patch 8.2.2133: Vim9: checking for a non-empty string is too strict

Problem:    Vim9: checking for a non-empty string is too strict.
Solution:   Check for any string. (closes #7447)

src/errors.h

@@ -313,3 +313,5 @@ EXTERN char e_for_argument_must_be_sequence_of_lists[]
 	INIT(= N_("E1140: For argument must be a sequence of lists"));
 EXTERN char e_indexable_type_required[]
 	INIT(= N_("E1141: Indexable type required"));
+EXTERN char e_non_empty_string_required[]
+	INIT(= N_("E1142: Non-empty string required"));

src/filepath.c

@@ -876,7 +876,7 @@ f_exepath(typval_T *argvars, typval_T *rettv)
 {
     char_u *p = NULL;
 
-    if (in_vim9script() && check_for_string(&argvars[0]) == FAIL)
+    if (in_vim9script() && check_for_nonempty_string(&argvars[0]) == FAIL)
 	return;
     (void)mch_can_exe(tv_get_string(&argvars[0]), &p, TRUE);
     rettv->v_type = VAR_STRING;
@@ -942,7 +942,7 @@ findfilendir(
 
     rettv->vval.v_string = NULL;
     rettv->v_type = VAR_STRING;
-    if (in_vim9script() && check_for_string(&argvars[0]) == FAIL)
+    if (in_vim9script() && check_for_nonempty_string(&argvars[0]) == FAIL)
 	return;
 
 #ifdef FEAT_SEARCHPATH
@@ -1028,9 +1028,9 @@ f_fnamemodify(typval_T *argvars, typval_T *rettv)
 	return;
     fname = tv_get_string_chk(&argvars[0]);
     mods = tv_get_string_buf_chk(&argvars[1], buf);
-    if (fname == NULL || mods == NULL)
+    if (fname == NULL)
 	fname = NULL;
-    else
+    else if (mods != NULL && *mods != NUL)
     {
 	len = (int)STRLEN(fname);
 	(void)modify_fname(mods, FALSE, &usedlen, &fname, &fbuf, &len);

src/proto/typval.pro

@@ -10,6 +10,7 @@ varnumber_T tv_get_bool(typval_T *varp);
 varnumber_T tv_get_bool_chk(typval_T *varp, int *denote);
 float_T tv_get_float(typval_T *varp);
 int check_for_string(typval_T *tv);
+int check_for_nonempty_string(typval_T *tv);
 char_u *tv_get_string(typval_T *varp);
 char_u *tv_get_string_buf(typval_T *varp, char_u *buf);
 char_u *tv_get_string_chk(typval_T *varp);

src/testdir/test_vim9_builtin.vim

@@ -186,15 +186,17 @@ def Test_count()
 enddef
 
 def Test_executable()
+  assert_false(executable(""))
+  assert_false(executable(test_null_string()))
+
+  CheckDefExecFailure(['echo executable(123)'], 'E928:')
   CheckDefExecFailure(['echo executable(true)'], 'E928:')
-  CheckDefExecFailure(['echo executable(v:null)'], 'E928:')
-  CheckDefExecFailure(['echo executable("")'], 'E928:')
 enddef
 
 def Test_exepath()
   CheckDefExecFailure(['echo exepath(true)'], 'E928:')
   CheckDefExecFailure(['echo exepath(v:null)'], 'E928:')
-  CheckDefExecFailure(['echo exepath("")'], 'E928:')
+  CheckDefExecFailure(['echo exepath("")'], 'E1142:')
 enddef
 
 def Test_expand()
@@ -254,36 +256,42 @@ def Test_map_function_arg()
 enddef
 
 def Test_filereadable()
+  assert_false(filereadable(""))
+  assert_false(filereadable(test_null_string()))
+
+  CheckDefExecFailure(['echo filereadable(123)'], 'E928:')
   CheckDefExecFailure(['echo filereadable(true)'], 'E928:')
-  CheckDefExecFailure(['echo filereadable(v:null)'], 'E928:')
-  CheckDefExecFailure(['echo filereadable("")'], 'E928:')
 enddef
 
 def Test_filewritable()
+  assert_false(filewritable(""))
+  assert_false(filewritable(test_null_string()))
+
+  CheckDefExecFailure(['echo filewritable(123)'], 'E928:')
   CheckDefExecFailure(['echo filewritable(true)'], 'E928:')
-  CheckDefExecFailure(['echo filewritable(v:null)'], 'E928:')
-  CheckDefExecFailure(['echo filewritable("")'], 'E928:')
 enddef
 
