src/libsyntax_pos/symbol.rs

   1 //! An "interner" is a data structure that associates values with usize tags and
   2 //! allows bidirectional lookup; i.e., given a value, one can easily find the
   3 //! type, and vice versa.
   4
   5 use arena::DroplessArena;
   6 use rustc_data_structures::fx::FxHashMap;
   7 use rustc_index::vec::Idx;
   8 use rustc_macros::symbols;
   9 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
  10 use rustc_serialize::{UseSpecializedDecodable, UseSpecializedEncodable};
  11
  12 use std::cmp::{PartialEq, PartialOrd, Ord};
  13 use std::fmt;
  14 use std::hash::{Hash, Hasher};
  15 use std::str;
  16
  17 use crate::{Span, DUMMY_SP, GLOBALS};
  18
  19 #[cfg(test)]
  20 mod tests;
  21
  22 symbols! {
  23     // After modifying this list adjust `is_special`, `is_used_keyword`/`is_unused_keyword`,
  24     // this should be rarely necessary though if the keywords are kept in alphabetic order.
  25     Keywords {
  26         // Special reserved identifiers used internally for elided lifetimes,
  27         // unnamed method parameters, crate root module, error recovery etc.
  28         Invalid:            "",
  29         PathRoot:           "{{root}}",
  30         DollarCrate:        "$crate",
  31         Underscore:         "_",
  32
  33         // Keywords that are used in stable Rust.
  34         As:                 "as",
  35         Break:              "break",
  36         Const:              "const",
  37         Continue:           "continue",
  38         Crate:              "crate",
  39         Else:               "else",
  40         Enum:               "enum",
  41         Extern:             "extern",
  42         False:              "false",
  43         Fn:                 "fn",
  44         For:                "for",
  45         If:                 "if",
  46         Impl:               "impl",
  47         In:                 "in",
  48         Let:                "let",
  49         Loop:               "loop",
  50         Match:              "match",
  51         Mod:                "mod",
  52         Move:               "move",
  53         Mut:                "mut",
  54         Pub:                "pub",
  55         Ref:                "ref",
  56         Return:             "return",
  57         SelfLower:          "self",
  58         SelfUpper:          "Self",
  59         Static:             "static",
  60         Struct:             "struct",
  61         Super:              "super",
  62         Trait:              "trait",
  63         True:               "true",
  64         Type:               "type",
  65         Unsafe:             "unsafe",
  66         Use:                "use",
  67         Where:              "where",
  68         While:              "while",
  69
  70         // Keywords that are used in unstable Rust or reserved for future use.
  71         Abstract:           "abstract",
  72         Become:             "become",
  73         Box:                "box",
  74         Do:                 "do",
  75         Final:              "final",
  76         Macro:              "macro",
  77         Override:           "override",
  78         Priv:               "priv",
  79         Typeof:             "typeof",
  80         Unsized:            "unsized",
  81         Virtual:            "virtual",
  82         Yield:              "yield",
  83
  84         // Edition-specific keywords that are used in stable Rust.
  85         Async:              "async", // >= 2018 Edition only
  86         Await:              "await", // >= 2018 Edition only
  87         Dyn:                "dyn", // >= 2018 Edition only
  88
  89         // Edition-specific keywords that are used in unstable Rust or reserved for future use.
  90         Try:                "try", // >= 2018 Edition only
  91
  92         // Special lifetime names
  93         UnderscoreLifetime: "'_",
  94         StaticLifetime:     "'static",
  95
  96         // Weak keywords, have special meaning only in specific contexts.
  97         Auto:               "auto",
  98         Catch:              "catch",
  99         Default:            "default",
 100         Union:              "union",
 101     }
 102
 103     // Symbols that can be referred to with syntax_pos::sym::*. The symbol is
 104     // the stringified identifier unless otherwise specified (e.g.
 105     // `proc_dash_macro` represents "proc-macro").
 106     //
 107     // As well as the symbols listed, there are symbols for the the strings
 108     // "0", "1", ..., "9", which are accessible via `sym::integer`.
