Make Region::as_var infallible.

It's what all the call sites require.

Author: nnethercote

compiler/rustc_borrowck/src/lib.rs

@@ -507,9 +507,7 @@ impl<'cx, 'tcx> BorrowckInferCtxt<'cx, 'tcx> {
         F: Fn() -> RegionCtxt,
     {
         let next_region = self.infcx.next_region_var(origin);
-        let vid = next_region
-            .as_var()
-            .unwrap_or_else(|| bug!("expected RegionKind::RegionVar on {:?}", next_region));
+        let vid = next_region.as_var();
 
         if cfg!(debug_assertions) && !self.inside_canonicalization_ctxt() {
             debug!("inserting vid {:?} with origin {:?} into var_to_origin", vid, origin);
@@ -531,9 +529,7 @@ impl<'cx, 'tcx> BorrowckInferCtxt<'cx, 'tcx> {
         F: Fn() -> RegionCtxt,
     {
         let next_region = self.infcx.next_nll_region_var(origin.clone());
-        let vid = next_region
-            .as_var()
-            .unwrap_or_else(|| bug!("expected RegionKind::RegionVar on {:?}", next_region));
+        let vid = next_region.as_var();
 
         if cfg!(debug_assertions) && !self.inside_canonicalization_ctxt() {
             debug!("inserting vid {:?} with origin {:?} into var_to_origin", vid, origin);

compiler/rustc_borrowck/src/type_check/relate_tys.rs

@@ -131,13 +131,9 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, 'tcx>
             ty::BoundRegionKind::BrEnv => BoundRegionInfo::Name(sym::env),
         };
 
-        let reg_var =
-            reg.as_var().unwrap_or_else(|| bug!("expected region {:?} to be of kind ReVar", reg));
-
         if cfg!(debug_assertions) && !self.type_checker.infcx.inside_canonicalization_ctxt() {
             let mut var_to_origin = self.type_checker.infcx.reg_var_to_origin.borrow_mut();
-            debug!(?reg_var);
-            var_to_origin.insert(reg_var, RegionCtxt::Placeholder(reg_info));
+            var_to_origin.insert(reg.as_var(), RegionCtxt::Placeholder(reg_info));
         }
 
         reg
@@ -150,12 +146,9 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, 'tcx>
             universe,
         );
 
-        let reg_var =
-            reg.as_var().unwrap_or_else(|| bug!("expected region {:?} to be of kind ReVar", reg));
-
         if cfg!(debug_assertions) && !self.type_checker.infcx.inside_canonicalization_ctxt() {
             let mut var_to_origin = self.type_checker.infcx.reg_var_to_origin.borrow_mut();
-            var_to_origin.insert(reg_var, RegionCtxt::Existential(None));
+            var_to_origin.insert(reg.as_var(), RegionCtxt::Existential(None));
         }
 
         reg

compiler/rustc_middle/src/ty/sty.rs

@@ -1772,10 +1772,10 @@ impl<'tcx> Region<'tcx> {
         matches!(self.kind(), ty::ReVar(_))
     }
 
-    pub fn as_var(self) -> Option<RegionVid> {
+    pub fn as_var(self) -> RegionVid {
         match self.kind() {
-            ty::ReVar(vid) => Some(vid),
-            _ => None,
+            ty::ReVar(vid) => vid,
+            _ => bug!("expected region {:?} to be of kind ReVar", self),
         }
     }
 }