patch 8.2.4841: empty string considered an error for expand()

Problem:    Empty string considered an error for expand() when 'verbose' is
            set. (Christian Brabandt)
Solution:   Do not give an error for an empty result. (closes #10307)

src/evalfunc.c

@@ -4105,7 +4105,7 @@ f_expand(typval_T *argvars, typval_T *rettv)
 
 	if (p_verbose == 0)
 	    ++emsg_off;
-	result = eval_vars(s, s, &len, NULL, &errormsg, NULL);
+	result = eval_vars(s, s, &len, NULL, &errormsg, NULL, FALSE);
 	if (p_verbose == 0)
 	    --emsg_off;
 	else if (errormsg != NULL)

src/ex_docmd.c

@@ -4924,7 +4924,7 @@ expand_filename(
 	 * Try to find a match at this position.
 	 */
 	repl = eval_vars(p, eap->arg, &srclen, &(eap->do_ecmd_lnum),
-							 errormsgp, &escaped);
+						    errormsgp, &escaped, TRUE);
 	if (*errormsgp != NULL)		// error detected
 	    return FAIL;
 	if (repl == NULL)		// no match found
@@ -9045,8 +9045,9 @@ eval_vars(
     int		*usedlen,	// characters after src that are used
     linenr_T	*lnump,		// line number for :e command, or NULL
     char	**errormsg,	// pointer to error message
-    int		*escaped)	// return value has escaped white space (can
+    int		*escaped,	// return value has escaped white space (can
 				// be NULL)
+    int		empty_is_error)	// empty result is considered an error
 {
     int		i;
     char_u	*s;
@@ -9348,7 +9349,7 @@ eval_vars(
 	}
     }
 
-    if (resultlen == 0 || valid != VALID_HEAD + VALID_PATH)
+    if (empty_is_error && (resultlen == 0 || valid != VALID_HEAD + VALID_PATH))
     {
 	if (valid != VALID_HEAD + VALID_PATH)
 	    *errormsg = _(e_empty_file_name_for_percent_or_hash_only_works_with_ph);
@@ -9389,7 +9390,7 @@ expand_sfile(char_u *arg)
 	else
 	{
 	    // replace "<sfile>" with the sourced file name, and do ":" stuff
-	    repl = eval_vars(p, result, &srclen, NULL, &errormsg, NULL);
+	    repl = eval_vars(p, result, &srclen, NULL, &errormsg, NULL, TRUE);
 	    if (errormsg != NULL)
 	    {
 		if (*errormsg)

src/filepath.c

@@ -3097,7 +3097,7 @@ expand_wildcards_eval(
     {
 	++emsg_off;
 	eval_pat = eval_vars(exp_pat, exp_pat, &usedlen,
-						    NULL, &ignored_msg, NULL);
+					       NULL, &ignored_msg, NULL, TRUE);
 	--emsg_off;
 	if (eval_pat != NULL)
 	    exp_pat = concat_str(eval_pat, exp_pat + usedlen);

src/proto/ex_docmd.pro

@@ -63,7 +63,7 @@ void ex_normal(exarg_T *eap);
 void exec_normal_cmd(char_u *cmd, int remap, int silent);
 void exec_normal(int was_typed, int use_vpeekc, int may_use_terminal_loop);
 int find_cmdline_var(char_u *src, int *usedlen);
-char_u *eval_vars(char_u *src, char_u *srcstart, int *usedlen, linenr_T *lnump, char **errormsg, int *escaped);
+char_u *eval_vars(char_u *src, char_u *srcstart, int *usedlen, linenr_T *lnump, char **errormsg, int *escaped, int empty_is_error);
 char_u *expand_sfile(char_u *arg);
 void dialog_msg(char_u *buff, char *format, char_u *fname);
 void set_no_hlsearch(int flag);

src/testdir/test_expand_func.vim

@@ -82,10 +82,14 @@ endfunc
 
 func Test_expand()
   new
-  call assert_equal("",  expand('%:S'))
+  call assert_equal("''", expand('%:S'))
   call assert_equal('3', '<slnum>'->expand())
   call assert_equal(['4'], expand('<slnum>', v:false, v:true))
   " Don't add any line above this, otherwise <slnum> will change.
+  call assert_equal("", expand('%'))
+  set verbose=1
+  call assert_equal("", expand('%'))
+  set verbose=0
   quit
 endfunc
 

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4841,
 /**/
     4840,
 /**/