Rollup merge of #41734 - nikomatsakis:incr-comp-refactor-variance, r=pnkfelix

Refactor variance and remove last `[pub]` map

This PR refactors variance to work in a more red-green friendly way. Because red-green doesn't exist yet, it has to be a bit hacky. The basic idea is this:

- We compute a big map with the variance for all items in the crate; when you request variances for a particular item, we read it from the crate
- We now hard-code that traits are invariant (which they are, for deep reasons, not gonna' change)
- When building constraints, we compute the transitive closure of all things within the crate that depend on what using `TransitiveRelation`
    - this lets us gin up the correct dependencies when requesting variance of a single item

Ah damn, just remembered, one TODO:

- [x] Update the variance README -- ah, I guess the README updates I did are sufficient

r? @michaelwoerister

Author: frewsxcv

src/librustc/dep_graph/dep_node.rs

@@ -81,6 +81,7 @@ pub enum DepNode<D: Clone + Debug> {
     TransCrateItem(D),
     TransInlinedItem(D),
     TransWriteMetadata,
+    CrateVariances,
 
     // Nodes representing bits of computed IR in the tcx. Each shared
     // table in the tcx (or elsewhere) maps to one of these
@@ -89,6 +90,8 @@ pub enum DepNode<D: Clone + Debug> {
     // predicates for an item wind up in `ItemSignature`).
     AssociatedItems(D),
     ItemSignature(D),
+    ItemVarianceConstraints(D),
+    ItemVariances(D),
     IsForeignItem(D),
     TypeParamPredicates((D, D)),
     SizedConstraint(D),
@@ -180,6 +183,7 @@ impl<D: Clone + Debug> DepNode<D> {
             TransCrateItem,
             AssociatedItems,
             ItemSignature,
+            ItemVariances,
             IsForeignItem,
             AssociatedItemDefIds,
             InherentImpls,
@@ -201,6 +205,7 @@ impl<D: Clone + Debug> DepNode<D> {
             MirKrate => Some(MirKrate),
             TypeckBodiesKrate => Some(TypeckBodiesKrate),
             Coherence => Some(Coherence),
+            CrateVariances => Some(CrateVariances),
             Resolve => Some(Resolve),
             Variance => Some(Variance),
             PrivacyAccessLevels(k) => Some(PrivacyAccessLevels(k)),
@@ -232,6 +237,8 @@ impl<D: Clone + Debug> DepNode<D> {
             TransInlinedItem(ref d) => op(d).map(TransInlinedItem),
             AssociatedItems(ref d) => op(d).map(AssociatedItems),
             ItemSignature(ref d) => op(d).map(ItemSignature),
+            ItemVariances(ref d) => op(d).map(ItemVariances),
+            ItemVarianceConstraints(ref d) => op(d).map(ItemVarianceConstraints),
             IsForeignItem(ref d) => op(d).map(IsForeignItem),
             TypeParamPredicates((ref item, ref param)) => {
                 Some(TypeParamPredicates((try_opt!(op(item)), try_opt!(op(param)))))

src/librustc/dep_graph/mod.rs

@@ -18,7 +18,6 @@ mod raii;
 mod safe;
 mod shadow;
 mod thread;
-mod visit;
 
 pub use self::dep_tracking_map::{DepTrackingMap, DepTrackingMapConfig};
 pub use self::dep_node::DepNode;
@@ -28,5 +27,4 @@ pub use self::graph::WorkProduct;
 pub use self::query::DepGraphQuery;
 pub use self::safe::AssertDepGraphSafe;
 pub use self::safe::DepGraphSafe;
-pub use self::visit::visit_all_item_likes_in_krate;
 pub use self::raii::DepTask;

src/librustc/dep_graph/visit.rs

@@ -88,7 +88,7 @@ pub enum NestedVisitorMap<'this, 'tcx: 'this> {
     /// that are inside of an item-like.
     ///
     /// **This is the most common choice.** A very commmon pattern is
-    /// to use `tcx.visit_all_item_likes_in_krate()` as an outer loop,
+    /// to use `visit_all_item_likes()` as an outer loop,
     /// and to have the visitor that visits the contents of each item
     /// using this setting.
     OnlyBodies(&'this Map<'tcx>),

