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//! Thread-local data specific to LR(1) processing.

use crate::grammar::repr::TerminalSet;
use std::cell::RefCell;

thread_local! {
    static TERMINALS: RefCell<Option<TerminalSet>> = const { RefCell::new(None) }
}

pub struct Lr1Tls {
    old_value: Option<TerminalSet>,
}

impl Lr1Tls {
    pub fn install(terminals: TerminalSet) -> Lr1Tls {
        let old_value = TERMINALS.with(|s| s.borrow_mut().replace(terminals));
        Lr1Tls { old_value }
    }

    pub fn with<OP, RET>(op: OP) -> RET
    where
        OP: FnOnce(&TerminalSet) -> RET,
    {
        TERMINALS.with(|s| op(s.borrow().as_ref().expect("LR1 TLS not installed")))
    }
}

impl Drop for Lr1Tls {
    fn drop(&mut self) {
        TERMINALS.with(|s| *s.borrow_mut() = self.old_value.take());
    }
}