1 files changed, 60 insertions, 6 deletions

diff --git a/compiler/rustc_smir/src/stable_mir/mod.rs b/compiler/rustc_smir/src/stable_mir/mod.rs
index 1d2efb5eab9..612777b9c75 100644
--- a/compiler/rustc_smir/src/stable_mir/mod.rs
+++ b/compiler/rustc_smir/src/stable_mir/mod.rs
@@ -11,7 +11,14 @@
 //! There shouldn't be any direct references to internal compiler constructs in this module.
 //! If you need an internal construct, consider using `rustc_internal` or `rustc_smir`.
 
+use std::cell::Cell;
+
+use crate::rustc_smir::Tables;
+
+use self::ty::{Ty, TyKind};
+
 pub mod mir;
+pub mod ty;
 
 /// Use String for now but we should replace it.
 pub type Symbol = String;
@@ -41,7 +48,7 @@ pub struct CrateItem(pub(crate) DefId);
 
 impl CrateItem {
     pub fn body(&self) -> mir::Body {
-        crate::rustc_smir::mir_body(self)
+        with(|cx| cx.mir_body(self))
     }
 }
 
@@ -49,25 +56,72 @@ impl CrateItem {
 /// crate defines that. This is usually `main`, but could be
 /// `start` if the crate is a no-std crate.
 pub fn entry_fn() -> Option<CrateItem> {
-    crate::rustc_smir::entry_fn()
+    with(|cx| cx.entry_fn())
 }
 
 /// Access to the local crate.
 pub fn local_crate() -> Crate {
-    crate::rustc_smir::local_crate()
+    with(|cx| cx.local_crate())
 }
 
 /// Try to find a crate with the given name.
 pub fn find_crate(name: &str) -> Option<Crate> {
-    crate::rustc_smir::find_crate(name)
+    with(|cx| cx.find_crate(name))
 }
 
 /// Try to find a crate with the given name.
 pub fn external_crates() -> Vec<Crate> {
-    crate::rustc_smir::external_crates()
+    with(|cx| cx.external_crates())
 }
 
 /// Retrieve all items in the local crate that have a MIR associated with them.
 pub fn all_local_items() -> CrateItems {
-    crate::rustc_smir::all_local_items()
+    with(|cx| cx.all_local_items())
+}
+
+pub trait Context {
+    fn entry_fn(&mut self) -> Option<CrateItem>;
+    /// Retrieve all items of the local crate that have a MIR associated with them.
+    fn all_local_items(&mut self) -> CrateItems;
+    fn mir_body(&mut self, item: &CrateItem) -> mir::Body;
+    /// Get information about the local crate.
+    fn local_crate(&self) -> Crate;
+    /// Retrieve a list of all external crates.
+    fn external_crates(&self) -> Vec<Crate>;
+
+    /// Find a crate with the given name.
+    fn find_crate(&self, name: &str) -> Option<Crate>;
+
+    /// Obtain the representation of a type.
+    fn ty_kind(&mut self, ty: Ty) -> TyKind;
+
+    /// HACK: Until we have fully stable consumers, we need an escape hatch
+    /// to get `DefId`s out of `CrateItem`s.
+    fn rustc_tables(&mut self, f: &mut dyn FnMut(&mut Tables<'_>));
+}
+
+thread_local! {
+    /// A thread local variable that stores a pointer to the tables mapping between TyCtxt
+    /// datastructures and stable MIR datastructures.
+    static TLV: Cell<*mut ()> = const { Cell::new(std::ptr::null_mut()) };
+}
+
+pub fn run(mut context: impl Context, f: impl FnOnce()) {
+    assert!(TLV.get().is_null());
+    fn g<'a>(mut context: &mut (dyn Context + 'a), f: impl FnOnce()) {
+        TLV.set(&mut context as *mut &mut _ as _);
+        f();
+        TLV.replace(std::ptr::null_mut());
+    }
+    g(&mut context, f);
+}
+
+/// Loads the current context and calls a function with it.
+/// Do not nest these, as that will ICE.
+pub(crate) fn with<R>(f: impl FnOnce(&mut dyn Context) -> R) -> R {
+    let ptr = TLV.replace(std::ptr::null_mut()) as *mut &mut dyn Context;
+    assert!(!ptr.is_null());
+    let ret = f(unsafe { *ptr });
+    TLV.set(ptr as _);
+    ret
 }