Remove ReEmpty

Author: jackh726

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -357,11 +357,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                 ty::BoundRegionKind::BrAnon(_) => None,
             },
 
-            ty::ReLateBound(..)
-            | ty::ReVar(..)
-            | ty::RePlaceholder(..)
-            | ty::ReEmpty(_)
-            | ty::ReErased => None,
+            ty::ReLateBound(..) | ty::ReVar(..) | ty::RePlaceholder(..) | ty::ReErased => None,
         }
     }
 

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -486,9 +486,9 @@ impl<'tcx> TypeFolder<'tcx> for ReverseMapper<'tcx> {
             ty::ReErased => return r,
 
             // The regions that we expect from borrow checking.
-            ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReEmpty(ty::UniverseIndex::ROOT) => {}
+            ty::ReEarlyBound(_) | ty::ReFree(_) => {}
 
-            ty::ReEmpty(_) | ty::RePlaceholder(_) | ty::ReVar(_) => {
+            ty::RePlaceholder(_) | ty::ReVar(_) => {
                 // All of the regions in the type should either have been
                 // erased by writeback, or mapped back to named regions by
                 // borrow checking.

compiler/rustc_borrowck/src/type_check/free_region_relations.rs

@@ -347,13 +347,6 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
 
             match outlives_bound {
                 OutlivesBound::RegionSubRegion(r1, r2) => {
-                    // `where Type:` is lowered to `where Type: 'empty` so that
-                    // we check `Type` is well formed, but there's no use for
-                    // this bound here.
-                    if r1.is_empty() {
-                        return;
-                    }
-
                     // The bound says that `r1 <= r2`; we store `r2: r1`.
                     let r1 = self.universal_regions.to_region_vid(r1);
                     let r2 = self.universal_regions.to_region_vid(r2);

compiler/rustc_borrowck/src/universal_regions.rs

@@ -54,13 +54,6 @@ pub struct UniversalRegions<'tcx> {
     /// The total number of universal region variables instantiated.
     num_universals: usize,
 
-    /// A special region variable created for the `'empty(U0)` region.
-    /// Note that this is **not** a "universal" region, as it doesn't
-    /// represent a universally bound placeholder or any such thing.
-    /// But we do create it here in this type because it's a useful region
-    /// to have around in a few limited cases.
-    pub root_empty: RegionVid,
-
     /// The "defining" type for this function, with all universal
     /// regions instantiated. For a closure or generator, this is the
     /// closure type, but for a top-level function it's the `FnDef`.
@@ -323,11 +316,7 @@ impl<'tcx> UniversalRegions<'tcx> {
 
     /// See `UniversalRegionIndices::to_region_vid`.
     pub fn to_region_vid(&self, r: ty::Region<'tcx>) -> RegionVid {
-        if let ty::ReEmpty(ty::UniverseIndex::ROOT) = *r {
-            self.root_empty
-        } else {
-            self.indices.to_region_vid(r)
-        }
+        self.indices.to_region_vid(r)
     }
 
     /// As part of the NLL unit tests, you can annotate a function with
@@ -501,16 +490,10 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
             _ => None,
         };
 
-        let root_empty = self
-            .infcx
-            .next_nll_region_var(NllRegionVariableOrigin::Existential { from_forall: true })
-            .to_region_vid();
-
         UniversalRegions {
             indices,
             fr_static,
             fr_fn_body,
-            root_empty,
             first_extern_index,
             first_local_index,
             num_universals,

compiler/rustc_infer/src/errors/note_and_explain.rs

@@ -27,13 +27,6 @@ impl<'a> DescriptionCtx<'a> {
                 me.kind = "restatic";
             }
 
-            ty::ReEmpty(ty::UniverseIndex::ROOT) => me.kind = "reempty",
-
-            ty::ReEmpty(ui) => {
-                me.kind = "reemptyuni";
-                me.arg = format!("{:?}", ui);
-            }
-
             ty::RePlaceholder(_) => return None,
 
             // FIXME(#13998) RePlaceholder should probably print like

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -180,11 +180,7 @@ impl CanonicalizeMode for CanonicalizeQueryResponse {
         r: ty::Region<'tcx>,
     ) -> ty::Region<'tcx> {
         match *r {
-            ty::ReFree(_)
-            | ty::ReErased
-            | ty::ReStatic
-            | ty::ReEmpty(ty::UniverseIndex::ROOT)
-            | ty::ReEarlyBound(..) => r,
+            ty::ReFree(_) | ty::ReErased | ty::ReStatic | ty::ReEarlyBound(..) => r,
 
             ty::RePlaceholder(placeholder) => canonicalizer.canonical_var_for_region(
                 CanonicalVarInfo { kind: CanonicalVarKind::PlaceholderRegion(placeholder) },
@@ -199,10 +195,6 @@ impl CanonicalizeMode for CanonicalizeQueryResponse {
                 )
             }
 
