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.
5 use rustc_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};
12 use std::cmp::{Ord, PartialEq, PartialOrd};
14 use std::hash::{Hash, Hasher};
17 use crate::{Span, DUMMY_SP, SESSION_GLOBALS};
22 // The proc macro code for this is in `src/librustc_macros/src/symbols.rs`.
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.
27 // Special reserved identifiers used internally for elided lifetimes,
28 // unnamed method parameters, crate root module, error recovery etc.
31 DollarCrate: "$crate",
34 // Keywords that are used in stable Rust.
71 // Keywords that are used in unstable Rust or reserved for future use.
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
90 // Edition-specific keywords that are used in unstable Rust or reserved for future use.
91 Try: "try", // >= 2018 Edition only
93 // Special lifetime names
94 UnderscoreLifetime: "'_",
95 StaticLifetime: "'static",
97 // Weak keywords, have special meaning only in specific contexts.
101 MacroRules: "macro_rules",
106 // Pre-interned symbols that can be referred to with `rustc_span::sym::*`.
108 // The symbol is the stringified identifier unless otherwise specified, in
109 // which case the name should mention the non-identifier punctuation.
110 // E.g. `sym::proc_dash_macro` represents "proc-macro", and it shouldn't be
111 // called `sym::proc_macro` because then it's easy to mistakenly think it
112 // represents "proc_macro".
114 // As well as the symbols listed, there are symbols for the the strings
115 // "0", "1", ..., "9", which are accessible via `sym::integer`.
117 // The proc macro will abort if symbols are not in alphabetical order (as
118 // defined by `impl Ord for str`) or if any symbols are duplicated. Vim
119 // users can sort the list by selecting it and executing the command
120 // `:'<,'>!LC_ALL=C sort`.
122 // There is currently no checking that all symbols are used; that would be
179 ProceduralMasqueradeDummyType,
216 aarch64_target_feature,
221 abi_msp430_interrupt,
234 advanced_slice_patterns,
249 allow_internal_unsafe,
250 allow_internal_unstable,
251 allow_internal_unstable_backcompat_hack,
257 arbitrary_enum_discriminant,
258 arbitrary_self_types,
266 assert_receiver_is_total_eq,
270 associated_type_bounds,
271 associated_type_defaults,
282 augmented_assignments,
283 automatically_derived,
284 avx512_target_feature,
290 bind_by_move_pattern_guards,
301 borrowck_graphviz_format,
302 borrowck_graphviz_postflow,
303 borrowck_graphviz_preflow,
307 braced_empty_structs,
326 cfg_target_has_atomic,
327 cfg_target_thread_local,
336 closure_to_fn_coercion,
338 cmpxchg16b_target_feature,
346 conservative_impl_trait,
348 const_compare_raw_pointers,
357 const_in_array_repeat_expressions,
363 const_precise_live_drops,
366 const_raw_ptr_to_usize_cast,
368 const_trait_bound_opt_out,
384 coverage_counter_add,
385 coverage_counter_subtract,
386 coverage_unreachable,
392 crate_visibility_modifier,
393 crt_dash_static: "crt-static",
401 custom_inner_attributes,
402 custom_test_frameworks,
415 default_lib_allocator,
416 default_type_parameter_fallback,
418 delay_span_bug_from_inside_query,
439 document_private_items,
440 dotdot_in_tuple_patterns,
441 dotdoteq_in_patterns,
442 double_braced_closure: "{{closure}}",
443 double_braced_constant: "{{constant}}",
444 double_braced_constructor: "{{constructor}}",
445 double_braced_crate: "{{crate}}",
446 double_braced_impl: "{{impl}}",
447 double_braced_misc: "{{misc}}",
448 double_braced_opaque: "{{opaque}}",
453 dropck_parametricity,
460 emit_enum_variant_arg,
472 exclusive_range_pattern,
473 exhaustive_integer_patterns,
483 extern_absolute_paths,
