fix(java): Correctly pass variadic arguments (#465)

The previous iteration was incorrectly forwarding variadic methods'
"rest" argument to the JSII runtime, causing a runtime failure at the
deserialization site.

Author: RomainMuller

packages/jsii-java-runtime-test/project/src/test/java/software/amazon/jsii/testing/ComplianceTest.java

@@ -50,6 +50,7 @@
 import software.amazon.jsii.tests.calculator.SyncVirtualMethods;
 import software.amazon.jsii.tests.calculator.UnionProperties;
 import software.amazon.jsii.tests.calculator.UsesInterfaceWithProperties;
+import software.amazon.jsii.tests.calculator.VariadicMethod;
 import software.amazon.jsii.tests.calculator.composition.CompositeOperation;
 import software.amazon.jsii.tests.calculator.lib.EnumFromScopedModule;
 import software.amazon.jsii.tests.calculator.lib.IFriendly;
@@ -1029,6 +1030,13 @@ public void objectIdDoesNotGetReallocatedWhenTheConstructorPassesThisOut() {
         assertTrue(object != null);
     }
 
+    @Test
+    public void variadicMethodCanBeInvoked() {
+        final VariadicMethod variadicMethod = new VariadicMethod(1);
+        final List<java.lang.Number> result = variadicMethod.asArray(3, 4, 5, 6);
+        assertEquals(Arrays.asList(1, 3, 4, 5, 6), result);
+    }
+
     static class PartiallyInitializedThisConsumerImpl extends PartiallyInitializedThisConsumer {
         @Override
         public String consumePartiallyInitializedThis(final ConstructorPassesThisOut obj,

packages/jsii-pacmak/lib/targets/java.ts

@@ -997,9 +997,28 @@ class JavaGenerator extends Generator {
 
     private renderMethodCallArguments(method: spec.Method) {
         if (!method.parameters || method.parameters.length === 0) { return ''; }
-        const values = method.parameters.map(param =>
-            isNullable(param) ? param.name : `java.util.Objects.requireNonNull(${param.name}, "${param.name} is required")`);
-        return `, new Object[] { ${values.join(', ')} }`;
+        const regularParams = method.parameters.filter(p => !p.variadic);
+        const values = regularParams.map(_renderParameter);
+        const valueStr = `new Object[] { ${values.join(', ')} }`;
+        if (method.variadic) {
+            const valuesStream = `java.util.Arrays.<Object>stream(${valueStr})`;
+
+            const lastParam = method.parameters[method.parameters.length - 1];
+            const restStream = `java.util.Arrays.<Object>stream(${lastParam.name})`;
+
+            const fullStream = regularParams.length > 0
+                ? `java.util.stream.Stream.concat(${valuesStream}, ${restStream})`
+                : restStream;
+            return `, ${fullStream}.toArray(Object[]::new)`;
+        } else {
+            return `, ${valueStr}`;
+        }
+
+        function _renderParameter(param: spec.Parameter) {
+            return isNullable(param)
+                ? param.name
+                : `java.util.Objects.requireNonNull(${param.name}, "${param.name} is required")`;
+        }
     }
 
     private renderMethodCall(cls: spec.TypeReference, method: spec.Method, async: boolean) {

packages/jsii-pacmak/test/expected.jsii-calc/java/src/main/java/software/amazon/jsii/tests/calculator/DontComplainAboutVariadicAfterOptional.java

@@ -12,6 +12,6 @@ public DontComplainAboutVariadicAfterOptional() {
     }
 
     public java.lang.String optionalAndVariadic(@javax.annotation.Nullable final java.lang.String optional, final java.lang.String... things) {
-        return this.jsiiCall("optionalAndVariadic", java.lang.String.class, new Object[] { optional, java.util.Objects.requireNonNull(things, "things is required") });
+        return this.jsiiCall("optionalAndVariadic", java.lang.String.class, java.util.stream.Stream.concat(java.util.Arrays.<Object>stream(new Object[] { optional }), java.util.Arrays.<Object>stream(things)).toArray(Object[]::new));
     }
 }

packages/jsii-pacmak/test/expected.jsii-calc/java/src/main/java/software/amazon/jsii/tests/calculator/VariadicMethod.java

@@ -11,14 +11,14 @@ protected VariadicMethod(final software.amazon.jsii.JsiiObject.InitializationMod
      */
     public VariadicMethod(final java.lang.Number... prefix) {
         super(software.amazon.jsii.JsiiObject.InitializationMode.Jsii);
-        software.amazon.jsii.JsiiEngine.getInstance().createNewObject(this, new Object[] { java.util.Objects.requireNonNull(prefix, "prefix is required") });
+        software.amazon.jsii.JsiiEngine.getInstance().createNewObject(this, java.util.Arrays.<Object>stream(prefix).toArray(Object[]::new));
     }
 
     /**
      * @param first the first element of the array to be returned (after the `prefix` provided at construction time).
      * @param others other elements to be included in the array.
      */
     public java.util.List<java.lang.Number> asArray(final java.lang.Number first, final java.lang.Number... others) {
-        return this.jsiiCall("asArray", java.util.List.class, new Object[] { java.util.Objects.requireNonNull(first, "first is required"), java.util.Objects.requireNonNull(others, "others is required") });
+        return this.jsiiCall("asArray", java.util.List.class, java.util.stream.Stream.concat(java.util.Arrays.<Object>stream(new Object[] { java.util.Objects.requireNonNull(first, "first is required") }), java.util.Arrays.<Object>stream(others)).toArray(Object[]::new));
     }
 }