 109     Symbols {
 110         aarch64_target_feature,
 111         abi,
 112         abi_amdgpu_kernel,
 113         abi_efiapi,
 114         abi_msp430_interrupt,
 115         abi_ptx,
 116         abi_sysv64,
 117         abi_thiscall,
 118         abi_unadjusted,
 119         abi_vectorcall,
 120         abi_x86_interrupt,
 121         aborts,
 122         advanced_slice_patterns,
 123         adx_target_feature,
 124         alias,
 125         align,
 126         alignstack,
 127         all,
 128         allocator,
 129         allocator_internals,
 130         alloc_error_handler,
 131         allow,
 132         allowed,
 133         allow_fail,
 134         allow_internal_unsafe,
 135         allow_internal_unstable,
 136         allow_internal_unstable_backcompat_hack,
 137         always,
 138         and,
 139         any,
 140         arbitrary_enum_discriminant,
 141         arbitrary_self_types,
 142         Arguments,
 143         ArgumentV1,
 144         arm_target_feature,
 145         asm,
 146         assert,
 147         associated_consts,
 148         associated_type_bounds,
 149         associated_type_defaults,
 150         associated_types,
 151         assume_init,
 152         async_await,
 153         async_closure,
 154         attr,
 155         attributes,
 156         attr_literals,
 157         augmented_assignments,
 158         automatically_derived,
 159         avx512_target_feature,
 160         await_macro,
 161         begin_panic,
 162         bench,
 163         bin,
 164         bind_by_move_pattern_guards,
 165         block,
 166         bool,
 167         borrowck_graphviz_postflow,
 168         borrowck_graphviz_preflow,
 169         box_patterns,
 170         box_syntax,
 171         braced_empty_structs,
 172         C,
 173         cdylib,
 174         cfg,
 175         cfg_attr,
 176         cfg_attr_multi,
 177         cfg_doctest,
 178         cfg_target_feature,
 179         cfg_target_has_atomic,
 180         cfg_target_thread_local,
 181         cfg_target_vendor,
 182         char,
 183         clippy,
 184         clone,
 185         Clone,
 186         clone_closures,
 187         clone_from,
 188         closure_to_fn_coercion,
 189         cmp,
 190         cmpxchg16b_target_feature,
 191         cold,
 192         column,
 193         compile_error,
 194         compiler_builtins,
 195         concat,
 196         concat_idents,
 197         conservative_impl_trait,
 198         console,
 199         const_compare_raw_pointers,
 200         const_constructor,
 201         const_extern_fn,
 202         const_fn,
 203         const_fn_union,
 204         const_generics,
 205         const_indexing,
 206         const_in_array_repeat_expressions,
 207         const_let,
 208         const_panic,
 209         const_raw_ptr_deref,
 210         const_raw_ptr_to_usize_cast,
 211         const_transmute,
 212         contents,
 213         context,
 214         convert,
 215         Copy,
 216         copy_closures,
 217         core,
 218         core_intrinsics,
 219         crate_id,
 220         crate_in_paths,
 221         crate_local,
 222         crate_name,
 223         crate_type,
 224         crate_visibility_modifier,
 225         custom_attribute,
 226         custom_derive,
 227         custom_inner_attributes,
 228         custom_test_frameworks,
 229         c_variadic,
 230         debug_trait,
 231         declare_lint_pass,
 232         decl_macro,
 233         Debug,
 234         Decodable,
 235         Default,
 236         default_lib_allocator,
 237         default_type_parameter_fallback,
 238         default_type_params,
 239         deny,
 240         deprecated,
 241         deref,
 242         deref_mut,
 243         derive,
 244         diagnostic,
 245         direct,
 246         doc,
 247         doc_alias,
 248         doc_cfg,
 249         doc_keyword,
 250         doc_masked,
 251         doc_spotlight,
 252         doctest,
 253         document_private_items,
 254         dotdoteq_in_patterns,
 255         dotdot_in_tuple_patterns,
 256         double_braced_crate: "{{crate}}",
 257         double_braced_impl: "{{impl}}",
 258         double_braced_misc: "{{misc}}",
 259         double_braced_closure: "{{closure}}",
 260         double_braced_constructor: "{{constructor}}",
 261         double_braced_constant: "{{constant}}",
 262         double_braced_opaque: "{{opaque}}",
 263         dropck_eyepatch,
 264         dropck_parametricity,
 265         drop_types_in_const,
 266         dylib,
 267         dyn_trait,
 268         eh_personality,
 269         eh_unwind_resume,
 270         enable,
