Report nicer errors for HRTB NLL errors from queries

compiler/rustc_infer/src/infer/mod.rs

@@ -1111,7 +1111,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// etc) this is the root universe U0. For inference variables or
     /// placeholders, however, it will return the universe which which
     /// they are associated.
-    fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
+    pub fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
         self.inner.borrow_mut().unwrap_region_constraints().universe(r)
     }
 
@@ -1289,6 +1289,17 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         op(inner.unwrap_region_constraints().data())
     }
 
+    pub fn region_var_origin(&self, vid: ty::RegionVid) -> RegionVariableOrigin {
+        let mut inner = self.inner.borrow_mut();
+        let inner = &mut *inner;
+        inner
+            .region_constraint_storage
+            .as_mut()
+            .expect("regions already resolved")
+            .with_log(&mut inner.undo_log)
+            .var_origin(vid)
+    }
+
     /// Takes ownership of the list of variable regions. This implies
     /// that all the region constraints have already been taken, and
     /// hence that `resolve_regions_and_report_errors` can never be

compiler/rustc_infer/src/infer/region_constraints/mod.rs

@@ -445,6 +445,11 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
         self.var_infos[vid].universe
     }
 
+    /// Returns the origin for the given variable.
+    pub fn var_origin(&self, vid: RegionVid) -> RegionVariableOrigin {
+        self.var_infos[vid].origin
+    }
+
     fn add_constraint(&mut self, constraint: Constraint<'tcx>, origin: SubregionOrigin<'tcx>) {
         // cannot add constraints once regions are resolved
         debug!("RegionConstraintCollector: add_constraint({:?})", constraint);