Avoid unnecessary internings.

Most involving `Symbol::intern` on string literals.

src/librustc/hir/lowering.rs

@@ -1145,9 +1145,7 @@ impl<'a> LoweringContext<'a> {
         let unstable_span = self.sess.source_map().mark_span_with_reason(
             CompilerDesugaringKind::Async,
             span,
-            Some(vec![
+            Some(vec![sym::gen_future].into()),
-                Symbol::intern("gen_future"),
-            ].into()),
         );
         let gen_future = self.expr_std_path(
             unstable_span, &[sym::future, sym::from_generator], None, ThinVec::new());
@@ -4177,9 +4175,7 @@ impl<'a> LoweringContext<'a> {
                     let unstable_span = this.sess.source_map().mark_span_with_reason(
                         CompilerDesugaringKind::TryBlock,
                         body.span,
-                        Some(vec![
+                        Some(vec![sym::try_trait].into()),
-                            Symbol::intern("try_trait"),
-                        ].into()),
                     );
                     let mut block = this.lower_block(body, true).into_inner();
                     let tail = block.expr.take().map_or_else(

src/librustc/middle/lang_items.rs

@@ -210,8 +210,8 @@ impl<'a, 'tcx> LanguageItemCollector<'a, 'tcx> {
 pub fn extract(attrs: &[ast::Attribute]) -> Option<(Symbol, Span)> {
     attrs.iter().find_map(|attr| Some(match attr {
         _ if attr.check_name(sym::lang) => (attr.value_str()?, attr.span),
-        _ if attr.check_name(sym::panic_handler) => (Symbol::intern("panic_impl"), attr.span),
+        _ if attr.check_name(sym::panic_handler) => (sym::panic_impl, attr.span),
-        _ if attr.check_name(sym::alloc_error_handler) => (Symbol::intern("oom"), attr.span),
+        _ if attr.check_name(sym::alloc_error_handler) => (sym::oom, attr.span),
         _ => return None,
     }))
 }

src/librustc/middle/stability.rs

@@ -437,7 +437,7 @@ impl<'a, 'tcx> Index<'tcx> {
                         reason: Some(Symbol::intern(reason)),
                         issue: 27812,
                     },
-                    feature: Symbol::intern("rustc_private"),
+                    feature: sym::rustc_private,
                     rustc_depr: None,
                     const_stability: None,
                     promotable: false,
@@ -880,7 +880,7 @@ pub fn check_unused_or_stable_features<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
     // FIXME: only remove `libc` when `stdbuild` is active.
     // FIXME: remove special casing for `test`.
     remaining_lib_features.remove(&Symbol::intern("libc"));
-    remaining_lib_features.remove(&Symbol::intern("test"));
+    remaining_lib_features.remove(&sym::test);
 
     let check_features =
         |remaining_lib_features: &mut FxHashMap<_, _>, defined_features: &[_]| {

src/librustc/session/config.rs

@@ -19,7 +19,7 @@ use syntax::source_map::{FileName, FilePathMapping};
 use syntax::edition::{Edition, EDITION_NAME_LIST, DEFAULT_EDITION};
 use syntax::parse::token;
 use syntax::parse;
-use syntax::symbol::Symbol;
+use syntax::symbol::{sym, Symbol};
 use syntax::feature_gate::UnstableFeatures;
 use errors::emitter::HumanReadableErrorType;
 