 271         Encodable,
 272         env,
 273         eq,
 274         err,
 275         Err,
 276         Eq,
 277         Equal,
 278         except,
 279         exclusive_range_pattern,
 280         exhaustive_integer_patterns,
 281         exhaustive_patterns,
 282         existential_type,
 283         expected,
 284         export_name,
 285         expr,
 286         extern_absolute_paths,
 287         external_doc,
 288         extern_crate_item_prelude,
 289         extern_crate_self,
 290         extern_in_paths,
 291         extern_prelude,
 292         extern_types,
 293         f16c_target_feature,
 294         f32,
 295         f64,
 296         feature,
 297         ffi_returns_twice,
 298         field,
 299         field_init_shorthand,
 300         file,
 301         fmt,
 302         fmt_internals,
 303         fn_must_use,
 304         forbid,
 305         format_args,
 306         format_args_nl,
 307         from,
 308         From,
 309         from_desugaring,
 310         from_error,
 311         from_generator,
 312         from_method,
 313         from_ok,
 314         from_usize,
 315         fundamental,
 316         future,
 317         Future,
 318         FxHashSet,
 319         FxHashMap,
 320         gen_future,
 321         generators,
 322         generic_associated_types,
 323         generic_param_attrs,
 324         global_allocator,
 325         global_asm,
 326         globs,
 327         hash,
 328         Hash,
 329         HashSet,
 330         HashMap,
 331         hexagon_target_feature,
 332         hidden,
 333         homogeneous_aggregate,
 334         html_favicon_url,
 335         html_logo_url,
 336         html_no_source,
 337         html_playground_url,
 338         html_root_url,
 339         i128,
 340         i128_type,
 341         i16,
 342         i32,
 343         i64,
 344         i8,
 345         ident,
 346         if_let,
 347         if_while_or_patterns,
 348         ignore,
 349         impl_header_lifetime_elision,
 350         impl_lint_pass,
 351         impl_trait_in_bindings,
 352         import_shadowing,
 353         index,
 354         index_mut,
 355         in_band_lifetimes,
 356         include,
 357         include_bytes,
 358         include_str,
 359         inclusive_range_syntax,
 360         infer_outlives_requirements,
 361         infer_static_outlives_requirements,
 362         inline,
 363         intel,
 364         into_iter,
 365         IntoIterator,
 366         into_result,
 367         intrinsics,
 368         irrefutable_let_patterns,
 369         isize,
 370         issue,
 371         issue_5723_bootstrap,
 372         issue_tracker_base_url,
 373         item,
 374         item_context: "ItemContext",
 375         item_like_imports,
 376         iter,
 377         Iterator,
 378         keyword,
 379         kind,
 380         label,
 381         label_break_value,
 382         lang,
 383         lang_items,
 384         let_chains,
 385         lhs,
 386         lib,
 387         lifetime,
 388         line,
 389         link,
 390         linkage,
 391         link_args,
 392         link_cfg,
 393         link_llvm_intrinsics,
 394         link_name,
 395         link_ordinal,
 396         link_section,
 397         LintPass,
 398         lint_reasons,
 399         literal,
 400         local_inner_macros,
 401         log_syntax,
 402         loop_break_value,
 403         macro_at_most_once_rep,
 404         macro_escape,
 405         macro_export,
 406         macro_lifetime_matcher,
 407         macro_literal_matcher,
 408         macro_reexport,
 409         macro_rules,
 410         macros_in_extern,
 411         macro_use,
 412         macro_vis_matcher,
 413         main,
 414         managed_boxes,
 415         marker,
 416         marker_trait_attr,
 417         masked,
 418         match_beginning_vert,
 419         match_default_bindings,
 420         may_dangle,
 421         maybe_uninit_uninit,
 422         maybe_uninit_zeroed,
 423         mem_uninitialized,
 424         mem_zeroed,
 425         member_constraints,
 426         message,
 427         meta,
 428         min_const_fn,
 429         min_const_unsafe_fn,
 430         mips_target_feature,
 431         mmx_target_feature,
 432         module,
 433         module_path,
 434         more_struct_aliases,
 435         movbe_target_feature,
 436         must_use,
 437         naked,
 438         naked_functions,
 439         name,
 440         needs_allocator,
 441         needs_panic_runtime,
 442         negate_unsigned,
 443         never,
 444         never_type,
 445         new,
 446         next,
 447         __next,
