ty/walk: switch walk_shallow from Ty to GenericArg.

Author: eddyb

src/librustc_infer/infer/outlives/verify.rs

@@ -3,11 +3,9 @@ use crate::infer::{GenericKind, VerifyBound};
 use crate::traits;
 use rustc_data_structures::captures::Captures;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::subst::{InternalSubsts, Subst};
+use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, Subst};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 
-use smallvec::smallvec;
-
 /// The `TypeOutlives` struct has the job of "lowering" a `T: 'a`
 /// obligation into a series of `'a: 'b` constraints and "verifys", as
 /// described on the module comment. The final constraints are emitted
@@ -44,7 +42,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         match ty.kind {
             ty::Param(p) => self.param_bound(p),
             ty::Projection(data) => self.projection_bound(data),
-            _ => self.recursive_type_bound(ty),
+            _ => self.recursive_bound(ty.into()),
         }
     }
 
@@ -144,25 +142,33 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
 
         // see the extensive comment in projection_must_outlive
         let ty = self.tcx.mk_projection(projection_ty.item_def_id, projection_ty.substs);
-        let recursive_bound = self.recursive_type_bound(ty);
+        let recursive_bound = self.recursive_bound(ty.into());
 
         VerifyBound::AnyBound(env_bounds.chain(trait_bounds).collect()).or(recursive_bound)
     }
 
-    fn recursive_type_bound(&self, ty: Ty<'tcx>) -> VerifyBound<'tcx> {
-        let mut bounds = ty.walk_shallow().map(|subty| self.type_bound(subty)).collect::<Vec<_>>();
-
-        let mut regions = smallvec![];
-        ty.push_regions(&mut regions);
-        regions.retain(|r| !r.is_late_bound()); // ignore late-bound regions
-        bounds.push(VerifyBound::AllBounds(
-            regions.into_iter().map(|r| VerifyBound::OutlivedBy(r)).collect(),
-        ));
-
-        // remove bounds that must hold, since they are not interesting
-        bounds.retain(|b| !b.must_hold());
+    fn recursive_bound(&self, parent: GenericArg<'tcx>) -> VerifyBound<'tcx> {
+        let mut bounds = parent
+            .walk_shallow()
+            .filter_map(|child| match child.unpack() {
+                GenericArgKind::Type(ty) => Some(self.type_bound(ty)),
+                GenericArgKind::Lifetime(lt) => {
+                    // Ignore late-bound regions.
+                    if !lt.is_late_bound() { Some(VerifyBound::OutlivedBy(lt)) } else { None }
+                }
+                GenericArgKind::Const(_) => Some(self.recursive_bound(child)),
+            })
+            .filter(|bound| {
+                // Remove bounds that must hold, since they are not interesting.
+                !bound.must_hold()
+            });
 
-        if bounds.len() == 1 { bounds.pop().unwrap() } else { VerifyBound::AllBounds(bounds) }
+        match (bounds.next(), bounds.next()) {
+            (Some(first), None) => first,
+            (first, second) => {
+                VerifyBound::AllBounds(first.into_iter().chain(second).chain(bounds).collect())
+            }
+        }
     }
 
     /// Searches the environment for where-clauses like `G: 'a` where

src/librustc_middle/ty/mod.rs

@@ -2701,13 +2701,6 @@ impl<'tcx> TyS<'tcx> {
         TypeWalker::new(self.into())
     }
 
-    /// Iterator that walks the immediate children of `self`. Hence
-    /// `Foo<Bar<i32>, u32>` yields the sequence `[Bar<i32>, u32]`
-    /// (but not `i32`, like `walk`).
-    pub fn walk_shallow(&'tcx self) -> impl Iterator<Item = Ty<'tcx>> {
-        walk::walk_shallow(self.into())
-    }
-
     /// Walks `ty` and any types appearing within `ty`, invoking the
     /// callback `f` on each type. If the callback returns `false`, then the
     /// children of the current type are ignored.

src/librustc_middle/ty/outlives.rs

@@ -2,6 +2,7 @@
 // refers to rules defined in RFC 1214 (`OutlivesFooBar`), so see that
 // RFC for reference.
 
+use crate::ty::subst::{GenericArg, GenericArgKind};
 use crate::ty::{self, Ty, TyCtxt, TypeFoldable};
 use smallvec::SmallVec;
 
@@ -107,8 +108,9 @@ fn compute_components(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, out: &mut SmallVec<[Compo
                     // fallback case: hard code
                     // OutlivesProjectionComponents.  Continue walking
                     // through and constrain Pi.
-                    let subcomponents = capture_components(tcx, ty);
-                    out.push(Component::EscapingProjection(subcomponents));
+                    let mut subcomponents = smallvec![];
+                    compute_components_recursive(tcx, ty.into(), &mut subcomponents);
+                    out.push(Component::EscapingProjection(subcomponents.into_iter().collect()));
                 }
             }
 
