fix: force both implementations

Author: juliusmarminge

packages/start-client-core/src/createIsomorphicFn.ts

@@ -36,14 +36,17 @@ export interface ClientOnlyFnWithType<TArgs extends Array<any>, TReturnType>
   ) => IsomorphicFn<TArgs, TReturnType, TReturnType>
 }
 
-export interface IsomorphicFnWithType<TArgs extends Array<any>, TReturnType>
-  extends IsomorphicFn<TArgs, TReturnType> {
-  server: (
-    serverImpl: (...args: TArgs) => TReturnType,
-  ) => ServerOnlyFnWithType<TArgs, TReturnType>
-  client: (
-    clientImpl: (...args: TArgs) => TReturnType,
-  ) => ClientOnlyFnWithType<TArgs, TReturnType>
+export interface IsomorphicFnWithType<TArgs extends Array<any>, TReturnType> {
+  server: (serverImpl: (...args: TArgs) => TReturnType) => {
+    client: (
+      clientImpl: (...args: TArgs) => TReturnType,
+    ) => IsomorphicFn<TArgs, TReturnType, TReturnType>
+  }
+  client: (clientImpl: (...args: TArgs) => TReturnType) => {
+    server: (
+      serverImpl: (...args: TArgs) => TReturnType,
+    ) => IsomorphicFn<TArgs, TReturnType, TReturnType>
+  }
 }
 
 export interface IsomorphicFnBase extends IsomorphicFn {
@@ -63,10 +66,12 @@ export interface IsomorphicFnBase extends IsomorphicFn {
 // if we use `createIsomorphicFn` in this library itself, vite tries to execute it before the transformer runs
 // therefore we must return a dummy function that allows calling `server` and `client` method chains.
 export function createIsomorphicFn(): IsomorphicFnBase {
-  return {
-    $withType: () => {},
+  const baseFns = {
     server: () => ({ client: () => () => {} }),
     client: () => ({ server: () => () => {} }),
+  }
+  return {
+    $withType: () => baseFns,
+    ...baseFns,
   } as any
 }
-

packages/start-client-core/src/tests/createIsomorphicFn.test-d.ts

@@ -100,6 +100,17 @@ test('createIsomorphicFn with type', () => {
   expectTypeOf(fn2).toBeCallableWith('foo', 1)
   expectTypeOf(fn2).returns.toEqualTypeOf<boolean>()
 
+  const noServerImpl = createIsomorphicFn()
+    .$withType<(a: string) => string>()
+    .client((a) => 'data')
+    expectTypeOf(noServerImpl).not.toBeFunction()
+
+    // Missing server implementation
+  const noClientImpl = createIsomorphicFn()
+  .$withType<(a: string) => string>()
+  .server((a) => 'data')
+  expectTypeOf(noClientImpl).not.toBeFunction()
+
   const _invalidFnReturn = createIsomorphicFn()
     .$withType<(a: string) => string>()
     .server(() => '1')