 448         nll,
 449         no_builtins,
 450         no_core,
 451         no_crate_inject,
 452         no_debug,
 453         no_default_passes,
 454         no_implicit_prelude,
 455         no_inline,
 456         no_link,
 457         no_main,
 458         no_mangle,
 459         non_ascii_idents,
 460         None,
 461         non_exhaustive,
 462         non_modrs_mods,
 463         no_stack_check,
 464         no_start,
 465         no_std,
 466         not,
 467         note,
 468         object_safe_for_dispatch,
 469         Ok,
 470         omit_gdb_pretty_printer_section,
 471         on,
 472         on_unimplemented,
 473         oom,
 474         ops,
 475         optimize,
 476         optimize_attribute,
 477         optin_builtin_traits,
 478         option,
 479         Option,
 480         option_env,
 481         opt_out_copy,
 482         or,
 483         or_patterns,
 484         Ord,
 485         Ordering,
 486         Output,
 487         overlapping_marker_traits,
 488         packed,
 489         panic,
 490         panic_handler,
 491         panic_impl,
 492         panic_implementation,
 493         panic_runtime,
 494         parent_trait,
 495         partial_cmp,
 496         param_attrs,
 497         PartialEq,
 498         PartialOrd,
 499         passes,
 500         pat,
 501         path,
 502         pattern_parentheses,
 503         Pending,
 504         pin,
 505         Pin,
 506         pinned,
 507         platform_intrinsics,
 508         plugin,
 509         plugin_registrar,
 510         plugins,
 511         Poll,
 512         poll_with_tls_context,
 513         powerpc_target_feature,
 514         precise_pointer_size_matching,
 515         prelude,
 516         prelude_import,
 517         primitive,
 518         proc_dash_macro: "proc-macro",
 519         proc_macro,
 520         proc_macro_attribute,
 521         proc_macro_def_site,
 522         proc_macro_derive,
 523         proc_macro_expr,
 524         proc_macro_gen,
 525         proc_macro_hygiene,
 526         proc_macro_internals,
 527         proc_macro_mod,
 528         proc_macro_non_items,
 529         proc_macro_path_invoc,
 530         profiler_runtime,
 531         pub_restricted,
 532         pushpop_unsafe,
 533         quad_precision_float,
 534         question_mark,
 535         quote,
 536         Range,
 537         RangeFrom,
 538         RangeFull,
 539         RangeInclusive,
 540         RangeTo,
 541         RangeToInclusive,
 542         raw_dylib,
 543         raw_identifiers,
 544         Ready,
 545         reason,
 546         recursion_limit,
 547         reexport_test_harness_main,
 548         reflect,
 549         register_attr,
 550         register_tool,
 551         relaxed_adts,
 552         repr,
 553         repr128,
 554         repr_align,
 555         repr_align_enum,
 556         repr_packed,
 557         repr_simd,
 558         repr_transparent,
 559         re_rebalance_coherence,
 560         result,
 561         Result,
 562         Return,
 563         rhs,
 564         rlib,
 565         rt,
 566         rtm_target_feature,
 567         rust,
 568         rust_2015_preview,
 569         rust_2018_preview,
 570         rust_begin_unwind,
 571         rustc,
 572         Rust,
 573         RustcDecodable,
 574         RustcEncodable,
 575         rustc_allocator,
 576         rustc_allocator_nounwind,
 577         rustc_allow_const_fn_ptr,
 578         rustc_args_required_const,
 579         rustc_attrs,
 580         rustc_builtin_macro,
 581         rustc_clean,
 582         rustc_const_unstable,
 583         rustc_conversion_suggestion,
 584         rustc_def_path,
 585         rustc_deprecated,
 586         rustc_diagnostic_item,
 587         rustc_diagnostic_macros,
 588         rustc_dirty,
 589         rustc_dummy,
 590         rustc_dump_env_program_clauses,
 591         rustc_dump_program_clauses,
 592         rustc_dump_user_substs,
 593         rustc_error,
 594         rustc_expected_cgu_reuse,
 595         rustc_if_this_changed,
 596         rustc_inherit_overflow_checks,
 597         rustc_layout,
 598         rustc_layout_scalar_valid_range_end,
 599         rustc_layout_scalar_valid_range_start,
 600         rustc_macro_transparency,
 601         rustc_mir,
 602         rustc_nonnull_optimization_guaranteed,
 603         rustc_object_lifetime_default,
 604         rustc_on_unimplemented,
 605         rustc_outlives,
 606         rustc_paren_sugar,
 607         rustc_partition_codegened,
 608         rustc_partition_reused,
 609         rustc_peek,
 610         rustc_peek_definite_init,
 611         rustc_peek_maybe_init,
