[PR] Fix single-node labeled pattern expressions not filtering by label (#2443) [age]

["gregfelice (via GitHub)" <gi...@apache.org>]

gregfelice opened a new pull request, #2444:
URL: https://github.com/apache/age/pull/2444

   ## Problem
   
   A single-node labeled pattern used as a boolean expression — e.g. `WHERE (a:Person)` or `WHERE EXISTS((a:Person))` — is accepted but does **not** test the bound vertex's label. It evaluates as trivially true, so the predicate matches every row.
   
   Repro (on `master`):
   
   ```sql
   SELECT * FROM cypher('g', $$ CREATE (:Person {name:'Alice'}), (:Animal {name:'Rex'}) $$) AS (r agtype);
   
   -- returns BOTH Alice and Rex; should return only Alice
   SELECT * FROM cypher('g', $$ MATCH (a) WHERE (a:Person) RETURN a.name $$) AS (n agtype);
   ```
   
   ## Root cause
   
   A single-node pattern expression desugars to an `EXISTS` sub-pattern. `make_path_join_quals()` returns early for vertex-only patterns (`list_length(entities) < 3`), emitting no quals. With no edge to carry a correlation, the sub-pattern references nothing from the enclosing query, so the planner produces an **uncorrelated one-time InitPlan** that is true whenever any vertex of that label exists — independent of the outer row.
   
   Relationship patterns are unaffected: the edge-driven join (`start_id = a.id`) correlates them to the outer variable, which is why `WHERE (a)-[:R]->(b)` works correctly.
   
   `EXPLAIN` before the fix — uncorrelated `InitPlan` with a `One-Time Filter`:
   
   ```
   InitPlan 1
     ->  Result
   One-Time Filter: ((InitPlan 1).col1)::agtype
   ```
   
   After the fix — correlated `SubPlan` referencing the outer `a_1`:
   
   ```
   SubPlan 1
     ->  Result
           One-Time Filter: ((_extract_label_id(a_1.id))::integer = 3)
   ```
   
   ## Fix
   
   In `make_path_join_quals()`, for a vertex-only pattern whose vertex carries a non-default label **and** whose variable is declared in an ancestor parse state (a correlated reference), emit an explicit label-id filter. `make_qual()` builds a name-based id reference that resolves to the outer variable, so the filter both **correlates** the sub-pattern to that variable and **enforces** the label.
   
   Freshly scanned, non-correlated vertices (no ancestor binding) are untouched, so `MATCH (a:Person)` and "does any X exist" `EXISTS` checks behave exactly as before.
   
   ## Testing
   
   Added regression coverage to `pattern_expression` against a graph containing a non-`Person` vertex:
   
   - `WHERE (a:Person)` → only the `:Person` vertices
   - `WHERE NOT (a:Person)` → only the non-`Person` vertex
   - `WHERE EXISTS((a:Company))` → only the `:Company` vertex
   
   All 41 regression tests pass (`make installcheck`).
   
   ## Note
   
   `RETURN (a:Label)` in a **projection** on an unlabeled bound variable still errors with "multiple labels for variable" — that is a separate, pre-existing guard, orthogonal to this fix, and is intentionally left unchanged.
   
   Fixes #2443
   


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Re: [PR] Fix single-node labeled pattern expressions not filtering by label (#2443) [age]

["gregfelice (via GitHub)" <gi...@apache.org>]

gregfelice commented on PR #2444:
URL: https://github.com/apache/age/pull/2444#issuecomment-4773185821

   Ready for review.
   
   - Fix verified in a clean PG18 build: `WHERE (a:Person)` / `EXISTS((a:Person))` now filter correctly (correlated `SubPlan` on `_extract_label_id(a.id) = <label_id>`) instead of producing a trivially-true uncorrelated one-time `InitPlan`.
   - Full regression suite green (41/41), `regression.diffs` empty, including the new `pattern_expression` cases.
   - Scope kept tight: only correlated bound vertices with a non-default label are affected; plain `MATCH (a:Person)` and "does any X exist" `EXISTS` checks are unchanged.
   - The pre-existing single-node-pattern NOTE in `pattern_expression.sql` was updated to reflect the corrected behavior (and the orthogonal, still-present "multiple labels" projection limitation).
   
   Fixes #2443.
   


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Re: [PR] Fix single-node labeled pattern expressions not filtering by label (#2443) [age]

["jrgemignani (via GitHub)" <gi...@apache.org>]

jrgemignani merged PR #2444:
URL: https://github.com/apache/age/pull/2444


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