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_msp430_interrupt,
 114         abi_ptx,
 115         abi_sysv64,
 116         abi_thiscall,
 117         abi_unadjusted,
 118         abi_vectorcall,
 119         abi_x86_interrupt,
 120         aborts,
 121         advanced_slice_patterns,
 122         adx_target_feature,
 123         alias,
 124         align,
 125         alignstack,
 126         all,
 127         allocator,
 128         allocator_internals,
 129         alloc_error_handler,
 130         allow,
 131         allowed,
 132         allow_fail,
 133         allow_internal_unsafe,
 134         allow_internal_unstable,
 135         allow_internal_unstable_backcompat_hack,
 136         always,
 137         and,
 138         any,
 139         arbitrary_enum_discriminant,
 140         arbitrary_self_types,
 141         Arguments,
 142         ArgumentV1,
 143         arm_target_feature,
 144         asm,
 145         assert,
 146         associated_consts,
 147         associated_type_bounds,
 148         associated_type_defaults,
 149         associated_types,
 150         async_await,
 151         async_closure,
 152         attr,
 153         attributes,
 154         attr_literals,
 155         augmented_assignments,
 156         automatically_derived,
 157         avx512_target_feature,
 158         await_macro,
 159         begin_panic,
 160         bench,
 161         bin,
 162         bind_by_move_pattern_guards,
 163         block,
 164         bool,
 165         borrowck_graphviz_postflow,
 166         borrowck_graphviz_preflow,
 167         box_patterns,
 168         box_syntax,
 169         braced_empty_structs,
 170         C,
 171         cdylib,
 172         cfg,
 173         cfg_attr,
 174         cfg_attr_multi,
 175         cfg_doctest,
 176         cfg_target_feature,
 177         cfg_target_has_atomic,
 178         cfg_target_thread_local,
 179         cfg_target_vendor,
 180         char,
 181         clippy,
 182         clone,
 183         Clone,
 184         clone_closures,
 185         clone_from,
 186         closure_to_fn_coercion,
 187         cmp,
 188         cmpxchg16b_target_feature,
 189         cold,
 190         column,
 191         compile_error,
 192         compiler_builtins,
 193         concat,
 194         concat_idents,
 195         conservative_impl_trait,
 196         console,
 197         const_compare_raw_pointers,
 198         const_constructor,
 199         const_extern_fn,
 200         const_fn,
 201         const_fn_union,
 202         const_generics,
 203         const_indexing,
 204         const_in_array_repeat_expressions,
 205         const_let,
 206         const_panic,
 207         const_raw_ptr_deref,
 208         const_raw_ptr_to_usize_cast,
 209         const_transmute,
 210         contents,
 211         context,
 212         convert,
 213         Copy,
 214         copy_closures,
 215         core,
 216         core_intrinsics,
 217         crate_id,
 218         crate_in_paths,
 219         crate_local,
 220         crate_name,
 221         crate_type,
 222         crate_visibility_modifier,
 223         custom_attribute,
 224         custom_derive,
 225         custom_inner_attributes,
 226         custom_test_frameworks,
 227         c_variadic,
 228         debug_trait,
 229         declare_lint_pass,
 230         decl_macro,
 231         Debug,
 232         Decodable,
 233         Default,
 234         default_lib_allocator,
 235         default_type_parameter_fallback,
 236         default_type_params,
 237         deny,
 238         deprecated,
 239         deref,
 240         deref_mut,
 241         derive,
 242         diagnostic,
 243         direct,
 244         doc,
 245         doc_alias,
 246         doc_cfg,
 247         doc_keyword,
 248         doc_masked,
 249         doc_spotlight,
 250         doctest,
 251         document_private_items,
 252         dotdoteq_in_patterns,
 253         dotdot_in_tuple_patterns,
 254         double_braced_crate: "{{crate}}",
 255         double_braced_impl: "{{impl}}",
