Rollup merge of #64141 - nnethercote:minimize-LocalInternedString, r=petrochenkov

Minimize uses of `LocalInternedString`

`LocalInternedString` is described as "An alternative to `Symbol` and `InternedString`, useful when the chars within the symbol need to be accessed. It is best used for temporary values."

This PR makes the code match that comment, by removing all non-local uses of `LocalInternedString`. This allows the removal of a number of operations on `LocalInternedString` and a couple of uses of `unsafe`.

src/librustc/hir/map/collector.rs

@@ -186,7 +186,7 @@ impl<'a, 'hir> NodeCollector<'a, 'hir> {
             });
 
         let mut upstream_crates: Vec<_> = cstore.crates_untracked().iter().map(|&cnum| {
-            let name = cstore.crate_name_untracked(cnum).as_str();
+            let name = cstore.crate_name_untracked(cnum).as_interned_str();
             let disambiguator = cstore.crate_disambiguator_untracked(cnum).to_fingerprint();
             let hash = cstore.crate_hash_untracked(cnum);
             (name, disambiguator, hash)

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::{InternedString, LocalInternedString};
+use syntax::symbol::InternedString;
 use syntax::tokenstream;
 use syntax_pos::SourceFile;
 
@@ -39,27 +39,6 @@ impl<'a> ToStableHashKey<StableHashingContext<'a>> for InternedString {
     }
 }
 
-impl<'a> HashStable<StableHashingContext<'a>> for LocalInternedString {
-    #[inline]
-    fn hash_stable<W: StableHasherResult>(&self,
-                                          hcx: &mut StableHashingContext<'a>,
-                                          hasher: &mut StableHasher<W>) {
-        let s: &str = &**self;
-        s.hash_stable(hcx, hasher);
-    }
-}
-
-impl<'a> ToStableHashKey<StableHashingContext<'a>> for LocalInternedString {
-    type KeyType = LocalInternedString;
-
-    #[inline]
-    fn to_stable_hash_key(&self,
-                          _: &StableHashingContext<'a>)
-                          -> LocalInternedString {
-        self.clone()
-    }
-}
-
 impl<'a> HashStable<StableHashingContext<'a>> for ast::Name {
     #[inline]
     fn hash_stable<W: StableHasherResult>(&self,

src/librustc/lint/context.rs

@@ -33,7 +33,7 @@ use crate::util::common::time;
 use std::default::Default as StdDefault;
 use syntax::ast;
 use syntax::edition;
-use syntax_pos::{MultiSpan, Span, symbol::{LocalInternedString, Symbol}};
+use syntax_pos::{MultiSpan, Span, symbol::Symbol};
 use errors::DiagnosticBuilder;
 use crate::hir;
 use crate::hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
@@ -405,7 +405,7 @@ impl LintStore {
     pub fn check_lint_name(
         &self,
         lint_name: &str,
-        tool_name: Option<LocalInternedString>,
+        tool_name: Option<Symbol>,
     ) -> CheckLintNameResult<'_> {
         let complete_name = if let Some(tool_name) = tool_name {
             format!("{}::{}", tool_name, lint_name)

src/librustc/lint/levels.rs

@@ -291,7 +291,7 @@ impl<'a> LintLevelsBuilder<'a> {
                         continue;
                     }
 
-                    Some(tool_ident.as_str())
+                    Some(tool_ident.name)
                 } else {
                     None
                 };

src/librustc/traits/on_unimplemented.rs

@@ -9,10 +9,9 @@ use syntax::ast::{MetaItem, NestedMetaItem};
 use syntax::attr;
 use syntax::symbol::{Symbol, kw, sym};
 use syntax_pos::Span;
-use syntax_pos::symbol::LocalInternedString;
 
 #[derive(Clone, Debug)]
-pub struct OnUnimplementedFormatString(LocalInternedString);
+pub struct OnUnimplementedFormatString(Symbol);
 