484 extern_crate_item_prelude,
505 field_init_shorthand,
510 float_to_int_unchecked,
536 from_size_align_unchecked,
549 generic_associated_types,
556 half_open_range_patterns,
558 hexagon_target_feature,
560 homogeneous_aggregate,
575 if_while_or_patterns,
577 impl_header_lifetime_elision,
579 impl_trait_in_bindings,
585 inclusive_range_syntax,
588 infer_outlives_requirements,
589 infer_static_outlives_requirements,
597 irrefutable_let_patterns,
600 issue_5723_bootstrap,
601 issue_tracker_base_url,
612 lazy_normalization_consts,
624 link_llvm_intrinsics,
642 macro_at_most_once_rep,
645 macro_lifetime_matcher,
646 macro_literal_matcher,
658 match_beginning_vert,
659 match_default_bindings,
684 movbe_target_feature,
733 nontrapping_dash_fptoint: "nontrapping-fptoint",
738 object_safe_for_dispatch,
740 omit_gdb_pretty_printer_section,
749 optin_builtin_traits,
758 overlapping_marker_traits,
766 panic_implementation,
789 post_dash_lto: "post-lto",
790 powerpc_target_feature,
795 pre_dash_lto: "pre-lto",
796 precise_pointer_size_matching,
800 prefetch_read_instruction,
802 prefetch_write_instruction,
807 proc_dash_macro: "proc-macro",
809 proc_macro_attribute,
815 proc_macro_internals,
817 proc_macro_non_items,
818 proc_macro_path_invoc,
827 quad_precision_float,
833 re_rebalance_coherence,
836 read_enum_variant_arg,
844 reexport_test_harness_main,
865 riscv_target_feature,
878 rust_eh_register_frames,
879 rust_eh_unregister_frames,
883 rustc_allocator_nounwind,
884 rustc_allow_const_fn_ptr,
885 rustc_args_required_const,
890 rustc_const_unstable,
891 rustc_conversion_suggestion,
894 rustc_diagnostic_item,
895 rustc_diagnostic_macros,
898 rustc_dump_env_program_clauses,
899 rustc_dump_program_clauses,
900 rustc_dump_user_substs,
902 rustc_expected_cgu_reuse,
903 rustc_if_this_changed,
904 rustc_inherit_overflow_checks,
906 rustc_layout_scalar_valid_range_end,
907 rustc_layout_scalar_valid_range_start,
908 rustc_macro_transparency,
910 rustc_nonnull_optimization_guaranteed,
911 rustc_object_lifetime_default,
912 rustc_on_unimplemented,
915 rustc_partition_codegened,
916 rustc_partition_reused,
918 rustc_peek_definite_init,
919 rustc_peek_indirectly_mutable,
921 rustc_peek_maybe_init,
922 rustc_peek_maybe_uninit,
923 rustc_polymorphize_error,
925 rustc_proc_macro_decls,
928 rustc_reservation_impl,
930 rustc_specialization_trait,
932 rustc_std_internal_symbol,
936 rustc_then_this_would_need,
937 rustc_unsafe_specialization_marker,
940 rvalue_static_promotion,
988 simd_reduce_add_ordered,
989 simd_reduce_add_unordered,
994 simd_reduce_max_nanless,
996 simd_reduce_min_nanless,
997 simd_reduce_mul_ordered,
998 simd_reduce_mul_unordered,
1002 simd_saturating_add,
1003 simd_saturating_sub,
1006 simd_select_bitmask,
1030 sse4a_target_feature,
1042 stmt_expr_attributes,
1043 stop_after_dataflow,
1048 struct_field_attributes,
1069 target_has_atomic_load_store,
1071 target_pointer_width,
1072 target_target_vendor,
1073 target_thread_local,
1079 termination_trait_test,
1082 test_accepted_feature,
1084 test_removed_feature,
1108 type_alias_enum_variants,
1109 type_alias_impl_trait,
1120 unaligned_volatile_load,
1121 unaligned_volatile_store,
1130 underscore_const_names,
1132 underscore_lifetimes,
1135 universal_impl_trait,
1142 unrestricted_attribute_tokens,
1143 unsafe_block_in_unsafe_fn,
1145 unsafe_no_drop_flag,
1148 unsized_tuple_coercion,
1151 unused_qualifications,
1172 visible_private_types,
1174 volatile_copy_memory,
1175 volatile_copy_nonoverlapping_memory,
1177 volatile_set_memory,
1181 wasm_target_feature,
1193 #[derive(Copy, Clone, Eq, HashStable_Generic)]
1201 /// Constructs a new identifier from a symbol and a span.