@@ -1503,31 +1503,31 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
         Some(Symbol::intern(vendor)),
     ));
     if sess.target.target.options.has_elf_tls {
-        ret.insert((Symbol::intern("target_thread_local"), None));
+        ret.insert((sym::target_thread_local, None));
     }
     for &i in &[8, 16, 32, 64, 128] {
         if i >= min_atomic_width && i <= max_atomic_width {
             let s = i.to_string();
             ret.insert((
-                Symbol::intern("target_has_atomic"),
+                sym::target_has_atomic,
                 Some(Symbol::intern(&s)),
             ));
             if &s == wordsz {
                 ret.insert((
-                    Symbol::intern("target_has_atomic"),
+                    sym::target_has_atomic,
                     Some(Symbol::intern("ptr")),
                 ));
             }
         }
     }
     if atomic_cas {
-        ret.insert((Symbol::intern("target_has_atomic"), Some(Symbol::intern("cas"))));
+        ret.insert((sym::target_has_atomic, Some(Symbol::intern("cas"))));
     }
     if sess.opts.debug_assertions {
         ret.insert((Symbol::intern("debug_assertions"), None));
     }
     if sess.opts.crate_types.contains(&CrateType::ProcMacro) {
-        ret.insert((Symbol::intern("proc_macro"), None));
+        ret.insert((sym::proc_macro, None));
     }
     ret
 }
@@ -1547,7 +1547,7 @@ pub fn build_configuration(sess: &Session, mut user_cfg: ast::CrateConfig) -> as
     let default_cfg = default_configuration(sess);
     // If the user wants a test runner, then add the test cfg
     if sess.opts.test {
-        user_cfg.insert((Symbol::intern("test"), None));
+        user_cfg.insert((sym::test, None));
     }
     user_cfg.extend(default_cfg.iter().cloned());
     user_cfg
@@ -2702,7 +2702,7 @@ mod tests {
     use std::path::PathBuf;
     use super::{Externs, OutputType, OutputTypes};
     use rustc_target::spec::{MergeFunctions, PanicStrategy, RelroLevel};
-    use syntax::symbol::Symbol;
+    use syntax::symbol::sym;
     use syntax::edition::{Edition, DEFAULT_EDITION};
     use syntax;
     use super::Options;
@@ -2744,7 +2744,7 @@ mod tests {
             let (sessopts, cfg) = build_session_options_and_crate_config(matches);
             let sess = build_session(sessopts, None, registry);
             let cfg = build_configuration(&sess, to_crate_config(cfg));
-            assert!(cfg.contains(&(Symbol::intern("test"), None)));
+            assert!(cfg.contains(&(sym::test, None)));
         });
     }
 
@@ -2752,7 +2752,6 @@ mod tests {
     // another --cfg test
     #[test]
     fn test_switch_implies_cfg_test_unless_cfg_test() {
-        use syntax::symbol::sym;
         syntax::with_default_globals(|| {
             let matches = &match optgroups().parse(&["--test".to_string(),
                                                      "--cfg=test".to_string()]) {

src/librustc_allocator/expand.rs

@@ -91,9 +91,7 @@ impl MutVisitor for ExpandAllocatorDirectives<'_> {
             call_site: item.span, // use the call site of the static
             def_site: None,
             format: MacroAttribute(Symbol::intern(name)),
-            allow_internal_unstable: Some(vec![
+            allow_internal_unstable: Some(vec![sym::rustc_attrs].into()),
-                Symbol::intern("rustc_attrs"),
-            ].into()),
             allow_internal_unsafe: false,
             local_inner_macros: false,
             edition: self.sess.edition,
@@ -223,7 +221,7 @@ impl AllocFnFactory<'_> {
     }
 
     fn attrs(&self) -> Vec<Attribute> {
-        let special = Symbol::intern("rustc_std_internal_symbol");
+        let special = sym::rustc_std_internal_symbol;
         let special = self.cx.meta_word(self.span, special);
         vec![self.cx.attribute(self.span, special)]
     }

src/librustc_interface/util.rs

@@ -68,7 +68,7 @@ pub fn add_configuration(
     sess: &Session,
     codegen_backend: &dyn CodegenBackend,
 ) {
-    let tf = Symbol::intern("target_feature");
+    let tf = sym::target_feature;
 
     cfg.extend(
         codegen_backend

src/librustc_metadata/cstore_impl.rs

@@ -431,9 +431,7 @@ impl cstore::CStore {
             let client = proc_macro::bridge::client::Client::expand1(proc_macro::quote);
             let ext = SyntaxExtension::ProcMacro {
                 expander: Box::new(BangProcMacro { client }),
-                allow_internal_unstable: Some(vec![
+                allow_internal_unstable: Some(vec![sym::proc_macro_def_site].into()),
-                    Symbol::intern("proc_macro_def_site"),
-                ].into()),
                 edition: data.root.edition,
             };
             return LoadedMacro::ProcMacro(Lrc::new(ext));

src/librustc_typeck/check/mod.rs

@@ -4944,7 +4944,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 // This is less than ideal, it will not suggest a return type span on any
                 // method called `main`, regardless of whether it is actually the entry point,
                 // but it will still present it as the reason for the expected type.
-                Some((decl, ident, ident.name != Symbol::intern("main")))
+                Some((decl, ident, ident.name != sym::main))
             }),
             Node::TraitItem(&hir::TraitItem {
                 ident, node: hir::TraitItemKind::Method(hir::MethodSig {

