fix: preserve nested semantic style properties - #59223

🤔 This is a ...

• 🆕 New feature
• 🐞 Bug fix
• 📝 Site / documentation improvement
• 📽️ Demo improvement
• 💄 Component style improvement
• 🤖 TypeScript definition improvement
• 📦 Bundle size optimization
• ⚡️ Performance optimization
• ⭐️ Feature enhancement
• 🌐 Internationalization
• 🛠 Refactoring
• 🎨 Code style optimization
• ✅ Test Case
• 🔀 Branch merge
• ⏩ Workflow
• ⌨️ Accessibility improvement
• ❓ Other (about what?)

🔗 Related Issues

Follow-up to the separate existing merge behavior identified in the review of #59221. This fix is based on master and does not depend on the Tabs popup projection change.

💡 Background and Solution

Overriding one nested semantic style currently replaces the whole nested CSS object. For example, changing a Select popup's color drops the padding supplied by ConfigProvider:

<ConfigProvider
  select={{ styles: { popup: { root: { color: 'red', padding: 12 } } } }}
>
  <Select
    open
    options={[{ value: 'example' }]}
    styles={{ popup: { root: { color: 'blue' } } }}
  />
</ConfigProvider>

The popup should be blue and retain 12px padding. Nested styles now reuse the component's existing semantic schema. Style recursion ignores the className-only _default mapping and follows only explicit semantic child keys, without inferring structure from runtime style values. Select, Cascader, TreeSelect, and the shared DatePicker/TimePicker hook now explicitly list their supported popup child nodes in the schema, so a local popup override preserves other ConfigProvider CSS properties and sibling semantic nodes. AutoComplete has only one local style source at its merge point and already delegates popup rendering to Select. Flat mergeStyles(...styles) callers retain their existing behavior. Explicitly resetting a CSS property to undefined still clears it, and schema changes invalidate the memoized result.

Validation at signed exact head cebdc5aebbd8208228ed8d0ffe9939a600ac2995, based on the master merge commit 316e9d330e4329ffa99dd8b6bcb9626cecdb0045:

• The original five regressions fail on base 58b0ee1554835b3ea2d0541f4986306f3d70d0ce and pass with this fix. Three additional rendered-popup regressions for Cascader, TreeSelect, and DatePicker fail without their respective schema changes and pass with the fix. They cover preserved CSS properties and sibling popup nodes across ConfigProvider and component styles.
• The expanded six-component run passes 46 suites: 719 tests passed, 10 skipped, and 457 snapshots passed. It includes Select, AutoComplete, Cascader, TreeSelect, DatePicker, and TimePicker.
• Full TypeScript checking, ESLint and Biome on the six touched files, and git diff --check pass. The TreeSelect semantic suite also passes in both Jest and Vitest after querying the portal from document.body. GitHub verifies the signed exact-head commit. Remote CI has no pending or failing checks at the latest exact-head checkpoint (45 successful, 3 skipped), including React 18/latest, Vitest, build, coverage, Preview, size, security, and visual regression. No review threads remain unresolved; maintainer review is still required.

Implemented and validated with OpenAI Codex assistance.

📝 Change Log