fix: keep vertically shifted popups within the visible area

[1328837476-hug]

Related to ant-design/ant-design#59115

Problem

When there is not enough space above or below the target, a popup can remain partially outside the visible area even with shiftY enabled. The existing shift calculation retains the vertical placement offset, which can leave a 4px overflow with the offsets used by DatePicker.

Changes

• Constrain the final vertical position after the existing shift calculation while the target remains within the shift range.
• Preserve the existing behavior when the target moves beyond that range.
• Keep the top of the panel visible when the panel is taller than the available area. This does not add a height limit or scrolling behavior.
• Leave horizontal alignment and public APIs unchanged.

Verification

• Added 5 regression cases to the existing flip/shift suite, covering positive and negative placement offsets, both placement directions, different target positions, and a panel taller than the viewport.
• Confirmed that all 5 new cases fail before the fix and pass afterward.
• Full test suite: 17 suites passed, 138 tests passed, 1 existing test skipped.
• TypeScript no-emit check passed.
• npm run lint completed with 0 errors and 11 existing React Hook dependency warnings.
• Prettier checks for both changed files and git diff --check passed.
• Existing tests for targets outside the visible area continue to pass.

I also tested this with a local picker patch against the Ant Design 6.6.1 source in Chromium. With a 400px viewport and an approximately 347px date panel, the panel's top position changed from -132px to 0. Single-date and range selection worked. I have not separately tested the originally reported Ant Design 5.20.0 / React 18.2.0 / Edge combination or every custom scrolling-container configuration.

Follow-up

This PR addresses the trigger part of the issue. Picker also needs to enable shiftY in its default placements and consume the released trigger fix. The related Ant Design issue should remain open until that follow-up is complete.

Summary by CodeRabbit

• Bug Fixes

  • 优化弹层垂直定位，避免方向偏移将弹层再次推到视口外。
  • 当弹层高度超过视口时，优先保留顶部内容，提升可见性与使用体验。

• Tests

  • 新增多种放置方向、偏移量及超高弹层场景的定位测试。

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ℹ️ Recent review info

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Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: d1fcbdf1-1e3c-42e2-b1e2-d04dcbe5349c

📥 Commits

Reviewing files that changed from the base of the PR and between 3ff7d68 and aa2160e.

📒 Files selected for processing (2)

• src/hooks/useAlign.ts
• tests/flipShift.test.tsx

Included review availability: Your plan provides up to 2 included reviews per hour; 1 remains after this review.

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Walkthrough

useAlign 新增纵向偏移钳制逻辑。测试覆盖 top/bottom 放置、正负偏移量，以及弹层高度超过视口时的定位结果。

Changes

纵向平移钳制

Layer / File(s)	Summary
纵向偏移边界计算 src/hooks/useAlign.ts	当目标仍处于平移范围内时，nextOffsetY 被限制在可见区域的最小和最大偏移之间。
平移边界回归测试 tests/flipShift.test.tsx	测试使用可变的 popupHeight，覆盖不同放置方向、偏移量和超高弹层场景。

Estimated code review effort: 2 (简单) | ~10 minutes

Merge Risk: ⚪ Minimal · up to aa216

The change keeps vertically shifted popups within the visible area without altering horizontal alignment or public APIs. Focused regression tests and normal validation pass, so no actionable merge-blocking risk remains.

Suggested reviewers: zombiej

Poem

小兔检查偏移线
弹层稳稳留视边
上下方向都验证
高高面板守住顶
测试跳过每个点

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	标题准确概括了主要变更：确保启用 shiftY 的弹层保持在可见区域内。标题简洁、明确，并与代码和回归测试一致。
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

• Fix all pre-merge checks with AI

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[nrps9909]

Approved at exact head aa2160e9f1cc74e608b6de74cebe4cbd390f3d4d.

I independently checked the clamp against the existing shift transaction: it is limited to targets that still overlap the permitted vertical shift band; for a normal-height popup, the derived min/max bounds keep both edges inside the visible region, while Math.max(minOffsetY, ...) deliberately pins an oversized popup to the visible top. Targets fully beyond the band retain the existing follow-target behavior. The positive/negative placement offsets and both target positions pass in the focused 8-test flip/shift file.

I also ran the complete repository at this head: 17 suites passed with 138 tests and one existing skip. TypeScript passed; ESLint completed with 0 errors and 11 existing Hook warnings; changed-file Prettier and diff validation passed. The remaining Vercel result is fork deployment authorization, not a source failure.

This approval is scoped to the trigger geometry. As the description notes, the downstream picker placement must still enable shiftY and consume the released version before ant-design/ant-design#59115 is complete.