Auto merge of #51536 - davidtwco:nll-dyn-trait-underscore-error-improvements, r=nikomatsakis

NLL: bad error message when converting anonymous lifetime to `'static`

Contributes to #46983. This PR doesn't introduce fantastic errors, but it should hopefully lay some groundwork for diagnostic improvements.
r? @nikomatsakis

Author: bors

src/librustc_mir/borrow_check/nll/constraint_generation.rs

@@ -10,9 +10,10 @@
 
 use borrow_check::borrow_set::BorrowSet;
 use borrow_check::location::LocationTable;
+use borrow_check::nll::ToRegionVid;
 use borrow_check::nll::facts::AllFacts;
 use borrow_check::nll::region_infer::{Cause, RegionInferenceContext};
-use borrow_check::nll::ToRegionVid;
+use borrow_check::nll::type_check::AtLocation;
 use rustc::hir;
 use rustc::infer::InferCtxt;
 use rustc::mir::visit::TyContext;
@@ -310,12 +311,10 @@ impl<'cx, 'cg, 'gcx, 'tcx> ConstraintGeneration<'cx, 'cg, 'gcx, 'tcx> {
                     debug!("add_reborrow_constraint - base_ty = {:?}", base_ty);
                     match base_ty.sty {
                         ty::TyRef(ref_region, _, mutbl) => {
-                            let span = self.mir.source_info(location).span;
                             self.regioncx.add_outlives(
-                                span,
+                                location.boring(),
                                 ref_region.to_region_vid(),
                                 borrow_region.to_region_vid(),
-                                location.successor_within_block(),
                             );
 
                             if let Some(all_facts) = self.all_facts {

src/librustc_mir/borrow_check/nll/constraint_set.rs

@@ -8,12 +8,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use rustc::mir::Location;
 use rustc::ty::RegionVid;
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
+use borrow_check::nll::type_check::Locations;
 
 use std::fmt;
-use syntax_pos::Span;
 use std::ops::Deref;
 
 #[derive(Clone, Default)]
@@ -24,8 +23,8 @@ crate struct ConstraintSet {
 impl ConstraintSet {
     pub fn push(&mut self, constraint: OutlivesConstraint) {
         debug!(
-            "add_outlives({:?}: {:?} @ {:?}",
-            constraint.sup, constraint.sub, constraint.point
+            "add_outlives({:?}: {:?} @ {:?})",
+            constraint.sup, constraint.sub, constraint.locations
         );
         if constraint.sup == constraint.sub {
             // 'a: 'a is pretty uninteresting
@@ -86,9 +85,6 @@ pub struct OutlivesConstraint {
     /// Region that must be outlived.
     pub sub: RegionVid,
 
-    /// At this location.
-    pub point: Location,
-
     /// Later on, we thread the constraints onto a linked list
     /// grouped by their `sub` field. So if you had:
     ///
@@ -100,15 +96,15 @@ pub struct OutlivesConstraint {
     pub next: Option<ConstraintIndex>,
 
     /// Where did this constraint arise?
-    pub span: Span,
+    pub locations: Locations,
 }
 
 impl fmt::Debug for OutlivesConstraint {
     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
         write!(
             formatter,
-            "({:?}: {:?} @ {:?}) due to {:?}",
-            self.sup, self.sub, self.point, self.span
+            "({:?}: {:?}) due to {:?}",
+            self.sup, self.sub, self.locations
         )
     }
 }

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

@@ -82,16 +82,14 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             let OutlivesConstraint {
                 sup,
                 sub,
-                point,
-                span,
+                locations,
                 next: _,
             } = constraint;
             with_msg(&format!(
-                "{:?}: {:?} @ {:?} due to {:?}",
+                "{:?}: {:?} due to {:?}",
                 sup,
                 sub,
-                point,
-                span
+                locations,
             ))?;
         }