (look_inside)
+	     specification if it is not a regular file.  */
+	  if (regular && !NILP (Vset_auto_coding_function))
 	    {
 	      /* Find a coding system specified in the heading two
 		 lines or in the tailing several lines of the file.