I see an issue here anyway: This assumes that the function call is its own statement. Adding a semi-colon before will not fix the issue, it will just change it. The issue is that Twig does not ensure that function calls are their own statement (quite the opposite actually), so this way to trigger the deprecation notice is just broken.

Any suggestion how this can be fixed properly?
The FormEnctypeNode can be changed to trigger the deprecation notice when it hits this Node, but that will only trigger the notice during compile time (and may potentially break the compiler).

The problem persists and I don't see any clean way to trigger deprecation notice here. You could use some sort of a hack, like:

$compiler->raw('""; trigger_error(\'The helper form_enctype(form) is deprecated since version 2.3 and will be removed in 3.0. Use form_start(form) instead.\', E_USER_DEPRECATED); echo ');
parent::compile($compiler);

It would echo an empty string, trigger the warning and then go on with the compilation, but as I said it is ugly. I'm affraid, the only way to trigger the deprecation warning in a clean, nice matter would be to change

Symfony\Bridge\Twig\Extension\FormExtension

add something like

public function renderFormEnctype(FormView $form) {
        trigger_error('The helper form_enctype(form) is deprecated since version 2.3 and will be removed in 3.0. Use form_start(form) instead.', E_USER_DEPRECATED);
        return $this->renderer->searchAndRenderBlock($form, 'enctype');
}

and rewrite the 'form_enctype' function in getFunctions(), to use the above function instead of FormEnctypeNode (which then could be deleted). The alternative is to remove the deprecation warning. Either way something has to be done, beacause the current code breaks form_enctype completely.

if there is no proper solution, can we just revert the change? this is completely breaking things, as in Parse error: syntax error, unexpected 'trigger_error' (T_STRING), expecting ',' or ';' in ...

that way, it is certainly and utterly pointless breaking BC...

did #13125 to re-add the call to raw. lets either merge that, remove the deprecation or find a better fix but not leave code in here that triggers a fatal error. heck, even die('Do not use form_enctype anymore.'); would be more user friendly than what we currently have.

As there is no way to get it right, I've reverted #12673

alright, thanks fabien!