Copied from http://groups.google.com/group/liftweb/browse_thread/thread/54e059516001a518

>> For example, trying to use
>> a SessionVar before the session has been created shouldn't just refuse to be set. It
>> would be nice to have an exception reporting the problem.
>
> I think your points are valid to a certain degree, but for this
> specific problem there's a solution in LiftRules:
>
> /**
> * Should an exception be thrown on out of scope Session and RequestVar
> * access. By default, no.
> */
> @volatile var throwOnOutOfScopeVarAccess: Boolean = false
>
> /Jeppe

Thanks for the pointer, but I don't think it's working. After messing around with it in my own project, I did the following:

1. downloaded the examples from https://github.com/lift/lift_23_sbt.git

2. Compiled and ran fine using sbt

3. Added

// Find out if we access SessionVars or RequestVars inappropriately..
LiftRules.throwOnOutOfScopeVarAccess = true

as the last line in Boot.boot


4. Ran again and it threw an exception:

[info] == jetty-run ==
[success] Successful.
[info]
[info] Total time: 2 s, completed Jun 30, 2011 11:48:02 AM
> 11:48:04.848 [1193485506@qtp-1743791445-0] ERROR net.liftweb.http.LiftRules$$anon$1 - Exception being returned to browser when processing /: Message: java.lang.IllegalAccessException: Access to SessionVar outside a request or comet actor scope
net.liftweb.http.SessionVar.findFunc(Vars.scala:71)
net.liftweb.util.AnyVarTrait$$anonfun$is$1.apply(AnyVar.scala:137)
net.liftweb.http.SessionVar.doSync(Vars.scala:125)
net.liftweb.util.AnyVarTrait$class.is(AnyVar.scala:136)
net.liftweb.util.AnyVar.is(AnyVar.scala:89)
net.liftweb.util.AnyVarTrait$class.get(AnyVar.scala:161)
net.liftweb.util.AnyVar.get(AnyVar.scala:89)
net.liftweb.util.StackableMaker$class.find(Maker.scala:150)
net.liftweb.http.Factory$FactoryMaker.find(Factory.scala:37)
net.liftweb.http.Factory$FactoryMaker$$anonfun$make$1.apply(Factory.scala:87)
net.liftweb.http.Factory$FactoryMaker$$anonfun$make$1.apply(Factory.scala:87)
net.liftweb.common.EmptyBox.or(Box.scala:563)
net.liftweb.http.Factory$FactoryMaker.make(Factory.scala:87)
net.liftweb.http.Factory$FactoryMaker.vend(Factory.scala:82)
net.liftweb.http.S$class.statelessInit(S.scala:1186)
net.liftweb.http.LiftServlet.doService(LiftServlet.scala:244)
net.liftweb.http.LiftServlet$$anonfun$doIt$1$1.apply(LiftServlet.scala:122)
net.liftweb.http.LiftServlet$$anonfun$doIt$1$1.apply(LiftServlet.scala:121)

(lots omitted)