feat(gg): simplify and make safer __resolveType (#411)

* feat(gg): simplify and make safer resolver type resovler

Safer because:

- strings constants are used to specifiy which graphql
objects names may be returned.
- null cannot be returned
- undefined cannot be returned

Simpler because:

- no nesting of type-generics
- only permits returning names of graphql objects (not objects)

closes #409

packages/graphqlgen/src/generators/common.ts

@@ -226,7 +226,7 @@ const array = (
   return config.innerUnion ? `${innerType}[]` : `Array<${innerType}>`
 }
 
-const union = (types: string[]): string => {
+export const union = (types: string[]): string => {
   return types.join(' | ')
 }
 

packages/graphqlgen/src/generators/flow-generator.ts

@@ -24,6 +24,7 @@ import {
   createInterfacesMap,
   createUnionsMap,
 } from './common'
+import { renderTypeResolveTypeResolver } from './ts-generator'
 
 export function format(code: string, options: prettier.Options = {}) {
   try {
@@ -76,11 +77,9 @@ export function generate(args: GenerateArgs): string {
 
   const interfacesMap = createInterfacesMap(args.interfaces)
   const unionsMap = createUnionsMap(args.unions)
-  const hasPolymorphicObjects =
-    Object.keys(interfacesMap).length > 0 || Object.keys(unionsMap).length > 0
 
   return `\
-  ${renderHeader(args, { hasPolymorphicObjects })}
+  ${renderHeader(args)}
 
   ${renderEnums(args)}
 
@@ -97,14 +96,7 @@ export function generate(args: GenerateArgs): string {
   `
 }
 
-type HeaderOptions = {
-  hasPolymorphicObjects?: boolean
-}
-
-function renderHeader(
-  args: GenerateArgs,
-  { hasPolymorphicObjects = false }: HeaderOptions = {},
-): string {
+function renderHeader(args: GenerateArgs): string {
   const modelsToImport = Object.keys(args.modelMap).map(k => args.modelMap[k])
   const modelsByImportPaths = groupModelsNameByImportPath(modelsToImport)
 
@@ -117,9 +109,7 @@ function renderHeader(
     )
     .join(os.EOL)
 
-  const graphQLImports = hasPolymorphicObjects
-    ? ['GraphQLResolveInfo', 'GraphQLTypeResolver']
-    : ['GraphQLResolveInfo']
+  const graphQLImports = ['GraphQLResolveInfo']
 
   return `/* @flow */
 // Code generated by github.com/prisma/graphqlgen, DO NOT EDIT.
@@ -223,9 +213,7 @@ function renderUnionNamespace(
 ): string {
   return `\
     export interface ${graphQLTypeObject.name}_Resolvers {
-      __resolveType?: GraphQLTypeResolver<${graphQLTypeObject.types
-        .map(interfaceType => getModelName(interfaceType, args.modelMap))
-        .join(' | ')}, ${getContextName(args.context)}>;
+      __resolveType?: ${renderTypeResolveTypeResolver(graphQLTypeObject, args)}
     }
   `
 }

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

@@ -23,6 +23,7 @@ import {
   UnionsMap,
   createInterfacesMap,
   createUnionsMap,
+  union,
 } from './common'
 import { TypeAliasDefinition } from '../introspection/types'
 import { upperFirst } from '../utils'
@@ -108,7 +109,7 @@ function renderHeader(
   { hasPolymorphicObjects = false }: HeaderOptions = {},
 ): string {
   const imports = hasPolymorphicObjects
-    ? ['GraphQLResolveInfo', 'GraphQLTypeResolver', 'GraphQLIsTypeOfFn']
+    ? ['GraphQLResolveInfo', 'GraphQLIsTypeOfFn']
     : ['GraphQLResolveInfo']
 
   return `
@@ -237,24 +238,50 @@ function renderInterfaceNamespace(
       )}
 
       export interface Type {
-        __resolveType: GraphQLTypeResolver<${graphQLTypeObject.implementors
-          .map(interfaceType => getModelName(interfaceType, args.modelMap))
-          .join(' | ')}, ${getContextName(args.context)}>;
+        __resolveType: ${renderTypeResolveTypeResolver(graphQLTypeObject, args)}
       }
     }
   `
 }
 
+export const renderTypeResolveTypeResolver = (
+  abstractType: GraphQLInterfaceObject | GraphQLUnionObject,
+  args: GenerateArgs,
+): string => {
+  const modelNames: string[] = []
+  const gqlObjectNameTypes: string[] = []
+  const gqlObjects =
+    abstractType.kind === 'interface'
+      ? abstractType.implementors
+      : abstractType.types
+
+  for (const gqlObj of gqlObjects) {
+    modelNames.push(getModelName(gqlObj, args.modelMap))
+    gqlObjectNameTypes.push(renderStringConstant(gqlObj.name))
+  }
+
+  return `
+  (
+    value: ${union(modelNames)},
+    context: ${getContextName(args.context)},
+    info: GraphQLResolveInfo
+  ) => ${resolverReturnType(union(gqlObjectNameTypes))}
+  `
+}
+
+const renderStringConstant = (x: unknown) => `"${x}"`
+
 function renderUnionNamespace(
   graphQLTypeObject: GraphQLUnionObject,
   args: GenerateArgs,
 ): string {
   return `\
     export namespace ${graphQLTypeObject.name}Resolvers {
       export interface Type {
-        __resolveType?: GraphQLTypeResolver<${graphQLTypeObject.types
-          .map(interfaceType => getModelName(interfaceType, args.modelMap))
-          .join(' | ')}, ${getContextName(args.context)}>;
+        __resolveType?: ${renderTypeResolveTypeResolver(
+          graphQLTypeObject,
+          args,
+        )}
       }
     }
   `
@@ -430,6 +457,7 @@ function renderResolverFunctionInterfaces(
     .join(os.EOL)
 }
 