 256         double_braced_misc: "{{misc}}",
 257         double_braced_closure: "{{closure}}",
 258         double_braced_constructor: "{{constructor}}",
 259         double_braced_constant: "{{constant}}",
 260         double_braced_opaque: "{{opaque}}",
 261         dropck_eyepatch,
 262         dropck_parametricity,
 263         drop_types_in_const,
 264         dylib,
 265         dyn_trait,
 266         eh_personality,
 267         eh_unwind_resume,
 268         enable,
 269         Encodable,
 270         env,
 271         eq,
 272         err,
 273         Err,
 274         Eq,
 275         Equal,
 276         except,
 277         exclusive_range_pattern,
 278         exhaustive_integer_patterns,
 279         exhaustive_patterns,
 280         existential_type,
 281         expected,
 282         export_name,
 283         expr,
 284         extern_absolute_paths,
 285         external_doc,
 286         extern_crate_item_prelude,
 287         extern_crate_self,
 288         extern_in_paths,
 289         extern_prelude,
 290         extern_types,
 291         f16c_target_feature,
 292         f32,
 293         f64,
 294         feature,
 295         ffi_returns_twice,
 296         field,
 297         field_init_shorthand,
 298         file,
 299         fmt,
 300         fmt_internals,
 301         fn_must_use,
 302         forbid,
 303         format_args,
 304         format_args_nl,
 305         from,
 306         From,
 307         from_desugaring,
 308         from_error,
 309         from_generator,
 310         from_method,
 311         from_ok,
 312         from_usize,
 313         fundamental,
 314         future,
 315         Future,
 316         FxHashSet,
 317         FxHashMap,
 318         gen_future,
 319         generators,
 320         generic_associated_types,
 321         generic_param_attrs,
 322         global_allocator,
 323         global_asm,
 324         globs,
 325         hash,
 326         Hash,
 327         HashSet,
 328         HashMap,
 329         hexagon_target_feature,
 330         hidden,
 331         homogeneous_aggregate,
 332         html_favicon_url,
 333         html_logo_url,
 334         html_no_source,
 335         html_playground_url,
 336         html_root_url,
 337         i128,
 338         i128_type,
 339         i16,
 340         i32,
 341         i64,
 342         i8,
 343         ident,
 344         if_let,
 345         if_while_or_patterns,
 346         ignore,
 347         impl_header_lifetime_elision,
 348         impl_lint_pass,
 349         impl_trait_in_bindings,
 350         import_shadowing,
 351         index,
 352         index_mut,
 353         in_band_lifetimes,
 354         include,
 355         include_bytes,
 356         include_str,
 357         inclusive_range_syntax,
 358         infer_outlives_requirements,
 359         infer_static_outlives_requirements,
 360         inline,
 361         intel,
 362         into_iter,
 363         IntoIterator,
 364         into_result,
 365         intrinsics,
 366         irrefutable_let_patterns,
 367         isize,
 368         issue,
 369         issue_5723_bootstrap,
 370         issue_tracker_base_url,
 371         item,
 372         item_like_imports,
 373         iter,
 374         Iterator,
 375         keyword,
 376         kind,
 377         label,
 378         label_break_value,
 379         lang,
 380         lang_items,
 381         let_chains,
 382         lhs,
 383         lib,
 384         lifetime,
 385         line,
 386         link,
 387         linkage,
 388         link_args,
 389         link_cfg,
 390         link_llvm_intrinsics,
 391         link_name,
 392         link_ordinal,
 393         link_section,
 394         LintPass,
 395         lint_reasons,
 396         literal,
 397         local_inner_macros,
 398         log_syntax,
 399         loop_break_value,
 400         macro_at_most_once_rep,
 401         macro_escape,
 402         macro_export,
 403         macro_lifetime_matcher,
 404         macro_literal_matcher,
