Rollup merge of #65776 - nnethercote:rename-LocalInternedString-and-more, r=estebank

Rename `LocalInternedString` and more

This PR renames `LocalInternedString` as `SymbolStr`, removes an unnecessary `impl` from it, improves comments, and cleans up some `SymbolStr` uses.

r? @estebank

41 files changed, 103 insertions, 114 deletions

diff --git a/src/librustc/dep_graph/dep_node.rs b/src/librustc/dep_graph/dep_node.rs
index dea8d70aaf4..cea790375fc 100644
--- a/src/librustc/dep_graph/dep_node.rs
+++ b/src/librustc/dep_graph/dep_node.rs
@@ -525,7 +525,7 @@ impl<'tcx> DepNodeParams<'tcx> for CrateNum {
     }
 
     fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
-        tcx.crate_name(*self).as_str().to_string()
+        tcx.crate_name(*self).to_string()
     }
 }
 
diff --git a/src/librustc/hir/lowering.rs b/src/librustc/hir/lowering.rs
index c6acdf53de3..c8bb35202f5 100644
--- a/src/librustc/hir/lowering.rs
+++ b/src/librustc/hir/lowering.rs
@@ -3382,7 +3382,7 @@ pub fn is_range_literal(sess: &Session, expr: &hir::Expr) -> bool {
     // either in std or core, i.e. has either a `::std::ops::Range` or
     // `::core::ops::Range` prefix.
     fn is_range_path(path: &Path) -> bool {
-        let segs: Vec<_> = path.segments.iter().map(|seg| seg.ident.as_str().to_string()).collect();
+        let segs: Vec<_> = path.segments.iter().map(|seg| seg.ident.to_string()).collect();
         let segs: Vec<_> = segs.iter().map(|seg| &**seg).collect();
 
         // "{{root}}" is the equivalent of `::` prefix in `Path`.
@@ -3423,7 +3423,7 @@ pub fn is_range_literal(sess: &Session, expr: &hir::Expr) -> bool {
         ExprKind::Call(ref func, _) => {
             if let ExprKind::Path(QPath::TypeRelative(ref ty, ref segment)) = func.kind {
                 if let TyKind::Path(QPath::Resolved(None, ref path)) = ty.kind {
-                    let new_call = segment.ident.as_str() == "new";
+                    let new_call = segment.ident.name == sym::new;
                     return is_range_path(&path) && is_lit(sess, &expr.span) && new_call;
                 }
             }
diff --git a/src/librustc/hir/print.rs b/src/librustc/hir/print.rs
index 64b355f6ec9..328d475be06 100644
--- a/src/librustc/hir/print.rs
+++ b/src/librustc/hir/print.rs
@@ -564,7 +564,7 @@ impl<'a> State<'a> {
             }
             hir::ItemKind::GlobalAsm(ref ga) => {
                 self.head(visibility_qualified(&item.vis, "global asm"));
-                self.s.word(ga.asm.as_str().to_string());
+                self.s.word(ga.asm.to_string());
                 self.end()
             }
             hir::ItemKind::TyAlias(ref ty, ref generics) => {
@@ -1855,7 +1855,7 @@ impl<'a> State<'a> {
         self.commasep(Inconsistent, &decl.inputs, |s, ty| {
             s.ibox(INDENT_UNIT);
             if let Some(arg_name) = arg_names.get(i) {
-                s.s.word(arg_name.as_str().to_string());
+                s.s.word(arg_name.to_string());
                 s.s.word(":");
                 s.s.space();
             } else if let Some(body_id) = body_id {
diff --git a/src/librustc/ich/impls_syntax.rs b/src/librustc/ich/impls_syntax.rs
index 4fd4e25f641..304735fb1c7 100644
--- a/src/librustc/ich/impls_syntax.rs
+++ b/src/librustc/ich/impls_syntax.rs
@@ -9,7 +9,7 @@ use std::mem;
 use syntax::ast;
 use syntax::feature_gate;
 use syntax::parse::token;
-use syntax::symbol::LocalInternedString;
+use syntax::symbol::SymbolStr;
 use syntax::tokenstream;
 use syntax_pos::SourceFile;
 
@@ -18,7 +18,7 @@ use crate::hir::def_id::{DefId, CrateNum, CRATE_DEF_INDEX};
 use smallvec::SmallVec;
 use rustc_data_structures::stable_hasher::{HashStable, ToStableHashKey, StableHasher};
 
-impl<'a> HashStable<StableHashingContext<'a>> for LocalInternedString {
+impl<'a> HashStable<StableHashingContext<'a>> for SymbolStr {
     #[inline]
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
         let str = self as &str;
@@ -26,13 +26,13 @@ impl<'a> HashStable<StableHashingContext<'a>> for LocalInternedString {
     }
 }
 
-impl<'a> ToStableHashKey<StableHashingContext<'a>> for LocalInternedString {
-    type KeyType = LocalInternedString;
+impl<'a> ToStableHashKey<StableHashingContext<'a>> for SymbolStr {
+    type KeyType = SymbolStr;
 
     #[inline]
     fn to_stable_hash_key(&self,
                           _: &StableHashingContext<'a>)
-                          -> LocalInternedString {
+                          -> SymbolStr {
         self.clone()
     }
 }
@@ -45,12 +45,12 @@ impl<'a> HashStable<StableHashingContext<'a>> for ast::Name {
 }
 
 impl<'a> ToStableHashKey<StableHashingContext<'a>> for ast::Name {
-    type KeyType = LocalInternedString;
+    type KeyType = SymbolStr;
 