 #[derive(Debug)]
 pub struct OnUnimplementedDirective {
@@ -89,19 +88,19 @@ impl<'tcx> OnUnimplementedDirective {
             if item.check_name(sym::message) && message.is_none() {
                 if let Some(message_) = item.value_str() {
                     message = Some(OnUnimplementedFormatString::try_parse(
-                        tcx, trait_def_id, message_.as_str(), span)?);
+                        tcx, trait_def_id, message_, span)?);
                     continue;
                 }
             } else if item.check_name(sym::label) && label.is_none() {
                 if let Some(label_) = item.value_str() {
                     label = Some(OnUnimplementedFormatString::try_parse(
-                        tcx, trait_def_id, label_.as_str(), span)?);
+                        tcx, trait_def_id, label_, span)?);
                     continue;
                 }
             } else if item.check_name(sym::note) && note.is_none() {
                 if let Some(note_) = item.value_str() {
                     note = Some(OnUnimplementedFormatString::try_parse(
-                        tcx, trait_def_id, note_.as_str(), span)?);
+                        tcx, trait_def_id, note_, span)?);
                     continue;
                 }
             } else if item.check_name(sym::on) && is_root &&
@@ -154,7 +153,7 @@ impl<'tcx> OnUnimplementedDirective {
                 message: None,
                 subcommands: vec![],
                 label: Some(OnUnimplementedFormatString::try_parse(
-                    tcx, trait_def_id, value.as_str(), attr.span)?),
+                    tcx, trait_def_id, value, attr.span)?),
                 note: None,
             }))
         } else {
@@ -218,7 +217,7 @@ impl<'tcx> OnUnimplementedFormatString {
     fn try_parse(
         tcx: TyCtxt<'tcx>,
         trait_def_id: DefId,
-        from: LocalInternedString,
+        from: Symbol,
         err_sp: Span,
     ) -> Result<Self, ErrorReported> {
         let result = OnUnimplementedFormatString(from);
@@ -234,7 +233,8 @@ impl<'tcx> OnUnimplementedFormatString {
     ) -> Result<(), ErrorReported> {
         let name = tcx.item_name(trait_def_id);
         let generics = tcx.generics_of(trait_def_id);
-        let parser = Parser::new(&self.0, None, vec![], false);
+        let s = self.0.as_str();
+        let parser = Parser::new(&s, None, vec![], false);
         let mut result = Ok(());
         for token in parser {
             match token {
@@ -294,7 +294,8 @@ impl<'tcx> OnUnimplementedFormatString {
         }).collect::<FxHashMap<Symbol, String>>();
         let empty_string = String::new();
 
-        let parser = Parser::new(&self.0, None, vec![], false);
+        let s = self.0.as_str();
+        let parser = Parser::new(&s, None, vec![], false);
         parser.map(|p|
             match p {
                 Piece::String(s) => s,

src/librustc/ty/mod.rs

@@ -46,7 +46,7 @@ use std::ops::Range;
 use syntax::ast::{self, Name, Ident, NodeId};
 use syntax::attr;
 use syntax::ext::hygiene::ExpnId;
-use syntax::symbol::{kw, sym, Symbol, LocalInternedString, InternedString};
+use syntax::symbol::{kw, sym, Symbol, InternedString};
 use syntax_pos::Span;
 
 use smallvec;
@@ -3386,10 +3386,6 @@ impl SymbolName {
             name: InternedString::intern(name)
         }
     }
-
-    pub fn as_str(&self) -> LocalInternedString {
-        self.name.as_str()
-    }
 }
 
 impl fmt::Display for SymbolName {

src/librustc_codegen_llvm/builder.rs

@@ -5,7 +5,6 @@ use crate::context::CodegenCx;
 use crate::type_::Type;
 use crate::type_of::LayoutLlvmExt;
 use crate::value::Value;
-use syntax::symbol::LocalInternedString;
 use rustc_codegen_ssa::common::{IntPredicate, TypeKind, RealPredicate};
 use rustc_codegen_ssa::MemFlags;
 use libc::{c_uint, c_char};
@@ -24,6 +23,7 @@ use std::ffi::CStr;
 use std::ops::{Deref, Range};
 use std::ptr;
 use std::iter::TrustedLen;
+use syntax::symbol::Symbol;
 
 // All Builders must have an llfn associated with them
 #[must_use]
@@ -1082,8 +1082,8 @@ impl StaticBuilderMethods for Builder<'a, 'll, 'tcx> {
 
     fn static_panic_msg(
         &mut self,
-        msg: Option<LocalInternedString>,
-        filename: LocalInternedString,
+        msg: Option<Symbol>,
+        filename: Symbol,
         line: Self::Value,
         col: Self::Value,
         kind: &str,

src/librustc_codegen_llvm/callee.rs

@@ -37,7 +37,7 @@ pub fn get_fn(
         return llfn;
     }
 
-    let sym = tcx.symbol_name(instance).as_str();
+    let sym = tcx.symbol_name(instance).name.as_str();
     debug!("get_fn({:?}: {:?}) => {}", instance, sig, sym);
 
