Hono•4w ago

adding generic error output type to App type

Hey all, I am using the typed RPC feature of hono and got it working, except for the errors I have an .onError that consstruct a json from error thrown and I would like that error type to be unioned with each of the output type of all path Is there a way to do this ? Like is there some type generic magic I could add to my exported App type to add an extra type for all outputs Something like export type App = AddErrorType<typeof app, {success: false, errors: {message: string, code: number}[]}> ?

1 Reply

ronan(wighawag)OP•4w ago

I got something working with

type WithErrorResponse<T, ErrorType> = T extends {output: infer O}
  ? O extends string | number | boolean | null | undefined
    ? Omit<T, 'output'> & {output: O | ErrorType}
    : Omit<T, 'output'> & {output: O | ErrorType}
  : T;

export type AddToAllOutputs<T, ErrorType> =
  T extends HonoBase<infer E, infer S>
    ? HonoBase<
        E,
        {
          [K in keyof S]: S[K] extends {[method: string]: any}
            ? {
                [M in keyof S[K]]: M extends `$${string}` ? WithErrorResponse<S[K][M], ErrorType> : S[K][M];
              }
            : S[K] extends object
              ? AddToAllOutputs<S[K], ErrorType>
              : S[K];
        }
      >
    : T;

type WithErrorResponse<T, ErrorType> = T extends {output: infer O}
  ? O extends string | number | boolean | null | undefined
    ? Omit<T, 'output'> & {output: O | ErrorType}
    : Omit<T, 'output'> & {output: O | ErrorType}
  : T;

export type AddToAllOutputs<T, ErrorType> =
  T extends HonoBase<infer E, infer S>
    ? HonoBase<
        E,
        {
          [K in keyof S]: S[K] extends {[method: string]: any}
            ? {
                [M in keyof S[K]]: M extends `$${string}` ? WithErrorResponse<S[K][M], ErrorType> : S[K][M];
              }
            : S[K] extends object
              ? AddToAllOutputs<S[K], ErrorType>
              : S[K];
        }
      >
    : T;

you can then do

type ErrorType = {
    success: false;
    errors: {message: string; code: number}[];
};
export type App = AddToAllOutputs<MyApp, ErrorType>;

type ErrorType = {
    success: false;
    errors: {message: string; code: number}[];
};
export type App = AddToAllOutputs<MyApp, ErrorType>;

but maybe hono should handle it automatically somehow ? Got it simplified to

type WithErrorResponse<T extends Endpoint, ErrorType> = T extends {output: infer O}
    ? O extends string | number | boolean | null | undefined
        ? Omit<T, 'output'> & {output: O | ErrorType}
        : Omit<T, 'output'> & {output: O | ErrorType}
    : T;
type AddToAllSchemaOutputs<S extends Schema, ErrorType> = {
    [K in keyof S]: {
        [M in keyof S[K]]: S[K][M] extends Endpoint ? WithErrorResponse<S[K][M], ErrorType> : never;
    };
};
export type AddToAllOutputs<T extends HonoBase<any, any>, ErrorType> =
    T extends HonoBase<infer E, infer S> ? HonoBase<E, AddToAllSchemaOutputs<S, ErrorType>> : T;

type WithErrorResponse<T extends Endpoint, ErrorType> = T extends {output: infer O}
    ? O extends string | number | boolean | null | undefined
        ? Omit<T, 'output'> & {output: O | ErrorType}
        : Omit<T, 'output'> & {output: O | ErrorType}
    : T;
type AddToAllSchemaOutputs<S extends Schema, ErrorType> = {
    [K in keyof S]: {
        [M in keyof S[K]]: S[K][M] extends Endpoint ? WithErrorResponse<S[K][M], ErrorType> : never;
    };
};
export type AddToAllOutputs<T extends HonoBase<any, any>, ErrorType> =
    T extends HonoBase<infer E, infer S> ? HonoBase<E, AddToAllSchemaOutputs<S, ErrorType>> : T;

wanted to have the error happen only when response is not ok, but did not managed

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adding generic error output type to App type