skol -> placeholder

Author: lcnr

src/librustc_infer/infer/region_constraints/mod.rs

@@ -290,7 +290,7 @@ pub(crate) enum UndoLog<'tcx> {
     /// We added a GLB/LUB "combination variable".
     AddCombination(CombineMapType, TwoRegions<'tcx>),
 
-    /// During skolemization, we sometimes purge entries from the undo
+    /// During freshening, we sometimes purge entries from the undo
     /// log in a kind of minisnapshot (unlike other snapshots, this
     /// purging actually takes place *on success*). In that case, we
     /// replace the corresponding entry with `Noop` so as to avoid the
@@ -489,7 +489,7 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
     }
 
     /// Removes all the edges to/from the placeholder regions that are
-    /// in `skols`. This is used after a higher-ranked operation
+    /// in `placeholders`. This is used after a higher-ranked operation
     /// completes to remove all trace of the placeholder regions
     /// created in that time.
     pub fn pop_placeholders(&mut self, placeholders: &FxHashSet<ty::Region<'tcx>>) {

src/librustc_trait_selection/traits/select/mod.rs

@@ -1754,38 +1754,37 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     ) -> Vec<PredicateObligation<'tcx>> {
         // Because the types were potentially derived from
         // higher-ranked obligations they may reference late-bound
-        // regions. For example, `for<'a> Foo<&'a int> : Copy` would
-        // yield a type like `for<'a> &'a int`. In general, we
+        // regions. For example, `for<'a> Foo<&'a i32> : Copy` would
+        // yield a type like `for<'a> &'a i32`. In general, we
         // maintain the invariant that we never manipulate bound
         // regions, so we have to process these bound regions somehow.
         //
         // The strategy is to:
         //
         // 1. Instantiate those regions to placeholder regions (e.g.,
-        //    `for<'a> &'a int` becomes `&0 int`.
-        // 2. Produce something like `&'0 int : Copy`
-        // 3. Re-bind the regions back to `for<'a> &'a int : Copy`
+        //    `for<'a> &'a int` becomes `&0 i32`.
+        // 2. Produce something like `&'0 i32 : Copy`
+        // 3. Re-bind the regions back to `for<'a> &'a i32 : Copy`
 
         types
-            .skip_binder()
+            .skip_binder() // binder moved -\
             .iter()
             .flat_map(|ty| {
-                // binder moved -\
                 let ty: ty::Binder<Ty<'tcx>> = ty::Binder::bind(ty); // <----/
 
                 self.infcx.commit_unconditionally(|_| {
-                    let (skol_ty, _) = self.infcx.replace_bound_vars_with_placeholders(&ty);
+                    let (placeholder_ty, _) = self.infcx.replace_bound_vars_with_placeholders(&ty);
                     let Normalized { value: normalized_ty, mut obligations } =
                         ensure_sufficient_stack(|| {
                             project::normalize_with_depth(
                                 self,
                                 param_env,
                                 cause.clone(),
                                 recursion_depth,
-                                &skol_ty,
+                                &placeholder_ty,
                             )
                         });
-                    let skol_obligation = predicate_for_trait_def(
+                    let placeholder_obligation = predicate_for_trait_def(
                         self.tcx(),
                         param_env,
                         cause.clone(),
@@ -1794,7 +1793,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         normalized_ty,
                         &[],
                     );
-                    obligations.push(skol_obligation);
+                    obligations.push(placeholder_obligation);
                     obligations
                 })
             })
@@ -1844,9 +1843,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             return Err(());
         }
 
-        let (skol_obligation, placeholder_map) =
+        let (placeholder_obligation, placeholder_map) =
             self.infcx().replace_bound_vars_with_placeholders(&obligation.predicate);
-        let skol_obligation_trait_ref = skol_obligation.trait_ref;
+        let placeholder_obligation_trait_ref = placeholder_obligation.trait_ref;
 
         let impl_substs = self.infcx.fresh_substs_for_item(obligation.cause.span, impl_def_id);
 
@@ -1865,14 +1864,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         debug!(
             "match_impl(impl_def_id={:?}, obligation={:?}, \
-             impl_trait_ref={:?}, skol_obligation_trait_ref={:?})",
-            impl_def_id, obligation, impl_trait_ref, skol_obligation_trait_ref
+             impl_trait_ref={:?}, placeholder_obligation_trait_ref={:?})",
+            impl_def_id, obligation, impl_trait_ref, placeholder_obligation_trait_ref
         );
 
         let InferOk { obligations, .. } = self
             .infcx
             .at(&obligation.cause, obligation.param_env)
-            .eq(skol_obligation_trait_ref, impl_trait_ref)
+            .eq(placeholder_obligation_trait_ref, impl_trait_ref)
             .map_err(|e| debug!("match_impl: failed eq_trait_refs due to `{}`", e))?;
         nested_obligations.extend(obligations);
 

src/librustc_trait_selection/traits/specialize/mod.rs

@@ -130,7 +130,7 @@ pub(super) fn specializes(tcx: TyCtxt<'_>, (impl1_def_id, impl2_def_id): (DefId,
 
