rust/compiler/rustc_middle/src/ty/context/tls.rs

use super::{GlobalCtxt, TyCtxt};

use crate::dep_graph::TaskDepsRef;
use crate::ty::query;
use rustc_data_structures::sync::{self, Lock};
use rustc_errors::Diagnostic;
use std::mem;
use std::ptr;
use thin_vec::ThinVec;

/// This is the implicit state of rustc. It contains the current
/// `TyCtxt` and query. It is updated when creating a local interner or
/// executing a new query. Whenever there's a `TyCtxt` value available
/// you should also have access to an `ImplicitCtxt` through the functions
/// in this module.
#[derive(Clone)]
pub struct ImplicitCtxt<'a, 'tcx> {
    /// The current `TyCtxt`.
    pub tcx: TyCtxt<'tcx>,

    /// The current query job, if any. This is updated by `JobOwner::start` in
    /// `ty::query::plumbing` when executing a query.
    pub query: Option<query::QueryJobId>,

    /// Where to store diagnostics for the current query job, if any.
    /// This is updated by `JobOwner::start` in `ty::query::plumbing` when executing a query.
    pub diagnostics: Option<&'a Lock<ThinVec<Diagnostic>>>,

    /// Used to prevent queries from calling too deeply.
    pub query_depth: usize,

    /// The current dep graph task. This is used to add dependencies to queries
    /// when executing them.
    pub task_deps: TaskDepsRef<'a>,
}

impl<'a, 'tcx> ImplicitCtxt<'a, 'tcx> {
    pub fn new(gcx: &'tcx GlobalCtxt<'tcx>) -> Self {
        let tcx = TyCtxt { gcx };
        ImplicitCtxt {
            tcx,
            query: None,
            diagnostics: None,
            query_depth: 0,
            task_deps: TaskDepsRef::Ignore,
        }
    }
}

#[cfg(parallel_compiler)]
mod tlv {
    use rustc_rayon_core as rayon_core;
    use std::ptr;

    /// Gets Rayon's thread-local variable, which is preserved for Rayon jobs.
    /// This is used to get the pointer to the current `ImplicitCtxt`.
    #[inline]
    pub(super) fn get_tlv() -> *const () {
        ptr::from_exposed_addr(rayon_core::tlv::get())
    }

    /// Sets Rayon's thread-local variable, which is preserved for Rayon jobs
    /// to `value` during the call to `f`. It is restored to its previous value after.
    /// This is used to set the pointer to the new `ImplicitCtxt`.
    #[inline]
    pub(super) fn with_tlv<F: FnOnce() -> R, R>(value: *const (), f: F) -> R {
        rayon_core::tlv::with(value.expose_addr(), f)
    }
}

#[cfg(not(parallel_compiler))]
mod tlv {
    use std::cell::Cell;
    use std::ptr;

    thread_local! {
        /// A thread local variable that stores a pointer to the current `ImplicitCtxt`.
        static TLV: Cell<*const ()> = const { Cell::new(ptr::null()) };
    }

    /// Gets the pointer to the current `ImplicitCtxt`.
    #[inline]
    pub(super) fn get_tlv() -> *const () {
        TLV.with(|tlv| tlv.get())
    }

    /// Sets TLV to `value` during the call to `f`.
    /// It is restored to its previous value after.
    /// This is used to set the pointer to the new `ImplicitCtxt`.
    #[inline]
    pub(super) fn with_tlv<F: FnOnce() -> R, R>(value: *const (), f: F) -> R {
        let old = TLV.replace(value);
        let _reset = rustc_data_structures::OnDrop(move || TLV.set(old));
        f()
    }
}

#[inline]
fn erase(context: &ImplicitCtxt<'_, '_>) -> *const () {
    context as *const _ as *const ()
}

#[inline]
unsafe fn downcast<'a, 'tcx>(context: *const ()) -> &'a ImplicitCtxt<'a, 'tcx> {
    &*(context as *const ImplicitCtxt<'a, 'tcx>)
}

/// Sets `context` as the new current `ImplicitCtxt` for the duration of the function `f`.
#[inline]
pub fn enter_context<'a, 'tcx, F, R>(context: &ImplicitCtxt<'a, 'tcx>, f: F) -> R
where
    F: FnOnce() -> R,
{
    tlv::with_tlv(erase(context), f)
}

/// Allows access to the current `ImplicitCtxt` in a closure if one is available.
#[inline]
pub fn with_context_opt<F, R>(f: F) -> R
where
    F: for<'a, 'tcx> FnOnce(Option<&ImplicitCtxt<'a, 'tcx>>) -> R,
{
    let context = tlv::get_tlv();
    if context.is_null() {
        f(None)
    } else {
        // We could get an `ImplicitCtxt` pointer from another thread.
        // Ensure that `ImplicitCtxt` is `Sync`.
        sync::assert_sync::<ImplicitCtxt<'_, '_>>();

        unsafe { f(Some(downcast(context))) }
    }
}

/// Allows access to the current `ImplicitCtxt`.
/// Panics if there is no `ImplicitCtxt` available.
#[inline]
pub fn with_context<F, R>(f: F) -> R
where
    F: for<'a, 'tcx> FnOnce(&ImplicitCtxt<'a, 'tcx>) -> R,
{
    with_context_opt(|opt_context| f(opt_context.expect("no ImplicitCtxt stored in tls")))
}

/// Allows access to the current `ImplicitCtxt` whose tcx field is the same as the tcx argument
/// passed in. This means the closure is given an `ImplicitCtxt` with the same `'tcx` lifetime
/// as the `TyCtxt` passed in.
/// This will panic if you pass it a `TyCtxt` which is different from the current
/// `ImplicitCtxt`'s `tcx` field.
#[inline]
pub fn with_related_context<'tcx, F, R>(tcx: TyCtxt<'tcx>, f: F) -> R
where
    F: FnOnce(&ImplicitCtxt<'_, 'tcx>) -> R,
{
    with_context(|context| {
        // The two gcx have different invariant lifetimes, so we need to erase them for the comparison.
        assert!(ptr::eq(
            context.tcx.gcx as *const _ as *const (),
            tcx.gcx as *const _ as *const ()
        ));

        let context: &ImplicitCtxt<'_, '_> = unsafe { mem::transmute(context) };

        f(context)
    })
}

/// Allows access to the `TyCtxt` in the current `ImplicitCtxt`.
/// Panics if there is no `ImplicitCtxt` available.
#[inline]
pub fn with<F, R>(f: F) -> R
where
    F: for<'tcx> FnOnce(TyCtxt<'tcx>) -> R,
{
    with_context(|context| f(context.tcx))
}

/// Allows access to the `TyCtxt` in the current `ImplicitCtxt`.
/// The closure is passed None if there is no `ImplicitCtxt` available.
#[inline]
pub fn with_opt<F, R>(f: F) -> R
where
    F: for<'tcx> FnOnce(Option<TyCtxt<'tcx>>) -> R,
{
    with_context_opt(|opt_context| f(opt_context.map(|context| context.tcx)))
}