support openCypher-like relationsiop-type edge alternation

[eeshwarg]

Apache AGE's MATCH grammar rejects openCypher's relationship-type alternation syntax - MATCH ()-[:A|B]->() fails at parse time with syntax error at or near "|". For example, a query like SELECT * FROM cypher('kg_s7', $$ MATCH (p)-[:WORKS_AT|REPORTS_TO]->(c) RETURN c $$) AS (c agtype); throws a syntax error. A workaround for this today is to run something like SELECT * FROM cypher('kg_s7', $$ MATCH (p)-[r]->(c) WHERE type(r) IN ['WORKS_AT','REPORTS_TO'] RETURN c $$) AS (c agtype);.

This change enables support for relationship-type alternation in accordance with the openCypher standard. Changes are made in the grammar, AST and during transformation from the AST to Postgres Query struct by adding the types to the quals list.

Variable-length relationship patterns with alternation ([:A|B*1..2]) are explicitly rejected with ERRCODE_FEATURE_NOT_SUPPORTED.

Testing:

• Added regress test with cases with directed/undirected edges, and variable length edges

Future work:

• openCypher also supports node-type alternation (like n:Person|Customer), which could be added to AGE in a future PR

[Copilot]

Pull request overview

This PR adds openCypher-compatible relationship-type alternation in MATCH patterns (e.g. ()-[:A|B]->()), by extending the Cypher grammar/AST and injecting an additional edge-label filter qual during transformation to a PostgreSQL Query. It also explicitly rejects variable-length edges combined with alternation.

Changes:

• Extend the grammar and cypher_relationship AST node to represent multi-label edge patterns like [:A|B|C].
• During MATCH transformation, inject a synthetic qual restricting matched edges to the alternation’s label-id set.
• Add regression coverage for directed/undirected alternation, unknown labels, and the VLE rejection case.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/include/nodes/cypher_nodes.h	Adds labels list to cypher_relationship to represent relationship-type alternation.
src/backend/parser/cypher_gram.y	Parses `[:A
src/backend/parser/cypher_clause.c	Injects an IN qual over _extract_label_id(edge.id) for alternation; rejects alternation with VLE.
src/backend/nodes/cypher_outfuncs.c	Serializes the new labels field for cypher_relationship.
regress/sql/cypher_match_rel_label_alternation.sql	Adds regression test cases covering alternation behavior and the VLE rejection.
regress/expected/cypher_match_rel_label_alternation.out	Expected output for the new regression test.
Makefile	Registers the new regression test in REGRESS.

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[gregfelice]

Hitting it tomorrow

[jrgemignani]

@eeshwarg Please look at Copilot's suggestions. Additionally, how could this impact performance?

[eeshwarg]

@eeshwarg Please look at Copilot's suggestions. Additionally, how could this impact performance?

In short, this shouldn't affect performance of already supported queries, but only adds support for a new query shape.

All the code changes are during plan generation, not execution time. Existing query shapes take an unchanged code path - the multi-label logic is gated behind list_length(labels) > 1, which is false for every single-label/unlabeled pattern, so they produce an identical Query tree and therefore an identical plan. The new path adds a single integer IN filter on a scan that already existed, with all label resolution done at plan time.