 405         macro_reexport,
 406         macro_rules,
 407         macros_in_extern,
 408         macro_use,
 409         macro_vis_matcher,
 410         main,
 411         managed_boxes,
 412         marker,
 413         marker_trait_attr,
 414         masked,
 415         match_beginning_vert,
 416         match_default_bindings,
 417         may_dangle,
 418         mem,
 419         member_constraints,
 420         message,
 421         meta,
 422         min_const_fn,
 423         min_const_unsafe_fn,
 424         mips_target_feature,
 425         mmx_target_feature,
 426         module,
 427         module_path,
 428         more_struct_aliases,
 429         movbe_target_feature,
 430         must_use,
 431         naked,
 432         naked_functions,
 433         name,
 434         needs_allocator,
 435         needs_panic_runtime,
 436         negate_unsigned,
 437         never,
 438         never_type,
 439         new,
 440         next,
 441         __next,
 442         nll,
 443         no_builtins,
 444         no_core,
 445         no_crate_inject,
 446         no_debug,
 447         no_default_passes,
 448         no_implicit_prelude,
 449         no_inline,
 450         no_link,
 451         no_main,
 452         no_mangle,
 453         non_ascii_idents,
 454         None,
 455         non_exhaustive,
 456         non_modrs_mods,
 457         no_stack_check,
 458         no_start,
 459         no_std,
 460         not,
 461         note,
 462         object_safe_for_dispatch,
 463         Ok,
 464         omit_gdb_pretty_printer_section,
 465         on,
 466         on_unimplemented,
 467         oom,
 468         ops,
 469         optimize,
 470         optimize_attribute,
 471         optin_builtin_traits,
 472         option,
 473         Option,
 474         option_env,
 475         opt_out_copy,
 476         or,
 477         or_patterns,
 478         Ord,
 479         Ordering,
 480         Output,
 481         overlapping_marker_traits,
 482         packed,
 483         panic,
 484         panic_handler,
 485         panic_impl,
 486         panic_implementation,
 487         panic_runtime,
 488         parent_trait,
 489         partial_cmp,
 490         param_attrs,
 491         PartialEq,
 492         PartialOrd,
 493         passes,
 494         pat,
 495         path,
 496         pattern_parentheses,
 497         Pending,
 498         pin,
 499         Pin,
 500         pinned,
 501         platform_intrinsics,
 502         plugin,
 503         plugin_registrar,
 504         plugins,
 505         Poll,
 506         poll_with_tls_context,
 507         powerpc_target_feature,
 508         precise_pointer_size_matching,
 509         prelude,
 510         prelude_import,
 511         primitive,
 512         proc_dash_macro: "proc-macro",
 513         proc_macro,
 514         proc_macro_attribute,
 515         proc_macro_def_site,
 516         proc_macro_derive,
 517         proc_macro_expr,
 518         proc_macro_gen,
 519         proc_macro_hygiene,
 520         proc_macro_internals,
 521         proc_macro_mod,
 522         proc_macro_non_items,
 523         proc_macro_path_invoc,
 524         profiler_runtime,
 525         pub_restricted,
 526         pushpop_unsafe,
 527         quad_precision_float,
 528         question_mark,
 529         quote,
 530         Range,
 531         RangeFrom,
 532         RangeFull,
 533         RangeInclusive,
 534         RangeTo,
 535         RangeToInclusive,
 536         raw_dylib,
 537         raw_identifiers,
 538         Ready,
 539         reason,
 540         recursion_limit,
 541         reexport_test_harness_main,
 542         reflect,
 543         relaxed_adts,
 544         repr,
 545         repr128,
 546         repr_align,
 547         repr_align_enum,
 548         repr_packed,
 549         repr_simd,
 550         repr_transparent,
 551         re_rebalance_coherence,
 552         result,
 553         Result,
 554         Return,
 555         rhs,
 556         rlib,
 557         rt,