src/libsyntax/ext/derive.rs

@@ -58,10 +58,7 @@ pub fn add_derived_markers<T>(cx: &mut ExtCtxt<'_>, span: Span, traits: &[ast::P
         call_site: span,
         def_site: None,
         format: ExpnFormat::MacroAttribute(Symbol::intern(&pretty_name)),
-        allow_internal_unstable: Some(vec![
+        allow_internal_unstable: Some(vec![sym::rustc_attrs, sym::structural_match].into()),
-            Symbol::intern("rustc_attrs"),
-            Symbol::intern("structural_match"),
-        ].into()),
         allow_internal_unsafe: false,
         local_inner_macros: false,
         edition: cx.parse_sess.edition,
@@ -74,7 +71,7 @@ pub fn add_derived_markers<T>(cx: &mut ExtCtxt<'_>, span: Span, traits: &[ast::P
             attrs.push(cx.attribute(span, meta));
         }
         if names.contains(&Symbol::intern("Copy")) {
-            let meta = cx.meta_word(span, Symbol::intern("rustc_copy_clone_marker"));
+            let meta = cx.meta_word(span, sym::rustc_copy_clone_marker);
             attrs.push(cx.attribute(span, meta));
         }
     });

src/libsyntax/ext/expand.rs

@@ -938,7 +938,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             }
             BuiltinDerive(func) => {
                 expn_info.allow_internal_unstable = Some(vec![
-                    Symbol::intern("rustc_attrs"),
+                    sym::rustc_attrs,
                     Symbol::intern("derive_clone_copy"),
                     Symbol::intern("derive_eq"),
                     Symbol::intern("libstd_sys_internals"), // RustcDeserialize and RustcSerialize

src/libsyntax/ext/tt/macro_rules.rs

@@ -396,7 +396,7 @@ pub fn compile(
                         future this will become a hard error. Please use `allow_internal_unstable(\
                         foo, bar)` to only allow the `foo` and `bar` features",
                     );
-                    vec![Symbol::intern("allow_internal_unstable_backcompat_hack")].into()
+                    vec![sym::allow_internal_unstable_backcompat_hack].into()
                 })
             );
         let allow_internal_unsafe = attr::contains_name(&def.attrs, sym::allow_internal_unsafe);

src/libsyntax/parse/parser.rs

@@ -5787,7 +5787,7 @@ impl<'a> Parser<'a> {
             VisibilityKind::Inherited => {}
             _ => {
                 let is_macro_rules: bool = match self.token {
-                    token::Ident(sid, _) => sid.name == Symbol::intern("macro_rules"),
+                    token::Ident(sid, _) => sid.name == sym::macro_rules,
                     _ => false,
                 };
                 let mut err = if is_macro_rules {

src/libsyntax/std_inject.rs

@@ -20,9 +20,7 @@ fn ignored_span(sp: Span, edition: Edition) -> Span {
         call_site: DUMMY_SP,
         def_site: None,
         format: MacroAttribute(Symbol::intern("std_inject")),
-        allow_internal_unstable: Some(vec![
+        allow_internal_unstable: Some(vec![sym::prelude_import].into()),
-            Symbol::intern("prelude_import"),
-        ].into()),
         allow_internal_unsafe: false,
         local_inner_macros: false,
         edition,
@@ -98,7 +96,7 @@ pub fn maybe_inject_crates_ref(
     krate.module.items.insert(0, P(ast::Item {
         attrs: vec![ast::Attribute {
             style: ast::AttrStyle::Outer,
-            path: ast::Path::from_ident(ast::Ident::new(Symbol::intern("prelude_import"), span)),
+            path: ast::Path::from_ident(ast::Ident::new(sym::prelude_import, span)),
             tokens: TokenStream::empty(),
             id: attr::mk_attr_id(),
             is_sugared_doc: false,

src/libsyntax/test.rs

@@ -283,12 +283,8 @@ fn generate_test_harness(sess: &ParseSess,
     mark.set_expn_info(ExpnInfo {
         call_site: DUMMY_SP,
         def_site: None,
-        format: MacroAttribute(Symbol::intern("test_case")),
+        format: MacroAttribute(sym::test_case),
-        allow_internal_unstable: Some(vec![
+        allow_internal_unstable: Some(vec![sym::main, sym::test, sym::rustc_attrs].into()),
-            Symbol::intern("main"),
-            Symbol::intern("test"),
-            Symbol::intern("rustc_attrs"),
-        ].into()),
         allow_internal_unsafe: false,
         local_inner_macros: false,
         edition: sess.edition,
@@ -347,14 +343,14 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
     let call_test_main = ecx.stmt_expr(call_test_main);
 
