Related to Nullable Tuples: Fix exception in Array-to-QBit conversion with nullable source

[alexey-milovidov]

Summary

• Fix LOGICAL_ERROR exception in convertArrayToQBit when nullable_source wraps a different column type (e.g., ColumnTuple instead of ColumnArray)
• The bug occurs when casting types like Nullable(Tuple(Array(Variant(...)), String)) to Nullable(Tuple(QBit(BFloat16, N), String)) — the outer nullable_source wraps the Tuple, but convertArrayToQBit uses getNestedColumnPtr expecting an Array
• Fix: stop propagating nullable_source in createArrayToQBitWrapper, matching the pattern already used by createArrayWrapper

BuzzHouse CI report: https://s3.amazonaws.com/clickhouse-test-reports/json.html?REF=master&sha=58b9b010eb7d1210b0c0ec88118ab153a9db0f4d&name_0=MasterCI&name_1=BuzzHouse%20%28arm_asan%29

Test plan

• Added regression test 03926_qbit_cast_from_nullable_array exercising nullable Tuple with Array-to-QBit conversion
• Build passes
• CI passes

Changelog category (leave one):

• Critical Bug Fix (crash, data loss, RBAC) or LOGICAL_ERROR

Changelog entry (a user-readable short description of the changes that goes into CHANGELOG.md):

Fix LOGICAL_ERROR exception in Array-to-QBit conversion when nullable_source from an outer Tuple wrapper replaces the converted array column with a mismatched column type. Closes #97389.

🤖 Generated with Claude Code

[clickhouse-gh]

Workflow [PR], commit [fd75b84]

Summary: ✅

[alexey-milovidov]

Yes, it reproduces the issue.

[nihalzp]

Yes, the fix is on the right path.

The remaining issue is that we need nullable_source to skip rows where we have NULL. For example,

SELECT CAST(
    [NULL::Nullable(Tuple(Array(Float64), String))],
    'Array(Nullable(Tuple(QBit(BFloat16, 3), String)))'
);

In PR, now throws with:

Code: 190. DB::Exception: Array arguments must have size 3 for QBit conversion, got 0: In scope SELECT CAST([CAST(NULL, 'Nullable(Tuple(Array(Float64), String))')], 'Array(Nullable(Tuple(QBit(BFloat16, 3), String)))'). (SIZES_OF_ARRAYS_DONT_MATCH)

But it should return NULL.

We have to use nullable_source to get the null map data and only try to convert array to QBit for non-null rows in convertArrayToQBit.

We can also add the following query for proper validation of the logic:

SELECT
    CAST(v, 'Array(Nullable(Tuple(QBit(BFloat16, 3), String)))') AS converted
FROM VALUES(
    'v Array(Nullable(Tuple(Array(Float64), String)))',
    [([1.0, 2.0, 3.0], 'hello')],
    [NULL]
);

It should return:

[([1,2,3],'hello')]
[NULL]

[CLAassistant]

All committers have signed the CLA.