--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -1,4 +1,4 @@
-*eval.txt*	For Vim version 9.1.  Last change: 2024 Jul 28
+*eval.txt*	For Vim version 9.1.  Last change: 2024 Oct 22
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -2223,7 +2223,8 @@ v:fcs_choice	What should happen after a 
 
 					*v:fname* *fname-variable*
 v:fname		When evaluating 'includeexpr': the file name that was
-		detected.  Empty otherwise.
+		detected.  When evaluating 'findexpr': the argument passed to
+		the |:find| command.  Empty otherwise.
 
 					*v:fname_in* *fname_in-variable*
 v:fname_in	The name of the input file.  Valid while evaluating:

--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -3552,6 +3552,51 @@ A jump table for the options with a shor
 	  eob		EndOfBuffer		|hl-EndOfBuffer|
 	  lastline	NonText			|hl-NonText|
 
+						*'findexpr'* *'fexpr'*
+'findexpr' 'fexpr'	string	(default "")
+			global or local to buffer |global-local|
+			{not available when compiled without the |+eval|
+			feature}
+	Expression that is evaluated to obtain the filename(s) for the |:find|
+	command.  When this option is empty, the internal |file-searching|
+	mechanism is used.
+
+	While evaluating the expression, the |v:fname| variable is set to the
+	argument of the |:find| command.
+
+	The expression is evaluated only once per |:find| command invocation.
+	The expression can process all the directories specified in 'path'.
+
+	If a match is found, the expression should return a |List| containing
+	one or more file names.  If a match is not found, the expression
+	should return an empty List.
+
+	If any errors are encountered during the expression evaluation, an
+	empty List is used as the return value.
+
+	Using a function call without arguments is faster |expr-option-function|
+
+	It is not allowed to change text or jump to another window while
+	evaluating 'findexpr' |textlock|.
+
+	This option cannot be set from a |modeline| or in the |sandbox|, for
+	security reasons.
+
+	Examples:
+>
+	    " Use glob()
+	    func FindExprGlob()
+		return glob(v:fname, v:false, v:true)
+	    endfunc
+	    set findexpr=FindExprGlob()
+
+	    " Use the 'git ls-files' output
+	    func FindGitFiles()
+		let fnames = systemlist('git ls-files')
+		return fnames->filter('v:val =~? v:fname')
+	    endfunc
+	    set findexpr=FindGitFiles()
+<
 		*'fixendofline'* *'fixeol'* *'nofixendofline'* *'nofixeol'*
 'fixendofline' 'fixeol'	boolean	(default on)
 			local to buffer

--- a/runtime/doc/quickref.txt
+++ b/runtime/doc/quickref.txt
@@ -1,4 +1,4 @@
-*quickref.txt*  For Vim version 9.1.  Last change: 2024 Mar 03
+*quickref.txt*  For Vim version 9.1.  Last change: 2024 Oct 22
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -707,6 +707,7 @@ Short explanation of each option:		*opti
 'fileignorecase'  'fic'     ignore case when using file names
 'filetype'	  'ft'	    type of file, used for autocommands
 'fillchars'	  'fcs'     characters to use for displaying special items
+'findexpr'	  'fexpr'   expression to evaluate for |:find|
 'fixendofline'	  'fixeol'  make sure last line in file has <EOL>
 'fkmap'		  'fk'	    obsolete option for Farsi
 'foldclose'	  'fcl'     close a fold when the cursor leaves it

--- a/runtime/doc/tags
+++ b/runtime/doc/tags
@@ -267,6 +267,7 @@
 'fenc'	options.txt	/*'fenc'*
 'fencs'	options.txt	/*'fencs'*
 'fex'	options.txt	/*'fex'*
+'fexpr'	options.txt	/*'fexpr'*
 'ff'	options.txt	/*'ff'*
 'ffs'	options.txt	/*'ffs'*
 'fic'	options.txt	/*'fic'*
@@ -277,6 +278,7 @@
 'fileignorecase'	options.txt	/*'fileignorecase'*
 'filetype'	options.txt	/*'filetype'*
 'fillchars'	options.txt	/*'fillchars'*
+'findexpr'	options.txt	/*'findexpr'*
 'fixendofline'	options.txt	/*'fixendofline'*
 'fixeol'	options.txt	/*'fixeol'*
 'fk'	options.txt	/*'fk'*

