vim-patch:9.0.1515: reverse() does not work for a String

Problem:    reverse() does not work for a String.
Solution:   Implement reverse() for a String. (Yegappan Lakshmanan,
            closes vim/vim#12179)

03ff1c2dde

vim-patch:9.0.1738: Duplicate code to reverse a string

Problem:  Duplicate code to reverse a string
Solution: Move reverse_text() to strings.c and remove string_reverse().

closes: vim/vim#12847

4dd266cb66

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

src/nvim/eval.lua

@@ -8151,11 +8151,13 @@ M.funcs = {
     args = 1,
     base = 1,
     desc = [=[
-      Reverse the order of items in {object} in-place.
-      {object} can be a |List| or a |Blob|.
-      Returns {object}.
-      Returns zero if {object} is not a List or a Blob.
-      If you want an object to remain unmodified make a copy first: >vim
+      Reverse the order of items in {object}.  {object} can be a
+      |List|, a |Blob| or a |String|.  For a List and a Blob the
+      items are reversed in-place and {object} is returned.
+      For a String a new String is returned.
+      Returns zero if {object} is not a List, Blob or a String.
+      If you want a List or Blob to remain unmodified make a copy
+      first: >vim
       	let revlist = reverse(copy(mylist))
       <
     ]=],

src/nvim/eval/funcs.c

@@ -6209,6 +6209,13 @@ static void f_reverse(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
       tv_blob_set(b, len - i - 1, tmp);
     }
     tv_blob_set_ret(rettv, b);
+  } else if (argvars[0].v_type == VAR_STRING) {
+    rettv->v_type = VAR_STRING;
+    if (argvars[0].vval.v_string != NULL) {
+      rettv->vval.v_string = reverse_text(argvars[0].vval.v_string);
+    } else {
+      rettv->vval.v_string = NULL;
+    }
   } else if (argvars[0].v_type != VAR_LIST) {
     semsg(_(e_listblobarg), "reverse()");
   } else {

src/nvim/strings.c

@@ -2168,20 +2168,17 @@ int kv_do_printf(StringBuilder *str, const char *fmt, ...)
 ///
 /// @return  the allocated string.
 char *reverse_text(char *s)
-  FUNC_ATTR_NONNULL_RET
+  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_NONNULL_RET
 {
-  // Reverse the pattern.
   size_t len = strlen(s);
   char *rev = xmalloc(len + 1);
-  size_t rev_i = len;
-  for (size_t s_i = 0; s_i < len; s_i++) {
+  for (size_t s_i = 0, rev_i = len; s_i < len; s_i++) {
     const int mb_len = utfc_ptr2len(s + s_i);
     rev_i -= (size_t)mb_len;
     memmove(rev + rev_i, s + s_i, (size_t)mb_len);
     s_i += (size_t)mb_len - 1;
   }
   rev[len] = NUL;
-
   return rev;
 }