vim-patch:8.2.4924: maparg() may return a string that cannot be reused

Problem:    maparg() may return a string that cannot be reused.
Solution:   use msg_outtrans_special() instead of str2special().
            (closes vim/vim#10384)
0519ce0039

src/nvim/message.c

@@ -1618,6 +1618,10 @@ int msg_outtrans_special(const char_u *strstart, bool from, int maxlen)
     } else {
       text = str2special((const char **)&str, from, false);
     }
+    if (text[0] != NUL && text[1] == NUL) {
+      // single-byte character or illegal byte
+      text = (char *)transchar_byte((uint8_t)text[0]);
+    }
     const int len = vim_strsize((char_u *)text);
     if (maxlen > 0 && retval + len >= maxlen) {
       break;
@@ -1666,6 +1670,7 @@ char *str2special_save(const char *const str, const bool replace_spaces, const b
 /// @return Converted key code, in a static buffer. Buffer is always one and the
 ///         same, so save converted string somewhere before running str2special
 ///         for the second time.
+///         On illegal byte return a string with only that byte.
 const char *str2special(const char **const sp, const bool replace_spaces, const bool replace_lt)
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_RET
 {
@@ -1699,32 +1704,26 @@ const char *str2special(const char **const sp, const bool replace_spaces, const
     }
   }
 
-  if (!IS_SPECIAL(c)) {
+  if (!IS_SPECIAL(c) && MB_BYTE2LEN(c) > 1) {
     *sp = str;
     // Try to un-escape a multi-byte character after modifiers.
     const char *p = mb_unescape(sp);
-
-    if (p == NULL) {
-      const int len = utf_ptr2len(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;
+    if (p != NULL) {
+      // Since 'special' is true the multi-byte character 'c' will be
+      // processed by get_special_key_name().
+      c = utf_ptr2char(p);
+    } else {
+      // illegal byte
+      *sp = str + 1;
     }
-    // Since 'special' is true the multi-byte character 'c' will be
-    // processed by get_special_key_name().
-    c = utf_ptr2char(p);
   } else {
+    // single-byte character or illegal byte
     *sp = str + 1;
   }
 
-  // Make unprintable characters in <> form, also <M-Space> and <Tab>.
+  // Make special keys and C0 control characters in <> form, also <M-Space>.
   if (special
-      || char2cells(c) > 1
+      || c < ' '
       || (replace_spaces && c == ' ')
       || (replace_lt && c == '<')) {
     return (const char *)get_special_key_name(c, modifiers);

src/nvim/option.c

@@ -4980,7 +4980,11 @@ int get_option_value(const char *name, long *numval, char **stringval, int opt_f
       return -2;
     }
     if (stringval != NULL) {
-      *stringval = xstrdup(*(char **)varp);
+      if ((char_u **)varp == &p_pt) {  // 'pastetoggle'
+        *stringval = str2special_save(*(char **)(varp), false, false);
+      } else {
+        *stringval = xstrdup(*(char **)(varp));
+      }
     }
     return 0;
   }

src/nvim/testdir/test_maparg.vim

@@ -42,6 +42,20 @@ function Test_maparg()
   map abc y<S-char-114>y
   call assert_equal("yRy", maparg('abc'))
 
+  " character with K_SPECIAL byte
+  nmap abc …
+  call assert_equal('…', maparg('abc'))
+
+  " modified character with K_SPECIAL byte
+  nmap abc <M-…>
+  call assert_equal('<M-…>', maparg('abc'))
+
+  " illegal bytes
+  let str = ":\x7f:\x80:\x90:\xd0:"
+  exe 'nmap abc ' .. str
+  call assert_equal(str, maparg('abc'))
+  unlet str
+
   omap { w
   let d = maparg('{', 'o', 0, 1)
   call assert_equal(['{', 'w', 'o'], [d.lhs, d.rhs, d.mode])

src/nvim/testdir/test_mapping.vim

@@ -488,6 +488,13 @@ func Test_list_mappings()
   call assert_equal(['n  <M-…>         foo'],
         \ execute('nmap <M-…>')->trim()->split("\n"))
 
+  " illegal bytes
+  let str = ":\x7f:\x80:\x90:\xd0:"
+  exe 'nmap foo ' .. str
+  call assert_equal(['n  foo           ' .. strtrans(str)],
+        \ execute('nmap foo')->trim()->split("\n"))
+  unlet str
+
   " map to CTRL-V
   exe "nmap ,k \<C-V>"
   call assert_equal(['n  ,k            <Nop>'],

src/nvim/testdir/test_options.vim

@@ -31,6 +31,26 @@ func Test_isfname()
   set isfname&
 endfunc
 
+" Test for getting the value of 'pastetoggle'
+func Test_pastetoggle()
+  " character with K_SPECIAL byte
+  let &pastetoggle = '…'
+  call assert_equal('…', &pastetoggle)
+  call assert_equal("\n  pastetoggle=…", execute('set pastetoggle?'))
+
+  " modified character with K_SPECIAL byte
+  let &pastetoggle = '<M-…>'
+  call assert_equal('<M-…>', &pastetoggle)
+  call assert_equal("\n  pastetoggle=<M-…>", execute('set pastetoggle?'))
+
+  " illegal bytes
+  let str = ":\x7f:\x80:\x90:\xd0:"
+  let &pastetoggle = str
+  call assert_equal(str, &pastetoggle)
+  call assert_equal("\n  pastetoggle=" .. strtrans(str), execute('set pastetoggle?'))
+  unlet str
+endfunc
+
 func Test_wildchar()
   " Empty 'wildchar' used to access invalid memory.
   call assert_fails('set wildchar=', 'E521:')