[9.x] Alternative database name in Postgres DSN, allow pgbouncer aliased databases to continue working on 9.x (#43542)

* feat: allow creating a Postgres DSN string with a different database name than is used for information_schema queries

See #43536

* formatting

Co-authored-by: Taylor Otwell <taylor@laravel.com>

Author: AlbinoDrought

src/Illuminate/Database/Connectors/PostgresConnector.php

@@ -163,6 +163,11 @@ protected function getDsn(array $config)
 
         $host = isset($host) ? "host={$host};" : '';
 
+        // Sometimes - users may need to connect to a database that has a different
+        // name than the database used for "information_schema" queries. This is
+        // typically the case if using "pgbouncer" type software when pooling.
+        $database = $connect_via_database ?? $database;
+
         $dsn = "pgsql:{$host}dbname='{$database}'";
 
         // If a port was specified, we will add it to this Postgres DSN connections

tests/Database/DatabaseConnectorTest.php

@@ -216,6 +216,22 @@ public function testPostgresApplicationNameIsSet()
         $this->assertSame($result, $connection);
     }
 
+    public function testPostgresApplicationUseAlternativeDatabaseName()
+    {
+        $dsn = 'pgsql:dbname=\'baz\'';
+        $config = ['database' => 'bar', 'connect_via_database' => 'baz'];
+        $connector = $this->getMockBuilder(PostgresConnector::class)->onlyMethods(['createConnection', 'getOptions'])->getMock();
+        $connection = m::mock(stdClass::class);
+        $connector->expects($this->once())->method('getOptions')->with($this->equalTo($config))->willReturn(['options']);
+        $connector->expects($this->once())->method('createConnection')->with($this->equalTo($dsn), $this->equalTo($config), $this->equalTo(['options']))->willReturn($connection);
+        $statement = m::mock(PDOStatement::class);
+        $connection->shouldReceive('prepare')->zeroOrMoreTimes()->andReturn($statement);
+        $statement->shouldReceive('execute')->zeroOrMoreTimes();
+        $result = $connector->connect($config);
+
+        $this->assertSame($result, $connection);
+    }
+
     public function testPostgresConnectorReadsIsolationLevelFromConfig()
     {
         $dsn = 'pgsql:host=foo;dbname=\'bar\';port=111';