 612         rustc_peek_maybe_uninit,
 613         rustc_peek_indirectly_mutable,
 614         rustc_private,
 615         rustc_proc_macro_decls,
 616         rustc_promotable,
 617         rustc_regions,
 618         rustc_stable,
 619         rustc_std_internal_symbol,
 620         rustc_symbol_name,
 621         rustc_synthetic,
 622         rustc_reservation_impl,
 623         rustc_test_marker,
 624         rustc_then_this_would_need,
 625         rustc_variance,
 626         rustdoc,
 627         rustfmt,
 628         rust_eh_personality,
 629         rust_eh_unwind_resume,
 630         rust_oom,
 631         rvalue_static_promotion,
 632         sanitizer_runtime,
 633         _Self,
 634         self_in_typedefs,
 635         self_struct_ctor,
 636         should_panic,
 637         simd,
 638         simd_ffi,
 639         since,
 640         size,
 641         slice_patterns,
 642         slicing_syntax,
 643         soft,
 644         Some,
 645         specialization,
 646         speed,
 647         spotlight,
 648         sse4a_target_feature,
 649         stable,
 650         staged_api,
 651         start,
 652         static_in_const,
 653         staticlib,
 654         static_nobundle,
 655         static_recursion,
 656         std,
 657         std_inject,
 658         str,
 659         stringify,
 660         stmt,
 661         stmt_expr_attributes,
 662         stop_after_dataflow,
 663         struct_field_attributes,
 664         struct_inherit,
 665         structural_match,
 666         struct_variant,
 667         sty,
 668         suggestion,
 669         target_feature,
 670         target_has_atomic,
 671         target_has_atomic_load_store,
 672         target_thread_local,
 673         task,
 674         tbm_target_feature,
 675         termination_trait,
 676         termination_trait_test,
 677         test,
 678         test_2018_feature,
 679         test_accepted_feature,
 680         test_case,
 681         test_removed_feature,
 682         test_runner,
 683         then_with,
 684         thread_local,
 685         tool_attributes,
 686         tool_lints,
 687         trace_macros,
 688         track_caller,
 689         trait_alias,
 690         transmute,
 691         transparent,
 692         transparent_enums,
 693         transparent_unions,
 694         trivial_bounds,
 695         Try,
 696         try_blocks,
 697         try_trait,
 698         tt,
 699         tuple_indexing,
 700         Ty,
 701         ty,
 702         type_alias_impl_trait,
 703         TyCtxt,
 704         TyKind,
 705         type_alias_enum_variants,
 706         type_ascription,
 707         type_length_limit,
 708         type_macros,
 709         u128,
 710         u16,
 711         u32,
 712         u64,
 713         u8,
 714         unboxed_closures,
 715         underscore_const_names,
 716         underscore_imports,
 717         underscore_lifetimes,
 718         uniform_paths,
 719         universal_impl_trait,
 720         unmarked_api,
 721         unreachable_code,
 722         unrestricted_attribute_tokens,
 723         unsafe_no_drop_flag,
 724         unsized_locals,
 725         unsized_tuple_coercion,
 726         unstable,
 727         untagged_unions,
 728         unwind,
 729         unwind_attributes,
 730         unwrap_or,
 731         used,
 732         use_extern_macros,
 733         use_nested_groups,
 734         usize,
 735         v1,
 736         val,
 737         vec,
 738         Vec,
 739         vis,
 740         visible_private_types,
 741         volatile,
 742         warn,
 743         wasm_import_module,
 744         wasm_target_feature,
 745         while_let,
 746         windows,
 747         windows_subsystem,
 748         Yield,
 749     }
 750 }
 751
 752 #[derive(Copy, Clone, Eq)]
 753 pub struct Ident {
 754     pub name: Symbol,
 755     pub span: Span,
 756 }
 757
 758 impl Ident {
 759     #[inline]
 760     /// Constructs a new identifier from a symbol and a span.
 761     pub const fn new(name: Symbol, span: Span) -> Ident {
 762         Ident { name, span }
 763     }
 764
 765     /// Constructs a new identifier with a dummy span.
 766     #[inline]
 767     pub const fn with_dummy_span(name: Symbol) -> Ident {
 768         Ident::new(name, DUMMY_SP)
 769     }
 770
 771     #[inline]
 772     pub fn invalid() -> Ident {
 773         Ident::with_dummy_span(kw::Invalid)
 774     }
 775
 776     /// Maps a string to an identifier with a dummy span.
 777     pub fn from_str(string: &str) -> Ident {
 778         Ident::with_dummy_span(Symbol::intern(string))
 779     }
 780
 781     /// Maps a string and a span to an identifier.
