Turn features() into a query.

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,

src/librustc/ich/impls_syntax.rs

@@ -17,6 +17,7 @@ use std::hash as std_hash;
 use std::mem;
 
 use syntax::ast;
+use syntax::feature_gate;
 use syntax::parse::token;
 use syntax::symbol::InternedString;
 use syntax::tokenstream;
@@ -460,3 +461,21 @@ fn stable_non_narrow_char(swc: ::syntax_pos::NonNarrowChar,
 
     (pos.0 - filemap_start.0, width as u32)
 }
+
+
+
+impl<'gcx> HashStable<StableHashingContext<'gcx>> for feature_gate::Features {
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hasher: &mut StableHasher<W>) {
+        // Unfortunately we cannot exhaustively list fields here, since the
+        // struct is macro generated.
+        self.declared_stable_lang_features.hash_stable(hcx, hasher);
+        self.declared_lib_features.hash_stable(hcx, hasher);
+
+        self.walk_feature_fields(|feature_name, value| {
+            feature_name.hash_stable(hcx, hasher);
+            value.hash_stable(hcx, hasher);
+        });
+    }
+}

src/librustc/infer/error_reporting/mod.rs

@@ -262,11 +262,11 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                 will_later_be_reported_by_nll: bool) {
         debug!("report_region_errors(): {} errors to start", errors.len());
 
-        if will_later_be_reported_by_nll && self.tcx.sess.nll() {
+        if will_later_be_reported_by_nll && self.tcx.nll() {
             // With `#![feature(nll)]`, we want to present a nice user
             // experience, so don't even mention the errors from the
             // AST checker.
-            if self.tcx.sess.features.borrow().nll {
+            if self.tcx.features().nll {
                 return;
             }
 

src/librustc/middle/stability.rs

@@ -131,7 +131,7 @@ impl<'a, 'tcx: 'a> Annotator<'a, 'tcx> {
                    item_sp: Span, kind: AnnotationKind, visit_children: F)
         where F: FnOnce(&mut Self)
     {
-        if self.tcx.sess.features.borrow().staged_api {
+        if self.tcx.features().staged_api {
             // This crate explicitly wants staged API.
             debug!("annotate(id = {:?}, attrs = {:?})", id, attrs);
             if let Some(..) = attr::find_deprecation(self.tcx.sess.diagnostic(), attrs, item_sp) {
@@ -398,7 +398,7 @@ impl<'a, 'tcx> Index<'tcx> {
     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Index<'tcx> {
         let is_staged_api =
             tcx.sess.opts.debugging_opts.force_unstable_if_unmarked ||
-            tcx.sess.features.borrow().staged_api;
+            tcx.features().staged_api;
         let mut staged_api = FxHashMap();
         staged_api.insert(LOCAL_CRATE, is_staged_api);
         let mut index = Index {
@@ -408,7 +408,7 @@ impl<'a, 'tcx> Index<'tcx> {
             active_features: FxHashSet(),
         };
 
-        let ref active_lib_features = tcx.sess.features.borrow().declared_lib_features;
+        let ref active_lib_features = tcx.features().declared_lib_features;
 
         // Put the active features into a map for quick lookup
         index.active_features = active_lib_features.iter().map(|&(ref s, _)| s.clone()).collect();
@@ -677,7 +677,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
 
             // There's no good place to insert stability check for non-Copy unions,
             // so semi-randomly perform it here in stability.rs
-            hir::ItemUnion(..) if !self.tcx.sess.features.borrow().untagged_unions => {
+            hir::ItemUnion(..) if !self.tcx.features().untagged_unions => {
                 let def_id = self.tcx.hir.local_def_id(item.id);
                 let adt_def = self.tcx.adt_def(def_id);
                 let ty = self.tcx.type_of(def_id);
@@ -721,8 +721,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 /// were expected to be library features), and the list of features used from
 /// libraries, identify activated features that don't exist and error about them.
 pub fn check_unused_or_stable_features<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
-    let sess = &tcx.sess;
-
     let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
 
     if tcx.stability().staged_api[&LOCAL_CRATE] {
@@ -736,12 +734,12 @@ pub fn check_unused_or_stable_features<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
         krate.visit_all_item_likes(&mut missing.as_deep_visitor());
     }
 
-    let ref declared_lib_features = sess.features.borrow().declared_lib_features;
+    let ref declared_lib_features = tcx.features().declared_lib_features;
     let mut remaining_lib_features: FxHashMap<Symbol, Span>
         = declared_lib_features.clone().into_iter().collect();
     remaining_lib_features.remove(&Symbol::intern("proc_macro"));
 
