My talk at the Symfony Online 2023 Conference. Many developers fail to use a debugger like Xdebug in their day to day activities. In this talk we explain: - Why you really want to be using a debugger - How do you install and configure it easily - How it interacts with your Symfony application - How you can use it for more than just debugging your application, how you can actually use it to drive your development.

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DDD
Debugger Driven Development
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Hello world!
Carlos Granados
I have been a software developer for more than 30 years. In the development space I have
done everything: I have done games, e-commerce, APIs, backend, frontend, Android, SRE,
DevOps... And I have worked with multiple languages and technologies: C++, PHP
, Java,
JavaScript, SQL, MongoDB, Docker…
PHP 100%
Symfony 100%
Debugging 100%

4. https://fastdebug.io
Looking for beta users!

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DDD
Debugger Driven Development
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- What is Xdebug and some reasons why people don’t use it
- How to enable and configure it in a Symfony project
- Use cases, going beyond just debugging
- Other alternatives

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What is Xdebug ?
The most widely used step-by-
step debugger for the PHP
language.
An open source PHP
extension created by
Derick Rethans and
launched in 2002
Provides all the expected
tools: breakpoints, step-by-
step, stack traces, variables,
expression evaluation…
It is more than a debugger:
profiling, code coverage,
tracing, improved error
handling…
https://xdebug.org/

7. 2 0 1 9 . A l l R i g h t s R e s e r v e d
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8. 2 0 1 9 . A l l R i g h t s R e s e r v e d
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Xdebug is slow
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- It can make your code between 60% and 300% slower
- It has improved a lot in version 3
- Make sure you use the right configuration
- You can always give FastDebug a go!

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Xdebug is hard to set up
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- It can really be difficult to configure and get it running
- You only need to do it once
- Derick has produced some really good helper videos
- I am working on a wizard that will greatly simplify the process

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I don’t need a debugger
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- My code is fully tested so I don’t have any bugs
- Don’t believe this can be the case in a real world scenario
- The system is not complex enough
- Symfony has 279 open bugs at the time of writing

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What do people use
instead of a Xdebug?
D & D
Dump & Die

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What’s wrong with dump & die?
It only provides a very narrow
and limited view into your code.
It usually requires
several iterations to get
to the heart of the
problem
Many times it can be difficult to
record the output.
Requires modification of your
code, with the possibility of
leaving debugging code behind.
It’s like using alert()!

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Debugging is like using a
security camera
Using Dump & die is like using a
camera that only takes photos of a
limited part of the scene.
Using a Debugger is like using a
camera that records video and which
you can pan around.

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1. # Dockerfile
2. ...
3. FROM app_php AS app_php_dev
4.
5. ENV APP_ENV=dev XDEBUG_MODE=off
6. ...
7. RUN set -eux;
8. install-php-extensions xdebug
Using Xdebug with Symfony
It’s loaded by default if using symfony-docker

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1. > docker-compose exec php php -v
2.
3. PHP 8.1.19 (cli) (built: May 13 2023 01:08:01) (NTS)
4. Copyright (c) The PHP Group
5. Zend Engine v4.1.19, Copyright (c) Zend Technologies
6. with Zend OPcache v8.1.19, Copyright (c), by Zend Technologies
7. with Xdebug v3.2.1, Copyright (c) 2002-2023, by Derick Rethans
Using Xdebug with Symfony
Check that it is correctly loaded

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Using Xdebug with Symfony
Check it using the profiler

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1. ;docker/php/conf.d/app.dev.ini
2. ...
3. xdebug.client_host = 'host.docker.internal’
4. xdebug.start_with_request = yes
Using Xdebug with Symfony
Enabling the debugger
1. > docker-compose build

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1. # Dockerfile
2. ...
3. ENV APP_ENV=dev XDEBUG_MODE=debug
Using Xdebug with Symfony
Enabling the debugger
1. > XDEBUG_MODE=debug docker-compose up -d

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Use the debugger to explore code
Learn about the internals of the
framework (recommended in the
Symfony docs).
Learn about the inner
working of your
dependencies.
Learn about the interface to
APIs, investigate requests and
responses.
Understand legacy code or
functionality which is not well
documented.

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Use the debugger to test code
Step through code to understand
how it works and what needs to
be tested.
Experiment with your
code to understand how
it behaves under different
inputs.
Look under the hod when
doing black box testing.
Remember that Xdebug can
also provide code coverage,
which is really important for
testing.

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Use the debugger to review code
Specially useful if you are
reviewing code that you are not
very familiar with.
Check out the previous
version of the code and
check how it works.
Check out the new version of
the code and check out how
the functionality has changed.
Experiment with new inputs to
confirm that the new code is
behaving as expected.

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Use the debugger for concurrency
Concurrency issues can be
specially difficult to debug or test.
Setup a breakpoint in
one of the processes and
let it run until it is hit.
Set another breakpoint in
another process and again let
it run until it is hit.
Now use step debugging
alternating in both processes to
test what happens when they
run concurrently.

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Alternatives:
SnapshotDebugger
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- Based on the Stackdriver Debugger by Google (deprecated)
- Open source tool developed by Google
- Allows you to debug code running in production
- Works using a daemon that communicates with a Firebase RTDB

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Alternatives:
SnapshotDebugger
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- Requires adding a PHP extension to enable the breakpoints
- When a breakpoint is hit it just records info without stopping
- When the request finishes this info is sent to Firebase or logged
- It is throttled so that it does not use too much CPU or memory

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Alternatives:
SnapshotDebugger
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https://github.com/i6systems/stackdriver-debugger-php-extension
https://github.com/googleapis/google-cloud-php-debugger
https://github.com/GoogleCloudPlatform/snapshot-debugger

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Alternatives:
Ray
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- It is like Dump & Die on steroids
- Adds a new “Ray()” function that allows you to record any data
- This information is collected by a desktop application
- It is a paid tool and it requires modifications to your code
https://myray.app/

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Thank you!
carlos@fastdebug.io
carlos-granados
@carlos_granados