Type 'Effect<{ message: string; }, CreatePasswordResetTokenError | ConfigError | CreatePasswordResetUrlError, never>' is not assignable to type 'Effect<{ readonly message: string; } | HttpServerResponse, CreatePasswordResetTokenError | CreatePasswordResetUrlError | HttpApiDecodeError | ConfigError, never>'.

[sundaray]

I am working on a Next.js project and I am trying to write the API endpoints using effect/platform.

I have run into a TS error that I am not able to solve even after consulting the LLMs.

Here is my app/effect/[[...path]]/route.ts file:

import { HttpApiBuilder, HttpServer } from "@effect/platform";
import { Layer } from "effect";
import { mainLayer } from "@/app/effect/server";

const WebHandlerLayer = Layer.mergeAll(mainLayer, HttpServer.layerContext)

const { handler } = HttpApiBuilder.toWebHandler(WebHandlerLayer);

export {
  handler as GET,
  handler as POST,
  handler as PUT,
  handler as DELETE,
  handler as PATCH,
  handler as HEAD,
  handler as OPTIONS,
};

Here is the app/effect/server.ts file:

import { HttpApiBuilder, HttpMiddleware } from "@effect/platform";
import { Layer } from "effect";

import { PodwiseApi } from "@/lib/api";
import { forgotPasswordHandler } from "@/lib/api/auth/handlers/forgot-password-handler";

const AuthGroupLive = HttpApiBuilder.group(PodwiseApi, "auth", (handlers) =>
  handlers
    .handle("forgotPassword", (req) => forgotPasswordHandler(req))

);

export const PodwiseApiLive = HttpApiBuilder.api(PodwiseApi).pipe(
  Layer.provide(AuthGroupLive),
);

const MiddlewareLive = HttpApiBuilder.middleware(HttpMiddleware.logger);

export const mainLayer = Layer.mergeAll(PodwiseApiLive, MiddlewareLive);

Here is the endpoint definition:

lib/api/auth/endpoints/index.ts:

import { HttpApiEndpoint, HttpApiGroup } from "@effect/platform";
import { Schema } from "effect";

import {
  ConfigError,
  CreatePasswordResetTokenError,
  CreatePasswordResetUrlError,
} from "@/lib/api/auth/errors";

// ============================================================================
// forgotPassword
// ============================================================================

const ForgotPasswordPayload = Schema.Struct({
  email: Schema.String,
});

const ForgotPasswordResponse = Schema.Struct({
  message: Schema.String,
});

export const ForgotPasswordError = Schema.Union(
  CreatePasswordResetTokenError,
  CreatePasswordResetUrlError,
  ConfigError,
);

const forgotPasswordEndpoint = HttpApiEndpoint.post(
  "forgotPassword",
  "/auth/forgot-password",
)
  .setPayload(ForgotPasswordPayload)
  .addSuccess(ForgotPasswordResponse)
  .addError(ForgotPasswordError);

/**************************************
 * authGroup
 *************************************/

export const authGroup = HttpApiGroup.make("auth")
  .add(forgotPasswordEndpoint)

Here is the group file:

lib/api/auth/group/index.ts:

import { HttpApiGroup } from "@effect/platform";

import { forgotPasswordEndpoint } from "@/lib/api/auth/endpoints";

export const authGroup = HttpApiGroup.make("auth").add(forgotPasswordEndpoint);

Here is the forgotPasswordHandler file:

import { HttpServerResponse } from "@effect/platform";
import { Effect } from "effect";

import { ConfigError } from "@/lib/api/auth/errors";

import "@/lib/api";

import { createPasswordResetSession } from "@/lib/create-password-reset-session";
import { createPasswordResetToken } from "@/lib/create-password-reset-token";
import { createPasswordResetUrl } from "@/lib/create-password-reset-url";
import { sendPasswordResetEmail } from "@/lib/send-password-reset-email";

export function forgotPasswordHandler(req: { payload: { email: string } }) {
  console.log("Request in forgtoPasswordHandler: ", req);
  const { email } = req.payload;

  const program = Effect.gen(function* () {
    const token = yield* createPasswordResetToken();
    const url = yield* createPasswordResetUrl(token);
  });

  const handledProgram = program.pipe(
    Effect.matchEffect({
      onFailure: (error) => Effect.fail(error),
      onSuccess: () => Effect.succeed({ message: "success" }),
    }),
  );

  return handledProgram;
}

Here is the createPasswordResetToken file;

import "server-only";

import { Effect } from "effect";
import { base64url } from "jose";
import { getRandomValues } from "uncrypto";

import { CreatePasswordResetTokenError } from "@/lib/api/auth/errors";

// ============================================================================
// Create password reset token
// ============================================================================

export function createPasswordResetToken() {
  return Effect.try({
    try: () => {
      const randomValues = new Uint8Array(32);
      getRandomValues(randomValues);
      return base64url.encode(randomValues);
    },
    catch: (error) =>
      new CreatePasswordResetTokenError({
        operation: "createPasswordResetToken",
        cause: error,
      }),
  }).pipe(Effect.tapError((error) => Effect.logError(error)));
}