     // #![main]
-    let main_meta = ecx.meta_word(sp, Symbol::intern("main"));
+    let main_meta = ecx.meta_word(sp, sym::main);
     let main_attr = ecx.attribute(sp, main_meta);
 
     // extern crate test as test_gensym
     let test_extern_stmt = ecx.stmt_item(sp, ecx.item(sp,
         test_id,
         vec![],
-        ast::ItemKind::ExternCrate(Some(Symbol::intern("test")))
+        ast::ItemKind::ExternCrate(Some(sym::test))
     ));
 
     // pub fn main() { ... }

src/libsyntax_ext/asm.rs

@@ -11,7 +11,7 @@ use syntax::ext::base::{self, *};
 use syntax::feature_gate;
 use syntax::parse::{self, token};
 use syntax::ptr::P;
-use syntax::symbol::{Symbol, sym};
+use syntax::symbol::{kw, sym, Symbol};
 use syntax::ast::AsmDialect;
 use syntax_pos::Span;
 use syntax::tokenstream;
@@ -93,7 +93,7 @@ fn parse_inline_asm<'a>(
         })
         .unwrap_or(tts.len());
     let mut p = cx.new_parser_from_tts(&tts[first_colon..]);
-    let mut asm = Symbol::intern("");
+    let mut asm = kw::Invalid;
     let mut asm_str_style = None;
     let mut outputs = Vec::new();
     let mut inputs = Vec::new();

src/libsyntax_ext/assert.rs

@@ -8,7 +8,7 @@ use syntax::parse::token::{self, Token};
 use syntax::parse::parser::Parser;
 use syntax::print::pprust;
 use syntax::ptr::P;
-use syntax::symbol::Symbol;
+use syntax::symbol::{sym, Symbol};
 use syntax::tokenstream::{TokenStream, TokenTree};
 use syntax_pos::{Span, DUMMY_SP};
 
@@ -27,7 +27,7 @@ pub fn expand_assert<'cx>(
 
     let sp = sp.apply_mark(cx.current_expansion.mark);
     let panic_call = Mac_ {
-        path: Path::from_ident(Ident::new(Symbol::intern("panic"), sp)),
+        path: Path::from_ident(Ident::new(sym::panic, sp)),
         tts: custom_message.unwrap_or_else(|| {
             TokenStream::from(TokenTree::Token(
                 DUMMY_SP,

src/libsyntax_ext/deriving/clone.rs

@@ -7,7 +7,7 @@ use syntax::attr;
 use syntax::ext::base::{Annotatable, ExtCtxt};
 use syntax::ext::build::AstBuilder;
 use syntax::ptr::P;
-use syntax::symbol::{Symbol, kw, sym};
+use syntax::symbol::{kw, sym};
 use syntax_pos::Span;
 
 pub fn expand_deriving_clone(cx: &mut ExtCtxt<'_>,
@@ -76,7 +76,7 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt<'_>,
         _ => cx.span_bug(span, "#[derive(Clone)] on trait item or impl item"),
     }
 
-    let inline = cx.meta_word(span, Symbol::intern("inline"));
+    let inline = cx.meta_word(span, sym::inline);
     let attrs = vec![cx.attribute(span, inline)];
     let trait_def = TraitDef {
         span,

src/libsyntax_ext/deriving/cmp/eq.rs

@@ -6,7 +6,7 @@ use syntax::ast::{self, Expr, MetaItem, GenericArg};
 use syntax::ext::base::{Annotatable, ExtCtxt};
 use syntax::ext::build::AstBuilder;
 use syntax::ptr::P;
-use syntax::symbol::Symbol;
+use syntax::symbol::sym;
 use syntax_pos::Span;
 