     #[inline]
     fn to_stable_hash_key(&self,
                           _: &StableHashingContext<'a>)
-                          -> LocalInternedString {
+                          -> SymbolStr {
         self.as_str()
     }
 }
diff --git a/src/librustc/mir/mono.rs b/src/librustc/mir/mono.rs
index 58f99667cb3..a54635c3d51 100644
--- a/src/librustc/mir/mono.rs
+++ b/src/librustc/mir/mono.rs
@@ -486,7 +486,7 @@ impl CodegenUnitNameBuilder<'tcx> {
         if self.tcx.sess.opts.debugging_opts.human_readable_cgu_names {
             cgu_name
         } else {
-            let cgu_name = &cgu_name.as_str()[..];
+            let cgu_name = &cgu_name.as_str();
             Symbol::intern(&CodegenUnit::mangle_name(cgu_name))
         }
     }
diff --git a/src/librustc/traits/error_reporting.rs b/src/librustc/traits/error_reporting.rs
index 888d84d69fa..b5e8fdb6ca5 100644
--- a/src/librustc/traits/error_reporting.rs
+++ b/src/librustc/traits/error_reporting.rs
@@ -1130,7 +1130,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     let restrict_msg = "consider further restricting this bound";
                     let param_name = self_ty.to_string();
                     for param in generics.params.iter().filter(|p| {
-                        &param_name == std::convert::AsRef::<str>::as_ref(&p.name.ident().as_str())
+                        p.name.ident().as_str() == param_name
                     }) {
                         if param_name.starts_with("impl ") {
                             // `impl Trait` in argument:
diff --git a/src/librustc/traits/on_unimplemented.rs b/src/librustc/traits/on_unimplemented.rs
index b39c00a56e3..b64e44b6a5a 100644
--- a/src/librustc/traits/on_unimplemented.rs
+++ b/src/librustc/traits/on_unimplemented.rs
@@ -180,7 +180,7 @@ impl<'tcx> OnUnimplementedDirective {
                     c.ident().map_or(false, |ident| {
                         options.contains(&(
                             ident.name,
-                            c.value_str().map(|s| s.as_str().to_string())
+                            c.value_str().map(|s| s.to_string())
                         ))
                     })
                 }) {
diff --git a/src/librustc/ty/query/on_disk_cache.rs b/src/librustc/ty/query/on_disk_cache.rs
index 4dabea01c9e..4031eb62194 100644
--- a/src/librustc/ty/query/on_disk_cache.rs
+++ b/src/librustc/ty/query/on_disk_cache.rs
@@ -264,7 +264,7 @@ impl<'sess> OnDiskCache<'sess> {
             let sorted_cnums = sorted_cnums_including_local_crate(tcx);
             let prev_cnums: Vec<_> = sorted_cnums.iter()
                 .map(|&cnum| {
-                    let crate_name = tcx.original_crate_name(cnum).as_str().to_string();
+                    let crate_name = tcx.original_crate_name(cnum).to_string();
                     let crate_disambiguator = tcx.crate_disambiguator(cnum);
                     (cnum.as_u32(), crate_name, crate_disambiguator)
                 })
diff --git a/src/librustc_codegen_llvm/attributes.rs b/src/librustc_codegen_llvm/attributes.rs
index 6a36a4a50cb..6f4e7d0f0ca 100644
--- a/src/librustc_codegen_llvm/attributes.rs
+++ b/src/librustc_codegen_llvm/attributes.rs
@@ -314,7 +314,7 @@ pub fn from_fn_attrs(
             codegen_fn_attrs.target_features
                 .iter()
                 .map(|f| {
-                    let feature = &*f.as_str();
+                    let feature = &f.as_str();
                     format!("+{}", llvm_util::to_llvm_feature(cx.tcx.sess, feature))
                 })
         )
diff --git a/src/librustc_codegen_llvm/debuginfo/namespace.rs b/src/librustc_codegen_llvm/debuginfo/namespace.rs
index 628d1372b57..482bcf2aa58 100644
--- a/src/librustc_codegen_llvm/debuginfo/namespace.rs
+++ b/src/librustc_codegen_llvm/debuginfo/namespace.rs
@@ -34,11 +34,11 @@ pub fn item_namespace(cx: &CodegenCx<'ll, '_>, def_id: DefId) -> &'ll DIScope {
     });
 
     let namespace_name = match def_key.disambiguated_data.data {
-        DefPathData::CrateRoot => cx.tcx.crate_name(def_id.krate).as_str(),
-        data => data.as_symbol().as_str()
+        DefPathData::CrateRoot => cx.tcx.crate_name(def_id.krate),
+        data => data.as_symbol()
     };
 
-    let namespace_name = SmallCStr::new(&namespace_name);
+    let namespace_name = SmallCStr::new(&namespace_name.as_str());
 
     let scope = unsafe {
         llvm::LLVMRustDIBuilderCreateNameSpace(
diff --git a/src/librustc_codegen_ssa/back/command.rs b/src/librustc_codegen_ssa/back/command.rs
index 2d84d67e3c8..b8501f0e12a 100644
--- a/src/librustc_codegen_ssa/back/command.rs
+++ b/src/librustc_codegen_ssa/back/command.rs
@@ -53,7 +53,7 @@ impl Command {
     }
 
     pub fn sym_arg(&mut self, arg: Symbol) -> &mut Command {
-        self.arg(&arg.as_str());
+        self.arg(&*arg.as_str());
         self
     }
 
