perf: predicate push-down for Expr clauses + mixed rule optimization (#207, #206)

[adityamukho]

Summary

• perf(post-1.0): predicate push-down for expression clauses #207: Extends optimizer::plan() to accept Vec<WhereClause> (Pattern + Expr) and return an interleaved plan. Each Expr predicate clause is positioned at the earliest point where all its variables are bound by preceding patterns, rather than being applied as a post-pass over the full binding set.
• perf(post-1.0): optimize mixed rule evaluation #206: Routes the StratifiedEvaluator mixed-rules path through the updated plan(), giving mixed rules both selectivity-based pattern ordering and Expr push-down with no separate implementation.

Changes

src/query/datalog/optimizer.rs

• New expr_vars() helper — recursively collects ?foo variable names from an Expr tree
• New pattern_bound_vars() helper — collects variables bound by a Pattern's EAV slots
• plan() signature changed: Vec<Pattern> → Vec<(Pattern, IndexHint)> becomes Vec<WhereClause> → Vec<(WhereClause, Option<IndexHint>)>
• Push-down algorithm: after sorting patterns by selectivity, each Expr is inserted at pos + 1 after the last pattern that completes its variable set

src/query/datalog/matcher.rs

• New pub(crate) match_with_hint_seeded() — uses the index hint for the first pattern (unit seed), falls back to hash-join for subsequent patterns; used by the executor/evaluator plan loops

src/query/datalog/executor.rs

• execute_query() and execute_query_with_rules(): replaced two-phase match-then-filter with a single ordered loop processing Pattern (join) and Expr (filter/extend) clauses in plan order
• Removed both top-level apply_expr_clauses post-passes
• Not/NotJoin/Or/OrJoin handling is unchanged

src/query/datalog/evaluator.rs

• StratifiedEvaluator mixed-rules loop now routes through plan() instead of bypassing it, gaining both pattern selectivity ordering and Expr push-down

benches/minigraf_bench.rs

• New query/predicate_pushdown benchmark group (1K/10K/100K scales, 90th-percentile threshold → ~10% pass rate)

Test plan

• cargo test — all 598+ tests pass
• cargo clippy -- -D warnings — no warnings
• cargo bench --bench minigraf_bench -- query/predicate_pushdown — benchmark runs without panic

Follow-up

• Not/NotJoin push-down (same mechanism, more complex safety rules): perf: push-down not/not-join clauses to earliest valid position #248

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 84.14634% with 26 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/query/datalog/executor.rs	74.60%	16 Missing ⚠️
src/query/datalog/evaluator.rs	86.66%	6 Missing ⚠️
src/query/datalog/optimizer.rs	92.00%	4 Missing ⚠️

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