Rollup merge of #107780 - compiler-errors:instantiate-binder, r=lcnr

Rename `replace_bound_vars_with_*` to `instantiate_binder_with_*`

Mentioning "binder" rather than "bound vars", imo, makes it clearer that we're doing something to the binder as a whole.

Also, "instantiate" is the verb that I'm always reaching for when I'm looking for these functions, and the name that we use in the new solver anyways.

r? types

4 files changed, 15 insertions, 8 deletions

diff --git a/compiler/rustc_infer/src/infer/equate.rs b/compiler/rustc_infer/src/infer/equate.rs
index 46e7813d99e..7db4d92a177 100644
--- a/compiler/rustc_infer/src/infer/equate.rs
+++ b/compiler/rustc_infer/src/infer/equate.rs
@@ -129,7 +129,7 @@ impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
                 let a_types = infcx.tcx.anonymize_bound_vars(a_types);
                 let b_types = infcx.tcx.anonymize_bound_vars(b_types);
                 if a_types.bound_vars() == b_types.bound_vars() {
-                    let (a_types, b_types) = infcx.replace_bound_vars_with_placeholders(
+                    let (a_types, b_types) = infcx.instantiate_binder_with_placeholders(
                         a_types.map_bound(|a_types| (a_types, b_types.skip_binder())),
                     );
                     for (a, b) in std::iter::zip(a_types, b_types) {
diff --git a/compiler/rustc_infer/src/infer/higher_ranked/mod.rs b/compiler/rustc_infer/src/infer/higher_ranked/mod.rs
index 31be107b354..412e52d8fd7 100644
--- a/compiler/rustc_infer/src/infer/higher_ranked/mod.rs
+++ b/compiler/rustc_infer/src/infer/higher_ranked/mod.rs
@@ -38,13 +38,13 @@ impl<'a, 'tcx> CombineFields<'a, 'tcx> {
         // First, we instantiate each bound region in the supertype with a
         // fresh placeholder region. Note that this automatically creates
         // a new universe if needed.
-        let sup_prime = self.infcx.replace_bound_vars_with_placeholders(sup);
+        let sup_prime = self.infcx.instantiate_binder_with_placeholders(sup);
 
         // Next, we instantiate each bound region in the subtype
         // with a fresh region variable. These region variables --
         // but no other pre-existing region variables -- can name
         // the placeholders.
-        let sub_prime = self.infcx.replace_bound_vars_with_fresh_vars(span, HigherRankedType, sub);
+        let sub_prime = self.infcx.instantiate_binder_with_fresh_vars(span, HigherRankedType, sub);
 
         debug!("a_prime={:?}", sub_prime);
         debug!("b_prime={:?}", sup_prime);
@@ -70,7 +70,7 @@ impl<'tcx> InferCtxt<'tcx> {
     ///
     /// [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/hrtb.html
     #[instrument(level = "debug", skip(self), ret)]
-    pub fn replace_bound_vars_with_placeholders<T>(&self, binder: ty::Binder<'tcx, T>) -> T
+    pub fn instantiate_binder_with_placeholders<T>(&self, binder: ty::Binder<'tcx, T>) -> T
     where
         T: TypeFoldable<'tcx> + Copy,
     {
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 8e0bcff8d0a..35918b8bae1 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -995,7 +995,7 @@ impl<'tcx> InferCtxt<'tcx> {
 
         Ok(self.commit_if_ok(|_snapshot| {
             let ty::SubtypePredicate { a_is_expected, a, b } =
-                self.replace_bound_vars_with_placeholders(predicate);
+                self.instantiate_binder_with_placeholders(predicate);
 
             let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
 
@@ -1008,7 +1008,7 @@ impl<'tcx> InferCtxt<'tcx> {
         cause: &traits::ObligationCause<'tcx>,
         predicate: ty::PolyRegionOutlivesPredicate<'tcx>,
     ) {
-        let ty::OutlivesPredicate(r_a, r_b) = self.replace_bound_vars_with_placeholders(predicate);
+        let ty::OutlivesPredicate(r_a, r_b) = self.instantiate_binder_with_placeholders(predicate);
         let origin =
             SubregionOrigin::from_obligation_cause(cause, || RelateRegionParamBound(cause.span));
         self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
@@ -1447,7 +1447,14 @@ impl<'tcx> InferCtxt<'tcx> {
         value
     }
 
-    pub fn replace_bound_vars_with_fresh_vars<T>(
+    // Instantiates the bound variables in a given binder with fresh inference
+    // variables in the current universe.
+    //
+    // Use this method if you'd like to find some substitution of the binder's
+    // variables (e.g. during a method call). If there isn't a [`LateBoundRegionConversionTime`]
+    // that corresponds to your use case, consider whether or not you should
+    // use [`InferCtxt::instantiate_binder_with_placeholders`] instead.
+    pub fn instantiate_binder_with_fresh_vars<T>(
         &self,
         span: Span,
         lbrct: LateBoundRegionConversionTime,
diff --git a/compiler/rustc_infer/src/infer/sub.rs b/compiler/rustc_infer/src/infer/sub.rs
index 51c34f0d55f..532fbd0ffe4 100644
--- a/compiler/rustc_infer/src/infer/sub.rs
+++ b/compiler/rustc_infer/src/infer/sub.rs
@@ -161,7 +161,7 @@ impl<'tcx> TypeRelation<'tcx> for Sub<'_, '_, 'tcx> {
                 let a_types = infcx.tcx.anonymize_bound_vars(a_types);
                 let b_types = infcx.tcx.anonymize_bound_vars(b_types);
                 if a_types.bound_vars() == b_types.bound_vars() {
-                    let (a_types, b_types) = infcx.replace_bound_vars_with_placeholders(
+                    let (a_types, b_types) = infcx.instantiate_binder_with_placeholders(
                         a_types.map_bound(|a_types| (a_types, b_types.skip_binder())),
                     );
                     for (a, b) in std::iter::zip(a_types, b_types) {