Cannot scan/insert user defined UUIDs.

[dfonnegra]

Describe the bug
After migrating from v4 to v5. Inserting or scanning custom defined uuid's stopped working.

To Reproduce
Steps to reproduce the behavior:

If possible, please provide runnable example such as:

package main

import (
	"context"
	"fmt"
	"os"

	"github.com/gofrs/uuid/v5"
	pgxuuid "github.com/jackc/pgx-gofrs-uuid"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"
)

type ProviderID uuid.UUID

func main() {
	dbconfig, err := pgxpool.ParseConfig(os.Getenv("DATABASE_URL"))
	if err != nil {
		fmt.Println("could not parse db config: ", err)
		return
	}

	ctx := context.Background()
	dbconfig.AfterConnect = func(_ context.Context, conn *pgx.Conn) error {
		pgxuuid.Register(conn.TypeMap())
		return nil
	}

	pool, err := pgxpool.NewWithConfig(ctx, dbconfig)
	if err != nil {
		fmt.Println("could not create pool: ", err)
		return
	}
	defer pool.Close()

	_, err = pool.Exec(ctx, "CREATE TABLE IF NOT EXISTS test (id UUID PRIMARY KEY)")
	if err != nil {
		fmt.Println("could not create table: ", err)
		return
	}

	_, err = pool.Exec(ctx, "INSERT INTO test (id) VALUES ($1)", ProviderID(uuid.Must(uuid.NewV4())))
	if err != nil {
		fmt.Println("could not insert value: ", err)
		return
	}

	rows, err := pool.Query(ctx, "SELECT id FROM test")
	if err != nil {
		fmt.Println("could not query: ", err)
		return
	}
	defer rows.Close()
	for rows.Next() {
		var id ProviderID
		if err := rows.Scan(&id); err != nil {
			fmt.Println("could not scan: ", err)
			return
		}
		fmt.Println("id: ", id)
	}
}

Expected behavior
pgx should detect that the variable is an uuid and encode/decode it properly.

Actual behavior
It fails. When scanning this is the error:

could not scan:  can't scan into dest[0]: cannot scan uuid (OID 2950) in binary format into *main.ProviderID

when inserting this is the error:

could not insert value:  failed to encode args[0]: unable to encode main.ProviderID{0x84, 0x33, 0x6c, 0x48, 0x7, 0x10, 0x4a, 0xe2, 0x88, 0xc5, 0x49, 0xbb, 0xef, 0x7a, 0x3f, 0x30} into binary format for uuid (OID 2950): cannot find encode plan

However if I change the custom uuids by raw uuids, it works.

Version

• Go: $ go version -> go version go1.21.5 darwin/arm64
• pgx: $ grep 'github.com/jackc/pgx/v[0-9]' go.mod -> github.com/jackc/pgx/v5 v5.6.0

Additional context
This represents a huge migration burden as the app contains more than 1.000 places where this needs to be fixed and I'm sure it's not uncommon.