vim-patch:8.2.4867: listing of mapping with K_SPECIAL is wrong (#18419)

Problem:    Listing of mapping with K_SPECIAL is wrong.
Solution:   Adjust escaping of special characters. (closes vim/vim#10351)
ac402f4d64

Avoid overshadowing.
Cherry-pick Test_list_mapping() from Vim patches 8.2.{0148,2994}.
Fix rhs_is_noop.

src/nvim/getchar.c

@@ -2902,7 +2902,8 @@ void set_maparg_lhs_rhs(const char_u *const orig_lhs, const size_t orig_lhs_len,
       replaced = replace_termcodes(orig_rhs, orig_rhs_len, &rhs_buf,
                                    REPTERM_DO_LT | REPTERM_NO_SIMPLIFY, NULL, cpo_flags);
       mapargs->rhs_len = STRLEN(replaced);
-      mapargs->rhs_is_noop = false;
+      // XXX: even when orig_rhs is non-empty, replace_termcodes may produce an empty string.
+      mapargs->rhs_is_noop = orig_rhs[0] != NUL && mapargs->rhs_len == 0;
       mapargs->rhs = xcalloc(mapargs->rhs_len + 1, sizeof(char_u));
       STRLCPY(mapargs->rhs, replaced, mapargs->rhs_len + 1);
     }
@@ -3765,12 +3766,7 @@ static void showmap(mapblock_T *mp, bool local)
   } else if (mp->m_str[0] == NUL) {
     msg_puts_attr("<Nop>", HL_ATTR(HLF_8));
   } else {
-    // Remove escaping of K_SPECIAL, because "m_str" is in a format to be used
-    // as typeahead.
-    char_u *s = vim_strsave(mp->m_str);
-    vim_unescape_ks(s);
-    msg_outtrans_special(s, false, 0);
-    xfree(s);
+    msg_outtrans_special(mp->m_str, false, 0);
   }
 
   if (mp->m_desc != NULL) {

src/nvim/message.c

@@ -1671,11 +1671,13 @@ const char *str2special(const char **const sp, const bool replace_spaces, const
 {
   static char buf[7];
 
-  // Try to un-escape a multi-byte character.  Return the un-escaped
-  // string if it is a multi-byte character.
-  const char *const p = mb_unescape(sp);
-  if (p != NULL) {
-    return p;
+  {
+    // Try to un-escape a multi-byte character.  Return the un-escaped
+    // string if it is a multi-byte character.
+    const char *const p = mb_unescape(sp);
+    if (p != NULL) {
+      return p;
+    }
   }
 
   const char *str = *sp;
@@ -1698,18 +1700,24 @@ const char *str2special(const char **const sp, const bool replace_spaces, const
   }
 
   if (!IS_SPECIAL(c)) {
-    const int len = utf_ptr2len((const char_u *)str);
+    *sp = str;
+    // Try to un-escape a multi-byte character after modifiers.
+    const char *p = mb_unescape(sp);
 
-    // Check for an illegal byte.
-    if (MB_BYTE2LEN((uint8_t)(*str)) > len) {
-      transchar_nonprint(curbuf, (char_u *)buf, c);
-      *sp = str + 1;
-      return buf;
+    if (p == NULL) {
+      const int len = utf_ptr2len((const char_u *)str);
+      // Check for an illegal byte.
+      if (MB_BYTE2LEN((uint8_t)(*str)) > len) {
+        transchar_nonprint(curbuf, (char_u *)buf, c);
+        *sp = str + 1;
+        return buf;
+      }
+      *sp = str + len;
+      p = str;
     }
-    // Since 'special' is TRUE the multi-byte character 'c' will be
+    // Since 'special' is true the multi-byte character 'c' will be
     // processed by get_special_key_name().
-    c = utf_ptr2char((const char_u *)str);
-    *sp = str + len;
+    c = utf_ptr2char((const char_u *)p);
   } else {
     *sp = str + 1;
   }

src/nvim/testdir/test_mapping.vim

@@ -464,6 +464,40 @@ func Test_list_mappings()
   call assert_equal(['n  ,n            <Nop>'],
         \ execute('nmap ,n')->trim()->split("\n"))
 
+  " verbose map
+  call assert_match("\tLast set from .*/test_mapping.vim line \\d\\+$",
+        \ execute('verbose map ,n')->trim()->split("\n")[1])
+
+  " character with K_SPECIAL byte in rhs
+  nmap foo …
+  call assert_equal(['n  foo           …'],
+        \ execute('nmap foo')->trim()->split("\n"))
+
+  " modified character with K_SPECIAL byte in rhs
+  nmap foo <M-…>
+  call assert_equal(['n  foo           <M-…>'],
+        \ execute('nmap foo')->trim()->split("\n"))
+
+  " character with K_SPECIAL byte in lhs
+  nmap … foo
+  call assert_equal(['n  …             foo'],
+        \ execute('nmap …')->trim()->split("\n"))
+
+  " modified character with K_SPECIAL byte in lhs
+  nmap <M-…> foo
+  call assert_equal(['n  <M-…>         foo'],
+        \ execute('nmap <M-…>')->trim()->split("\n"))
+
+  " map to CTRL-V
+  exe "nmap ,k \<C-V>"
+  call assert_equal(['n  ,k            <Nop>'],
+        \ execute('nmap ,k')->trim()->split("\n"))
+
+  " map with space at the beginning
+  exe "nmap \<C-V> w <Nop>"
+  call assert_equal(['n  <Space>w      <Nop>'],
+        \ execute("nmap \<C-V> w")->trim()->split("\n"))
+
   nmapclear
 endfunc