vim-patch:8.2.3663: using %S in printf() does not work correctly

Problem:    Using %S in printf() does not work correctly.
Solution:   Fix the problem and add more tests. (closes vim/vim#9208)
https://github.com/vim/vim/commit/1f2453fec6f8f0f315f00ca7b562a02090cb1e37

2 files changed, 71 insertions, 16 deletions

diff --git a/src/nvim/strings.c b/src/nvim/strings.c
index efcd40bb75..291138ef23 100644
--- a/src/nvim/strings.c
+++ b/src/nvim/strings.c
@@ -1001,25 +1001,20 @@ int vim_vsnprintf_typval(char *str, size_t str_m, const char *fmt, va_list ap, t
                                  - str_arg);
           }
           if (fmt_spec == 'S') {
-            size_t base_width = min_field_width;
-            size_t pad_cell = 0;
-
-            if (precision) {
-              char_u *p1;
-              size_t i = 0;
-
-              for (p1 = (char_u *)str_arg; *p1;
-                   p1 += utfc_ptr2len(p1)) {
-                i += (size_t)utf_ptr2cells(p1);
-                if (i > precision) {
-                  break;
-                }
+            char_u *p1;
+            size_t i;
+
+            for (i = 0, p1 = (char_u *)str_arg; *p1; p1 += utfc_ptr2len(p1)) {
+              size_t cell = (size_t)utf_ptr2cells(p1);
+              if (precision_specified && i + cell > precision) {
+                break;
               }
-              pad_cell = min_field_width - precision;
-              base_width = str_arg_l = (size_t)(p1 - (char_u *)str_arg);
+              i += cell;
             }
+
+            str_arg_l = (size_t)(p1 - (char_u *)str_arg);
             if (min_field_width != 0) {
-              min_field_width = base_width + pad_cell;
+              min_field_width += str_arg_l - i;
             }
           }
           break;
diff --git a/src/nvim/testdir/test_expr.vim b/src/nvim/testdir/test_expr.vim
index 447a519f2c..5b10e691e5 100644
--- a/src/nvim/testdir/test_expr.vim
+++ b/src/nvim/testdir/test_expr.vim
@@ -288,6 +288,66 @@ function Test_printf_misc()
   call assert_equal('[あいうえお]', printf('[%10.10S]', 'あいうえお'))
   call assert_equal('[あいうえお]', printf('[%10.12S]', 'あいうえお'))
 
+  call assert_equal('あいう', printf('%S', 'あいう'))
+  call assert_equal('あいう', printf('%#S', 'あいう'))
+
+  call assert_equal('あb', printf('%2S', 'あb'))
+  call assert_equal('あb', printf('%.4S', 'あb'))
+  call assert_equal('あ', printf('%.2S', 'あb'))
+  call assert_equal(' あb', printf('%4S', 'あb'))
+  call assert_equal('0あb', printf('%04S', 'あb'))
+  call assert_equal('あb ', printf('%-4S', 'あb'))
+  call assert_equal('あ  ', printf('%-4.2S', 'あb'))
+
+  call assert_equal('aい', printf('%2S', 'aい'))
+  call assert_equal('aい', printf('%.4S', 'aい'))
+  call assert_equal('a', printf('%.2S', 'aい'))
+  call assert_equal(' aい', printf('%4S', 'aい'))
+  call assert_equal('0aい', printf('%04S', 'aい'))
+  call assert_equal('aい ', printf('%-4S', 'aい'))
+  call assert_equal('a   ', printf('%-4.2S', 'aい'))
+
+  call assert_equal('[あいう]', printf('[%05S]', 'あいう'))
+  call assert_equal('[あいう]', printf('[%06S]', 'あいう'))
+  call assert_equal('[0あいう]', printf('[%07S]', 'あいう'))
+
+  call assert_equal('[あiう]', printf('[%05S]', 'あiう'))
+  call assert_equal('[0あiう]', printf('[%06S]', 'あiう'))
+  call assert_equal('[00あiう]', printf('[%07S]', 'あiう'))
+
+  call assert_equal('[0あい]', printf('[%05.4S]', 'あいう'))
+  call assert_equal('[00あい]', printf('[%06.4S]', 'あいう'))
+  call assert_equal('[000あい]', printf('[%07.4S]', 'あいう'))
+
+  call assert_equal('[00あi]', printf('[%05.4S]', 'あiう'))
+  call assert_equal('[000あi]', printf('[%06.4S]', 'あiう'))
+  call assert_equal('[0000あi]', printf('[%07.4S]', 'あiう'))
+
+  call assert_equal('[0あい]', printf('[%05.5S]', 'あいう'))
+  call assert_equal('[00あい]', printf('[%06.5S]', 'あいう'))
+  call assert_equal('[000あい]', printf('[%07.5S]', 'あいう'))
+
+  call assert_equal('[あiう]', printf('[%05.5S]', 'あiう'))
+  call assert_equal('[0あiう]', printf('[%06.5S]', 'あiう'))
+  call assert_equal('[00あiう]', printf('[%07.5S]', 'あiう'))
+
+  call assert_equal('[0000000000]', printf('[%010.0S]', 'あいう'))
+  call assert_equal('[0000000000]', printf('[%010.1S]', 'あいう'))
+  call assert_equal('[00000000あ]', printf('[%010.2S]', 'あいう'))
+  call assert_equal('[00000000あ]', printf('[%010.3S]', 'あいう'))
+  call assert_equal('[000000あい]', printf('[%010.4S]', 'あいう'))
+  call assert_equal('[000000あい]', printf('[%010.5S]', 'あいう'))
+  call assert_equal('[0000あいう]', printf('[%010.6S]', 'あいう'))
+  call assert_equal('[0000あいう]', printf('[%010.7S]', 'あいう'))
+
+  call assert_equal('[0000000000]', printf('[%010.1S]', 'あiう'))
+  call assert_equal('[00000000あ]', printf('[%010.2S]', 'あiう'))
+  call assert_equal('[0000000あi]', printf('[%010.3S]', 'あiう'))
+  call assert_equal('[0000000あi]', printf('[%010.4S]', 'あiう'))
+  call assert_equal('[00000あiう]', printf('[%010.5S]', 'あiう'))
+  call assert_equal('[00000あiう]', printf('[%010.6S]', 'あiう'))
+  call assert_equal('[00000あiう]', printf('[%010.7S]', 'あiう'))
+
   call assert_equal('1%', printf('%d%%', 1))
 endfunc