feat: add externalUnionsAsInterfaces config (#13)

Author: danadajian

src/config.ts

@@ -34,6 +34,11 @@ export const configSchema = object({
    * @description If `MyType` depends on `MyDependentType1` and `MyDependentType2`, we can allow `MyDependentType2` to be imported externally by including its import in `extraImports` and omitting it in the `dependentTypesInScope` list: `["MyType", "MyDependentType1"]`
    */
   dependentTypesInScope: optional(array(string())),
+  /**
+   * Denotes Kotlin classes representing union types to be treated as interfaces rather than annotation classes.
+   * This should be used for types outside `dependentTypesInScope` that are not generated by the plugin.
+   */
+  externalUnionsAsInterfaces: optional(array(string())),
   /**
    * Additional imports to add to the generated file.
    * @example ["com.example.additional.import.*"]

src/helpers/build-annotations.ts

@@ -55,8 +55,8 @@ export function buildAnnotations({
   const directiveAnnotations = definitionNode
     ? buildDirectiveAnnotations(definitionNode, config, description)
     : "";
-  const unionAnnotation = resolvedType?.annotation
-    ? `@${resolvedType.annotation}\n`
+  const unionAnnotation = resolvedType?.unionAnnotation
+    ? `@${resolvedType.unionAnnotation}\n`
     : "";
 
   const annotations = [

src/helpers/build-type-metadata.ts

@@ -25,7 +25,7 @@ import { CodegenConfig } from "../plugin";
 
 export interface TypeMetadata {
   typeName: string;
-  annotation?: string;
+  unionAnnotation?: string;
   defaultValue: string;
   isNullable: boolean;
 }
@@ -59,10 +59,17 @@ export function buildTypeMetadata(
       typeName: buildListType(typeNode, scalarTypeName),
     };
   } else if (isUnionType(schemaType)) {
+    const shouldTreatUnionAsInterface =
+      config.externalUnionsAsInterfaces?.includes(schemaType.name);
     return {
       ...commonMetadata,
-      annotation: schemaType.name,
-      typeName: buildListType(typeNode, "Any"),
+      unionAnnotation: shouldTreatUnionAsInterface
+        ? undefined
+        : schemaType.name,
+      typeName: buildListType(
+        typeNode,
+        shouldTreatUnionAsInterface ? schemaType.name : "Any",
+      ),
     };
   } else {
     return {