src/librustc_span/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_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
   8 use rustc_macros::{symbols, HashStable_Generic};
   9 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
  10 use rustc_serialize::{UseSpecializedDecodable, UseSpecializedEncodable};
  11
  12 use std::cmp::{Ord, PartialEq, PartialOrd};
  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         Raw:                "raw",
 101         Union:              "union",
 102     }
 103
 104     // Symbols that can be referred to with rustc_span::sym::*. The symbol is
 105     // the stringified identifier unless otherwise specified (e.g.
 106     // `proc_dash_macro` represents "proc-macro").
 107     //
 108     // As well as the symbols listed, there are symbols for the the strings
 109     // "0", "1", ..., "9", which are accessible via `sym::integer`.
 110     Symbols {
 111         aarch64_target_feature,
 112         abi,
 113         abi_amdgpu_kernel,
 114         abi_efiapi,
 115         abi_msp430_interrupt,
 116         abi_ptx,
 117         abi_sysv64,
 118         abi_thiscall,
 119         abi_unadjusted,
 120         abi_vectorcall,
 121         abi_x86_interrupt,
 122         aborts,
 123         add_with_overflow,
 124         advanced_slice_patterns,
 125         adx_target_feature,
 126         alias,
 127         align,
 128         alignstack,
 129         all,
 130         allocator,
 131         allocator_internals,
 132         alloc_error_handler,
 133         allow,
 134         allowed,
 135         allow_fail,
 136         allow_internal_unsafe,
 137         allow_internal_unstable,
 138         allow_internal_unstable_backcompat_hack,
 139         always,
 140         and,
 141         any,
 142         arbitrary_enum_discriminant,
 143         arbitrary_self_types,
 144         Arguments,
 145         ArgumentV1,
 146         arm_target_feature,
 147         asm,
 148         assert,
 149         associated_consts,
 150         associated_type_bounds,
 151         associated_type_defaults,
 152         associated_types,
 153         assume_init,
 154         async_await,
 155         async_closure,
 156         attr,
 157         attributes,
 158         attr_literals,
 159         augmented_assignments,
 160         automatically_derived,
 161         avx512_target_feature,
 162         await_macro,
 163         begin_panic,
 164         bench,
 165         bin,
 166         bind_by_move_pattern_guards,
 167         bindings_after_at,
 168         block,
 169         bool,
 170         borrowck_graphviz_postflow,
 171         borrowck_graphviz_preflow,
 172         box_patterns,
 173         box_syntax,
 174         braced_empty_structs,
 175         bswap,
 176         bitreverse,
 177         C,
 178         caller_location,
 179         cdylib,
 180         cfg,
 181         cfg_attr,
 182         cfg_attr_multi,
 183         cfg_doctest,
 184         cfg_sanitize,
 185         cfg_target_feature,
 186         cfg_target_has_atomic,
 187         cfg_target_thread_local,
 188         cfg_target_vendor,
 189         char,
 190         clippy,
 191         clone,
 192         Clone,
 193         clone_closures,
 194         clone_from,
 195         closure_to_fn_coercion,
 196         cmp,
 197         cmpxchg16b_target_feature,
 198         cold,
 199         column,
 200         compile_error,
 201         compiler_builtins,
 202         concat,
 203         concat_idents,
 204         conservative_impl_trait,
 205         console,
 206         const_compare_raw_pointers,
 207         const_constructor,
 208         const_extern_fn,
 209         const_fn,
 210         const_fn_union,
 211         const_generics,
 212         const_if_match,
 213         const_indexing,
 214         const_in_array_repeat_expressions,
 215         const_let,
 216         const_loop,
 217         const_mut_refs,
 218         const_panic,
 219         const_raw_ptr_deref,
 220         const_raw_ptr_to_usize_cast,
 221         const_transmute,
 222         contents,
 223         context,
 224         convert,
 225         Copy,
 226         copy_closures,
 227         core,
 228         core_intrinsics,
 229         crate_id,
 230         crate_in_paths,
 231         crate_local,
 232         crate_name,
 233         crate_type,
 234         crate_visibility_modifier,
 235         ctpop,
 236         cttz,
 237         cttz_nonzero,
