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>

runtime/doc/builtin.txt

@@ -5666,11 +5666,13 @@ resolve({filename})                                             *resolve()* *E65
 		path name) and also keeps a trailing path separator.
 
 reverse({object})                                                    *reverse()*
-		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))
 <
 

runtime/doc/usr_41.txt

@@ -626,6 +626,7 @@ String manipulation:					*string-functions*
 	strdisplaywidth()	size of string when displayed, deals with tabs
 	setcellwidths()		set character cell width overrides
 	getcellwidths()		get character cell width overrides
+	reverse()		reverse the order of characters in a string
 	substitute()		substitute a pattern match with a string
 	submatch()		get a specific match in ":s" and substitute()
 	strpart()		get part of a string using byte index
@@ -664,7 +665,7 @@ List manipulation:					*list-functions*
 	reduce()		reduce a List to a value
 	slice()			take a slice of a List
 	sort()			sort a List
-	reverse()		reverse the order of a List or Blob
+	reverse()		reverse the order of items in a List
 	uniq()			remove copies of repeated adjacent items
 	split()			split a String into a List
 	join()			join List items into a String
@@ -731,6 +732,7 @@ Floating point computation:				*float-functions*
 Blob manipulation:					*blob-functions*
 	blob2list()		get a list of numbers from a blob
 	list2blob()		get a blob from a list of numbers
+	reverse()		reverse the order of numbers in a blob
 
 Other computation:					*bitwise-function*
 	and()			bitwise AND

runtime/lua/vim/_meta/vimfn.lua

@@ -6762,11 +6762,13 @@ vim.fn['repeat'] = function(expr, count) end
 --- @return any
 function vim.fn.resolve(filename) end
 
---- 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.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;
 }
 

test/old/testdir/test_functions.vim

@@ -3148,4 +3148,21 @@ func Test_delfunc_while_listing()
   call StopVimInTerminal(buf)
 endfunc
 
+" Test for the reverse() function with a string
+func Test_string_reverse()
+  call assert_equal('', reverse(v:_null_string))
+  for [s1, s2] in [['', ''], ['a', 'a'], ['ab', 'ba'], ['abc', 'cba'],
+        \ ['abcd', 'dcba'], ['«-«-»-»', '»-»-«-«'],
+        \ ['🇦', '🇦'], ['🇦🇧', '🇧🇦'], ['🇦🇧🇨', '🇨🇧🇦'],
+        \ ['🇦«🇧-🇨»🇩', '🇩»🇨-🇧«🇦']]
+    call assert_equal(s2, reverse(s1))
+  endfor
+
+  " test in latin1 encoding
+  let save_enc = &encoding
+  " set encoding=latin1
+  call assert_equal('dcba', reverse('abcd'))
+  let &encoding = save_enc
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

test/old/testdir/test_listdict.vim

@@ -894,7 +894,7 @@ func Test_reverse_sort_uniq()
   END
   call CheckLegacyAndVim9Success(lines)
 
-  call assert_fails('call reverse("")', 'E899:')
+  call assert_fails('call reverse({})', 'E899:')
   call assert_fails('call uniq([1, 2], {x, y -> []})', 'E745:')
   call assert_fails("call sort([1, 2], function('min'), 1)", "E1206:")
   call assert_fails("call sort([1, 2], function('invalid_func'))", "E700:")