Add nullable JS API parameter support

This change allows to define JS APIs which receive nullable primitive
type parameters. E.g. before the change it was not possible to pass
null to JS function with string parameter, instead the function
received a string "null".

As standard Java doesn't have nullable types, this feature currently
can only be used if the files are written in Kotlin. Kotlin metadata
library is used to detect nullable parameter types.

rhino/build.gradle

@@ -2,6 +2,9 @@ plugins {
     id 'rhino.library-conventions'
 }
 
+dependencies {
+    implementation "org.jetbrains.kotlin:kotlin-metadata-jvm:2.1.0"
+}
 
 publishing {
     publications {

rhino/src/main/java/module-info.java

@@ -14,4 +14,5 @@
     requires java.compiler;
     requires jdk.dynalink;
     requires transitive java.desktop;
+    requires kotlin.metadata.jvm;
 }

rhino/src/main/java/org/mozilla/javascript/AccessorSlot.java

@@ -235,8 +235,9 @@ public boolean setValue(Object value, Scriptable owner, Scriptable start) {
             // XXX: cache tag since it is already calculated in
             // defineProperty ?
             Class<?> valueType = pTypes[pTypes.length - 1];
+            boolean isNullable = member.argNullability[pTypes.length - 1];
             int tag = FunctionObject.getTypeTag(valueType);
-            Object actualArg = FunctionObject.convertArg(cx, start, value, tag);
+            Object actualArg = FunctionObject.convertArg(cx, start, value, tag, isNullable);
 
             if (member.delegateTo == null) {
                 member.invoke(start, new Object[] {actualArg});

rhino/src/main/java/org/mozilla/javascript/FunctionObject.java

@@ -163,20 +163,29 @@ public static int getTypeTag(Class<?> type) {
         return JAVA_UNSUPPORTED_TYPE;
     }
 
-    public static Object convertArg(Context cx, Scriptable scope, Object arg, int typeTag) {
+    public static Object convertArg(
+            Context cx, Scriptable scope, Object arg, int typeTag, boolean isNullable) {
         switch (typeTag) {
             case JAVA_STRING_TYPE:
                 if (arg instanceof String) return arg;
-                return ScriptRuntime.toString(arg);
+                return (arg == null && isNullable) ? null : ScriptRuntime.toString(arg);
             case JAVA_INT_TYPE:
                 if (arg instanceof Integer) return arg;
-                return Integer.valueOf(ScriptRuntime.toInt32(arg));
+                return (arg == null && isNullable)
+                        ? null
+                        : Integer.valueOf(ScriptRuntime.toInt32(arg));
             case JAVA_BOOLEAN_TYPE:
                 if (arg instanceof Boolean) return arg;
-                return ScriptRuntime.toBoolean(arg) ? Boolean.TRUE : Boolean.FALSE;
+                if (arg == null && isNullable) {
+                    return null;
+                } else {
+                    return ScriptRuntime.toBoolean(arg) ? Boolean.TRUE : Boolean.FALSE;
+                }
             case JAVA_DOUBLE_TYPE:
                 if (arg instanceof Double) return arg;
-                return Double.valueOf(ScriptRuntime.toNumber(arg));
+                return (arg == null && isNullable)
+                        ? null
+                        : Double.valueOf(ScriptRuntime.toNumber(arg));
             case JAVA_SCRIPTABLE_TYPE:
                 return ScriptRuntime.toObjectOrNull(cx, arg, scope);
             case JAVA_OBJECT_TYPE:
@@ -321,15 +330,15 @@ void initAsConstructor(Scriptable scope, Scriptable prototype, int attributes) {
 
     /**
      * @deprecated Use {@link #getTypeTag(Class)} and {@link #convertArg(Context, Scriptable,
-     *     Object, int)} for type conversion.
+     *     Object, int, boolean)} for type conversion.
      */
     @Deprecated
     public static Object convertArg(Context cx, Scriptable scope, Object arg, Class<?> desired) {
         int tag = getTypeTag(desired);
         if (tag == JAVA_UNSUPPORTED_TYPE) {
             throw Context.reportRuntimeErrorById("msg.cant.convert", desired.getName());
         }
-        return convertArg(cx, scope, arg, tag);
+        return convertArg(cx, scope, arg, tag, false);
     }
 
