[I] `reduce()`/list comprehension in a `LIMIT` or `SKIP` clause raises internal error `unsupported SubLink` (0A000) [age]

["hkjiang26 (via GitHub)" <gi...@apache.org>]

hkjiang26 opened a new issue, #2518:
URL: https://github.com/apache/age/issues/2518

   ## Bug description
   
   Putting a `reduce()` expression — or a list comprehension — inside a `LIMIT` or `SKIP` clause makes AGE 1.8.0 fail with the internal error `ERROR: 0A000: unsupported SubLink`. The query has no subquery and no outer variable; the trigger is the `reduce`'s own list iteration variable (`b IN [0]`). Neo4j runs the same statement normally. 
   
   ## Access method
   
   - Command line via `psql`, inside the official Docker container `apache/age:1.8.0`
   
   ## Data setup
   
   No data is required — the error reproduces on an empty graph. Only the graph itself must exist:
   
   ```pgsql
   CREATE EXTENSION IF NOT EXISTS age;
   LOAD 'age';
   SET search_path = ag_catalog, "$user", public;
   SELECT create_graph('graph_test');
   ```
   
   ## Configuration
   
   - None beyond the stock AGE extension. No additional modules (no PostGIS, etc.), default `search_path` handling as shown above.
   
   ## Command that triggers the error
   
   ```pgsql
   SELECT * FROM cypher('graph_test', $$ RETURN 1 LIMIT reduce(a = 1, b IN [0] | a + b) $$) AS (c0 agtype);
   ```
   
   ```
   ERROR:  unsupported SubLink
   ```
   
   (SQLSTATE `0A000`, internal error.) Run the statement on its own (e.g. `psql -c "..."`): when several statements are piped to `psql` at once, stdout/stderr buffering can push the `ERROR` line to a different position in the output and make it look like the query succeeded.
   
   The failure is specific to `LIMIT`/`SKIP`: the same `reduce` returns a row without one, and `LIMIT` accepts other data-free expressions:
   
   ```pgsql
   -- works: reduce without LIMIT
   SELECT * FROM cypher('graph_test', $$ RETURN reduce(a = 1, b IN [0] | a + b) $$) AS (c0 agtype);
   -- works: arithmetic / function in LIMIT
   SELECT * FROM cypher('graph_test', $$ RETURN 1 LIMIT 1 + 1 $$) AS (c0 agtype);
   SELECT * FROM cypher('graph_test', $$ RETURN 1 LIMIT size([0, 0]) $$) AS (c0 agtype);
   ```
   
   ## Environment
   
   - Version: 1.8.0 (official `apache/age:1.8.0` Docker image)
   - PostgreSQL: 18.1 (Debian 18.1-1.pgdg13+2), x86_64
   


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Re: [I] `reduce()`/list comprehension in a `LIMIT` or `SKIP` clause raises internal error `unsupported SubLink` (0A000) [age]

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

gregfelice commented on issue #2518:
URL: https://github.com/apache/age/issues/2518#issuecomment-5370015307

   Confirmed still reproducing on current master (`4d9b2506`, AGE 1.8.0) built against PostgreSQL 18.4, in a fresh database:
   
   ```
   ERROR:  unsupported SubLink
   LINE 1: ...ECT * FROM cypher('graph_test', $$ RETURN 1 LIMIT reduce(a =...
   ```
   
   Triaged as part of a sweep over the current fuzz-report backlog against master. This one is a clean error rather than a crash — recording it so it is not assumed stale just because it was filed against an older image.
   


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