 782     pub fn from_str_and_span(string: &str, span: Span) -> Ident {
 783         Ident::new(Symbol::intern(string), span)
 784     }
 785
 786     /// Replaces `lo` and `hi` with those from `span`, but keep hygiene context.
 787     pub fn with_span_pos(self, span: Span) -> Ident {
 788         Ident::new(self.name, span.with_ctxt(self.span.ctxt()))
 789     }
 790
 791     pub fn without_first_quote(self) -> Ident {
 792         Ident::new(Symbol::intern(self.as_str().trim_start_matches('\'')), self.span)
 793     }
 794
 795     /// "Normalize" ident for use in comparisons using "item hygiene".
 796     /// Identifiers with same string value become same if they came from the same "modern" macro
 797     /// (e.g., `macro` item, but not `macro_rules` item) and stay different if they came from
 798     /// different "modern" macros.
 799     /// Technically, this operation strips all non-opaque marks from ident's syntactic context.
 800     pub fn modern(self) -> Ident {
 801         Ident::new(self.name, self.span.modern())
 802     }
 803
 804     /// "Normalize" ident for use in comparisons using "local variable hygiene".
 805     /// Identifiers with same string value become same if they came from the same non-transparent
 806     /// macro (e.g., `macro` or `macro_rules!` items) and stay different if they came from different
 807     /// non-transparent macros.
 808     /// Technically, this operation strips all transparent marks from ident's syntactic context.
 809     pub fn modern_and_legacy(self) -> Ident {
 810         Ident::new(self.name, self.span.modern_and_legacy())
 811     }
 812
 813     /// Convert the name to a `SymbolStr`. This is a slowish operation because
 814     /// it requires locking the symbol interner.
 815     pub fn as_str(self) -> SymbolStr {
 816         self.name.as_str()
 817     }
 818 }
 819
 820 impl PartialEq for Ident {
 821     fn eq(&self, rhs: &Self) -> bool {
 822         self.name == rhs.name && self.span.ctxt() == rhs.span.ctxt()
 823     }
 824 }
 825
 826 impl Hash for Ident {
 827     fn hash<H: Hasher>(&self, state: &mut H) {
 828         self.name.hash(state);
 829         self.span.ctxt().hash(state);
 830     }
 831 }
 832
 833 impl fmt::Debug for Ident {
 834     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 835         write!(f, "{}{:?}", self.name, self.span.ctxt())
 836     }
 837 }
 838
 839 impl fmt::Display for Ident {
 840     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 841         fmt::Display::fmt(&self.name, f)
 842     }
 843 }
 844
 845 impl UseSpecializedEncodable for Ident {
 846     fn default_encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
 847         s.emit_struct("Ident", 2, |s| {
 848             s.emit_struct_field("name", 0, |s| {
 849                 self.name.encode(s)
 850             })?;
 851             s.emit_struct_field("span", 1, |s| {
 852                 self.span.encode(s)
 853             })
 854         })
 855     }
 856 }
 857
 858 impl UseSpecializedDecodable for Ident {
 859     fn default_decode<D: Decoder>(d: &mut D) -> Result<Self, D::Error> {
 860         d.read_struct("Ident", 2, |d| {
 861             Ok(Ident {
 862                 name: d.read_struct_field("name", 0, Decodable::decode)?,
 863                 span: d.read_struct_field("span", 1, Decodable::decode)?,
 864             })
 865         })
 866     }
 867 }
 868
 869 /// An interned string.
 870 ///
 871 /// Internally, a `Symbol` is implemented as an index, and all operations
 872 /// (including hashing, equality, and ordering) operate on that index. The use
 873 /// of `rustc_index::newtype_index!` means that `Option<Symbol>` only takes up 4 bytes,
 874 /// because `rustc_index::newtype_index!` reserves the last 256 values for tagging purposes.
 875 ///
 876 /// Note that `Symbol` cannot directly be a `rustc_index::newtype_index!` because it
 877 /// implements `fmt::Debug`, `Encodable`, and `Decodable` in special ways.
 878 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 879 pub struct Symbol(SymbolIndex);
 880
 881 rustc_index::newtype_index! {
 882     pub struct SymbolIndex { .. }
 883 }
 884
 885 impl Symbol {
 886     const fn new(n: u32) -> Self {
 887         Symbol(SymbolIndex::from_u32_const(n))
 888     }
 889
 890     /// Maps a string to its interned representation.
