JSNI method compilation error with javascript regular expression

Hello everyone，

To simplify the description of the problem, I use an official example to illustrate the problem。

1. Follow the GWT Getting Started to create a GWT project 
   
   
   webAppCreator -out MyWebApp com.mycompany.mywebapp.MyWebApp
   
   
   
2. Define a JSNI method with java regular expression and call it  in the EntryPoint class com.mycompany.mywebapp.client.MyWebApp
   
   
       public static native void methodWithRegularExpression()/*-{

           var reg = /^[\\w+/_-]+[=]{0,2}$/

           console.log("reg:" + reg)

       }-*/;

   
   

       /**

        * This is the entry point method.

        */

       public void onModuleLoad() {

           methodWithRegularExpression();

       }
   
   
3. Compile the project with the following Ant task(gwtc)
   
   
   
      <!-- Arguments to gwtc and devmode targets -->
   

     <property name="gwt.args" value="" />

   
   

     <!-- Configure path to GWT SDK -->

     <property name="gwt.sdk" location="G:/Google/gwt-2.8.2" />

   
   

     <path id="project.class.path">

       <fileset dir="lib" includes="**/*.jar"/>

       <pathelement location="war/WEB-INF/classes"/>

       <pathelement location="${gwt.sdk}/gwt-user.jar"/>

       <pathelement location="${gwt.sdk}/gwt-dev.jar"/>

       <pathelement location="${gwt.sdk}/validation-api-1.0.0.GA.jar"/>

       <pathelement location="${gwt.sdk}/validation-api-1.0.0.GA-sources.jar"/>

       <fileset dir="war/WEB-INF/lib" includes="**/*.jar"/>

       <!-- Add any additional non-server libs (such as JUnit) here -->

     </path>

   
   

     <target name="libs" description="Copy libs to WEB-INF/lib">

       <mkdir dir="war/WEB-INF/lib" />

       <copy todir="war/WEB-INF/lib" file="${gwt.sdk}/gwt-servlet.jar" />

       <copy todir="war/WEB-INF/lib" file="${gwt.sdk}/gwt-servlet-deps.jar" />

       <!-- Add any additional server libs that need to be copied -->

     </target>

   
   

     <target name="javac" depends="libs" description="Compile java source to bytecode">

       <mkdir dir="war/WEB-INF/classes"/>

       <javac srcdir="src" includes="**" encoding="utf-8"

           destdir="war/WEB-INF/classes"

           source="1.7" target="1.7" nowarn="true"

           debug="true" debuglevel="lines,vars,source">

         <classpath refid="project.class.path"/>

       </javac>

       <copy todir="war/WEB-INF/classes">

         <fileset dir="src" excludes="**/*.java"/>

       </copy>

     </target>

   
   

     <target name="gwtc" depends="javac" description="GWT compile to JavaScript (production mode)">

       <java failonerror="true" fork="true" classname="com.google.gwt.dev.Compiler" maxmemory="512m">

         <classpath>

           <pathelement location="src"/>

           <path refid="project.class.path"/>

         </classpath>

         <arg line="-war"/>

         <arg value="war"/>

         <!-- Additional arguments like -style PRETTY or -logLevel DEBUG -->

         <arg line="${gwt.args}"/>

         <arg line="-strict"/>

         <arg value="com.mycompany.mywebapp.MyWebApp"/>

       </java>

     </target>
   
   
4. Build failed
   
   
   javac:

       [javac] G:\Google\MyWebApp\build.xml:34: warning: 'includeantruntime' was not set, defaulting to build.sysclasspath=last; set to false for repeatable builds

       [javac] Compiling 1 source file to G:\Google\MyWebApp\war\WEB-INF\classes

   
   

   gwtc:

        [java] 七月 29, 2019 10:31:07 上午 java.util.prefs.WindowsPreferences <init>

        [java] 警告: Could not open/create prefs root node Software\JavaSoft\Prefs at root 0x80000002. Windows RegCreateKeyEx(...) returned error code 5.

        [java] Compiling module com.mycompany.mywebapp.MyWebApp

        [java]    Tracing compile failure path for type 'com.mycompany.mywebapp.client.MyWebApp'

        [java]       [ERROR] Errors in 'file:/G:/Google/MyWebApp/src/com/mycompany/mywebapp/client/MyWebApp.java'

        [java]          [ERROR] Line 44: missing ; before statement

        [java] >         var reg = /^[\\w+/_-]+[=]{0,2}$/

        [java] > ---------------------------^

        [java]    Finding entry point classes

        [java]       Tracing compile failure path for type 'com.mycompany.mywebapp.client.MyWebApp'

        [java]          [ERROR] Errors in 'file:/G:/Google/MyWebApp/src/com/mycompany/mywebapp/client/MyWebApp.java'

        [java]             [ERROR] Line 44: missing ; before statement

        [java] >         var reg = /^[\\w+/_-]+[=]{0,2}$/

        [java] > ---------------------------^

        [java]       [ERROR] Hint: Check the inheritance chain from your module; it may not be inheriting a required module or a module may not be adding its source path entries properly

   
   

   BUILD FAILED
   
   

More information:

ant version:

Apache Ant(TM) version 1.9.14 compiled on March 12 2019

GWT SDK version:

2.8.2

In the end, does anyone know how to solve this problem? 

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