De-implement several traits for LocalInternedString.

`Clone` and `Copy` haven't been needed for some time.

`Eq`, `PartialOrd`, `Ord` are no longer necessary now that `Symbol` is
ordered by chars rather than index.

Author: nnethercote

src/librustc/middle/lib_features.rs

@@ -32,7 +32,7 @@ impl LibFeatures {
         let mut all_features: Vec<_> = self.stable.iter().map(|(f, s)| (*f, Some(*s)))
             .chain(self.unstable.iter().map(|f| (*f, None)))
             .collect();
-        all_features.sort_unstable_by_key(|f| f.0.as_str());
+        all_features.sort_unstable_by_key(|f| f.0);
         all_features
     }
 }

src/librustc_resolve/diagnostics.rs

@@ -1,5 +1,3 @@
-use std::cmp::Reverse;
-
 use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
 use log::debug;
 use rustc::bug;
@@ -496,7 +494,7 @@ impl<'a> Resolver<'a> {
         });
 
         // Make sure error reporting is deterministic.
-        suggestions.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
+        suggestions.sort_by_key(|suggestion| suggestion.candidate);
 
         match find_best_match_for_name(
             suggestions.iter().map(|suggestion| &suggestion.candidate),
@@ -798,7 +796,8 @@ impl<'a, 'b> ImportResolver<'a, 'b> {
         // 2) `std` suggestions before `core` suggestions.
         let mut extern_crate_names =
             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
-        extern_crate_names.sort_by_key(|name| Reverse(name.as_str()));
+        extern_crate_names.sort();
+        extern_crate_names.reverse();
 
         for name in extern_crate_names.into_iter() {
             // Replace first ident with a crate name and check if that is valid.

src/librustc_resolve/late/diagnostics.rs

@@ -618,7 +618,7 @@ impl<'a> LateResolutionVisitor<'a, '_> {
 
         let name = path[path.len() - 1].ident.name;
         // Make sure error reporting is deterministic.
-        names.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
+        names.sort_by_key(|suggestion| suggestion.candidate);
 
         match find_best_match_for_name(
             names.iter().map(|suggestion| &suggestion.candidate),

src/librustc_typeck/check/expr.rs

@@ -1182,9 +1182,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             let mut displayable_field_names = remaining_fields
                                               .keys()
-                                              .map(|ident| ident.as_str())
+                                              .map(|ident| ident.name)
                                               .collect::<Vec<_>>();
-
             displayable_field_names.sort();
 
             let truncated_fields_error = if len <= 3 {

src/librustc_typeck/check/method/probe.rs

@@ -958,7 +958,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             .collect();
 
         // Sort them by the name so we have a stable result.
-        names.sort_by_cached_key(|n| n.as_str());
+        names.sort_by_key(|n| n.name);
         names
     }
 

src/libsyntax_pos/symbol.rs

@@ -1128,7 +1128,6 @@ fn with_interner<T, F: FnOnce(&mut Interner) -> T>(f: F) -> T {
 // FIXME: ensure that the interner outlives any thread which uses
 // `LocalInternedString`, by creating a new thread right after constructing the
 // interner.
-#[derive(Clone, Copy, Eq, PartialOrd, Ord)]
 pub struct LocalInternedString {
     string: &'static str,
 }