Deprecate PostgreSQL-specific connection parameters and behavior

[morozov]

The default_dbname parameter was introduced in #2284 as a hack that was supposed to address doctrine/DoctrineBundle#402.

My understanding of the hack is that it would force the connection to return the database currently connected to instead of the database specified in the configuration:

dbal/lib/Doctrine/DBAL/Driver/AbstractPostgreSQLDriver.php

Lines 134 to 136 in 253b602

	return (isset($params['dbname']))
	? $params['dbname']
	: $conn->query('SELECT CURRENT_DATABASE()')->fetchColumn();

This hack is irrelevant as of #3606. Since 3.0.0, the connection will always return the name of the database currently connected to. Therefore, this parameter is no longer necessary.

---

The reason to hardcode postgres as the default database doesn't seem valid:

dbal/src/Driver/PDO/PgSQL/Driver.php

Line 79 in d5da8b4

// Connecting without an explicit database does not work, therefore "postgres" database is used

According to this article,

The default name of the database is the same as that of the user.

This could be reproduced with the following script:

<?php

$conn = new PDO('pgsql:host=localhost;port=5432;user=postgres;password=Passw0rd');

if (!$conn) {
    exit(1);
}

echo $conn->query('SELECT CURRENT_DATABASE()')
    ->fetch(PDO::FETCH_COLUMN), PHP_EOL;
// postgres

In any event, it is not the job of the DBAL to provide such defaults. If the user is not happy with the defaults provided by the driver, they should provide the database name explicitly.

[greg0ire]

This parameter appears to be unused

[greg0ire]

Same here