Improve validation of synctactically bad regexes

The following regex are not rejected as invalid when
using built-in regex objects:

    /abc]/
    /a7,18}/
    /a{7,18/

However, as per documentation, they are not supposed to
be valid, as `{` and `}` are special characters and as
such should be escaped:

    /abc\]/
    /a7,18\}/
    /a\{7,18/

With this commit, the regexes will additionally be
validated using the regex analyzer library in the editor
to ensure strict regex syntax compliance so as to avoid
what are likely mistakes in regex crafting by authors.

src/js/static-filtering-parser.js

@@ -114,6 +114,9 @@ const Parser = class {
         this.rePlainEntity = /^(?:[\w-]+\.)+\*$/;
         this.reEntity = /^[^*]+\.\*$/;
         this.punycoder = new URL(self.location);
+        // TODO: mind maxTokenLength
+        this.reGoodRegexToken
+            = /[^\x01%0-9A-Za-z][%0-9A-Za-z]{7,}|[^\x01%0-9A-Za-z][%0-9A-Za-z]{1,6}[^\x01%0-9A-Za-z]/;
         this.selectorCompiler = new this.SelectorCompiler(this);
         // TODO: reuse for network filtering analysis
         this.result = {
@@ -639,12 +642,8 @@ const Parser = class {
     }
 
     analyzeNetExtra() {
-        // Validate regex
         if ( this.patternIsRegex() ) {
-            try {
-                void new RegExp(this.getNetPattern());
-            }
-            catch (ex) {
+            if ( this.regexUtils.isValid(this.getNetPattern()) === false ) {
                 this.markSpan(this.patternSpan, BITError);
             }
         } else if (
@@ -1006,13 +1005,9 @@ const Parser = class {
     patternIsTokenizable() {
         // TODO: not necessarily true, this needs more work.
         if ( this.patternIsRegex === false ) { return true; }
-        const s = Parser.tokenizableStrFromRegex(this.getNetPattern());
-        try {
-            return /(?<![\x01%0-9A-Za-z]|^)[%0-9A-Za-z]{7,}/.test(s) ||
-                /(?<![\x01%0-9A-Za-z]|^)[%0-9A-Za-z]{1,6}(?![\x01%0-9A-Za-z]|$)/.test(s);
-        } catch(ex) {
-        }
-        return true;
+        return this.reGoodRegexToken.test(
+            this.regexUtils.toTokenizableStr(this.getNetPattern())
+        );
     }
 
     patternHasWildcard() {
@@ -2763,7 +2758,7 @@ const ExtOptionsIterator = class {
 // Depends on:
 // https://github.com/foo123/RegexAnalyzer
 
-Parser.tokenizableStrFromRegex = (( ) => {
+Parser.regexUtils = Parser.prototype.regexUtils = (( ) => {
 
     const firstCharCodeClass = s => {
         return /^[\x01%0-9A-Za-z]/.test(s) ? 1 : 0;
@@ -2773,12 +2768,12 @@ Parser.tokenizableStrFromRegex = (( ) => {
         return /[\x01%0-9A-Za-z]$/.test(s) ? 1 : 0;
     };
 
-    const toTokenizableString = node => {
+    const toTokenizableStr = node => {
         switch ( node.type ) {
             case 1: /* T_SEQUENCE, 'Sequence' */ {
                 let s = '';
                 for ( let i = 0; i < node.val.length; i++ ) {
-                    s += toTokenizableString(node.val[i]);
+                    s += toTokenizableStr(node.val[i]);
                 }
                 return s;
             }
@@ -2787,7 +2782,7 @@ Parser.tokenizableStrFromRegex = (( ) => {
                 let firstChar = 0;
                 let lastChar = 0;
                 for ( let i = 0; i < node.val.length; i++ ) {
-                    const s = toTokenizableString(node.val[i]);
+                    const s = toTokenizableStr(node.val[i]);
                     if ( firstChar === 0 && firstCharCodeClass(s) === 1 ) {
                         firstChar = 1;
                     }
@@ -2801,10 +2796,10 @@ Parser.tokenizableStrFromRegex = (( ) => {
             case 4: /* T_GROUP, 'Group' */ {
                 if ( node.flags.NegativeLookAhead === 1 ) { return '\x01'; }
                 if ( node.flags.NegativeLookBehind === 1 ) { return '\x01'; }
-                return toTokenizableString(node.val);
+                return toTokenizableStr(node.val);
             }
             case 16: /* T_QUANTIFIER, 'Quantifier' */ {
-                const s = toTokenizableString(node.val);
+                const s = toTokenizableStr(node.val);
                 const first = firstCharCodeClass(s);
                 const last = lastCharCodeClass(s);
                 if ( node.flags.min === 0 && first === 0 && last === 0 ) {
@@ -2817,10 +2812,18 @@ Parser.tokenizableStrFromRegex = (( ) => {
             }
             case 128: /* T_SPECIAL, 'Special' */ {
                 const flags = node.flags;
-                if ( flags.MatchEnd === 1 ) { return '\x00'; }
-                if ( flags.MatchStart === 1 ) { return '\x00'; }
-                if ( flags.MatchWordBoundary === 1 ) { return '\x00'; }
-                return '\x01';
+                if (
+                    flags.EndCharGroup === 1 || // dangling `]`
+                    flags.EndGroup === 1 ||     // dangling `)`
+                    flags.EndRepeats === 1      // dangling `}`
+                ) {
+                    throw new Error('Unmatched bracket');
+                }
+                return flags.MatchEnd === 1 ||
+                       flags.MatchStart === 1 ||
+                       flags.MatchWordBoundary === 1
+                    ? '\x00'
+                    : '\x01';
             }
             case 256: /* T_CHARS, 'Characters' */ {
                 for ( let i = 0; i < node.val.length; i++ ) {
@@ -2846,18 +2849,41 @@ Parser.tokenizableStrFromRegex = (( ) => {
         return '\x01';
     };
 
-    return function(reStr) {
-        if (
-            self.Regex instanceof Object === false ||
-            self.Regex.Analyzer instanceof Object === false
-        ) {
+    const Regex = self.Regex;
+    if (
+        Regex instanceof Object === false ||
+        Regex.Analyzer instanceof Object === false
+    ) {
+        return {
+            isValid: function(reStr)  {
+                try {
+                    void new RegExp(reStr);
+                } catch(ex) {
+                    return false;
+                }
+                return true;
+            },
+            toTokenizableStr: ( ) => '',
+        };
+    }
+
+    return {
+        isValid: function(reStr) {
+            try {
+                void new RegExp(reStr);
+                void toTokenizableStr(Regex.Analyzer(reStr, false).tree());
+            } catch(ex) {
+                return false;
+            }
+            return true;
+        },
+        toTokenizableStr: function(reStr) {
+            try {
+                return toTokenizableStr(Regex.Analyzer(reStr, false).tree());
+            } catch(ex) {
+            }
             return '';
-        }
-        try {
-            return toTokenizableString(self.Regex.Analyzer(reStr, false).tree());
-        } catch(ex) {
-        }
-        return '';
+        },
     };
 })();
 

src/js/static-net-filtering.js

@@ -3170,7 +3170,7 @@ const FilterParser = class {
     extractTokenFromRegex() {
         this.reToken.lastIndex = 0;
         const pattern =
-            vAPI.StaticFilteringParser.tokenizableStrFromRegex(this.pattern);
+            vAPI.StaticFilteringParser.regexUtils.toTokenizableStr(this.pattern);
         let bestToken;
         let bestBadness = 0x7FFFFFFF;
         for (;;) {