fix(java): support abstract return types (#224)

Generate a $proxy class for all abstract classes
and use them when the return type is abstract,
similar to interface proxies.

This change also adds "abstract: true" to all
interface members, so the proxy generator can
treat interfaces and classes polymorphically.

Added a compliance test "returnAbstract" which
verifies this behavior.

Fixes #220
Related to #223 (.NET)
Related to aws/aws-cdk#680 (require jsii update)

Author: Elad Ben-Israel

package-lock.json

@@ -58,6 +58,7 @@
       "name": "VeryBaseProps",
       "properties": [
         {
+          "abstract": true,
           "name": "foo",
           "type": {
             "fqn": "@scope/jsii-calc-base-of-base.Very"
@@ -67,5 +68,5 @@
     }
   },
   "version": "0.7.4",
-  "fingerprint": "xM+yEz06NDR7n4G5n4VDoITs275dSqMhFDXgKOErl/M="
+  "fingerprint": "uxjBWk0nRDSHNR2FL01kRusKUoxa53smUFsizIJYBSs="
 }

packages/codemaker/package-lock.json

@@ -91,6 +91,7 @@
       "name": "BaseProps",
       "properties": [
         {
+          "abstract": true,
           "name": "bar",
           "type": {
             "primitive": "string"
@@ -100,5 +101,5 @@
     }
   },
   "version": "0.7.4",
-  "fingerprint": "/t6/DercTjOI1TLjj3MowD7pZkpm70sJQdeKwQMpa9M="
+  "fingerprint": "6NsGM++itCYmctZJdOp8kPJ3CfBnajQ78wNpY+EwZIQ="
 }

packages/jsii-build-tools/package-lock.json

@@ -101,6 +101,7 @@
       "kind": "interface",
       "methods": [
         {
+          "abstract": true,
           "docs": {
             "comment": "Say hello!"
           },
@@ -123,6 +124,7 @@
       "name": "MyFirstStruct",
       "properties": [
         {
+          "abstract": true,
           "docs": {
             "comment": "An awesome number value"
           },
@@ -132,6 +134,7 @@
           }
         },
         {
+          "abstract": true,
           "docs": {
             "comment": "A string value"
           },
@@ -141,6 +144,7 @@
           }
         },
         {
+          "abstract": true,
           "name": "firstOptional",
           "type": {
             "collection": {
@@ -250,6 +254,7 @@
       "name": "StructWithOnlyOptionals",
       "properties": [
         {
+          "abstract": true,
           "docs": {
             "comment": "The first optional!"
           },
@@ -260,13 +265,15 @@
           }
         },
         {
+          "abstract": true,
           "name": "optional2",
           "type": {
             "optional": true,
             "primitive": "number"
           }
         },
         {
+          "abstract": true,
           "name": "optional3",
           "type": {
             "optional": true,
@@ -317,5 +324,5 @@
     }
   },
   "version": "0.7.4",
-  "fingerprint": "dGLkY7rPKJjBMLQCOCj5AXR3Q1+cZcoiazcIhDUV++8="
+  "fingerprint": "PD1bhVhBjZ0dNrD8K4FK6RT+W5RhpkTEJDml/OiM7Ws="
 }

packages/jsii-calc-base-of-base/test/assembly.jsii

@@ -813,4 +813,56 @@ export namespace InterfaceInNamespaceIncludesClasses {
  */
 export interface InterfaceWithOptionalMethodArguments {
     hello(arg1: string, arg2?: number): void
+}
+
+/**
+ * awslabs/jsii#220
+ * Abstract return type
+ */
+
+export interface InterfaceImplementedByAbstractClass {
+    readonly propFromInterface: string;
+}
+
+export abstract class AbstractClassBase {
+    public abstract readonly abstractProperty: string;
+}
+
+export abstract class AbstractClass extends AbstractClassBase implements InterfaceImplementedByAbstractClass {
+    public nonAbstractMethod() {
+        return 42;
+    }
+
+    public abstract abstractMethod(name: string): string;
+
+    public get propFromInterface() {
+        return 'propFromInterfaceValue';
+    }
+}
+
+class ConcreteClass extends AbstractClass {
+    public abstractMethod(name: string) {
+        return `Hello, ${name}!!`;
+    }
+
+    public get abstractProperty() {
+        return 'Hello, dude!';
+    }
+}
+
+
+export class AbstractClassReturner {
+    public giveMeAbstract(): AbstractClass {
+        return new ConcreteClass();
+    }
+
+    public giveMeInterface(): InterfaceImplementedByAbstractClass {
+        return new ConcreteClass();
+    }
+
+    public get returnAbstractFromProperty(): AbstractClassBase {
+        return {
+            abstractProperty: 'hello-abstract-property'
+        }
+    }
 }