1202 pub const fn new(name: Symbol, span: Span) -> Ident {
1203 Ident { name, span }
1206 /// Constructs a new identifier with a dummy span.
1208 pub const fn with_dummy_span(name: Symbol) -> Ident {
1209 Ident::new(name, DUMMY_SP)
1213 pub fn invalid() -> Ident {
1214 Ident::with_dummy_span(kw::Invalid)
1217 /// Maps a string to an identifier with a dummy span.
1218 pub fn from_str(string: &str) -> Ident {
1219 Ident::with_dummy_span(Symbol::intern(string))
1222 /// Maps a string and a span to an identifier.
1223 pub fn from_str_and_span(string: &str, span: Span) -> Ident {
1224 Ident::new(Symbol::intern(string), span)
1227 /// Replaces `lo` and `hi` with those from `span`, but keep hygiene context.
1228 pub fn with_span_pos(self, span: Span) -> Ident {
1229 Ident::new(self.name, span.with_ctxt(self.span.ctxt()))
1232 pub fn without_first_quote(self) -> Ident {
1233 Ident::new(Symbol::intern(self.as_str().trim_start_matches('\'')), self.span)
1236 /// "Normalize" ident for use in comparisons using "item hygiene".
1237 /// Identifiers with same string value become same if they came from the same macro 2.0 macro
1238 /// (e.g., `macro` item, but not `macro_rules` item) and stay different if they came from
1239 /// different macro 2.0 macros.
1240 /// Technically, this operation strips all non-opaque marks from ident's syntactic context.
1241 pub fn normalize_to_macros_2_0(self) -> Ident {
1242 Ident::new(self.name, self.span.normalize_to_macros_2_0())
1245 /// "Normalize" ident for use in comparisons using "local variable hygiene".
1246 /// Identifiers with same string value become same if they came from the same non-transparent
1247 /// macro (e.g., `macro` or `macro_rules!` items) and stay different if they came from different
1248 /// non-transparent macros.
1249 /// Technically, this operation strips all transparent marks from ident's syntactic context.
1250 pub fn normalize_to_macro_rules(self) -> Ident {
1251 Ident::new(self.name, self.span.normalize_to_macro_rules())
1254 /// Convert the name to a `SymbolStr`. This is a slowish operation because
1255 /// it requires locking the symbol interner.
1256 pub fn as_str(self) -> SymbolStr {
1261 impl PartialEq for Ident {
1262 fn eq(&self, rhs: &Self) -> bool {
1263 self.name == rhs.name && self.span.ctxt() == rhs.span.ctxt()
1267 impl Hash for Ident {
1268 fn hash<H: Hasher>(&self, state: &mut H) {
1269 self.name.hash(state);
1270 self.span.ctxt().hash(state);
1274 impl fmt::Debug for Ident {
1275 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1276 fmt::Display::fmt(self, f)?;
1277 fmt::Debug::fmt(&self.span.ctxt(), f)
1281 /// This implementation is supposed to be used in error messages, so it's expected to be identical
1282 /// to printing the original identifier token written in source code (`token_to_string`),
1283 /// except that AST identifiers don't keep the rawness flag, so we have to guess it.
1284 impl fmt::Display for Ident {
1285 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1286 fmt::Display::fmt(&IdentPrinter::new(self.name, self.is_raw_guess(), None), f)
1290 impl UseSpecializedEncodable for Ident {
1291 fn default_encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
1292 s.emit_struct("Ident", 2, |s| {
1293 s.emit_struct_field("name", 0, |s| self.name.encode(s))?;
1294 s.emit_struct_field("span", 1, |s| self.span.encode(s))
1299 impl UseSpecializedDecodable for Ident {
1300 fn default_decode<D: Decoder>(d: &mut D) -> Result<Self, D::Error> {
1301 d.read_struct("Ident", 2, |d| {
1303 name: d.read_struct_field("name", 0, Decodable::decode)?,
1304 span: d.read_struct_field("span", 1, Decodable::decode)?,
1310 /// This is the most general way to print identifiers.
1311 /// AST pretty-printer is used as a fallback for turning AST structures into token streams for
1312 /// proc macros. Additionally, proc macros may stringify their input and expect it survive the
1313 /// stringification (especially true for proc macro derives written between Rust 1.15 and 1.30).