--- a/runtime/doc/version9.txt
+++ b/runtime/doc/version9.txt
@@ -1,4 +1,4 @@
-*version9.txt*  For Vim version 9.1.  Last change: 2024 Oct 14
+*version9.txt*  For Vim version 9.1.  Last change: 2024 Oct 22
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -41649,6 +41649,8 @@ Options: ~
 
 'completeitemalign'	Order of |complete-items| in Insert mode completion
 			popup
+'findexpr'		Vim expression to obtain the results for a |:find|
+			command
 'winfixbuf'		Keep buffer focused in a window
 'tabclose'		Which tab page to focus after closing a tab page
 't_xo'			Terminal uses XON/XOFF handshaking (e.g. vt420)

--- a/src/buffer.c
+++ b/src/buffer.c
@@ -2412,6 +2412,7 @@ free_buf_options(
     clear_string_option(&buf->b_p_fp);
 #if defined(FEAT_EVAL)
     clear_string_option(&buf->b_p_fex);
+    clear_string_option(&buf->b_p_fexpr);
 #endif
 #ifdef FEAT_CRYPT
 # ifdef FEAT_SODIUM

--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -6923,6 +6923,103 @@ ex_wrongmodifier(exarg_T *eap)
     eap->errmsg = ex_errmsg(e_invalid_command_str, eap->cmd);
 }
 
