Remove some stuff we don't need or can't use anymore

Author: amandasystems

compiler/rustc_borrowck/src/nll.rs

@@ -119,15 +119,14 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
     // base constraints generated by the type-check.
     let var_origins = infcx.get_region_var_origins();
     let MirTypeckRegionConstraints {
-        placeholder_indices,
+        placeholder_indices: _,
         placeholder_index_to_region: _,
         liveness_constraints,
         mut outlives_constraints,
         mut member_constraints,
         universe_causes,
         type_tests,
     } = constraints;
-    let placeholder_indices = Rc::new(placeholder_indices);
 
     // If requested, emit legacy polonius facts.
     polonius::emit_facts(
@@ -155,7 +154,6 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
         infcx,
         var_origins,
         universal_regions,
-        placeholder_indices,
         universal_region_relations,
         outlives_constraints,
         member_constraints,

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -493,7 +493,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         infcx: &BorrowckInferCtxt<'tcx>,
         var_infos: VarInfos,
         universal_regions: Rc<UniversalRegions<'tcx>>,
-        placeholder_indices: Rc<PlaceholderIndices>,
         universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
         mut outlives_constraints: OutlivesConstraintSet<'tcx>,
         member_constraints_in: MemberConstraintSet<'tcx, RegionVid>,
@@ -504,7 +503,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     ) -> Self {
         debug!("universal_regions: {:#?}", universal_regions);
         debug!("outlives constraints: {:#?}", outlives_constraints);
-        debug!("placeholder_indices: {:#?}", placeholder_indices);
         debug!("type tests: {:#?}", type_tests);
 
         // Create a RegionDefinition for each inference variable.
@@ -1672,9 +1670,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             debug!(
                 "check_bound_universal_region, error_element: {error_element:?} for placeholder {placeholder:?} in scc: {longer_fr_scc:?}"
             );
-            match error_element {
-                RegionElement::Location(_) | RegionElement::RootUniversalRegion(_) => {}
-            }
 
             errors_buffer.push(RegionErrorKind::BoundUniversalRegionError {
                 longer_fr,

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -212,18 +212,12 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
                 // Special handling of higher-ranked regions.
                 if !self.scc_universe(scc).is_root() {
-                    if self
-                        .constraint_sccs
-                        .annotation(scc)
-                        .placeholder_representative()
-                        .is_some_and(|scc_placeholder| vid == scc_placeholder)
-                    {
-                        // FIXME: somehow construct the right type out of the representative!
-                        return region;
-                    } else {
-                        // Fallback: this will produce a cryptic error message.
-                        return region;
-                    }
+                    // FIXME: the original logic was: if this SCC contains one single
+                    // placeholder, equal to vid, then construct a
+                    // ty::Region::new_placeholder out of it, somehow. This no longer
+                    // works as an approach, since we cannot get the prerequisite indices.
+                    debug!("Cannot get a nice name for higher-ranked region {vid:?} as {region:?}");
+                    return region;
                 }
 
                 // Find something that we can name