diff --git a/src/librustc_codegen_ssa/back/symbol_export.rs b/src/librustc_codegen_ssa/back/symbol_export.rs
index 85a90459f5e..35b62603b07 100644
--- a/src/librustc_codegen_ssa/back/symbol_export.rs
+++ b/src/librustc_codegen_ssa/back/symbol_export.rs
@@ -129,9 +129,9 @@ fn reachable_non_generics_provider(
                 //
                 // In general though we won't link right if these
                 // symbols are stripped, and LTO currently strips them.
-                if &*name == "rust_eh_personality" ||
-                   &*name == "rust_eh_register_frames" ||
-                   &*name == "rust_eh_unregister_frames" {
+                if name == "rust_eh_personality" ||
+                   name == "rust_eh_register_frames" ||
+                   name == "rust_eh_unregister_frames" {
                     SymbolExportLevel::C
                 } else {
                     SymbolExportLevel::Rust
diff --git a/src/librustc_codegen_ssa/base.rs b/src/librustc_codegen_ssa/base.rs
index ee4ec7fb41e..c3f2a5161ae 100644
--- a/src/librustc_codegen_ssa/base.rs
+++ b/src/librustc_codegen_ssa/base.rs
@@ -552,8 +552,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
     } else if let Some(kind) = *tcx.sess.allocator_kind.get() {
         let llmod_id = cgu_name_builder.build_cgu_name(LOCAL_CRATE,
                                                        &["crate"],
-                                                       Some("allocator")).as_str()
-                                                                         .to_string();
+                                                       Some("allocator")).to_string();
         let mut modules = backend.new_metadata(tcx, &llmod_id);
         time(tcx.sess, "write allocator module", || {
             backend.codegen_allocator(tcx, &mut modules, kind)
@@ -576,8 +575,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         // Codegen the encoded metadata.
         let metadata_cgu_name = cgu_name_builder.build_cgu_name(LOCAL_CRATE,
                                                                 &["crate"],
-                                                                Some("metadata")).as_str()
-                                                                                 .to_string();
+                                                                Some("metadata")).to_string();
         let mut metadata_llvm_module = backend.new_metadata(tcx, &metadata_cgu_name);
         time(tcx.sess, "write compressed metadata", || {
             backend.write_compressed_metadata(tcx, &ongoing_codegen.metadata,
diff --git a/src/librustc_codegen_utils/symbol_names/legacy.rs b/src/librustc_codegen_utils/symbol_names/legacy.rs
index 601a33a66bb..66e1b6d949e 100644
--- a/src/librustc_codegen_utils/symbol_names/legacy.rs
+++ b/src/librustc_codegen_utils/symbol_names/legacy.rs
@@ -121,9 +121,10 @@ fn get_symbol_hash<'tcx>(
         substs.hash_stable(&mut hcx, &mut hasher);
 
         if let Some(instantiating_crate) = instantiating_crate {
-            (&tcx.original_crate_name(instantiating_crate).as_str()[..])
+            tcx.original_crate_name(instantiating_crate).as_str()
+                .hash_stable(&mut hcx, &mut hasher);
+            tcx.crate_disambiguator(instantiating_crate)
                 .hash_stable(&mut hcx, &mut hasher);
-            (&tcx.crate_disambiguator(instantiating_crate)).hash_stable(&mut hcx, &mut hasher);
         }
 
         // We want to avoid accidental collision between different types of instances.
diff --git a/src/librustc_incremental/assert_module_sources.rs b/src/librustc_incremental/assert_module_sources.rs
index ca035d0cdcb..483b515f2ba 100644
--- a/src/librustc_incremental/assert_module_sources.rs
+++ b/src/librustc_incremental/assert_module_sources.rs
@@ -31,10 +31,6 @@ use syntax::symbol::{Symbol, sym};
 use rustc::ich::{ATTR_PARTITION_REUSED, ATTR_PARTITION_CODEGENED,
                  ATTR_EXPECTED_CGU_REUSE};
 
-const MODULE: Symbol = sym::module;
-const CFG: Symbol = sym::cfg;
-const KIND: Symbol = sym::kind;
-
 pub fn assert_module_sources(tcx: TyCtxt<'_>) {
     tcx.dep_graph.with_ignore(|| {
         if tcx.sess.opts.incremental.is_none() {
@@ -71,7 +67,7 @@ impl AssertModuleSource<'tcx> {
         } else if attr.check_name(ATTR_PARTITION_CODEGENED) {
             (CguReuse::No, ComparisonKind::Exact)
         } else if attr.check_name(ATTR_EXPECTED_CGU_REUSE) {
-            match &self.field(attr, KIND).as_str()[..] {
+            match &*self.field(attr, sym::kind).as_str() {
                 "no" => (CguReuse::No, ComparisonKind::Exact),
                 "pre-lto" => (CguReuse::PreLto, ComparisonKind::Exact),
                 "post-lto" => (CguReuse::PostLto, ComparisonKind::Exact),
@@ -98,8 +94,8 @@ impl AssertModuleSource<'tcx> {
             return;
         }
 
-        let user_path = self.field(attr, MODULE).as_str().to_string();
-        let crate_name = self.tcx.crate_name(LOCAL_CRATE).as_str().to_string();
+        let user_path = self.field(attr, sym::module).to_string();
+        let crate_name = self.tcx.crate_name(LOCAL_CRATE).to_string();
 
         if !user_path.starts_with(&crate_name) {
             let msg = format!("Found malformed codegen unit name `{}`. \
@@ -125,7 +121,7 @@ impl AssertModuleSource<'tcx> {
                                                        cgu_path_components,
                                                        cgu_special_suffix);
 
