Add ExtraConstraintInfo

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -15,7 +15,7 @@ use rustc_middle::ty::{self, RegionVid, TyCtxt};
 use rustc_span::symbol::{kw, Symbol};
 use rustc_span::{sym, DesugaringKind, Span};
 
-use crate::region_infer::BlameConstraint;
+use crate::region_infer::{BlameConstraint, ExtraConstraintInfo};
 use crate::{
     borrow_set::BorrowData, nll::ConstraintDescription, region_infer::Cause, MirBorrowckCtxt,
     WriteKind,
@@ -38,6 +38,7 @@ pub(crate) enum BorrowExplanation<'tcx> {
         span: Span,
         region_name: RegionName,
         opt_place_desc: Option<String>,
+        extra_info: Vec<ExtraConstraintInfo>,
     },
     Unexplained,
 }
@@ -243,6 +244,7 @@ impl<'tcx> BorrowExplanation<'tcx> {
                 ref region_name,
                 ref opt_place_desc,
                 from_closure: _,
+                ref extra_info,
             } => {
                 region_name.highlight_region_name(err);
 
@@ -268,6 +270,11 @@ impl<'tcx> BorrowExplanation<'tcx> {
                     );
                 };
 
+                for extra in extra_info {
+                    match extra {
+                        _ => {}
+                    }
+                }
                 self.add_lifetime_bound_suggestion_to_diagnostic(err, &category, span, region_name);
             }
             _ => {}
@@ -309,8 +316,8 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         &self,
         borrow_region: RegionVid,
         outlived_region: RegionVid,
-    ) -> (ConstraintCategory<'tcx>, bool, Span, Option<RegionName>) {
-        let blame_constraint = self.regioncx.best_blame_constraint(
+    ) -> (ConstraintCategory<'tcx>, bool, Span, Option<RegionName>, Vec<ExtraConstraintInfo>) {
+        let (blame_constraint, extra_info) = self.regioncx.best_blame_constraint(
             borrow_region,
             NllRegionVariableOrigin::FreeRegion,
             |r| self.regioncx.provides_universal_region(r, borrow_region, outlived_region),
@@ -319,7 +326,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
         let outlived_fr_name = self.give_region_a_name(outlived_region);
 
-        (category, from_closure, cause.span, outlived_fr_name)
+        (category, from_closure, cause.span, outlived_fr_name, extra_info)
     }
 
     /// Returns structured explanation for *why* the borrow contains the
@@ -391,7 +398,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
             None => {
                 if let Some(region) = self.to_error_region_vid(borrow_region_vid) {
-                    let (category, from_closure, span, region_name) =
+                    let (category, from_closure, span, region_name, extra_info) =
                         self.free_region_constraint_info(borrow_region_vid, region);
                     if let Some(region_name) = region_name {
                         let opt_place_desc = self.describe_place(borrow.borrowed_place.as_ref());
@@ -401,6 +408,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                             span,
                             region_name,
                             opt_place_desc,
+                            extra_info,
                         }
                     } else {
                         debug!("Could not generate a region name");

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -354,10 +354,12 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
     ) {
         debug!("report_region_error(fr={:?}, outlived_fr={:?})", fr, outlived_fr);
 
-        let BlameConstraint { category, cause, variance_info, .. } =
-            self.regioncx.best_blame_constraint(fr, fr_origin, |r| {
+        let BlameConstraint { category, cause, variance_info, .. } = self
+            .regioncx
+            .best_blame_constraint(fr, fr_origin, |r| {
                 self.regioncx.provides_universal_region(r, fr, outlived_fr)
-            });
+            })
+            .0;
 
         debug!("report_region_error: category={:?} {:?} {:?}", category, cause, variance_info);
 

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -245,6 +245,9 @@ enum Trace<'tcx> {
     NotVisited,
 }
 
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub enum ExtraConstraintInfo {}
+
 impl<'tcx> RegionInferenceContext<'tcx> {
     /// Creates a new region inference context with a total of
     /// `num_region_variables` valid inference variables; the first N
@@ -1818,10 +1821,9 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         fr1_origin: NllRegionVariableOrigin,
         fr2: RegionVid,
     ) -> (ConstraintCategory<'tcx>, ObligationCause<'tcx>) {
-        let BlameConstraint { category, cause, .. } =
-            self.best_blame_constraint(fr1, fr1_origin, |r| {
-                self.provides_universal_region(r, fr1, fr2)
-            });
+        let BlameConstraint { category, cause, .. } = self
+            .best_blame_constraint(fr1, fr1_origin, |r| self.provides_universal_region(r, fr1, fr2))
+            .0;
         (category, cause)
     }
 
@@ -2010,7 +2012,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         from_region: RegionVid,
         from_region_origin: NllRegionVariableOrigin,
         target_test: impl Fn(RegionVid) -> bool,
-    ) -> BlameConstraint<'tcx> {
+    ) -> (BlameConstraint<'tcx>, Vec<ExtraConstraintInfo>) {
         // Find all paths
         let (path, target_region) =
             self.find_constraint_paths_between_regions(from_region, target_test).unwrap();
@@ -2026,6 +2028,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 .collect::<Vec<_>>()
         );
 
+        let extra_info = vec![];
+
         // We try to avoid reporting a `ConstraintCategory::Predicate` as our best constraint.
         // Instead, we use it to produce an improved `ObligationCauseCode`.
         // FIXME - determine what we should do if we encounter multiple `ConstraintCategory::Predicate`
@@ -2175,7 +2179,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         let best_choice =
             if blame_source { range.rev().find(find_region) } else { range.find(find_region) };
 
-        debug!(?best_choice, ?blame_source);
+        debug!(?best_choice, ?blame_source, ?extra_info);
 
         if let Some(i) = best_choice {
             if let Some(next) = categorized_path.get(i + 1) {
@@ -2184,7 +2188,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 {
                     // The return expression is being influenced by the return type being
                     // impl Trait, point at the return type and not the return expr.
-                    return next.clone();
+                    return (next.clone(), extra_info);
                 }
             }
 
@@ -2204,7 +2208,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 }
             }
 
-            return categorized_path[i].clone();
+            return (categorized_path[i].clone(), extra_info);
         }
 
         // If that search fails, that is.. unusual. Maybe everything
@@ -2214,7 +2218,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         categorized_path.sort_by(|p0, p1| p0.category.cmp(&p1.category));
         debug!("sorted_path={:#?}", categorized_path);
 
-        categorized_path.remove(0)
+        (categorized_path.remove(0), extra_info)
     }
 
     pub(crate) fn universe_info(&self, universe: ty::UniverseIndex) -> UniverseInfo<'tcx> {