src/librustc/hir/intravisit.rs

@@ -19,9 +19,8 @@ use super::intravisit::Visitor;
 ///
 /// 1. **Shallow visit**: Get a simple callback for every item (or item-like thing) in the HIR.
 ///    - Example: find all items with a `#[foo]` attribute on them.
-///    - How: Implement `ItemLikeVisitor` and call `tcx.visit_all_item_likes_in_krate()`.
+///    - How: Implement `ItemLikeVisitor` and call `tcx.hir.krate().visit_all_item_likes()`.
 ///    - Pro: Efficient; just walks the lists of item-like things, not the nodes themselves.
-///    - Pro: Integrates well into dependency tracking.
 ///    - Con: Don't get information about nesting
 ///    - Con: Don't have methods for specific bits of HIR, like "on
 ///      every expr, do this".
@@ -30,7 +29,7 @@ use super::intravisit::Visitor;
 ///    within one another.
 ///    - Example: Examine each expression to look for its type and do some check or other.
 ///    - How: Implement `intravisit::Visitor` and use
-///      `tcx.visit_all_item_likes_in_krate(visitor.as_deep_visitor())`. Within
+///      `tcx.hir.krate().visit_all_item_likes(visitor.as_deep_visitor())`. Within
 ///      your `intravisit::Visitor` impl, implement methods like
 ///      `visit_expr()`; don't forget to invoke
 ///      `intravisit::walk_visit_expr()` to keep walking the subparts.

src/librustc/hir/itemlikevisit.rs

@@ -470,9 +470,6 @@ pub struct GlobalCtxt<'tcx> {
 
     pub lang_items: middle::lang_items::LanguageItems,
 
-    /// True if the variance has been computed yet; false otherwise.
-    pub variance_computed: Cell<bool>,
-
     /// Set of used unsafe nodes (functions or blocks). Unsafe nodes not
     /// present in this set can be warned about.
     pub used_unsafe: RefCell<NodeSet>,
@@ -744,7 +741,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             dep_graph: dep_graph.clone(),
             types: common_types,
             named_region_map: named_region_map,
-            variance_computed: Cell::new(false),
             trait_map: resolutions.trait_map,
             export_map: resolutions.export_map,
             fulfilled_predicates: RefCell::new(fulfilled_predicates),

src/librustc/ty/context.rs

@@ -266,6 +266,12 @@ impl<'tcx> QueryDescription for queries::crate_inherent_impls_overlap_check<'tcx
     }
 }
 
+impl<'tcx> QueryDescription for queries::crate_variances<'tcx> {
+    fn describe(_tcx: TyCtxt, _: CrateNum) -> String {
+        format!("computing the variances for items in this crate")
+    }
+}
+
 impl<'tcx> QueryDescription for queries::mir_shims<'tcx> {
     fn describe(tcx: TyCtxt, def: ty::InstanceDef<'tcx>) -> String {
         format!("generating MIR shim for `{}`",
@@ -549,18 +555,6 @@ macro_rules! define_map_struct {
         }
     };
 
-    // Detect things with the `pub` modifier
-    (tcx: $tcx:tt,
-     input: (([pub $($other_modifiers:tt)*] $attrs:tt $name:tt) $($input:tt)*),
-     output: $output:tt) => {
-        define_map_struct! {
-            tcx: $tcx,
-            ready: ([pub] $attrs $name),
-            input: ($($input)*),
-            output: $output
-        }
-    };
-
     // No modifiers left? This is a private item.
     (tcx: $tcx:tt,
      input: (([] $attrs:tt $name:tt) $($input:tt)*),
@@ -687,9 +681,13 @@ define_maps! { <'tcx>
     /// True if this is a foreign item (i.e., linked via `extern { ... }`).
     [] is_foreign_item: IsForeignItem(DefId) -> bool,
 
+    /// Get a map with the variance of every item; use `item_variance`
+    /// instead.
+    [] crate_variances: crate_variances(CrateNum) -> Rc<ty::CrateVariancesMap>,
+
     /// Maps from def-id of a type or region parameter to its
     /// (inferred) variance.
-    [pub] variances_of: ItemSignature(DefId) -> Rc<Vec<ty::Variance>>,
+    [] variances_of: ItemVariances(DefId) -> Rc<Vec<ty::Variance>>,
 