+#ifdef FEAT_EVAL
+/*
+ * Evaluate the 'findexpr' expression and return the result.  When evaluating
+ * the expression, v:fname is set to the ":find" command argument.
+ */
+    static list_T *
+eval_findexpr(char_u *ptr, int len)
+{
+    sctx_T	saved_sctx = current_sctx;
+    int		use_sandbox = FALSE;
+    char_u	*findexpr;
+    char_u	*arg;
+    typval_T	tv;
+    list_T	*retlist = NULL;
+
+    if (*curbuf->b_p_fexpr == NUL)
+    {
+	use_sandbox = was_set_insecurely((char_u *)"findexpr", OPT_GLOBAL);
+	findexpr = p_fexpr;
+    }
+    else
+    {
+	use_sandbox = was_set_insecurely((char_u *)"findexpr", OPT_LOCAL);
+	findexpr = curbuf->b_p_fexpr;
+    }
+
+    set_vim_var_string(VV_FNAME, ptr, len);
+    current_sctx = curbuf->b_p_script_ctx[BV_FEXPR];
+
+    arg = skipwhite(findexpr);
+
+    if (use_sandbox)
+	++sandbox;
+    ++textlock;
+
+    // Evaluate the expression.  If the expression is "FuncName()" call the
+    // function directly.
+    if (eval0_simple_funccal(arg, &tv, NULL, &EVALARG_EVALUATE) == FAIL)
+	retlist = NULL;
+    else
+    {
+	if (tv.v_type == VAR_LIST)
+	    retlist = list_copy(tv.vval.v_list, TRUE, TRUE, get_copyID());
+	clear_tv(&tv);
+    }
+    if (use_sandbox)
+	--sandbox;
+    --textlock;
+    clear_evalarg(&EVALARG_EVALUATE, NULL);
+
+    set_vim_var_string(VV_FNAME, NULL, 0);
+    current_sctx = saved_sctx;
+
+    return retlist;
+}
+
+/*
+ * Use 'findexpr' to find file 'findarg'.  The 'count' argument is used to find
+ * the n'th matching file.
+ */
+    static char_u *
+findexpr_find_file(char_u *findarg, int findarg_len, int count)
+{
+    list_T	*fname_list;
+    char_u	*ret_fname = NULL;
+    char_u	cc;
+    int		fname_count;
+
+    cc = findarg[findarg_len];
+    findarg[findarg_len] = NUL;
+
+    fname_list = eval_findexpr(findarg, findarg_len);
+    fname_count = list_len(fname_list);
+
+    if (fname_count == 0)
+	semsg(_(e_cant_find_file_str_in_path), findarg);
+    else
+    {
+	if (count > fname_count)
+	    semsg(_(e_no_more_file_str_found_in_path), findarg);
+	else
+	{
+	    listitem_T *li = list_find(fname_list, count - 1);
+	    if (li != NULL && li->li_tv.v_type == VAR_STRING)
+		ret_fname = vim_strsave(li->li_tv.vval.v_string);
+	}
+    }
+
+    if (fname_list != NULL)
+	list_free(fname_list);
+
+    findarg[findarg_len] = cc;
+
+    return ret_fname;
+}
+#endif
+
 /*
  * :sview [+command] file	split window with new file, read-only
  * :split [[+command] file]	split window with current or new file
@@ -6972,11 +7069,22 @@ ex_splitview(exarg_T *eap)
     {
 	char_u	*file_to_find = NULL;
 	char	*search_ctx = NULL;
-	fname = find_file_in_path(eap->arg, (int)STRLEN(eap->arg),
-					  FNAME_MESS, TRUE, curbuf->b_ffname,
-					  &file_to_find, &search_ctx);
-	vim_free(file_to_find);
-	vim_findfile_cleanup(search_ctx);
+
+	if (*get_findexpr() != NUL)
+	{
+#ifdef FEAT_EVAL
+	    fname = findexpr_find_file(eap->arg, (int)STRLEN(eap->arg),
+				       eap->addr_count > 0 ? eap->line2 : 1);
+#endif
+	}
+	else
+	{
+	    fname = find_file_in_path(eap->arg, (int)STRLEN(eap->arg),
+					      FNAME_MESS, TRUE, curbuf->b_ffname,
+					      &file_to_find, &search_ctx);
+	    vim_free(file_to_find);
+	    vim_findfile_cleanup(search_ctx);
+	}
 	if (fname == NULL)
 	    goto theend;
 	eap->arg = fname;
@@ -7241,27 +7349,37 @@ ex_find(exarg_T *eap)
     if (!check_can_set_curbuf_forceit(eap->forceit))
 	return;
 
-    char_u	*fname;
+    char_u	*fname = NULL;
     int		count;
     char_u	*file_to_find = NULL;
     char	*search_ctx = NULL;
 
-    fname = find_file_in_path(eap->arg, (int)STRLEN(eap->arg), FNAME_MESS,
-			   TRUE, curbuf->b_ffname, &file_to_find, &search_ctx);
-    if (eap->addr_count > 0)
-    {
-	// Repeat finding the file "count" times.  This matters when it appears
-	// several times in the path.
-	count = eap->line2;
-	while (fname != NULL && --count > 0)
-	{
-	    vim_free(fname);
-	    fname = find_file_in_path(NULL, 0, FNAME_MESS,
-			  FALSE, curbuf->b_ffname, &file_to_find, &search_ctx);
-	}
-    }
-    VIM_CLEAR(file_to_find);
-    vim_findfile_cleanup(search_ctx);
+    if (*get_findexpr() != NUL)
+    {
+#ifdef FEAT_EVAL
+	fname = findexpr_find_file(eap->arg, (int)STRLEN(eap->arg),
+					eap->addr_count > 0 ? eap->line2 : 1);
+#endif
+    }
+    else
+    {
+	fname = find_file_in_path(eap->arg, (int)STRLEN(eap->arg), FNAME_MESS,
+			       TRUE, curbuf->b_ffname, &file_to_find, &search_ctx);
+	if (eap->addr_count > 0)
+	{
+	    // Repeat finding the file "count" times.  This matters when it appears
+	    // several times in the path.
+	    count = eap->line2;
+	    while (fname != NULL && --count > 0)
+	    {
+		vim_free(fname);
+		fname = find_file_in_path(NULL, 0, FNAME_MESS,
+			      FALSE, curbuf->b_ffname, &file_to_find, &search_ctx);
+	    }
+	}
+	VIM_CLEAR(file_to_find);
+	vim_findfile_cleanup(search_ctx);
+    }
 
     if (fname == NULL)
 	return;

