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, HashStable_Generic};
   9 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
  10 use rustc_serialize::{UseSpecializedDecodable, UseSpecializedEncodable};
  11 use rustc_data_structures::stable_hasher::{HashStable, ToStableHashKey, StableHasher};
  12
  13 use std::cmp::{PartialEq, PartialOrd, Ord};
  14 use std::fmt;
  15 use std::hash::{Hash, Hasher};
  16 use std::str;
  17
  18 use crate::{Span, DUMMY_SP, GLOBALS};
  19
  20 #[cfg(test)]
  21 mod tests;
  22
  23 symbols! {
  24     // After modifying this list adjust `is_special`, `is_used_keyword`/`is_unused_keyword`,
  25     // this should be rarely necessary though if the keywords are kept in alphabetic order.
  26     Keywords {
  27         // Special reserved identifiers used internally for elided lifetimes,
  28         // unnamed method parameters, crate root module, error recovery etc.
  29         Invalid:            "",
  30         PathRoot:           "{{root}}",
  31         DollarCrate:        "$crate",
  32         Underscore:         "_",
  33
  34         // Keywords that are used in stable Rust.
  35         As:                 "as",
  36         Break:              "break",
  37         Const:              "const",
  38         Continue:           "continue",
  39         Crate:              "crate",
  40         Else:               "else",
  41         Enum:               "enum",
  42         Extern:             "extern",
  43         False:              "false",
  44         Fn:                 "fn",
  45         For:                "for",
  46         If:                 "if",
  47         Impl:               "impl",
  48         In:                 "in",
  49         Let:                "let",
  50         Loop:               "loop",
  51         Match:              "match",
  52         Mod:                "mod",
  53         Move:               "move",
  54         Mut:                "mut",
  55         Pub:                "pub",
  56         Ref:                "ref",
  57         Return:             "return",
  58         SelfLower:          "self",
  59         SelfUpper:          "Self",
  60         Static:             "static",
  61         Struct:             "struct",
  62         Super:              "super",
  63         Trait:              "trait",
  64         True:               "true",
  65         Type:               "type",
  66         Unsafe:             "unsafe",
  67         Use:                "use",
  68         Where:              "where",
  69         While:              "while",
  70
  71         // Keywords that are used in unstable Rust or reserved for future use.
  72         Abstract:           "abstract",
  73         Become:             "become",
  74         Box:                "box",
  75         Do:                 "do",
  76         Final:              "final",
  77         Macro:              "macro",
  78         Override:           "override",
  79         Priv:               "priv",
  80         Typeof:             "typeof",
  81         Unsized:            "unsized",
  82         Virtual:            "virtual",
  83         Yield:              "yield",
  84
  85         // Edition-specific keywords that are used in stable Rust.
  86         Async:              "async", // >= 2018 Edition only
  87         Await:              "await", // >= 2018 Edition only
  88         Dyn:                "dyn", // >= 2018 Edition only
  89
  90         // Edition-specific keywords that are used in unstable Rust or reserved for future use.
  91         Try:                "try", // >= 2018 Edition only
  92
  93         // Special lifetime names
  94         UnderscoreLifetime: "'_",
  95         StaticLifetime:     "'static",
  96
  97         // Weak keywords, have special meaning only in specific contexts.
  98         Auto:               "auto",
  99         Catch:              "catch",
 100         Default:            "default",
 101         Raw:                "raw",
 102         Union:              "union",
 103     }
 104
 105     // Symbols that can be referred to with syntax_pos::sym::*. The symbol is
 106     // the stringified identifier unless otherwise specified (e.g.
 107     // `proc_dash_macro` represents "proc-macro").
 108     //
 109     // As well as the symbols listed, there are symbols for the the strings
 110     // "0", "1", ..., "9", which are accessible via `sym::integer`.
