feat: make apollo iresolvers compatible with gg resolvers

closes #15

docs/01-configuration.md

@@ -15,6 +15,7 @@ The configuration file must be called **`graphqlgen.yml`**.
   - `output`: Specifies where the scaffolded resolvers should be located. Must point to a **directory**.
   - `layout`: Specifies the [_layout_](#layouts) for the generated files. Possible values: `file-per-type` (more layouts [coming soon](https://github.com/prisma/graphqlgen/issues/106): `single-file`, `file-per-type-classes`, `single-file-classes`).
 - `default-resolvers`: A boolean dictating if default resolvers will be generated or not. Defaults to `true`.
+- `iresolvers-augmentation`: A boolean dictating if Apollo Server IResolvers type should be augmented so that it is compatible with graphqlgen `Resolvers` type. Defaults to `true`.
 
 Whether a property is required or not depends on whether you're doing [Generation](#generation) or [Scaffolding](#scaffolding).
 

packages/graphqlgen-json-schema/src/definition.ts

@@ -6,6 +6,7 @@ export interface GraphQLGenDefinition {
   output: string
   ['resolver-scaffolding']?: ResolverScaffolding
   ['default-resolvers']?: boolean
+  ['iresolvers-augmentation']?: boolean
 }
 
 export interface Models {

packages/graphqlgen/src/generators/typescript/generator.ts

@@ -98,6 +98,33 @@ export function generate(args: GenerateArgs): string {
 
   ${renderResolvers(args)}
 
+  ${
+    args.iResolversAugmentationEnabled
+      ? renderGraphqlToolsModuleAugmentationIResolvers()
+      : ''
+  }
+
+  `
+}
+
+/**
+ * This renders a TypeScript module augmentation against graphql-tools
+ * IResolvers type. Apollo Server uses that type to type its resolvers.
+ * The problem with that type is that it is very loose compared to
+ * graphqlgen including being an index type. The index type in particular
+ * breaks compatibility with the resolvers generated by graphqlgen. We
+ * fix this by augmenting the IResolvers type.
+ *
+ * References:
+ *
+ *  - https://www.typescriptlang.org/docs/handbook/declaration-merging.html
+ *  - https://github.com/prisma/graphqlgen/issues/15
+ */
+const renderGraphqlToolsModuleAugmentationIResolvers = (): string => {
+  return `
+    declare module "graphql-tools" {
+      interface IResolvers extends Resolvers {}
+    }
   `
 }
 

packages/graphqlgen/src/index.ts

@@ -105,6 +105,10 @@ export function generateCode(codeGenArgs: CodeGenArgs): CodeGenResult {
       typeof codeGenArgs.config['default-resolvers'] === 'boolean'
         ? codeGenArgs.config['default-resolvers']
         : true,
+    iResolversAugmentationEnabled:
+      typeof codeGenArgs.config['iresolvers-augmentation'] === 'boolean'
+        ? codeGenArgs.config['iresolvers-augmentation']
+        : true,
   }
 
   const generatedTypes = generateTypes(generateArgs, codeGenArgs)

packages/graphqlgen/src/types.ts

@@ -15,6 +15,7 @@ export interface GenerateArgs {
   context?: ContextDefinition
   modelMap: ModelMap
   defaultResolversEnabled: boolean
+  iResolversAugmentationEnabled: boolean
 }
 
 export interface ModelMap {