Remove kw::Empty uses from rustc_middle.

There are several places in `rustc_middle` that check for an empty
lifetime name. These checks appear to be totally unnecessary, because
empty lifetime names aren't produced here. (Empty lifetime names *are*
possible in `hir::Lifetime`. Perhaps there was some confusion between
it and the `rustc_middle` types?)

This commit removes the `kw::Empty` checks.

Author: nnethercote

compiler/rustc_middle/src/ty/generics.rs

@@ -73,9 +73,7 @@ impl GenericParamDef {
 
     pub fn is_anonymous_lifetime(&self) -> bool {
         match self.kind {
-            GenericParamDefKind::Lifetime => {
-                self.name == kw::UnderscoreLifetime || self.name == kw::Empty
-            }
+            GenericParamDefKind::Lifetime => self.name == kw::UnderscoreLifetime,
             _ => false,
         }
     }

compiler/rustc_middle/src/ty/mod.rs

@@ -457,7 +457,7 @@ impl EarlyParamRegion {
     /// Does this early bound region have a name? Early bound regions normally
     /// always have names except when using anonymous lifetimes (`'_`).
     pub fn has_name(&self) -> bool {
-        self.name != kw::UnderscoreLifetime && self.name != kw::Empty
+        self.name != kw::UnderscoreLifetime
     }
 }
 

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -2591,11 +2591,9 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
         // to fit that into a short string. Hence the recommendation to use
         // `explain_region()` or `note_and_explain_region()`.
         match *region {
-            ty::ReEarlyParam(ref data) => {
-                if data.name != kw::Empty {
-                    p!(write("{}", data.name));
-                    return Ok(());
-                }
+            ty::ReEarlyParam(data) => {
+                p!(write("{}", data.name));
+                return Ok(());
             }
             ty::ReLateParam(ty::LateParamRegion { kind, .. }) => {
                 if let Some(name) = kind.get_name() {
@@ -2834,7 +2832,7 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
 
                         (name, ty::BoundRegionKind::Named(CRATE_DEF_ID.to_def_id(), name))
                     }
-                    ty::BoundRegionKind::Named(def_id, kw::UnderscoreLifetime | kw::Empty) => {
+                    ty::BoundRegionKind::Named(def_id, kw::UnderscoreLifetime) => {
                         let name = next_name(self);
 
                         if let Some(lt_idx) = lifetime_idx {

compiler/rustc_middle/src/ty/region.rs

@@ -400,9 +400,7 @@ impl LateParamRegionKind {
 
     pub fn is_named(&self) -> bool {
         match *self {
-            LateParamRegionKind::Named(_, name) => {
-                name != kw::UnderscoreLifetime && name != kw::Empty
-            }
+            LateParamRegionKind::Named(_, name) => name != kw::UnderscoreLifetime,
             _ => false,
         }
     }
@@ -475,7 +473,7 @@ impl core::fmt::Debug for BoundRegion {
 impl BoundRegionKind {
     pub fn is_named(&self) -> bool {
         match *self {
-            BoundRegionKind::Named(_, name) => name != kw::UnderscoreLifetime && name != kw::Empty,
+            BoundRegionKind::Named(_, name) => name != kw::UnderscoreLifetime,
             _ => false,
         }
     }