--- a/src/option.c
+++ b/src/option.c
@@ -6313,6 +6313,11 @@ unset_global_local_option(char_u *name, 
 	case PV_FP:
 	    clear_string_option(&buf->b_p_fp);
 	    break;
+# ifdef FEAT_EVAL
+	case PV_FEXPR:
+	    clear_string_option(&buf->b_p_fexpr);
+	    break;
+# endif
 # ifdef FEAT_QUICKFIX
 	case PV_EFM:
 	    clear_string_option(&buf->b_p_efm);
@@ -6391,6 +6396,9 @@ get_varp_scope(struct vimoption *p, int 
 	switch ((int)p->indir)
 	{
 	    case PV_FP:   return (char_u *)&(curbuf->b_p_fp);
+#ifdef FEAT_EVAL
+	    case PV_FEXPR:   return (char_u *)&(curbuf->b_p_fexpr);
+#endif
 #ifdef FEAT_QUICKFIX
 	    case PV_EFM:  return (char_u *)&(curbuf->b_p_efm);
 	    case PV_GP:   return (char_u *)&(curbuf->b_p_gp);
@@ -6501,6 +6509,10 @@ get_varp(struct vimoption *p)
 #endif
 	case PV_FP:	return *curbuf->b_p_fp != NUL
 				    ? (char_u *)&(curbuf->b_p_fp) : p->var;
+#ifdef FEAT_EVAL
+	case PV_FEXPR:	return *curbuf->b_p_fexpr != NUL
+				    ? (char_u *)&curbuf->b_p_fexpr : p->var;
+#endif
 #ifdef FEAT_QUICKFIX
 	case PV_EFM:	return *curbuf->b_p_efm != NUL
 				    ? (char_u *)&(curbuf->b_p_efm) : p->var;
@@ -6748,6 +6760,21 @@ get_equalprg(void)
 }
 
 /*
+ * Get the value of 'findexpr', either the buffer-local one or the global one.
+ */
+    char_u *
+get_findexpr(void)
+{
+#ifdef FEAT_EVAL
+    if (*curbuf->b_p_fexpr == NUL)
+	return p_fexpr;
+    return curbuf->b_p_fexpr;
+#else
+    return (char_u *)"";
+#endif
+}
+
+/*
  * Copy options from one window to another.
  * Used when splitting a window.
  */
@@ -7275,6 +7302,10 @@ buf_copy_options(buf_T *buf, int flags)
 	    buf->b_p_efm = empty_option;
 #endif
 	    buf->b_p_ep = empty_option;
+#if defined(FEAT_EVAL)
+	    buf->b_p_fexpr = vim_strsave(p_fexpr);
+	    COPY_OPT_SCTX(buf, BV_FEXPR);
+#endif
 	    buf->b_p_kp = empty_option;
 	    buf->b_p_path = empty_option;
 	    buf->b_p_tags = empty_option;

--- a/src/option.h
+++ b/src/option.h
@@ -596,6 +596,9 @@ EXTERN char_u	*p_ffs;		// 'fileformats'
 EXTERN int	p_fic;		// 'fileignorecase'
 EXTERN char_u	*p_ft;		// 'filetype'
 EXTERN char_u	*p_fcs;		// 'fillchar'
+#ifdef FEAT_EVAL
+EXTERN char_u	*p_fexpr;	// 'findexpr'
+#endif
 EXTERN int	p_fixeol;	// 'fixendofline'
 #ifdef FEAT_FOLDING
 EXTERN char_u	*p_fcl;		// 'foldclose'
@@ -1168,6 +1171,7 @@ enum
     , BV_EP
     , BV_ET
     , BV_FENC
+    , BV_FEXPR
     , BV_FP
 #ifdef FEAT_EVAL
     , BV_BEXPR

