fix(clickhouse): coerce LIMIT before SQL interpolation

[Bartok9]

Summary

Coerce limit to a non-negative int before ClickHouse LIMIT subquery wrapping.

Failure / reproduction

Before this change, ClickHouseConnector.query interpolated the raw {limit} directly into the generated SQL:

sql = f"SELECT * FROM ({sql}) LIMIT {limit}"

So a client-supplied bad value flowed straight into the query text. E.g. calling query(sql, limit=-1) produced:

SELECT * FROM (...) LIMIT -1

and a non-numeric value like limit="1; DROP TABLE t" interpolated verbatim — an injection-shaped input that should never reach the driver.

Fix

Add _coerce_limit and apply it at the start of query: reject negatives and non-integer strings, accept numeric strings, so only a validated non-negative int is ever interpolated.

Verification

cd core/wren && .venv/bin/python -m pytest tests/unit/test_clickhouse_coerce_limit.py -q
3 passed

Covers: negative rejection, injection-like/non-numeric rejection, numeric-string acceptance.

Duplicate check

Searched open PRs/issues for existing ClickHouse limit coercion. Related sibling connector PRs (#2624/#2625/#2626) apply the same pattern to other connectors; this PR is the ClickHouse-specific counterpart and does not overlap their files.

Summary by CodeRabbit

• Bug Fixes
  • Improved validation of query LIMIT inputs by rejecting negative numeric values, including fractional inputs (decimals and fractions), before execution.
  • Prevented negative fractional values from being truncated into non-negative LIMIT values.
  • Strengthened limit handling to ensure only valid, non-negative integers are used in generated queries.
• Tests
  • Updated and tightened unit coverage for fractional negative LIMIT coercion scenarios.

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---

Walkthrough

The ClickHouse connector now rejects negative numeric limits before integer coercion and validates limits before SQL interpolation. Unit tests cover fractional negatives, invalid strings, and numeric-string SQL generation.

Changes

ClickHouse limit validation

Layer / File(s)	Summary
Limit coercion and query wiring core/wren/src/wren/connector/clickhouse.py	Rejects negative numeric values before coercion and applies validated limits before SQL rewriting.
Limit validation tests core/wren/tests/unit/test_clickhouse_coerce_limit.py	Tests integer, float, Decimal, and Fraction negatives, invalid strings, and safe numeric-string limit interpolation.

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

Possibly related PRs

• Canner/WrenAI#2625: Adds analogous connector limit coercion and validation tests.
• Canner/WrenAI#2626: Applies parallel connector limit validation before SQL interpolation.

Poem

I’m a bunny guarding LIMIT seven,
No sneaky DROP shall enter heaven.
Negative hops are turned away,
Safe little integers lead the way.
SQL sprouts clean beneath the moon.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately summarizes the main behavioral change to ClickHouse LIMIT handling.
Description check	✅ Passed	The description covers summary, reproduction, fix, verification, and duplicate check, with only minor template details left implicit.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

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Actionable comments posted: 1

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Verify each finding against current code. Fix only still-valid issues, skip the
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Inline comments:
In `@core/wren/src/wren/connector/clickhouse.py`:
- Around line 386-397: Update _coerce_limit to reject negative numeric inputs
before int() truncates fractional values, while preserving safe coercion for
valid limits and existing None handling. Add a regression test covering
limit=-0.5 and assert that it raises ValueError rather than producing LIMIT 0.

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• core/wren/src/wren/connector/clickhouse.py
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[Bartok9]

Good catch, @coderabbitai — int(-0.5) truncates to 0 and slipped past the guard. Pushed eebb5ad: _coerce_limit now rejects any negative numeric (int/float) before int() truncation, plus a regression test for limit=-0.5.

[coderabbitai]

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@Bartok9 Thanks for fixing this. Rejecting negative numeric inputs before int() truncation, with the -0.5 regression test, addresses the bypass.

🐇 ✅

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@core/wren/src/wren/connector/clickhouse.py`:
- Around line 394-400: Update the limit validation before int() coercion to
reject negative values for every accepted numeric type, including Decimal and
Fraction, so values such as -0.5 cannot become zero; alternatively, explicitly
reject unsupported numeric types. Preserve the existing non-negative coercion
and error behavior in the surrounding limit handling.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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• core/wren/src/wren/connector/clickhouse.py
• core/wren/tests/unit/test_clickhouse_coerce_limit.py

[Bartok9]

Thanks @coderabbitai — good follow-up. Broadened the pre-int() negative guard from (int, float) to numbers.Number in 6c3053a, so Decimal('-0.5') and Fraction(-1, 2) are now rejected too rather than truncating to LIMIT 0. Added regression tests for both.

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🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail

git show --format=fuller --stat 6c3053a --
git diff 6c3053a^ 6c3053a -- \
  core/wren/src/wren/connector/clickhouse.py \
  core/wren/tests/unit/test_clickhouse_coerce_limit.py

Length of output: 3210

---

@Bartok9 Confirmed. numbers.Number now guards negative numeric values before int() in _coerce_limit, and the new Decimal("-0.5") and Fraction(-1, 2) regressions directly cover the prior truncation path. This closes the generalized negative-fraction bypass.

🐇 ✅

---

✏️ Learnings added

Learnt from: Bartok9
URL: https://github.com/Canner/WrenAI/pull/2627

Timestamp: 2026-07-30T06:19:05.981Z
Learning: In `core/wren/src/wren/connector/clickhouse.py`, `_coerce_limit` must reject negative `numbers.Number` inputs before calling `int()` because fractional negative values such as `Decimal("-0.5")` and `Fraction(-1, 2)` would otherwise truncate to `0` and be emitted as `LIMIT 0`.

Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure review instructions. You can manage existing learnings in the app.

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[Bartok9]

Fixed the lint failure in a9773cc — hoisted the Decimal/Fraction imports to module top-level (ruff PLC0415); they were function-local in the regression tests. ruff check is clean locally now.