pg-parity-harness: shared PostgreSQL parity harness (D-QSP-H) - #2022

D-QSP-H from d-qsp-parity-roadmap-v1.md §3 is one harness that every parity slice reuses. Before this, each *_pg_parity.rs example ran psql its own way.

What it does

crates/pg-parity-harness is a new workspace member with no dependencies; other crates use it as a dev-dependency.

Pg

• Runs psql against a real server inside a scratch schema, which Drop removes.
• Keeps NULL distinct from the empty string.
• Reads result column types with \gdesc and reads SQLSTATE with VERBOSITY=sqlstate.
• connect returns Skip when no server answers.

compare checks, in order:

1. column types;
2. the rows, either as a multiset (duplicates kept) or as an ordered sequence that allows reordering only inside ties of the ORDER BY keys;
3. the SQLSTATE, when an error is expected.

An unsupported feature is a typed Refusal, never a silent skip.

Report / check_mutation record each case. A mutation that leaves PostgreSQL's answer unchanged is reported as VacuousMutation.

Migration. lance-graph-r2il/examples/null_aggs_pg_parity.rs now runs on the harness. It prints SKIP without a server and panics on any failure after connecting.

CI. A new line in rust-test.yml runs the harness's unit tests. The live test prints SKIP there, because CI has no PostgreSQL.

Evidence (local PostgreSQL 16.15)

• 12 unit tests pass. clippy -D warnings and fmt are clean.
• tests/pg_live.rs live_server_roundtrip passes against the live server. The run prints 9 cases, 5 pass, 3 fail, 1 unsupported; the fails and the refusal are the test's own negative cases, which it asserts on.
• The migrated r2il example ran 300 queries; bool_or, bool_and and count(DISTINCT) equal PostgreSQL on value and NULL state for all of them. With validity disabled it differs on 224.

Disable runs. For each, the anchor was asserted to occur exactly once and the file was restored afterwards.

• Red: duplicate counting, both tie closures, NULL to empty string, the unterminated-record check, the SQLSTATE run length, both mutation guards, and the unsupported count.
• Red against the live server: NULL to empty string, dropping VERBOSITY=sqlstate, and an empty Drop.
• Stayed green: removing the trailing-; strip in Pg::query. On psql 16 a query ending in ; followed by \gdesc still describes the right columns, so that trim is defensive and not load-bearing. It is kept, and no test claims it.

Not verified

• Only the r2il example was migrated. The other per-slice examples (quack, contract) still run their own psql and move over one by one.
• The ordered comparison checks ties only through the declared key columns; NULL placement is whatever PostgreSQL returned.

Generated by Claude Code