query! macros fail against CockroachDB in 0.9.0: SET inside DO block not supported

[BastienClement]

I have found these related issues/pull requests

This was introduced in #3541 (force generic plans for nullability inference).

Description

Since 0.9.0, every compile-time query macro (query!, query_as!, query_scalar!) fails when run against a CockroachDB database. On each new describe connection, sqlx-macros-core runs a DO $$ … $$ block containing a SET SESSION statement, and CockroachDB does not implement SET inside a function/DO body. This breaks compile-time-checked queries against CockroachDB entirely.

This is a regression from 0.8.x, which had no such statement. It is significant, as this makes compile-time checked SQL unusable!

Error

error: error returned from database: unimplemented: SET usage inside a function definition
(SQLSTATE 0A000)

Root cause

sqlx-macros-core/src/database/mod.rs, in CachingDescribeBlocking::describe (the hash_map::Entry::Vacant arm), runs the following on every newly opened Postgres describe connection:

DO $$
BEGIN
    IF EXISTS (SELECT 1 FROM pg_settings WHERE name = 'plan_cache_mode') THEN
        SET SESSION plan_cache_mode = 'force_generic_plan';
    END IF;
END $$;

CockroachDB rejects SET inside a routine/DO body at parse/build time, so the IF EXISTS (… 'plan_cache_mode') guard does not help — the block is rejected before it ever runs, regardless of whether plan_cache_mode exists. The failure happens during connection setup, before any user query is described, so it is independent of the query and the schema.

Proposed fix

Skip the plan_cache_mode setup for CockroachDB. sqlx already detects CockroachDB elsewhere — is_explain_available() in sqlx-postgres/src/connection/describe.rs checks for the crdb_version parameter status. The same detection could gate this block.

Reproduction steps

Point DATABASE_URL at a CockroachDB instance and compile any crate containing a query! macro. Or run the block above directly against CockroachDB.

SQLx version

0.9.0

Enabled SQLx features

postgres

Database server and version

CockroachDB v26.2

Operating system

Linux

Rust version

1.95.0