--- a/src/optiondefs.h
+++ b/src/optiondefs.h
@@ -74,6 +74,7 @@
 #define PV_FP		OPT_BOTH(OPT_BUF(BV_FP))
 #ifdef FEAT_EVAL
 # define PV_FEX		OPT_BUF(BV_FEX)
+# define PV_FEXPR	OPT_BOTH(OPT_BUF(BV_FEXPR))
 #endif
 #define PV_FF		OPT_BUF(BV_FF)
 #define PV_FLP		OPT_BUF(BV_FLP)
@@ -958,6 +959,15 @@ static struct vimoption options[] =
 			    {(char_u *)"vert:|,fold:-,eob:~,lastline:@",
 								  (char_u *)0L}
 			    SCTX_INIT},
+    {"findexpr",   "fexpr", P_STRING|P_ALLOCED|P_VI_DEF|P_VIM|P_SECURE,
+#if defined(FEAT_EVAL)
+			    (char_u *)&p_fexpr, PV_FEXPR, did_set_optexpr, NULL,
+			    {(char_u *)"", (char_u *)0L}
+#else
+			    (char_u *)NULL, PV_NONE, NULL, NULL,
+			    {(char_u *)0L, (char_u *)0L}
+#endif
+			    SCTX_INIT},
     {"fixendofline",  "fixeol", P_BOOL|P_VI_DEF|P_RSTAT,
 			    (char_u *)&p_fixeol, PV_FIXEOL,
 			    did_set_eof_eol_fixeol_bomb, NULL,

--- a/src/optionstr.c
+++ b/src/optionstr.c
@@ -324,6 +324,9 @@ check_buf_options(buf_T *buf)
     check_string_option(&buf->b_p_efm);
 #endif
     check_string_option(&buf->b_p_ep);
+#ifdef FEAT_EVAL
+    check_string_option(&buf->b_p_fexpr);
+#endif
     check_string_option(&buf->b_p_path);
     check_string_option(&buf->b_p_tags);
     check_string_option(&buf->b_p_tc);
@@ -3132,8 +3135,8 @@ expand_set_nrformats(optexpand_T *args, 
 #if defined(FEAT_EVAL) || defined(PROTO)
 /*
  * One of the '*expr' options is changed: 'balloonexpr', 'diffexpr',
- * 'foldexpr', 'foldtext', 'formatexpr', 'includeexpr', 'indentexpr',
- * 'patchexpr', 'printexpr' and 'charconvert'.
+ * 'findexpr', 'foldexpr', 'foldtext', 'formatexpr', 'includeexpr',
+ * 'indentexpr', 'patchexpr', 'printexpr' and 'charconvert'.
  *
  */
     char *

--- a/src/proto/option.pro
+++ b/src/proto/option.pro
@@ -120,6 +120,7 @@ char_u *get_option_var(int opt_idx);
 char_u *get_option_fullname(int opt_idx);
 opt_did_set_cb_T get_option_did_set_cb(int opt_idx);
 char_u *get_equalprg(void);
+char_u *get_findexpr(void);
 void win_copy_options(win_T *wp_from, win_T *wp_to);
 void after_copy_winopt(win_T *wp);
 void copy_winopt(winopt_T *from, winopt_T *to);

--- a/src/structs.h
+++ b/src/structs.h
@@ -3327,6 +3327,9 @@ struct file_buffer
     char_u	*b_p_efm;	// 'errorformat' local value
 #endif
     char_u	*b_p_ep;	// 'equalprg' local value
+#ifdef FEAT_EVAL
+    char_u	*b_p_fexpr;	// 'findexpr' local value
+#endif
     char_u	*b_p_path;	// 'path' local value
     int		b_p_ar;		// 'autoread' local value
     char_u	*b_p_tags;	// 'tags' local value