     // Create a fn pointer with the substituted signature.

src/librustc_codegen_llvm/common.rs

@@ -17,7 +17,7 @@ use rustc_codegen_ssa::mir::place::PlaceRef;
 
 use libc::{c_uint, c_char};
 
-use syntax::symbol::LocalInternedString;
+use syntax::symbol::Symbol;
 use syntax::ast::Mutability;
 
 pub use crate::context::CodegenCx;
@@ -122,7 +122,7 @@ impl CodegenCx<'ll, 'tcx> {
 
     fn const_cstr(
         &self,
-        s: LocalInternedString,
+        s: Symbol,
         null_terminated: bool,
     ) -> &'ll Value {
         unsafe {
@@ -130,9 +130,10 @@ impl CodegenCx<'ll, 'tcx> {
                 return llval;
             }
 
+            let s_str = s.as_str();
             let sc = llvm::LLVMConstStringInContext(self.llcx,
-                                                    s.as_ptr() as *const c_char,
-                                                    s.len() as c_uint,
+                                                    s_str.as_ptr() as *const c_char,
+                                                    s_str.len() as c_uint,
                                                     !null_terminated as Bool);
             let sym = self.generate_local_symbol_name("str");
             let g = self.define_global(&sym[..], self.val_ty(sc)).unwrap_or_else(||{
@@ -147,8 +148,8 @@ impl CodegenCx<'ll, 'tcx> {
         }
     }
 
-    pub fn const_str_slice(&self, s: LocalInternedString) -> &'ll Value {
-        let len = s.len();
+    pub fn const_str_slice(&self, s: Symbol) -> &'ll Value {
+        let len = s.as_str().len();
         let cs = consts::ptrcast(self.const_cstr(s, false),
             self.type_ptr_to(self.layout_of(self.tcx.mk_str()).llvm_type(self)));
         self.const_fat_ptr(cs, self.const_usize(len as u64))

src/librustc_codegen_llvm/consts.rs

@@ -11,12 +11,11 @@ use rustc::mir::interpret::{ConstValue, Allocation, read_target_uint,
     Pointer, ErrorHandled, GlobalId};
 use rustc::mir::mono::MonoItem;
 use rustc::hir::Node;
-use syntax_pos::Span;
 use rustc_target::abi::HasDataLayout;
-use syntax::symbol::sym;
-use syntax_pos::symbol::LocalInternedString;
 use rustc::ty::{self, Ty, Instance};
 use rustc_codegen_ssa::traits::*;
+use syntax::symbol::{Symbol, sym};
+use syntax_pos::Span;
 
 use rustc::ty::layout::{self, Size, Align, LayoutOf};
 
@@ -122,10 +121,11 @@ fn check_and_apply_linkage(
     cx: &CodegenCx<'ll, 'tcx>,
     attrs: &CodegenFnAttrs,
     ty: Ty<'tcx>,
-    sym: LocalInternedString,
+    sym: Symbol,
     span: Span
 ) -> &'ll Value {
     let llty = cx.layout_of(ty).llvm_type(cx);
+    let sym = sym.as_str();
     if let Some(linkage) = attrs.linkage {
         debug!("get_static: sym={} linkage={:?}", sym, linkage);
 
@@ -221,7 +221,7 @@ impl CodegenCx<'ll, 'tcx> {
                  def_id);
 
         let ty = instance.ty(self.tcx);
-        let sym = self.tcx.symbol_name(instance).as_str();
+        let sym = self.tcx.symbol_name(instance).name.as_symbol();
 
         debug!("get_static: sym={} instance={:?}", sym, instance);
 
@@ -232,11 +232,12 @@ impl CodegenCx<'ll, 'tcx> {
                 Node::Item(&hir::Item {
                     ref attrs, span, node: hir::ItemKind::Static(..), ..
                 }) => {
-                    if self.get_declared_value(&sym[..]).is_some() {
+                    let sym_str = sym.as_str();
+                    if self.get_declared_value(&sym_str).is_some() {
                         span_bug!(span, "Conflicting symbol names for static?");
                     }
 
-                    let g = self.define_global(&sym[..], llty).unwrap();
+                    let g = self.define_global(&sym_str, llty).unwrap();
 
                     if !self.tcx.is_reachable_non_generic(def_id) {
                         unsafe {

src/librustc_codegen_llvm/context.rs

@@ -29,7 +29,7 @@ use std::cell::{Cell, RefCell};
 use std::iter;
 use std::str;
 use std::sync::Arc;
-use syntax::symbol::LocalInternedString;
+use syntax::symbol::Symbol;
 use syntax::source_map::{DUMMY_SP, Span};
 use crate::abi::Abi;
 
