Add changeset

Author: eddeee888

.changeset/gold-frogs-explain.md

@@ -0,0 +1,139 @@
+---
+'@graphql-codegen/visitor-plugin-common': major
+'@graphql-codegen/typescript-operations': major
+'@graphql-codegen/typescript': major
+'@graphql-codegen/typescript-resolvers': major
+---
+
+Implement Scalars with input/output types
+
+In GraphQL, Scalar types can be different for client and server. For example, given the native GraphQL ID:
+- A client may send `string` or `number` in the input
+- A client receives `string` in its selection set (i.e output)
+- A server receives `string` in the resolver (GraphQL parses `string` or `number` received from the client to `string`)
+- A server may return `string` or `number` (GraphQL serializes the value to `string` before sending it to the client )
+
+Currently, we represent every Scalar with only one type. This is what codegen generates as base type:
+
+```ts
+export type Scalars = {
+  ID: string;
+}
+```
+
+Then, this is used in both input and output type e.g.
+
+```ts
+export type Book = {
+  __typename?: "Book";
+  id: Scalars["ID"]; // Output's ID can be `string` 👍
+};
+
+export type QueryBookArgs = {
+  id: Scalars["ID"]; // Input's ID can be `string` or `number`. However, the type is only `string` here 👎
+};
+```
+
+This PR extends each Scalar to have input and output:
+
+```ts
+export type Scalars = {
+  ID: {
+    input: string | number;
+    output: string;
+  }
+}
+```
+
+Then, each input/output GraphQL type can correctly refer to the correct input/output scalar type:
+
+```ts
+export type Book = {
+  __typename?: "Book";
+  id: Scalars["ID"]['output']; // Output's ID can be `string` 👍
+};
+
+export type QueryBookArgs = {
+  id: Scalars["ID"]['input']; // Input's ID can be `string` or `number` 👍
+};
+```
+
+Note that for `typescript-resolvers`, the type of ID needs to be inverted. However, the referenced types in GraphQL input/output types should still work correctly:
+
+```ts
+export type Scalars = {
+  ID: {
+    input: string;
+    output: string | number;
+  }
+}
+
+export type Book = {
+  __typename?: "Book";
+  id: Scalars["ID"]['output']; // Resolvers can return `string` or `number` in ID fields 👍
+};
+
+export type QueryBookArgs = {
+  id: Scalars["ID"]['input']; // Resolvers receive `string` in ID fields 👍
+};
+
+export type ResolversTypes = {
+  ID: ID: ResolverTypeWrapper<Scalars['ID']['output']>; // Resolvers can return `string` or `number` in ID fields 👍
+}
+
+export type ResolversParentTypes = {
+  ID: Scalars['ID']['output']; // Resolvers receive `string` or `number` from parents 👍
+};
+```
+
+---
+
+Config changes:
+
+1. Scalars option can now take input/output types:
+
+```ts
+config: {
+  scalars: {
+    ID: {
+      input: 'string',
+      output: 'string | number'
+    }
+  }
+}
+```
+
+2. If a string is given (instead of an object with input/output fields), it will be used as both input and output types:
+
+```ts
+config: {
+  scalars: {
+    ID: 'string' // Means it `string` will be used for both ID's input and output types
+  }
+}
+```
+
+3. BREAKING CHANGE: External module Scalar types need to be an object with input/output fields
+
+```ts
+config: {
+  scalars: {
+    ID: './path/to/scalar-module'
+  }
+}
+```
+
+If correctly, wired up, the following will be generated:
+
+```ts
+// Previously, imported `ID` type can be a primitive type, now it must be an object with input/output fields
+import { ID } from "./path/to/scalar-module";
+
+export type Scalars = {
+  ID: { input: ID['input']; output: ID['output']; }
+};
+```
+
+---
+
+BREAKING CHANGES: This changes Scalar types could be referenced in other plugins. If you are a plugin maintainer and reference Scalar, please update your plugin to use the correct input/output types.