 111     Symbols {
 112         aarch64_target_feature,
 113         abi,
 114         abi_amdgpu_kernel,
 115         abi_efiapi,
 116         abi_msp430_interrupt,
 117         abi_ptx,
 118         abi_sysv64,
 119         abi_thiscall,
 120         abi_unadjusted,
 121         abi_vectorcall,
 122         abi_x86_interrupt,
 123         aborts,
 124         add_with_overflow,
 125         advanced_slice_patterns,
 126         adx_target_feature,
 127         alias,
 128         align,
 129         alignstack,
 130         all,
 131         allocator,
 132         allocator_internals,
 133         alloc_error_handler,
 134         allow,
 135         allowed,
 136         allow_fail,
 137         allow_internal_unsafe,
 138         allow_internal_unstable,
 139         allow_internal_unstable_backcompat_hack,
 140         always,
 141         and,
 142         any,
 143         arbitrary_enum_discriminant,
 144         arbitrary_self_types,
 145         Arguments,
 146         ArgumentV1,
 147         arm_target_feature,
 148         asm,
 149         assert,
 150         associated_consts,
 151         associated_type_bounds,
 152         associated_type_defaults,
 153         associated_types,
 154         assume_init,
 155         async_await,
 156         async_closure,
 157         attr,
 158         attributes,
 159         attr_literals,
 160         augmented_assignments,
 161         automatically_derived,
 162         avx512_target_feature,
 163         await_macro,
 164         begin_panic,
 165         bench,
 166         bin,
 167         bind_by_move_pattern_guards,
 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_mut_refs,
 217         const_panic,
 218         const_raw_ptr_deref,
 219         const_raw_ptr_to_usize_cast,
 220         const_transmute,
 221         contents,
 222         context,
 223         convert,
 224         Copy,
 225         copy_closures,
 226         core,
 227         core_intrinsics,
 228         crate_id,
 229         crate_in_paths,
 230         crate_local,
 231         crate_name,
 232         crate_type,
 233         crate_visibility_modifier,
 234         ctpop,
 235         cttz,
 236         cttz_nonzero,
 237         ctlz,
 238         ctlz_nonzero,
 239         custom_attribute,
 240         custom_derive,
 241         custom_inner_attributes,
 242         custom_test_frameworks,
 243         c_variadic,
 244         debug_trait,
 245         declare_lint_pass,
 246         decl_macro,
 247         Debug,
 248         Decodable,
 249         Default,
 250         default_lib_allocator,
 251         default_type_parameter_fallback,
 252         default_type_params,
 253         delay_span_bug_from_inside_query,
 254         deny,
 255         deprecated,
 256         deref,
 257         deref_mut,
 258         derive,
 259         diagnostic,
 260         direct,
 261         doc,
 262         doc_alias,
 263         doc_cfg,
 264         doc_keyword,
 265         doc_masked,
 266         doc_spotlight,
 267         doctest,
 268         document_private_items,
 269         dotdoteq_in_patterns,
 270         dotdot_in_tuple_patterns,
 271         double_braced_crate: "{{crate}}",
 272         double_braced_impl: "{{impl}}",
 273         double_braced_misc: "{{misc}}",
 274         double_braced_closure: "{{closure}}",
 275         double_braced_constructor: "{{constructor}}",
 276         double_braced_constant: "{{constant}}",
 277         double_braced_opaque: "{{opaque}}",
 278         dropck_eyepatch,
 279         dropck_parametricity,
 280         drop_types_in_const,
 281         dylib,
 282         dyn_trait,
 283         eh_personality,
 284         eh_unwind_resume,
 285         enable,
 286         Encodable,
 287         env,
 288         eq,
 289         err,
 290         Err,
 291         Eq,
 292         Equal,
 293         enclosing_scope,
 294         except,
 295         exclusive_range_pattern,
 296         exhaustive_integer_patterns,
 297         exhaustive_patterns,
 298         existential_type,
 299         expected,
 300         export_name,
 301         expr,
 302         extern_absolute_paths,
 303         external_doc,
 304         extern_crate_item_prelude,
 305         extern_crate_self,
 306         extern_in_paths,
 307         extern_prelude,
 308         extern_types,
 309         f16c_target_feature,
 310         f32,
 311         f64,
 312         feature,
 313         ffi_returns_twice,
 314         field,
 315         field_init_shorthand,
 316         file,
 317         fmt,
 318         fmt_internals,
 319         fn_must_use,
 320         forbid,
 321         format_args,
 322         format_args_nl,
 323         from,
 324         From,
 325         from_desugaring,
 326         from_error,
 327         from_generator,
 328         from_method,
 329         from_ok,
