[mv3] Better validate hostnames in "Filtering mode details" editor

Related issue:
uBlockOrigin/uBOL-home#564

Author: gorhill

platform/mv3/extension/css/develop.css

@@ -60,7 +60,7 @@ section[data-pane="develop"] > div > * {
 :root.dark #cm-container .cm-editor .cm-line .ubol-literal {
     color: #1dae74;
     }
-#cm-container .cm-editor .cm-line.badline:not(.cm-activeLine) {
+#cm-container .cm-editor .cm-line.badline {
     background-color: color-mix(in srgb, var(--info3-ink) 15%, transparent 85%);
     }
 

platform/mv3/extension/js/dnr-parser.js

@@ -515,7 +515,7 @@ export function rulesFromText(text) {
         if ( indices.length === 0 ) { continue; }
         const result = ruleFromLines(lines, indices);
         if ( result.bad ) {
-            bad.push(...result.bad.slice(4));
+            bad.push(...result.bad.slice(0, 4));
         } else if ( result.rule ) {
             rules.push(result.rule);
         }

platform/mv3/extension/js/mode-parser.js

@@ -89,8 +89,20 @@ const perScopeParsers = {
 };
 
 const addHostnameToMode = (modes, mode, node) => {
-    if ( node.list !== true ) { return false; }
-    modes[mode].push(punycode.toASCII(node.val));
+    if ( node.list !== true ) { return node.val === '-'; }
+    if ( node.key !== undefined ) { return false; }
+    if ( node.val === undefined ) { return false; }
+    const hn = punycode.toASCII(node.val.toLowerCase());
+    if ( hn.length > 253 ) { return false; }
+    if ( hn.split('.').some(isInvalidLabel) ) { return false; }
+    modes[mode].push(hn);
+};
+
+const isInvalidLabel = label => {
+    if ( label.length === 0 ) { return true; }
+    if ( label.length > 63 ) { return true; }
+    if ( /^[^\da-z]|[^\da-z]$|[^\da-z-]/.test(label) ) { return true; }
+    return false;
 };
 
 /******************************************************************************/