Here is the passwordresetTokenUrl function:

import { Config, Effect } from "effect";

import { CreatePasswordResetUrlError } from "@/lib/api/auth/errors";

// ============================================================================
// Create password reset URL
// ============================================================================

export function createPasswordResetUrl(token: string) {
  return Effect.gen(function* () {
    const baseUrl = yield* Config.string("NEXT_PUBLIC_APP_URL").pipe(
      Config.withDefault("http://localhost:3000"),
    );

    const url = yield* Effect.try({
      try: () => {
        const url = new URL("/api/auth/verify-password-reset", baseUrl);
        url.searchParams.set("token", token);
        return url.toString();
      },
      catch: (error) =>
        new CreatePasswordResetUrlError({
          operation: "createPasswordResetURL",
          cause: error,
        }),
    });

    return url;
  }).pipe(Effect.tapError((error) => Effect.logError(error)));
}

The Errors

Currently, I am getting two TS errors.

Error-1

I am seeing a red squiggly error under forgotPasswordHandler on this line:

    .handle("forgotPassword", (req) => forgotPasswordHandler(req))

The error says:

Type 'Effect<{ message: string; }, CreatePasswordResetTokenError | CreatePasswordResetUrlError | ConfigError, never>' is not assignable to type 'Effect<{ readonly message: string; } | HttpServerResponse, CreatePasswordResetTokenError | CreatePasswordResetUrlError | ConfigError | HttpApiDecodeError, never>'.
  Type 'CreatePasswordResetTokenError | CreatePasswordResetUrlError | ConfigError' is not assignable to type 'CreatePasswordResetTokenError | CreatePasswordResetUrlError | ConfigError | HttpApiDecodeError'.
    Type 'And' is not assignable to type 'CreatePasswordResetTokenError | CreatePasswordResetUrlError | ConfigError | HttpApiDecodeError'.
      Type 'And' is not assignable to type 'HttpApiDecodeError'.
        Type 'And' is not assignable to type '{ readonly _tag: "HttpApiDecodeError"; }'.
          Types of property '_tag' are incompatible.
            Type '"ConfigError"' is not assignable to type '"HttpApiDecodeError"'.ts(2322)
HttpApiEndpoint.d.ts(237, 48): The expected type comes from the return type of this signature.
(alias) forgotPasswordHandler(req: {
    payload: {
        email: string;
    };
}): Effect<{
    message: string;
}, CreatePasswordResetTokenError | CreatePasswordResetUrlError | ConfigError, never>
import forgotPasswordHandler
No quick fixes available

I don't know what do I do to fix this error?

Error-2

I am getting another red squiggly error under WebHandlerLayer on the line below:

const { handler } = HttpApiBuilder.toWebHandler(WebHandlerLayer);

The error says:

Argument of type 'Layer<HttpPlatform | Generator | FileSystem | Path | Api, never, unknown>' is not assignable to parameter of type 'Layer<DefaultServices | Api, never, never>'.
  Type 'unknown' is not assignable to type 'never'.ts(2345)
const WebHandlerLayer: Layer.Layer<HttpPlatform | Generator | FileSystem | Path | Api, never, unknown>
No quick fixes available

Please help me fix these errors.

Note

please note that all errors go away if I remove the following line:

    const url = yield* createPasswordResetUrl(token);

from the forgotPasswordHandler file.

[harshagarwalnyu]

The type error is because your handler returns Effect<{message}, errors> but the API endpoint type expects Effect<{message} | HttpServerResponse, errors, never>. The mismatch is that HttpApiBuilder handler signatures require you to return the response schema type, not a raw Effect.

Fix: use HttpApiBuilder.handler with the correct effect return type:

// The handler must return the type defined in your API schema
// If your endpoint is defined as returning { message: string }:
const handler = HttpApiBuilder.handler(MyApi, "sendResetEmail", (req) =>
  Effect.gen(function* () {
    const token = yield* createPasswordResetToken(req.payload.email);
    const url = yield* createPasswordResetUrl(token);
    return { message: "Reset email sent" };  // matches schema, not HttpServerResponse
  })
);

Common cause — returning HttpServerResponse directly when schema expects JSON:

If your endpoint schema returns Schema.Struct({ message: Schema.String }), the handler must return { message: string } — NOT HttpServerResponse.json({ message: ... }). The HttpApiBuilder wraps it automatically.

Conversely, if you need to return a custom response (e.g., redirect, set cookies), declare the endpoint as returning HttpServerResponse in your API schema:

const MyApi = HttpApi.make("my-api").add(
  HttpApiGroup.make("auth").add(
    HttpApiEndpoint.post("resetPassword", "/reset")
      .addSuccess(Schema.String)  // or HttpServerResponse
      .addError(CreatePasswordResetTokenError)
  )
);

The union {message} | HttpServerResponse in the error message suggests your API group has multiple endpoints with different return types, and TypeScript is merging them. Check that you're calling handler on the specific endpoint, not the group.

Could you share the API schema definition? That would pinpoint exactly which return type is expected.