@@ -52,7 +52,7 @@ pub struct CodegenCx<'ll, 'tcx> {
     pub vtables:
         RefCell<FxHashMap<(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>), &'ll Value>>,
     /// Cache of constant strings,
-    pub const_cstr_cache: RefCell<FxHashMap<LocalInternedString, &'ll Value>>,
+    pub const_cstr_cache: RefCell<FxHashMap<Symbol, &'ll Value>>,
 
     /// Reverse-direction for const ptrs cast from globals.
     /// Key is a Value holding a *T,

src/librustc_codegen_llvm/debuginfo/metadata.rs

@@ -2251,7 +2251,7 @@ pub fn create_global_var_metadata(
         None
     } else {
         let linkage_name = mangled_name_of_instance(cx, Instance::mono(tcx, def_id));
-        Some(SmallCStr::new(&linkage_name.as_str()))
+        Some(SmallCStr::new(&linkage_name.name.as_str()))
     };
 
     let global_align = cx.align_of(variable_type);

src/librustc_codegen_llvm/debuginfo/mod.rs

@@ -290,7 +290,7 @@ impl DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         let scope_line = span_start(self, span).line;
 
         let function_name = CString::new(name).unwrap();
-        let linkage_name = SmallCStr::new(&linkage_name.as_str());
+        let linkage_name = SmallCStr::new(&linkage_name.name.as_str());
 
         let mut flags = DIFlags::FlagPrototyped;
 

src/librustc_codegen_ssa/back/symbol_export.rs

@@ -121,7 +121,7 @@ fn reachable_non_generics_provider(
         })
         .map(|def_id| {
             let export_level = if special_runtime_crate {
-                let name = tcx.symbol_name(Instance::mono(tcx, def_id)).as_str();
+                let name = tcx.symbol_name(Instance::mono(tcx, def_id)).name.as_str();
                 // We can probably do better here by just ensuring that
                 // it has hidden visibility rather than public
                 // visibility, as this is primarily here to ensure it's

src/librustc_codegen_ssa/mir/block.rs

@@ -14,7 +14,7 @@ use crate::traits::*;
 
 use std::borrow::Cow;
 
-use syntax::symbol::LocalInternedString;
+use syntax::symbol::Symbol;
 use syntax_pos::Pos;
 
 use super::{FunctionCx, LocalRef};
@@ -397,7 +397,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
         // Get the location information.
         let loc = bx.sess().source_map().lookup_char_pos(span.lo());
-        let filename = LocalInternedString::intern(&loc.file.name.to_string());
+        let filename = Symbol::intern(&loc.file.name.to_string());
         let line = bx.const_u32(loc.line as u32);
         let col = bx.const_u32(loc.col.to_usize() as u32 + 1);
 
@@ -418,8 +418,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     vec![file_line_col, index, len])
             }
             _ => {
-                let str = msg.description();
-                let msg_str = LocalInternedString::intern(str);
+                let msg_str = Symbol::intern(msg.description());
                 let msg_file_line_col = bx.static_panic_msg(
                     Some(msg_str),
                     filename,
@@ -531,7 +530,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             let layout = bx.layout_of(ty);
             if layout.abi.is_uninhabited() {
                 let loc = bx.sess().source_map().lookup_char_pos(span.lo());
-                let filename = LocalInternedString::intern(&loc.file.name.to_string());
+                let filename = Symbol::intern(&loc.file.name.to_string());
                 let line = bx.const_u32(loc.line as u32);
                 let col = bx.const_u32(loc.col.to_usize() as u32 + 1);
 
@@ -539,7 +538,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     "Attempted to instantiate uninhabited type {}",
                     ty
                 );
-                let msg_str = LocalInternedString::intern(&str);
+                let msg_str = Symbol::intern(&str);
                 let msg_file_line_col = bx.static_panic_msg(
                     Some(msg_str),
                     filename,

src/librustc_codegen_ssa/mono_item.rs

@@ -58,7 +58,7 @@ impl<'a, 'tcx: 'a> MonoItemExt<'a, 'tcx> for MonoItem<'tcx> {
                self.to_raw_string(),
                cx.codegen_unit().name());
 