 558         rtm_target_feature,
 559         rust,
 560         rust_2015_preview,
 561         rust_2018_preview,
 562         rust_begin_unwind,
 563         rustc,
 564         RustcDecodable,
 565         RustcEncodable,
 566         rustc_allocator,
 567         rustc_allocator_nounwind,
 568         rustc_allow_const_fn_ptr,
 569         rustc_args_required_const,
 570         rustc_attrs,
 571         rustc_builtin_macro,
 572         rustc_clean,
 573         rustc_const_unstable,
 574         rustc_conversion_suggestion,
 575         rustc_def_path,
 576         rustc_deprecated,
 577         rustc_diagnostic_item,
 578         rustc_diagnostic_macros,
 579         rustc_dirty,
 580         rustc_dummy,
 581         rustc_dump_env_program_clauses,
 582         rustc_dump_program_clauses,
 583         rustc_dump_user_substs,
 584         rustc_error,
 585         rustc_expected_cgu_reuse,
 586         rustc_if_this_changed,
 587         rustc_inherit_overflow_checks,
 588         rustc_layout,
 589         rustc_layout_scalar_valid_range_end,
 590         rustc_layout_scalar_valid_range_start,
 591         rustc_macro_transparency,
 592         rustc_mir,
 593         rustc_nonnull_optimization_guaranteed,
 594         rustc_object_lifetime_default,
 595         rustc_on_unimplemented,
 596         rustc_outlives,
 597         rustc_paren_sugar,
 598         rustc_partition_codegened,
 599         rustc_partition_reused,
 600         rustc_peek,
 601         rustc_peek_definite_init,
 602         rustc_peek_maybe_init,
 603         rustc_peek_maybe_uninit,
 604         rustc_peek_indirectly_mutable,
 605         rustc_private,
 606         rustc_proc_macro_decls,
 607         rustc_promotable,
 608         rustc_regions,
 609         rustc_stable,
 610         rustc_std_internal_symbol,
 611         rustc_symbol_name,
 612         rustc_synthetic,
 613         rustc_reservation_impl,
 614         rustc_test_marker,
 615         rustc_then_this_would_need,
 616         rustc_variance,
 617         rustdoc,
 618         rustfmt,
 619         rust_eh_personality,
 620         rust_eh_unwind_resume,
 621         rust_oom,
 622         rvalue_static_promotion,
 623         sanitizer_runtime,
 624         _Self,
 625         self_in_typedefs,
 626         self_struct_ctor,
 627         should_panic,
 628         simd,
 629         simd_ffi,
 630         since,
 631         size,
 632         slice_patterns,
 633         slicing_syntax,
 634         soft,
 635         Some,
 636         specialization,
 637         speed,
 638         spotlight,
 639         sse4a_target_feature,
 640         stable,
 641         staged_api,
 642         start,
 643         static_in_const,
 644         staticlib,
 645         static_nobundle,
 646         static_recursion,
 647         std,
 648         std_inject,
 649         str,
 650         stringify,
 651         stmt,
 652         stmt_expr_attributes,
 653         stop_after_dataflow,
 654         struct_field_attributes,
 655         struct_inherit,
 656         structural_match,
 657         struct_variant,
 658         sty,
 659         suggestion,
 660         target_feature,
 661         target_has_atomic,
 662         target_has_atomic_load_store,
 663         target_thread_local,
 664         task,
 665         tbm_target_feature,
 666         termination_trait,
 667         termination_trait_test,
 668         test,
 669         test_2018_feature,
 670         test_accepted_feature,
 671         test_case,
 672         test_removed_feature,
 673         test_runner,
 674         then_with,
 675         thread_local,
 676         tool_attributes,
 677         tool_lints,
 678         trace_macros,
 679         track_caller,
 680         trait_alias,
 681         transmute,
 682         transparent,
 683         transparent_enums,
 684         transparent_unions,
 685         trivial_bounds,
 686         Try,
 687         try_blocks,
 688         try_trait,
 689         tt,
 690         tuple_indexing,
 691         Ty,
 692         ty,