-        debug!("mapping '{}' to cgu name '{}'", self.field(attr, MODULE), cgu_name);
+        debug!("mapping '{}' to cgu name '{}'", self.field(attr, sym::module), cgu_name);
 
         if !self.available_cgus.contains(&cgu_name) {
             self.tcx.sess.span_err(attr.span,
@@ -135,7 +131,7 @@ impl AssertModuleSource<'tcx> {
                     cgu_name,
                     self.available_cgus
                         .iter()
-                        .map(|cgu| cgu.as_str().to_string())
+                        .map(|cgu| cgu.to_string())
                         .collect::<Vec<_>>()
                         .join(", ")));
         }
@@ -169,7 +165,7 @@ impl AssertModuleSource<'tcx> {
     /// cfg flag called `foo`.
     fn check_config(&self, attr: &ast::Attribute) -> bool {
         let config = &self.tcx.sess.parse_sess.config;
-        let value = self.field(attr, CFG);
+        let value = self.field(attr, sym::cfg);
         debug!("check_config(config={:?}, value={:?})", config, value);
         if config.iter().any(|&(name, _)| name == value) {
             debug!("check_config: matched");
diff --git a/src/librustc_incremental/persist/dirty_clean.rs b/src/librustc_incremental/persist/dirty_clean.rs
index abe0ffb0e02..ea156a94ea1 100644
--- a/src/librustc_incremental/persist/dirty_clean.rs
+++ b/src/librustc_incremental/persist/dirty_clean.rs
@@ -303,7 +303,7 @@ impl DirtyCleanVisitor<'tcx> {
         for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
             if item.check_name(LABEL) {
                 let value = expect_associated_value(self.tcx, &item);
-                return Some(self.resolve_labels(&item, value.as_str().as_ref()));
+                return Some(self.resolve_labels(&item, &value.as_str()));
             }
         }
         None
@@ -314,7 +314,7 @@ impl DirtyCleanVisitor<'tcx> {
         for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
             if item.check_name(EXCEPT) {
                 let value = expect_associated_value(self.tcx, &item);
-                return self.resolve_labels(&item, value.as_str().as_ref());
+                return self.resolve_labels(&item, &value.as_str());
             }
         }
         // if no `label` or `except` is given, only the node's group are asserted
diff --git a/src/librustc_lint/builtin.rs b/src/librustc_lint/builtin.rs
index e3c3966c2f5..30d68fd0bfc 100644
--- a/src/librustc_lint/builtin.rs
+++ b/src/librustc_lint/builtin.rs
@@ -1476,14 +1476,12 @@ impl KeywordIdents {
         let mut lint = cx.struct_span_lint(
             KEYWORD_IDENTS,
             ident.span,
-            &format!("`{}` is a keyword in the {} edition",
-                     ident.as_str(),
-                     next_edition),
+            &format!("`{}` is a keyword in the {} edition", ident, next_edition),
         );
         lint.span_suggestion(
             ident.span,
             "you can use a raw identifier to stay compatible",
-            format!("r#{}", ident.as_str()),
+            format!("r#{}", ident),
             Applicability::MachineApplicable,
         );
         lint.emit()
diff --git a/src/librustc_metadata/creader.rs b/src/librustc_metadata/creader.rs
index 07c49d91797..483b1a40e44 100644
--- a/src/librustc_metadata/creader.rs
+++ b/src/librustc_metadata/creader.rs
@@ -121,7 +121,7 @@ impl<'a> CrateLoader<'a> {
             // `source` stores paths which are normalized which may be different
             // from the strings on the command line.
             let source = &self.cstore.get_crate_data(cnum).source;
-            if let Some(entry) = self.sess.opts.externs.get(&*name.as_str()) {
+            if let Some(entry) = self.sess.opts.externs.get(&name.as_str()) {
                 // Only use `--extern crate_name=path` here, not `--extern crate_name`.
                 let found = entry.locations.iter().filter_map(|l| l.as_ref()).any(|l| {
                     let l = fs::canonicalize(l).ok();
diff --git a/src/librustc_metadata/native_libs.rs b/src/librustc_metadata/native_libs.rs
index a58db6a903b..c9de66a5c87 100644
--- a/src/librustc_metadata/native_libs.rs
+++ b/src/librustc_metadata/native_libs.rs
@@ -68,7 +68,7 @@ impl ItemLikeVisitor<'tcx> for Collector<'tcx> {
                         Some(name) => name,
                         None => continue, // skip like historical compilers
                     };
-                    lib.kind = match &kind.as_str()[..] {
+                    lib.kind = match &*kind.as_str() {
                         "static" => cstore::NativeStatic,
                         "static-nobundle" => cstore::NativeStaticNobundle,
                         "dylib" => cstore::NativeUnknown,
diff --git a/src/librustc_mir/borrow_check/conflict_errors.rs b/src/librustc_mir/borrow_check/conflict_errors.rs
index 36db68a3372..0913d743328 100644
--- a/src/librustc_mir/borrow_check/conflict_errors.rs
+++ b/src/librustc_mir/borrow_check/conflict_errors.rs
@@ -974,7 +974,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let mut err = self.cannot_borrow_across_destructor(borrow_span);
 
         let what_was_dropped = match self.describe_place(place.as_ref()) {
-            Some(name) => format!("`{}`", name.as_str()),
+            Some(name) => format!("`{}`", name),
             None => String::from("temporary value"),
         };
 
diff --git a/src/librustc_mir/interpret/intrinsics.rs b/src/librustc_mir/interpret/intrinsics.rs
index 04032847385..fbf690fe5a7 100644
--- a/src/librustc_mir/interpret/intrinsics.rs
+++ b/src/librustc_mir/interpret/intrinsics.rs
@@ -95,7 +95,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     ) -> InterpResult<'tcx, bool> {
         let substs = instance.substs;
 