-        let symbol_name = self.symbol_name(cx.tcx()).as_str();
+        let symbol_name = self.symbol_name(cx.tcx()).name.as_str();
 
         debug!("symbol {}", &symbol_name);
 

src/librustc_codegen_ssa/traits/statics.rs

@@ -1,5 +1,5 @@
 use super::BackendTypes;
-use syntax_pos::symbol::LocalInternedString;
+use syntax_pos::symbol::Symbol;
 use rustc::hir::def_id::DefId;
 use rustc::ty::layout::Align;
 
@@ -12,8 +12,8 @@ pub trait StaticBuilderMethods: BackendTypes {
     fn get_static(&mut self, def_id: DefId) -> Self::Value;
     fn static_panic_msg(
         &mut self,
-        msg: Option<LocalInternedString>,
-        filename: LocalInternedString,
+        msg: Option<Symbol>,
+        filename: Symbol,
         line: Self::Value,
         col: Self::Value,
         kind: &str,

src/librustc_codegen_utils/symbol_names_test.rs

@@ -40,7 +40,7 @@ impl SymbolNamesTest<'tcx> {
                 let instance = Instance::mono(tcx, def_id);
                 let mangled = self.tcx.symbol_name(instance);
                 tcx.sess.span_err(attr.span, &format!("symbol-name({})", mangled));
-                if let Ok(demangling) = rustc_demangle::try_demangle(&mangled.as_str()) {
+                if let Ok(demangling) = rustc_demangle::try_demangle(&mangled.name.as_str()) {
                     tcx.sess.span_err(attr.span, &format!("demangling({})", demangling));
                     tcx.sess.span_err(attr.span, &format!("demangling-alt({:#})", demangling));
                 }

src/librustc_mir/borrow_check/error_reporting.rs

@@ -336,7 +336,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let local = &self.body.local_decls[local_index];
         match local.name {
             Some(name) if !local.from_compiler_desugaring() => {
-                buf.push_str(name.as_str().get());
+                buf.push_str(&name.as_str());
                 Ok(())
             }
             _ => Err(()),

src/librustc_mir/monomorphize/partitioning.rs

@@ -777,7 +777,7 @@ where
             debug!("CodegenUnit {}:", cgu.name());
 
             for (mono_item, linkage) in cgu.items() {
-                let symbol_name = mono_item.symbol_name(tcx).as_str();
+                let symbol_name = mono_item.symbol_name(tcx).name.as_str();
                 let symbol_hash_start = symbol_name.rfind('h');
                 let symbol_hash = symbol_hash_start.map(|i| &symbol_name[i ..])
                                                    .unwrap_or("<no hash>");

src/librustc_typeck/check/expr.rs

@@ -19,7 +19,7 @@ use crate::astconv::AstConv as _;
 
 use errors::{Applicability, DiagnosticBuilder};
 use syntax::ast;
-use syntax::symbol::{Symbol, LocalInternedString, kw, sym};
+use syntax::symbol::{Symbol, kw, sym};
 use syntax::source_map::Span;
 use syntax::util::lev_distance::find_best_match_for_name;
 use rustc::hir;
@@ -1244,7 +1244,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }
             _ => {
                 // prevent all specified fields from being suggested
-                let skip_fields = skip_fields.iter().map(|ref x| x.ident.as_str());
+                let skip_fields = skip_fields.iter().map(|ref x| x.ident.name);
                 if let Some(field_name) = Self::suggest_field_name(
                     variant,
                     &field.ident.as_str(),
@@ -1288,11 +1288,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     // Return an hint about the closest match in field names
     fn suggest_field_name(variant: &'tcx ty::VariantDef,
                           field: &str,
-                          skip: Vec<LocalInternedString>)
+                          skip: Vec<Symbol>)
                           -> Option<Symbol> {
         let names = variant.fields.iter().filter_map(|field| {
             // ignore already set fields and private fields from non-local crates
-            if skip.iter().any(|x| *x == field.ident.as_str()) ||
+            if skip.iter().any(|&x| x == field.ident.name) ||
                (!variant.def_id.is_local() && field.vis != Visibility::Public)
             {
                 None

src/libsyntax_pos/symbol.rs

@@ -818,10 +818,14 @@ impl Ident {
         with_interner(|interner| interner.is_gensymed(self.name))
     }
 
+    /// Convert the name to a `LocalInternedString`. This is a slowish
+    /// operation because it requires locking the symbol interner.
     pub fn as_str(self) -> LocalInternedString {
         self.name.as_str()
     }
 
