feat(plugin): Update plugin with null union support

Prior to these changes, the GraphQL plugin only supported decorating field properties when the
type of a class property was optional. However, sometimes typescript users like to use union
types that include null instead to indicate a nullable field. This change makes it possible to
support nullable fields when the union includes a null type.

lib/plugin/utils/ast-utils.ts

@@ -70,6 +70,14 @@ export function isEnumLiteral(type: Type) {
   return hasFlag(type, TypeFlags.EnumLiteral) && !type.isUnion();
 }
 
+export function isNull(type: Type) {
+  if (type.isUnion()) {
+    return Boolean(type.types.find((t) => hasFlag(t, TypeFlags.Null)));
+  } else {
+    return hasFlag(type, TypeFlags.Null);
+  }
+}
+
 export function hasFlag(type: Type, flag: TypeFlags) {
   return (type.flags & flag) === flag;
 }

lib/plugin/visitors/model-class.visitor.ts

@@ -3,7 +3,7 @@ import * as ts from 'typescript';
 import { HideField } from '../../decorators';
 import { PluginOptions } from '../merge-options';
 import { METADATA_FACTORY_NAME } from '../plugin-constants';
-import { getDescriptionOfNode } from '../utils/ast-utils';
+import { getDescriptionOfNode, isNull } from '../utils/ast-utils';
 import {
   getDecoratorOrUndefinedByNames,
   getTypeReferenceAsString,
@@ -134,7 +134,8 @@ export class ModelClassVisitor {
     sourceFile: ts.SourceFile,
     pluginOptions: PluginOptions,
   ): ts.ObjectLiteralExpression {
-    const isRequired = !node.questionToken;
+    const type = typeChecker.getTypeAtLocation(node);
+    const isRequired = !node.questionToken && !isNull(type);
 
     const properties = [
       ...existingProperties,

tests/plugin/fixtures/create-null-cat.dto.ts

@@ -0,0 +1,55 @@
+export const createNullCatDtoText = `
+enum Status {
+    ENABLED,
+    DISABLED
+}
+
+enum OneValueEnum {
+    ONE
+}
+
+interface Node {
+    id: number;
+}
+
+export class CreateCatDto {
+  name: string | null;
+  age: number = 3;
+  tags: string[];
+  status: Status = Status.ENABLED;
+  status2?: Status | null;
+  statusArr?: Status[];
+  readonly breed?: string;
+  nodes: Node[];
+  date: Date;
+  nil: null;
+
+  @HideField()
+  hidden: number;
+
+  static staticProperty: string;
+}
+`;
+
+export const createNullCatDtoTextTranspiled = `var Status;
+(function (Status) {
+    Status[Status[\"ENABLED\"] = 0] = \"ENABLED\";
+    Status[Status[\"DISABLED\"] = 1] = \"DISABLED\";
+})(Status || (Status = {}));
+var OneValueEnum;
+(function (OneValueEnum) {
+    OneValueEnum[OneValueEnum[\"ONE\"] = 0] = \"ONE\";
+})(OneValueEnum || (OneValueEnum = {}));
+export class CreateCatDto {
+    constructor() {
+        this.age = 3;
+        this.status = Status.ENABLED;
+    }
+    static _GRAPHQL_METADATA_FACTORY() {
+        return { name: { nullable: true, type: () => Object }, age: { nullable: false, type: () => Number }, tags: { nullable: false, type: () => [String] }, status: { nullable: false, type: () => Status }, status2: { nullable: true, type: () => Object }, statusArr: { nullable: true, type: () => [Status] }, breed: { nullable: true, type: () => String }, nodes: { nullable: false, type: () => [Object] }, date: { nullable: false, type: () => Date }, nil: { nullable: true, type: () => Object } };
+    }
+}
+__decorate([
+    HideField()
+], CreateCatDto.prototype, \"hidden\", void 0);
+`

tests/plugin/model-class-visitor.spec.ts

@@ -12,6 +12,10 @@ import {
   es5CreateCatDtoText,
   es5CreateCatDtoTextTranspiled,
 } from './fixtures/es5-class.dto';
+import {
+  createNullCatDtoText,
+  createNullCatDtoTextTranspiled
+} from './fixtures/create-null-cat.dto';
 
 describe('API model properties', () => {
   it('should add the metadata factory when no decorators exist', () => {
@@ -84,4 +88,25 @@ describe('API model properties', () => {
     });
     expect(result.outputText).toEqual(es5CreateCatDtoTextTranspiled);
   });
+
+  it('should add the decorator when union type includes null', () => {
+    const options: ts.CompilerOptions = {
+      module: ts.ModuleKind.ESNext,
+      target: ts.ScriptTarget.ESNext,
+      newLine: ts.NewLineKind.LineFeed,
+      noEmitHelpers: true,
+      strict: true,
+    };
+    const filename = 'create-cat.input.ts';
+    const fakeProgram = ts.createProgram([filename], options);
+
+    const result = ts.transpileModule(createNullCatDtoText, {
+      compilerOptions: options,
+      fileName: filename,
+      transformers: {
+        before: [before({}, fakeProgram)],
+      },
+    });
+    expect(result.outputText).toEqual(createNullCatDtoTextTranspiled);
+  });
 });