 330         from_usize,
 331         fundamental,
 332         future,
 333         Future,
 334         FxHashSet,
 335         FxHashMap,
 336         gen_future,
 337         generators,
 338         generic_associated_types,
 339         generic_param_attrs,
 340         global_allocator,
 341         global_asm,
 342         globs,
 343         hash,
 344         Hash,
 345         HashSet,
 346         HashMap,
 347         hexagon_target_feature,
 348         hidden,
 349         homogeneous_aggregate,
 350         html_favicon_url,
 351         html_logo_url,
 352         html_no_source,
 353         html_playground_url,
 354         html_root_url,
 355         i128,
 356         i128_type,
 357         i16,
 358         i32,
 359         i64,
 360         i8,
 361         ident,
 362         if_let,
 363         if_while_or_patterns,
 364         ignore,
 365         impl_header_lifetime_elision,
 366         impl_lint_pass,
 367         impl_trait_in_bindings,
 368         import_shadowing,
 369         index,
 370         index_mut,
 371         in_band_lifetimes,
 372         include,
 373         include_bytes,
 374         include_str,
 375         inclusive_range_syntax,
 376         infer_outlives_requirements,
 377         infer_static_outlives_requirements,
 378         inline,
 379         intel,
 380         into_iter,
 381         IntoIterator,
 382         into_result,
 383         intrinsics,
 384         irrefutable_let_patterns,
 385         isize,
 386         issue,
 387         issue_5723_bootstrap,
 388         issue_tracker_base_url,
 389         item,
 390         item_context: "ItemContext",
 391         item_like_imports,
 392         iter,
 393         Iterator,
 394         keyword,
 395         kind,
 396         label,
 397         label_break_value,
 398         lang,
 399         lang_items,
 400         let_chains,
 401         lhs,
 402         lib,
 403         lifetime,
 404         line,
 405         link,
 406         linkage,
 407         link_args,
 408         link_cfg,
 409         link_llvm_intrinsics,
 410         link_name,
 411         link_ordinal,
 412         link_section,
 413         LintPass,
 414         lint_reasons,
 415         literal,
 416         local_inner_macros,
 417         log_syntax,
 418         loop_break_value,
 419         macro_at_most_once_rep,
 420         macro_escape,
 421         macro_export,
 422         macro_lifetime_matcher,
 423         macro_literal_matcher,
 424         macro_reexport,
 425         macro_rules,
 426         macros_in_extern,
 427         macro_use,
 428         macro_vis_matcher,
 429         main,
 430         managed_boxes,
 431         marker,
 432         marker_trait_attr,
 433         masked,
 434         match_beginning_vert,
 435         match_default_bindings,
 436         may_dangle,
 437         maybe_uninit_uninit,
 438         maybe_uninit_zeroed,
 439         mem_uninitialized,
 440         mem_zeroed,
 441         member_constraints,
 442         message,
 443         meta,
 444         min_align_of,
 445         min_const_fn,
 446         min_const_unsafe_fn,
 447         mips_target_feature,
 448         mmx_target_feature,
 449         module,
 450         module_path,
 451         more_struct_aliases,
 452         move_val_init,
 453         movbe_target_feature,
 454         mul_with_overflow,
 455         must_use,
 456         naked,
 457         naked_functions,
 458         name,
 459         needs_allocator,
 460         needs_drop,
 461         needs_panic_runtime,
 462         negate_unsigned,
 463         never,
 464         never_type,
 465         never_type_fallback,
 466         new,
 467         next,
 468         __next,
 469         nll,
 470         no_builtins,
 471         no_core,
 472         no_crate_inject,
 473         no_debug,
 474         no_default_passes,
 475         no_implicit_prelude,
 476         no_inline,
 477         no_link,
 478         no_main,
 479         no_mangle,
 480         non_ascii_idents,
 481         None,
 482         non_exhaustive,
 483         non_modrs_mods,
 484         no_stack_check,
 485         no_start,
 486         no_std,
 487         not,
 488         note,
 489         object_safe_for_dispatch,
 490         Ok,
 491         omit_gdb_pretty_printer_section,
 492         on,
 493         on_unimplemented,
 494         oom,
 495         ops,
 496         optimize,
 497         optimize_attribute,
 498         optin_builtin_traits,
 499         option,
 500         Option,
 501         option_env,
 502         opt_out_copy,
 503         or,
 504         or_patterns,
 505         Ord,
 506         Ordering,
 507         Output,
 508         overlapping_marker_traits,
 509         packed,
 510         panic,
 511         panic_handler,
 512         panic_impl,
