Add an explicit Span field to OutlivesConstraint

Previously, we would retrieve the span from the `Body` using
the `locations` field. However, we may end up changing the
`locations` field when moving a constraint from a promoted
to a different body.

We now store the original `Span` in a dedication field, so that
changes to the `locations` do not affect the quality of our
diagnostics.

compiler/rustc_borrowck/src/constraints/graph.rs

@@ -156,6 +156,7 @@ impl<'s, 'tcx, D: ConstraintGraphDirecton> Iterator for Edges<'s, 'tcx, D> {
                 sup: self.static_region,
                 sub: next_static_idx.into(),
                 locations: Locations::All(DUMMY_SP),
+                span: DUMMY_SP,
                 category: ConstraintCategory::Internal,
                 variance_info: VarianceDiagInfo::default(),
             })

compiler/rustc_borrowck/src/constraints/mod.rs

@@ -2,6 +2,7 @@ use rustc_data_structures::graph::scc::Sccs;
 use rustc_index::vec::IndexVec;
 use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::{RegionVid, VarianceDiagInfo};
+use rustc_span::Span;
 use std::fmt;
 use std::ops::Index;
 
@@ -87,6 +88,12 @@ pub struct OutlivesConstraint<'tcx> {
     /// Where did this constraint arise?
     pub locations: Locations,
 
+    /// The `Span` associated with the creation of this constraint.
+    /// This should be used in preference to obtaining the span from
+    /// `locations`, since the `locations` may give a poor span
+    /// in some cases (e.g. converting a constraint from a promoted).
+    pub span: Span,
+
     /// What caused this constraint?
     pub category: ConstraintCategory,
 

compiler/rustc_borrowck/src/region_infer/dump_mir.rs

@@ -74,14 +74,18 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         let mut constraints: Vec<_> = self.constraints.outlives().iter().collect();
         constraints.sort_by_key(|c| (c.sup, c.sub));
         for constraint in &constraints {
-            let OutlivesConstraint { sup, sub, locations, category, variance_info: _ } = constraint;
+            let OutlivesConstraint { sup, sub, locations, category, span, variance_info: _ } =
+                constraint;
             let (name, arg) = match locations {
                 Locations::All(span) => {
                     ("All", tcx.sess.source_map().span_to_embeddable_string(*span))
                 }
                 Locations::Single(loc) => ("Single", format!("{:?}", loc)),
             };
-            with_msg(&format!("{:?}: {:?} due to {:?} at {}({})", sup, sub, category, name, arg))?;
+            with_msg(&format!(
+                "{:?}: {:?} due to {:?} at {}({}) ({:?}",
+                sup, sub, category, name, arg, span
+            ))?;
         }
 
         Ok(())

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -1733,7 +1733,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
     crate fn retrieve_closure_constraint_info(
         &self,
-        body: &Body<'tcx>,
+        _body: &Body<'tcx>,
         constraint: &OutlivesConstraint<'tcx>,
     ) -> BlameConstraint<'tcx> {
         let loc = match constraint.locations {
@@ -1760,7 +1760,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             .unwrap_or(BlameConstraint {
                 category: constraint.category,
                 from_closure: false,
-                cause: ObligationCause::dummy_with_span(body.source_info(loc).span),
+                cause: ObligationCause::dummy_with_span(constraint.span),
                 variance_info: constraint.variance_info,
             })
     }
@@ -1869,6 +1869,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                     sup: r,
                     sub: constraint.min_choice,
                     locations: Locations::All(p_c.definition_span),
+                    span: p_c.definition_span,
                     category: ConstraintCategory::OpaqueType,
                     variance_info: ty::VarianceDiagInfo::default(),
                 };
@@ -2017,7 +2018,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                         category: constraint.category,
                         from_closure: false,
                         cause: ObligationCause::new(
-                            constraint.locations.span(body),
+                            constraint.span,
                             CRATE_HIR_ID,
                             cause_code.clone(),
                         ),

compiler/rustc_borrowck/src/type_check/constraint_conversion.rs

@@ -8,7 +8,7 @@ use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::subst::GenericArgKind;
 use rustc_middle::ty::TypeFoldable;
 use rustc_middle::ty::{self, TyCtxt};
-use rustc_span::DUMMY_SP;
+use rustc_span::{Span, DUMMY_SP};
 
 use crate::{
     constraints::OutlivesConstraint,
@@ -26,6 +26,7 @@ crate struct ConstraintConversion<'a, 'tcx> {
     implicit_region_bound: Option<ty::Region<'tcx>>,
     param_env: ty::ParamEnv<'tcx>,
     locations: Locations,
+    span: Span,
     category: ConstraintCategory,
     constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
 }
@@ -38,6 +39,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         implicit_region_bound: Option<ty::Region<'tcx>>,
         param_env: ty::ParamEnv<'tcx>,
         locations: Locations,
+        span: Span,
         category: ConstraintCategory,
         constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
     ) -> Self {
@@ -49,6 +51,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
             implicit_region_bound,
             param_env,
             locations,
+            span,
             category,
             constraints,
         }
@@ -153,6 +156,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         self.constraints.outlives_constraints.push(OutlivesConstraint {
             locations: self.locations,
             category: self.category,
+            span: self.span,
             sub,
             sup,
             variance_info: ty::VarianceDiagInfo::default(),

compiler/rustc_borrowck/src/type_check/free_region_relations.rs

@@ -316,6 +316,7 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
                 self.implicit_region_bound,
                 self.param_env,
                 Locations::All(DUMMY_SP),
+                DUMMY_SP,
                 ConstraintCategory::Internal,
                 &mut self.constraints,
             )

compiler/rustc_borrowck/src/type_check/input_output.rs

@@ -235,6 +235,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 Some(self.implicit_region_bound),
                 self.param_env,
                 Locations::All(DUMMY_SP),
+                DUMMY_SP,
                 ConstraintCategory::Internal,
                 &mut self.borrowck_context.constraints,
             )

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1141,6 +1141,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             Some(self.implicit_region_bound),
             self.param_env,
             locations,
+            locations.span(self.body),
             category,
             &mut self.borrowck_context.constraints,
         )
@@ -2401,6 +2402,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                                 sup: ref_region.to_region_vid(),
                                 sub: borrow_region.to_region_vid(),
                                 locations: location.to_locations(),
+                                span: location.to_locations().span(body),
                                 category,
                                 variance_info: ty::VarianceDiagInfo::default(),
                             });

compiler/rustc_borrowck/src/type_check/relate_tys.rs

@@ -116,6 +116,7 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, 'tcx>
                 sup,
                 sub,
                 locations: self.locations,
+                span: self.locations.span(self.type_checker.body),
                 category: self.category,
                 variance_info: info,
             },