Symfony 4: Var-dumper not working properly

5
votes

I tried to use the wonderful dump function from the var-dumper bundle in symfony 4 and for some reason I get the following error:

Failed to start the session because headers have already been sent by "vendor\symfony\var-dumper\Dumper\AbstractDumper.php" at line 181.

Additionally, when I try to use the {% dump foo %} tag in a twig template I get an error:

Unknown "dump" tag.

Can anyone help me?

1
phpsymfonytwigbundlevar-dump
dump is not a tag, it's a function. So change {% dump foo %} into {% dump(foo) %} – Matias Kinnunen
Quoting from symfony.com/doc/current/templating/debug.html: {% dump foo.bar %} is the way to go when the original template output shall not be modified: variables are not dumped inline, but in the web debug toolbar; – iiirxs
Also if you want to use dump function in twig template you should use {{ dump(foo) }}, not {% dump(foo) %} – iiirxs
Oh, you are right about the dump tag. And yeah, my bad, I meant to say {{ dump(foo) }}. – Have you installed symfony/var-dumper or symfony/debug-bundle? See symfony.com/doc/current/components/var_dumper.html#installation – Matias Kinnunen
symfony/var-dumper is automagically disabled on production environment. Check your symfony environment. – Rendy Eko Prastiyo

1 Answers

12
votes

A guy named Simon Waldburger mentioned in the lesson's comments that installing "debug" fixed the issue (it fixed it for me). The instruction was in the next lesson.

composer require debug --dev

iiirxs is also correct, to output dump in twig file, do 

{{ dump(variable) }}