 513         panic_implementation,
 514         panic_runtime,
 515         parent_trait,
 516         partial_cmp,
 517         param_attrs,
 518         PartialEq,
 519         PartialOrd,
 520         passes,
 521         pat,
 522         path,
 523         pattern_parentheses,
 524         Pending,
 525         pin,
 526         Pin,
 527         pinned,
 528         platform_intrinsics,
 529         plugin,
 530         plugin_registrar,
 531         plugins,
 532         Poll,
 533         poll_with_tls_context,
 534         powerpc_target_feature,
 535         precise_pointer_size_matching,
 536         pref_align_of,
 537         prelude,
 538         prelude_import,
 539         primitive,
 540         proc_dash_macro: "proc-macro",
 541         proc_macro,
 542         proc_macro_attribute,
 543         proc_macro_def_site,
 544         proc_macro_derive,
 545         proc_macro_expr,
 546         proc_macro_gen,
 547         proc_macro_hygiene,
 548         proc_macro_internals,
 549         proc_macro_mod,
 550         proc_macro_non_items,
 551         proc_macro_path_invoc,
 552         profiler_runtime,
 553         ptr_offset_from,
 554         pub_restricted,
 555         pushpop_unsafe,
 556         quad_precision_float,
 557         question_mark,
 558         quote,
 559         Range,
 560         RangeFrom,
 561         RangeFull,
 562         RangeInclusive,
 563         RangeTo,
 564         RangeToInclusive,
 565         raw_dylib,
 566         raw_identifiers,
 567         raw_ref_op,
 568         Ready,
 569         reason,
 570         recursion_limit,
 571         reexport_test_harness_main,
 572         reflect,
 573         register_attr,
 574         register_tool,
 575         relaxed_adts,
 576         repr,
 577         repr128,
 578         repr_align,
 579         repr_align_enum,
 580         repr_packed,
 581         repr_simd,
 582         repr_transparent,
 583         re_rebalance_coherence,
 584         result,
 585         Result,
 586         Return,
 587         rhs,
 588         rlib,
 589         rotate_left,
 590         rotate_right,
 591         rt,
 592         rtm_target_feature,
 593         rust,
 594         rust_2015_preview,
 595         rust_2018_preview,
 596         rust_begin_unwind,
 597         rustc,
 598         RustcDecodable,
 599         RustcEncodable,
 600         rustc_allocator,
 601         rustc_allocator_nounwind,
 602         rustc_allow_const_fn_ptr,
 603         rustc_args_required_const,
 604         rustc_attrs,
 605         rustc_builtin_macro,
 606         rustc_clean,
 607         rustc_const_unstable,
 608         rustc_conversion_suggestion,
 609         rustc_def_path,
 610         rustc_deprecated,
 611         rustc_diagnostic_item,
 612         rustc_diagnostic_macros,
 613         rustc_dirty,
 614         rustc_dummy,
 615         rustc_dump_env_program_clauses,
 616         rustc_dump_program_clauses,
 617         rustc_dump_user_substs,
 618         rustc_error,
 619         rustc_expected_cgu_reuse,
 620         rustc_if_this_changed,
 621         rustc_inherit_overflow_checks,
 622         rustc_layout,
 623         rustc_layout_scalar_valid_range_end,
 624         rustc_layout_scalar_valid_range_start,
 625         rustc_macro_transparency,
 626         rustc_mir,
 627         rustc_nonnull_optimization_guaranteed,
 628         rustc_object_lifetime_default,
 629         rustc_on_unimplemented,
 630         rustc_outlives,
 631         rustc_paren_sugar,
 632         rustc_partition_codegened,
 633         rustc_partition_reused,
 634         rustc_peek,
 635         rustc_peek_definite_init,
 636         rustc_peek_maybe_init,
 637         rustc_peek_maybe_uninit,
 638         rustc_peek_indirectly_mutable,
 639         rustc_private,
 640         rustc_proc_macro_decls,
 641         rustc_promotable,
 642         rustc_regions,
 643         rustc_stable,
 644         rustc_std_internal_symbol,
 645         rustc_symbol_name,
 646         rustc_synthetic,
 647         rustc_reservation_impl,
 648         rustc_test_marker,
 649         rustc_then_this_would_need,
 650         rustc_variance,
 651         rustfmt,
 652         rust_eh_personality,
 653         rust_eh_unwind_resume,
 654         rust_oom,
 655         rvalue_static_promotion,
 656         sanitize,
 657         sanitizer_runtime,
 658         saturating_add,
 659         saturating_sub,
 660         _Self,
 661         self_in_typedefs,
 662         self_struct_ctor,
 663         should_panic,
 664         simd,
 665         simd_extract,
 666         simd_ffi,
 667         simd_insert,
 668         since,
 669         size,
 670         size_of,
 671         slice_patterns,
 672         slicing_syntax,
 673         soft,
 674         Some,
 675         specialization,
 676         speed,
