rustc_typeck: rework coherence to be almost completely on-demand.

Author: eddyb

src/librustc/dep_graph/dep_node.rs

@@ -70,6 +70,7 @@ pub enum DepNode<D: Clone + Debug> {
     Resolve,
     EntryPoint,
     CheckEntryFn,
+    CoherenceCheckTrait(D),
     CoherenceCheckImpl(D),
     CoherenceOverlapCheck(D),
     CoherenceOverlapCheckSpecial(D),
@@ -241,6 +242,7 @@ impl<D: Clone + Debug> DepNode<D> {
             MetaData(ref d) => op(d).map(MetaData),
             CollectItem(ref d) => op(d).map(CollectItem),
             CollectItemSig(ref d) => op(d).map(CollectItemSig),
+            CoherenceCheckTrait(ref d) => op(d).map(CoherenceCheckTrait),
             CoherenceCheckImpl(ref d) => op(d).map(CoherenceCheckImpl),
             CoherenceOverlapCheck(ref d) => op(d).map(CoherenceOverlapCheck),
             CoherenceOverlapCheckSpecial(ref d) => op(d).map(CoherenceOverlapCheckSpecial),

src/librustc/hir/lowering.rs

@@ -80,6 +80,9 @@ pub struct LoweringContext<'a> {
     impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem>,
     bodies: FxHashMap<hir::BodyId, hir::Body>,
 
+    trait_impls: BTreeMap<DefId, Vec<NodeId>>,
+    trait_default_impl: BTreeMap<DefId, NodeId>,
+
     loop_scopes: Vec<NodeId>,
     is_in_loop_condition: bool,
 
@@ -116,6 +119,8 @@ pub fn lower_crate(sess: &Session,
         trait_items: BTreeMap::new(),
         impl_items: BTreeMap::new(),
         bodies: FxHashMap(),
+        trait_impls: BTreeMap::new(),
+        trait_default_impl: BTreeMap::new(),
         loop_scopes: Vec::new(),
         is_in_loop_condition: false,
         type_def_lifetime_params: DefIdMap(),
@@ -201,6 +206,8 @@ impl<'a> LoweringContext<'a> {
             trait_items: self.trait_items,
             impl_items: self.impl_items,
             bodies: self.bodies,
+            trait_impls: self.trait_impls,
+            trait_default_impl: self.trait_default_impl,
         }
     }
 
@@ -1089,14 +1096,27 @@ impl<'a> LoweringContext<'a> {
                 hir::ItemUnion(vdata, self.lower_generics(generics))
             }
             ItemKind::DefaultImpl(unsafety, ref trait_ref) => {
+                let trait_ref = self.lower_trait_ref(trait_ref);
+
+                if let Def::Trait(def_id) = trait_ref.path.def {
+                    self.trait_default_impl.insert(def_id, id);
+                }
+
                 hir::ItemDefaultImpl(self.lower_unsafety(unsafety),
-                                     self.lower_trait_ref(trait_ref))
+                                     trait_ref)
             }
             ItemKind::Impl(unsafety, polarity, ref generics, ref ifce, ref ty, ref impl_items) => {
                 let new_impl_items = impl_items.iter()
                                                .map(|item| self.lower_impl_item_ref(item))
                                                .collect();
                 let ifce = ifce.as_ref().map(|trait_ref| self.lower_trait_ref(trait_ref));
+
+                if let Some(ref trait_ref) = ifce {
+                    if let Def::Trait(def_id) = trait_ref.path.def {
+                        self.trait_impls.entry(def_id).or_insert(vec![]).push(id);
+                    }
+                }
+
                 hir::ItemImpl(self.lower_unsafety(unsafety),
                               self.lower_impl_polarity(polarity),
                               self.lower_generics(generics),

src/librustc/hir/map/mod.rs

@@ -461,6 +461,26 @@ impl<'hir> Map<'hir> {
         }
     }
 
+    pub fn trait_impls(&self, trait_did: DefId) -> &'hir [NodeId] {
+        self.dep_graph.read(DepNode::TraitImpls(trait_did));
+
+        // NB: intentionally bypass `self.forest.krate()` so that we
+        // do not trigger a read of the whole krate here
+        self.forest.krate.trait_impls.get(&trait_did).map_or(&[], |xs| &xs[..])
+    }
+
+    pub fn trait_default_impl(&self, trait_did: DefId) -> Option<NodeId> {
+        self.dep_graph.read(DepNode::TraitImpls(trait_did));
+
+        // NB: intentionally bypass `self.forest.krate()` so that we
+        // do not trigger a read of the whole krate here
+        self.forest.krate.trait_default_impl.get(&trait_did).cloned()
+    }
+
+    pub fn trait_is_auto(&self, trait_did: DefId) -> bool {
+        self.trait_default_impl(trait_did).is_some()
+    }
+
     /// Get the attributes on the krate. This is preferable to
     /// invoking `krate.attrs` because it registers a tighter
     /// dep-graph access.

src/librustc/hir/mod.rs

@@ -410,6 +410,9 @@ pub struct Crate {
     pub trait_items: BTreeMap<TraitItemId, TraitItem>,
     pub impl_items: BTreeMap<ImplItemId, ImplItem>,
     pub bodies: FxHashMap<BodyId, Body>,
+
+    pub trait_impls: BTreeMap<DefId, Vec<NodeId>>,
+    pub trait_default_impl: BTreeMap<DefId, NodeId>,
 }
 
 impl Crate {

src/librustc/infer/mod.rs

@@ -505,7 +505,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
             evaluation_cache: traits::EvaluationCache::new(),
             projection_cache: RefCell::new(traits::ProjectionCache::new()),
             reported_trait_errors: RefCell::new(FxHashSet()),
-            projection_mode: Reveal::NotSpecializable,
+            projection_mode: Reveal::UserFacing,
             tainted_by_errors_flag: Cell::new(false),
             err_count_on_creation: self.sess.err_count(),
             obligations_in_snapshot: Cell::new(false),

src/librustc/middle/cstore.rs

@@ -191,7 +191,6 @@ pub trait CrateStore {
 
     // flags
     fn is_const_fn(&self, did: DefId) -> bool;
-    fn is_defaulted_trait(&self, did: DefId) -> bool;
     fn is_default_impl(&self, impl_did: DefId) -> bool;
     fn is_foreign_item(&self, did: DefId) -> bool;
     fn is_dllimport_foreign_item(&self, def: DefId) -> bool;
@@ -327,7 +326,6 @@ impl CrateStore for DummyCrateStore {
 
