Auto merge of #45298 - toidiu:ak-44493-infer-predicate, r=nikomatsakis

Ak 44493 infer predicate

 **WIP**  Implements #44493

Things to do:

- [x] add feature gate and appropriate tests (see [forge](https://forge.rust-lang.org/feature-guide.html) for some details)
- [x] add a unit testing system similar to `#[rustc_variance]`
  - [x] to see how, maybe `rg rustc_variance` and take some notes
- [ ] add more tests:
- [x] we need to decide how to handle `struct Foo<'a, T> { x: &'a T::Item }`
- [x] handle explicit predicates on types
- [ ] handle explicit predicates on `dyn Trait` (this could be put off to a follow-up PR)
- [ ] handle explicit predicates on projections (this could be put off to a follow-up PR)

.gitignore

@@ -83,6 +83,7 @@ __pycache__/
 /src/libstd_unicode/UnicodeData.txt
 /stage[0-9]+/
 /target
+target/
 /test/
 /tmp/
 TAGS

src/librustc/dep_graph/dep_node.rs

@@ -500,6 +500,7 @@ define_dep_nodes!( <'tcx>
     [] GenericsOfItem(DefId),
     [] PredicatesOfItem(DefId),
     [] InferredOutlivesOf(DefId),
+    [] InferredOutlivesCrate(CrateNum),
     [] SuperPredicatesOfItem(DefId),
     [] TraitDefOfItem(DefId),
     [] AdtDefOfItem(DefId),

src/librustc/ich/impls_ty.rs

@@ -1100,6 +1100,20 @@ impl<'a> HashStable<StableHashingContext<'a>> for ty::CrateVariancesMap {
     }
 }
 
+impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for ty::CratePredicatesMap<'gcx> {
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'a>,
+                                          hasher: &mut StableHasher<W>) {
+        let ty::CratePredicatesMap {
+            ref predicates,
+            // This is just an irrelevant helper value.
+            empty_predicate: _,
+        } = *self;
+
+        predicates.hash_stable(hcx, hasher);
+    }
+}
+
 impl_stable_hash_for!(struct ty::AssociatedItem {
     def_id,
     name,

src/librustc/ty/maps/config.rs

@@ -155,6 +155,12 @@ impl<'tcx> QueryDescription<'tcx> for queries::crate_variances<'tcx> {
     }
 }
 
+impl<'tcx> QueryDescription<'tcx> for queries::inferred_outlives_crate<'tcx> {
+    fn describe(_tcx: TyCtxt, _: CrateNum) -> String {
+        format!("computing the inferred outlives predicates for items in this crate")
+    }
+}
+
 impl<'tcx> QueryDescription<'tcx> for queries::mir_shims<'tcx> {
     fn describe(tcx: TyCtxt, def: ty::InstanceDef<'tcx>) -> String {
         format!("generating MIR shim for `{}`",

src/librustc/ty/maps/mod.rs

@@ -102,6 +102,7 @@ define_maps! { <'tcx>
     /// associated generics and predicates.
     [] fn generics_of: GenericsOfItem(DefId) -> &'tcx ty::Generics,
     [] fn predicates_of: PredicatesOfItem(DefId) -> ty::GenericPredicates<'tcx>,
+    [] fn explicit_predicates_of: PredicatesOfItem(DefId) -> ty::GenericPredicates<'tcx>,
 
     /// Maps from the def-id of a trait to the list of
     /// super-predicates. This is a subset of the full list of
@@ -139,7 +140,11 @@ define_maps! { <'tcx>
     [] fn variances_of: ItemVariances(DefId) -> Lrc<Vec<ty::Variance>>,
 
     /// Maps from def-id of a type to its (inferred) outlives.
-    [] fn inferred_outlives_of: InferredOutlivesOf(DefId) -> Vec<ty::Predicate<'tcx>>,
+    [] fn inferred_outlives_of: InferredOutlivesOf(DefId) -> Lrc<Vec<ty::Predicate<'tcx>>>,
+
+    /// Maps from def-id of a type to its (inferred) outlives.
+    [] fn inferred_outlives_crate: InferredOutlivesCrate(CrateNum)
+        -> Lrc<ty::CratePredicatesMap<'tcx>>,
 