-            ty::ReEmpty(ui) => {
-                bug!("canonicalizing 'empty in universe {:?}", ui) // FIXME
-            }
-
             _ => {
                 // Other than `'static` or `'empty`, the query
                 // response should be executing in a fully
@@ -381,7 +373,6 @@ impl<'cx, 'tcx> TypeFolder<'tcx> for Canonicalizer<'cx, 'tcx> {
             ty::ReStatic
             | ty::ReEarlyBound(..)
             | ty::ReFree(_)
-            | ty::ReEmpty(_)
             | ty::RePlaceholder(..)
             | ty::ReErased => self.canonicalize_mode.canonicalize_free_region(self, r),
         }

compiler/rustc_infer/src/infer/combine.rs

@@ -688,7 +688,6 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
 
             ty::RePlaceholder(..)
             | ty::ReVar(..)
-            | ty::ReEmpty(_)
             | ty::ReStatic
             | ty::ReEarlyBound(..)
             | ty::ReFree(..) => {
@@ -900,7 +899,6 @@ impl<'tcx> TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> {
 
             ty::RePlaceholder(..)
             | ty::ReVar(..)
-            | ty::ReEmpty(_)
             | ty::ReStatic
             | ty::ReEarlyBound(..)
             | ty::ReFree(..) => {

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

@@ -96,11 +96,6 @@ pub(super) fn note_and_explain_region<'tcx>(
             msg_span_from_free_region(tcx, region, alt_span)
         }
 
-        ty::ReEmpty(ty::UniverseIndex::ROOT) => ("the empty lifetime".to_owned(), alt_span),
-
-        // uh oh, hope no user ever sees THIS
-        ty::ReEmpty(ui) => (format!("the empty lifetime in universe {:?}", ui), alt_span),
-
         ty::RePlaceholder(_) => return,
 
         // FIXME(#13998) RePlaceholder should probably print like
@@ -139,8 +134,6 @@ fn msg_span_from_free_region<'tcx>(
             (msg, Some(span))
         }
         ty::ReStatic => ("the static lifetime".to_owned(), alt_span),
-        ty::ReEmpty(ty::UniverseIndex::ROOT) => ("an empty lifetime".to_owned(), alt_span),
-        ty::ReEmpty(ui) => (format!("an empty lifetime in universe {:?}", ui), alt_span),
         _ => bug!("{:?}", region),
     }
 }
@@ -250,17 +243,7 @@ pub fn unexpected_hidden_region_diagnostic<'tcx>(
 
     // Explain the region we are capturing.
     match *hidden_region {
-        ty::ReEmpty(ty::UniverseIndex::ROOT) => {
-            // All lifetimes shorter than the function body are `empty` in
-            // lexical region resolution. The default explanation of "an empty
-            // lifetime" isn't really accurate here.
-            let message = format!(
-                "hidden type `{}` captures lifetime smaller than the function body",
-                hidden_ty
-            );
-            err.span_note(span, &message);
-        }
-        ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic | ty::ReEmpty(_) => {
+        ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic => {
             // Assuming regionck succeeded (*), we ought to always be
             // capturing *some* region from the fn header, and hence it
             // ought to be free. So under normal circumstances, we will go

compiler/rustc_infer/src/infer/freshen.rs

@@ -126,7 +126,6 @@ impl<'a, 'tcx> TypeFolder<'tcx> for TypeFreshener<'a, 'tcx> {
             | ty::ReFree(_)
             | ty::ReVar(_)
             | ty::RePlaceholder(..)
-            | ty::ReEmpty(_)
             | ty::ReErased => {
                 // replace all free regions with 'erased
                 self.tcx().lifetimes.re_erased

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

@@ -16,7 +16,7 @@ use rustc_data_structures::intern::Interned;
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::{self, Ty, TyCtxt};
-use rustc_middle::ty::{ReEarlyBound, ReEmpty, ReErased, ReFree, ReStatic};
+use rustc_middle::ty::{ReEarlyBound, ReErased, ReFree, ReStatic};
 use rustc_middle::ty::{ReLateBound, RePlaceholder, ReVar};
 use rustc_middle::ty::{Region, RegionVid};
 use rustc_span::Span;
@@ -261,13 +261,6 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                                         cur_region
                                     }
 
