Function declares_session 

pub fn declares_session(stmts: &[Stmt<'_>], interner: &Interner) -> bool

Whether a lowered program declares a ## Session — read off the program itself, because the session’s loader is defined exactly when one is. A serving tier that composes page documents asks the router for the visitor’s token (CSRF_TOKEN_PATH) only then: without a session there is no token to ask for, and asking would run the handler for every page served.