fix(local): reject offset with order_by before the empty-collection fast path

[feiiiiii5]

Problem

In local mode, scroll() with order_by and offset behaves differently depending on whether the collection happens to contain any points:

from qdrant_client import QdrantClient, models

client = QdrantClient(":memory:")
client.create_collection("c", vectors_config=models.VectorParams(size=2, distance=models.Distance.DOT))

client.scroll("c", limit=3, order_by=models.OrderBy(key="k"), offset=1)
# before this change: ([], None)          <- empty collection
# after one upsert:   ValueError: Offset is not supported in conjunction with `order_by` scroll parameter

The server rejects the order_by + offset combination before it looks at stored points, and local mode does too — but only once a point exists, so a caller sees a successful empty page on an empty collection and the documented error on the identical call later.

Cause

LocalCollection.scroll() returns early for an empty collection:

if len(self.ids) == 0:
    validate_filter(scroll_filter, allow_jsonesque=True)  # "to have the same behaviour as the server"
    return [], None

That branch deliberately keeps server-side argument validation on the empty path, but the offset/order_by guard sits further down, inside the order_by section (previously at local_collection.py:2120), so the early return pre-empts it.

Change

Hoist the guard to the top of scroll(), so the request is rejected before the empty-collection fast path, the same way validate_filter already is. Behavior for offset without order_by (which is supported) is untouched, and local_collection.py has no generated async twin, so nothing needs regenerating.

Testing

New regression test qdrant_client/local/tests/test_scroll_validation.py runs the identical call against an empty and a non-empty collection:

(cd repo root) python -m pytest qdrant_client/local/tests/test_scroll_validation.py -q

• pristine 589a87a: 1 failed, 1 passed — the empty-collection case fails, which is the bug.
• this branch: 2 passed.

Wider local suites at head: python -m pytest qdrant_client/local/tests tests/test_in_memory.py -q → 145 passed.

Repo gates on the changed files: ruff format --check --line-length=99 → 2 files already formatted; ruff check → All checks passed!.

Notes for the reviewer

• local_collection.py is hand-written (not generated), so there is no async twin to regenerate, and the diff is the 5-line move plus the test.
• Targeting dev as the template asks.
• This PR was prepared with an AI assistant; I reviewed the diff and ran the commands above locally. Remote CI on a fork PR may still be awaiting maintainer approval, so the numbers here are local.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

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Run ID: d7b959c1-d152-4158-ae64-504f2f4dba30

📥 Commits

Reviewing files that changed from the base of the PR and between 589a87a and c998abb.

📒 Files selected for processing (2)

• qdrant_client/local/local_collection.py
• qdrant_client/local/tests/test_scroll_validation.py

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📝 Walkthrough

Walkthrough

scroll now validates the incompatible order_by and offset combination before handling empty collections or selecting a scrolling implementation. The duplicate validation in the value-ordered path was removed. A parameterized test verifies the ValueError for both empty and populated collections.

Priority: ⬇️ Low

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

Change: Bug fix · Severity of issue fixed: Low

Suggested reviewers: joein

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 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	The description clearly explains the local scroll validation bug, the code change, and the regression tests. It directly relates to the changeset.
Title check	✅ Passed	The title clearly and concisely identifies the main change: rejecting offset with order_by before the empty-collection fast path.
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

🧪 Generate unit tests (beta)

• Create a new PR

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