 891     pub fn intern(string: &str) -> Self {
 892         with_interner(|interner| interner.intern(string))
 893     }
 894
 895     /// Access the symbol's chars. This is a slowish operation because it
 896     /// requires locking the symbol interner.
 897     pub fn with<F: FnOnce(&str) -> R, R>(self, f: F) -> R {
 898         with_interner(|interner| {
 899             f(interner.get(self))
 900         })
 901     }
 902
 903     /// Convert to a `SymbolStr`. This is a slowish operation because it
 904     /// requires locking the symbol interner.
 905     pub fn as_str(self) -> SymbolStr {
 906         with_interner(|interner| unsafe {
 907             SymbolStr {
 908                 string: std::mem::transmute::<&str, &str>(interner.get(self))
 909             }
 910         })
 911     }
 912
 913     pub fn as_u32(self) -> u32 {
 914         self.0.as_u32()
 915     }
 916 }
 917
 918 impl fmt::Debug for Symbol {
 919     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 920         self.with(|str| fmt::Debug::fmt(&str, f))
 921     }
 922 }
 923
 924 impl fmt::Display for Symbol {
 925     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 926         self.with(|str| fmt::Display::fmt(&str, f))
 927     }
 928 }
 929
 930 impl Encodable for Symbol {
 931     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
 932         self.with(|string| s.emit_str(string))
 933     }
 934 }
 935
 936 impl Decodable for Symbol {
 937     fn decode<D: Decoder>(d: &mut D) -> Result<Symbol, D::Error> {
 938         Ok(Symbol::intern(&d.read_str()?))
 939     }
 940 }
 941
 942 // The `&'static str`s in this type actually point into the arena.
 943 #[derive(Default)]
 944 pub struct Interner {
 945     arena: DroplessArena,
 946     names: FxHashMap<&'static str, Symbol>,
 947     strings: Vec<&'static str>,
 948 }
 949
 950 impl Interner {
 951     fn prefill(init: &[&'static str]) -> Self {
 952         Interner {
 953             strings: init.into(),
 954             names: init.iter().copied().zip((0..).map(Symbol::new)).collect(),
 955             ..Default::default()
 956         }
 957     }
 958
 959     pub fn intern(&mut self, string: &str) -> Symbol {
 960         if let Some(&name) = self.names.get(string) {
 961             return name;
 962         }
 963
 964         let name = Symbol::new(self.strings.len() as u32);
 965
 966         // `from_utf8_unchecked` is safe since we just allocated a `&str` which is known to be
 967         // UTF-8.
 968         let string: &str = unsafe {
 969             str::from_utf8_unchecked(self.arena.alloc_slice(string.as_bytes()))
 970         };
 971         // It is safe to extend the arena allocation to `'static` because we only access
 972         // these while the arena is still alive.
 973         let string: &'static str =  unsafe {
 974             &*(string as *const str)
 975         };
 976         self.strings.push(string);
 977         self.names.insert(string, name);
 978         name
 979     }
 980
 981     // Get the symbol as a string. `Symbol::as_str()` should be used in
 982     // preference to this function.
 983     pub fn get(&self, symbol: Symbol) -> &str {
 984         self.strings[symbol.0.as_usize()]
 985     }
 986 }
 987
 988 // This module has a very short name because it's used a lot.
 989 pub mod kw {
 990     use super::Symbol;
 991     keywords!();
 992 }
 993
 994 // This module has a very short name because it's used a lot.
 995 pub mod sym {
 996     use std::convert::TryInto;
 997     use super::Symbol;
 998
 999     symbols!();
1000
1001     // Get the symbol for an integer. The first few non-negative integers each
1002     // have a static symbol and therefore are fast.
1003     pub fn integer<N: TryInto<usize> + Copy + ToString>(n: N) -> Symbol {
1004         if let Result::Ok(idx) = n.try_into() {
1005             if let Option::Some(&sym) = digits_array.get(idx) {
1006                 return sym;
1007             }
1008         }
1009         Symbol::intern(&n.to_string())
1010     }
1011 }
1012
1013 impl Symbol {
1014     fn is_used_keyword_2018(self) -> bool {
1015         self >= kw::Async && self <= kw::Dyn
1016     }
1017
1018     fn is_unused_keyword_2018(self) -> bool {
1019         self == kw::Try
1020     }
1021
1022     /// Used for sanity checking rustdoc keyword sections.
1023     pub fn is_doc_keyword(self) -> bool {
1024         self <= kw::Union
1025     }
1026
1027     /// A keyword or reserved identifier that can be used as a path segment.