@@ -153,26 +155,30 @@ fn compute_components(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, out: &mut SmallVec<[Compo
                 // "bound regions list".  In our representation, no such
                 // list is maintained explicitly, because bound regions
                 // themselves can be readily identified.
-
-                push_region_constraints(ty, out);
-                for subty in ty.walk_shallow() {
-                    compute_components(tcx, subty, out);
-                }
+                compute_components_recursive(tcx, ty.into(), out);
             }
         }
 }
 
-fn capture_components(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Vec<Component<'tcx>> {
-    let mut temp = smallvec![];
-    push_region_constraints(ty, &mut temp);
-    for subty in ty.walk_shallow() {
-        compute_components(tcx, subty, &mut temp);
+fn compute_components_recursive(
+    tcx: TyCtxt<'tcx>,
+    parent: GenericArg<'tcx>,
+    out: &mut SmallVec<[Component<'tcx>; 4]>,
+) {
+    for child in parent.walk_shallow() {
+        match child.unpack() {
+            GenericArgKind::Type(ty) => {
+                compute_components(tcx, ty, out);
+            }
+            GenericArgKind::Lifetime(lt) => {
+                // Ignore late-bound regions.
+                if !lt.is_late_bound() {
+                    out.push(Component::Region(lt));
+                }
+            }
+            GenericArgKind::Const(_) => {
+                compute_components_recursive(tcx, child, out);
+            }
+        }
     }
-    temp.into_iter().collect()
-}
-
-fn push_region_constraints<'tcx>(ty: Ty<'tcx>, out: &mut SmallVec<[Component<'tcx>; 4]>) {
-    let mut regions = smallvec![];
-    ty.push_regions(&mut regions);
-    out.extend(regions.iter().filter(|&r| !r.is_late_bound()).map(|r| Component::Region(r)));
 }

src/librustc_middle/ty/sty.rs

@@ -25,7 +25,6 @@ use rustc_macros::HashStable;
 use rustc_span::symbol::{kw, Symbol};
 use rustc_target::abi::{Size, VariantIdx};
 use rustc_target::spec::abi;
-use smallvec::SmallVec;
 use std::borrow::Cow;
 use std::cmp::Ordering;
 use std::marker::PhantomData;
@@ -2152,31 +2151,6 @@ impl<'tcx> TyS<'tcx> {
         }
     }
 
-    /// Pushes onto `out` the regions directly referenced from this type (but not
-    /// types reachable from this type via `walk_tys`). This ignores late-bound
-    /// regions binders.
-    pub fn push_regions(&self, out: &mut SmallVec<[ty::Region<'tcx>; 4]>) {
-        match self.kind {
-            Ref(region, _, _) => {
-                out.push(region);
-            }
-            Dynamic(ref obj, region) => {
-                out.push(region);
-                if let Some(principal) = obj.principal() {
-                    out.extend(principal.skip_binder().substs.regions());
-                }
-            }
-            Adt(_, substs) | Opaque(_, substs) => out.extend(substs.regions()),
-            Closure(_, ref substs) | Generator(_, ref substs, _) => out.extend(substs.regions()),
-            Projection(ref data) | UnnormalizedProjection(ref data) => {
-                out.extend(data.substs.regions())
-            }
-            FnDef(..) | FnPtr(_) | GeneratorWitness(..) | Bool | Char | Int(_) | Uint(_)
-            | Float(_) | Str | Array(..) | Slice(_) | RawPtr(_) | Never | Tuple(..)
-            | Foreign(..) | Param(_) | Bound(..) | Placeholder(..) | Infer(_) | Error => {}
-        }
-    }
-
     /// When we create a closure, we record its kind (i.e., what trait
     /// it implements) into its `ClosureSubsts` using a type
     /// parameter. This is kind of a phantom type, except that the

src/librustc_middle/ty/walk.rs

@@ -57,16 +57,15 @@ impl<'tcx> Iterator for TypeWalker<'tcx> {
     }
 }
 
-pub fn walk_shallow(parent: GenericArg<'tcx>) -> impl Iterator<Item = Ty<'tcx>> {
-    let mut stack = SmallVec::new();
-    push_inner(&mut stack, parent);
-    stack.into_iter().filter_map(|child| {
-        // FIXME(eddyb) remove this filter and expose all `GenericArg`s.
-        match child.unpack() {
-            GenericArgKind::Type(ty) => Some(ty),
-            GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => None,
-        }
-    })
+impl GenericArg<'tcx> {
+    /// Iterator that walks the immediate children of `self`. Hence
+    /// `Foo<Bar<i32>, u32>` yields the sequence `[Bar<i32>, u32]`
+    /// (but not `i32`, like `walk`).
+    pub fn walk_shallow(self) -> impl Iterator<Item = GenericArg<'tcx>> {
+        let mut stack = SmallVec::new();
+        push_inner(&mut stack, self);
+        stack.into_iter()
+    }
 }
 
 // We push `GenericArg`s on the stack in reverse order so as to