-        let intrinsic_name = &self.tcx.item_name(instance.def_id()).as_str()[..];
+        let intrinsic_name = &*self.tcx.item_name(instance.def_id()).as_str();
         match intrinsic_name {
             "caller_location" => {
                 let caller = self.tcx.sess.source_map().lookup_char_pos(span.lo());
diff --git a/src/librustc_mir/transform/check_unsafety.rs b/src/librustc_mir/transform/check_unsafety.rs
index d9b983ab790..7d550716858 100644
--- a/src/librustc_mir/transform/check_unsafety.rs
+++ b/src/librustc_mir/transform/check_unsafety.rs
@@ -642,8 +642,8 @@ pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
                 struct_span_err!(
                     tcx.sess, source_info.span, E0133,
                     "{} is unsafe and requires unsafe function or block", description)
-                    .span_label(source_info.span, &description.as_str()[..])
-                    .note(&details.as_str()[..])
+                    .span_label(source_info.span, &*description.as_str())
+                    .note(&details.as_str())
                     .emit();
             }
             UnsafetyViolationKind::ExternStatic(lint_hir_id) => {
@@ -651,8 +651,8 @@ pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
                               lint_hir_id,
                               source_info.span,
                               &format!("{} is unsafe and requires unsafe function or block \
-                                        (error E0133)", &description.as_str()[..]),
-                              &details.as_str()[..]);
+                                        (error E0133)", description),
+                              &details.as_str());
             }
             UnsafetyViolationKind::BorrowPacked(lint_hir_id) => {
                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
@@ -662,8 +662,8 @@ pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
                                   lint_hir_id,
                                   source_info.span,
                                   &format!("{} is unsafe and requires unsafe function or block \
-                                            (error E0133)", &description.as_str()[..]),
-                                  &details.as_str()[..]);
+                                            (error E0133)", description),
+                                  &details.as_str());
                 }
             }
         }
diff --git a/src/librustc_mir/transform/qualify_consts.rs b/src/librustc_mir/transform/qualify_consts.rs
index 5463b944473..76899dad41a 100644
--- a/src/librustc_mir/transform/qualify_consts.rs
+++ b/src/librustc_mir/transform/qualify_consts.rs
@@ -537,7 +537,7 @@ impl Qualif for IsNotPromotable {
                     Abi::RustIntrinsic |
                     Abi::PlatformIntrinsic => {
                         assert!(!cx.tcx.is_const_fn(def_id));
-                        match &cx.tcx.item_name(def_id).as_str()[..] {
+                        match &*cx.tcx.item_name(def_id).as_str() {
                             | "size_of"
                             | "min_align_of"
                             | "needs_drop"
@@ -1477,7 +1477,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
                         Abi::RustIntrinsic |
                         Abi::PlatformIntrinsic => {
                             assert!(!self.tcx.is_const_fn(def_id));
-                            match &self.tcx.item_name(def_id).as_str()[..] {
+                            match &*self.tcx.item_name(def_id).as_str() {
                                 // special intrinsic that can be called diretly without an intrinsic
                                 // feature gate needs a language feature gate
                                 "transmute" => {
diff --git a/src/librustc_mir/transform/qualify_min_const_fn.rs b/src/librustc_mir/transform/qualify_min_const_fn.rs
index c4e44091bc9..da1fba2518a 100644
--- a/src/librustc_mir/transform/qualify_min_const_fn.rs
+++ b/src/librustc_mir/transform/qualify_min_const_fn.rs
@@ -402,7 +402,7 @@ fn check_terminator(
 ///
 /// Adding more intrinsics requires sign-off from @rust-lang/lang.
 fn is_intrinsic_whitelisted(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
-    match &tcx.item_name(def_id).as_str()[..] {
+    match &*tcx.item_name(def_id).as_str() {
         | "size_of"
         | "min_align_of"
         | "needs_drop"
diff --git a/src/librustc_resolve/late.rs b/src/librustc_resolve/late.rs
index 004d86cee8d..58af4b817d2 100644
--- a/src/librustc_resolve/late.rs
+++ b/src/librustc_resolve/late.rs
@@ -1876,7 +1876,7 @@ impl<'a, 'b> LateResolutionVisitor<'a, '_> {
                                     None
                                 }
                             });
-                            find_best_match_for_name(names, &*ident.as_str(), None)
+                            find_best_match_for_name(names, &ident.as_str(), None)
                         });
                         self.r.record_partial_res(expr.id, PartialRes::new(Res::Err));
                         self.r.report_error(
diff --git a/src/librustc_typeck/check/demand.rs b/src/librustc_typeck/check/demand.rs
index af892bf8179..309e73f57c9 100644
--- a/src/librustc_typeck/check/demand.rs
+++ b/src/librustc_typeck/check/demand.rs
@@ -308,7 +308,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }) = parent {
                 if let Ok(src) = cm.span_to_snippet(sp) {
                     for field in fields {
-                        if field.ident.as_str() == src.as_str() && field.is_shorthand {
+                        if field.ident.as_str() == src && field.is_shorthand {
                             return true;
                         }
                     }
@@ -409,13 +409,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     let mut sugg_sp = sp;
                     if let hir::ExprKind::MethodCall(segment, _sp, args) = &expr.kind {
                         let clone_trait = self.tcx.lang_items().clone_trait().unwrap();
-                        if let ([arg], Some(true), "clone") = (
+                        if let ([arg], Some(true), sym::clone) = (
                             &args[..],
                             self.tables.borrow().type_dependent_def_id(expr.hir_id).map(|did| {
                                 let ai = self.tcx.associated_item(did);
                                 ai.container == ty::TraitContainer(clone_trait)
                             }),
-                            &segment.ident.as_str()[..],
+                            segment.ident.name,
                         ) {
                             // If this expression had a clone call when suggesting borrowing
                             // we want to suggest removing it because it'd now be unecessary.
diff --git a/src/librustc_typeck/check/method/suggest.rs b/src/librustc_typeck/check/method/suggest.rs
index d90ed2a790b..b7b7861ebef 100644
--- a/src/librustc_typeck/check/method/suggest.rs
+++ b/src/librustc_typeck/check/method/suggest.rs
@@ -835,11 +835,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                     sp,
                                     &message(format!(
                                         "restrict type parameter `{}` with",
-                                        param.name.ident().as_str(),
+                                        param.name.ident(),
                                     )),
                                     candidates.iter().map(|t| format!(
                                         "{}{} {}{}",
-                                        param.name.ident().as_str(),
+                                        param.name.ident(),
                                         if impl_trait { " +" } else { ":" },
                                         self.tcx.def_path_str(t.def_id),
                                         if has_bounds.is_some() { " + "} else { "" },
diff --git a/src/librustc_typeck/check/pat.rs b/src/librustc_typeck/check/pat.rs
index 950ae7c1d62..f3f4abf01eb 100644
--- a/src/librustc_typeck/check/pat.rs
+++ b/src/librustc_typeck/check/pat.rs
@@ -978,7 +978,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     );
 