 693         type_alias_impl_trait,
 694         TyCtxt,
 695         TyKind,
 696         type_alias_enum_variants,
 697         type_ascription,
 698         type_length_limit,
 699         type_macros,
 700         u128,
 701         u16,
 702         u32,
 703         u64,
 704         u8,
 705         unboxed_closures,
 706         underscore_const_names,
 707         underscore_imports,
 708         underscore_lifetimes,
 709         uniform_paths,
 710         uninitialized,
 711         universal_impl_trait,
 712         unmarked_api,
 713         unreachable_code,
 714         unrestricted_attribute_tokens,
 715         unsafe_no_drop_flag,
 716         unsized_locals,
 717         unsized_tuple_coercion,
 718         unstable,
 719         untagged_unions,
 720         unwind,
 721         unwind_attributes,
 722         unwrap_or,
 723         used,
 724         use_extern_macros,
 725         use_nested_groups,
 726         usize,
 727         v1,
 728         val,
 729         vec,
 730         Vec,
 731         vis,
 732         visible_private_types,
 733         volatile,
 734         warn,
 735         warn_directory_ownership,
 736         wasm_import_module,
 737         wasm_target_feature,
 738         while_let,
 739         windows,
 740         windows_subsystem,
 741         Yield,
 742         zeroed,
 743     }
 744 }
 745
 746 #[derive(Copy, Clone, Eq)]
 747 pub struct Ident {
 748     pub name: Symbol,
 749     pub span: Span,
 750 }
 751
 752 impl Ident {
 753     #[inline]
 754     /// Constructs a new identifier from a symbol and a span.
 755     pub const fn new(name: Symbol, span: Span) -> Ident {
 756         Ident { name, span }
 757     }
 758
 759     /// Constructs a new identifier with a dummy span.
 760     #[inline]
 761     pub const fn with_dummy_span(name: Symbol) -> Ident {
 762         Ident::new(name, DUMMY_SP)
 763     }
 764
 765     #[inline]
 766     pub fn invalid() -> Ident {
 767         Ident::with_dummy_span(kw::Invalid)
 768     }
 769
 770     /// Maps a string to an identifier with a dummy span.
 771     pub fn from_str(string: &str) -> Ident {
 772         Ident::with_dummy_span(Symbol::intern(string))
 773     }
 774
 775     /// Maps a string and a span to an identifier.
 776     pub fn from_str_and_span(string: &str, span: Span) -> Ident {
 777         Ident::new(Symbol::intern(string), span)
 778     }
 779
 780     /// Replaces `lo` and `hi` with those from `span`, but keep hygiene context.
 781     pub fn with_span_pos(self, span: Span) -> Ident {
 782         Ident::new(self.name, span.with_ctxt(self.span.ctxt()))
 783     }
 784
 785     pub fn without_first_quote(self) -> Ident {
 786         Ident::new(Symbol::intern(self.as_str().trim_start_matches('\'')), self.span)
 787     }
 788
 789     /// "Normalize" ident for use in comparisons using "item hygiene".
 790     /// Identifiers with same string value become same if they came from the same "modern" macro
 791     /// (e.g., `macro` item, but not `macro_rules` item) and stay different if they came from
 792     /// different "modern" macros.
 793     /// Technically, this operation strips all non-opaque marks from ident's syntactic context.
 794     pub fn modern(self) -> Ident {
 795         Ident::new(self.name, self.span.modern())
 796     }
 797
 798     /// "Normalize" ident for use in comparisons using "local variable hygiene".
 799     /// Identifiers with same string value become same if they came from the same non-transparent
 800     /// macro (e.g., `macro` or `macro_rules!` items) and stay different if they came from different
 801     /// non-transparent macros.
 802     /// Technically, this operation strips all transparent marks from ident's syntactic context.
 803     pub fn modern_and_legacy(self) -> Ident {
 804         Ident::new(self.name, self.span.modern_and_legacy())
 805     }
 806
 807     /// Convert the name to a `LocalInternedString`. This is a slowish
 808     /// operation because it requires locking the symbol interner.
