PG18: Fix multi-shard MIN/MAX on composite types by blessing record aggregates

[m3hm3t]

DESCRIPTION: Fix multi-shard MIN/MAX on composite types by blessing record aggregates

fixes #8400

PG18 adds MIN/MAX support for composite values.

postgres/postgres@a0f1fce

On Citus distributed tables, multi-shard execution computes MIN/MAX per shard on workers and then re-aggregates those shard results on the coordinator. The shard results arrive as record without a concrete record typmod/tuple descriptor, so the coordinator cannot parse/compare them and fails with:

ERROR: input of anonymous composite types is not implemented

Solution

Extend BlessRecordExpression() to handle Aggref nodes that return RECORDOID. For min/max over a composite column, derive the tuple descriptor from the aggregate’s input argument rowtype, convert it to a record tupledesc, and call BlessTupleDesc() so Postgres assigns a non-anonymous record typmod. This preserves enough metadata across the worker→coordinator boundary for the coordinator-stage aggregate to work.

Tests

Add a PG18 regression case that creates a distributed table with a composite type and verifies distributed MIN/MAX returns the expected composite values instead of raising the anonymous composite error.

[codecov]

Codecov Report

❌ Patch coverage is 73.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.80%. Comparing base (8cec88d) to head (bb5c32d).

Additional details and impacted files

@@                     Coverage Diff                      @@
##           m3hm3t/pg18_minmax_array    #8429      +/-   ##
============================================================
- Coverage                     88.81%   88.80%   -0.01%     
============================================================
  Files                           287      287              
  Lines                         63255    63271      +16     
  Branches                       7932     7934       +2     
============================================================
+ Hits                          56179    56190      +11     
- Misses                         4745     4746       +1     
- Partials                       2331     2335       +4     

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.