 def Test_finddir()
   CheckDefExecFailure(['echo finddir(true)'], 'E928:')
   CheckDefExecFailure(['echo finddir(v:null)'], 'E928:')
-  CheckDefExecFailure(['echo finddir("")'], 'E928:')
+  CheckDefExecFailure(['echo finddir("")'], 'E1142:')
 enddef
 
 def Test_findfile()
   CheckDefExecFailure(['echo findfile(true)'], 'E928:')
   CheckDefExecFailure(['echo findfile(v:null)'], 'E928:')
-  CheckDefExecFailure(['echo findfile("")'], 'E928:')
+  CheckDefExecFailure(['echo findfile("")'], 'E1142:')
 enddef
 
 def Test_fnamemodify()
+  CheckDefSuccess(['echo fnamemodify(test_null_string(), ":p")'])
+  CheckDefSuccess(['echo fnamemodify("", ":p")'])
+  CheckDefSuccess(['echo fnamemodify("file", test_null_string())'])
+  CheckDefSuccess(['echo fnamemodify("file", "")'])
+
   CheckDefExecFailure(['echo fnamemodify(true, ":p")'], 'E928:')
   CheckDefExecFailure(['echo fnamemodify(v:null, ":p")'], 'E928:')
-  CheckDefExecFailure(['echo fnamemodify("", ":p")'], 'E928:')
   CheckDefExecFailure(['echo fnamemodify("file", true)'], 'E928:')
-  CheckDefExecFailure(['echo fnamemodify("file", v:null)'], 'E928:')
-  CheckDefExecFailure(['echo fnamemodify("file", "")'], 'E928:')
 enddef
 
 def Test_filter_wrong_dict_key_type()
@@ -359,27 +367,35 @@ def Test_getloclist_return_type()
 enddef
 
 def Test_getfperm()
+  assert_equal('', getfperm(""))
+  assert_equal('', getfperm(test_null_string()))
+
   CheckDefExecFailure(['echo getfperm(true)'], 'E928:')
   CheckDefExecFailure(['echo getfperm(v:null)'], 'E928:')
-  CheckDefExecFailure(['echo getfperm("")'], 'E928:')
 enddef
 
 def Test_getfsize()
+  assert_equal(-1, getfsize(""))
+  assert_equal(-1, getfsize(test_null_string()))
+
   CheckDefExecFailure(['echo getfsize(true)'], 'E928:')
   CheckDefExecFailure(['echo getfsize(v:null)'], 'E928:')
-  CheckDefExecFailure(['echo getfsize("")'], 'E928:')
 enddef
 
 def Test_getftime()
+  assert_equal(-1, getftime(""))
+  assert_equal(-1, getftime(test_null_string()))
+
   CheckDefExecFailure(['echo getftime(true)'], 'E928:')
   CheckDefExecFailure(['echo getftime(v:null)'], 'E928:')
-  CheckDefExecFailure(['echo getftime("")'], 'E928:')
 enddef
 
 def Test_getftype()
+  assert_equal('', getftype(""))
+  assert_equal('', getftype(test_null_string()))
+
   CheckDefExecFailure(['echo getftype(true)'], 'E928:')
   CheckDefExecFailure(['echo getftype(v:null)'], 'E928:')
-  CheckDefExecFailure(['echo getftype("")'], 'E928:')
 enddef
 
 def Test_getqflist_return_type()

src/typval.c

@@ -341,14 +341,12 @@ tv_get_float(typval_T *varp)
 #endif
 
 /*
- * Give an error and return FAIL unless "tv" is a non-empty string.
+ * Give an error and return FAIL unless "tv" is a string.
  */
     int
 check_for_string(typval_T *tv)
 {
-    if (tv->v_type != VAR_STRING
-	    || tv->vval.v_string == NULL
-	    || *tv->vval.v_string == NUL)
+    if (tv->v_type != VAR_STRING)
     {
 	emsg(_(e_stringreq));
 	return FAIL;
@@ -356,6 +354,22 @@ check_for_string(typval_T *tv)
     return OK;
 }
 
+/*
+ * Give an error and return FAIL unless "tv" is a non-empty string.
+ */
+    int
+check_for_nonempty_string(typval_T *tv)
+{
+    if (check_for_string(tv) == FAIL)
+	return FAIL;
+    if (tv->vval.v_string == NULL || *tv->vval.v_string == NUL)
+    {
+	emsg(_(e_non_empty_string_required));
+	return FAIL;
+    }
+    return OK;
+}
+
 /*
  * Get the string value of a variable.
  * If it is a Number variable, the number is converted into a string.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2133,
 /**/
     2132,
 /**/