     /// Maps from an impl/trait def-id to a list of the def-ids of its items
     [] associated_item_def_ids: AssociatedItemDefIds(DefId) -> Rc<Vec<DefId>>,
@@ -825,3 +823,7 @@ fn const_eval_dep_node((def_id, _): (DefId, &Substs)) -> DepNode<DefId> {
 fn mir_keys(_: CrateNum) -> DepNode<DefId> {
     DepNode::MirKeys
 }
+
+fn crate_variances(_: CrateNum) -> DepNode<DefId> {
+    DepNode::CrateVariances
+}

src/librustc/ty/maps.rs

@@ -15,7 +15,7 @@ pub use self::IntVarValue::*;
 pub use self::LvaluePreference::*;
 pub use self::fold::TypeFoldable;
 
-use dep_graph::{self, DepNode};
+use dep_graph::DepNode;
 use hir::{map as hir_map, FreevarMap, TraitMap};
 use hir::def::{Def, CtorKind, ExportMap};
 use hir::def_id::{CrateNum, DefId, DefIndex, CRATE_DEF_INDEX, LOCAL_CRATE};
@@ -55,9 +55,9 @@ use rustc_const_math::ConstInt;
 use rustc_data_structures::accumulate_vec::IntoIter as AccIntoIter;
 use rustc_data_structures::stable_hasher::{StableHasher, StableHasherResult,
                                            HashStable};
+use rustc_data_structures::transitive_relation::TransitiveRelation;
 
 use hir;
-use hir::itemlikevisit::ItemLikeVisitor;
 
 pub use self::sty::{Binder, DebruijnIndex};
 pub use self::sty::{FnSig, PolyFnSig};
@@ -309,6 +309,27 @@ pub enum Variance {
     Bivariant,      // T<A> <: T<B>            -- e.g., unused type parameter
 }
 
+/// The crate variances map is computed during typeck and contains the
+/// variance 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.variances_of()` to get the variance for a *particular*
+/// item.
+pub struct CrateVariancesMap {
+    /// This relation tracks the dependencies between the variance of
+    /// various items. In particular, if `a < b`, then the variance of
+    /// `a` depends on the sources of `b`.
+    pub dependencies: TransitiveRelation<DefId>,
+
+    /// For each item with generics, maps to a vector of the variance
+    /// of its generics.  If an item has no generics, it will have no
+    /// entry.
+    pub variances: FxHashMap<DefId, Rc<Vec<ty::Variance>>>,
+
+    /// An empty vector, useful for cloning.
+    pub empty_variance: Rc<Vec<ty::Variance>>,
+}
+
 #[derive(Clone, Copy, Debug, RustcDecodable, RustcEncodable)]
 pub struct MethodCallee<'tcx> {
     /// Impl method ID, for inherent methods, or trait method ID, otherwise.
@@ -2543,14 +2564,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         self.mk_region(ty::ReScope(self.node_extent(id)))
     }
 
-    pub fn visit_all_item_likes_in_krate<V,F>(self,
-                                              dep_node_fn: F,
-                                              visitor: &mut V)
-        where F: FnMut(DefId) -> DepNode<DefId>, V: ItemLikeVisitor<'gcx>
-    {
-        dep_graph::visit_all_item_likes_in_krate(self.global_tcx(), dep_node_fn, visitor);
-    }
-
     /// Looks up the span of `impl_did` if the impl is local; otherwise returns `Err`
     /// with the name of the crate containing the impl.
     pub fn span_of_impl(self, impl_did: DefId) -> Result<Span, Symbol> {

src/librustc/ty/mod.rs

@@ -124,14 +124,8 @@ fn relate_item_substs<'a, 'gcx, 'tcx, R>(relation: &mut R,
            a_subst,
            b_subst);
 
-    let variances;
-    let opt_variances = if relation.tcx().variance_computed.get() {
-        variances = relation.tcx().variances_of(item_def_id);
-        Some(&*variances)
-    } else {
-        None
-    };
-    relate_substs(relation, opt_variances, a_subst, b_subst)
+    let opt_variances = relation.tcx().variances_of(item_def_id);
+    relate_substs(relation, Some(&opt_variances), a_subst, b_subst)
 }
 
 pub fn relate_substs<'a, 'gcx, 'tcx, R>(relation: &mut R,