 677         spotlight,
 678         sse4a_target_feature,
 679         stable,
 680         staged_api,
 681         start,
 682         static_in_const,
 683         staticlib,
 684         static_nobundle,
 685         static_recursion,
 686         std,
 687         std_inject,
 688         str,
 689         stringify,
 690         stmt,
 691         stmt_expr_attributes,
 692         stop_after_dataflow,
 693         struct_field_attributes,
 694         struct_inherit,
 695         structural_match,
 696         struct_variant,
 697         sty,
 698         sub_with_overflow,
 699         suggestion,
 700         target_feature,
 701         target_has_atomic,
 702         target_has_atomic_load_store,
 703         target_thread_local,
 704         task,
 705         tbm_target_feature,
 706         termination_trait,
 707         termination_trait_test,
 708         test,
 709         test_2018_feature,
 710         test_accepted_feature,
 711         test_case,
 712         test_removed_feature,
 713         test_runner,
 714         then_with,
 715         thread_local,
 716         tool_attributes,
 717         tool_lints,
 718         trace_macros,
 719         track_caller,
 720         trait_alias,
 721         transmute,
 722         transparent,
 723         transparent_enums,
 724         transparent_unions,
 725         trivial_bounds,
 726         Try,
 727         try_blocks,
 728         try_trait,
 729         tt,
 730         tuple_indexing,
 731         Ty,
 732         ty,
 733         type_alias_impl_trait,
 734         type_id,
 735         type_name,
 736         TyCtxt,
 737         TyKind,
 738         type_alias_enum_variants,
 739         type_ascription,
 740         type_length_limit,
 741         type_macros,
 742         u128,
 743         u16,
 744         u32,
 745         u64,
 746         u8,
 747         unboxed_closures,
 748         unchecked_shl,
 749         unchecked_shr,
 750         underscore_const_names,
 751         underscore_imports,
 752         underscore_lifetimes,
 753         uniform_paths,
 754         universal_impl_trait,
 755         unmarked_api,
 756         unreachable_code,
 757         unrestricted_attribute_tokens,
 758         unsafe_no_drop_flag,
 759         unsized_locals,
 760         unsized_tuple_coercion,
 761         unstable,
 762         untagged_unions,
 763         unwind,
 764         unwind_attributes,
 765         unwrap_or,
 766         used,
 767         use_extern_macros,
 768         use_nested_groups,
 769         usize,
 770         v1,
 771         val,
 772         vec,
 773         Vec,
 774         vis,
 775         visible_private_types,
 776         volatile,
 777         warn,
 778         wasm_import_module,
 779         wasm_target_feature,
 780         while_let,
 781         windows,
 782         windows_subsystem,
 783         wrapping_add,
 784         wrapping_sub,
 785         wrapping_mul,
 786         Yield,
 787     }
 788 }
 789
 790 #[derive(Copy, Clone, Eq, HashStable_Generic)]
 791 pub struct Ident {
 792     pub name: Symbol,
 793     pub span: Span,
 794 }
 795
 796 impl Ident {
 797     #[inline]
 798     /// Constructs a new identifier from a symbol and a span.
 799     pub const fn new(name: Symbol, span: Span) -> Ident {
 800         Ident { name, span }
 801     }
 802
 803     /// Constructs a new identifier with a dummy span.
 804     #[inline]
 805     pub const fn with_dummy_span(name: Symbol) -> Ident {
 806         Ident::new(name, DUMMY_SP)
 807     }
 808
 809     #[inline]
 810     pub fn invalid() -> Ident {
 811         Ident::with_dummy_span(kw::Invalid)
 812     }
 813
 814     /// Maps a string to an identifier with a dummy span.
 815     pub fn from_str(string: &str) -> Ident {
 816         Ident::with_dummy_span(Symbol::intern(string))
 817     }
 818
 819     /// Maps a string and a span to an identifier.
 820     pub fn from_str_and_span(string: &str, span: Span) -> Ident {
 821         Ident::new(Symbol::intern(string), span)
 822     }
 823
 824     /// Replaces `lo` and `hi` with those from `span`, but keep hygiene context.
 825     pub fn with_span_pos(self, span: Span) -> Ident {
 826         Ident::new(self.name, span.with_ctxt(self.span.ctxt()))
 827     }
 828
 829     pub fn without_first_quote(self) -> Ident {
 830         Ident::new(Symbol::intern(self.as_str().trim_start_matches('\'')), self.span)
 831     }
 832
 833     /// "Normalize" ident for use in comparisons using "item hygiene".
 834     /// Identifiers with same string value become same if they came from the same "modern" macro
 835     /// (e.g., `macro` item, but not `macro_rules` item) and stay different if they came from
 836     /// different "modern" macros.
 837     /// Technically, this operation strips all non-opaque marks from ident's syntactic context.
