regex: escaped closing square bracket is not redundant for JS Unicode Regex (WEB-45812)

GitOrigin-RevId: 9e6a4180d995f96937954318bfbb01aff525cbce

RegExpSupport/src/org/intellij/lang/regexp/regexp-lexer.flex

@@ -253,6 +253,7 @@ BACK_REFERENCES_GROUP = [1-9][0-9]{0,2}
 
   {ESCAPE}  {LBRACE}            { return (allowDanglingMetacharacters != TRUE) ? RegExpTT.ESC_CHARACTER : RegExpTT.REDUNDANT_ESCAPE; }
   {ESCAPE}  {RBRACE}            { return (allowDanglingMetacharacters == FALSE) ? RegExpTT.ESC_CHARACTER : RegExpTT.REDUNDANT_ESCAPE; }
+  {ESCAPE}  {RBRACKET}          { return (allowDanglingMetacharacters != TRUE) ? RegExpTT.ESC_CHARACTER : RegExpTT.REDUNDANT_ESCAPE; }
   {ESCAPE}  {META2}             { return RegExpTT.ESC_CHARACTER; }
 }
 {ESCAPE}  {META1}             { return RegExpTT.ESC_CHARACTER; }

RegExpSupport/test/org/intellij/lang/regexp/ecmascript/EcmaScriptRegExpParsingTest.java

@@ -1,4 +1,4 @@
-// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package org.intellij.lang.regexp.ecmascript;
 
 import com.intellij.openapi.application.ex.PathManagerEx;
@@ -33,6 +33,11 @@ public class EcmaScriptRegExpParsingTest extends ParsingTestCase {
     doCodeTest("]");
   }
 
+  public void testEscapedMetaCharacter() throws IOException {
+    //noinspection RegExpRedundantEscape
+    doCodeTest("\\]");
+  }
+
   public void testExtendedUnicode() throws IOException {
     doCodeTest("\\u{9}");
   }

RegExpSupport/testData/ecmascript_psi/EscapedMetaCharacter.txt

@@ -0,0 +1,5 @@
+JS_UNICODE_REGEXP_FILE
+  RegExpPatternImpl: <\]>
+    RegExpBranchImpl: <\]>
+      RegExpCharImpl: <\]>
+        PsiElement(ESC_CHARACTER)('\]')