feat(3vl): SQL three-valued logic for AND/OR/NOT + null cast pass-through

[Felipe705x]

What & why

Make null propagation follow SQL three-valued logic (3VL) for the boolean connectives AND / OR / NOT.

Today a null/missing operand of a logical operator is routed through the implicit argument-cast wrapper, which turns a missing attribute (Failure) or a null into a hard failure and drops the whole row. The headline symptom:

MATCH (x:Person) WHERE x.status OR true RETURN x.name

When status is absent this returns no rows (every row dropped) instead of all of them. Correct 3VL: unknown OR true = true.

Changes

Runtime — src/runtime/engine.rs

• Dedicated AND/OR arms in run_expr, outside the operator wrapper, with real short-circuit (true OR _, false AND _) and the 3VL truth table. Both Value::Null and Failure (missing attribute / unbound var / type error) are read as the 3VL unknown, matching the existing IsNull/Coalesce/aggregate convention.
• NOT null → null.
• null AS T → null in the BinOp::As arm — null inhabits every type; this also lets a null operand reach the 3VL logic (the runtime relaxation of the SimpleType-only argument check) without touching the IS/TYPED predicate.
• eval_binop AND/OR arms updated to the same 3VL table for any direct caller.

Typechecker — src/typing/checker.rs

• Short-circuit override of the codomain (c̃od) check for AND/OR: result is B unless both operands meet bottom (⊥) against B (a ⊥/null operand beside a valid Bool still yields Bool — e.g. Integer OR true → B).

Truth tables (now)

true OR null → true · false OR null → null · false AND null → false · true AND null → null · null · null → null · NOT null → null.

Scope / no-regression

Boolean connectives only. Comparison/equality operators (=, <>, <, …) keep their pre-existing behavior in this PR — including the known null = null → true wart. 3VL for comparisons + the cmp_values↔eval_binop (pushdown) unification is a follow-up PR. New tests pin the current comparison behavior as a no-regression guard.

Tests — tests/three_valued_logic_test.rs (17)

3VL truth tables, missing-property-as-unknown, WHERE-clause differentiators that fail under the old behavior, null/invalid cast handling, the typechecker short-circuit, and comparison no-regression guards.

Verified the differentiators genuinely catch the bug: reverting just the two source files (test file kept) makes 7 of 17 tests fail — exactly the 3VL differentiators (e.g. WHERE x.status OR true → [] old vs ["A","B","C"] fixed) — while the 10 guards stay green.

Checklist

• cargo fmt --all
• cargo clippy --workspace --all-targets -- -D clippy::all
• Full test sweep (cargo test --lib + the integration list in CLAUDE.md) — no regressions
• Follow-up: comparison-operator 3VL + pushdown unification

🤖 Generated with Claude Code

[Felipe705x]

Superseded by #73 — closing.

#73 reaches the same goal at the correct altitude, validated against both the ISO GQL and FPPC oracles:

• Read-site nulls (FPPC Ra): a missing property/field reads as null, so a missing value (lenient 3VL) is distinct from a genuine type error (empties the path). This is the split feat(3vl): SQL three-valued logic for AND/OR/NOT + null cast pass-through #63 couldn't express — it kept missing reads as Failure and absorbed them at the connective, which also laundered real type errors into booleans (e.g. ('a' AS INTEGER) OR true wrongly kept all rows).
• Classic 3VL for comparisons/arithmetic/IN (null = null → null), plus the SQL truth tables for AND/OR and NOT null → null.
• cod override for the short-circuit connectives (kept from feat(3vl): SQL three-valued logic for AND/OR/NOT + null cast pass-through #63; confirmed necessary for the vacuity under-approximation, FPPC Thm 6.5).
• Type errors empty the path regardless of essential/inessential position — the strict, portable subset of ISO UA004; static B imposes no runtime success obligation (FPPC DGG Thm 6.8).

Known ISO gap (pre-existing, out of scope, shrunk by #73): essential type errors / NOT NULL-site nulls should raise a hard data exception (22G12/22G03) rather than empty — tracked as a future ISO data-exceptions workstream.