 238         ctlz,
 239         ctlz_nonzero,
 240         custom_attribute,
 241         custom_derive,
 242         custom_inner_attributes,
 243         custom_test_frameworks,
 244         c_variadic,
 245         debug_trait,
 246         declare_lint_pass,
 247         decl_macro,
 248         Debug,
 249         Decodable,
 250         Default,
 251         default_lib_allocator,
 252         default_type_parameter_fallback,
 253         default_type_params,
 254         delay_span_bug_from_inside_query,
 255         deny,
 256         deprecated,
 257         deref,
 258         deref_mut,
 259         derive,
 260         diagnostic,
 261         direct,
 262         doc,
 263         doc_alias,
 264         doc_cfg,
 265         doc_keyword,
 266         doc_masked,
 267         doc_spotlight,
 268         doctest,
 269         document_private_items,
 270         dotdoteq_in_patterns,
 271         dotdot_in_tuple_patterns,
 272         double_braced_crate: "{{crate}}",
 273         double_braced_impl: "{{impl}}",
 274         double_braced_misc: "{{misc}}",
 275         double_braced_closure: "{{closure}}",
 276         double_braced_constructor: "{{constructor}}",
 277         double_braced_constant: "{{constant}}",
 278         double_braced_opaque: "{{opaque}}",
 279         dropck_eyepatch,
 280         dropck_parametricity,
 281         drop_types_in_const,
 282         dylib,
 283         dyn_trait,
 284         eh_personality,
 285         eh_unwind_resume,
 286         enable,
 287         Encodable,
 288         env,
 289         eq,
 290         err,
 291         Err,
 292         Eq,
 293         Equal,
 294         enclosing_scope,
 295         except,
 296         exclusive_range_pattern,
 297         exhaustive_integer_patterns,
 298         exhaustive_patterns,
 299         existential_type,
 300         expected,
 301         export_name,
 302         expr,
 303         extern_absolute_paths,
 304         external_doc,
 305         extern_crate_item_prelude,
 306         extern_crate_self,
 307         extern_in_paths,
 308         extern_prelude,
 309         extern_types,
 310         f16c_target_feature,
 311         f32,
 312         f64,
 313         feature,
 314         ffi_returns_twice,
 315         field,
 316         field_init_shorthand,
 317         file,
 318         fmt,
 319         fmt_internals,
 320         fn_must_use,
 321         forbid,
 322         format_args,
 323         format_args_nl,
 324         from,
 325         From,
 326         from_desugaring,
 327         from_error,
 328         from_generator,
 329         from_method,
 330         from_ok,
 331         from_usize,
 332         fundamental,
 333         future,
 334         Future,
 335         FxHashSet,
 336         FxHashMap,
 337         gen_future,
 338         generators,
 339         generic_associated_types,
 340         generic_param_attrs,
 341         global_allocator,
 342         global_asm,
 343         globs,
 344         hash,
 345         Hash,
 346         HashSet,
 347         HashMap,
 348         hexagon_target_feature,
 349         hidden,
 350         homogeneous_aggregate,
 351         html_favicon_url,
 352         html_logo_url,
 353         html_no_source,
 354         html_playground_url,
 355         html_root_url,
 356         i128,
 357         i128_type,
 358         i16,
 359         i32,
 360         i64,
 361         i8,
 362         ident,
 363         if_let,
 364         if_while_or_patterns,
 365         ignore,
 366         impl_header_lifetime_elision,
 367         impl_lint_pass,
 368         impl_trait_in_bindings,
 369         import_shadowing,
 370         index,
 371         index_mut,
 372         in_band_lifetimes,
 373         include,
 374         include_bytes,
 375         include_str,
 376         inclusive_range_syntax,
 377         infer_outlives_requirements,
 378         infer_static_outlives_requirements,
 379         inline,
 380         intel,
 381         into_iter,
 382         IntoIterator,
 383         into_result,
 384         intrinsics,
 385         irrefutable_let_patterns,
 386         isize,
 387         issue,
 388         issue_5723_bootstrap,
 389         issue_tracker_base_url,
 390         item,
 391         item_context: "ItemContext",
 392         item_like_imports,
 393         iter,
 394         Iterator,
 395         keyword,
 396         kind,
 397         label,
 398         label_break_value,
