Summary

Enum names that contain escaped single quotes (e.g. DateTime(\'UTC\')) are not parsed correctly when:

1. A single enum name contains more than one escape sequence, or
2. Any earlier enum value contains escape sequences (positions bleed into the next value).

Root Cause

In lib/column/enum.go, extractEnumNamedValues has two bugs:

Bug 1 — skippedValueTokens is never reset between values

The slice that records backslash positions is declared before the main loop and is never cleared when a new string starts. Positions from a previous enum value are re-applied to the next value's foundName, corrupting it.

Bug 2 — stale positions when removing multiple backslashes

The removal loop (lines 152-154) applies the original source positions without adjusting for prior removals. Each removal shortens the slice by 1, so subsequent positions are off-by-one per preceding removal.

Reproducing Query

SELECT variantType(CAST(toDateTime('2024-01-15 10:30:00', 'UTC'), 'Variant(String, DateTime(\'UTC\'))'))

ClickHouse returns a value of type Enum8('String' = 0, 'DateTime(\'UTC\')' = 1). The Go client parses the enum name incorrectly, yielding a corrupted string instead of DateTime('UTC').

Related

Central tracking issue: ClickHouse/integrations-ai-playground#17