Do you think it's technically possible to enable only the var_dump with JIT?

I just had a look, and that looks technically feasible. However, I maintain that Xdebug should not be installed on production environments, and that this issue will not have my high priority.

If not, is there any option to install it as a stand-alone?

No, there is not.

or do you know of a php function that can format the var_dump the same way Xdebug does it?

I don't think that there is anything that does the exact same format, but there are similar tools in

• Kint: https://kint-php.github.io/kint/
• Symfony's varDumper: https://symfony.com/doc/current/components/var_dumper.html

Turns out that I am wrong, and that you can do this already :-)

If you start xdebug.mode=off then the function overload that JIT doesn't like (zend_execute_ex) does not get changed, and hence JIT should function. You can then use Xdebug's xdebug_var_dump() function without problems.

Compare:

<pre>
$ php -dopcache.enable_cli=1 -dopcache.jit_buffer_size=100M -dxdebug.cli_color=2 -r 'xdebug_var_dump("FOO");'

Warning: JIT is incompatible with third party extensions that override zend_execute_ex(). JIT disabled. in Unknown on line 0
Command line code:1:
string(3) "FOO"
</pre>

with:
<pre>
$ php -dopcache.enable_cli=1 -dopcache.jit_buffer_size=100M -dxdebug.cli_color=2 -dxdebug.mode=off -r 'xdebug_var_dump("FOO");'
Command line code:1:
string(3) "FOO"
</pre>