rustc: Convert freevars to a query

This removes a public mutable (but not actually used mutably) field from the
`TyCtxt`, moving it over to a query to ensure that it's tracked over time.

src/librustc/dep_graph/dep_node.rs

@@ -569,6 +569,8 @@ define_dep_nodes!( <'tcx>
     [] MissingExternCrateItem(CrateNum),
     [] UsedCrateSource(CrateNum),
     [] PostorderCnums,
+
+    [] Freevars(HirId),
 );
 
 trait DepNodeParams<'a, 'gcx: 'tcx + 'a, 'tcx: 'a> : fmt::Debug {

src/librustc/ty/context.rs

@@ -33,7 +33,6 @@ use traits;
 use ty::{self, Ty, TypeAndMut};
 use ty::{TyS, TypeVariants, Slice};
 use ty::{AdtKind, AdtDef, ClosureSubsts, GeneratorInterior, Region};
-use hir::FreevarMap;
 use ty::{PolyFnSig, InferTy, ParamTy, ProjectionTy, ExistentialPredicate, Predicate};
 use ty::RegionKind;
 use ty::{TyVar, TyVid, IntVar, IntVid, FloatVar, FloatVid};
@@ -837,7 +836,7 @@ pub struct GlobalCtxt<'tcx> {
     // Records the free variables refrenced by every closure
     // expression. Do not track deps for this, just recompute it from
     // scratch every time.
-    pub freevars: RefCell<FreevarMap>,
+    freevars: FxHashMap<HirId, Rc<Vec<hir::Freevar>>>,
 
     pub maybe_unused_trait_imports: NodeSet,
 
@@ -1066,11 +1065,13 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             export_map: resolutions.export_map.into_iter().map(|(k, v)| {
                 (hir.node_to_hir_id(k), Rc::new(v))
             }).collect(),
+            freevars: resolutions.freevars.into_iter().map(|(k, v)| {
+                (hir.node_to_hir_id(k), Rc::new(v))
+            }).collect(),
             hir,
             def_path_hash_to_def_id,
             maps: maps::Maps::new(providers),
             mir_passes,
-            freevars: RefCell::new(resolutions.freevars),
             maybe_unused_trait_imports: resolutions.maybe_unused_trait_imports,
             maybe_unused_extern_crates: resolutions.maybe_unused_extern_crates,
             rcache: RefCell::new(FxHashMap()),
@@ -2018,4 +2019,5 @@ pub fn provide(providers: &mut ty::maps::Providers) {
         assert_eq!(id, LOCAL_CRATE);
         Rc::new(middle::lang_items::collect(tcx))
     };
+    providers.freevars = |tcx, id| tcx.gcx.freevars.get(&id).cloned();
 }

src/librustc/ty/maps.rs

@@ -730,6 +730,12 @@ impl<'tcx> QueryDescription for queries::postorder_cnums<'tcx> {
     }
 }
 
+impl<'tcx> QueryDescription for queries::freevars<'tcx> {
+    fn describe(_tcx: TyCtxt, _: HirId) -> String {
+        format!("looking up free variables for a node")
+    }
+}
+
 // If enabled, send a message to the profile-queries thread
 macro_rules! profq_msg {
     ($tcx:expr, $msg:expr) => {
@@ -1345,6 +1351,8 @@ define_maps! { <'tcx>
     [] missing_extern_crate_item: MissingExternCrateItem(CrateNum) -> bool,
     [] used_crate_source: UsedCrateSource(CrateNum) -> Rc<CrateSource>,
     [] postorder_cnums: postorder_cnums_node(CrateNum) -> Rc<Vec<CrateNum>>,
+
+    [] freevars: Freevars(HirId) -> Option<Rc<Vec<hir::Freevar>>>,
 }
 
 fn type_param_predicates<'tcx>((item_id, param_id): (DefId, DefId)) -> DepConstructor<'tcx> {

src/librustc/ty/mod.rs

@@ -2340,9 +2340,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     pub fn with_freevars<T, F>(self, fid: NodeId, f: F) -> T where
         F: FnOnce(&[hir::Freevar]) -> T,
     {
-        match self.freevars.borrow().get(&fid) {
+        let hir_id = self.hir.node_to_hir_id(fid);
+        match self.freevars(hir_id) {
             None => f(&[]),
-            Some(d) => f(&d[..])
+            Some(d) => f(&d),
         }
     }
 }