 pub fn expand_deriving_eq(cx: &mut ExtCtxt<'_>,
@@ -14,9 +14,9 @@ pub fn expand_deriving_eq(cx: &mut ExtCtxt<'_>,
                           mitem: &MetaItem,
                           item: &Annotatable,
                           push: &mut dyn FnMut(Annotatable)) {
-    let inline = cx.meta_word(span, Symbol::intern("inline"));
+    let inline = cx.meta_word(span, sym::inline);
-    let hidden = cx.meta_list_item_word(span, Symbol::intern("hidden"));
+    let hidden = cx.meta_list_item_word(span, sym::hidden);
-    let doc = cx.meta_list(span, Symbol::intern("doc"), vec![hidden]);
+    let doc = cx.meta_list(span, sym::doc, vec![hidden]);
     let attrs = vec![cx.attribute(span, inline), cx.attribute(span, doc)];
     let trait_def = TraitDef {
         span,

src/libsyntax_ext/deriving/cmp/ord.rs

@@ -6,7 +6,7 @@ use syntax::ast::{self, Expr, MetaItem};
 use syntax::ext::base::{Annotatable, ExtCtxt};
 use syntax::ext::build::AstBuilder;
 use syntax::ptr::P;
-use syntax::symbol::Symbol;
+use syntax::symbol::sym;
 use syntax_pos::Span;
 
 pub fn expand_deriving_ord(cx: &mut ExtCtxt<'_>,
@@ -14,7 +14,7 @@ pub fn expand_deriving_ord(cx: &mut ExtCtxt<'_>,
                            mitem: &MetaItem,
                            item: &Annotatable,
                            push: &mut dyn FnMut(Annotatable)) {
-    let inline = cx.meta_word(span, Symbol::intern("inline"));
+    let inline = cx.meta_word(span, sym::inline);
     let attrs = vec![cx.attribute(span, inline)];
     let trait_def = TraitDef {
         span,

src/libsyntax_ext/deriving/cmp/partial_eq.rs

@@ -6,7 +6,7 @@ use syntax::ast::{BinOpKind, Expr, MetaItem};
 use syntax::ext::base::{Annotatable, ExtCtxt};
 use syntax::ext::build::AstBuilder;
 use syntax::ptr::P;
-use syntax::symbol::Symbol;
+use syntax::symbol::sym;
 use syntax_pos::Span;
 
 pub fn expand_deriving_partial_eq(cx: &mut ExtCtxt<'_>,
@@ -62,7 +62,7 @@ pub fn expand_deriving_partial_eq(cx: &mut ExtCtxt<'_>,
 
     macro_rules! md {
         ($name:expr, $f:ident) => { {
-            let inline = cx.meta_word(span, Symbol::intern("inline"));
+            let inline = cx.meta_word(span, sym::inline);
             let attrs = vec![cx.attribute(span, inline)];
             MethodDef {
                 name: $name,

src/libsyntax_ext/deriving/cmp/partial_ord.rs

@@ -8,7 +8,7 @@ use syntax::ast::{self, BinOpKind, Expr, MetaItem};
 use syntax::ext::base::{Annotatable, ExtCtxt};
 use syntax::ext::build::AstBuilder;
 use syntax::ptr::P;
-use syntax::symbol::Symbol;
+use syntax::symbol::sym;
 use syntax_pos::Span;
 
 pub fn expand_deriving_partial_ord(cx: &mut ExtCtxt<'_>,
@@ -18,7 +18,7 @@ pub fn expand_deriving_partial_ord(cx: &mut ExtCtxt<'_>,
                                    push: &mut dyn FnMut(Annotatable)) {
     macro_rules! md {
         ($name:expr, $op:expr, $equal:expr) => { {
-            let inline = cx.meta_word(span, Symbol::intern("inline"));
+            let inline = cx.meta_word(span, sym::inline);
             let attrs = vec![cx.attribute(span, inline)];
             MethodDef {
                 name: $name,
@@ -42,7 +42,7 @@ pub fn expand_deriving_partial_ord(cx: &mut ExtCtxt<'_>,
                                     vec![Box::new(ordering_ty)],
                                     PathKind::Std));
 
