vim-patch:9.0.0449: there is no easy way to translate a key code into a string (#20168)

Problem:    There is no easy way to translate a string with a key code into a
            readable string.
Solution:   Add the keytrans() function. (closes vim/vim#11114)
https://github.com/vim/vim/commit/cdc839353f68ca43db6446e1b727fc7ba657b738

vim-patch:7b2d87220c6c

Add missing part of patch
https://github.com/vim/vim/commit/7b2d87220c6c974d5cdae672b6f9620a6bcbd1dc

6 files changed, 47 insertions, 9 deletions

diff --git a/src/nvim/eval.lua b/src/nvim/eval.lua
index 5c500af899..837fef23f4 100644
--- a/src/nvim/eval.lua
+++ b/src/nvim/eval.lua
@@ -236,6 +236,7 @@ return {
     json_decode={args=1, base=1},
     json_encode={args=1, base=1},
     keys={args=1, base=1},
+    keytrans={args=1, base=1},
     last_buffer_nr={},  -- obsolete
     len={args=1, base=1},
     libcall={args=3, base=3},
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 3c08acc10b..b5ae24953f 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -4673,6 +4673,20 @@ static void f_json_encode(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
   rettv->vval.v_string = encode_tv2json(&argvars[0], NULL);
 }
 
+/// "keytrans()" function
+static void f_keytrans(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
+{
+  rettv->v_type = VAR_STRING;
+  if (tv_check_for_string_arg(argvars, 0) == FAIL
+      || argvars[0].vval.v_string == NULL) {
+    return;
+  }
+  // Need to escape K_SPECIAL for mb_unescape().
+  char *escaped = vim_strsave_escape_ks(argvars[0].vval.v_string);
+  rettv->vval.v_string = str2special_save(escaped, true, true);
+  xfree(escaped);
+}
+
 /// "last_buffer_nr()" function.
 static void f_last_buffer_nr(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
 {
diff --git a/src/nvim/menu.c b/src/nvim/menu.c
index b38e832c77..57116170aa 100644
--- a/src/nvim/menu.c
+++ b/src/nvim/menu.c
@@ -685,8 +685,7 @@ static dict_T *menu_get_recursive(const vimmenu_T *menu, int modes)
       if ((menu->modes & modes & (1 << bit)) != 0) {
         dict_T *impl = tv_dict_alloc();
         tv_dict_add_allocated_str(impl, S_LEN("rhs"),
-                                  str2special_save(menu->strings[bit],
-                                                   false, false));
+                                  str2special_save(menu->strings[bit], false, false));
         tv_dict_add_nr(impl, S_LEN("silent"), menu->silent[bit]);
         tv_dict_add_nr(impl, S_LEN("enabled"),
                        (menu->enabled & (1 << bit)) ? 1 : 0);
diff --git a/src/nvim/message.c b/src/nvim/message.c
index 46f6adec47..fd8aa00d7b 100644
--- a/src/nvim/message.c
+++ b/src/nvim/message.c
@@ -1681,8 +1681,8 @@ int msg_outtrans_special(const char *strstart, bool from, int maxlen)
 /// Used for lhs or rhs of mappings.
 ///
 /// @param[in]  str  String to convert.
-/// @param[in]  replace_spaces  Convert spaces into `<Space>`, normally used fo
-///                             lhs, but not rhs.
+/// @param[in]  replace_spaces  Convert spaces into `<Space>`, normally used for
+///                             lhs of mapping and keytrans(), but not rhs.
 /// @param[in]  replace_lt  Convert `<` into `<lt>`.
 ///
 /// @return [allocated] Converted string.
@@ -1704,8 +1704,8 @@ char *str2special_save(const char *const str, const bool replace_spaces, const b
 /// Convert character, replacing key with printable representation.
 ///
 /// @param[in,out]  sp  String to convert. Is advanced to the next key code.
-/// @param[in]  replace_spaces  Convert spaces into <Space>, normally used for
-///                             lhs, but not rhs.
+/// @param[in]  replace_spaces  Convert spaces into `<Space>`, normally used for
+///                             lhs of mapping and keytrans(), but not rhs.
 /// @param[in]  replace_lt  Convert `<` into `<lt>`.
 ///
 /// @return Converted key code, in a static buffer. Buffer is always one and the
diff --git a/src/nvim/option.c b/src/nvim/option.c
index de9510cf8a..5adec084e6 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -3558,9 +3558,7 @@ static int put_setstring(FILE *fd, char *cmd, char *name, char **valuep, uint64_
     if (valuep == &p_pt) {
       s = (char_u *)(*valuep);
       while (*s != NUL) {
-        if (put_escstr(fd, (char_u *)str2special((const char **)&s, false,
-                                                 false), 2)
-            == FAIL) {
+        if (put_escstr(fd, (char_u *)str2special((const char **)&s, false, false), 2) == FAIL) {
           return FAIL;
         }
       }
diff --git a/src/nvim/testdir/test_functions.vim b/src/nvim/testdir/test_functions.vim
index c41884936e..1750a600f3 100644
--- a/src/nvim/testdir/test_functions.vim
+++ b/src/nvim/testdir/test_functions.vim
@@ -1907,6 +1907,32 @@ func Test_eval()
   call assert_fails("call eval('5 a')", 'E488:')
 endfunc
 
+" Test for the keytrans() function
+func Test_keytrans()
+  call assert_equal('<Space>', keytrans(' '))
+  call assert_equal('<lt>', keytrans('<'))
+  call assert_equal('<lt>Tab>', keytrans('<Tab>'))
+  call assert_equal('<Tab>', keytrans("\<Tab>"))
+  call assert_equal('<C-V>', keytrans("\<C-V>"))
+  call assert_equal('<BS>', keytrans("\<BS>"))
+  call assert_equal('<Home>', keytrans("\<Home>"))
+  call assert_equal('<C-Home>', keytrans("\<C-Home>"))
+  call assert_equal('<M-Home>', keytrans("\<M-Home>"))
+  call assert_equal('<C-Space>', keytrans("\<C-Space>"))
+  call assert_equal('<M-Space>', keytrans("\<*M-Space>"))
+  call assert_equal('<M-x>', "\<*M-x>"->keytrans())
+  call assert_equal('<C-I>', "\<*C-I>"->keytrans())
+  call assert_equal('<S-3>', "\<*S-3>"->keytrans())
+  call assert_equal('π', 'π'->keytrans())
+  call assert_equal('<M-π>', "\<M-π>"->keytrans())
+  call assert_equal('ě', 'ě'->keytrans())
+  call assert_equal('<M-ě>', "\<M-ě>"->keytrans())
+  call assert_equal('', ''->keytrans())
+  call assert_equal('', v:_null_string->keytrans())
+  call assert_fails('call keytrans(1)', 'E1174:')
+  call assert_fails('call keytrans()', 'E119:')
+endfunc
+
 " Test for the nr2char() function
 func Test_nr2char()
   " set encoding=latin1