Handle integer-backed Arrow decimals via logical type metadata

[rahul-iyer]

Summary

ADBC exposes Arrow schemas and arrays, but some Snowflake types are not fully recoverable from the Arrow
physical type alone. In particular, Snowflake NUMBER/DECIMAL columns may arrive with their semantics
encoded in field metadata rather than standard Arrow decimal format.

The Snowflake ADBC driver documents two relevant metadata channels:

• query-result field metadata such as logicalType=FIXED, precision, and scale
• table-schema metadata such as DATA_TYPE=NUMBER(p,s)

Without interpreting those annotations, Ladybug can bind Snowflake decimals as plain numeric storage
types.

What changed

• Added Snowflake-specific decoding for decimal types from:

  • logicalType=FIXED metadata on Arrow fields
  • DATA_TYPE=NUMBER(...), NUMERIC(...), and DECIMAL(...) metadata on Arrow fields

• Added decimal scanning support for Snowflake FIXED values when the Arrow batch is:

  • integer-backed
  • float32-backed
  • float64-backed

• Refactored Arrow metadata handling into separate decoder components:

  • shared metadata utilities
  • Snowflake decoder
  • generic metadata decoder
  • a single orchestrator entrypoint

Design

The refactor separates three concerns:

• Arrow physical type parsing
• logical type recovery from metadata
• vendor-specific metadata decoding

The rest of the Arrow pipeline still consumes normalized logical type information only. This keeps
Snowflake-specific behavior out of the core binding and scan code paths except where the recovered
logical type is applied.

This structure is intended to make future support for other sources, such as Databricks/Spark-specific
metadata, straightforward to add as separate decoders rather than as scattered conditionals.

https://arrow.apache.org/adbc/current/driver/snowflake.html

Snowflake signal	Example metadata	Arrow physical storage	Ladybug result	Notes
Raw Snowflake decimal type via DATA_TYPE	DATA_TYPE=NUMBER(12,4)	Any Arrow storage type	DECIMAL(12,4)	Parsed from Snowflake table-schema metadata.
Raw Snowflake decimal type via DATA_TYPE with implicit scale	DATA_TYPE=NUMBER(18)	Any Arrow storage type	DECIMAL(18,0)	Missing scale defaults to 0.
Raw Snowflake decimal aliases via DATA_TYPE	DATA_TYPE=NUMERIC(10,3) or DATA_TYPE=DECIMAL(10,3)	Any Arrow storage type	DECIMAL(10,3)	Matching is case-insensitive and whitespace-tolerant.
Snowflake logical decimal metadata	logicalType=FIXED, precision=7, scale=2	Integer-backed Arrow (INT8/16/32/64, UINT8/16/32/64)	DECIMAL(7,2)	Used for query-result Arrow schemas.
Snowflake logical decimal metadata	logicalType=FIXED, precision=9, scale=2	Float-backed Arrow (FLOAT, DOUBLE)	DECIMAL(9,2)	Values are cast into decimal backing storage during scan.
Snowflake raw type fallback to logical metadata	malformed DATA_TYPE plus valid logicalType=FIXED metadata	Integer-backed or float-backed Arrow	DECIMAL(p,s) from logicalType metadata	If raw DATA_TYPE parsing fails, Snowflake logicalType parsing is tried next.
Snowflake metadata precedence over generic metadata	DATA_TYPE=NUMBER(12,4) plus generic logicalType=DECIMAL, precision=9, scale=3	Any Arrow storage type	DECIMAL(12,4)	Snowflake raw type metadata wins over generic metadata.