feat(graphql): type check field default value

Author: Martin Kagamino Lehoux

packages/graphql/lib/decorators/field.decorator.ts

@@ -9,15 +9,19 @@ import { Type } from '@nestjs/common';
 import { isFunction } from '@nestjs/common/utils/shared.utils';
 import { Complexity, FieldMiddleware } from '../interfaces';
 import { BaseTypeOptions } from '../interfaces/base-type-options.interface';
-import { ReturnTypeFunc } from '../interfaces/return-type-func.interface';
+import {
+  GqlTypeReference,
+  ReturnTypeFunc,
+  ReturnTypeFuncValue,
+} from '../interfaces/return-type-func.interface';
 import { LazyMetadataStorage } from '../schema-builder/storages/lazy-metadata.storage';
 import { TypeMetadataStorage } from '../schema-builder/storages/type-metadata.storage';
 import { reflectTypeFromMetadata } from '../utils/reflection.utilts';
 
 /**
  * Interface defining options that can be passed to `@Field()` decorator.
  */
-export interface FieldOptions extends BaseTypeOptions {
+export interface FieldOptions<T = any> extends BaseTypeOptions<T> {
   /**
    * Name of the field.
    */
@@ -40,6 +44,12 @@ export interface FieldOptions extends BaseTypeOptions {
   middleware?: FieldMiddleware[];
 }
 
+type FieldOptionsExtractor<T> = T extends [GqlTypeReference<infer P>]
+  ? FieldOptions<P[]>
+  : T extends GqlTypeReference<infer P>
+  ? FieldOptions<P>
+  : never;
+
 /**
  * @Field() decorator is used to mark a specific class property as a GraphQL field.
  * Only properties decorated with this decorator will be defined in the schema.
@@ -49,24 +59,25 @@ export function Field(): PropertyDecorator & MethodDecorator;
  * @Field() decorator is used to mark a specific class property as a GraphQL field.
  * Only properties decorated with this decorator will be defined in the schema.
  */
-export function Field(
-  options: FieldOptions,
+export function Field<T extends ReturnTypeFuncValue>(
+  options: FieldOptionsExtractor<T>,
 ): PropertyDecorator & MethodDecorator;
 /**
  * @Field() decorator is used to mark a specific class property as a GraphQL field.
  * Only properties decorated with this decorator will be defined in the schema.
  */
-export function Field(
-  returnTypeFunction?: ReturnTypeFunc,
-  options?: FieldOptions,
+export function Field<T extends ReturnTypeFuncValue>(
+  returnTypeFunction?: ReturnTypeFunc<T>,
+  options?: FieldOptionsExtractor<T>,
 ): PropertyDecorator & MethodDecorator;
+
 /**
  * @Field() decorator is used to mark a specific class property as a GraphQL field.
  * Only properties decorated with this decorator will be defined in the schema.
  */
-export function Field(
-  typeOrOptions?: ReturnTypeFunc | FieldOptions,
-  fieldOptions?: FieldOptions,
+export function Field<T extends ReturnTypeFuncValue>(
+  typeOrOptions?: ReturnTypeFunc<T> | FieldOptionsExtractor<T>,
+  fieldOptions?: FieldOptionsExtractor<T>,
 ): PropertyDecorator & MethodDecorator {
   return (
     prototype: Object,
@@ -83,9 +94,9 @@ export function Field(
   };
 }
 
-export function addFieldMetadata(
-  typeOrOptions: ReturnTypeFunc | FieldOptions,
-  fieldOptions: FieldOptions,
+export function addFieldMetadata<T extends ReturnTypeFuncValue>(
+  typeOrOptions: ReturnTypeFunc<T> | FieldOptionsExtractor<T>,
+  fieldOptions: FieldOptionsExtractor<T>,
   prototype: Object,
   propertyKey?: string,
   descriptor?: TypedPropertyDescriptor<any>,
@@ -103,7 +114,7 @@ export function addFieldMetadata(
       metadataKey: isResolverMethod ? 'design:returntype' : 'design:type',
       prototype,
       propertyKey,
-      explicitTypeFn: typeFunc as ReturnTypeFunc,
+      explicitTypeFn: typeFunc as ReturnTypeFunc<T>,
       typeOptions: options,
     });
 

packages/graphql/lib/interfaces/base-type-options.interface.ts

@@ -1,11 +1,11 @@
 export type NullableList = 'items' | 'itemsAndList';
-export interface BaseTypeOptions {
+export interface BaseTypeOptions<T = any> {
   /**
    * Determines whether field/argument/etc is nullable.
    */
   nullable?: boolean | NullableList;
   /**
    * Default value.
    */
-  defaultValue?: any;
+  defaultValue?: T;
 }

packages/graphql/lib/interfaces/return-type-func.interface.ts

@@ -1,11 +1,13 @@
 import { Type } from '@nestjs/common';
 import { GraphQLScalarType } from 'graphql';
 
-export type GqlTypeReference =
-  | Type<any>
+export type GqlTypeReference<T = any> =
+  | Type<T>
   | GraphQLScalarType
   | Function
   | object
   | symbol;
 export type ReturnTypeFuncValue = GqlTypeReference | [GqlTypeReference];
-export type ReturnTypeFunc = (returns?: void) => ReturnTypeFuncValue;
+export type ReturnTypeFunc<T extends ReturnTypeFuncValue = any> = (
+  returns?: void,
+) => T;

packages/graphql/lib/interfaces/type-options.interface.ts

@@ -1,6 +1,6 @@
 import { BaseTypeOptions } from './base-type-options.interface';
 
-export interface TypeOptions extends BaseTypeOptions {
+export interface TypeOptions<T = any> extends BaseTypeOptions<T> {
   isArray?: boolean;
   arrayDepth?: number;
 }

packages/graphql/tests/plugin/decorators/field.decorator.spec.ts

@@ -0,0 +1,41 @@
+import { Field } from '../../../lib/decorators';
+
+class Inner {
+  test: string;
+}
+
+// It should expect the right primitive as defaultValue
+class WrongPrimitive {
+  // @ts-expect-error The defaultValue should be a boolean
+  @Field(() => Boolean, { defaultValue: 'true' })
+  bool: boolean;
+}
+
+class CorrectPrimitive {
+  @Field(() => Boolean, { defaultValue: true })
+  bool: boolean;
+}
+
+// It should expect the right object as defaultValue
+class WrongObject {
+  // @ts-expect-error The defaultValue should be of the shape of Inner
+  @Field(() => Inner, { defaultValue: { success: true } })
+  inner: Inner;
+}
+
+class CorrectObject {
+  @Field(() => Inner, { defaultValue: { test: 'hello' } })
+  inner: Inner;
+}
+
+// It should expect an Array as defaultValue
+class WrongArray {
+  // @ts-expect-error The defaultValue should be an Array
+  @Field(() => [Inner], { defaultValue: { test: 'test' } })
+  inners: Inner[];
+}
+
+class CorrectArray {
+  @Field(() => [Inner], { defaultValue: [{ test: 'test' }] })
+  inner: Inner;
+}