✨ feat: Add infer to infer TypeScript type from GraphQL schema

README.md

@@ -56,7 +56,7 @@ const allUsers = await query('users').select((user) => [
   ]),
 ]);
 
-/**
+/*
  * The type of `post` is inferred as
  * {
  *   title: string;
@@ -258,6 +258,59 @@ The `subscribe` method accepts three parameters:
 - onError: Optional. The error handler. It will be called when an error is emitted by the subscription. It accepts one parameter, which is the error emitted by the subscription.
 - onComplete: Optional. The completion handler. It will be called when the subscription is completed. It accepts no parameter.
 
+### Infer TypeScript types from GraphQL schema
+
+It is annoying to define a type in GraphQL schema and repeat the same type in TypeScript. graphql-intuitive-request provides a convenient way to infer TypeScript types from the GraphQL schema.
+
+`schema` is a helper function to validate a GraphQL schema. It simply returns the schema itself and does nothing at runtime, but it is useful for TypeScript to ensure that the schema is valid.
+
+```typescript
+import { createClient, enumOf, infer, schema } from 'graphql-intuitive-request';
+
+const $ = schema({
+  User: {
+    id: 'Int!',
+    username: 'String!',
+    email: 'String',
+  },
+  Post: {
+    id: 'Int!',
+    status: 'PostStatus!',
+    title: 'String!',
+    content: 'String!',
+    author: 'User!',
+  },
+  PostStatus: enumOf('DRAFT', 'PUBLISHED', 'ARCHIVED'),
+
+  Query: {
+    users: [{}, '[User!]!'],
+    post: [{ id: 'Int!' }, 'Post'],
+  },
+});
+
+export const client = createClient('https://example.com/graphql').withSchema($);
+```
+
+After that, you can use the `infer` helper function to infer TypeScript types from the schema.
+
+```typescript
+const $$ = infer($);
+
+/*
+ * The type of `Post` is inferred as
+ * Array<{
+ *   id: number;
+ *   status: "DRAFT" | "PUBLISHED" | "ARCHIVED";
+ *   title: string;
+ *   content: string;
+ *   author: { id: number; username: string; email: string | null };
+ * }>
+ */
+export type Post = typeof $$.Post;
+```
+
+As you can see, you can use `typeof inferred.<Type>` to get the inferred TypeScript type of a type in the schema. Like `schema`, `infer` also does nothing at runtime, it is only used to infer TypeScript types from the schema.
+
 ### Create object selector to eliminate duplication
 
 It is annoying to repeat the same object selector every time when you want to select some fields of an object. graphql-intuitive-request provides a convenient way to eliminate the duplication of object selector.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "graphql-intuitive-request",
-  "version": "0.1.3-dev",
+  "version": "0.1.3",
   "private": true,
   "description": "Intuitive and (more importantly) TS-friendly GraphQL client for queries, mutations and subscriptions",
   "homepage": "https://github.com/Snowfly-T/graphql-intuitive-request",

src/index.ts

@@ -1,7 +1,7 @@
 export { createClient } from './client';
 export { queryString, mutationString, subscriptionString } from './query-builder';
 export { selectorBuilder } from './selector';
-export { schema, enumOf } from './types';
+export { infer, enumOf, schema } from './types';
 
 /**
  * Error thrown when the client receives an error from the server.

src/types.proof.ts

@@ -0,0 +1,79 @@
+import { describe, equal, expect, it } from 'typroof';
+
+import { enumOf, infer, schema } from './types';
+
+import type { GraphQLEnum } from './types/graphql-types';
+
+let $: {
+  User: {
+    id: 'Int!';
+    username: 'String!';
+    email: 'String';
+  };
+  Post: {
+    id: 'Int!';
+    status: 'PostStatus!';
+    title: 'String!';
+    content: 'String!';
+    author: 'User!';
+  };
+  PostStatus: GraphQLEnum<'DRAFT' | 'PUBLISHED' | 'ARCHIVED'>;
+
+  Query: {
+    users: [NonNullable<unknown>, '[User!]!'];
+    post: [{ id: 'Int!' }, 'Post'];
+  };
+};
+
+describe('schema', () => {
+  it('should validate a GraphQL schema', () => {
+    const _ = schema({
+      User: {
+        id: 'Int!',
+        username: 'String!',
+        email: 'String',
+      },
+      Post: {
+        id: 'Int!',
+        status: 'PostStatus!',
+        title: 'String!',
+        content: 'String!',
+        author: 'User!',
+      },
+      PostStatus: enumOf('DRAFT', 'PUBLISHED', 'ARCHIVED'),
+
+      Query: {
+        users: [{}, '[User!]!'],
+        post: [{ id: 'Int!' }, 'Post'],
+      },
+    });
+    expect(_).to(equal<typeof $>);
+    $ = _;
+  });
+});
+
+describe('compile', () => {
+  it('should infer the type of a GraphQL schema', () => {
+    const $$ = infer($);
+
+    type User = typeof $$.User;
+    expect<User>().to(
+      equal<{
+        id: number;
+        username: string;
+        email: string | null;
+      }>(),
+    );
+
+    type Post = typeof $$.Post;
+    expect<Post>().to(
+      equal<{
+        id: number;
+        status: 'DRAFT' | 'PUBLISHED' | 'ARCHIVED';
+        title: string;
+        content: string;
+        author: User;
+      }>(),
+    );
+  });
+});

src/types.ts

@@ -1,10 +1,11 @@
-import type { StringLiteral, ValueOf } from './types/common';
+import type { StringKeyOf, StringLiteral, ValueOf } from './types/common';
 import type {
   BaseEnvironment,
   FunctionCollection,
   GraphQLEnum,
   TypeCollection,
 } from './types/graphql-types';
+import type { Parse } from './types/parser';
 import type { Validate } from './types/validator';
 
 export const GRAPHQL_BASE_TYPES = ['ID', 'Int', 'Float', 'String', 'Boolean'] as const;
@@ -57,6 +58,34 @@ export const schema = <
   schema: Schema<T>,
 ) => schema;
 
+/**
+ * Infer the type of a GraphQL schema in TypeScript.
+ * @param _ The schema to infer.
+ * @returns
+ */
+export const infer = <
+  $ extends
+    | {
+        Query?: FunctionCollection;
+        Mutation?: FunctionCollection;
+        Subscription?: FunctionCollection;
+      }
+    | TypeCollection,
+>(
+  _: $,
+) => {
+  const createInfiniteProxy = <T extends object>() =>
+    new Proxy({} as T, {
+      get: (): any => createInfiniteProxy(),
+    });
+  return createInfiniteProxy<{
+    [P in StringKeyOf<Omit<$, 'Query' | 'Mutation' | 'Subscription'>>]: Exclude<
+      Parse<$[P], $ & BaseEnvironment>,
+      null
+    >;
+  }>();
+};
+
 /**
  * Create a GraphQL enum type.
  * @param values The values of the enum.