Implement bootstrap file autodiscovering

features/configuration/autodiscovering_application_kernel.feature

@@ -49,7 +49,7 @@ Feature: Autodiscovering the application kernel
                     - "@service_container"
         """
 
-    Scenario: Autodiscovering kernel in Symfony 3 directory structure application
+    Scenario: Autodiscovering kernel in Symfony 4 directory structure application
         Given a kernel file "src/Kernel.php" containing:
         """
         <?php
@@ -91,7 +91,7 @@ Feature: Autodiscovering the application kernel
         When I run Behat
         Then it should pass
 
-    Scenario: Autodiscovering kernel in Symfony 4 directory structure application
+    Scenario: Autodiscovering kernel in Symfony 3 directory structure application
         Given a kernel file "app/AppKernel.php" containing:
         """
         <?php

features/configuration/autodiscovering_bootstrap_file.feature

@@ -0,0 +1,101 @@
+Feature: Autodiscovering bootstrap file
+
+    Background:
+        Given a working Symfony application with SymfonyExtension configured
+        And a Behat configuration containing:
+        """
+        default:
+            suites:
+                default:
+                    contexts:
+                        - App\Tests\SomeContext
+        """
+        And a context file "tests/SomeContext.php" containing:
+        """
+        <?php
+
+        namespace App\Tests;
+
+        use Behat\Behat\Context\Context;
+
+        final class SomeContext implements Context {
+            private $parameter;
+
+            public function __construct(?string $parameter = null) { $this->parameter = $parameter; }
+
+            /** @Then the passed parameter should be :expected */
+            public function parameterShouldBe(string $expected): void { assert($this->parameter === $expected); }
+        }
+        """
+        And a YAML services file containing:
+        """
+        services:
+            App\Tests\SomeContext:
+                public: true
+                arguments:
+                    - "%env(CUSTOM_VARIABLE)%"
+        """
+        And a feature file containing:
+        """
+        Feature:
+            Scenario:
+                Then the passed parameter should be "lol2"
+        """
+
+    Scenario: Autodiscovering bootstrap file in Symfony 4 directory structure application
+        Given a boostrap file "config/bootstrap.php" containing:
+        """
+        <?php
+
+        putenv("CUSTOM_VARIABLE=lol2");
+        $_SERVER['CUSTOM_VARIABLE'] = $_ENV['CUSTOM_VARIABLE'] = 'lol2';
+        """
+        When I run Behat
+        Then it should pass
+
+    Scenario: Autodiscovering bootstrap file in Symfony 3 directory structure application
+        Given a boostrap file "app/autoload.php" containing:
+        """
+        <?php
+
+        putenv("CUSTOM_VARIABLE=lol2");
+        $_SERVER['CUSTOM_VARIABLE'] = $_ENV['CUSTOM_VARIABLE'] = 'lol2';
+        """
+        When I run Behat
+        Then it should pass
+
+    Scenario: Failing to autodiscover the bootstrap file
+        Given a boostrap file "config/bootstrap.php" containing:
+        """
+        <?php
+
+        putenv("CUSTOM_VARIABLE=lol2");
+        $_SERVER['CUSTOM_VARIABLE'] = $_ENV['CUSTOM_VARIABLE'] = 'lol2';
+        """
+        And a boostrap file "app/autoload.php" containing:
+        """
+        <?php
+
+        putenv("CUSTOM_VARIABLE=lol2");
+        $_SERVER['CUSTOM_VARIABLE'] = $_ENV['CUSTOM_VARIABLE'] = 'lol2';
+        """
+        When I run Behat
+        Then it should fail with "Could not autodiscover the bootstrap file"
+
+    Scenario: Not loading autodiscovered bootstrap file if explicitly disabled
+        Given a boostrap file "config/bootstrap.php" containing:
+        """
+        <?php
+
+        putenv("CUSTOM_VARIABLE=lol2");
+        $_SERVER['CUSTOM_VARIABLE'] = $_ENV['CUSTOM_VARIABLE'] = 'lol2';
+        """
+        And a Behat configuration containing:
+        """
+        default:
+            extensions:
+                FriendsOfBehat\SymfonyExtension:
+                    bootstrap: false
+        """
+        When I run Behat
+        Then it should fail with "Symfony\Component\DependencyInjection\Exception\EnvNotFoundException"

src/ServiceContainer/SymfonyExtension.php

@@ -86,7 +86,7 @@ final class SymfonyExtension implements Extension
 
     public function process(ContainerBuilder $container): void
     {
-        $this->processBootstrap($container->getParameter('fob_symfony.bootstrap'));
+        $this->processBootstrap($this->autodiscoverBootstrap($container->getParameter('fob_symfony.bootstrap')));
     }
 
     private function registerMinkDriver(ExtensionManager $extensionManager): void
@@ -193,6 +193,44 @@ final class SymfonyExtension implements Extension
         return $config;
     }
 
+    /**
+     * @param string|bool|null $bootstrap
+     */
+    private function autodiscoverBootstrap($bootstrap): ?string
+    {
+        if (is_string($bootstrap)) {
+            return $bootstrap;
+        }
+
+        if ($bootstrap === false) {
+            return null;
+        }
+
+        $autoconfigured = 0;
+
+        if (file_exists('config/bootstrap.php')) {
+            $bootstrap = 'config/bootstrap.php';
+
+            ++$autoconfigured;
+        }
+
+        if (file_exists('app/autoload.php')) {
+            $bootstrap = 'app/autoload.php';
+
+            ++$autoconfigured;
+        }
+
+        if ($autoconfigured === 2) {
+            throw new \RuntimeException(
+                'Could not autodiscover the bootstrap file. ' .
+                'Please define it manually with "FriendsOfBehat\SymfonyExtension.bootstrap" configuration option. ' .
+                'Setting that option to "false" disables autodiscovering.'
+            );
+        }
+
+        return is_string($bootstrap) ? $bootstrap : null;
+    }
+
     private function processBootstrap(?string $bootstrap): void
     {
         if ($bootstrap === null) {