-    for &(ref stable_lang_feature, span) in &sess.features.borrow().declared_stable_lang_features {
+    for &(ref stable_lang_feature, span) in &tcx.features().declared_stable_lang_features {
         let version = find_lang_feature_accepted_version(&stable_lang_feature.as_str())
             .expect("unexpectedly couldn't find version feature was stabilized");
         tcx.lint_node(lint::builtin::STABLE_FEATURES,

src/librustc/session/mod.rs

@@ -19,7 +19,7 @@ use lint;
 use middle::allocator::AllocatorKind;
 use middle::dependency_format;
 use session::search_paths::PathKind;
-use session::config::{BorrowckMode, DebugInfoLevel, OutputType, Epoch};
+use session::config::{DebugInfoLevel, OutputType, Epoch};
 use ty::tls;
 use util::nodemap::{FxHashMap, FxHashSet};
 use util::common::{duration_to_secs_str, ErrorReported};
@@ -91,7 +91,8 @@ pub struct Session {
     /// multiple crates with the same name to coexist. See the
     /// trans::back::symbol_names module for more information.
     pub crate_disambiguator: RefCell<Option<CrateDisambiguator>>,
-    pub features: RefCell<feature_gate::Features>,
+
+    features: RefCell<Option<feature_gate::Features>>,
 
     /// The maximum recursion limit for potentially infinitely recursive
     /// operations such as auto-dereference and monomorphization.
@@ -192,6 +193,7 @@ impl Session {
             None => bug!("accessing disambiguator before initialization"),
         }
     }
+
     pub fn struct_span_warn<'a, S: Into<MultiSpan>>(&'a self,
                                                     sp: S,
                                                     msg: &str)
@@ -443,16 +445,22 @@ impl Session {
         self.opts.debugging_opts.print_llvm_passes
     }
 
-    /// If true, we should use NLL-style region checking instead of
-    /// lexical style.
-    pub fn nll(&self) -> bool {
-        self.features.borrow().nll || self.opts.debugging_opts.nll
+    /// Get the features enabled for the current compilation session. Do not use
+    /// DO NOT USE THIS METHOD if there is a TyCtxt available, as it circumvents
+    /// dependency tracking. Use tcx.features() instead.
+    #[inline]
+    pub fn features_untracked(&self) -> cell::Ref<feature_gate::Features> {
+        let features = self.features.borrow();
+
+        if features.is_none() {
+            bug!("Access to Session::features before it is initialized");
+        }
+
+        cell::Ref::map(features, |r| r.as_ref().unwrap())
     }
 
-    /// If true, we should use the MIR-based borrowck (we may *also* use
-    /// the AST-based borrowck).
-    pub fn use_mir(&self) -> bool {
-        self.borrowck_mode().use_mir()
+    pub fn init_features(&self, features: feature_gate::Features) {
+        *(self.features.borrow_mut()) = Some(features);
     }
 
     /// If true, we should gather causal information during NLL
@@ -462,42 +470,6 @@ impl Session {
         self.opts.debugging_opts.nll_dump_cause
     }
 
-    /// If true, we should enable two-phase borrows checks. This is
-    /// done with either `-Ztwo-phase-borrows` or with
-    /// `#![feature(nll)]`.
-    pub fn two_phase_borrows(&self) -> bool {
-        self.features.borrow().nll || self.opts.debugging_opts.two_phase_borrows
-    }
-
-    /// What mode(s) of borrowck should we run? AST? MIR? both?
-    /// (Also considers the `#![feature(nll)]` setting.)
-    pub fn borrowck_mode(&self) -> BorrowckMode {
-        match self.opts.borrowck_mode {
-            mode @ BorrowckMode::Mir |
-            mode @ BorrowckMode::Compare => mode,
-
-            mode @ BorrowckMode::Ast => {
-                if self.nll() {
-                    BorrowckMode::Mir
-                } else {
-                    mode
-                }
-            }
-
-        }
-    }
-
-    /// Should we emit EndRegion MIR statements? These are consumed by
-    /// MIR borrowck, but not when NLL is used. They are also consumed
-    /// by the validation stuff.
-    pub fn emit_end_regions(&self) -> bool {
-        // FIXME(#46875) -- we should not emit end regions when NLL is enabled,
-        // but for now we can't stop doing so because it causes false positives
-        self.opts.debugging_opts.emit_end_regions ||
-            self.opts.debugging_opts.mir_emit_validate > 0 ||
-            self.use_mir()
-    }
-
     /// Calculates the flavor of LTO to use for this compilation.
     pub fn lto(&self) -> config::Lto {
         // If our target has codegen requirements ignore the command line
@@ -1009,7 +981,7 @@ pub fn build_session_(sopts: config::Options,
         crate_types: RefCell::new(Vec::new()),
         dependency_formats: RefCell::new(FxHashMap()),
         crate_disambiguator: RefCell::new(None),
-        features: RefCell::new(feature_gate::Features::new()),
+        features: RefCell::new(None),
         recursion_limit: Cell::new(64),
         type_length_limit: Cell::new(1048576),
         next_node_id: Cell::new(NodeId::new(1)),

