parser: existential subquery brace form EXISTS { pattern } (+2 TCK) - #86
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`MATCH (n) WHERE exists { (n)-->() } RETURN n` (ExistentialSubquery1 [1]/[3])
raised a parse error — only the parenthesized `EXISTS(pattern)` form was
accepted, not the openCypher existential-subquery brace form `EXISTS { ... }`.
Added `EXISTS '{' pattern_list '}'` to the expr grammar, reusing the existing
`make_exists_pattern_expr` / `EXISTS_TYPE_PATTERN` transform. That emitter
already handles correlated outer variables (the outer-bound `n` resolves via
transform_var_get_alias and is referenced without being added to the subquery
FROM), producing `EXISTS (SELECT 1 FROM ... WHERE ...)`.
No bison conflicts (still `%expect 15` / `%expect-rr 3`).
Scoped to the no-inner-WHERE form. The brace form with an inner WHERE
([2]/[4]) and the full-query / aggregation / nested forms
(ExistentialSubquery2/3) need inner-variable registration in the subquery
scope and are deferred.
Fixes ExistentialSubquery1 [1] and [3]. Zero TCK regressions. 3708 -> 3710.
Unit 944/944, functional clean.
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`MATCH (n) WHERE exists { (n)-->() } RETURN n` (ExistentialSubquery1 [1]/[3]) raised a parse error — only the parenthesized `EXISTS(pattern)` form was accepted, not the openCypher existential-subquery brace form `EXISTS { ... }`.
Fix
Added `EXISTS '{' pattern_list '}'` to the expr grammar, reusing the existing `make_exists_pattern_expr` / `EXISTS_TYPE_PATTERN` transform. That emitter already handles correlated outer variables — the outer-bound `n` resolves via `transform_var_get_alias` and is referenced without being added to the subquery FROM, producing `EXISTS (SELECT 1 FROM ... WHERE ...)`.
No bison conflicts (still `%expect 15` / `%expect-rr 3`).
Scope
No-inner-WHERE form only. The brace form with an inner WHERE ([2]/[4]) and the full-query / aggregation / nested forms (ExistentialSubquery2/3) need inner-variable registration in the subquery scope — deferred to a follow-up.
Verification
Fixes ExistentialSubquery1 [1] and [3]. Zero TCK regressions (fail steady at 132). 3708 → 3710. Unit 944/944, functional clean.