How can I import ActionData?

I'm evaluating Svelte for a project, and I'm stuck on importing ActionData; here's the error:

Module '"./$types"' has no exported member 'ActionData'.

Here's how I'm trying to import it, in a +page.svelte:

    import type { ActionData } from './$types';    export let form: ActionData;

Here's my form, in that same page:

<form on:submit={loginWithEmail} use:enhance method="POST">        {#if form?.wrongPassword}<p class="error">Wrong password.</p>{/if}        {#if form?.missingPassword}<p class="error">Missing password.</p>{/if}        {#if form?.invalidEmail}<p class="error">Malformed email.</p>{/if}        {#if form?.unknown}<p class="error">Authentication error.</p>{/if}<input bind:value={email} type="text" placeholder="Email" /><input bind:value={password} type="password" placeholder="Password" /><button type="submit">Login</button></form>

I added the use:enhance and method="POST" in the hopes that those might get this generated.

Here are the contents of the generated $types.d.ts for this page:

import type * as Kit from '@sveltejs/kit';type Expand<T> = T extends infer O ? { [K in keyof O]: O[K] } : never;// @ts-ignoretype MatcherParam<M> = M extends (param: string) => param is infer U ? U extends string ? U : string : string;type RouteParams = {};type RouteId = '/login';type MaybeWithVoid<T> = {} extends T ? T | void : T;export type RequiredKeys<T> = { [K in keyof T]-?: {} extends { [P in K]: T[K] } ? never : K; }[keyof T];type OutputDataShape<T> = MaybeWithVoid<Omit<App.PageData, RequiredKeys<T>> & Partial<Pick<App.PageData, keyof T & keyof App.PageData>> & Record<string, any>>type EnsureDefined<T> = T extends null | undefined ? {} : T;type OptionalUnion<U extends Record<string, any>, A extends keyof U = U extends U ? keyof U : never> = U extends unknown ? { [P in Exclude<A, keyof U>]?: never } & U : never;export type Snapshot<T = any> = Kit.Snapshot<T>;type PageParentData = EnsureDefined<import('../$types.js').LayoutData>;export type PageServerData = null;export type PageData = Expand<PageParentData>;

When looking into this error, I read that form is a keyword that should be available without importing the ActionData type, but export let form; yielded a nullform value.

How can I get access to the form variable here? And why isn't this working for me?