 399         lang,
 400         lang_items,
 401         let_chains,
 402         lhs,
 403         lib,
 404         lifetime,
 405         line,
 406         link,
 407         linkage,
 408         link_args,
 409         link_cfg,
 410         link_llvm_intrinsics,
 411         link_name,
 412         link_ordinal,
 413         link_section,
 414         LintPass,
 415         lint_reasons,
 416         literal,
 417         local_inner_macros,
 418         log_syntax,
 419         loop_break_value,
 420         macro_at_most_once_rep,
 421         macro_escape,
 422         macro_export,
 423         macro_lifetime_matcher,
 424         macro_literal_matcher,
 425         macro_reexport,
 426         macro_rules,
 427         macros_in_extern,
 428         macro_use,
 429         macro_vis_matcher,
 430         main,
 431         managed_boxes,
 432         marker,
 433         marker_trait_attr,
 434         masked,
 435         match_beginning_vert,
 436         match_default_bindings,
 437         may_dangle,
 438         maybe_uninit_uninit,
 439         maybe_uninit_zeroed,
 440         mem_uninitialized,
 441         mem_zeroed,
 442         member_constraints,
 443         message,
 444         meta,
 445         min_align_of,
 446         min_const_fn,
 447         min_const_unsafe_fn,
 448         mips_target_feature,
 449         mmx_target_feature,
 450         module,
 451         module_path,
 452         more_struct_aliases,
 453         move_val_init,
 454         movbe_target_feature,
 455         mul_with_overflow,
 456         must_use,
 457         naked,
 458         naked_functions,
 459         name,
 460         needs_allocator,
 461         needs_drop,
 462         needs_panic_runtime,
 463         negate_unsigned,
 464         never,
 465         never_type,
 466         never_type_fallback,
 467         new,
 468         next,
 469         __next,
 470         nll,
 471         no_builtins,
 472         no_core,
 473         no_crate_inject,
 474         no_debug,
 475         no_default_passes,
 476         no_implicit_prelude,
 477         no_inline,
 478         no_link,
 479         no_main,
 480         no_mangle,
 481         non_ascii_idents,
 482         None,
 483         non_exhaustive,
 484         non_modrs_mods,
 485         no_stack_check,
 486         no_start,
 487         no_std,
 488         not,
 489         note,
 490         object_safe_for_dispatch,
 491         Ok,
 492         omit_gdb_pretty_printer_section,
 493         on,
 494         on_unimplemented,
 495         oom,
 496         ops,
 497         optimize,
 498         optimize_attribute,
 499         optin_builtin_traits,
 500         option,
 501         Option,
 502         option_env,
 503         opt_out_copy,
 504         or,
 505         or_patterns,
 506         Ord,
 507         Ordering,
 508         Output,
 509         overlapping_marker_traits,
 510         packed,
 511         panic,
 512         panic_handler,
 513         panic_impl,
 514         panic_implementation,
 515         panic_runtime,
 516         parent_trait,
 517         partial_cmp,
 518         param_attrs,
 519         PartialEq,
 520         PartialOrd,
 521         passes,
 522         pat,
 523         path,
 524         pattern_parentheses,
 525         Pending,
 526         pin,
 527         Pin,
 528         pinned,
 529         platform_intrinsics,
 530         plugin,
 531         plugin_registrar,
 532         plugins,
 533         Poll,
 534         poll_with_tls_context,
 535         powerpc_target_feature,
 536         precise_pointer_size_matching,
 537         pref_align_of,
 538         prelude,
 539         prelude_import,
 540         primitive,
 541         proc_dash_macro: "proc-macro",
 542         proc_macro,
 543         proc_macro_attribute,
 544         proc_macro_def_site,
 545         proc_macro_derive,
 546         proc_macro_expr,
 547         proc_macro_gen,
 548         proc_macro_hygiene,
 549         proc_macro_internals,
 550         proc_macro_mod,
 551         proc_macro_non_items,
 552         proc_macro_path_invoc,
 553         profiler_runtime,
 554         ptr_offset_from,
 555         pub_restricted,
 556         pushpop_unsafe,
 557         quad_precision_float,
 558         question_mark,
 559         quote,
 560         Range,
 561         RangeFrom,
 562         RangeFull,
 563         RangeInclusive,
 564         RangeTo,