1314 /// So we need to somehow pretty-print `$crate` in a way preserving at least some of its
1315 /// hygiene data, most importantly name of the crate it refers to.
1316 /// As a result we print `$crate` as `crate` if it refers to the local crate
1317 /// and as `::other_crate_name` if it refers to some other crate.
1318 /// Note, that this is only done if the ident token is printed from inside of AST pretty-pringing,
1319 /// but not otherwise. Pretty-printing is the only way for proc macros to discover token contents,
1320 /// so we should not perform this lossy conversion if the top level call to the pretty-printer was
1321 /// done for a token stream or a single token.
1322 pub struct IdentPrinter {
1325 /// Span used for retrieving the crate name to which `$crate` refers to,
1326 /// if this field is `None` then the `$crate` conversion doesn't happen.
1327 convert_dollar_crate: Option<Span>,
1331 /// The most general `IdentPrinter` constructor. Do not use this.
1332 pub fn new(symbol: Symbol, is_raw: bool, convert_dollar_crate: Option<Span>) -> IdentPrinter {
1333 IdentPrinter { symbol, is_raw, convert_dollar_crate }
1336 /// This implementation is supposed to be used when printing identifiers
1337 /// as a part of pretty-printing for larger AST pieces.
1338 /// Do not use this either.
1339 pub fn for_ast_ident(ident: Ident, is_raw: bool) -> IdentPrinter {
1340 IdentPrinter::new(ident.name, is_raw, Some(ident.span))
1344 impl fmt::Display for IdentPrinter {
1345 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1349 if self.symbol == kw::DollarCrate {
1350 if let Some(span) = self.convert_dollar_crate {
1351 let converted = span.ctxt().dollar_crate_name();
1352 if !converted.is_path_segment_keyword() {
1355 return fmt::Display::fmt(&converted, f);
1359 fmt::Display::fmt(&self.symbol, f)
1363 /// An newtype around `Ident` that calls [Ident::normalize_to_macro_rules] on
1365 // FIXME(matthewj, petrochenkov) Use this more often, add a similar
1366 // `ModernIdent` struct and use that as well.
1367 #[derive(Copy, Clone, Eq, PartialEq, Hash)]
1368 pub struct MacroRulesNormalizedIdent(Ident);
1370 impl MacroRulesNormalizedIdent {
1371 pub fn new(ident: Ident) -> Self {
1372 Self(ident.normalize_to_macro_rules())
1376 impl fmt::Debug for MacroRulesNormalizedIdent {
1377 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1378 fmt::Debug::fmt(&self.0, f)
1382 impl fmt::Display for MacroRulesNormalizedIdent {
1383 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1384 fmt::Display::fmt(&self.0, f)
1388 /// An interned string.
1390 /// Internally, a `Symbol` is implemented as an index, and all operations
1391 /// (including hashing, equality, and ordering) operate on that index. The use
1392 /// of `rustc_index::newtype_index!` means that `Option<Symbol>` only takes up 4 bytes,
1393 /// because `rustc_index::newtype_index!` reserves the last 256 values for tagging purposes.
1395 /// Note that `Symbol` cannot directly be a `rustc_index::newtype_index!` because it
1396 /// implements `fmt::Debug`, `Encodable`, and `Decodable` in special ways.
1397 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
1398 pub struct Symbol(SymbolIndex);
1400 rustc_index::newtype_index! {
1401 pub struct SymbolIndex { .. }
1405 const fn new(n: u32) -> Self {
1406 Symbol(SymbolIndex::from_u32(n))
1409 /// Maps a string to its interned representation.
1410 pub fn intern(string: &str) -> Self {
1411 with_interner(|interner| interner.intern(string))
1414 /// Access the symbol's chars. This is a slowish operation because it
1415 /// requires locking the symbol interner.
1416 pub fn with<F: FnOnce(&str) -> R, R>(self, f: F) -> R {
1417 with_interner(|interner| f(interner.get(self)))
1420 /// Convert to a `SymbolStr`. This is a slowish operation because it
1421 /// requires locking the symbol interner.
