NEW DatabaselessKernel to support operation without DB

This is required for GraphQL code generation in CI (without a working runtime database/webserver environment).
Context: silverstripe/silverstripe-graphql#388

composer.json

@@ -32,6 +32,7 @@
         "psr/container": "1.0.0",
         "silverstripe/config": "^1@dev",
         "silverstripe/assets": "^1@dev",
+        "silverstripe/event-dispatcher": "^0.1.0",
         "silverstripe/vendor-plugin": "^1.4",
         "sminnee/callbacklist": "^0.1",
         "swiftmailer/swiftmailer": "~5.4",

src/Core/DatabaselessKernel.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace SilverStripe\Core;
+
+use SilverStripe\EventDispatcher\Dispatch\Dispatcher;
+use SilverStripe\EventDispatcher\Event\EventContextInterface;
+use SilverStripe\EventDispatcher\Event\EventHandlerInterface;
+use SilverStripe\ORM\Connect\NullDatabase;
+use SilverStripe\ORM\DB;
+
+/**
+ * Boot a kernel without requiring a database connection.
+ * This is a workaround for the lack of composition in the boot stages
+ * of CoreKernel, as well as for the framework's misguided assumptions
+ * around the availability of a database for every execution path.
+ *
+ * @internal
+ */
+class DatabaselessKernel extends CoreKernel
+{
+    protected $queryErrorMessage = 'Booted with DatabaseLessKernel, cannot execute query: %s';
+
+    /**
+     * Allows disabling of the configured error handling.
+     * This can be useful to ensure the execution context (e.g. composer)
+     * can consistently use its own error handling.
+     *
+     * @var boolean
+     */
+    protected $bootErrorHandling = true;
+
+    public function setBootErrorHandling(bool $bool)
+    {
+        $this->bootErrorHandling = $bool;
+        return $this;
+    }
+
+    public function boot($flush = false)
+    {
+        $this->flush = $flush;
+
+        $this->bootPHP();
+        $this->bootManifests($flush);
+
+        if ($this->bootErrorHandling) {
+            $this->bootErrorHandling();
+        }
+
+        $this->bootConfigs();
+
+        $this->booted = true;
+    }
+}

