[coverage] Conformance findings: METADATA-037

Comienza con la prueba fallida test_empty_string_name_argument_matches_only_the_empty_string en el diff del PR de cobertura bajo tests/ y, después, sigue las rutas de metadatos de Thrift y kernel/SEA que esta prueba ejercita. Se considera completado cuando los argumentos de nombre vacíos coinciden únicamente con la cadena vacía, NULL permanece sin restricciones, todas las llamadas se completan sin errores y los resultados de tablas y columnas con cero filas conservan sus esquemas normales.

Summary

Surfaced by the multi-language coverage fan-out while conformance-testing these SPEC-IDs against databricks/databricks-sql-python. 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-python) is fixed, then flips green as a tripwire.

Findings

• METADATA-037 [thrift]: Thrift forwards an empty catalog argument verbatim, so the server fails the metadata call with INVALID_PARAMETER_VALUE ('name "" is not a valid name') instead of returning a correctly-shaped 0-row result; an empty name argument is a valid filter matching only "", not an invalid argument (databricks-odbc#204).
  • failing test: test_empty_string_name_argument_matches_only_the_empty_string (see the coverage PR diff under tests/)
• METADATA-037 [sea]: The kernel/SEA backend widens every present-but-empty metadata name argument into "match all" (_none_if_blank/_catalog_or_none map "" to None): tables(schema="") returned 30 rows and tables(catalog=""), tables(table=""), columns(column="") returned rows where the contract is 0 — silently turning a narrowly-scoped lookup into a catalog-wide scan (databricks-odbc#204).
  • failing test: test_empty_string_name_argument_matches_only_the_empty_string (see the coverage PR diff under tests/)
• METADATA-037: A present-but-empty ("") metadata name argument is not treated as matching only the empty string: on the kernel/SEA backend _none_if_blank()/_catalog_or_none() map "" to None ("match all"), so tables(schema="") returns every table in the catalog (30 rows) and tables(catalog="") / tables(table="") / columns(column="") likewise return rows instead of 0 — silently widening a narrowly-scoped metadata lookup into a catalog-wide scan; on Thrift an empty catalog argument is forwarded verbatim and the server fails the call with INVALID_PARAMETER_VALUE instead of returning a correctly-shaped 0-row result (databricks-odbc#204/#209).

Reproduce & Expected

METADATA-037 — Validates that a PRESENT-BUT-EMPTY (zero-length, non-null) catalog / schema / table / column name argument to a metadata call matches ONLY the empty string — i.e.

Reproduce:

• Phase 1 (baseline) — GetTables with a NULL/unset schema argument: unconstrained, returns rows
• Phase 2 — GetTables with an EMPTY schema argument ("", not NULL): matches only "", so 0 rows
• Phase 3 — GetTables with an EMPTY catalog argument: 0 rows (must NOT widen to all catalogs)
• Phase 4 — GetTables with an EMPTY table argument: 0 rows (must NOT drop the table filter)
• Phase 5 (baseline) — GetColumns with a NULL/unset column argument: returns the table's columns
• Phase 6 — GetColumns with an EMPTY column argument: 0 rows (must NOT drop the column filter)

Expected (per the shared spec):

• Every phase completes without error. An empty name argument is a valid filter that matches nothing — not an invalid-argument error.
• NULL/unset schema argument is unconstrained and returns rows, proving the fixture catalog is populated — so phase 2's zero rows are caused by the "" semantics, not by an empty scope.
• An empty schema argument matches only "" — no schema is named "", so zero rows.
• An empty catalog argument matches only "" — zero rows. It must NOT be reinterpreted as "all catalogs" (the widening measured in databricks-odbc#204).
• An empty table argument matches only "" — the table filter must not be dropped.
• NULL/unset column argument returns the table's columns, proving the table is populated — so phase 6's zero rows are caused by the "" semantics.
• An empty column argument matches only "" — the column filter must not be dropped.
• The zero-row table-listing results are correctly shaped, not degenerate: the metadata call's normal column schema is reported so a client can bind columns before fetching zero rows. ODBC: 5 columns, TABLE_CAT first. Other drivers: the same column schema their non-empty table-listing result carries.
• Likewise for the zero-row column listing. ODBC: 19 columns, COLUMN_NAME 4th. Other drivers: the same column schema their non-empty column-listing result carries.

Context

• The behavior was first fixed in a DIFFERENT driver — reference PR: https://github.com/databricks/databricks-odbc/pull/208 — which seeded the shared language-neutral spec. This issue tracks the same conformance gap in databricks/databricks-sql-python; 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/1163