fix: MaybePromiseDeep case of null with .then (graphql-nexus#475)

closes graphql-nexus#470
closes graphql-nexus#474 (thanks @Sytten)

package.json

@@ -45,9 +45,10 @@
     "release:pr": "dripip pr",
     "release:preview": "dripip preview",
     "release:stable": "dripip stable",
-    "test": "jest",
-    "test:ci": "jest --coverage --maxWorkers 2",
+    "test": "yarn test:types && jest",
+    "test:ci": "yarn test:types && jest --coverage --maxWorkers 2",
     "test:debug": "node --inspect-brk $(yarn bin)/jest -i --watch",
+    "test:types": "tsc -p tsconfig.spec.types.json",
     "ts-ast-reader": "cd examples/ts-ast-reader && yarn start",
     "unlink-examples": "cd website && yarn && yarn gulp unlink-examples",
     "upgrade-deps": "cd website && yarn && yarn gulp upgrade-deps",
@@ -95,6 +96,7 @@
     "sort-package-json": "^1.22.1",
     "ts-jest": "^26.0.0",
     "ts-node": "^7.0.1",
+    "tsd": "^0.13.1",
     "tslint": "^5.11.0",
     "tslint-config-prettier": "^1.15.0",
     "typescript": "^3.9.6"

src/typegenTypeHelpers.spec.types.ts

@@ -0,0 +1,19 @@
+import { expectAssignable } from 'tsd'
+import { MaybePromiseDeep } from './typegenTypeHelpers'
+
+/**
+ * MaybePromiseDeep
+ */
+
+// A case found by Sytten https://github.com/graphql-nexus/schema/issues/470
+// The presence of .then was leading to type errors
+type Ones = 1[]
+type GraphQLResponse = Ones | null
+const getOnes = () => Promise.resolve([] as Ones)
+expectAssignable<MaybePromiseDeep<GraphQLResponse>>(getOnes().then((ones) => ones))
+// object with array
+expectAssignable<MaybePromiseDeep<{ a: 1[] }>>({ a: [1] })
+expectAssignable<MaybePromiseDeep<{ a: 1[] }>>(Promise.resolve({ a: [1] }))
+// array
+expectAssignable<MaybePromiseDeep<1[]>>([1])
+expectAssignable<MaybePromiseDeep<1[]>>(Promise.resolve([1]))

src/typegenTypeHelpers.ts

@@ -34,22 +34,24 @@ export type MaybePromise<T> = PromiseLike<T> | T
  * to help signify that.
  */
 export type MaybePromiseDeep<T> = Date extends T
+  ? MaybePromise<T>
+  : null extends T
   ? MaybePromise<T>
   : boolean extends T
   ? MaybePromise<T>
   : number extends T
   ? MaybePromise<T>
   : string extends T
   ? MaybePromise<T>
+  : T extends Array<infer U>
+  ? MaybePromise<Array<MaybePromiseDeep<U>>>
+  : T extends ReadonlyArray<infer Y>
+  ? MaybePromise<ReadonlyArray<MaybePromiseDeep<Y>>>
   : T extends object
   ? MaybePromise<
       | T
       | {
-          [P in keyof T]: T[P] extends Array<infer U>
-            ? MaybePromise<Array<MaybePromiseDeep<U>>>
-            : T[P] extends ReadonlyArray<infer Y>
-            ? MaybePromise<ReadonlyArray<MaybePromiseDeep<Y>>>
-            : MaybePromiseDeep<T[P]>
+          [P in keyof T]: MaybePromiseDeep<T[P]>
         }
     >
   : MaybePromise<T>

tsconfig.build.json

@@ -0,0 +1,20 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "module": "CommonJS",
+    "outDir": "dist",
+    "declaration": true,
+    // "declarationMap": true,
+    "sourceMap": true
+  },
+  "exclude": [
+    "./**/*.spec.types.ts",
+    "./examples",
+    "./scripts",
+    "./dist",
+    "./tests",
+    "./website",
+    "./gulpfile.ts",
+    "./package.json"
+  ]
+}

tsconfig.cjs.json

@@ -1,5 +1,5 @@
 {
-  "extends": "./tsconfig.json",
+  "extends": "./tsconfig.build.json",
   "compilerOptions": {
     "module": "CommonJS",
     "outDir": "dist"

tsconfig.esm.json

@@ -1,5 +1,5 @@
 {
-  "extends": "./tsconfig.json",
+  "extends": "./tsconfig.build.json",
   "compilerOptions": {
     "moduleResolution": "node",
     "module": "ES2015",

tsconfig.json

@@ -8,19 +8,8 @@
     "rootDir": "src",
     "strict": true,
     "noUnusedLocals": true,
-    "declaration": true,
-    // "declarationMap": true,
     "importHelpers": true,
-    "resolveJsonModule": true,
-    "sourceMap": true
+    "resolveJsonModule": true
   },
-  "exclude": [
-    "./examples",
-    "./scripts",
-    "./dist",
-    "./tests",
-    "./website",
-    "./gulpfile.ts",
-    "./package.json"
-  ]
+  "exclude": ["./examples", "./scripts", "./dist", "./tests", "./website", "./gulpfile.ts", "./package.json"]
 }

tsconfig.spec.types.json

@@ -0,0 +1,7 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "noEmit": true
+  },
+  "include": ["./**/*.spec.types.ts"]
+}