Fix crash during ALTER TABLE REMOVE SETTING in iceberg

[alesapin]

Changelog category (leave one):

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

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

Fix crash in ALTER TABLE ... REMOVE SETTINGS query for Iceberg table engine. Fixes #86330.

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

This PR was created with help of Claude Code.

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Note

Low Risk
Low risk: change is a narrow validation guard for Iceberg ALTER TABLE plus a regression test, with no impact outside Iceberg DDL handling.

Overview
Prevents a crash when running ALTER TABLE ... MODIFY COLUMN ... REMOVE SETTINGS on Iceberg tables by explicitly rejecting any MODIFY_COLUMN command that attempts to remove column properties (returns NOT_IMPLEMENTED).

Adds a stateless regression test that creates an IcebergLocal table, inserts a snapshot, runs the unsupported ALTER, and asserts the NOT_IMPLEMENTED error instead of a segfault.

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[clickhouse-gh]

Workflow [PR], commit [0924cd5]

Summary: ✅

[Copilot]

Pull request overview

Fixes a crash triggered by ALTER TABLE ... MODIFY COLUMN ... REMOVE SETTINGS on Iceberg by explicitly rejecting unsupported “remove column properties” alters and adding a stateless regression test to assert NOT_IMPLEMENTED is returned instead of crashing.

Changes:

• Add a guard in Iceberg ALTER validation to throw NOT_IMPLEMENTED when column properties are removed via MODIFY COLUMN.
• Add a stateless bash test reproducing the original segfault scenario.
• Add a reference output asserting NOT_IMPLEMENTED.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
tests/queries/0_stateless/04033_iceberg_alter_remove_settings_segfault.sh	Adds regression coverage for the crashing ALTER by asserting NOT_IMPLEMENTED.
tests/queries/0_stateless/04033_iceberg_alter_remove_settings_segfault.reference	Expected output for the new regression test.
src/Storages/ObjectStorage/DataLakes/Iceberg/IcebergMetadata.cpp	Adds validation to reject unsupported column property removals instead of crashing.

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[tiandiwonder]

Workflow [PR], commit [d3e4b12]

Summary: ❌

job_name test_name status info comment
Upgrade check (amd_release) failure
Error message in clickhouse-server.log (see upgrade_error_messages.txt) FAIL cidb

rebase to d15162f (lastest master)，upgrade test will pass!

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[clickhouse-gh]

LLVM Coverage Report

Metric	Baseline	Current	Δ
Lines	83.80%	83.80%	+0.00%
Functions	23.90%	23.90%	+0.00%
Branches	76.30%	76.30%	+0.00%

PR changed lines: PR changed-lines coverage: 88.89% (8/9)
Diff coverage report
Uncovered code