 838     pub fn modern(self) -> Ident {
 839         Ident::new(self.name, self.span.modern())
 840     }
 841
 842     /// "Normalize" ident for use in comparisons using "local variable hygiene".
 843     /// Identifiers with same string value become same if they came from the same non-transparent
 844     /// macro (e.g., `macro` or `macro_rules!` items) and stay different if they came from different
 845     /// non-transparent macros.
 846     /// Technically, this operation strips all transparent marks from ident's syntactic context.
 847     pub fn modern_and_legacy(self) -> Ident {
 848         Ident::new(self.name, self.span.modern_and_legacy())
 849     }
 850
 851     /// Convert the name to a `SymbolStr`. This is a slowish operation because
 852     /// it requires locking the symbol interner.
 853     pub fn as_str(self) -> SymbolStr {
 854         self.name.as_str()
 855     }
 856 }
 857
 858 impl PartialEq for Ident {
 859     fn eq(&self, rhs: &Self) -> bool {
 860         self.name == rhs.name && self.span.ctxt() == rhs.span.ctxt()
 861     }
 862 }
 863
 864 impl Hash for Ident {
 865     fn hash<H: Hasher>(&self, state: &mut H) {
 866         self.name.hash(state);
 867         self.span.ctxt().hash(state);
 868     }
 869 }
 870
 871 impl fmt::Debug for Ident {
 872     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 873         if self.is_raw_guess() {
 874             write!(f, "r#")?;
 875         }
 876         write!(f, "{}{:?}", self.name, self.span.ctxt())
 877     }
 878 }
 879
 880 impl fmt::Display for Ident {
 881     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 882         if self.is_raw_guess() {
 883             write!(f, "r#")?;
 884         }
 885         fmt::Display::fmt(&self.name, f)
 886     }
 887 }
 888
 889 impl UseSpecializedEncodable for Ident {
 890     fn default_encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
 891         s.emit_struct("Ident", 2, |s| {
 892             s.emit_struct_field("name", 0, |s| {
 893                 self.name.encode(s)
 894             })?;
 895             s.emit_struct_field("span", 1, |s| {
 896                 self.span.encode(s)
 897             })
 898         })
 899     }
 900 }
 901
 902 impl UseSpecializedDecodable for Ident {
 903     fn default_decode<D: Decoder>(d: &mut D) -> Result<Self, D::Error> {
 904         d.read_struct("Ident", 2, |d| {
 905             Ok(Ident {
 906                 name: d.read_struct_field("name", 0, Decodable::decode)?,
 907                 span: d.read_struct_field("span", 1, Decodable::decode)?,
 908             })
 909         })
 910     }
 911 }
 912
 913 /// An interned string.
 914 ///
 915 /// Internally, a `Symbol` is implemented as an index, and all operations
 916 /// (including hashing, equality, and ordering) operate on that index. The use
 917 /// of `rustc_index::newtype_index!` means that `Option<Symbol>` only takes up 4 bytes,
 918 /// because `rustc_index::newtype_index!` reserves the last 256 values for tagging purposes.
 919 ///
 920 /// Note that `Symbol` cannot directly be a `rustc_index::newtype_index!` because it
 921 /// implements `fmt::Debug`, `Encodable`, and `Decodable` in special ways.
 922 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 923 pub struct Symbol(SymbolIndex);
 924
 925 rustc_index::newtype_index! {
 926     pub struct SymbolIndex { .. }
 927 }
 928
 929 impl Symbol {
 930     const fn new(n: u32) -> Self {
 931         Symbol(SymbolIndex::from_u32_const(n))
 932     }
 933
 934     /// Maps a string to its interned representation.
 935     pub fn intern(string: &str) -> Self {
 936         with_interner(|interner| interner.intern(string))
 937     }
 938
 939     /// Access the symbol's chars. This is a slowish operation because it
 940     /// requires locking the symbol interner.
 941     pub fn with<F: FnOnce(&str) -> R, R>(self, f: F) -> R {
 942         with_interner(|interner| {
 943             f(interner.get(self))
 944         })
 945     }
 946
 947     /// Convert to a `SymbolStr`. This is a slowish operation because it
 948     /// requires locking the symbol interner.