 565         RangeToInclusive,
 566         raw_dylib,
 567         raw_identifiers,
 568         raw_ref_op,
 569         Ready,
 570         reason,
 571         recursion_limit,
 572         reexport_test_harness_main,
 573         reflect,
 574         register_attr,
 575         register_tool,
 576         relaxed_adts,
 577         repr,
 578         repr128,
 579         repr_align,
 580         repr_align_enum,
 581         repr_packed,
 582         repr_simd,
 583         repr_transparent,
 584         re_rebalance_coherence,
 585         result,
 586         Result,
 587         Return,
 588         rhs,
 589         rlib,
 590         rotate_left,
 591         rotate_right,
 592         rt,
 593         rtm_target_feature,
 594         rust,
 595         rust_2015_preview,
 596         rust_2018_preview,
 597         rust_begin_unwind,
 598         rustc,
 599         RustcDecodable,
 600         RustcEncodable,
 601         rustc_allocator,
 602         rustc_allocator_nounwind,
 603         rustc_allow_const_fn_ptr,
 604         rustc_args_required_const,
 605         rustc_attrs,
 606         rustc_builtin_macro,
 607         rustc_clean,
 608         rustc_const_unstable,
 609         rustc_const_stable,
 610         rustc_conversion_suggestion,
 611         rustc_def_path,
 612         rustc_deprecated,
 613         rustc_diagnostic_item,
 614         rustc_diagnostic_macros,
 615         rustc_dirty,
 616         rustc_dummy,
 617         rustc_dump_env_program_clauses,
 618         rustc_dump_program_clauses,
 619         rustc_dump_user_substs,
 620         rustc_error,
 621         rustc_expected_cgu_reuse,
 622         rustc_if_this_changed,
 623         rustc_inherit_overflow_checks,
 624         rustc_layout,
 625         rustc_layout_scalar_valid_range_end,
 626         rustc_layout_scalar_valid_range_start,
 627         rustc_macro_transparency,
 628         rustc_mir,
 629         rustc_nonnull_optimization_guaranteed,
 630         rustc_object_lifetime_default,
 631         rustc_on_unimplemented,
 632         rustc_outlives,
 633         rustc_paren_sugar,
 634         rustc_partition_codegened,
 635         rustc_partition_reused,
 636         rustc_peek,
 637         rustc_peek_definite_init,
 638         rustc_peek_maybe_init,
 639         rustc_peek_maybe_uninit,
 640         rustc_peek_indirectly_mutable,
 641         rustc_private,
 642         rustc_proc_macro_decls,
 643         rustc_promotable,
 644         rustc_regions,
 645         rustc_stable,
 646         rustc_std_internal_symbol,
 647         rustc_symbol_name,
 648         rustc_synthetic,
 649         rustc_reservation_impl,
 650         rustc_test_marker,
 651         rustc_then_this_would_need,
 652         rustc_variance,
 653         rustfmt,
 654         rust_eh_personality,
 655         rust_eh_unwind_resume,
 656         rust_oom,
 657         rvalue_static_promotion,
 658         sanitize,
 659         sanitizer_runtime,
 660         saturating_add,
 661         saturating_sub,
 662         _Self,
 663         self_in_typedefs,
 664         self_struct_ctor,
 665         send_trait,
 666         should_panic,
 667         simd,
 668         simd_extract,
 669         simd_ffi,
 670         simd_insert,
 671         since,
 672         size,
 673         size_of,
 674         slice_patterns,
 675         slicing_syntax,
 676         soft,
 677         Some,
 678         specialization,
 679         speed,
 680         spotlight,
 681         sse4a_target_feature,
 682         stable,
 683         staged_api,
 684         start,
 685         static_in_const,
 686         staticlib,
 687         static_nobundle,
 688         static_recursion,
 689         std,
 690         std_inject,
 691         str,
 692         stringify,
 693         stmt,
 694         stmt_expr_attributes,
 695         stop_after_dataflow,
 696         struct_field_attributes,
 697         struct_inherit,
 698         structural_match,
 699         struct_variant,
 700         sty,
 701         sub_with_overflow,
 702         suggestion,
 703         sync_trait,
 704         target_feature,
 705         target_has_atomic,
 706         target_has_atomic_load_store,
 707         target_thread_local,
 708         task,
 709         tbm_target_feature,
 710         termination_trait,
 711         termination_trait_test,
 712         test,
 713         test_2018_feature,
 714         test_accepted_feature,