--- a/src/testdir/test_findfile.vim
+++ b/src/testdir/test_findfile.vim
@@ -1,5 +1,7 @@
 " Test findfile() and finddir()
 
+source check.vim
+
 let s:files = [ 'Xfinddir1/foo',
       \         'Xfinddir1/bar',
       \         'Xfinddir1/Xdir2/foo',
@@ -281,4 +283,170 @@ func Test_find_non_existing_path()
   let &path = save_path
 endfunc
 
+" Test for 'findexpr'
+func Test_findexpr()
+  CheckUnix
+  call assert_equal('', &findexpr)
+  call writefile(['aFile'], 'Xfindexpr1.c', 'D')
+  call writefile(['bFile'], 'Xfindexpr2.c', 'D')
+  call writefile(['cFile'], 'Xfindexpr3.c', 'D')
+
+  " basic tests
+  func FindExpr1()
+    let fnames = ['Xfindexpr1.c', 'Xfindexpr2.c', 'Xfindexpr3.c']
+    "return fnames->copy()->filter('v:val =~? v:fname')->join("\n")
+    return fnames->copy()->filter('v:val =~? v:fname')
+  endfunc
+
+  set findexpr=FindExpr1()
+  find Xfindexpr3
+  call assert_match('Xfindexpr3.c', @%)
+  bw!
+  2find Xfind
+  call assert_match('Xfindexpr2.c', @%)
+  bw!
+  call assert_fails('4find Xfind', 'E347: No more file "Xfind" found in path')
+  call assert_fails('find foobar', 'E345: Can''t find file "foobar" in path')
+
+  sfind Xfindexpr2.c
+  call assert_match('Xfindexpr2.c', @%)
+  call assert_equal(2, winnr('$'))
+  %bw!
+  call assert_fails('sfind foobar', 'E345: Can''t find file "foobar" in path')
+
+  tabfind Xfindexpr3.c
+  call assert_match('Xfindexpr3.c', @%)
+  call assert_equal(2, tabpagenr())
+  %bw!
+  call assert_fails('tabfind foobar', 'E345: Can''t find file "foobar" in path')
+
+  " Buffer-local option
+  set findexpr=['abc']
+  new
+  setlocal findexpr=['def']
+  find xxxx
+  call assert_equal('def', @%)
+  wincmd w
+  find xxxx
+  call assert_equal('abc', @%)
+  aboveleft new
+  call assert_equal("['abc']", &findexpr)
+  wincmd k
+  aboveleft new
+  call assert_equal("['abc']", &findexpr)
+  %bw!
+
+  " Empty list
+  set findexpr=[]
+  call assert_fails('find xxxx', 'E345: Can''t find file "xxxx" in path')
+
+  " Error cases
+
+  " Syntax error in the expression
+  set findexpr=FindExpr1{}
+  call assert_fails('find Xfindexpr1.c', 'E15: Invalid expression')
+
+  " Find expression throws an error
+  func FindExpr2()
+    throw 'find error'
+  endfunc
+  set findexpr=FindExpr2()
+  call assert_fails('find Xfindexpr1.c', 'find error')
+
+  " Try using a null string as the expression
+  set findexpr=test_null_string()
+  call assert_fails('find Xfindexpr1.c', 'E345: Can''t find file "Xfindexpr1.c" in path')
+
+  " Try to create a new window from the find expression
+  func FindExpr3()
+    new
+    return ["foo"]
+  endfunc
+  set findexpr=FindExpr3()
+  call assert_fails('find Xfindexpr1.c', 'E565: Not allowed to change text or change window')
+
+  " Try to modify the current buffer from the find expression
+  func FindExpr4()
+    call setline(1, ['abc'])
+    return ["foo"]
+  endfunc
+  set findexpr=FindExpr4()
+  call assert_fails('find Xfindexpr1.c', 'E565: Not allowed to change text or change window')
+
+  set findexpr&
+  delfunc! FindExpr1
+  delfunc! FindExpr2
+  delfunc! FindExpr3
+  delfunc! FindExpr4
+endfunc
+
+" Test for using a script-local function for 'findexpr'
+func Test_findexpr_scriptlocal_func()
+  func! s:FindExprScript()
+    let g:FindExprArg = v:fname
+    return ['xxx']
+  endfunc
+
+  set findexpr=s:FindExprScript()
+  call assert_equal(expand('<SID>') .. 'FindExprScript()', &findexpr)
+  call assert_equal(expand('<SID>') .. 'FindExprScript()', &g:findexpr)
+  new | only
+  let g:FindExprArg = ''
+  find abc
+  call assert_equal('abc', g:FindExprArg)
+  bw!
+
+  set findexpr=<SID>FindExprScript()
+  call assert_equal(expand('<SID>') .. 'FindExprScript()', &findexpr)
+  call assert_equal(expand('<SID>') .. 'FindExprScript()', &g:findexpr)
+  new | only
+  let g:FindExprArg = ''
+  find abc
+  call assert_equal('abc', g:FindExprArg)
+  bw!
+
+  let &findexpr = 's:FindExprScript()'
+  call assert_equal(expand('<SID>') .. 'FindExprScript()', &g:findexpr)
+  new | only
+  let g:FindExprArg = ''
+  find abc
+  call assert_equal('abc', g:FindExprArg)
+  bw!
+
+  let &findexpr = '<SID>FindExprScript()'
+  call assert_equal(expand('<SID>') .. 'FindExprScript()', &g:findexpr)
+  new | only
+  let g:FindExprArg = ''
+  find abc
+  call assert_equal('abc', g:FindExprArg)
+  bw!
+
+  set findexpr=
+  setglobal findexpr=s:FindExprScript()
+  setlocal findexpr=
+  call assert_equal(expand('<SID>') .. 'FindExprScript()', &findexpr)
+  call assert_equal(expand('<SID>') .. 'FindExprScript()', &g:findexpr)
+  call assert_equal('', &l:findexpr)
+  new | only
+  let g:FindExprArg = ''
+  find abc
+  call assert_equal('abc', g:FindExprArg)
+  bw!
+
+  new | only
+  set findexpr=
+  setglobal findexpr=
+  setlocal findexpr=s:FindExprScript()
+  call assert_equal(expand('<SID>') .. 'FindExprScript()', &findexpr)
+  call assert_equal(expand('<SID>') .. 'FindExprScript()', &l:findexpr)
+  call assert_equal('', &g:findexpr)
+  let g:FindExprArg = ''
+  find abc
+  call assert_equal('abc', g:FindExprArg)
+  bw!
+
+  set findexpr=
+  delfunc s:FindExprScript
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

