system/Database/BaseUtils.php
public function listDatabases()
	{
		// Is there a cached result?
		if (isset($this->db->dataCache['db_names']))
		{
			return $this->db->dataCache['db_names'];
		}
		elseif ($this->listDatabases === false)
		{
			if ($this->db->DBDebug)
			{
				throw new DatabaseException('Unsupported feature of the database platform you are using.');
			}
			return false;
		}

		$this->db->dataCache['db_names'] = [];

		$query = $this->db->query($this->listDatabases);
		if ($query === false)
		{
			return $this->db->dataCache['db_names'];
		}

		for ($i = 0, $query = $query->getResultArray(), $c = count($query); $i < $c; $i ++)
		{
			$this->db->dataCache['db_names'][] = current($query[$i]);
		}

		return $this->db->dataCache['db_names'];
	}
public function listDatabases()
	{
		// Is there a cached result?
		if (isset($this->db->dataCache['db_names']))
		{
			return $this->db->dataCache['db_names'];
		}
		elseif ($this->listDatabases === false)
		{
			if ($this->db->DBDebug)
			{
				throw new DatabaseException('Unsupported feature of the database platform you are using.');
			}
			return false;
		}

		$this->db->dataCache['db_names'] = [];

		$query = $this->db->query($this->listDatabases);
		if ($query === false)
		{
			return $this->db->dataCache['db_names'];
		}

		for ($i = 0, $query = $query->getResultArray(), $c = count($query); $i < $c; $i ++)
		{
			$this->db->dataCache['db_names'][] = current($query[$i]);
		}

		return $this->db->dataCache['db_names'];
	}
List databases

@return array|boolean
@throws \CodeIgniter\Database\Exceptions\DatabaseException