src/librustc/traits/specialize/mod.rs

@@ -162,7 +162,7 @@ pub(super) fn specializes<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
     // The feature gate should prevent introducing new specializations, but not
     // taking advantage of upstream ones.
-    if !tcx.sess.features.borrow().specialization &&
+    if !tcx.features().specialization &&
         (impl1_def_id.is_local() || impl2_def_id.is_local()) {
         return false;
     }

src/librustc/ty/context.rs

@@ -14,7 +14,7 @@ use dep_graph::DepGraph;
 use dep_graph::{DepNode, DepConstructor};
 use errors::DiagnosticBuilder;
 use session::Session;
-use session::config::OutputFilenames;
+use session::config::{BorrowckMode, OutputFilenames};
 use middle;
 use hir::{TraitCandidate, HirId, ItemLocalId};
 use hir::def::{Def, Export};
@@ -71,6 +71,7 @@ use syntax::abi;
 use syntax::ast::{self, Name, NodeId};
 use syntax::attr;
 use syntax::codemap::MultiSpan;
+use syntax::feature_gate;
 use syntax::symbol::{Symbol, keywords};
 use syntax_pos::Span;
 
@@ -1251,6 +1252,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         self.stability_index(LOCAL_CRATE)
     }
 
+    pub fn features(self) -> Rc<feature_gate::Features> {
+        self.features_query(LOCAL_CRATE)
+    }
+
     pub fn crates(self) -> Rc<Vec<CrateNum>> {
         self.all_crate_nums(LOCAL_CRATE)
     }
@@ -1362,6 +1367,53 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         self.on_disk_query_result_cache.serialize(self.global_tcx(), encoder)
     }
 
+    /// If true, we should use NLL-style region checking instead of
+    /// lexical style.
+    pub fn nll(self) -> bool {
+        self.features().nll || self.sess.opts.debugging_opts.nll
+    }
+
+    /// If true, we should use the MIR-based borrowck (we may *also* use
+    /// the AST-based borrowck).
+    pub fn use_mir(self) -> bool {
+        self.borrowck_mode().use_mir()
+    }
+
+    /// If true, we should enable two-phase borrows checks. This is
+    /// done with either `-Ztwo-phase-borrows` or with
+    /// `#![feature(nll)]`.
+    pub fn two_phase_borrows(self) -> bool {
+        self.features().nll || self.sess.opts.debugging_opts.two_phase_borrows
+    }
+
+    /// What mode(s) of borrowck should we run? AST? MIR? both?
+    /// (Also considers the `#![feature(nll)]` setting.)
+    pub fn borrowck_mode(&self) -> BorrowckMode {
+        match self.sess.opts.borrowck_mode {
+            mode @ BorrowckMode::Mir |
+            mode @ BorrowckMode::Compare => mode,
+
+            mode @ BorrowckMode::Ast => {
+                if self.nll() {
+                    BorrowckMode::Mir
+                } else {
+                    mode
+                }
+            }
+
+        }
+    }
+
+    /// Should we emit EndRegion MIR statements? These are consumed by
+    /// MIR borrowck, but not when NLL is used. They are also consumed
+    /// by the validation stuff.
+    pub fn emit_end_regions(self) -> bool {
+        // FIXME(#46875) -- we should not emit end regions when NLL is enabled,
+        // but for now we can't stop doing so because it causes false positives
+        self.sess.opts.debugging_opts.emit_end_regions ||
+            self.sess.opts.debugging_opts.mir_emit_validate > 0 ||
+            self.use_mir()
+    }
 }
 
 impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
@@ -2020,7 +2072,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     }
 
     pub fn mk_diverging_default(self) -> Ty<'tcx> {
-        if self.sess.features.borrow().never_type {
+        if self.features().never_type {
             self.types.never
         } else {
             self.intern_tup(&[], true)
@@ -2395,13 +2447,17 @@ pub fn provide(providers: &mut ty::maps::Providers) {
     };
     providers.has_copy_closures = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);
-        tcx.sess.features.borrow().copy_closures
+        tcx.features().copy_closures
     };
     providers.has_clone_closures = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);
-        tcx.sess.features.borrow().clone_closures
+        tcx.features().clone_closures
     };
     providers.fully_normalize_monormophic_ty = |tcx, ty| {
         tcx.fully_normalize_associated_types_in(&ty)
     };
+    providers.features_query = |tcx, cnum| {
+        assert_eq!(cnum, LOCAL_CRATE);
+        Rc::new(tcx.sess.features_untracked().clone())
+    };
 }