-    let inline = cx.meta_word(span, Symbol::intern("inline"));
+    let inline = cx.meta_word(span, sym::inline);
     let attrs = vec![cx.attribute(span, inline)];
 
     let partial_cmp_def = MethodDef {

src/libsyntax_ext/deriving/debug.rs

@@ -9,6 +9,7 @@ use syntax::ast::{Expr, MetaItem};
 use syntax::ext::base::{Annotatable, ExtCtxt};
 use syntax::ext::build::AstBuilder;
 use syntax::ptr::P;
+use syntax::symbol::sym;
 use syntax_pos::{DUMMY_SP, Span};
 
 pub fn expand_deriving_debug(cx: &mut ExtCtxt<'_>,
@@ -82,7 +83,7 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
 
                 let expr = cx.expr_method_call(span,
                                                 builder_expr.clone(),
-                                                Ident::from_str("field"),
+                                                Ident::with_empty_ctxt(sym::field),
                                                 vec![field]);
 
                 // Use `let _ = expr;` to avoid triggering the
@@ -106,7 +107,7 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
                 let field = cx.expr_addr_of(field.span, field);
                 let expr = cx.expr_method_call(span,
                                                 builder_expr.clone(),
-                                                Ident::from_str("field"),
+                                                Ident::with_empty_ctxt(sym::field),
                                                 vec![name, field]);
                 stmts.push(stmt_let_undescore(cx, span, expr));
             }

src/libsyntax_ext/deriving/default.rs

@@ -6,7 +6,7 @@ use syntax::ast::{Expr, MetaItem};
 use syntax::ext::base::{Annotatable, DummyResult, ExtCtxt};
 use syntax::ext::build::AstBuilder;
 use syntax::ptr::P;
-use syntax::symbol::Symbol;
+use syntax::symbol::sym;
 use syntax::span_err;
 use syntax_pos::Span;
 
@@ -15,7 +15,7 @@ pub fn expand_deriving_default(cx: &mut ExtCtxt<'_>,
                                mitem: &MetaItem,
                                item: &Annotatable,
                                push: &mut dyn FnMut(Annotatable)) {
-    let inline = cx.meta_word(span, Symbol::intern("inline"));
+    let inline = cx.meta_word(span, sym::inline);
     let attrs = vec![cx.attribute(span, inline)];
     let trait_def = TraitDef {
         span,

src/libsyntax_ext/deriving/generic/mod.rs

@@ -666,14 +666,13 @@ impl<'a> TraitDef<'a> {
         let self_type = cx.ty_path(path);
 
         let attr = cx.attribute(self.span,
-                                cx.meta_word(self.span,
+                                cx.meta_word(self.span, sym::automatically_derived));
-                                             Symbol::intern("automatically_derived")));
         // Just mark it now since we know that it'll end up used downstream
         attr::mark_used(&attr);
         let opt_trait_ref = Some(trait_ref);
         let unused_qual = {
             let word = cx.meta_list_item_word(self.span, Symbol::intern("unused_qualifications"));
-            cx.attribute(self.span, cx.meta_list(self.span, Symbol::intern("allow"), vec![word]))
+            cx.attribute(self.span, cx.meta_list(self.span, sym::allow, vec![word]))
         };
 
         let mut a = vec![attr, unused_qual];

src/libsyntax_ext/deriving/mod.rs

@@ -145,7 +145,7 @@ fn call_intrinsic(cx: &ExtCtxt<'_>,
         span = span.with_ctxt(cx.backtrace());
     } else { // Avoid instability errors with user defined curstom derives, cc #36316
         let mut info = cx.current_expansion.mark.expn_info().unwrap();
-        info.allow_internal_unstable = Some(vec![Symbol::intern("core_intrinsics")].into());
+        info.allow_internal_unstable = Some(vec![sym::core_intrinsics].into());
         let mark = Mark::fresh(Mark::root());
         mark.set_expn_info(info);
         span = span.with_ctxt(SyntaxContext::empty().apply_mark(mark));

src/libsyntax_ext/lib.rs

@@ -42,8 +42,8 @@ pub mod proc_macro_impl;
 use rustc_data_structures::sync::Lrc;
 use syntax::ast;
 use syntax::ext::base::{MacroExpanderFn, NormalTT, NamedSyntaxExtension, MultiModifier};
-use syntax::symbol::Symbol;
 use syntax::edition::Edition;
+use syntax::symbol::{sym, Symbol};
 
 pub fn register_builtins(resolver: &mut dyn syntax::ext::base::Resolver,
                          user_exts: Vec<NamedSyntaxExtension>,
@@ -93,30 +93,26 @@ pub fn register_builtins(resolver: &mut dyn syntax::ext::base::Resolver,
         assert: assert::expand_assert,
     }
 