1422 pub fn as_str(self) -> SymbolStr {
1423 with_interner(|interner| unsafe {
1424 SymbolStr { string: std::mem::transmute::<&str, &str>(interner.get(self)) }
1428 pub fn as_u32(self) -> u32 {
1432 /// This method is supposed to be used in error messages, so it's expected to be
1433 /// identical to printing the original identifier token written in source code
1434 /// (`token_to_string`, `Ident::to_string`), except that symbols don't keep the rawness flag
1435 /// or edition, so we have to guess the rawness using the global edition.
1436 pub fn to_ident_string(self) -> String {
1437 Ident::with_dummy_span(self).to_string()
1441 impl fmt::Debug for Symbol {
1442 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1443 self.with(|str| fmt::Debug::fmt(&str, f))
1447 impl fmt::Display for Symbol {
1448 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1449 self.with(|str| fmt::Display::fmt(&str, f))
1453 impl Encodable for Symbol {
1454 fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
1455 self.with(|string| s.emit_str(string))
1459 impl Decodable for Symbol {
1461 fn decode<D: Decoder>(d: &mut D) -> Result<Symbol, D::Error> {
1462 Ok(Symbol::intern(&d.read_str()?))
1466 impl<CTX> HashStable<CTX> for Symbol {
1468 fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
1469 self.as_str().hash_stable(hcx, hasher);
1473 impl<CTX> ToStableHashKey<CTX> for Symbol {
1474 type KeyType = SymbolStr;
1477 fn to_stable_hash_key(&self, _: &CTX) -> SymbolStr {
1482 // The `&'static str`s in this type actually point into the arena.
1484 pub struct Interner {
1485 arena: DroplessArena,
1486 names: FxHashMap<&'static str, Symbol>,
1487 strings: Vec<&'static str>,
1491 fn prefill(init: &[&'static str]) -> Self {
1493 strings: init.into(),
1494 names: init.iter().copied().zip((0..).map(Symbol::new)).collect(),
1495 ..Default::default()
1500 pub fn intern(&mut self, string: &str) -> Symbol {
1501 if let Some(&name) = self.names.get(string) {
1505 let name = Symbol::new(self.strings.len() as u32);
1507 // `from_utf8_unchecked` is safe since we just allocated a `&str` which is known to be
1510 unsafe { str::from_utf8_unchecked(self.arena.alloc_slice(string.as_bytes())) };
1511 // It is safe to extend the arena allocation to `'static` because we only access
1512 // these while the arena is still alive.
1513 let string: &'static str = unsafe { &*(string as *const str) };
1514 self.strings.push(string);
1515 self.names.insert(string, name);
1519 // Get the symbol as a string. `Symbol::as_str()` should be used in
1520 // preference to this function.
1521 pub fn get(&self, symbol: Symbol) -> &str {
1522 self.strings[symbol.0.as_usize()]
1526 // This module has a very short name because it's used a lot.
1527 /// This module contains all the defined keyword `Symbol`s.
1529 /// Given that `kw` is imported, use them like `kw::keyword_name`.
1530 /// For example `kw::Loop` or `kw::Break`.
1536 // This module has a very short name because it's used a lot.
1537 /// This module contains all the defined non-keyword `Symbol`s.
1539 /// Given that `sym` is imported, use them like `sym::symbol_name`.
1540 /// For example `sym::rustfmt` or `sym::u8`.
1541 #[allow(rustc::default_hash_types)]
1544 use std::convert::TryInto;
1548 // Used from a macro in `librustc_feature/accepted.rs`
1549 pub use super::kw::MacroRules as macro_rules;
1551 // Get the symbol for an integer. The first few non-negative integers each
1552 // have a static symbol and therefore are fast.
1553 pub fn integer<N: TryInto<usize> + Copy + ToString>(n: N) -> Symbol {
1554 if let Result::Ok(idx) = n.try_into() {
1555 if let Option::Some(&sym_) = digits_array.get(idx) {
1559 Symbol::intern(&n.to_string())
1564 fn is_used_keyword_2018(self) -> bool {
1565 self >= kw::Async && self <= kw::Dyn
1568 fn is_unused_keyword_2018(self) -> bool {
1572 /// Used for sanity checking rustdoc keyword sections.
1573 pub fn is_doc_keyword(self) -> bool {
1577 /// A keyword or reserved identifier that can be used as a path segment.