+// MARK
 function renderResolverFunctionInterface(
   field: GraphQLTypeField,
   type: GraphQLTypeObject,
@@ -468,10 +496,15 @@ function renderResolverFunctionInterface(
   }
 
   return `
-  export type ${resolverName} = ${resolverDefinition} => ${returnType} | Promise<${returnType}>
+  export type ${resolverName} = ${resolverDefinition} => ${resolverReturnType(
+    returnType,
+  )}
   `
 }
 
+const resolverReturnType = (returnType: string): string =>
+  union([returnType, `Promise<${returnType}>`])
+
 function renderResolverTypeInterface(
   type: GraphQLTypeObject | GraphQLInterfaceObject,
   modelMap: ModelMap,

packages/graphqlgen/src/source-helper.ts

@@ -80,12 +80,14 @@ export type GraphQLEnumObject = {
 
 export type GraphQLUnionObject = {
   name: string
+  kind: 'union'
   type: GraphQLTypeDefinition
   types: GraphQLTypeDefinition[]
 }
 
 export type GraphQLInterfaceObject = {
   name: string
+  kind: 'interface'
   type: GraphQLTypeDefinition
   fields: GraphQLTypeField[]
   implementors: GraphQLTypeDefinition[]
@@ -345,6 +347,7 @@ function extractGraphQLUnions(schema: GraphQLSchema) {
       })
       types.push({
         name: node.name,
+        kind: 'union',
         type: {
           name: node.name,
           isObject: false,
@@ -380,6 +383,7 @@ function extractGraphQLInterfaces(
         if (implementorTypes.length) {
           interfaces.push({
             name: node.name,
+            kind: 'interface',
             type: {
               name: node.name,
               isObject: false,

packages/graphqlgen/tests/flow/__snapshots__/basic.test.ts.snap

@@ -613,7 +613,7 @@ exports[`basic union 1`] = `
 "/* @flow */
 // Code generated by github.com/prisma/graphqlgen, DO NOT EDIT.
 
-import type { GraphQLResolveInfo, GraphQLTypeResolver } from \\"graphql\\";
+import type { GraphQLResolveInfo } from \\"graphql\\";
 import type { Student, Professor, User } from \\"../../fixtures/union/flow-types\\";
 type Context = any;
 
@@ -719,7 +719,11 @@ export interface User_Resolvers {
 }
 
 export interface UserType_Resolvers {
-  __resolveType?: GraphQLTypeResolver<Student | Professor, Context>;
+  __resolveType?: (
+    value: Student | Professor,
+    context: Context,
+    info: GraphQLResolveInfo
+  ) => \\"Student\\" | \\"Professor\\" | Promise<\\"Student\\" | \\"Professor\\">;
 }
 
 export interface Resolvers {

packages/graphqlgen/tests/typescript/__snapshots__/basic.test.ts.snap

@@ -339,11 +339,7 @@ export const resolvers: Resolvers = {
 exports[`basic interface 1`] = `
 "// Code generated by github.com/prisma/graphqlgen, DO NOT EDIT.
 
-import {
-  GraphQLResolveInfo,
-  GraphQLTypeResolver,
-  GraphQLIsTypeOfFn
-} from \\"graphql\\";
+import { GraphQLResolveInfo, GraphQLIsTypeOfFn } from \\"graphql\\";
 import { Dimensions, Image, Video } from \\"../../../fixtures/interface/types\\";
 type Context = any;
 
@@ -518,7 +514,11 @@ export namespace VideoResolvers {
 
 export namespace MediaResolvers {
   export interface Type {
-    __resolveType: GraphQLTypeResolver<Image | Video, Context>;
+    __resolveType: (
+      value: Image | Video,
+      context: Context,
+      info: GraphQLResolveInfo
+    ) => \\"Image\\" | \\"Video\\" | Promise<\\"Image\\" | \\"Video\\">;
   }
 }
 
@@ -1106,11 +1106,7 @@ export const resolvers: Resolvers = {
 exports[`basic union 1`] = `
 "// Code generated by github.com/prisma/graphqlgen, DO NOT EDIT.
 
-import {
-  GraphQLResolveInfo,
-  GraphQLTypeResolver,
-  GraphQLIsTypeOfFn
-} from \\"graphql\\";
+import { GraphQLResolveInfo, GraphQLIsTypeOfFn } from \\"graphql\\";
 import { Student, Professor, User } from \\"../../fixtures/union/types\\";
 type Context = any;
 
@@ -1225,7 +1221,11 @@ export namespace UserResolvers {
 
 export namespace UserTypeResolvers {
   export interface Type {
-    __resolveType?: GraphQLTypeResolver<Student | Professor, Context>;
+    __resolveType?: (
+      value: Student | Professor,
+      context: Context,
+      info: GraphQLResolveInfo
+    ) => \\"Student\\" | \\"Professor\\" | Promise<\\"Student\\" | \\"Professor\\">;
   }
 }