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 #10384)

src/message.c

@@ -1721,6 +1721,9 @@ msg_outtrans_special(
 	}
 	else
 	    text = (char *)str2special(&str, from);
+	if (text[0] != NUL && text[1] == NUL)
+	    // single-byte character or illegal byte
+	    text = (char *)transchar_byte((char_u)text[0]);
 	len = vim_strsize((char_u *)text);
 	if (maxlen > 0 && retval + len >= maxlen)
 	    break;
@@ -1755,6 +1758,7 @@ str2special_save(
 
 /*
  * Return the printable string for the key codes at "*sp".
+ * On illegal byte return a string with only that byte.
  * Used for translating the lhs or rhs of a mapping to printable chars.
  * Advances "sp" to the next code.
  */
@@ -1798,38 +1802,28 @@ str2special(
 	    special = TRUE;
     }
 
-    if (has_mbyte && !IS_SPECIAL(c))
+    if (has_mbyte && !IS_SPECIAL(c) && MB_BYTE2LEN(c) > 1)
     {
 	char_u	*p;
 
 	*sp = str;
 	// Try to un-escape a multi-byte character after modifiers.
 	p = mb_unescape(sp);
-
-	if (p == NULL)
-	{
-	    int len = (*mb_ptr2len)(str);
-
-	    // Check for an illegal byte.
-	    if (MB_BYTE2LEN(*str) > len)
-	    {
-		transchar_nonprint(curbuf, buf, c);
-		*sp = str + 1;
-		return buf;
-	    }
-	    *sp = str + len;
-	    p = str;
-	}
-	// Since 'special' is TRUE the multi-byte character 'c' will be
-	// processed by get_special_key_name()
-	c = (*mb_ptr2char)(p);
+	if (p != NULL)
+	    // Since 'special' is TRUE the multi-byte character 'c' will be
+	    // processed by get_special_key_name()
+	    c = (*mb_ptr2char)(p);
+	else
+	    // illegal byte
+	    *sp = str + 1;
     }
     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>.
     // Use <Space> only for lhs of a mapping.
-    if (special || char2cells(c) > 1 || (from && c == ' '))
+    if (special || c < ' ' || (from && c == ' '))
 	return get_special_key_name(c, modifiers);
     buf[0] = c;
     buf[1] = NUL;

src/option.c

@@ -4017,6 +4017,8 @@ get_option_value(
 	    if ((char_u **)varp == &curbuf->b_p_key
 						&& **(char_u **)(varp) != NUL)
 		*stringval = vim_strsave((char_u *)"*****");
+	    else if ((char_u **)varp == &p_pt)	// 'pastetoggle'
+		*stringval = str2special_save(*(char_u **)(varp), FALSE);
 	    else
 #endif
 		*stringval = vim_strsave(*(char_u **)(varp));

src/testdir/test_map_functions.vim

@@ -58,6 +58,20 @@ func 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/testdir/test_mapping.vim

@@ -502,6 +502,13 @@ 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/testdir/test_options.vim

@@ -48,6 +48,26 @@ 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:')

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4924,
 /**/
     4923,
 /**/