Error Formatting

import { initTRPC } from '@trpc/server';

export const t = initTRPC.context<Context>().create({
  errorFormatter(opts) {
    const { shape, error } = opts;
    return {
      ...shape,
      data: {
        ...shape.data,
        zodError:
          error.code === 'BAD_REQUEST' && error.cause instanceof ZodError
            ? error.cause.flatten()
            : null,
      },
    };
  },
});

export function MyComponent() {
  const mutation = trpc.addPost.useMutation();

  useEffect(() => {
    mutation.mutate({ title: 'example' });
  }, []);

  if (mutation.error?.data?.zodError) {
    // zodError will be inferred
    return (
      <pre>Error: {JSON.stringify(mutation.error.data.zodError, null, 2)}</pre>
    );
  }
  return <>[...]</>;
}

{
  error: TRPCError;
  type: ProcedureType | 'unknown';
  path: string | undefined;
  input: unknown;
  ctx: undefined | TContext;
  shape: DefaultErrorShape; // the default error shape
}

interface DefaultErrorData {
  code: TRPC_ERROR_CODE_KEY;
  httpStatus: number;
  path?: string;
  stack?: string;
}

interface DefaultErrorShape
  extends TRPCErrorShape<TRPC_ERROR_CODE_NUMBER, DefaultErrorData> {
  message: string;
  code: TRPC_ERROR_CODE_NUMBER;
}