1 files changed, 186 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/ty/context/tls.rs b/compiler/rustc_middle/src/ty/context/tls.rs
new file mode 100644
index 000000000..5426ac8d7
--- /dev/null
+++ b/compiler/rustc_middle/src/ty/context/tls.rs
@@ -0,0 +1,186 @@
+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)))
+}