patch 9.2.0499: modeline: allow to disable modelines with modelinestrict

Problem:  Cannot disable modeline processing when loading a file
          (Mao-Yining, after v9.2.0350)
Solution: Allow to disable modeline processing even when
          'modelienstrict' is in effect.

fixes:  #20103
closes: #20229

Signed-off-by: Christian Brabandt <cb@256bit.org>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/options.txt

@@ -1,4 +1,4 @@
-*options.txt*	For Vim version 9.2.  Last change: 2026 May 17
+*options.txt*	For Vim version 9.2.  Last change: 2026 May 18
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -6239,6 +6239,11 @@ A jump table for the options with a short description can be found at |Q_op|.
 	This option cannot be set from a |modeline| or in the |sandbox|, for
 	security reasons.
 
+	As an exception, `set nomodeline` is honored from within a modeline
+	even when 'modelinestrict' is on.  Other forms (`set modeline=0`,
+	`set modeline!`, `set invmodeline`) are still silently ignored.
+	This lets a file disable further modeline processing for itself.
+
 	The behaviour of 'modeline', 'modelinestrict' and 'modelineexpr' is
 	as follows:
 

src/option.c

@@ -1589,7 +1589,12 @@ is_modeline_whitelisted(char *name)
  * if it can be changed.
  */
     static int
-validate_opt_idx(int opt_idx, int opt_flags, long_u flags, char **errmsg)
+validate_opt_idx(
+	int opt_idx,
+	int opt_flags,
+	long_u flags,
+	char **errmsg,
+	set_prefix_T prefix)
 {
     // Skip all options that are not window-local (used when showing
     // an already loaded buffer in a window).
@@ -1617,9 +1622,14 @@ validate_opt_idx(int opt_idx, int opt_flags, long_u flags, char **errmsg)
 	}
 	// When 'modelinestrict' is on, only whitelisted options may be
 	// set from a modeline.  Silently skip others.
-	if (p_mlstr && opt_idx >= 0
-		&& !is_modeline_whitelisted(options[opt_idx].fullname))
-	    return FAIL;
+	if (p_mlstr && opt_idx >= 0)
+	{
+	    // special case: allow disabling modeline
+	    if (options[opt_idx].indir == PV_ML && prefix == PREFIX_NO)
+		return OK;
+	    else if (!is_modeline_whitelisted(options[opt_idx].fullname))
+		return FAIL;
+	}
 #ifdef FEAT_DIFF
 	// In diff mode some options are overruled.  This avoids that
 	// 'foldmethod' becomes "marker" instead of "diff" and that
@@ -2864,7 +2874,7 @@ do_set_option(
     }
 
     // Make sure the option value can be changed.
-    if (validate_opt_idx(opt_idx, opt_flags, flags, &errmsg) == FAIL)
+    if (validate_opt_idx(opt_idx, opt_flags, flags, &errmsg, prefix) == FAIL)
 	goto skip;
 
     int cp_val = p_cp;

src/testdir/test_modeline.vim

@@ -666,4 +666,56 @@ func Test_modeline_strict_cannot_be_set_from_modeline()
   let &modeline = modeline
 endfunc
 
+func Test_modeline_nomodeline_with_modelinestrict()
+	let modeline = &modeline
+	let modelinestrict = &modelinestrict
+	let modelines = &modelines
+	set modelinestrict modeline modelines=5
+	let ml_before = &g:modeline
+
+	call writefile(['# vim: set nomodeline:', 'line2'], 'Xnoml', 'D')
+	split Xnoml
+	call assert_equal(0, &l:modeline, 'b_p_ml should be off')
+	call assert_equal(ml_before, &g:modeline, 'global p_ml must not change')
+	bwipe!
+
+	" A fresh buffer must still inherit the unchanged global default
+	new
+	call assert_equal(ml_before, &l:modeline,
+				\ 'new buffer should inherit unchanged global')
+	bwipe!
+
+	let &modeline = modeline
+	let &modelinestrict = modelinestrict
+	let &modelines = modelines
+endfunc
+
+func Test_modeline_nomodeline_skips_trailing_modelines()
+	let modeline = &modeline
+	let modelinestrict = &modelinestrict
+	let ts_save = &ts
+	set modeline modelinestrict ts=8
+
+	" Line 1 disables modelines; the trailing modeline must therefore
+	" never execute even though 'tabstop' is whitelisted.
+	call writefile([
+				\ '# vim: set nomodeline :',
+				\ 'middle line 1',
+				\ 'middle line 2',
+				\ 'middle line 3',
+				\ '# vim: set ts=99 :',
+				\ ], 'Xmodeline_disable_top', 'D')
+	split Xmodeline_disable_top
+
+	call assert_equal(0, &l:modeline,
+				\ 'top modeline must have disabled b_p_ml')
+	call assert_equal(8, &ts,
+				\ 'trailing modeline must not have run after nomodeline')
+
+	bwipe!
+	let &modeline = modeline
+	let &modelinestrict = modelinestrict
+	let &ts = ts_save
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -729,6 +729,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    499,
 /**/
     498,
 /**/