                     // we don't want to throw `E0027` in case we have thrown `E0026` for them
-                    unmentioned_fields.retain(|&x| x.as_str() != suggested_name.as_str());
+                    unmentioned_fields.retain(|&x| x.name != suggested_name);
                 }
             }
         }
diff --git a/src/librustc_typeck/collect.rs b/src/librustc_typeck/collect.rs
index 7ef842cb757..ffe034759a8 100644
--- a/src/librustc_typeck/collect.rs
+++ b/src/librustc_typeck/collect.rs
@@ -2408,7 +2408,7 @@ fn compute_sig_of_foreign_fn_decl<'tcx>(
     abi: abi::Abi,
 ) -> ty::PolyFnSig<'tcx> {
     let unsafety = if abi == abi::Abi::RustIntrinsic {
-        intrinsic_operation_unsafety(&*tcx.item_name(def_id).as_str())
+        intrinsic_operation_unsafety(&tcx.item_name(def_id).as_str())
     } else {
         hir::Unsafety::Unsafe
     };
diff --git a/src/librustdoc/clean/cfg.rs b/src/librustdoc/clean/cfg.rs
index 11f45c5f6d0..09f4873967e 100644
--- a/src/librustdoc/clean/cfg.rs
+++ b/src/librustdoc/clean/cfg.rs
@@ -404,7 +404,7 @@ impl<'a> fmt::Display for Html<'a> {
                 if !human_readable.is_empty() {
                     fmt.write_str(human_readable)
                 } else if let Some(v) = value {
-                    write!(fmt, "<code>{}=\"{}\"</code>", Escape(n), Escape(&*v.as_str()))
+                    write!(fmt, "<code>{}=\"{}\"</code>", Escape(n), Escape(&v.as_str()))
                 } else {
                     write!(fmt, "<code>{}</code>", Escape(n))
                 }
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index bdc02062230..e7f76155252 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -1167,7 +1167,7 @@ fn external_path(cx: &DocContext<'_>, name: Symbol, trait_did: Option<DefId>, ha
         global: false,
         res: Res::Err,
         segments: vec![PathSegment {
-            name: name.as_str().to_string(),
+            name: name.to_string(),
             args: external_generic_args(cx, trait_did, has_self, bindings, substs)
         }],
     }
@@ -3704,7 +3704,7 @@ fn qpath_to_string(p: &hir::QPath) -> String {
             s.push_str("::");
         }
         if seg.ident.name != kw::PathRoot {
-            s.push_str(&*seg.ident.as_str());
+            s.push_str(&seg.ident.as_str());
         }
     }
     s
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index c4ee84d33f3..29f0b99d8ee 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -2964,7 +2964,7 @@ fn render_attribute(attr: &ast::MetaItem) -> Option<String> {
     if attr.is_word() {
         Some(path)
     } else if let Some(v) = attr.value_str() {
-        Some(format!("{} = {:?}", path, v.as_str()))
+        Some(format!("{} = {:?}", path, v))
     } else if let Some(values) = attr.meta_item_list() {
         let display: Vec<_> = values.iter().filter_map(|attr| {
             attr.meta_item().and_then(|mi| render_attribute(mi))
diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 8b967048848..8af38507b48 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -90,7 +90,7 @@ impl fmt::Debug for Lifetime {
 
 impl fmt::Display for Lifetime {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{}", self.ident.name.as_str())
+        write!(f, "{}", self.ident.name)
     }
 }
 
diff --git a/src/libsyntax/feature_gate/check.rs b/src/libsyntax/feature_gate/check.rs
index 13a24ca046d..d9cc5f6c169 100644
--- a/src/libsyntax/feature_gate/check.rs
+++ b/src/libsyntax/feature_gate/check.rs
@@ -823,7 +823,7 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
             }
 