     // flags
     fn is_const_fn(&self, did: DefId) -> bool { bug!("is_const_fn") }
-    fn is_defaulted_trait(&self, did: DefId) -> bool { bug!("is_defaulted_trait") }
     fn is_default_impl(&self, impl_did: DefId) -> bool { bug!("is_default_impl") }
     fn is_foreign_item(&self, did: DefId) -> bool { bug!("is_foreign_item") }
     fn is_dllimport_foreign_item(&self, id: DefId) -> bool { false }

src/librustc/traits/mod.rs

@@ -473,7 +473,7 @@ pub fn normalize_param_env_or_error<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
     let elaborated_env = unnormalized_env.with_caller_bounds(predicates);
 
-    tcx.infer_ctxt(elaborated_env, Reveal::NotSpecializable).enter(|infcx| {
+    tcx.infer_ctxt(elaborated_env, Reveal::UserFacing).enter(|infcx| {
         let predicates = match fully_normalize(&infcx, cause,
                                                &infcx.parameter_environment.caller_bounds) {
             Ok(predicates) => predicates,

src/librustc/traits/project.rs

@@ -38,36 +38,6 @@ use util::common::FN_OUTPUT_NAME;
 /// more or less conservative.
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub enum Reveal {
-    /// FIXME (#32205)
-    /// At coherence-checking time, we're still constructing the
-    /// specialization graph, and thus we only project
-    /// non-`default` associated types that are defined directly in
-    /// the applicable impl. (This behavior should be improved over
-    /// time, to allow for successful projections modulo cycles
-    /// between different impls).
-    ///
-    /// Here's an example that will fail due to the restriction:
-    ///
-    /// ```
-    /// trait Assoc {
-    ///     type Output;
-    /// }
-    ///
-    /// impl<T> Assoc for T {
-    ///     type Output = bool;
-    /// }
-    ///
-    /// impl Assoc for u8 {} // <- inherits the non-default type from above
-    ///
-    /// trait Foo {}
-    /// impl Foo for u32 {}
-    /// impl Foo for <u8 as Assoc>::Output {}  // <- this projection will fail
-    /// ```
-    ///
-    /// The projection would succeed if `Output` had been defined
-    /// directly in the impl for `u8`.
-    ExactMatch,
-
     /// At type-checking time, we refuse to project any associated
     /// type that is marked `default`. Non-`default` ("final") types
     /// are always projected. This is necessary in general for
@@ -90,7 +60,7 @@ pub enum Reveal {
     /// fn main() {
     ///     let <() as Assoc>::Output = true;
     /// }
-    NotSpecializable,
+    UserFacing,
 
     /// At trans time, all monomorphic projections will succeed.
     /// Also, `impl Trait` is normalized to the concrete type,
@@ -1347,8 +1317,9 @@ fn assoc_ty_def<'cx, 'gcx, 'tcx>(
     -> Option<specialization_graph::NodeItem<ty::AssociatedItem>>
 {
     let trait_def_id = selcx.tcx().impl_trait_ref(impl_def_id).unwrap().def_id;
+    let trait_def = selcx.tcx().lookup_trait_def(trait_def_id);
 
-    if selcx.projection_mode() == Reveal::ExactMatch {
+    if !trait_def.is_complete(selcx.tcx()) {
         let impl_node = specialization_graph::Node::Impl(impl_def_id);
         for item in impl_node.items(selcx.tcx()) {
             if item.kind == ty::AssociatedKind::Type && item.name == assoc_ty_name {
@@ -1360,7 +1331,7 @@ fn assoc_ty_def<'cx, 'gcx, 'tcx>(
         }
         None
     } else {
-        selcx.tcx().lookup_trait_def(trait_def_id)
+        trait_def
             .ancestors(impl_def_id)
             .defs(selcx.tcx(), assoc_ty_name, ty::AssociatedKind::Type)
             .next()

src/librustc/traits/specialize/mod.rs

@@ -189,7 +189,7 @@ pub fn specializes<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                              .subst(tcx, &penv.free_substs);
 
     // Create a infcx, taking the predicates of impl1 as assumptions:
-    let result = tcx.infer_ctxt(penv, Reveal::ExactMatch).enter(|infcx| {
+    let result = tcx.infer_ctxt(penv, Reveal::UserFacing).enter(|infcx| {
         // Normalize the trait reference. The WF rules ought to ensure
         // that this always succeeds.
         let impl1_trait_ref =

src/librustc/traits/specialize/specialization_graph.rs

@@ -108,7 +108,7 @@ impl<'a, 'gcx, 'tcx> Children {
             let possible_sibling = *slot;
 
             let tcx = tcx.global_tcx();
-            let (le, ge) = tcx.infer_ctxt((), Reveal::ExactMatch).enter(|infcx| {
+            let (le, ge) = tcx.infer_ctxt((), Reveal::UserFacing).enter(|infcx| {
                 let overlap = traits::overlapping_impls(&infcx,
                                                         possible_sibling,
                                                         impl_def_id);