PG compatibility: reviewed witnesses and report generation (Tasks 7-8) #46

Context

This issue tracks Tasks 7-8 from docs/superpowers/plans/2026-06-11-postgresql-libpg-query-compatibility.md and follows #51.

Task 7: reviewed witnesses and metadata validation

Implemented on PR #50 in commit 1f9122e test: add reviewed PostgreSQL syntax witnesses.

Added

• tests/pg_compat/witnesses.sql
• tests/pg_compat/witnesses.json
• tests/pg_compat/structural_dispositions.json

Updated

• scripts/pg_compat/baseline.py
• tests/pg_compat/test_baseline.py

Behavior

• Parses witness SQL through a target pg_compat runner via load_reviewed_witnesses().
• Validates metadata count against parsed SQL statement count.
• Rejects duplicate witness IDs.
• Rejects unsupported first_postgresql_major values above the target major.
• Requires structural_feature_ids to be present and a list of strings.
• Rejects oracle node mismatches against expected_oracle_node.
• Reports empty feature links as unlinked_witnesses for later refresh review.

Seed witnesses

• pg-json-object-constructor: SQL/JSON constructor through SELECT.
• pg-merge-statement: PostgreSQL MERGE statement currently surfaced by ParserSQL as TYPE_MISMATCH.

Task 8: Markdown compatibility reports

Implemented on PR #50 in commit 7663f51 feat: generate PostgreSQL compatibility reports.

Added

• scripts/pg_compat/generate_report.py
• tests/pg_compat/test_generate_report.py

Report content

• PostgreSQL target-version header.
• Generation timestamp.
• ParserSQL commit.
• Previous and target libpg_query branches, SHAs, and PostgreSQL patch versions.
• Result totals for all six compatibility outcomes.
• PG18 backlog excluding DEEP_SUPPORTED.
• CLASSIFIED_ONLY routing coverage.
• PG17-to-PG18 release delta outcomes.
• Newly supported and regressed baseline transitions.
• Structural feature witness links.
• Unwitnessed structural features.
• Unlinked witnesses.
• Reproduction commands.

Determinism

• Statement rows sort by result, oracle node, and statement ID.
• Structural feature rows sort by kind, symbol, and feature ID.
• SQL shown in Markdown is normalized and limited to 200 characters; complete SQL remains in JSONL inputs.

Verification

• PYTHONDONTWRITEBYTECODE=1 python3 -m unittest discover -s tests/pg_compat -p "test_baseline.py" -v: 13 tests passed.
• Actual PG18 runner accepted both seed witnesses; SQL/JSON was DEEP_SUPPORTED, MERGE was TYPE_MISMATCH.
• PYTHONDONTWRITEBYTECODE=1 python3 -m unittest discover -s tests/pg_compat -p "test_generate_report.py" -v: 2 tests passed.
• PYTHONDONTWRITEBYTECODE=1 PG_COMPAT_RUNNER=/tmp/parsersql-pg-compat-test/bin/pg_compat-18 python3 -m unittest discover -s tests/pg_compat -p "test_*.py" -v: 79 tests passed.

Status

Implementation is complete on PR #50. The issue will close when that PR merges.