src/ORM/Connect/NullDatabase.php

@@ -0,0 +1,314 @@
+<?php
+
+namespace SilverStripe\ORM\Connect;
+
+use BadMethodCallException;
+use Exception;
+
+/**
+ * Utility class required due to bad coupling in framework.
+ * Not every framework execution should require a working database connection.
+ * For example, when generating class and config manifests for deployment bundles,
+ * or when generating code in a silverstripe/graphql schema build.
+ *
+ * This class creates the required no-ops to fulfill the contract,
+ * and create exceptions as required.
+ *
+ * It also avoids introducing new third party core dependencies that
+ * would be required with https://github.com/tractorcow/silverstripe-proxy-db.
+ *
+ * @internal
+ */
+class NullDatabase extends Database
+{
+
+    /**
+     * @var string
+     */
+    protected $errorMessage = 'Using NullDatabase, cannot interact with database';
+
+    /**
+     * @var string
+     */
+    protected $queryErrorMessage = 'Using NullDatabase, cannot execute query: %s';
+
+    /**
+     * @param string $msg
+     * @return self
+     */
+    public function setErrorMessage(string $msg)
+    {
+        $this->errorMessage = $msg;
+        return $this;
+    }
+
+    /**
+     * @param string $msg
+     * @return self
+     */
+    public function setQueryErrorMessage(string $msg)
+    {
+        $this->queryErrorMessage = $msg;
+        return $this;
+    }
+
+    public function query($sql, $errorLevel = E_USER_ERROR)
+    {
+        throw new \LogicException(sprintf($this->queryErrorMessage, $sql));
+    }
+
+    public function preparedQuery($sql, $parameters, $errorLevel = E_USER_ERROR)
+    {
+        throw new \LogicException(sprintf($this->queryErrorMessage, $sql));
+    }
+
+    public function getConnector()
+    {
+        throw new \LogicException($this->errorMessage);
+    }
+
+    public function getSchemaManager()
+    {
+        throw new \LogicException($this->errorMessage);
+    }
+
+    public function getQueryBuilder()
+    {
+        throw new \LogicException($this->errorMessage);
+    }
+
+    public function getGeneratedID($table)
+    {
+        // no-op
+    }
+
+    public function isActive()
+    {
+        return true;
+    }
+
+    public function escapeString($value)
+    {
+        return $value;
+    }
+
+    public function quoteString($value)
+    {
+        return $value;
+    }
+
+    public function escapeIdentifier($value, $separator = '.')
+    {
+        return $value;
+    }
+
+    protected function escapeColumnKeys($fieldValues)
+    {
+        return $fieldValues;
+    }
+
+    public function manipulate($manipulation)
+    {
+        throw new \LogicException($this->errorMessage);
+    }
+
+    public function clearAllData()
+    {
+        throw new \LogicException($this->errorMessage);
+    }
+
+    public function clearTable($table)
+    {
+        throw new \LogicException($this->errorMessage);
+    }
+
+    public function nullCheckClause($field, $isNull)
+    {
+        return '';
+    }
+
+    public function comparisonClause(
+        $field,
+        $value,
+        $exact = false,
+        $negate = false,
+        $caseSensitive = null,
+        $parameterised = false
+    ) {
+        return '';
+    }
+
+    public function formattedDatetimeClause($date, $format)
+    {
+        return '';
+    }
+
+    public function datetimeIntervalClause($date, $interval)
+    {
+        return '';
+    }
+
+    public function datetimeDifferenceClause($date1, $date2)
+    {
+        return '';
+    }
+
+    public function concatOperator()
+    {
+        return '';
+    }
+
+    public function supportsCollations()
+    {
+        return false;
+    }
+
+    public function supportsTimezoneOverride()
+    {
+        return false;
+    }
+
+    public function getVersion()
+    {
+        return '';
+    }
+
+    public function getDatabaseServer()
+    {
+        return '';
+    }
+
+    public function affectedRows()
+    {
+        return 0;
+    }
+
+    public function searchEngine(
+        $classesToSearch,
+        $keywords,
+        $start,
+        $pageLength,
+        $sortBy = "Relevance DESC",
+        $extraFilter = "",
+        $booleanSearch = false,
+        $alternativeFileFilter = "",
+        $invertedMatch = false
+    ) {
+        // no-op
+    }
+
+    public function supportsTransactions()
+    {
+        return false;
+    }
+
+    public function supportsSavepoints()
+    {
+        return false;
+    }
+
+
+    public function supportsTransactionMode(string $mode): bool
+    {
+        return false;
+    }
+
+    public function withTransaction(
+        $callback,
+        $errorCallback = null,
+        $transactionMode = false,
+        $errorIfTransactionsUnsupported = false
+    ) {
+        // no-op
+    }
+
+    public function supportsExtensions($extensions)
+    {
+        return false;
+    }
+
+    public function transactionStart($transactionMode = false, $sessionCharacteristics = false)
+    {
+        // no-op
+    }
+
+    public function transactionSavepoint($savepoint)
+    {
+        // no-op
+    }
+
+    public function transactionRollback($savepoint = false)
+    {
+        // no-op
+    }
+
+    public function transactionEnd($chain = false)
+    {
+        // no-op
+    }
+
+    public function transactionDepth()
+    {
+        return 0;
+    }
+
+    public function supportsLocks()
+    {
+        return false;
+    }
+
+    public function canLock($name)
+    {
+        return false;
+    }
+
+    public function getLock($name, $timeout = 5)
+    {
+        return false;
+    }
+
+    public function releaseLock($name)
+    {
+        return false;
+    }
+
+    public function connect($parameters)
+    {
+        // no-op
+    }
+
+    public function databaseExists($name)
+    {
+        return false;
+    }
+
+    public function databaseList()
+    {
+        return [];
+    }
+
+    public function selectDatabase($name, $create = false, $errorLevel = E_USER_ERROR)
+    {
+        // no-op
+    }
+
+    public function dropSelectedDatabase()
+    {
+        // no-op
+    }
+
+    public function getSelectedDatabase()
+    {
+        // no-op
+    }
+
+    public function now()
+    {
+        return '';
+    }
+
+    public function random()
+    {
+        return '';
+    }
+}