Twig trans placeholders with extra filters result in broken strings

I tried finding some proof on whether this should be identified in the first place (based on API docs), but the allowed characters do not seem to be identified in the API docs.

Did it depend on the filter?

Aham, so extra filters will not be found rather :D However based on #2547639: Rename ambiguous "Menu" toggle in Bartik for accessibility, those would not work in trans anyway. So what should potx do is do throw a warning that the use of the trans block this way is pointless and skip the string entirely instead of detecting it in the wrong way.

So this is a bit complex... Core's TwigTransTokenParser allows filters and getattr, and a couple other thigns:

  protected function checkTransString(\Twig_Node $body, $lineno) {
    foreach ($body as $node) {
      if (
        $node instanceof \Twig_Node_Text
        ||
        ($node instanceof \Twig_Node_Print && $node->getNode('expr') instanceof \Twig_Node_Expression_Name)
        ||
        ($node instanceof \Twig_Node_Print && $node->getNode('expr') instanceof \Twig_Node_Expression_GetAttr)
        ||
        ($node instanceof \Twig_Node_Print && $node->getNode('expr') instanceof \Twig_Node_Expression_Filter)
      ) {
        continue;
      }
      throw new \Twig_Error_Syntax(sprintf('The text to be translated with "trans" can only contain references to simple variables'), $lineno);
    }
  }

However in TwigNodeTrans, only the placeholder filter is explicitly supported. It does not seem to support any other filter.

So I think we should assume the @ prefix the same way TwigNodeTrans does and alter it if we find a placeholder marker. That would keep adding the variable name to the string even if an unexpected filter was found. Updated patch for this plus removing support for passthrough which was removed from core as well.

Even more tests.

One more test combination for fun :D Not 100% sure we expect it to work this way.

Ok, let's get this out.