1028     pub fn is_path_segment_keyword(self) -> bool {
1029         self == kw::Super ||
1030         self == kw::SelfLower ||
1031         self == kw::SelfUpper ||
1032         self == kw::Crate ||
1033         self == kw::PathRoot ||
1034         self == kw::DollarCrate
1035     }
1036
1037     /// Returns `true` if the symbol is `true` or `false`.
1038     pub fn is_bool_lit(self) -> bool {
1039         self == kw::True || self == kw::False
1040     }
1041
1042     /// This symbol can be a raw identifier.
1043     pub fn can_be_raw(self) -> bool {
1044         self != kw::Invalid && self != kw::Underscore && !self.is_path_segment_keyword()
1045     }
1046 }
1047
1048 impl Ident {
1049     // Returns `true` for reserved identifiers used internally for elided lifetimes,
1050     // unnamed method parameters, crate root module, error recovery etc.
1051     pub fn is_special(self) -> bool {
1052         self.name <= kw::Underscore
1053     }
1054
1055     /// Returns `true` if the token is a keyword used in the language.
1056     pub fn is_used_keyword(self) -> bool {
1057         // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1058         self.name >= kw::As && self.name <= kw::While ||
1059         self.name.is_used_keyword_2018() && self.span.rust_2018()
1060     }
1061
1062     /// Returns `true` if the token is a keyword reserved for possible future use.
1063     pub fn is_unused_keyword(self) -> bool {
1064         // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1065         self.name >= kw::Abstract && self.name <= kw::Yield ||
1066         self.name.is_unused_keyword_2018() && self.span.rust_2018()
1067     }
1068
1069     /// Returns `true` if the token is either a special identifier or a keyword.
1070     pub fn is_reserved(self) -> bool {
1071         self.is_special() || self.is_used_keyword() || self.is_unused_keyword()
1072     }
1073
1074     /// A keyword or reserved identifier that can be used as a path segment.
1075     pub fn is_path_segment_keyword(self) -> bool {
1076         self.name.is_path_segment_keyword()
1077     }
1078
1079     /// We see this identifier in a normal identifier position, like variable name or a type.
1080     /// How was it written originally? Did it use the raw form? Let's try to guess.
1081     pub fn is_raw_guess(self) -> bool {
1082         self.name.can_be_raw() && self.is_reserved()
1083     }
1084 }
1085
1086 #[inline]
1087 fn with_interner<T, F: FnOnce(&mut Interner) -> T>(f: F) -> T {
1088     GLOBALS.with(|globals| f(&mut *globals.symbol_interner.lock()))
1089 }
1090
1091 /// An alternative to `Symbol`, useful when the chars within the symbol need to
1092 /// be accessed. It deliberately has limited functionality and should only be
1093 /// used for temporary values.
1094 ///
1095 /// Because the interner outlives any thread which uses this type, we can
1096 /// safely treat `string` which points to interner data, as an immortal string,
1097 /// as long as this type never crosses between threads.
1098 //
1099 // FIXME: ensure that the interner outlives any thread which uses `SymbolStr`,
1100 // by creating a new thread right after constructing the interner.
1101 #[derive(Clone, Eq, PartialOrd, Ord)]
1102 pub struct SymbolStr {
1103     string: &'static str,
1104 }
1105
1106 // This impl allows a `SymbolStr` to be directly equated with a `String` or
1107 // `&str`.
1108 impl<T: std::ops::Deref<Target = str>> std::cmp::PartialEq<T> for SymbolStr {
1109     fn eq(&self, other: &T) -> bool {
1110         self.string == other.deref()
1111     }
1112 }
1113
1114 impl !Send for SymbolStr {}
1115 impl !Sync for SymbolStr {}
1116
1117 /// This impl means that if `ss` is a `SymbolStr`:
1118 /// - `*ss` is a `str`;
1119 /// - `&*ss` is a `&str`;
1120 /// - `&ss as &str` is a `&str`, which means that `&ss` can be passed to a
1121 ///   function expecting a `&str`.
1122 impl std::ops::Deref for SymbolStr {
1123     type Target = str;
1124     #[inline]
1125     fn deref(&self) -> &str { self.string }
1126 }
1127
1128 impl fmt::Debug for SymbolStr {
1129     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1130         fmt::Debug::fmt(self.string, f)
1131     }
1132 }
1133
1134 impl fmt::Display for SymbolStr {
1135     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1136         fmt::Display::fmt(self.string, f)
1137     }
1138 }