 715         test_case,
 716         test_removed_feature,
 717         test_runner,
 718         then_with,
 719         thread_local,
 720         tool_attributes,
 721         tool_lints,
 722         trace_macros,
 723         track_caller,
 724         trait_alias,
 725         transmute,
 726         transparent,
 727         transparent_enums,
 728         transparent_unions,
 729         trivial_bounds,
 730         Try,
 731         try_blocks,
 732         try_trait,
 733         tt,
 734         tuple_indexing,
 735         Ty,
 736         ty,
 737         type_alias_impl_trait,
 738         type_id,
 739         type_name,
 740         TyCtxt,
 741         TyKind,
 742         type_alias_enum_variants,
 743         type_ascription,
 744         type_length_limit,
 745         type_macros,
 746         u128,
 747         u16,
 748         u32,
 749         u64,
 750         u8,
 751         unboxed_closures,
 752         unchecked_shl,
 753         unchecked_shr,
 754         underscore_const_names,
 755         underscore_imports,
 756         underscore_lifetimes,
 757         uniform_paths,
 758         universal_impl_trait,
 759         unmarked_api,
 760         unreachable_code,
 761         unrestricted_attribute_tokens,
 762         unsafe_no_drop_flag,
 763         unsized_locals,
 764         unsized_tuple_coercion,
 765         unstable,
 766         untagged_unions,
 767         unwind,
 768         unwind_attributes,
 769         unwrap_or,
 770         used,
 771         use_extern_macros,
 772         use_nested_groups,
 773         usize,
 774         v1,
 775         val,
 776         var,
 777         vec,
 778         Vec,
 779         vis,
 780         visible_private_types,
 781         volatile,
 782         warn,
 783         wasm_import_module,
 784         wasm_target_feature,
 785         while_let,
 786         windows,
 787         windows_subsystem,
 788         wrapping_add,
 789         wrapping_sub,
 790         wrapping_mul,
 791         Yield,
 792     }
 793 }
 794
 795 #[derive(Copy, Clone, Eq, HashStable_Generic)]
 796 pub struct Ident {
 797     pub name: Symbol,
 798     pub span: Span,
 799 }
 800
 801 impl Ident {
 802     #[inline]
 803     /// Constructs a new identifier from a symbol and a span.
 804     pub const fn new(name: Symbol, span: Span) -> Ident {
 805         Ident { name, span }
 806     }
 807
 808     /// Constructs a new identifier with a dummy span.
 809     #[inline]
 810     pub const fn with_dummy_span(name: Symbol) -> Ident {
 811         Ident::new(name, DUMMY_SP)
 812     }
 813
 814     #[inline]
 815     pub fn invalid() -> Ident {
 816         Ident::with_dummy_span(kw::Invalid)
 817     }
 818
 819     /// Maps a string to an identifier with a dummy span.
 820     pub fn from_str(string: &str) -> Ident {
 821         Ident::with_dummy_span(Symbol::intern(string))
 822     }
 823
 824     /// Maps a string and a span to an identifier.
 825     pub fn from_str_and_span(string: &str, span: Span) -> Ident {
 826         Ident::new(Symbol::intern(string), span)
 827     }
 828
 829     /// Replaces `lo` and `hi` with those from `span`, but keep hygiene context.
 830     pub fn with_span_pos(self, span: Span) -> Ident {
 831         Ident::new(self.name, span.with_ctxt(self.span.ctxt()))
 832     }
 833
 834     pub fn without_first_quote(self) -> Ident {
 835         Ident::new(Symbol::intern(self.as_str().trim_start_matches('\'')), self.span)
 836     }
 837
 838     /// "Normalize" ident for use in comparisons using "item hygiene".
 839     /// Identifiers with same string value become same if they came from the same "modern" macro
 840     /// (e.g., `macro` item, but not `macro_rules` item) and stay different if they came from
 841     /// different "modern" macros.
 842     /// Technically, this operation strips all non-opaque marks from ident's syntactic context.
 843     pub fn modern(self) -> Ident {
 844         Ident::new(self.name, self.span.modern())
 845     }
 846
 847     /// "Normalize" ident for use in comparisons using "local variable hygiene".
 848     /// Identifiers with same string value become same if they came from the same non-transparent
 849     /// macro (e.g., `macro` or `macro_rules!` items) and stay different if they came from different
 850     /// non-transparent macros.
 851     /// Technically, this operation strips all transparent marks from ident's syntactic context.
