[coverage] Conformance findings: DATATYPE-043 #500

Summary

Surfaced by the multi-language coverage fan-out while conformance-testing these SPEC-IDs against databricks/databricks-sql-go. Each finding is committed as an expected-failure (xfail) test in the coverage PR — the test asserts the CORRECT (post-fix) behavior and stays red until THIS driver (databricks/databricks-sql-go) is fixed, then flips green as a tripwire.

Findings

• DATATYPE-043 [thrift, sea]: Result metadata reports no DECIMAL precision/scale: the rows type does not implement driver.RowsColumnTypeDecimalSize, so sql.ColumnType.DecimalSize() returns ok=false for DECIMAL(10,2)/(38,0)/(38,38) on both the with-rows and schema-only paths, losing the declared qualifiers for every metadata consumer while the value stays correct
  • failing test: TestDecimalPrecisionAndScaleInResultMetadata (see the coverage PR diff under tests/)

Reproduce & Expected

DATATYPE-043 — Verify the driver's RESULT-SET METADATA reports a DECIMAL column's DECLARED precision and scale -- for a result that has rows AND for a schema-only (zero-row) result, and including the scale-0 case.

Reproduce:

SELECT
  CAST(3.5 AS DECIMAL(10, 2))  AS amount,
  CAST(1 AS DECIMAL(38, 0))    AS whole,
  CAST(0.1 AS DECIMAL(38, 38)) AS all_fraction
SELECT
  CAST(3.5 AS DECIMAL(10, 2))  AS amount,
  CAST(1 AS DECIMAL(38, 0))    AS whole,
  CAST(0.1 AS DECIMAL(38, 38)) AS all_fraction
WHERE 1 = 0

Expected (per the shared spec):

• result has exactly 1 row(s)
• col amount, row 0 == 3.5
• result has exactly 0 row(s)
• full assertion contract:

result:
- label: with_rows
  row_count: 1
- label: with_rows
  decimal_type_qualifiers:
    column: amount
    precision: 10
    scale: 2
- label: with_rows
  decimal_type_qualifiers:
    column: whole
    precision: 38
    scale: 0
- label: with_rows
  decimal_type_qualifiers:
    column: all_fraction
    precision: 38
    scale: 38
- label: with_rows
  column:
    name: amount
    equals: 3.5
- label: schema_only
  row_count: 0
- label: schema_only
  decimal_type_qualifiers:
    column: amount
    precision: 10
    scale: 2
- label: schema_only
  decimal_type_qualifiers:
    column: whole
    precision: 38
    scale: 0
- label: schema_only
  decimal_type_qualifiers:
    column: all_fraction
    precision: 38
    scale: 38

Context

• The behavior was first fixed in a DIFFERENT driver — reference PR: feat: support geospatial results on the kernel path databricks-sql-nodejs#535 — which seeded the shared language-neutral spec. This issue tracks the same conformance gap in databricks/databricks-sql-go; the reference PR is for cross-referencing the intended behavior, NOT a change to this repo.
• Coverage PR carrying the reproducing xfail test(s): https://github.com/databricks/databricks-driver-test/pull/1848