 949     pub fn as_str(self) -> SymbolStr {
 950         with_interner(|interner| unsafe {
 951             SymbolStr {
 952                 string: std::mem::transmute::<&str, &str>(interner.get(self))
 953             }
 954         })
 955     }
 956
 957     pub fn as_u32(self) -> u32 {
 958         self.0.as_u32()
 959     }
 960 }
 961
 962 impl fmt::Debug for Symbol {
 963     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 964         self.with(|str| fmt::Debug::fmt(&str, f))
 965     }
 966 }
 967
 968 impl fmt::Display for Symbol {
 969     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 970         self.with(|str| fmt::Display::fmt(&str, f))
 971     }
 972 }
 973
 974 impl Encodable for Symbol {
 975     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
 976         self.with(|string| s.emit_str(string))
 977     }
 978 }
 979
 980 impl Decodable for Symbol {
 981     fn decode<D: Decoder>(d: &mut D) -> Result<Symbol, D::Error> {
 982         Ok(Symbol::intern(&d.read_str()?))
 983     }
 984 }
 985
 986 impl<CTX> HashStable<CTX> for Symbol {
 987     #[inline]
 988     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
 989         self.as_str().hash_stable(hcx, hasher);
 990     }
 991 }
 992
 993 impl<CTX> ToStableHashKey<CTX> for Symbol {
 994     type KeyType = SymbolStr;
 995
 996     #[inline]
 997     fn to_stable_hash_key(&self, _: &CTX) -> SymbolStr {
 998         self.as_str()
 999     }
1000 }
1001
1002 // The `&'static str`s in this type actually point into the arena.
1003 #[derive(Default)]
1004 pub struct Interner {
1005     arena: DroplessArena,
1006     names: FxHashMap<&'static str, Symbol>,
1007     strings: Vec<&'static str>,
1008 }
1009
1010 impl Interner {
1011     fn prefill(init: &[&'static str]) -> Self {
1012         Interner {
1013             strings: init.into(),
1014             names: init.iter().copied().zip((0..).map(Symbol::new)).collect(),
1015             ..Default::default()
1016         }
1017     }
1018
1019     pub fn intern(&mut self, string: &str) -> Symbol {
1020         if let Some(&name) = self.names.get(string) {
1021             return name;
1022         }
1023
1024         let name = Symbol::new(self.strings.len() as u32);
1025
1026         // `from_utf8_unchecked` is safe since we just allocated a `&str` which is known to be
1027         // UTF-8.
1028         let string: &str = unsafe {
1029             str::from_utf8_unchecked(self.arena.alloc_slice(string.as_bytes()))
1030         };
1031         // It is safe to extend the arena allocation to `'static` because we only access
1032         // these while the arena is still alive.
1033         let string: &'static str =  unsafe {
1034             &*(string as *const str)
1035         };
1036         self.strings.push(string);
1037         self.names.insert(string, name);
1038         name
1039     }
1040
1041     // Get the symbol as a string. `Symbol::as_str()` should be used in
1042     // preference to this function.
1043     pub fn get(&self, symbol: Symbol) -> &str {
1044         self.strings[symbol.0.as_usize()]
1045     }
1046 }
1047
1048 // This module has a very short name because it's used a lot.
1049 pub mod kw {
1050     use super::Symbol;
1051     keywords!();
1052 }
1053
1054 // This module has a very short name because it's used a lot.
1055 pub mod sym {
1056     use std::convert::TryInto;
1057     use super::Symbol;
1058
1059     symbols!();
1060
1061     // Get the symbol for an integer. The first few non-negative integers each
1062     // have a static symbol and therefore are fast.
1063     pub fn integer<N: TryInto<usize> + Copy + ToString>(n: N) -> Symbol {
1064         if let Result::Ok(idx) = n.try_into() {
1065             if let Option::Some(&sym) = digits_array.get(idx) {
1066                 return sym;
1067             }
1068         }
1069         Symbol::intern(&n.to_string())
1070     }
1071 }
1072
1073 impl Symbol {
1074     fn is_used_keyword_2018(self) -> bool {
1075         self >= kw::Async && self <= kw::Dyn
1076     }
1077
1078     fn is_unused_keyword_2018(self) -> bool {
1079         self == kw::Try
1080     }
1081
1082     /// Used for sanity checking rustdoc keyword sections.
1083     pub fn is_doc_keyword(self) -> bool {
1084         self <= kw::Union
1085     }
1086
1087     /// A keyword or reserved identifier that can be used as a path segment.
1088     pub fn is_path_segment_keyword(self) -> bool {
1089         self == kw::Super ||
1090         self == kw::SelfLower ||
1091         self == kw::SelfUpper ||
1092         self == kw::Crate ||
1093         self == kw::PathRoot ||
1094         self == kw::DollarCrate
1095     }
1096
1097     /// Returns `true` if the symbol is `true` or `false`.
