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fix: restore correct RemoteFormFields typing for nullable array fields#15723

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fix: restore correct RemoteFormFields typing for nullable array fields#15723
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@elliott-with-the-longest-name-on-github elliott-with-the-longest-name-on-github commented Apr 17, 2026

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Closes #15722

Problem

Accessing .as(...) on a remote form field whose schema input type includes undefined (e.g. Zod's z.something().array().default([]), which produces string[] | undefined for StandardSchemaV1.InferInput) no longer typechecks.

const schema = z.object({
  policyAvailableAccessTypes: z.enum([...]).array().default(['unlimited'])
});
// `.as()` is missing from the type, even though it works at runtime
form.fields.policyAvailableAccessTypes.as('checkbox', 'unlimited');
Cause
Regression from #15687, which switched the array-detection branches of RemoteFormFields<T> from distributive (T extends string[] | File[]) to non-distributive ([T] extends [string[] | File[]]) to stop distribution over object unions.
With the new non-distributive check, [string[] | undefined] does not extend [string[] | File[]] (nor [Array<infer U>]), so nullable array types fall through to the generic object-property branch, which doesn't expose .as(...).
Fix
Wrap T in NonNullable<T> on the array-detection branches, consistent with how the primitive branch right above it already works:
: [NonNullable<T>] extends [string[] | File[]]
    ? RemoteFormField<NonNullable<T>> & { [K in number]: RemoteFormField<NonNullable<T>[number]> }
    : [NonNullable<T>] extends [Array<infer U>]
        ? RemoteFormFieldContainer<NonNullable<T>> & { [K in number]: RemoteFormFields<U> }
        : // object-union branch unchanged — still uses KeysOfUnion / ValueOfUnionKey on raw T
The final object-union branch is unchanged, so #15687's fix for discriminated-union objects is preserved.

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🦋 Changeset detected

Latest commit: 3acf83e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package
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@sveltejs/kit Patch

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Preview: https://svelte-dev-git-preview-kit-15723-svelte.vercel.app/

@Conduitry Conduitry changed the title fix: restor correct RemoteFormFields typing for nullable array fields fix: restore correct RemoteFormFields typing for nullable array fields Apr 17, 2026
@elliott-with-the-longest-name-on-github elliott-with-the-longest-name-on-github merged commit 394470c into main Apr 18, 2026
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@elliott-with-the-longest-name-on-github elliott-with-the-longest-name-on-github deleted the elliott/nullable-array-fields-form branch April 18, 2026 14:04
This was referenced Apr 13, 2026
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elliott-with-the-longest-name-on-github pushed a commit that referenced this pull request Apr 23, 2026
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Version Packages (#15716)
a21582c 
This PR was opened by the [Changesets
release](https://github.com/changesets/action) GitHub action. When
you're ready to do a release, you can merge this and the packages will
be published to npm automatically. If you're not ready to do a release
yet, that's fine, whenever you add more changesets to main, this PR will
be updated.


# Releases
## @sveltejs/kit@2.58.0

### Minor Changes

- breaking: require `limit` in `requested` (as originally intended)
([#15739](#15739))


- feat: `RemoteQueryFunction` gains an optional third generic parameter
`Validated` (defaulting to `Input`) that represents the argument type
after schema validation/transformation
([#15739](#15739))


- breaking: `requested` now yields `{ arg, query }` entries instead of
the validated argument
([#15739](#15739))

### Patch Changes

- fix: allow `query().current`, `.error`, `.loading`, and `.ready` to
work in non-reactive contexts
([#15699](#15699))


- fix: prevent `deep_set` crash on nullish nested values
([#15600](#15600))


- fix: restore correct `RemoteFormFields` typing for nullable array
fields (e.g. when a schema uses `.default([])`), so `.as('checkbox')`
and friends work again
([#15723](#15723))


- fix: don't warn about removed SSI comments in `transformPageChunk`
([#15695](#15695))

Server-side include (SSI) directives like `<!--#include virtual="..."
-->` are HTML comments that are replaced by servers such as nginx.
Previously, removing them in `transformPageChunk` would trigger a false
positive warning about breaking Svelte's hydration. Since SSI comments
always start with `<!--#` and Svelte's hydration comments never do, they
can be safely excluded from the check.

- Change enhance function return type from void to MaybePromise<void>.
([#15710](#15710))


- fix: throw an error when `resolve` is called with an external URL
([#15733](#15733))


- fix: avoid FOUC for CSR-only pages by loading styles and fonts before
CSR starts ([#15718](#15718))


- fix: reset form result on redirect
([#15724](#15724))

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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[Remote forms][regression] Zod4 enum array does not type correctly when using .as('checkbox')

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