 809     pub fn as_str(self) -> LocalInternedString {
 810         self.name.as_str()
 811     }
 812 }
 813
 814 impl PartialEq for Ident {
 815     fn eq(&self, rhs: &Self) -> bool {
 816         self.name == rhs.name && self.span.ctxt() == rhs.span.ctxt()
 817     }
 818 }
 819
 820 impl Hash for Ident {
 821     fn hash<H: Hasher>(&self, state: &mut H) {
 822         self.name.hash(state);
 823         self.span.ctxt().hash(state);
 824     }
 825 }
 826
 827 impl fmt::Debug for Ident {
 828     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 829         write!(f, "{}{:?}", self.name, self.span.ctxt())
 830     }
 831 }
 832
 833 impl fmt::Display for Ident {
 834     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 835         fmt::Display::fmt(&self.name, f)
 836     }
 837 }
 838
 839 impl UseSpecializedEncodable for Ident {
 840     fn default_encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
 841         s.emit_struct("Ident", 2, |s| {
 842             s.emit_struct_field("name", 0, |s| {
 843                 self.name.encode(s)
 844             })?;
 845             s.emit_struct_field("span", 1, |s| {
 846                 self.span.encode(s)
 847             })
 848         })
 849     }
 850 }
 851
 852 impl UseSpecializedDecodable for Ident {
 853     fn default_decode<D: Decoder>(d: &mut D) -> Result<Self, D::Error> {
 854         d.read_struct("Ident", 2, |d| {
 855             Ok(Ident {
 856                 name: d.read_struct_field("name", 0, Decodable::decode)?,
 857                 span: d.read_struct_field("span", 1, Decodable::decode)?,
 858             })
 859         })
 860     }
 861 }
 862
 863 /// An interned string.
 864 ///
 865 /// Internally, a `Symbol` is implemented as an index, and all operations
 866 /// (including hashing, equality, and ordering) operate on that index. The use
 867 /// of `rustc_index::newtype_index!` means that `Option<Symbol>` only takes up 4 bytes,
 868 /// because `rustc_index::newtype_index!` reserves the last 256 values for tagging purposes.
 869 ///
 870 /// Note that `Symbol` cannot directly be a `rustc_index::newtype_index!` because it
 871 /// implements `fmt::Debug`, `Encodable`, and `Decodable` in special ways.
 872 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 873 pub struct Symbol(SymbolIndex);
 874
 875 rustc_index::newtype_index! {
 876     pub struct SymbolIndex { .. }
 877 }
 878
 879 impl Symbol {
 880     const fn new(n: u32) -> Self {
 881         Symbol(SymbolIndex::from_u32_const(n))
 882     }
 883
 884     /// Maps a string to its interned representation.
 885     pub fn intern(string: &str) -> Self {
 886         with_interner(|interner| interner.intern(string))
 887     }
 888
 889     /// Access the symbol's chars. This is a slowish operation because it
 890     /// requires locking the symbol interner.
 891     pub fn with<F: FnOnce(&str) -> R, R>(self, f: F) -> R {
 892         with_interner(|interner| {
 893             f(interner.get(self))
 894         })
 895     }
 896
 897     /// Convert to a `LocalInternedString`. This is a slowish operation because
 898     /// it requires locking the symbol interner.
 899     pub fn as_str(self) -> LocalInternedString {
 900         with_interner(|interner| unsafe {
 901             LocalInternedString {
 902                 string: std::mem::transmute::<&str, &str>(interner.get(self))
 903             }
 904         })
 905     }
 906
 907     pub fn as_u32(self) -> u32 {
 908         self.0.as_u32()
 909     }
 910 }
 911
 912 impl fmt::Debug for Symbol {
 913     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 914         self.with(|str| fmt::Debug::fmt(&str, f))
 915     }
 916 }
 917
 918 impl fmt::Display for Symbol {
 919     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 920         self.with(|str| fmt::Display::fmt(&str, f))
 921     }
 922 }
 923
 924 impl Encodable for Symbol {
 925     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
 926         self.with(|string| s.emit_str(string))
 927     }
 928 }
 929
 930 impl Decodable for Symbol {
 931     fn decode<D: Decoder>(d: &mut D) -> Result<Symbol, D::Error> {
 932         Ok(Symbol::intern(&d.read_str()?))
 933     }
 934 }
 935
 936 // The `&'static str`s in this type actually point into the arena.