             if let Some(allowed) = allow_features.as_ref() {
-                if allowed.iter().find(|&f| f == &name.as_str() as &str).is_none() {
+                if allowed.iter().find(|&f| name.as_str() == *f).is_none() {
                     span_err!(span_handler, mi.span(), E0725,
                               "the feature `{}` is not in the list of allowed features",
                               name);
diff --git a/src/libsyntax/parse/literal.rs b/src/libsyntax/parse/literal.rs
index 7952e293a53..c42f4aa25cc 100644
--- a/src/libsyntax/parse/literal.rs
+++ b/src/libsyntax/parse/literal.rs
@@ -134,9 +134,9 @@ impl LitKind {
         let (kind, symbol, suffix) = match *self {
             LitKind::Str(symbol, ast::StrStyle::Cooked) => {
                 // Don't re-intern unless the escaped string is different.
-                let s: &str = &symbol.as_str();
+                let s = symbol.as_str();
                 let escaped = s.escape_default().to_string();
-                let symbol = if escaped == *s { symbol } else { Symbol::intern(&escaped) };
+                let symbol = if s == escaped { symbol } else { Symbol::intern(&escaped) };
                 (token::Str, symbol, None)
             }
             LitKind::Str(symbol, ast::StrStyle::Raw(n)) => {
diff --git a/src/libsyntax/parse/parser/module.rs b/src/libsyntax/parse/parser/module.rs
index a0e4d2bbb7a..242a17659a0 100644
--- a/src/libsyntax/parse/parser/module.rs
+++ b/src/libsyntax/parse/parser/module.rs
@@ -210,7 +210,7 @@ impl<'a> Parser<'a> {
             // `/` to `\`.
             #[cfg(windows)]
             let s = s.replace("/", "\\");
-            Some(dir_path.join(s))
+            Some(dir_path.join(&*s))
         } else {
             None
         }
@@ -229,7 +229,7 @@ impl<'a> Parser<'a> {
         // `./<id>.rs` and `./<id>/mod.rs`.
         let relative_prefix_string;
         let relative_prefix = if let Some(ident) = relative {
-            relative_prefix_string = format!("{}{}", ident.as_str(), path::MAIN_SEPARATOR);
+            relative_prefix_string = format!("{}{}", ident, path::MAIN_SEPARATOR);
             &relative_prefix_string
         } else {
             ""
@@ -314,7 +314,7 @@ impl<'a> Parser<'a> {
 
     fn push_directory(&mut self, id: Ident, attrs: &[Attribute]) {
         if let Some(path) = attr::first_attr_value_str_by_name(attrs, sym::path) {
-            self.directory.path.to_mut().push(&path.as_str());
+            self.directory.path.to_mut().push(&*path.as_str());
             self.directory.ownership = DirectoryOwnership::Owned { relative: None };
         } else {
             // We have to push on the current module name in the case of relative
@@ -325,10 +325,10 @@ impl<'a> Parser<'a> {
             // directory path to `/x/y/z`, not `/x/z` with a relative offset of `y`.
             if let DirectoryOwnership::Owned { relative } = &mut self.directory.ownership {
                 if let Some(ident) = relative.take() { // remove the relative offset
-                    self.directory.path.to_mut().push(ident.as_str());
+                    self.directory.path.to_mut().push(&*ident.as_str());
                 }
             }
-            self.directory.path.to_mut().push(&id.as_str());
+            self.directory.path.to_mut().push(&*id.as_str());
         }
     }
 }
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 136fc355f89..74ab5c79019 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -623,7 +623,7 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
         }
         self.maybe_print_comment(attr.span.lo());
         if attr.is_sugared_doc {
-            self.word(attr.value_str().unwrap().as_str().to_string());
+            self.word(attr.value_str().unwrap().to_string());
             self.hardbreak()
         } else {
             match attr.style {
@@ -1234,7 +1234,7 @@ impl<'a> State<'a> {
             }
             ast::ItemKind::GlobalAsm(ref ga) => {
                 self.head(visibility_qualified(&item.vis, "global_asm!"));
-                self.s.word(ga.asm.as_str().to_string());
+                self.s.word(ga.asm.to_string());
                 self.end();
             }
             ast::ItemKind::TyAlias(ref ty, ref generics) => {
@@ -2335,7 +2335,7 @@ impl<'a> State<'a> {
     }
 
     crate fn print_name(&mut self, name: ast::Name) {
-        self.s.word(name.as_str().to_string());
+        self.s.word(name.to_string());
         self.ann.post(self, AnnNode::Name(&name))
     }
 
diff --git a/src/libsyntax_expand/mbe/macro_rules.rs b/src/libsyntax_expand/mbe/macro_rules.rs
index bfdc4c52b5a..7a772b0d31d 100644
--- a/src/libsyntax_expand/mbe/macro_rules.rs
+++ b/src/libsyntax_expand/mbe/macro_rules.rs
@@ -225,7 +225,7 @@ fn generic_extension<'cx>(
                 };
                 let mut p = Parser::new(cx.parse_sess(), tts, Some(directory), true, false, None);
                 p.root_module_name =
-                    cx.current_expansion.module.mod_path.last().map(|id| id.as_str().to_string());
+                    cx.current_expansion.module.mod_path.last().map(|id| id.to_string());
                 p.last_type_ascription = cx.current_expansion.prior_type_ascription;
 