 852     pub fn modern_and_legacy(self) -> Ident {
 853         Ident::new(self.name, self.span.modern_and_legacy())
 854     }
 855
 856     /// Convert the name to a `SymbolStr`. This is a slowish operation because
 857     /// it requires locking the symbol interner.
 858     pub fn as_str(self) -> SymbolStr {
 859         self.name.as_str()
 860     }
 861 }
 862
 863 impl PartialEq for Ident {
 864     fn eq(&self, rhs: &Self) -> bool {
 865         self.name == rhs.name && self.span.ctxt() == rhs.span.ctxt()
 866     }
 867 }
 868
 869 impl Hash for Ident {
 870     fn hash<H: Hasher>(&self, state: &mut H) {
 871         self.name.hash(state);
 872         self.span.ctxt().hash(state);
 873     }
 874 }
 875
 876 impl fmt::Debug for Ident {
 877     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 878         if self.is_raw_guess() {
 879             write!(f, "r#")?;
 880         }
 881         write!(f, "{}{:?}", self.name, self.span.ctxt())
 882     }
 883 }
 884
 885 impl fmt::Display for Ident {
 886     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 887         if self.is_raw_guess() {
 888             write!(f, "r#")?;
 889         }
 890         fmt::Display::fmt(&self.name, f)
 891     }
 892 }
 893
 894 impl UseSpecializedEncodable for Ident {
 895     fn default_encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
 896         s.emit_struct("Ident", 2, |s| {
 897             s.emit_struct_field("name", 0, |s| self.name.encode(s))?;
 898             s.emit_struct_field("span", 1, |s| self.span.encode(s))
 899         })
 900     }
 901 }
 902
 903 impl UseSpecializedDecodable for Ident {
 904     fn default_decode<D: Decoder>(d: &mut D) -> Result<Self, D::Error> {
 905         d.read_struct("Ident", 2, |d| {
 906             Ok(Ident {
 907                 name: d.read_struct_field("name", 0, Decodable::decode)?,
 908                 span: d.read_struct_field("span", 1, Decodable::decode)?,
 909             })
 910         })
 911     }
 912 }
 913
 914 /// An interned string.
 915 ///
 916 /// Internally, a `Symbol` is implemented as an index, and all operations
 917 /// (including hashing, equality, and ordering) operate on that index. The use
 918 /// of `rustc_index::newtype_index!` means that `Option<Symbol>` only takes up 4 bytes,
 919 /// because `rustc_index::newtype_index!` reserves the last 256 values for tagging purposes.
 920 ///
 921 /// Note that `Symbol` cannot directly be a `rustc_index::newtype_index!` because it
 922 /// implements `fmt::Debug`, `Encodable`, and `Decodable` in special ways.
 923 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 924 pub struct Symbol(SymbolIndex);
 925
 926 rustc_index::newtype_index! {
 927     pub struct SymbolIndex { .. }
 928 }
 929
 930 impl Symbol {
 931     const fn new(n: u32) -> Self {
 932         Symbol(SymbolIndex::from_u32_const(n))
 933     }
 934
 935     /// Maps a string to its interned representation.
 936     pub fn intern(string: &str) -> Self {
 937         with_interner(|interner| interner.intern(string))
 938     }
 939
 940     /// Access the symbol's chars. This is a slowish operation because it
 941     /// requires locking the symbol interner.
 942     pub fn with<F: FnOnce(&str) -> R, R>(self, f: F) -> R {
 943         with_interner(|interner| f(interner.get(self)))
 944     }
 945
 946     /// Convert to a `SymbolStr`. This is a slowish operation because it
 947     /// requires locking the symbol interner.
 948     pub fn as_str(self) -> SymbolStr {
 949         with_interner(|interner| unsafe {
 950             SymbolStr { string: std::mem::transmute::<&str, &str>(interner.get(self)) }
 951         })
 952     }
 953
 954     pub fn as_u32(self) -> u32 {
 955         self.0.as_u32()
 956     }
 957 }
 958
 959 impl fmt::Debug for Symbol {
 960     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 961         self.with(|str| fmt::Debug::fmt(&str, f))
 962     }
 963 }
 964
 965 impl fmt::Display for Symbol {
 966     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 967         self.with(|str| fmt::Display::fmt(&str, f))
 968     }
 969 }
 970
 971 impl Encodable for Symbol {
 972     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
 973         self.with(|string| s.emit_str(string))
