minor fixes

src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs

@@ -56,6 +56,7 @@ enum Trace {
 
 /// Various pieces of state used when reporting borrow checker errors.
 pub struct ErrorReportingCtx<'a, 'b, 'tcx> {
+    #[allow(dead_code)] // FIXME(mark-i-m): used by outlives suggestions
     rinfcx: &'b RegionInferenceContext<'tcx>,
     infcx: &'b InferCtxt<'a, 'tcx>,
 
@@ -335,12 +336,12 @@ pub(super) fn report_error<'a>(
             }
             (ConstraintCategory::Assignment, true, false)
             | (ConstraintCategory::CallArgument, true, false) => {
-                let mut db = self.report_escaping_data_error(&errctx, &errci, renctx);
+                let db = self.report_escaping_data_error(&errctx, &errci, renctx);
 
                 db
             }
             _ => {
-                let mut db = self.report_general_error(&errctx, &errci, renctx);
+                let db = self.report_general_error(&errctx, &errci, renctx);
 
                 db
             }

src/librustc_mir/borrow_check/nll/region_infer/mod.rs

@@ -11,7 +11,6 @@
     region_infer::values::{
         PlaceholderIndices, RegionElement, ToElementIndex
     },
-    region_infer::error_reporting::outlives_suggestion::OutlivesSuggestionBuilder,
     type_check::{free_region_relations::UniversalRegionRelations, Locations},
 };
 use crate::borrow_check::Upvar;
@@ -1340,6 +1339,7 @@ fn check_universal_regions(
                         mir_def_id,
                         fr,
                         &mut propagated_outlives_requirements,
+                        errors_buffer,
                         region_naming,
                     );
                 }
@@ -1371,6 +1371,7 @@ fn check_universal_region(
         mir_def_id: DefId,
         longer_fr: RegionVid,
         propagated_outlives_requirements: &mut Option<&mut Vec<ClosureOutlivesRequirement<'tcx>>>,
+        errors_buffer: &mut Vec<Diagnostic>,
         region_naming: &mut RegionErrorNamingCtx,
     ) {
         debug!("check_universal_region(fr={:?})", longer_fr);
@@ -1398,6 +1399,7 @@ fn check_universal_region(
                 upvars,
                 mir_def_id,
                 propagated_outlives_requirements,
+                errors_buffer,
                 region_naming,
             );
             return;
@@ -1414,6 +1416,7 @@ fn check_universal_region(
                 upvars,
                 mir_def_id,
                 propagated_outlives_requirements,
+                errors_buffer,
                 region_naming,
             ) {
                 // continuing to iterate just reports more errors than necessary
@@ -1435,6 +1438,7 @@ fn check_universal_region_relation(
         upvars: &[Upvar],
         mir_def_id: DefId,
         propagated_outlives_requirements: &mut Option<&mut Vec<ClosureOutlivesRequirement<'tcx>>>,
+        errors_buffer: &mut Vec<Diagnostic>,
         region_naming: &mut RegionErrorNamingCtx,
     ) -> Option<ErrorReported> {
         // If it is known that `fr: o`, carry on.