     /// Maps from an impl/trait def-id to a list of the def-ids of its items
     [] fn associated_item_def_ids: AssociatedItemDefIds(DefId) -> Lrc<Vec<DefId>>,

src/librustc/ty/maps/plumbing.rs

@@ -1007,6 +1007,7 @@ pub fn force_from_dep_node<'a, 'gcx, 'lcx>(tcx: TyCtxt<'a, 'gcx, 'lcx>,
         DepKind::GenericsOfItem => { force!(generics_of, def_id!()); }
         DepKind::PredicatesOfItem => { force!(predicates_of, def_id!()); }
         DepKind::InferredOutlivesOf => { force!(inferred_outlives_of, def_id!()); }
+        DepKind::InferredOutlivesCrate => { force!(inferred_outlives_crate, LOCAL_CRATE); }
         DepKind::SuperPredicatesOfItem => { force!(super_predicates_of, def_id!()); }
         DepKind::TraitDefOfItem => { force!(trait_def, def_id!()); }
         DepKind::AdtDefOfItem => { force!(adt_def, def_id!()); }

src/librustc/ty/mod.rs

@@ -956,6 +956,22 @@ pub enum Predicate<'tcx> {
     ConstEvaluatable(DefId, &'tcx Substs<'tcx>),
 }
 
+/// The crate outlives map is computed during typeck and contains the
+/// outlives of every item in the local crate. You should not use it
+/// directly, because to do so will make your pass dependent on the
+/// HIR of every item in the local crate. Instead, use
+/// `tcx.inferred_outlives_of()` to get the outlives for a *particular*
+/// item.
+pub struct CratePredicatesMap<'tcx> {
+    /// For each struct with outlive bounds, maps to a vector of the
+    /// predicate of its outlive bounds. If an item has no outlives
+    /// bounds, it will have no entry.
+    pub predicates: FxHashMap<DefId, Lrc<Vec<ty::Predicate<'tcx>>>>,
+
+    /// An empty vector, useful for cloning.
+    pub empty_predicate: Lrc<Vec<ty::Predicate<'tcx>>>,
+}
+
 impl<'tcx> AsRef<Predicate<'tcx>> for Predicate<'tcx> {
     fn as_ref(&self) -> &Predicate<'tcx> {
         self

src/librustc_typeck/collect.rs

@@ -64,6 +64,7 @@ pub fn provide(providers: &mut Providers) {
         type_of,
         generics_of,
         predicates_of,
+        explicit_predicates_of,
         super_predicates_of,
         type_param_predicates,
         trait_def,
@@ -1296,13 +1297,17 @@ fn predicates_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                            def_id: DefId)
                            -> ty::GenericPredicates<'tcx> {
     let explicit = explicit_predicates_of(tcx, def_id);
+    let predicates = if tcx.sess.features_untracked().infer_outlives_requirements {
+        [&explicit.predicates[..], &tcx.inferred_outlives_of(def_id)[..]].concat()
+    } else { explicit.predicates };
+
     ty::GenericPredicates {
         parent: explicit.parent,
-        predicates: [&explicit.predicates[..], &tcx.inferred_outlives_of(def_id)[..]].concat()
+        predicates: predicates,
     }
 }
 
-fn explicit_predicates_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+pub fn explicit_predicates_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                            def_id: DefId)
                            -> ty::GenericPredicates<'tcx> {
     use rustc::hir::map::*;

src/librustc_typeck/diagnostics.rs

@@ -4840,11 +4840,11 @@ register_diagnostics! {
     E0588, // packed type cannot transitively contain a `[repr(align)]` type
     E0592, // duplicate definitions with name `{}`
 //  E0613, // Removed (merged with E0609)
-    E0640, // infer outlives
     E0627, // yield statement outside of generator literal
     E0632, // cannot provide explicit type parameters when `impl Trait` is used in
            // argument position.
     E0634, // type has conflicting packed representaton hints
+    E0640, // infer outlives requirements
     E0641, // cannot cast to/from a pointer with an unknown kind
     E0645, // trait aliases not finished
     E0907, // type inside generator must be known in this context

src/librustc_typeck/lib.rs

@@ -82,6 +82,7 @@ This API is completely unstable and subject to change.
 #![feature(slice_patterns)]
 #![feature(slice_sort_by_cached_key)]
 #![feature(dyn_trait)]
+#![feature(underscore_lifetimes)]
 
