patch 9.1.2138: win_execute() and 'autochdir' can corrupt buffer name

Problem:  With 'autochdir' win_execute() can corrupt the buffer name,
          causing :write to use wrong path.
Solution: Save and restore b_fname when 'autochdir' is active
          (Ingo Karkat).

This is caused by a bad interaction of the 'autochdir' behavior,
overriding of the current directory via :lchdir, and the temporary
window switching done by win_execute(), manifesting when e.g. a custom
completion inspects other buffers:
1. In the initial state after the :lcd .. we have curbuf->b_fname =
   "Xsubdir/file".
2. do_autochdir() is invoked, temporarily undoing the :lcd .., changing
   back into the Xsubdir/ subdirectory.
3. win_execute() switches windows, triggering win_enter_ext() →
   win_fix_current_dir() → shorten_fnames(TRUE)
4. shorten_fnames() processes *all* buffers
5. shorten_buf_fname() makes the filename relative to the current
   (wrong) directory; b_fname becomes "file" instead of "Xsubdir/file"
6. Directory restoration correctly restores working directory via
   mch_chdir() (skipping a second do_autochdir() invocation because
   apply_acd is FALSE), but b_fname remains corrupted, with the
   "Xsubdir/" part missing.
7. expand("%:p") (and commands like :write) continue to use the
   corrupted filename, resolving to a wrong path that's missing the
   "Xsubdir/" part.

To fix the problem the short filename is saved if its in effect (i.e.
pointed to by curbuf->b_fname) and 'autochdir' happened. It's then
restored in case of a local cwd override. The conditions limit this
workaround to when 'autochdir' is active *and* overridden by a :lchdir.

closes: #19343

Co-authored-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Ingo Karkat <swdev@ingo-karkat.de>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/version9.txt

@@ -52512,4 +52512,9 @@ Problem:  Some tests are not valid on OpenBSD.
 Solution: Add CheckNotOpenBSD, use it to skip certain tests
           (Kevin Goodsell).
 
+Patch 9.1.2138
+Problem:  With 'autochdir' win_execute() can corrupt the buffer name, causing
+          :write to use wrong path.
+Solution: Save and restore b_fname when 'autochdir' is active (Ingo Karkat).
+
  vim:tw=78:ts=8:noet:ft=help:norl:fdm=manual:nofoldenable

src/evalwindow.c

@@ -732,6 +732,7 @@ f_win_execute(typval_T *argvars, typval_T *rettv)
 # ifdef FEAT_AUTOCHDIR
     char_u	autocwd[MAXPATHL];
     int	apply_acd = FALSE;
+    char_u	*save_sfname = NULL;
 # endif
 
     // Getting and setting directory can be slow on some systems, only do
@@ -754,6 +755,8 @@ f_win_execute(typval_T *argvars, typval_T *rettv)
     // apply 'acd' afterwards, otherwise restore the current directory.
     if (cwd_status == OK && p_acd)
     {
+	if (curbuf->b_sfname != NULL && curbuf->b_fname == curbuf->b_sfname)
+	    save_sfname = vim_strsave(curbuf->b_sfname);
 	do_autochdir();
 	apply_acd = mch_dirname(autocwd, MAXPATHL) == OK
 	    && STRCMP(cwd, autocwd) == 0;
@@ -768,11 +771,24 @@ f_win_execute(typval_T *argvars, typval_T *rettv)
     restore_win_noblock(&switchwin, TRUE);
 # ifdef FEAT_AUTOCHDIR
     if (apply_acd)
+    {
+	vim_free(save_sfname);
 	do_autochdir();
+    }
     else
 # endif
 	if (cwd_status == OK)
+	{
 	    mch_chdir((char *)cwd);
+# ifdef FEAT_AUTOCHDIR
+	    if (save_sfname != NULL)
+	    {
+		vim_free(curbuf->b_sfname);
+		curbuf->b_sfname = save_sfname;
+		curbuf->b_fname = curbuf->b_sfname;
+	    }
+# endif
+	}
 
     // Update the status line if the cursor moved.
     if (win_valid(wp) && !EQUAL_POS(curpos, wp->w_cursor))

src/testdir/test_cd.vim

@@ -189,6 +189,27 @@ func Test_lcd_split()
   quit!
 endfunc
 
+" Test that a temporary override of 'autochdir' via :lcd isn't clobbered by win_execute() in a split window.
+func Test_lcd_win_execute()
+  CheckOption autochdir
+
+  let startdir = getcwd()
+  call mkdir('Xsubdir', 'R')
+  call test_autochdir()
+  set autochdir
+  edit Xsubdir/file
+  call assert_match('testdir.Xsubdir.file$', expand('%:p'))
+  split
+  lcd ..
+  call assert_match('testdir.Xsubdir.file$', expand('%:p'))
+  call win_execute(win_getid(2), "")
+  call assert_match('testdir.Xsubdir.file$', expand('%:p'))
+
+  set noautochdir
+  bwipe!
+  call chdir(startdir)
+endfunc
+
 func Test_cd_from_non_existing_dir()
   CheckNotMSWindows
 

src/version.c

@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2138,
 /**/
     2137,
 /**/