1098     pub fn is_bool_lit(self) -> bool {
1099         self == kw::True || self == kw::False
1100     }
1101
1102     /// This symbol can be a raw identifier.
1103     pub fn can_be_raw(self) -> bool {
1104         self != kw::Invalid && self != kw::Underscore && !self.is_path_segment_keyword()
1105     }
1106 }
1107
1108 impl Ident {
1109     // Returns `true` for reserved identifiers used internally for elided lifetimes,
1110     // unnamed method parameters, crate root module, error recovery etc.
1111     pub fn is_special(self) -> bool {
1112         self.name <= kw::Underscore
1113     }
1114
1115     /// Returns `true` if the token is a keyword used in the language.
1116     pub fn is_used_keyword(self) -> bool {
1117         // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1118         self.name >= kw::As && self.name <= kw::While ||
1119         self.name.is_used_keyword_2018() && self.span.rust_2018()
1120     }
1121
1122     /// Returns `true` if the token is a keyword reserved for possible future use.
1123     pub fn is_unused_keyword(self) -> bool {
1124         // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1125         self.name >= kw::Abstract && self.name <= kw::Yield ||
1126         self.name.is_unused_keyword_2018() && self.span.rust_2018()
1127     }
1128
1129     /// Returns `true` if the token is either a special identifier or a keyword.
1130     pub fn is_reserved(self) -> bool {
1131         self.is_special() || self.is_used_keyword() || self.is_unused_keyword()
1132     }
1133
1134     /// A keyword or reserved identifier that can be used as a path segment.
1135     pub fn is_path_segment_keyword(self) -> bool {
1136         self.name.is_path_segment_keyword()
1137     }
1138
1139     /// We see this identifier in a normal identifier position, like variable name or a type.
1140     /// How was it written originally? Did it use the raw form? Let's try to guess.
1141     pub fn is_raw_guess(self) -> bool {
1142         self.name.can_be_raw() && self.is_reserved()
1143     }
1144 }
1145
1146 #[inline]
1147 fn with_interner<T, F: FnOnce(&mut Interner) -> T>(f: F) -> T {
1148     GLOBALS.with(|globals| f(&mut *globals.symbol_interner.lock()))
1149 }
1150
1151 /// An alternative to `Symbol`, useful when the chars within the symbol need to
1152 /// be accessed. It deliberately has limited functionality and should only be
1153 /// used for temporary values.
1154 ///
1155 /// Because the interner outlives any thread which uses this type, we can
1156 /// safely treat `string` which points to interner data, as an immortal string,
1157 /// as long as this type never crosses between threads.
1158 //
1159 // FIXME: ensure that the interner outlives any thread which uses `SymbolStr`,
1160 // by creating a new thread right after constructing the interner.
1161 #[derive(Clone, Eq, PartialOrd, Ord)]
1162 pub struct SymbolStr {
1163     string: &'static str,
1164 }
1165
1166 // This impl allows a `SymbolStr` to be directly equated with a `String` or
1167 // `&str`.
1168 impl<T: std::ops::Deref<Target = str>> std::cmp::PartialEq<T> for SymbolStr {
1169     fn eq(&self, other: &T) -> bool {
1170         self.string == other.deref()
1171     }
1172 }
1173
1174 impl !Send for SymbolStr {}
1175 impl !Sync for SymbolStr {}
1176
1177 /// This impl means that if `ss` is a `SymbolStr`:
1178 /// - `*ss` is a `str`;
1179 /// - `&*ss` is a `&str`;
1180 /// - `&ss as &str` is a `&str`, which means that `&ss` can be passed to a
1181 ///   function expecting a `&str`.
1182 impl std::ops::Deref for SymbolStr {
1183     type Target = str;
1184     #[inline]
1185     fn deref(&self) -> &str { self.string }
1186 }
1187
1188 impl fmt::Debug for SymbolStr {
1189     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1190         fmt::Debug::fmt(self.string, f)
1191     }
1192 }
1193
1194 impl fmt::Display for SymbolStr {
1195     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1196         fmt::Display::fmt(self.string, f)
1197     }
1198 }
1199
1200 impl<CTX> HashStable<CTX> for SymbolStr {
1201     #[inline]
1202     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
1203         self.string.hash_stable(hcx, hasher)
1204     }
1205 }
1206
1207 impl<CTX> ToStableHashKey<CTX> for SymbolStr {
1208     type KeyType = SymbolStr;
1209
1210     #[inline]
1211     fn to_stable_hash_key(&self, _: &CTX) -> SymbolStr {
1212         self.clone()
1213     }
1214 }