Improve manual TS typings for go utils

Author: Siegrift

src/go/go.ts

@@ -41,7 +41,7 @@ const createGoError = <E extends Error>(err: unknown): GoResultError<E> => {
   return fail(new GoWrappedError(err));
 };
 
-export const goSync = <T, E extends Error>(fn: () => T): GoResult<T, E> => {
+export const goSync = <T, E extends Error = Error>(fn: () => T): GoResult<T, E> => {
   try {
     return success(fn());
   } catch (err) {
@@ -72,8 +72,8 @@ export interface GoAsyncOptions {
   timeoutMs: number;
 }
 
-export const go = async <T, E extends Error>(
-  fn: () => T,
+export const go = async <T, E extends Error = Error>(
+  fn: () => Promise<T>,
   options?: GoAsyncOptions
 ): Promise<GoResult<Awaited<T>, E>> => {
   try {

test/go.test.ts

@@ -100,6 +100,21 @@ describe('basic go usage', () => {
     });
     expect(res).toEqual(fail(err));
   });
+
+  it('allows to specify the type of the returned value', async () => {
+    const goResOnlyData = await go<string | number>(() => {
+      return Promise.resolve(123);
+    });
+    assertGoSuccess(goResOnlyData);
+    expectType<string | number>(goResOnlyData.data);
+
+    class CustomError extends Error {}
+    const goResBoth = await go<string | number, CustomError>(() => {
+      return Promise.resolve(123);
+    });
+    assertGoSuccess(goResBoth);
+    expectType<string | number>(goResBoth.data);
+  });
 });
 
 describe('basic timeout usage', () => {