L3 IR structural inconsistency: SQL and PromQL heavy-hitter topk produce different tree shapes

[milindsrivastava1997]

Summary

When the heavy-hitter path fires, SQL and PromQL produce Aggregate(TopK) nodes with different child structures. In SQL the Count is implicit (TopK wraps the raw scan); in PromQL the Count is an explicit child aggregate. An L4 rule matching on AggIntent::TopK sees structurally different subtrees depending on which language the query came from.

Reproduction

-- S2 — SQL heavy-hitter (inline COUNT)
SELECT service, COUNT(*)
FROM metrics GROUP BY service
ORDER BY COUNT(*) DESC LIMIT 5

L3 output:

Aggregate { by: [1], aggs: [TopK { k:5 }], child: Scan }

# P1 — PromQL heavy-hitter
topk(5, count_over_time(http_requests_total[5m]))

# P10 — PromQL heavy-hitter with by
topk by (service) (5, count_over_time(http_requests_total[5m]))

L3 output for P1:

Aggregate { by: [], aggs: [TopK { k:5 }],
    child: Aggregate { aggs: [Count],
        child: TimeRange { child: Scan }
    }
}

Difference

	SQL S2	PromQL P1/P10
TopK child	Scan (raw rows)	Aggregate(Count) { TimeRange { Scan } }
Count	Implicit within TopK	Explicit child node

Notes

The difference may be partially intentional (SQL counts table rows; PromQL counts time-series samples over a window). But L4 rules need to be aware that AggIntent::TopK's child has a different shape depending on origin language. Worth deciding whether to normalize this.

Reproduce via example

cargo run -p asap-control-lower --example topk_ir

Labels: S2, P1, P10

[zzylol]

Resolved by #34 (PR #91, merged). The shared L3 `canonicalize` pass now promotes both languages' count-ranked topk to the same canonical shape — an outer `Aggregate([TopK{k}])` over an explicit inner `Aggregate([Count])` — so SQL S2 and PromQL P1 no longer differ in tree structure (only in the genuinely-intentional leaf: SQL counts rows, PromQL counts windowed samples).

Pinned by `crates/lower/tests/cross_language.rs::sql_and_promql_heavy_hitter_share_the_canonical_shape`, which asserts both reach the canonical shape via the same helper. Closing.