-                                    ReEmpty(b_ui) => {
-                                        // Empty regions are ordered according to the universe
-                                        // they are associated with.
-                                        let ui = a_universe.min(b_ui);
-                                        self.tcx().mk_region(ReEmpty(ui))
-                                    }
-
                                     RePlaceholder(placeholder) => {
                                         // If the empty and placeholder regions are in the same universe,
                                         // then the LUB is the Placeholder region (which is the cur_region).
@@ -399,13 +392,6 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                         a_region
                     }
 
-                    ReEmpty(a_ui) => {
-                        // Empty regions are ordered according to the universe
-                        // they are associated with.
-                        let ui = a_ui.min(empty_ui);
-                        self.tcx().mk_region(ReEmpty(ui))
-                    }
-
                     RePlaceholder(placeholder) => {
                         // If this empty region is from a universe that can
                         // name the placeholder, then the placeholder is
@@ -428,9 +414,6 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                 // check below for a common case, here purely as an
                 // optimization.
                 let b_universe = self.var_infos[b_vid].universe;
-                if let ReEmpty(a_universe) = *a_region && a_universe == b_universe {
-                    return false;
-                }
 
                 let mut lub = self.lub_concrete_regions(a_region, cur_region);
                 if lub == cur_region {
@@ -470,7 +453,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                 // they are associated with.
                 a_ui.min(b_ui) == b_ui
             }
-            (VarValue::Value(a), VarValue::Empty(b_ui)) => {
+            (VarValue::Value(a), VarValue::Empty(_)) => {
                 match *a {
                     ReLateBound(..) | ReErased => {
                         bug!("cannot relate region: {:?}", a);
@@ -493,12 +476,6 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                         false
                     }
 
-                    ReEmpty(a_ui) => {
-                        // Empty regions are ordered according to the universe
-                        // they are associated with.
-                        a_ui.min(b_ui) == b_ui
-                    }
-
                     RePlaceholder(_) => {
                         // The LUB is either `a` or `'static`
                         false
@@ -526,12 +503,6 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                         true
                     }
 
-                    ReEmpty(b_ui) => {
-                        // Empty regions are ordered according to the universe
-                        // they are associated with.
-                        a_ui.min(b_ui) == b_ui
-                    }
-
                     RePlaceholder(placeholder) => {
                         // If this empty region is from a universe that can
                         // name the placeholder, then the placeholder is
@@ -599,37 +570,6 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                 self.tcx().lifetimes.re_static
             }
 
-            (ReEmpty(_), ReEarlyBound(_) | ReFree(_)) => {
-                // All empty regions are less than early-bound, free,
-                // and scope regions.
-                b
-            }
-
-            (ReEarlyBound(_) | ReFree(_), ReEmpty(_)) => {
-                // All empty regions are less than early-bound, free,
-                // and scope regions.
-                a
-            }
-
-            (ReEmpty(a_ui), ReEmpty(b_ui)) => {
-                // Empty regions are ordered according to the universe
-                // they are associated with.
-                let ui = a_ui.min(b_ui);
-                self.tcx().mk_region(ReEmpty(ui))
-            }
-
-            (ReEmpty(empty_ui), RePlaceholder(placeholder))
-            | (RePlaceholder(placeholder), ReEmpty(empty_ui)) => {
-                // If this empty region is from a universe that can
-                // name the placeholder, then the placeholder is
-                // larger; otherwise, the only ancestor is `'static`.
-                if empty_ui.can_name(placeholder.universe) {
-                    self.tcx().mk_region(RePlaceholder(placeholder))
-                } else {
-                    self.tcx().lifetimes.re_static
-                }
-            }
-
             (ReEarlyBound(_) | ReFree(_), ReEarlyBound(_) | ReFree(_)) => {
                 self.region_rels.lub_free_regions(a, b)
             }
@@ -1088,9 +1028,9 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                 ty::ReVar(rid) => match var_values.values[rid] {
                     VarValue::ErrorValue => false,
                     VarValue::Empty(_) => true,
-                    VarValue::Value(min) => matches!(*min, ty::ReEmpty(_)),
+                    VarValue::Value(_) => false,
                 },
-                _ => matches!(*min, ty::ReEmpty(_)),
+                _ => false,
             },
 
             VerifyBound::AnyBound(bs) => {