Rollup merge of rust-lang#48208 - michaelwoerister:track-features, r=petrochenkov

Turn feature-gate table into a query so it is covered by dependency tracking.

Turn access to feature gates into a query so we handle them correctly during incremental compilation.

Features are still available via `Session` through `features_untracked()`. I wish we had a better way of hiding untracked information. It would be great if we could remove the `sess` field from `TyCtxt`.

Fixes rust-lang#47003.

Author: Manishearth

src/librustc/dep_graph/dep_node.rs

@@ -436,6 +436,9 @@ impl DepKind {
 }
 
 define_dep_nodes!( <'tcx>
+    // We use this for most things when incr. comp. is turned off.
+    [] Null,
+
     // Represents the `Krate` as a whole (the `hir::Krate` value) (as
     // distinct from the krate module). This is basically a hash of
     // the entire krate, so if you read from `Krate` (e.g., by calling
@@ -605,8 +608,8 @@ define_dep_nodes!( <'tcx>
     [input] MissingExternCrateItem(CrateNum),
     [input] UsedCrateSource(CrateNum),
     [input] PostorderCnums,
-    [input] HasCloneClosures(CrateNum),
-    [input] HasCopyClosures(CrateNum),
+    [] HasCloneClosures(CrateNum),
+    [] HasCopyClosures(CrateNum),
 
     // This query is not expected to have inputs -- as a result, it's
     // not a good candidate for "replay" because it's essentially a
@@ -630,8 +633,6 @@ define_dep_nodes!( <'tcx>
     [] CompileCodegenUnit(InternedString),
     [input] OutputFilenames,
     [anon] NormalizeTy,
-    // We use this for most things when incr. comp. is turned off.
-    [] Null,
 
     [] SubstituteNormalizeAndTestPredicates { key: (DefId, &'tcx Substs<'tcx>) },
 
@@ -642,6 +643,7 @@ define_dep_nodes!( <'tcx>
 
     [] GetSymbolExportLevel(DefId),
 
+    [input] Features,
 );
 
 trait DepNodeParams<'a, 'gcx: 'tcx + 'a, 'tcx: 'a> : fmt::Debug {

src/librustc/hir/lowering.rs

@@ -550,7 +550,7 @@ impl<'a> LoweringContext<'a> {
     {
         assert!(!self.is_collecting_in_band_lifetimes);
         assert!(self.lifetimes_to_define.is_empty());
-        self.is_collecting_in_band_lifetimes = self.sess.features.borrow().in_band_lifetimes;
+        self.is_collecting_in_band_lifetimes = self.sess.features_untracked().in_band_lifetimes;
 
         assert!(self.in_band_ty_params.is_empty());
 
@@ -957,7 +957,7 @@ impl<'a> LoweringContext<'a> {
                 let span = t.span;
                 match itctx {
                     ImplTraitContext::Existential => {
-                        let has_feature = self.sess.features.borrow().conservative_impl_trait;
+                        let has_feature = self.sess.features_untracked().conservative_impl_trait;
                         if !t.span.allows_unstable() && !has_feature {
                             emit_feature_err(&self.sess.parse_sess, "conservative_impl_trait",
                                              t.span, GateIssue::Language,
@@ -981,7 +981,7 @@ impl<'a> LoweringContext<'a> {
                         }, lifetimes)
                     },
                     ImplTraitContext::Universal(def_id) => {
-                        let has_feature = self.sess.features.borrow().universal_impl_trait;
+                        let has_feature = self.sess.features_untracked().universal_impl_trait;
                         if !t.span.allows_unstable() && !has_feature {
                             emit_feature_err(&self.sess.parse_sess, "universal_impl_trait",
                                              t.span, GateIssue::Language,