+    /// Convert the name to an `InternedString`. This is a slowish operation
+    /// because it requires locking the symbol interner.
     pub fn as_interned_str(self) -> InternedString {
         self.name.as_interned_str()
     }
@@ -916,6 +920,25 @@ impl Symbol {
         with_interner(|interner| interner.intern(string))
     }
 
+    /// Access the symbol's chars. This is a slowish operation because it
+    /// requires locking the symbol interner.
+    pub fn with<F: FnOnce(&str) -> R, R>(self, f: F) -> R {
+        with_interner(|interner| {
+            f(interner.get(self))
+        })
+    }
+
+    /// Access two symbols' chars. This is a slowish operation because it
+    /// requires locking the symbol interner, but it is faster than calling
+    /// `with()` twice.
+    fn with2<F: FnOnce(&str, &str) -> R, R>(self, other: Symbol, f: F) -> R {
+        with_interner(|interner| {
+            f(interner.get(self), interner.get(other))
+        })
+    }
+
+    /// Convert to a `LocalInternedString`. This is a slowish operation because
+    /// it requires locking the symbol interner.
     pub fn as_str(self) -> LocalInternedString {
         with_interner(|interner| unsafe {
             LocalInternedString {
@@ -924,6 +947,8 @@ impl Symbol {
         })
     }
 
+    /// Convert to an `InternedString`. This is a slowish operation because it
+    /// requires locking the symbol interner.
     pub fn as_interned_str(self) -> InternedString {
         with_interner(|interner| InternedString {
             symbol: interner.interned(self)
@@ -1152,39 +1177,11 @@ 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, Hash, PartialOrd, Eq, Ord)]
+#[derive(Clone, Copy, Eq, PartialOrd, Ord)]
 pub struct LocalInternedString {
     string: &'static str,
 }
 
-impl LocalInternedString {
-    /// Maps a string to its interned representation.
-    pub fn intern(string: &str) -> Self {
-        let string = with_interner(|interner| {
-            let symbol = interner.intern(string);
-            interner.strings[symbol.0.as_usize()]
-        });
-        LocalInternedString {
-            string: unsafe { std::mem::transmute::<&str, &str>(string) }
-        }
-    }
-
-    pub fn as_interned_str(self) -> InternedString {
-        InternedString {
-            symbol: Symbol::intern(self.string)
-        }
-    }
-
-    #[inline]
-    pub fn get(&self) -> &str {
-        // This returns a valid string since we ensure that `self` outlives the interner
-        // by creating the interner on a thread which outlives threads which can access it.
-        // This type cannot move to a thread which outlives the interner since it does
-        // not implement Send.
-        self.string
-    }
-}
-
 impl<U: ?Sized> std::convert::AsRef<U> for LocalInternedString
 where
     str: std::convert::AsRef<U>
@@ -1246,18 +1243,6 @@ impl fmt::Display for LocalInternedString {
     }
 }
 
-impl Decodable for LocalInternedString {
-    fn decode<D: Decoder>(d: &mut D) -> Result<LocalInternedString, D::Error> {
-        Ok(LocalInternedString::intern(&d.read_str()?))
-    }
-}
-
-impl Encodable for LocalInternedString {
-    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
-        s.emit_str(self.string)
-    }
-}
-
 /// An alternative to `Symbol` that is focused on string contents. It has two
 /// main differences to `Symbol`.
 ///
@@ -1285,28 +1270,19 @@ impl InternedString {
     }
 
     pub fn with<F: FnOnce(&str) -> R, R>(self, f: F) -> R {
-        let str = with_interner(|interner| {
-            interner.get(self.symbol) as *const str
-        });
-        // This is safe because the interner keeps string alive until it is dropped.
-        // We can access it because we know the interner is still alive since we use a
-        // scoped thread local to access it, and it was alive at the beginning of this scope
-        unsafe { f(&*str) }
+        self.symbol.with(f)
     }
 
     fn with2<F: FnOnce(&str, &str) -> R, R>(self, other: &InternedString, f: F) -> R {
-        let (self_str, other_str) = with_interner(|interner| {
-            (interner.get(self.symbol) as *const str,
-             interner.get(other.symbol) as *const str)
-        });
-        // This is safe for the same reason that `with` is safe.
-        unsafe { f(&*self_str, &*other_str) }
+        self.symbol.with2(other.symbol, f)
     }
 
     pub fn as_symbol(self) -> Symbol {
         self.symbol
     }
 
+    /// Convert to a `LocalInternedString`. This is a slowish operation because it
+    /// requires locking the symbol interner.
     pub fn as_str(self) -> LocalInternedString {
         self.symbol.as_str()
     }