 937 #[derive(Default)]
 938 pub struct Interner {
 939     arena: DroplessArena,
 940     names: FxHashMap<&'static str, Symbol>,
 941     strings: Vec<&'static str>,
 942 }
 943
 944 impl Interner {
 945     fn prefill(init: &[&'static str]) -> Self {
 946         Interner {
 947             strings: init.into(),
 948             names: init.iter().copied().zip((0..).map(Symbol::new)).collect(),
 949             ..Default::default()
 950         }
 951     }
 952
 953     pub fn intern(&mut self, string: &str) -> Symbol {
 954         if let Some(&name) = self.names.get(string) {
 955             return name;
 956         }
 957
 958         let name = Symbol::new(self.strings.len() as u32);
 959
 960         // `from_utf8_unchecked` is safe since we just allocated a `&str` which is known to be
 961         // UTF-8.
 962         let string: &str = unsafe {
 963             str::from_utf8_unchecked(self.arena.alloc_slice(string.as_bytes()))
 964         };
 965         // It is safe to extend the arena allocation to `'static` because we only access
 966         // these while the arena is still alive.
 967         let string: &'static str =  unsafe {
 968             &*(string as *const str)
 969         };
 970         self.strings.push(string);
 971         self.names.insert(string, name);
 972         name
 973     }
 974     // Get the symbol as a string. `Symbol::as_str()` should be used in
 975     // preference to this function.
 976     pub fn get(&self, symbol: Symbol) -> &str {
 977         self.strings[symbol.0.as_usize()]
 978     }
 979 }
 980
 981 // This module has a very short name because it's used a lot.
 982 pub mod kw {
 983     use super::Symbol;
 984     keywords!();
 985 }
 986
 987 // This module has a very short name because it's used a lot.
 988 pub mod sym {
 989     use std::convert::TryInto;
 990     use super::Symbol;
 991
 992     symbols!();
 993
 994     // Get the symbol for an integer. The first few non-negative integers each
 995     // have a static symbol and therefore are fast.
 996     pub fn integer<N: TryInto<usize> + Copy + ToString>(n: N) -> Symbol {
 997         if let Result::Ok(idx) = n.try_into() {
 998             if let Option::Some(&sym) = digits_array.get(idx) {
 999                 return sym;
1000             }
1001         }
1002         Symbol::intern(&n.to_string())
1003     }
1004 }
1005
1006 impl Symbol {
1007     fn is_used_keyword_2018(self) -> bool {
1008         self >= kw::Async && self <= kw::Dyn
1009     }
1010
1011     fn is_unused_keyword_2018(self) -> bool {
1012         self == kw::Try
1013     }
1014
1015     /// Used for sanity checking rustdoc keyword sections.
1016     pub fn is_doc_keyword(self) -> bool {
1017         self <= kw::Union
1018     }
1019
1020     /// A keyword or reserved identifier that can be used as a path segment.
1021     pub fn is_path_segment_keyword(self) -> bool {
1022         self == kw::Super ||
1023         self == kw::SelfLower ||
1024         self == kw::SelfUpper ||
1025         self == kw::Crate ||
1026         self == kw::PathRoot ||
1027         self == kw::DollarCrate
1028     }
1029
1030     /// Returns `true` if the symbol is `true` or `false`.
1031     pub fn is_bool_lit(self) -> bool {
1032         self == kw::True || self == kw::False
1033     }
1034
1035     /// This symbol can be a raw identifier.
