[xwiki-devs] [Proposal] Adding new velocity methods to simulate try/catch in Velocity

Hi Devs, Example of a use case: * In contentview.vm we need to be able to catch when getRenderedContent() throws an exception in order to be able to still display the page title, content menu and last modification line. We want only the content part to display an error. I’ve tried implementing the following: * Modified Document.getRenderedContent() to not throw exceptions any more * I’ve added Document.setError() and getError() * Then added a #displayRenderedContent($renderedContent) velocimacro to display an error, calling Document.getError() However that’s no good because we have lots of places in our code (and in extensions we don’t control) that call getRenderedContent() and they expect the whole page rendering to fail in case of an error… Thus after discussing quickly on IRC and with Thomas we’d like to propose instead: * Add a new #try() velocimacro that would push a new empty List<Exception> in the Execution Context to a Stack variable * Add a new uberspector that would, based on this flag do a try/catch around the method called (can be done easily by returning a custom VelMethod) * The uberspector catch would add the exception to the List<Exception> in the Execution Context * Add a new #catch() velocimacro that would pop from the Stack in the Execution Context and that would set 2 variables in the Velocity Context: ** $exception: the first exception ** $exceptions: the list of all exceptions that happened between the #try() and #catch() The good part with this is: * No change in behavior to all existing code * Code that want to do something in case of error can do it using #try()/#catch() for java methods throwing exceptions (like getRenderedContent()) Of course for the future we would need to decide if script services should stop doing try/catch or not but that’s another debate I’d prefer to separate from this thread. WDYT? Thanks -Vincent