Fixed issues #656 & #657 (#658)

* Fixing grammar for ID token to accept unicode ctrl characters in the range of \u0001 - \u001F

* Adding support for russian character set

* Fixed #657 to support registration of helpers written in ES6's const/let syntax

* Fixing CompositeTemplateLoaderTest.resolveSourceAtFs() to not fail on windows because of path separator '\'

* Fixing checkstyle errors

Author: swjain

handlebars/src/main/antlr4/com/github/jknack/handlebars/internal/HbsLexer.g4

@@ -333,7 +333,7 @@ ID
 fragment
 ID_START
   :
-   [a-zA-Z_$@:\u00C0-\u00FF]
+   [a-zA-ZА-Яа-я_$@:\u0001-\u001E\u00C0-\u00FF]
   ;
 
 fragment

handlebars/src/main/java/com/github/jknack/handlebars/helper/DefaultHelperRegistry.java

@@ -35,6 +35,8 @@
 import java.util.HashSet;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 import java.util.Set;
 
 import org.slf4j.Logger;
@@ -88,6 +90,9 @@ public class DefaultHelperRegistry implements HelperRegistry {
   /** Engine. */
   private ScriptEngine engine;
 
+  /** ES6's let/const declaration Pattern. */
+  private Pattern es6VarPattern = Pattern.compile("(?:^|[\\s(;])(let|const)\\s+");
+
   {
     // make sure default helpers are registered
     registerBuiltinsHelpers(this);
@@ -186,7 +191,7 @@ public HelperRegistry registerHelpers(final String filename, final String source
     notNull(filename, "The filename is required.");
     notEmpty(source, "The source is required.");
     ScriptEngine engine = engine();
-    Throwing.run(() -> engine.eval(source));
+    Throwing.run(() -> engine.eval(adaptES6Literals(source)));
     return this;
   }
 
@@ -195,6 +200,25 @@ public Set<Entry<String, Helper<?>>> helpers() {
     return this.helpers.entrySet();
   }
 
+  /**
+   * Since nashorn doesn't yet supports the ES6's "const" or "let" literals.
+   *  This method adapts the given helper source written in ES6 to work
+   *  with nashorn (by converting let/const to var).
+   *
+   * @param source the helper source.
+   * @return the adapted helper source.
+   **/
+  private String adaptES6Literals(final String source) {
+    Matcher m = es6VarPattern.matcher(source);
+    StringBuffer sb = new StringBuffer();
+    while (m.find()) {
+        StringBuffer buf = new StringBuffer(m.group());
+        buf.replace(m.start(1) - m.start(), m.end(1) - m.start(), "var");
+        m.appendReplacement(sb, buf.toString());
+    }
+    return m.appendTail(sb).toString();
+  }
+
   /**
    * <p>
    * Register all the helper methods for the given helper source.

handlebars/src/test/java/com/github/jknack/handlebars/internal/HbsParserTest.java

@@ -14,6 +14,12 @@ public class HbsParserTest {
   public void hello() {
     parse("Hello {{who}}\n!");
   }
+  
+  @Test
+  public void subExpr() {
+	  // below expression has unicode char with value: \u0001
+	  parse("{{data
withCtrlChar}}");
+  }
 
   @Test
   public void rawblock() {

handlebars/src/test/java/com/github/jknack/handlebars/io/CompositeTemplateLoaderTest.java

@@ -79,8 +79,9 @@ public void sourceAtFs() throws IOException {
 
   @Test
   public void resolveSourceAtFs() throws IOException {
-    assertEquals(new File("src/test/resources/inheritance", "home.hbs").getPath(),
-        loader.resolve("home"));
+    assertTrue(new File("src/test/resources/inheritance", "home.hbs").getPath()
+    		.compareTo(new File(loader.resolve("home")).getPath()) == 0
+        );
   }
 
   @Test(expected = UnsupportedOperationException.class)

handlebars/src/test/java/com/github/jknack/handlebars/issues/Issue657.java

@@ -0,0 +1,34 @@
+package com.github.jknack.handlebars.issues;
+
+import java.io.File;
+
+import org.junit.Test;
+
+import com.github.jknack.handlebars.AbstractTest;
+import com.github.jknack.handlebars.Handlebars;
+
+/**
+ * https://github.com/jknack/handlebars.java/issues/657
+ **/
+public class Issue657 extends AbstractTest {
+
+	@Override
+	protected void configure(final Handlebars handlebars) {
+		
+		try {
+			handlebars.registerHelpers(new File("src/test/resources/issue657.js"));
+		} catch (Exception ex) {
+			throw new IllegalStateException(ex);
+		}
+		
+	}
+
+	@Test
+	public void shouldAllowES6LetOrConstLiterals() throws Exception {
+
+		 shouldCompileTo("{{#and great magnificent}}Hello 657{{/and}}",
+			        $("great", true, "magnificent", true),
+			        "Hello 657");
+	}
+
+}

handlebars/src/test/resources/issue657.js

@@ -0,0 +1,11 @@
+Handlebars.registerHelper('and', function () {
+    const len = arguments.length - 1;
+    const options = arguments[len];
+    let val = true;
+    for (let i = 0; i < len; i++) {
+		if(!val)
+			break;
+		val = val && arguments[i];
+    }
+    return val ? options.fn(context) : options.inverse(context);
+});