fabpot/Twig — pull request #610 by Seldaek (2012-01-24 17:04:39+00:00)
Title: Make the parser Inception-Proof

Spent half a day debugging before I realized what happened, but I'll try to keep a long story short:

When the cache is empty, and the first template containing an assetic `{% javascripts %}` or similar tag is parsed, it will build up the assetic "assets" or recipes cache, this in turn will tokenize and parse all your templates to find assetic tags and cache that information.

At this point the parser is parsing something else in the middle of a parse() call, and since there is a single instance in the environment, it means all the instance vars are messed up and contain incorrect references to the latest TokenStream that was parsed by assetic, etc.

This had two effects on my application, both appearing seemingly randomly because it highly depends on the order of things, the state of your cache and probably other factors:

- The first thing that happened is that a template was compiled using the wrong template filename, which means I had a `__TwigTemplate_abcd` in the file named `dcba.php`, and it would never find the right class.
- The second issue (could not reproduce but I assume it was caused by this as well) is that the parse tree is completely broken and you end up with a parse error because it thinks it's at the end when it's not, or similar problem.

The proposed fix basically pushes/pops all the vars into a stack whenever the parser starts/stops, which worked very effectively here and does not introduce much breakage or complexity.