 #[macro_use] extern crate log;
 #[macro_use] extern crate syntax;

src/librustc_typeck/outlives/explicit.rs

@@ -0,0 +1,82 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use hir::map as hir_map;
+use rustc::hir;
+use rustc::hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
+use rustc::hir::itemlikevisit::ItemLikeVisitor;
+use rustc::ty::maps::Providers;
+use rustc::ty::{self, CratePredicatesMap, TyCtxt};
+use rustc_data_structures::sync::Lrc;
+use util::nodemap::FxHashMap;
+
+pub fn explicit_predicates<'tcx>(
+    tcx: TyCtxt<'_, 'tcx, 'tcx>,
+    crate_num: CrateNum,
+) -> FxHashMap<DefId, Lrc<Vec<ty::Predicate<'tcx>>>> {
+    assert_eq!(crate_num, LOCAL_CRATE);
+    let mut predicates: FxHashMap<DefId, Lrc<Vec<ty::Predicate<'tcx>>>> = FxHashMap();
+
+    // iterate over the entire crate
+    tcx.hir.krate().visit_all_item_likes(&mut ExplicitVisitor {
+        tcx: tcx,
+        explicit_predicates: &mut predicates,
+        crate_num: crate_num,
+    });
+
+    predicates
+}
+
+pub struct ExplicitVisitor<'cx, 'tcx: 'cx> {
+    tcx: TyCtxt<'cx, 'tcx, 'tcx>,
+    explicit_predicates: &'cx mut FxHashMap<DefId, Lrc<Vec<ty::Predicate<'tcx>>>>,
+    crate_num: CrateNum,
+}
+
+impl<'cx, 'tcx> ItemLikeVisitor<'tcx> for ExplicitVisitor<'cx, 'tcx> {
+    fn visit_item(&mut self, item: &'tcx hir::Item) {
+        let def_id = DefId {
+            krate: self.crate_num,
+            index: item.hir_id.owner,
+        };
+
+        let local_explicit_predicate = self.tcx.explicit_predicates_of(def_id);
+
+        let filtered_predicates = local_explicit_predicate
+            .predicates
+            .into_iter()
+            .filter(|pred| match pred {
+                ty::Predicate::TypeOutlives(..) | ty::Predicate::RegionOutlives(..) => true,
+
+                ty::Predicate::Trait(..)
+                | ty::Predicate::Projection(..)
+                | ty::Predicate::WellFormed(..)
+                | ty::Predicate::ObjectSafe(..)
+                | ty::Predicate::ClosureKind(..)
+                | ty::Predicate::Subtype(..)
+                | ty::Predicate::ConstEvaluatable(..) => false,
+            })
+            .collect();
+
+        match item.node {
+            hir::ItemStruct(..) | hir::ItemEnum(..) => {
+                self.tcx.adt_def(def_id);
+            }
+            _ => {}
+        }
+
+        self.explicit_predicates
+            .insert(def_id, Lrc::new(filtered_predicates));
+    }
+
+    fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {}
+
+    fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {}
+}

src/librustc_typeck/outlives/implicit_empty.rs

@@ -0,0 +1,52 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use hir::map as hir_map;
+use rustc::hir;
+use rustc::hir::def_id::{self, CrateNum, DefId, LOCAL_CRATE};
+use rustc::hir::itemlikevisit::ItemLikeVisitor;
+use rustc::ty::maps::Providers;
+use rustc::ty::{self, CratePredicatesMap, TyCtxt};
+use rustc_data_structures::sync::Lrc;
+use util::nodemap::FxHashMap;
+
+// Create the sets of inferred predicates for each type. These sets
+// are initially empty but will grow during the inference step.
+pub fn empty_predicate_map<'tcx>(
+    tcx: TyCtxt<'_, 'tcx, 'tcx>,
+) -> FxHashMap<DefId, Lrc<Vec<ty::Predicate<'tcx>>>> {
+    let mut predicates = FxHashMap();
+
+    // iterate over the entire crate
+    tcx.hir
+        .krate()
+        .visit_all_item_likes(&mut EmptyImplicitVisitor {
+            tcx,
+            predicates: &mut predicates,
+        });
+
+    predicates
+}
+
+pub struct EmptyImplicitVisitor<'cx, 'tcx: 'cx> {
+    tcx: TyCtxt<'cx, 'tcx, 'tcx>,
+    predicates: &'cx mut FxHashMap<DefId, Lrc<Vec<ty::Predicate<'tcx>>>>,
+}
+
+impl<'a, 'p, 'v> ItemLikeVisitor<'v> for EmptyImplicitVisitor<'a, 'p> {
+    fn visit_item(&mut self, item: &hir::Item) {
+        self.predicates
+            .insert(self.tcx.hir.local_def_id(item.id), Lrc::new(Vec::new()));
+    }
+
+    fn visit_trait_item(&mut self, trait_item: &hir::TraitItem) {}
+
+    fn visit_impl_item(&mut self, impl_item: &hir::ImplItem) {}
+}