rcfile: reject rebindings that have no effect or have side effects

Also, show in green only the ^ and M- combinations that are valid.

This fixes https://savannah.gnu.org/bugs/?49097

.
Signed-off-by: Rishabh Dave <rishabhddave@gmail.com>
Signed-off-by: Benno Schulenberg <bensberg@justemail.net>

doc/syntax/nanorc.nanorc

@@ -10,8 +10,8 @@ icolor brightred "^[[:space:]]*((un)?(bind|set)|include|syntax|header|comment|ma
 icolor brightgreen "^[[:space:]]*(set|unset)[[:space:]]+(allow_insecure_backup|autoindent|backup|backwards|boldtext|casesensitive|constantshow|cut|fill|historylog|justifytrim|locking|morespace|mouse|multibuffer|noconvert|nohelp|nonewlines|nowrap|positionlog|preserve|quickblank|quiet|rebinddelete|rebindkeypad|regexp|showcursor|smarthome|smooth|softwrap|suspend|tabsize|tabstospaces|tempfile|unix|view|wordbounds)\>"
 icolor yellow "^[[:space:]]*set[[:space:]]+(functioncolor|keycolor|statuscolor|titlecolor)[[:space:]]+(bright)?(white|black|red|blue|green|yellow|magenta|cyan)?(,(white|black|red|blue|green|yellow|magenta|cyan))?\>"
 icolor brightgreen "^[[:space:]]*set[[:space:]]+(backupdir|brackets|functioncolor|keycolor|matchbrackets|operatingdir|punct|quotestr|speller|statuscolor|titlecolor|whitespace|wordchars)[[:space:]]+"
-icolor brightgreen "^[[:space:]]*bind[[:space:]]+((\^|M-)([[:alpha:]]|space|[]]|[0-9^_=+{}|;:'\",./<>\?-])|F([1-9]|1[0-6])|Ins|Del)[[:space:]]+[[:alpha:]]+[[:space:]]+(all|main|search|replace(2|with)?|gotoline|writeout|insert|ext(ernal)?cmd|help|spell|linter|browser|whereisfile|gotodir)([[:space:]]+#|[[:space:]]*$)"
-icolor brightgreen "^[[:space:]]*unbind[[:space:]]+((\^|M-)([[:alpha:]]|space|[]]|[0-9^_=+{}|;:'\",./<>\?-])|F([1-9]|1[0-6])|Ins|Del)[[:space:]]+(all|main|search|replace(2|with)?|gotoline|writeout|insert|ext(ernal)?cmd|help|spell|linter|browser|whereisfile|gotodir)([[:space:]]+#|[[:space:]]*$)"
+icolor brightgreen "^[[:space:]]*bind[[:space:]]+((\^([[:alpha:]]|[]0-9\^_]|Space)|M-([[:alpha:]]|[]!"#$%&'()*+,./0-9:;<=>?@\^_`{|}~-]|Space))|F([1-9]|1[0-6])|Ins|Del)[[:space:]]+[[:alpha:]]+[[:space:]]+(all|main|search|replace(2|with)?|gotoline|writeout|insert|ext(ernal)?cmd|help|spell|linter|browser|whereisfile|gotodir)([[:space:]]+#|[[:space:]]*$)"
+icolor brightgreen "^[[:space:]]*unbind[[:space:]]+((\^([[:alpha:]]|[]0-9\^_]|Space)|M-([[:alpha:]]|[]!"#$%&'()*+,./0-9:;<=>?@\^_`{|}~-]|Space))|F([1-9]|1[0-6])|Ins|Del)[[:space:]]+(all|main|search|replace(2|with)?|gotoline|writeout|insert|ext(ernal)?cmd|help|spell|linter|browser|whereisfile|gotodir)([[:space:]]+#|[[:space:]]*$)"
 icolor brightgreen "^[[:space:]]*extendsyntax[[:space:]]+[[:alpha:]]+[[:space:]]+(i?color|header|magic|comment|linter|formatter)[[:space:]]+.*$"
 icolor green "^[[:space:]]*((un)?(bind|set)|include|syntax|header|magic|comment|linter|formatter|extendsyntax)\>"
 

src/rcfile.c

@@ -400,7 +400,8 @@ void parse_binding(char *ptr, bool dobind)
 	rcfile_error(N_("Key name must begin with \"^\", \"M\", or \"F\""));
 	goto free_copy;
     } else if ((keycopy[0] == 'M' && keycopy[1] != '-') ||
-		(keycopy[0] == '^' && ((keycopy[1] < 64 || keycopy[1] > 127) ||
+		(keycopy[0] == '^' && ((keycopy[1] < 'A' || keycopy[1] > 'z') ||
+		keycopy[1] == '[' || keycopy[1] == '`' ||
 		(strlen(keycopy) > 2 && strcmp(keycopy, "^Space") != 0))) ||
 		(strlen(keycopy) > 3 && strcmp(keycopy, "^Space") != 0 &&
 		strcmp(keycopy, "M-Space") != 0)) {