linux-x86/1.63.0/src/stdlibs/library/proc_macro/src/bridge/handle.rs

//! Server-side handles and storage for per-handle data.

use std::collections::{BTreeMap, HashMap};
use std::hash::{BuildHasher, Hash};
use std::num::NonZeroU32;
use std::ops::{Index, IndexMut};
use std::sync::atomic::{AtomicUsize, Ordering};

pub(super) type Handle = NonZeroU32;

/// A store that associates values of type `T` with numeric handles. A value can
/// be looked up using its handle.
pub(super) struct OwnedStore<T: 'static> {
    counter: &'static AtomicUsize,
    data: BTreeMap<Handle, T>,
}

impl<T> OwnedStore<T> {
    pub(super) fn new(counter: &'static AtomicUsize) -> Self {
        // Ensure the handle counter isn't 0, which would panic later,
        // when `NonZeroU32::new` (aka `Handle::new`) is called in `alloc`.
        assert_ne!(counter.load(Ordering::SeqCst), 0);

        OwnedStore { counter, data: BTreeMap::new() }
    }
}

impl<T> OwnedStore<T> {
    pub(super) fn alloc(&mut self, x: T) -> Handle {
        let counter = self.counter.fetch_add(1, Ordering::SeqCst);
        let handle = Handle::new(counter as u32).expect("`proc_macro` handle counter overflowed");
        assert!(self.data.insert(handle, x).is_none());
        handle
    }

    pub(super) fn take(&mut self, h: Handle) -> T {
        self.data.remove(&h).expect("use-after-free in `proc_macro` handle")
    }
}

impl<T> Index<Handle> for OwnedStore<T> {
    type Output = T;
    fn index(&self, h: Handle) -> &T {
        self.data.get(&h).expect("use-after-free in `proc_macro` handle")
    }
}

impl<T> IndexMut<Handle> for OwnedStore<T> {
    fn index_mut(&mut self, h: Handle) -> &mut T {
        self.data.get_mut(&h).expect("use-after-free in `proc_macro` handle")
    }
}

// HACK(eddyb) deterministic `std::collections::hash_map::RandomState` replacement
// that doesn't require adding any dependencies to `proc_macro` (like `rustc-hash`).
#[derive(Clone)]
struct NonRandomState;

impl BuildHasher for NonRandomState {
    type Hasher = std::collections::hash_map::DefaultHasher;
    #[inline]
    fn build_hasher(&self) -> Self::Hasher {
        Self::Hasher::new()
    }
}

/// Like `OwnedStore`, but avoids storing any value more than once.
pub(super) struct InternedStore<T: 'static> {
    owned: OwnedStore<T>,
    interner: HashMap<T, Handle, NonRandomState>,
}

impl<T: Copy + Eq + Hash> InternedStore<T> {
    pub(super) fn new(counter: &'static AtomicUsize) -> Self {
        InternedStore {
            owned: OwnedStore::new(counter),
            interner: HashMap::with_hasher(NonRandomState),
        }
    }

    pub(super) fn alloc(&mut self, x: T) -> Handle {
        let owned = &mut self.owned;
        *self.interner.entry(x).or_insert_with(|| owned.alloc(x))
    }

    pub(super) fn copy(&mut self, h: Handle) -> T {
        self.owned[h]
    }
}