Remove kw::Extra checks that are no longer necessary.

Thanks to the introduction of `PatKind::Missing`.

Author: nnethercote

Diff for: compiler/rustc_ast_lowering/src/lib.rs

@@ -1496,13 +1496,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Option<Ident>] {
         self.arena.alloc_from_iter(decl.inputs.iter().map(|param| match param.pat.kind {
             PatKind::Missing => None,
-            PatKind::Ident(_, ident, _) => {
-                if ident.name != kw::Empty {
-                    Some(self.lower_ident(ident))
-                } else {
-                    None
-                }
-            }
+            PatKind::Ident(_, ident, _) => Some(self.lower_ident(ident)),
             PatKind::Wild => Some(Ident::new(kw::Underscore, self.lower_span(param.pat.span))),
             _ => {
                 self.dcx().span_delayed_bug(

Diff for: compiler/rustc_passes/src/liveness.rs

@@ -96,7 +96,7 @@ use rustc_middle::query::Providers;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{self, RootVariableMinCaptureList, Ty, TyCtxt};
 use rustc_session::lint;
-use rustc_span::{BytePos, Span, Symbol, kw, sym};
+use rustc_span::{BytePos, Span, Symbol, sym};
 use tracing::{debug, instrument};
 
 use self::LiveNodeKind::*;
@@ -1481,9 +1481,6 @@ impl<'tcx> Liveness<'_, 'tcx> {
 
     fn should_warn(&self, var: Variable) -> Option<String> {
         let name = self.ir.variable_name(var);
-        if name == kw::Empty {
-            return None;
-        }
         let name = name.as_str();
         if name.as_bytes()[0] == b'_' {
             return None;

Diff for: compiler/rustc_resolve/src/late.rs

@@ -3999,22 +3999,17 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             self.report_error(ident.span, error(ident));
         }
 
-        // Record as bound if it's valid:
-        let ident_valid = ident.name != kw::Empty;
-        if ident_valid {
-            bindings.last_mut().unwrap().1.insert(ident);
-        }
+        // Record as bound.
+        bindings.last_mut().unwrap().1.insert(ident);
 
         if already_bound_or {
             // `Variant1(a) | Variant2(a)`, ok
             // Reuse definition from the first `a`.
             self.innermost_rib_bindings(ValueNS)[&ident]
         } else {
+            // A completely fresh binding is added to the set.
             let res = Res::Local(pat_id);
-            if ident_valid {
-                // A completely fresh binding add to the set if it's valid.
-                self.innermost_rib_bindings(ValueNS).insert(ident, res);
-            }
+            self.innermost_rib_bindings(ValueNS).insert(ident, res);
             res
         }
     }