[v3.9] Unable to use ob_start inside a custom twig method

[yellow1912]

Since the new version (I accidentally updated just yesterday), my calls to ob_start returns empty string now.

Before, I have 2 twig functions, which are simplified like this:

public function startInline()
{
    ob_start();
}

public function endInline()
{
    $content = ob_get_clean();
}

My twig may look like this:

{{ startInline() }}
something here
{{ endInline() }}

It used to work, but now with the new twig it always returns an empty string. Downgrading to 3.8 fixes the issue so I'm pretty sure this has something to do with the new code.

It was suggested that I could use the set block instead, but I want to know if and how I can update my code to work with the new version instead.

[stof]

Those custom functions were relying on the internal implementation of Twig being based on echoing things in PHP.

Thus, using paired functions like that is a weird API: this is not what Twig functions are meant to do and it would be very easy to break things by not pairing them properly (which cannot be properly reported). This is a job for a Twig tag instead (which seems to be exactly what the {% set %} tag does btw).
I don't see any way to make those paired functions work with the new Twig internal implementation, as there is no way for functions to inject some capturing behavior between the 2 calls (which are unrelated as far as the Twig AST is concerned).

[stof]

note that if endInline does more things than returning the content, you can do that by using a custom tag instead, for which the compilation would use a Twig\Node\CaptureNode to capture the output of the body and then do something with this output in the rest of the compiled code.

[fabpot]

Closing for reasons explained by @stof