EXPLAIN VERBOSE fails on INSERT into an IDENTITY column table: `T_NextValueExpr deparse arm unported`

[lrweck]

EXPLAIN VERBOSE fails on INSERT into an IDENTITY column table: T_NextValueExpr deparse arm unported

pgrust version: 0.2 (binary pgrust-0.2-linux-x86_64, PostgreSQL 18 compatible)
Component: ruleutils.c / get_rule_expr() deparse of T_NextValueExpr

Summary

EXPLAIN VERBOSE (with or without ANALYZE) errors out on any INSERT targeting a table with a GENERATED ALWAYS AS IDENTITY column, when the identity column is not listed in the INSERT's target list. PostgreSQL emits a T_NextValueExpr in the plan for the identity default and the pgrust deparse path for that node type is not ported (arm unported).

Reproducer

CREATE TABLE t (id bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY, v int);
EXPLAIN (VERBOSE) INSERT INTO t (v) VALUES (1);

Note: serial columns are NOT affected (deparse via DEFAULT nextval works); only GENERATED AS IDENTITY triggers the unported code path.

Expected behaviour

A normal query plan like PostgreSQL 18.6 produces, e.g.:

 Insert on t_identity  (cost=0.00..0.01 rows=0 width=0)
   ->  Result  (cost=0.00..0.01 rows=1 width=8)
         Output: nextval('t_identity_id_seq'::regclass), 1

Actual behaviour

ERROR:  ruleutils (get_rule_expr): T_NextValueExpr deparse arm unported

Workaround: re-run the EXPLAIN without VERBOSE (the plan prints, but the Output: line and any identity nextval expression are dropped from the output).

Notes

• Triggered regardless of ANALYZE/BUFFERS — VERBOSE alone is sufficient.
• Affects every table with a GENERATED ALWAYS AS IDENTITY pk column (8/9 tables in the benchmark schema use it).

[malisper]

Fixed on current main (PR #472, 2026-08-08): get_rule_expr deparses NextValueExpr as nextval('seq'), matching PostgreSQL 18.6 byte-for-byte (C's arm appends no ::regclass; that form belongs to a serial column's DEFAULT). Pinned in scripts/explain-verbose-e2e.sh with EXPLAIN (VERBOSE) INSERT statements into GENERATED ALWAYS AS IDENTITY tables (VALUES, INSERT … SELECT … RETURNING) and a serial control, byte-diffed against C 18 — landing in Pager-Free/pgrust-fast#2062. Closing.