1036     pub fn can_be_raw(self) -> bool {
1037         self != kw::Invalid && self != kw::Underscore && !self.is_path_segment_keyword()
1038     }
1039 }
1040
1041 impl Ident {
1042     // Returns `true` for reserved identifiers used internally for elided lifetimes,
1043     // unnamed method parameters, crate root module, error recovery etc.
1044     pub fn is_special(self) -> bool {
1045         self.name <= kw::Underscore
1046     }
1047
1048     /// Returns `true` if the token is a keyword used in the language.
1049     pub fn is_used_keyword(self) -> bool {
1050         // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1051         self.name >= kw::As && self.name <= kw::While ||
1052         self.name.is_used_keyword_2018() && self.span.rust_2018()
1053     }
1054
1055     /// Returns `true` if the token is a keyword reserved for possible future use.
1056     pub fn is_unused_keyword(self) -> bool {
1057         // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1058         self.name >= kw::Abstract && self.name <= kw::Yield ||
1059         self.name.is_unused_keyword_2018() && self.span.rust_2018()
1060     }
1061
1062     /// Returns `true` if the token is either a special identifier or a keyword.
1063     pub fn is_reserved(self) -> bool {
1064         self.is_special() || self.is_used_keyword() || self.is_unused_keyword()
1065     }
1066
1067     /// A keyword or reserved identifier that can be used as a path segment.
1068     pub fn is_path_segment_keyword(self) -> bool {
1069         self.name.is_path_segment_keyword()
1070     }
1071
1072     /// We see this identifier in a normal identifier position, like variable name or a type.
1073     /// How was it written originally? Did it use the raw form? Let's try to guess.
1074     pub fn is_raw_guess(self) -> bool {
1075         self.name.can_be_raw() && self.is_reserved()
1076     }
1077 }
1078
1079 // If an interner exists, return it. Otherwise, prepare a fresh one.
1080 #[inline]
1081 fn with_interner<T, F: FnOnce(&mut Interner) -> T>(f: F) -> T {
1082     GLOBALS.with(|globals| f(&mut *globals.symbol_interner.lock()))
1083 }
1084
1085 /// An alternative to `Symbol`, useful when the chars within the symbol need to
1086 /// be accessed. It deliberately has limited functionality and should only be
1087 /// used for temporary values.
1088 ///
1089 /// Because the interner outlives any thread which uses this type, we can
1090 /// safely treat `string` which points to interner data, as an immortal string,
1091 /// as long as this type never crosses between threads.
1092 //
1093 // FIXME: ensure that the interner outlives any thread which uses
1094 // `LocalInternedString`, by creating a new thread right after constructing the
1095 // interner.
1096 #[derive(Clone, Eq, PartialOrd, Ord)]
1097 pub struct LocalInternedString {
1098     string: &'static str,
1099 }
1100
1101 impl<U: ?Sized> std::convert::AsRef<U> for LocalInternedString
1102 where
1103     str: std::convert::AsRef<U>
1104 {
1105     #[inline]
1106     fn as_ref(&self) -> &U {
1107         self.string.as_ref()
1108     }
1109 }
1110
1111 impl<T: std::ops::Deref<Target = str>> std::cmp::PartialEq<T> for LocalInternedString {
1112     fn eq(&self, other: &T) -> bool {
1113         self.string == other.deref()
1114     }
1115 }
1116
1117 impl !Send for LocalInternedString {}
1118 impl !Sync for LocalInternedString {}
1119
1120 impl std::ops::Deref for LocalInternedString {
1121     type Target = str;
1122     #[inline]
1123     fn deref(&self) -> &str { self.string }
1124 }
1125
1126 impl fmt::Debug for LocalInternedString {
1127     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1128         fmt::Debug::fmt(self.string, f)
1129     }
1130 }
1131
1132 impl fmt::Display for LocalInternedString {
1133     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1134         fmt::Display::fmt(self.string, f)
1135     }
1136 }