gregfelice opened a new issue, #2443:
URL: https://github.com/apache/age/issues/2443
### Summary
Single-node labeled pattern expressions `(a:Label)` are accepted as boolean
expressions but do **not** filter by label — they evaluate as trivially true.
This is a pre-existing limitation in the vertex-only pattern transform,
surfaced by #2360 (which lets a bare pattern appear anywhere an expression is
valid).
### Reproduction
```sql
SELECT * FROM cypher('g', $$ CREATE (:Person {name:'Alice'}), (:Animal
{name:'Rex'}) $$) AS (r agtype);
-- expected: only "Alice"; actual: "Alice" AND "Rex"
SELECT * FROM cypher('g', $$ MATCH (a) WHERE (a:Person) RETURN a.name $$) AS
(n agtype);
-- expected: a boolean reflecting whether a has label Person; actual: always
true
SELECT * FROM cypher('g', $$ MATCH (a:Person) RETURN (a:Person) $$) AS (b
agtype);
```
### Root cause
`make_path_join_quals()` in `src/backend/parser/cypher_clause.c:5454`
early-returns for vertex-only patterns:
```c
/* for vertex only queries, there is no work to do */
if (list_length(entities) < 3)
{
return NIL;
}
```
The label-filter quals (`_extract_label_id(id) = label_id`) are only emitted
inside `make_join_condition_for_edge()`, which is never reached without a
relationship. So a single-vertex pattern desugars to an `EXISTS` subquery with
no label constraint → trivially true.
### Scope
- Relationship patterns (`(a)-[:R]->(b)`) correlate and filter correctly —
the path goes through the ≥3-entity branch. This is the feature #2360 targets
and it is unaffected.
- The buggy early-return is byte-identical on `master`; #2360 touches no
transform code. It only makes the limitation reachable via the new `(a:Label)`
expression surface.
### Suggested fix
Emit the label-filter qual for single bound vertices before the early return
in `make_path_join_quals` (or hoist the label-filter logic out of
`make_join_condition_for_edge` so it applies to vertex-only patterns), plus a
regression test asserting `WHERE (a:Person)` filters and `RETURN (a:Label)`
reflects the label.
Found during review of #2360.
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