-    register(Symbol::intern("test_case"), MultiModifier(Box::new(test_case::expand)));
+    register(sym::test_case, MultiModifier(Box::new(test_case::expand)));
-    register(Symbol::intern("test"), MultiModifier(Box::new(test::expand_test)));
+    register(sym::test, MultiModifier(Box::new(test::expand_test)));
-    register(Symbol::intern("bench"), MultiModifier(Box::new(test::expand_bench)));
+    register(sym::bench, MultiModifier(Box::new(test::expand_bench)));
 
     // format_args uses `unstable` things internally.
     register(Symbol::intern("format_args"),
              NormalTT {
                 expander: Box::new(format::expand_format_args),
                 def_info: None,
-                allow_internal_unstable: Some(vec![
+                allow_internal_unstable: Some(vec![sym::fmt_internals].into()),
-                    Symbol::intern("fmt_internals"),
-                ].into()),
                 allow_internal_unsafe: false,
                 local_inner_macros: false,
                 unstable_feature: None,
                 edition,
             });
-    register(Symbol::intern("format_args_nl"),
+    register(sym::format_args_nl,
              NormalTT {
                  expander: Box::new(format::expand_format_args_nl),
                  def_info: None,
-                 allow_internal_unstable: Some(vec![
+                 allow_internal_unstable: Some(vec![sym::fmt_internals].into()),
-                     Symbol::intern("fmt_internals"),
-                 ].into()),
                  allow_internal_unsafe: false,
                  local_inner_macros: false,
                  unstable_feature: None,

src/libsyntax_ext/proc_macro_decls.rs

@@ -351,9 +351,9 @@ fn mk_decls(
     mark.set_expn_info(ExpnInfo {
         call_site: DUMMY_SP,
         def_site: None,
-        format: MacroAttribute(Symbol::intern("proc_macro")),
+        format: MacroAttribute(sym::proc_macro),
         allow_internal_unstable: Some(vec![
-            Symbol::intern("rustc_attrs"),
+            sym::rustc_attrs,
             Symbol::intern("proc_macro_internals"),
         ].into()),
         allow_internal_unsafe: false,
@@ -420,7 +420,7 @@ fn mk_decls(
         ast::Mutability::Immutable,
         cx.expr_vec_slice(span, decls),
     ).map(|mut i| {
-        let attr = cx.meta_word(span, Symbol::intern("rustc_proc_macro_decls"));
+        let attr = cx.meta_word(span, sym::rustc_proc_macro_decls);
         i.attrs.push(cx.attribute(span, attr));
         i.vis = respan(span, ast::VisibilityKind::Public);
         i

src/libsyntax_ext/proc_macro_server.rs

@@ -14,7 +14,7 @@ use syntax::parse::lexer::comments;
 use syntax::parse::{self, token, ParseSess};
 use syntax::tokenstream::{self, DelimSpan, IsJoint::*, TokenStream, TreeAndJoint};
 use syntax_pos::hygiene::{SyntaxContext, Transparency};
-use syntax_pos::symbol::{kw, Symbol};
+use syntax_pos::symbol::{kw, sym, Symbol};
 use syntax_pos::{BytePos, FileName, MultiSpan, Pos, SourceFile, Span};
 
 trait FromInternal<T> {
@@ -159,7 +159,7 @@ impl FromInternal<(TreeAndJoint, &'_ ParseSess, &'_ mut Vec<Self>)>
                     escaped.extend(ch.escape_debug());
                 }
                 let stream = vec![
-                    Ident(ast::Ident::new(Symbol::intern("doc"), span), false),
+                    Ident(ast::Ident::new(sym::doc, span), false),
                     Eq,
                     Token::lit(token::Str, Symbol::intern(&escaped), None),
                 ]

