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Bug Reproducer

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Triaging issues and pull requests is seriously, the best. But, occasionally, you might be the person who finds the bug! That happened to me just today, and I want to report it!

To make the best possible bug report, we should create a "reproducer": a Symfony project that shows the bug with as little code as possible. I don't have the error I saw in front of me now, but it was pretty simple: I created a form class, tried to use it in my controller, then boom! I got a very strange container cache error.

Creating the Reproducer Project

The bug happened when I was playing with the master branch of Symfony. So, let's create our new reproducer project based on that:

composer create-project symfony/skeleton:dev-master container_bug_reproducer

When that finishes, move into the new directory:

cd container_bug_reproducer/

The one package I know I need is form. Get it installed:

composer require form

While we're waiting for this to finish, go back to PhpStorm, close a few files, and go into the new directory. To reproduce my error, I know I need a new form class. Right inside src/, create a new PHP class: SomeFormType. My creativity today is off the charts. Make this extend the usual AbstractType:

... lines 1 - 2
namespace App;
use Symfony\Component\Form\AbstractType;
class SomeFormType extends AbstractType

Normally, we would also add the buildForm() method. But... I'm not even sure that's needed to trigger the bug. So, in the spirit of making our reproducer as small and focused as possible, let's skip it, until we know it's needed.

In the Controller/ directory, create another new PHP class: ContainerTestController in the App\Controller namespace. Give it the usual public function test():

... lines 1 - 2
namespace App\Controller;
... lines 4 - 7
class ContainerTestController extends AbstractController
public function test()
... lines 12 - 13

Because we need to create a form, extend AbstractController from FrameworkBundle so we have that shortcut:

... lines 1 - 2
namespace App\Controller;
... lines 4 - 5
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
class ContainerTestController extends AbstractController
... lines 10 - 14

Then, $form = $this->createForm() and pass SomeFormType::class:

... lines 1 - 2
namespace App\Controller;
use App\SomeFormType;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
class ContainerTestController extends AbstractController
public function test()
$form = $this->createForm(SomeFormType::class);
// error will happen on previous line

If I'm right, the error will happen right here. To test this, find routes.yaml, uncomment the route and point the controller to our code:

path: /
controller: App\Controller\ContainerTestController::test

We're ready! Go back to the terminal and start the built-in web server:

php -S localhost:8000 -t public

Move back, find that browser tab and... refresh! Say hello to the super weird error:

Compile error: failed opening required file

... in some var/cache/dev directory. This is related to the container, and it's very low-level code. It's possible I'm doing something wrong, but this really looks like a bug.

To be sure, let's stop the web server, manually clear the cache directory with:

rm -rf var/cache/*

restart the server and try it again. Same error. Let's take a screenshot: it's so useful to be able to see the full stacktrace of an error.

Opening the Bug Issue

Go back to the Symfony repository and click to open a new issue. Yep, this is a "Bug Report". And, this is cool! We have a nice outline of all the info needed. Affected versions: master. This could be a bug on a stable version, and that is something we could check. But, since it would be such a critical and obvious bug, it's probably just on master.

For description, let's describe what we're trying to do. I'll also upload my error screenshot. Oh, and I forgot a title: I'll reference part of the error message for this.

Pushing the Reproducer to GitHub

Under "How to Reproduce", ah, this is where our issue will shine! Let's push our test project up to GitHub so we can share it.

Move back to the terminal, stop the web server, then initialize a new Git repository with:

git init git add . git commit

and a message. Next, go to GitHub, click "New", type a name and click "Create Repository". Copy the two lines near the bottom for an existing repository. Then, find your terminal and... paste!

That's it! Refresh the page on GitHub: here is our simple reproducer app. Copy its URL. Then, head back to the issue. Let's mention our reproducer app first and how to trigger the error on it.

Then, to make life even easier, summarize what we did to get the error. As extra credit, I'll even link right to the line that triggers it.

And... that's it! I don't have any possible solution: this error is way above my pay grade. And, that's ok. Finish the message and... submit!

We're done! This is a bug report worth being proud of.

And, to prove it! I have an update! This issue was fixed less than 3 hours after we posted this. That's amazing.

Next, let's jump into how we can contribute code to Symfony via a pull request.

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