Fix tidy error

Author: amandasystems

compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs

@@ -181,12 +181,12 @@ trait TypeOpInfo<'tcx> {
             bound: placeholder.bound,
         });
 
-        let error_region = None;
-
         debug!(?placeholder_region);
 
+        // FIXME: this is obviously weird; this whole argument now does nothing and maybe
+        // it should?
         let span = cause.span;
-        let nice_error = self.nice_error(mbcx, cause, placeholder_region, error_region);
+        let nice_error = self.nice_error(mbcx, cause, placeholder_region, None);
 
         debug!(?nice_error);
 

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -210,33 +210,16 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         let mut suggestions = vec![];
         let hir = self.infcx.tcx.hir();
 
-        // find generic associated types in the given region 'lower_bound'
-        // FIXME: this should find one of the special-case blamable
-        // new constraints instead!
-        //let gat_id_and_generics = vec![];
-        //debug!(?gat_id_and_generics);
-
         // find higher-ranked trait bounds bounded to the generic associated types
         let hrtb_bounds = vec![];
         /*
-        gat_id_and_generics.iter().flatten().for_each(|(gat_hir_id, generics)| {
-            for pred in generics.predicates {
-                let BoundPredicate(WhereBoundPredicate { bound_generic_params, bounds, .. }) = pred
-                else {
-                    continue;
-                };
-                if bound_generic_params
-                    .iter()
-                    .rfind(|bgp| self.infcx.tcx.local_def_id_to_hir_id(bgp.def_id) == *gat_hir_id)
-                    .is_some()
-                {
-                    for bound in *bounds {
-                        hrtb_bounds.push(bound);
-                    }
-                }
-            }
-        });
-        debug!(?hrtb_bounds);
+        // FIXME: the best we can do is look at the representative, using something like:
+        let scc = self.regioncx.constraint_sccs().scc(lower_bound);
+        let Some(representative) =
+            self.regioncx.constraint_sccs().annotation(scc).placeholder_representative()
+        else {
+            return;
+        };
         */
 
         hrtb_bounds.iter().for_each(|bound| {

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -153,7 +153,7 @@ impl RegionTracker {
 
     /// If the representative is a placeholder, return it,
     /// otherwise return None.
-    fn placeholder_representative(&self) -> Option<RegionVid> {
+    pub(crate) fn placeholder_representative(&self) -> Option<RegionVid> {
         if self.representative_origin == RepresentativeOrigin::Placeholder {
             Some(self.representative)
         } else {
@@ -1666,7 +1666,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         let longer_fr_scc = self.constraint_sccs.scc(longer_fr);
         debug!("check_bound_universal_region: longer_fr_scc={:?}", longer_fr_scc,);
 
-        for error_element in self.scc_values.elements_contained_in(longer_fr_scc) {
+        if let Some(error_element) = self.scc_values.elements_contained_in(longer_fr_scc).next() {
             debug!(
                 "check_bound_universal_region, error_element: {error_element:?} for placeholder {placeholder:?} in scc: {longer_fr_scc:?}"
             );
@@ -1676,11 +1676,10 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 error_element,
                 placeholder,
             });
-
             // Stop after the first error, it gets too noisy otherwise, and does not provide more information.
-            break;
+        } else {
+            debug!("check_bound_universal_region: all bounds satisfied");
         }
-        debug!("check_bound_universal_region: all bounds satisfied");
     }
 
     #[instrument(level = "debug", skip(self, infcx, errors_buffer))]