Make Steal thread-safe

src/librustc/ty/steal.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::cell::{Ref, RefCell};
+use rustc_data_structures::sync::{RwLock, ReadGuard};
 use std::mem;
 
 /// The `Steal` struct is intended to used as the value for a query.
@@ -32,25 +32,25 @@ use std::mem;
 ///
 /// FIXME(#41710) -- what is the best way to model linear queries?
 pub struct Steal<T> {
-    value: RefCell<Option<T>>
+    value: RwLock<Option<T>>
 }
 
 impl<T> Steal<T> {
     pub fn new(value: T) -> Self {
         Steal {
-            value: RefCell::new(Some(value))
+            value: RwLock::new(Some(value))
         }
     }
 
-    pub fn borrow(&self) -> Ref<T> {
-        Ref::map(self.value.borrow(), |opt| match *opt {
+    pub fn borrow(&self) -> ReadGuard<T> {
+        ReadGuard::map(self.value.borrow(), |opt| match *opt {
             None => bug!("attempted to read from stolen value"),
             Some(ref v) => v
         })
     }
 
     pub fn steal(&self) -> T {
-        let value_ref = &mut *self.value.borrow_mut();
+        let value_ref = &mut *self.value.try_write().expect("stealing value which is locked");
         let value = mem::replace(value_ref, None);
         value.expect("attempt to read from stolen value")
     }

src/librustc_borrowck/borrowck/mod.rs

@@ -128,7 +128,7 @@ fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
     // Note that `mir_validated` is a "stealable" result; the
     // thief, `optimized_mir()`, forces borrowck, so we know that
     // is not yet stolen.
-    tcx.mir_validated(owner_def_id).borrow();
+    ty::maps::queries::mir_validated::ensure(tcx, owner_def_id);
 
     // option dance because you can't capture an uninitialized variable
     // by mut-ref.