fix(napi-derive): invalid TypeScript return type

.github/workflows/test.yaml

@@ -68,5 +68,6 @@ jobs:
         run: |
           yarn build:test
           yarn test --verbose
+          yarn tsc -p examples/napi/tsconfig.json --noEmit
         env:
           RUST_BACKTRACE: 1

crates/backend/src/typegen.rs

@@ -181,6 +181,7 @@ static KNOWN_TYPES: Lazy<HashMap<&'static str, &'static str>> = Lazy::new(|| {
     ("Either5", "{} | {} | {} | {} | {}"),
     ("unknown", "unknown"),
     ("Null", "null"),
+    ("JsNull", "null"),
     ("null", "null"),
     ("Symbol", "symbol"),
     ("JsSymbol", "symbol"),
@@ -262,7 +263,7 @@ pub fn ty_to_ts_type(ty: &Type, is_return_ty: bool, is_struct_field: bool) -> (S
               if is_struct_field {
                 arg.to_string()
               } else if is_return_ty {
-                format!("{}?", arg)
+                format!("{} | null", arg)
               } else {
                 format!("{} | undefined | null", arg)
               },

examples/napi/__test__/typegen.spec.ts.md

@@ -106,7 +106,7 @@ Generated by [AVA](https://avajs.dev).
     export function xxh64Alias(input: Buffer): bigint␊
     export function getMapping(): Record<string, number>␊
     export function sumMapping(nums: Record<string, number>): number␊
-    export function mapOption(val?: number | undefined | null): number?␊
+    export function mapOption(val?: number | undefined | null): number | null␊
     export function returnNull(): null␊
     export function returnUndefined(): void␊
     export function add(a: number, b: number): number␊
@@ -115,7 +115,7 @@ Generated by [AVA](https://avajs.dev).
     export function createObj(): object␊
     export function getGlobal(): typeof global␊
     export function getUndefined(): void␊
-    export function getNull(): JsNull␊
+    export function getNull(): null␊
     export interface AllOptionalObject {␊
       name?: string␊
       age?: number␊
@@ -243,7 +243,7 @@ Generated by [AVA](https://avajs.dev).
     export type JsAssets = Assets␊
     export class Assets {␊
       constructor()␊
-      get(id: number): JsAsset?␊
+      get(id: number): JsAsset | null␊
     }␊
     export type JsAsset = Asset␊
     export class Asset {␊

examples/napi/index.d.ts

@@ -96,7 +96,7 @@ export function tsRename(a: { foo: number }): string[]
 export function xxh64Alias(input: Buffer): bigint
 export function getMapping(): Record<string, number>
 export function sumMapping(nums: Record<string, number>): number
-export function mapOption(val?: number | undefined | null): number?
+export function mapOption(val?: number | undefined | null): number | null
 export function returnNull(): null
 export function returnUndefined(): void
 export function add(a: number, b: number): number
@@ -105,7 +105,7 @@ export function listObjKeys(obj: object): Array<string>
 export function createObj(): object
 export function getGlobal(): typeof global
 export function getUndefined(): void
-export function getNull(): JsNull
+export function getNull(): null
 export interface AllOptionalObject {
   name?: string
   age?: number
@@ -233,7 +233,7 @@ export class NinjaTurtle {
 export type JsAssets = Assets
 export class Assets {
   constructor()
-  get(id: number): JsAsset?
+  get(id: number): JsAsset | null
 }
 export type JsAsset = Asset
 export class Asset {

examples/napi/tsconfig.json

@@ -4,7 +4,8 @@
   "compilerOptions": {
     "outDir": "./dist",
     "rootDir": "__test__",
-    "target": "ES2018"
+    "target": "ES2018",
+    "skipLibCheck": false
   },
-  "exclude": ["dist", "index.d.ts"]
+  "exclude": ["dist"]
 }