     // We determine whether there's a subset relationship by:
     //
-    // - skolemizing impl1,
+    // - replacing bound vars with placeholders in impl1,
     // - assuming the where clauses for impl1,
     // - instantiating impl2 with fresh inference variables,
     // - unifying,

src/librustc_typeck/check/compare_method.rs

@@ -91,14 +91,14 @@ fn compare_predicate_entailment<'tcx>(
 
     // This code is best explained by example. Consider a trait:
     //
-    //     trait Trait<'t,T> {
-    //          fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
+    //     trait Trait<'t, T> {
+    //         fn method<'a, M>(t: &'t T, m: &'a M) -> Self;
     //     }
     //
     // And an impl:
     //
     //     impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
-    //          fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
+    //          fn method<'b, N>(t: &'j &'i U, m: &'b N) -> Foo;
     //     }
     //
     // We wish to decide if those two method types are compatible.
@@ -116,9 +116,9 @@ fn compare_predicate_entailment<'tcx>(
     // regions (Note: but only early-bound regions, i.e., those
     // declared on the impl or used in type parameter bounds).
     //
-    //     impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
+    //     impl_to_placeholder_substs = {'i => 'i0, U => U0, N => N0 }
     //
-    // Now we can apply skol_substs to the type of the impl method
+    // Now we can apply placeholder_substs to the type of the impl method
     // to yield a new function type in terms of our fresh, placeholder
     // types:
     //
@@ -127,11 +127,11 @@ fn compare_predicate_entailment<'tcx>(
     // We now want to extract and substitute the type of the *trait*
     // method and compare it. To do so, we must create a compound
     // substitution by combining trait_to_impl_substs and
-    // impl_to_skol_substs, and also adding a mapping for the method
+    // impl_to_placeholder_substs, and also adding a mapping for the method
     // type parameters. We extend the mapping to also include
     // the method parameters.
     //
-    //     trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
+    //     trait_to_placeholder_substs = { T => &'i0 U0, Self => Foo, M => N0 }
     //
     // Applying this to the trait method type yields:
     //
@@ -145,20 +145,20 @@ fn compare_predicate_entailment<'tcx>(
     // satisfied by the implementation's method.
     //
     // We do this by creating a parameter environment which contains a
-    // substitution corresponding to impl_to_skol_substs. We then build
-    // trait_to_skol_substs and use it to convert the predicates contained
+    // substitution corresponding to impl_to_placeholder_substs. We then build
+    // trait_to_placeholder_substs and use it to convert the predicates contained
     // in the trait_m.generics to the placeholder form.
     //
     // Finally we register each of these predicates as an obligation in
     // a fresh FulfillmentCtxt, and invoke select_all_or_error.
 
     // Create mapping from impl to placeholder.
-    let impl_to_skol_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
+    let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
 
     // Create mapping from trait to placeholder.
-    let trait_to_skol_substs =
-        impl_to_skol_substs.rebase_onto(tcx, impl_m.container.id(), trait_to_impl_substs);
-    debug!("compare_impl_method: trait_to_skol_substs={:?}", trait_to_skol_substs);
+    let trait_to_placeholder_substs =
+        impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container.id(), trait_to_impl_substs);
+    debug!("compare_impl_method: trait_to_placeholder_substs={:?}", trait_to_placeholder_substs);
 
     let impl_m_generics = tcx.generics_of(impl_m.def_id);
     let trait_m_generics = tcx.generics_of(trait_m.def_id);
@@ -194,7 +194,7 @@ fn compare_predicate_entailment<'tcx>(
     // if all constraints hold.
     hybrid_preds
         .predicates
-        .extend(trait_m_predicates.instantiate_own(tcx, trait_to_skol_substs).predicates);
+        .extend(trait_m_predicates.instantiate_own(tcx, trait_to_placeholder_substs).predicates);
 
     // Construct trait parameter environment and then shift it into the placeholder viewpoint.
     // The key step here is to update the caller_bounds's predicates to be
@@ -220,7 +220,7 @@ fn compare_predicate_entailment<'tcx>(
 
         let mut selcx = traits::SelectionContext::new(&infcx);
 
-        let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_skol_substs);
+        let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_placeholder_substs);
         let (impl_m_own_bounds, _) = infcx.replace_bound_vars_with_fresh_vars(
             impl_m_span,
             infer::HigherRankedType,
@@ -261,7 +261,7 @@ fn compare_predicate_entailment<'tcx>(
         debug!("compare_impl_method: impl_fty={:?}", impl_fty);
 
         let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, &tcx.fn_sig(trait_m.def_id));
-        let trait_sig = trait_sig.subst(tcx, trait_to_skol_substs);
+        let trait_sig = trait_sig.subst(tcx, trait_to_placeholder_substs);
         let trait_sig =
             inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, &trait_sig);
         let trait_fty = tcx.mk_fn_ptr(ty::Binder::bind(trait_sig));