Re: [xwiki-devs] State of Velocity 2.0 upgrade

Hi devs, Some of you may know that I started working on upgrading our scripting engine to Velocity 2.0. The corresponding Jira issue is https://jira.xwiki.org/browse/XCOMMONS-1296. Those of you who want to take a look at breakages with standard Velocity 2.0 upgrade (if you directly use Velocity API) can take a look at http://velocity.apache.org/engine/2.0/upgrading.html. The following details are about XWiki Velocity "engine": = The code You can see the current state of the upgrade on the following branches: * https://github.com/xwiki/xwiki-commons/tree/feature-velocity2 * https://github.com/xwiki/xwiki-rendering/tree/feature-velocity2 * https://github.com/xwiki/xwiki-platform/tree/feature-velocity2 = Bad news == Definitive (probably) breakages * it was not easy in Velocity 1.7 but it's now impossible in Velocity 2.0 to use the hack we currently use to make macro "return" something. I mitigated this a bit by working on a #setVariable directive (the name of the helper we currently have in macros.vm) but it's not yet working in all situations and any code that was not going trough #setVariable will be broken anyway * the hypen ( - ) cannot be used in variable names anymore Those changes make impossible to upgrade to Velocity 2.0 in 10.x branch IMO, to big to be done in the middle of a cycle. == Temporary (hopefully) breakages * impossible to have $ or # at the end of a " based string literal (we have that a lot in various regex for example). This looks like an unplanned regression (since it's not documented) so I'm waiting for some kind reaction in the issues I reported (https://issues.apache.org/jira/browse/VELOCITY-897 and https://issues.apache.org/jira/browse/VELOCITY-896) == Not too impacting (hopefully) breakages The Velocity API changed quite a lot, fortunately not in classes we expose publicly (basically all we expose is VelocityContext). Also reminder: directly manipulating even XWiki Velocity API is considered legacy things (better use templates or wiki content and ScriptContext). = Good news == Macros handling The way to manage namespaces and macros has been completely changed (it does mean that lots of API has been broken in the process but we don't expose this API) and the good news is the new design will allow us to (finally) do proper caching of velocity scripts. I also removed a few hacks we had to do to not end up with endless memory leaks and milti-thread issues caused by the old namespace handling system. == Less stuff on our side I was able to move the following to legacy: * an equivalent of our chainable uberspector system has been implemented in Velocity standard * a DeprecatedCheckUberspector has been implemented in Velocity standard == Retro compatibility I was able to add * XWiki will keep supporting $velocityCount and $velocityHasNext (with a warning). It imply using XWikiVelocityContext instead of VelocityContext if you create it directly (which is a very bad idea) but you don't need to worry about that if you get your context from VelocityManager * a new #setVariable directive help supporting a few use case of macro "return" but unfortunately not all yet (Velocity AST is not super obvious to navigate...) == Performances Other than the caching on our side I already mentioned (huge boost planned when implemented) there is some memory and performance improvements claims in Velocity 2.0 release note (but I did not had time to do any testing myself yet). = TODO a) waiting for answer about the regressions I reported b) try find a way to make #setVariable directive works in a macro which is itself called in another macro (but it may not be possible) c) send a mail to discuss when to merge the Velocity 2 branch when at least a) is resolved Thanks, -- Thomas Mortagne