 974     }
 975 }
 976
 977 impl Decodable for Symbol {
 978     fn decode<D: Decoder>(d: &mut D) -> Result<Symbol, D::Error> {
 979         Ok(Symbol::intern(&d.read_str()?))
 980     }
 981 }
 982
 983 impl<CTX> HashStable<CTX> for Symbol {
 984     #[inline]
 985     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
 986         self.as_str().hash_stable(hcx, hasher);
 987     }
 988 }
 989
 990 impl<CTX> ToStableHashKey<CTX> for Symbol {
 991     type KeyType = SymbolStr;
 992
 993     #[inline]
 994     fn to_stable_hash_key(&self, _: &CTX) -> SymbolStr {
 995         self.as_str()
 996     }
 997 }
 998
 999 // The `&'static str`s in this type actually point into the arena.
1000 #[derive(Default)]
1001 pub struct Interner {
1002     arena: DroplessArena,
1003     names: FxHashMap<&'static str, Symbol>,
1004     strings: Vec<&'static str>,
1005 }
1006
1007 impl Interner {
1008     fn prefill(init: &[&'static str]) -> Self {
1009         Interner {
1010             strings: init.into(),
1011             names: init.iter().copied().zip((0..).map(Symbol::new)).collect(),
1012             ..Default::default()
1013         }
1014     }
1015
1016     pub fn intern(&mut self, string: &str) -> Symbol {
1017         if let Some(&name) = self.names.get(string) {
1018             return name;
1019         }
1020
1021         let name = Symbol::new(self.strings.len() as u32);
1022
1023         // `from_utf8_unchecked` is safe since we just allocated a `&str` which is known to be
1024         // UTF-8.
1025         let string: &str =
1026             unsafe { str::from_utf8_unchecked(self.arena.alloc_slice(string.as_bytes())) };
1027         // It is safe to extend the arena allocation to `'static` because we only access
1028         // these while the arena is still alive.
1029         let string: &'static str = unsafe { &*(string as *const str) };
1030         self.strings.push(string);
1031         self.names.insert(string, name);
1032         name
1033     }
1034
1035     // Get the symbol as a string. `Symbol::as_str()` should be used in
1036     // preference to this function.
1037     pub fn get(&self, symbol: Symbol) -> &str {
1038         self.strings[symbol.0.as_usize()]
1039     }
1040 }
1041
1042 // This module has a very short name because it's used a lot.
1043 pub mod kw {
1044     use super::Symbol;
1045     keywords!();
1046 }
1047
1048 // This module has a very short name because it's used a lot.
1049 pub mod sym {
1050     use super::Symbol;
1051     use std::convert::TryInto;
1052
1053     symbols!();
1054
1055     // Get the symbol for an integer. The first few non-negative integers each
1056     // have a static symbol and therefore are fast.
1057     pub fn integer<N: TryInto<usize> + Copy + ToString>(n: N) -> Symbol {
1058         if let Result::Ok(idx) = n.try_into() {
1059             if let Option::Some(&sym) = digits_array.get(idx) {
1060                 return sym;
1061             }
1062         }
1063         Symbol::intern(&n.to_string())
1064     }
1065 }
1066
1067 impl Symbol {
1068     fn is_used_keyword_2018(self) -> bool {
1069         self >= kw::Async && self <= kw::Dyn
1070     }
1071
1072     fn is_unused_keyword_2018(self) -> bool {
1073         self == kw::Try
1074     }
1075
1076     /// Used for sanity checking rustdoc keyword sections.
1077     pub fn is_doc_keyword(self) -> bool {
1078         self <= kw::Union
1079     }
1080
1081     /// A keyword or reserved identifier that can be used as a path segment.
1082     pub fn is_path_segment_keyword(self) -> bool {
1083         self == kw::Super
1084             || self == kw::SelfLower
1085             || self == kw::SelfUpper
1086             || self == kw::Crate
1087             || self == kw::PathRoot
1088             || self == kw::DollarCrate
1089     }
1090
1091     /// Returns `true` if the symbol is `true` or `false`.
1092     pub fn is_bool_lit(self) -> bool {
1093         self == kw::True || self == kw::False
1094     }
1095
1096     /// This symbol can be a raw identifier.