                 p.process_potential_macro_variable();
diff --git a/src/libsyntax_ext/env.rs b/src/libsyntax_ext/env.rs
index 58fe56bd235..6fb48bf8173 100644
--- a/src/libsyntax_ext/env.rs
+++ b/src/libsyntax_ext/env.rs
@@ -21,7 +21,7 @@ pub fn expand_option_env<'cx>(cx: &'cx mut ExtCtxt<'_>,
     };
 
     let sp = cx.with_def_site_ctxt(sp);
-    let e = match env::var(&*var.as_str()) {
+    let e = match env::var(&var.as_str()) {
         Err(..) => {
             let lt = cx.lifetime(sp, Ident::new(kw::StaticLifetime, sp));
             cx.expr_path(cx.path_all(sp,
diff --git a/src/libsyntax_ext/format.rs b/src/libsyntax_ext/format.rs
index 3c7f80aa399..1e1be2c0836 100644
--- a/src/libsyntax_ext/format.rs
+++ b/src/libsyntax_ext/format.rs
@@ -994,7 +994,7 @@ pub fn expand_preparsed_format_args(
         vec![]
     };
 
-    let fmt_str = &*fmt_str.as_str();  // for the suggestions below
+    let fmt_str = &fmt_str.as_str();  // for the suggestions below
     let mut parser = parse::Parser::new(fmt_str, str_style, skips, append_newline);
 
     let mut unverified_pieces = Vec::new();
diff --git a/src/libsyntax_pos/symbol.rs b/src/libsyntax_pos/symbol.rs
index 57131ffe18c..3f7b3e5b3d8 100644
--- a/src/libsyntax_pos/symbol.rs
+++ b/src/libsyntax_pos/symbol.rs
@@ -806,9 +806,9 @@ impl Ident {
         Ident::new(self.name, self.span.modern_and_legacy())
     }
 
-    /// Convert the name to a `LocalInternedString`. This is a slowish
-    /// operation because it requires locking the symbol interner.
-    pub fn as_str(self) -> LocalInternedString {
+    /// Convert the name to a `SymbolStr`. This is a slowish operation because
+    /// it requires locking the symbol interner.
+    pub fn as_str(self) -> SymbolStr {
         self.name.as_str()
     }
 }
@@ -896,11 +896,11 @@ impl Symbol {
         })
     }
 
-    /// Convert to a `LocalInternedString`. This is a slowish operation because
-    /// it requires locking the symbol interner.
-    pub fn as_str(self) -> LocalInternedString {
+    /// Convert to a `SymbolStr`. This is a slowish operation because it
+    /// requires locking the symbol interner.
+    pub fn as_str(self) -> SymbolStr {
         with_interner(|interner| unsafe {
-            LocalInternedString {
+            SymbolStr {
                 string: std::mem::transmute::<&str, &str>(interner.get(self))
             }
         })
@@ -973,6 +973,7 @@ impl Interner {
         self.names.insert(string, name);
         name
     }
+
     // Get the symbol as a string. `Symbol::as_str()` should be used in
     // preference to this function.
     pub fn get(&self, symbol: Symbol) -> &str {
@@ -1078,7 +1079,6 @@ impl Ident {
     }
 }
 
-// If an interner exists, return it. Otherwise, prepare a fresh one.
 #[inline]
 fn with_interner<T, F: FnOnce(&mut Interner) -> T>(f: F) -> T {
     GLOBALS.with(|globals| f(&mut *globals.symbol_interner.lock()))
@@ -1092,46 +1092,42 @@ fn with_interner<T, F: FnOnce(&mut Interner) -> T>(f: F) -> T {
 /// safely treat `string` which points to interner data, as an immortal string,
 /// as long as this type never crosses between threads.
 //
-// FIXME: ensure that the interner outlives any thread which uses
-// `LocalInternedString`, by creating a new thread right after constructing the
-// interner.
+// FIXME: ensure that the interner outlives any thread which uses `SymbolStr`,
+// by creating a new thread right after constructing the interner.
 #[derive(Clone, Eq, PartialOrd, Ord)]
-pub struct LocalInternedString {
+pub struct SymbolStr {
     string: &'static str,
 }
 
-impl<U: ?Sized> std::convert::AsRef<U> for LocalInternedString
-where
-    str: std::convert::AsRef<U>
-{
-    #[inline]
-    fn as_ref(&self) -> &U {
-        self.string.as_ref()
-    }
-}
-
-impl<T: std::ops::Deref<Target = str>> std::cmp::PartialEq<T> for LocalInternedString {
+// This impl allows a `SymbolStr` to be directly equated with a `String` or
+// `&str`.
+impl<T: std::ops::Deref<Target = str>> std::cmp::PartialEq<T> for SymbolStr {
     fn eq(&self, other: &T) -> bool {
         self.string == other.deref()
     }
 }
 
-impl !Send for LocalInternedString {}
-impl !Sync for LocalInternedString {}
+impl !Send for SymbolStr {}
+impl !Sync for SymbolStr {}
 
-impl std::ops::Deref for LocalInternedString {
+/// This impl means that if `ss` is a `SymbolStr`:
+/// - `*ss` is a `str`;
+/// - `&*ss` is a `&str`;
+/// - `&ss as &str` is a `&str`, which means that `&ss` can be passed to a
+///   function expecting a `&str`.
+impl std::ops::Deref for SymbolStr {
     type Target = str;
     #[inline]
     fn deref(&self) -> &str { self.string }
 }
 
-impl fmt::Debug for LocalInternedString {
+impl fmt::Debug for SymbolStr {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Debug::fmt(self.string, f)
     }
 }
 
-impl fmt::Display for LocalInternedString {
+impl fmt::Display for SymbolStr {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Display::fmt(self.string, f)
     }