--- a/src/testdir/test_modeline.vim
+++ b/src/testdir/test_modeline.vim
@@ -208,6 +208,7 @@ func Test_modeline_fails_always()
   call s:modeline_fails('equalprg', 'equalprg=Something()', 'E520:')
   call s:modeline_fails('errorfile', 'errorfile=Something()', 'E520:')
   call s:modeline_fails('exrc', 'exrc=Something()', 'E520:')
+  call s:modeline_fails('findexpr', 'findexpr=Something()', 'E520:')
   call s:modeline_fails('formatprg', 'formatprg=Something()', 'E520:')
   call s:modeline_fails('fsync', 'fsync=Something()', 'E520:')
   call s:modeline_fails('grepprg', 'grepprg=Something()', 'E520:')

--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -1570,7 +1570,7 @@ endfunc
 
 " Test for changing options in a sandbox
 func Test_opt_sandbox()
-  for opt in ['backupdir', 'cdpath', 'exrc']
+  for opt in ['backupdir', 'cdpath', 'exrc', 'findexpr']
     call assert_fails('sandbox set ' .. opt .. '?', 'E48:')
     call assert_fails('sandbox let &' .. opt .. ' = 1', 'E48:')
   endfor

--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@ static char *(features[]) =
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    810,
+/**/
     809,
 /**/
     808,