1097     pub fn can_be_raw(self) -> bool {
1098         self != kw::Invalid && self != kw::Underscore && !self.is_path_segment_keyword()
1099     }
1100 }
1101
1102 impl Ident {
1103     // Returns `true` for reserved identifiers used internally for elided lifetimes,
1104     // unnamed method parameters, crate root module, error recovery etc.
1105     pub fn is_special(self) -> bool {
1106         self.name <= kw::Underscore
1107     }
1108
1109     /// Returns `true` if the token is a keyword used in the language.
1110     pub fn is_used_keyword(self) -> bool {
1111         // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1112         self.name >= kw::As && self.name <= kw::While
1113             || self.name.is_used_keyword_2018() && self.span.rust_2018()
1114     }
1115
1116     /// Returns `true` if the token is a keyword reserved for possible future use.
1117     pub fn is_unused_keyword(self) -> bool {
1118         // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1119         self.name >= kw::Abstract && self.name <= kw::Yield
1120             || self.name.is_unused_keyword_2018() && self.span.rust_2018()
1121     }
1122
1123     /// Returns `true` if the token is either a special identifier or a keyword.
1124     pub fn is_reserved(self) -> bool {
1125         self.is_special() || self.is_used_keyword() || self.is_unused_keyword()
1126     }
1127
1128     /// A keyword or reserved identifier that can be used as a path segment.
1129     pub fn is_path_segment_keyword(self) -> bool {
1130         self.name.is_path_segment_keyword()
1131     }
1132
1133     /// We see this identifier in a normal identifier position, like variable name or a type.
1134     /// How was it written originally? Did it use the raw form? Let's try to guess.
1135     pub fn is_raw_guess(self) -> bool {
1136         self.name.can_be_raw() && self.is_reserved()
1137     }
1138 }
1139
1140 #[inline]
1141 fn with_interner<T, F: FnOnce(&mut Interner) -> T>(f: F) -> T {
1142     GLOBALS.with(|globals| f(&mut *globals.symbol_interner.lock()))
1143 }
1144
1145 /// An alternative to `Symbol`, useful when the chars within the symbol need to
1146 /// be accessed. It deliberately has limited functionality and should only be
1147 /// used for temporary values.
1148 ///
1149 /// Because the interner outlives any thread which uses this type, we can
1150 /// safely treat `string` which points to interner data, as an immortal string,
1151 /// as long as this type never crosses between threads.
1152 //
1153 // FIXME: ensure that the interner outlives any thread which uses `SymbolStr`,
1154 // by creating a new thread right after constructing the interner.
1155 #[derive(Clone, Eq, PartialOrd, Ord)]
1156 pub struct SymbolStr {
1157     string: &'static str,
1158 }
1159
1160 // This impl allows a `SymbolStr` to be directly equated with a `String` or
1161 // `&str`.
1162 impl<T: std::ops::Deref<Target = str>> std::cmp::PartialEq<T> for SymbolStr {
1163     fn eq(&self, other: &T) -> bool {
1164         self.string == other.deref()
1165     }
1166 }
1167
1168 impl !Send for SymbolStr {}
1169 impl !Sync for SymbolStr {}
1170
1171 /// This impl means that if `ss` is a `SymbolStr`:
1172 /// - `*ss` is a `str`;
1173 /// - `&*ss` is a `&str`;
1174 /// - `&ss as &str` is a `&str`, which means that `&ss` can be passed to a
1175 ///   function expecting a `&str`.
1176 impl std::ops::Deref for SymbolStr {
1177     type Target = str;
1178     #[inline]
1179     fn deref(&self) -> &str {
1180         self.string
1181     }
1182 }
1183
1184 impl fmt::Debug for SymbolStr {
1185     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1186         fmt::Debug::fmt(self.string, f)
1187     }
1188 }
1189
1190 impl fmt::Display for SymbolStr {
1191     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1192         fmt::Display::fmt(self.string, f)
1193     }
1194 }
1195
1196 impl<CTX> HashStable<CTX> for SymbolStr {
1197     #[inline]
1198     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
1199         self.string.hash_stable(hcx, hasher)
1200     }
1201 }
1202
1203 impl<CTX> ToStableHashKey<CTX> for SymbolStr {
1204     type KeyType = SymbolStr;
1205
1206     #[inline]
1207     fn to_stable_hash_key(&self, _: &CTX) -> SymbolStr {
1208         self.clone()
1209     }
1210 }