src/libsyntax_ext/test.rs

@@ -65,11 +65,8 @@ pub fn expand_test_or_bench(
         mark.set_expn_info(ExpnInfo {
             call_site: DUMMY_SP,
             def_site: None,
-            format: MacroAttribute(Symbol::intern("test")),
+            format: MacroAttribute(sym::test),
-            allow_internal_unstable: Some(vec![
+            allow_internal_unstable: Some(vec![sym::rustc_attrs, sym::test].into()),
-                Symbol::intern("rustc_attrs"),
-                Symbol::intern("test"),
-            ].into()),
             allow_internal_unsafe: false,
             local_inner_macros: false,
             edition: cx.parse_sess.edition,
@@ -130,11 +127,11 @@ pub fn expand_test_or_bench(
     let mut test_const = cx.item(sp, ast::Ident::new(item.ident.name, sp).gensym(),
         vec![
             // #[cfg(test)]
-            cx.attribute(attr_sp, cx.meta_list(attr_sp, Symbol::intern("cfg"), vec![
+            cx.attribute(attr_sp, cx.meta_list(attr_sp, sym::cfg, vec![
-                cx.meta_list_item_word(attr_sp, Symbol::intern("test"))
+                cx.meta_list_item_word(attr_sp, sym::test)
             ])),
             // #[rustc_test_marker]
-            cx.attribute(attr_sp, cx.meta_word(attr_sp, Symbol::intern("rustc_test_marker"))),
+            cx.attribute(attr_sp, cx.meta_word(attr_sp, sym::rustc_test_marker)),
         ],
         // const $ident: test::TestDescAndFn =
         ast::ItemKind::Const(cx.ty(sp, ast::TyKind::Path(None, test_path("TestDescAndFn"))),
@@ -180,7 +177,7 @@ pub fn expand_test_or_bench(
     let test_extern = cx.item(sp,
         test_id,
         vec![],
-        ast::ItemKind::ExternCrate(Some(Symbol::intern("test")))
+        ast::ItemKind::ExternCrate(Some(sym::test))
     );
 
     log::debug!("Synthetic test item:\n{}\n", pprust::item_to_string(&test_const));

src/libsyntax_ext/test_case.rs

@@ -14,7 +14,7 @@ use syntax::ext::build::AstBuilder;
 use syntax::ext::hygiene::{Mark, SyntaxContext};
 use syntax::ast;
 use syntax::source_map::respan;
-use syntax::symbol::{Symbol, sym};
+use syntax::symbol::sym;
 use syntax_pos::{DUMMY_SP, Span};
 use syntax::source_map::{ExpnInfo, MacroAttribute};
 use syntax::feature_gate;
@@ -40,11 +40,8 @@ pub fn expand(
         mark.set_expn_info(ExpnInfo {
             call_site: DUMMY_SP,
             def_site: None,
-            format: MacroAttribute(Symbol::intern("test_case")),
+            format: MacroAttribute(sym::test_case),
-            allow_internal_unstable: Some(vec![
+            allow_internal_unstable: Some(vec![sym::test, sym::rustc_attrs].into()),
-                Symbol::intern("test"),
-                Symbol::intern("rustc_attrs"),
-            ].into()),
             allow_internal_unsafe: false,
             local_inner_macros: false,
             edition: ecx.parse_sess.edition,
@@ -59,7 +56,7 @@ pub fn expand(
         item.ident = item.ident.gensym();
         item.attrs.push(
             ecx.attribute(sp,
-                ecx.meta_word(sp, Symbol::intern("rustc_test_marker")))
+                ecx.meta_word(sp, sym::rustc_test_marker))
         );
         item
     });

src/libsyntax_pos/symbol.rs

@@ -145,6 +145,7 @@ symbols! {
         automatically_derived,
         avx512_target_feature,
         await_macro,
+        bench,
         bin,
         bind_by_move_pattern_guards,
         block,
@@ -252,8 +253,10 @@ symbols! {
         f64,
         feature,
         ffi_returns_twice,
+        field,
         field_init_shorthand,
         file,
+        fmt_internals,
         fn_must_use,
         forbid,
         format_args_nl,
@@ -405,6 +408,7 @@ symbols! {
         Output,
         overlapping_marker_traits,
         packed,
+        panic,
         panic_handler,
         panic_impl,
         panic_implementation,
@@ -430,6 +434,7 @@ symbols! {
         proc_dash_macro: "proc-macro",
         proc_macro,
         proc_macro_attribute,
+        proc_macro_def_site,
         proc_macro_derive,
         proc_macro_expr,
         proc_macro_gen,
@@ -568,6 +573,7 @@ symbols! {
         test,
         test_2018_feature,
         test_accepted_feature,
+        test_case,
         test_removed_feature,
         test_runner,
         thread_local,