fix: clone settings locale data

[astandrik]

What changed

settings.getLocaleData() now clones dayjs locale data with a small internal clone helper instead of structuredClone.

The helper keeps function values intact while still returning a detached copy for plain objects and arrays.

Why

dayjs.Ls[locale] can contain functions, for example ordinal. structuredClone cannot clone functions and throws DataCloneError in browsers and Node:

import {settings} from '@gravity-ui/date-utils';

settings.getLocaleData(); // DataCloneError in 2.7.0

This surfaced in consumers that render date field/date picker components: date format expansion calls getLocaleData(), which crashes during render.

Tests

• npm test -- settings
• npm run typecheck
• npm run lint (passes with existing warnings)
• npm test
• npm run build

[korvin89]

Can you describe the use case when this is played?

[Copilot]

Pull request overview

Fixes settings.getLocaleData() to safely return a detached copy of Dayjs locale data even when the locale object contains function-valued properties (e.g., ordinal), avoiding structuredClone’s DataCloneError in browsers/Node.

Changes:

• Replaced structuredClone usage in settings.getLocaleData() with a small recursive clone helper that preserves function references.
• Added a unit test asserting locale data is cloned (new references) while function values remain callable.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/settings/settings.ts	Introduces cloneLocaleData and uses it in getLocaleData() instead of structuredClone.
src/settings/settings.test.ts	Adds a test to ensure locale data cloning works when locale objects contain functions.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[astandrik]

Can you describe the use case when this is played?

We hit this when rendering date controls in a downstream app.

DateField builds sections from a localized format:
useDateFieldState -> splitFormatIntoSections -> expandFormat -> settings.getLocaleData().

In 2.7.0 getLocaleData() uses structuredClone() on the dayjs locale object. The en locale contains ordinal as a function, so structuredClone() throws DataCloneError and the React subtree crashes.

Minimal repro:

import {settings} from '@gravity-ui/date-utils';

settings.getLocaleData(); // DataCloneError in 2.7.0

fixed with downgrade to 2.6.1 in our project

[astandrik]

Can you describe the use case when this is played?

We hit this when rendering date controls in a downstream app.

DateField builds sections from a localized format: useDateFieldState -> splitFormatIntoSections -> expandFormat -> settings.getLocaleData().

In 2.7.0 getLocaleData() uses structuredClone() on the dayjs locale object. The en locale contains ordinal as a function, so structuredClone() throws DataCloneError and the React subtree crashes.

Minimal repro:

import {settings} from '@gravity-ui/date-utils';

settings.getLocaleData(); // DataCloneError in 2.7.0

fixed with downgrade to 2.6.1 in our project

@korvin89 fyi

[korvin89]

Worth a one-line comment that this helper intentionally assumes locale data is function-or-JSON-shaped. Unlike structuredClone, it would stack-overflow on a circular reference and would flatten Date/RegExp/Map/Set to {}. None of those exist in dayjs locale objects today (only strings/numbers/arrays/plain objects/functions), so nothing to fix here — just a note so a future locale field doesn't silently get mangled.

[astandrik]

Fixed in 589af2a: added a one-line note that this helper is specific to Dayjs JSON-like locale data with function fields and is not a general structuredClone replacement.

[korvin89]

This test runs against whatever locale the previous test left set (de) rather than a locale it sets itself. It passes regardless since en also has ordinal + formats, but calling settings.setLocale('en') at the start would make it self-contained and order-independent.

[astandrik]

Fixed in 589af2a: added settings.setLocale('en') at the start of this test, so it is self-contained and order-independent.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.