support for $noarrow macro

By default, JSweet generates arrow functions for Java lambda (the 'this'
semantics is closer to Java). Wrapping a function in $noarrow will force
JSweet to produce a plain old JavaScript function rather than an arrow
function.

core-lib/es5/src/main/java/jsweet/util/Lang.java

@@ -206,6 +206,18 @@ public final class Lang {
      */
     native public static def.js.Function function(Supplier<?> function);
 
+    /**
+     * Forces JSweet to create a plain JavaScript function rather than an
+     * "arrow" function.
+     * 
+     * <p>
+     * Hence, <code>function((a) -> { return a * a; })</code> transpiles to
+     * <code>(a) => { return a * a; }</code>. But
+     * <code>$noarrow(function((a) -> { return a * a; }))</code> transpiles to
+     * <code>function(a) { return a * a; }</code>
+     */
+    native public static def.js.Function $noarrow(def.js.Function function);
+
     /**
      * Casts a functional interface to a JavaScript function object.
      * 

core-lib/es6/src/main/java/jsweet/util/Lang.java

@@ -157,6 +157,18 @@ public final class Lang {
      */
     native public static def.js.Array<Float> array(float[] array);
 
+    /**
+     * Forces JSweet to create a plain JavaScript function rather than an
+     * "arrow" function.
+     * 
+     * <p>
+     * Hence, <code>function((a) -> { return a * a; })</code> transpiles to
+     * <code>(a) => { return a * a; }</code>. But
+     * <code>$noarrow(function((a) -> { return a * a; }))</code> transpiles to
+     * <code>function(a) { return a * a; }</code>
+     */
+    native public static def.js.Function $noarrow(def.js.Function function);
+
     /**
      * Casts a functional interface to a JavaScript function object.
      * 

transpiler/src/main/java/org/jsweet/transpiler/Java2TypeScriptTranslator.java

@@ -4508,7 +4508,8 @@ public class Java2TypeScriptTranslator extends AbstractTreePrinter {
 	public void visitLambda(JCLambda lamba) {
 		boolean regularFunction = false;
 		if (getParent() instanceof JCMethodInvocation
-				&& ((JCMethodInvocation) getParent()).meth.toString().endsWith("function")) {
+				&& ((JCMethodInvocation) getParent()).meth.toString().endsWith("function") && getParentOfParent() instanceof JCMethodInvocation
+				&& ((JCMethodInvocation) getParentOfParent()).meth.toString().endsWith("$noarrow")) {
 			MethodInvocationElement invocation = (MethodInvocationElement) ExtendedElementFactory.INSTANCE
 					.create(getParent());
 			if (JSweetConfig.UTIL_CLASSNAME.equals(invocation.getMethod().getEnclosingElement().toString())) {

transpiler/src/main/java/org/jsweet/transpiler/extension/Java2TypeScriptAdapter.java

@@ -495,6 +495,10 @@ public class Java2TypeScriptAdapter extends PrinterAdapter {
 					print("typeof ").print(invocationElement.getArgument(0));
 					return true;
 
+				case "$noarrow":
+					print(invocationElement.getArgument(0));
+					return true;
+					
 				case "equalsStrict":
 					print("(").print(invocationElement.getArgument(0)).print(" === ")
 							.print(invocationElement.getArgument(1)).print(")");

transpiler/src/main/java/org/jsweet/transpiler/util/AbstractTreeScanner.java

@@ -266,6 +266,17 @@ public abstract class AbstractTreeScanner extends TreeScanner {
 		}
 	}
 
+	/**
+	 * Returns the parent of the immediate parent in the printer's scanning stack.
+	 */
+	public JCTree getParentOfParent() {
+		if (this.stack.size() >= 3) {
+			return this.stack.get(this.stack.size() - 3);
+		} else {
+			return null;
+		}
+	}
+	
 	/**
 	 * Gets the parent element in the printer's scanning stack.
 	 */

transpiler/src/test/java/source/decorator/SimpleDecorator.java

@@ -46,7 +46,7 @@ class Globals {
 		Function originalMethod = (Function) descriptor.$get("value");
 
 		// editing the descriptor/value parameter
-		descriptor.$set("value", function(() -> {
+		descriptor.$set("value", $noarrow(function(() -> {
 			Array<Object> args = $array();
 			for (int _i = 0; _i < arguments.length; _i++) {
 				array(args)[_i - 0] = arguments[_i];
@@ -58,7 +58,7 @@ class Globals {
 			console.log("Call: " + key + "(" + a + ") => " + r);
 			trace.push("Call: " + key + "(" + a + ") => " + r);
 			return result;
-		}));
+		})));
 
 		// return edited descriptor as opposed to overwriting the descriptor
 		return descriptor;