     /**
@@ -401,7 +410,8 @@ public Object call(Context cx, Scriptable scope, Scriptable thisObj, Object[] ar
                 invokeArgs = args;
                 for (int i = 0; i != parmsLength; ++i) {
                     Object arg = args[i];
-                    Object converted = convertArg(cx, scope, arg, typeTags[i]);
+                    Object converted =
+                            convertArg(cx, scope, arg, typeTags[i], member.argNullability[i]);
                     if (arg != converted) {
                         if (invokeArgs == args) {
                             invokeArgs = args.clone();
@@ -415,7 +425,8 @@ public Object call(Context cx, Scriptable scope, Scriptable thisObj, Object[] ar
                 invokeArgs = new Object[parmsLength];
                 for (int i = 0; i != parmsLength; ++i) {
                     Object arg = (i < argsLength) ? args[i] : Undefined.instance;
-                    invokeArgs[i] = convertArg(cx, scope, arg, typeTags[i]);
+                    invokeArgs[i] =
+                            convertArg(cx, scope, arg, typeTags[i], member.argNullability[i]);
                 }
             }
 

rhino/src/main/java/org/mozilla/javascript/MemberBox.java

@@ -6,6 +6,8 @@
 
 package org.mozilla.javascript;
 
+import static kotlin.metadata.Attributes.isNullable;
+
 import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
@@ -15,6 +17,13 @@
 import java.lang.reflect.Member;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
+import java.util.List;
+import java.util.Optional;
+import kotlin.Metadata;
+import kotlin.metadata.KmClass;
+import kotlin.metadata.KmFunction;
+import kotlin.metadata.KmValueParameter;
+import kotlin.metadata.jvm.KotlinClassMetadata;
 
 /**
  * Wrapper class for Method and Constructor instances to cache getParameterTypes() results, recover
@@ -27,6 +36,7 @@ final class MemberBox implements Serializable {
 
     private transient Member memberObject;
     transient Class<?>[] argTypes;
+    transient boolean[] argNullability;
     transient boolean vararg;
 
     transient Function asGetterFunction;
@@ -44,12 +54,56 @@ final class MemberBox implements Serializable {
     private void init(Method method) {
         this.memberObject = method;
         this.argTypes = method.getParameterTypes();
+        this.argNullability = getParameterNullability(method);
         this.vararg = method.isVarArgs();
     }
 
+    private boolean[] getParameterNullability(Method method) {
+        boolean[] result = new boolean[method.getParameters().length];
+        Metadata metadata = method.getDeclaringClass().getAnnotation(Metadata.class);
+        if (metadata != null) {
+            result = getParameterNullabilityFromKotlinMetadata(metadata, method.getName(), result);
+        }
+        return result;
+    }
+
+    private boolean[] getParameterNullability(Constructor<?> constructor) {
+        boolean[] result = new boolean[constructor.getParameters().length];
+        Metadata metadata = constructor.getDeclaringClass().getAnnotation(Metadata.class);
+        if (metadata != null) {
+            result =
+                    getParameterNullabilityFromKotlinMetadata(
+                            metadata, constructor.getName(), result);
+        }
+        return result;
+    }
+
+    private boolean[] getParameterNullabilityFromKotlinMetadata(
+            Metadata metadata, String methodName, boolean[] fallback) {
+        KotlinClassMetadata.Class kMetadata =
+                (KotlinClassMetadata.Class) KotlinClassMetadata.readLenient(metadata);
+        KmClass clazz = kMetadata.getKmClass();
+        Optional<KmFunction> function =
+                clazz.getFunctions().stream()
+                        .filter(f -> f.getName().equals(methodName))
+                        .findFirst();
+        if (function.isPresent()) {
+            List<KmValueParameter> params = function.get().getValueParameters();
+            boolean[] result = new boolean[params.size()];
+            int index = 0;
+            for (KmValueParameter parameter : params) {
+                result[index++] = isNullable(parameter.getType());
+            }
+            return result;
+        } else {
+            return fallback;
+        }
+    }
+
     private void init(Constructor<?> constructor) {
         this.memberObject = constructor;
         this.argTypes = constructor.getParameterTypes();
+        this.argNullability = getParameterNullability(constructor);
         this.vararg = constructor.isVarArgs();
     }
 
@@ -184,7 +238,8 @@ public Object call(
                                                     thisObj,
                                                     originalArgs[0],
                                                     FunctionObject.getTypeTag(
-                                                            nativeSetter.argTypes[0]))
+                                                            nativeSetter.argTypes[0]),
+                                                    nativeSetter.argNullability[0])
                                             : Undefined.instance;
                             if (nativeSetter.delegateTo == null) {
                                 setterThis = thisObj;