1578 pub fn is_path_segment_keyword(self) -> bool {
1580 || self == kw::SelfLower
1581 || self == kw::SelfUpper
1582 || self == kw::Crate
1583 || self == kw::PathRoot
1584 || self == kw::DollarCrate
1587 /// Returns `true` if the symbol is `true` or `false`.
1588 pub fn is_bool_lit(self) -> bool {
1589 self == kw::True || self == kw::False
1592 /// This symbol can be a raw identifier.
1593 pub fn can_be_raw(self) -> bool {
1594 self != kw::Invalid && self != kw::Underscore && !self.is_path_segment_keyword()
1599 // Returns `true` for reserved identifiers used internally for elided lifetimes,
1600 // unnamed method parameters, crate root module, error recovery etc.
1601 pub fn is_special(self) -> bool {
1602 self.name <= kw::Underscore
1605 /// Returns `true` if the token is a keyword used in the language.
1606 pub fn is_used_keyword(self) -> bool {
1607 // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1608 self.name >= kw::As && self.name <= kw::While
1609 || self.name.is_used_keyword_2018() && self.span.rust_2018()
1612 /// Returns `true` if the token is a keyword reserved for possible future use.
1613 pub fn is_unused_keyword(self) -> bool {
1614 // Note: `span.edition()` is relatively expensive, don't call it unless necessary.
1615 self.name >= kw::Abstract && self.name <= kw::Yield
1616 || self.name.is_unused_keyword_2018() && self.span.rust_2018()
1619 /// Returns `true` if the token is either a special identifier or a keyword.
1620 pub fn is_reserved(self) -> bool {
1621 self.is_special() || self.is_used_keyword() || self.is_unused_keyword()
1624 /// A keyword or reserved identifier that can be used as a path segment.
1625 pub fn is_path_segment_keyword(self) -> bool {
1626 self.name.is_path_segment_keyword()
1629 /// We see this identifier in a normal identifier position, like variable name or a type.
1630 /// How was it written originally? Did it use the raw form? Let's try to guess.
1631 pub fn is_raw_guess(self) -> bool {
1632 self.name.can_be_raw() && self.is_reserved()
1637 fn with_interner<T, F: FnOnce(&mut Interner) -> T>(f: F) -> T {
1638 SESSION_GLOBALS.with(|session_globals| f(&mut *session_globals.symbol_interner.lock()))
1641 /// An alternative to `Symbol`, useful when the chars within the symbol need to
1642 /// be accessed. It deliberately has limited functionality and should only be
1643 /// used for temporary values.
1645 /// Because the interner outlives any thread which uses this type, we can
1646 /// safely treat `string` which points to interner data, as an immortal string,
1647 /// as long as this type never crosses between threads.
1649 // FIXME: ensure that the interner outlives any thread which uses `SymbolStr`,
1650 // by creating a new thread right after constructing the interner.
1651 #[derive(Clone, Eq, PartialOrd, Ord)]
1652 pub struct SymbolStr {
1653 string: &'static str,
1656 // This impl allows a `SymbolStr` to be directly equated with a `String` or
1658 impl<T: std::ops::Deref<Target = str>> std::cmp::PartialEq<T> for SymbolStr {
1659 fn eq(&self, other: &T) -> bool {
1660 self.string == other.deref()
1664 impl !Send for SymbolStr {}
1665 impl !Sync for SymbolStr {}
1667 /// This impl means that if `ss` is a `SymbolStr`:
1668 /// - `*ss` is a `str`;
1669 /// - `&*ss` is a `&str` (and `match &*ss { ... }` is a common pattern).
1670 /// - `&ss as &str` is a `&str`, which means that `&ss` can be passed to a
1671 /// function expecting a `&str`.
1672 impl std::ops::Deref for SymbolStr {
1675 fn deref(&self) -> &str {
1680 impl fmt::Debug for SymbolStr {
1681 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1682 fmt::Debug::fmt(self.string, f)
1686 impl fmt::Display for SymbolStr {
1687 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1688 fmt::Display::fmt(self.string, f)
1692 impl<CTX> HashStable<CTX> for SymbolStr {
1694 fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
1695 self.string.hash_stable(hcx, hasher)
1699 impl<CTX> ToStableHashKey<CTX> for SymbolStr {
1700 type KeyType = SymbolStr;
1703 fn to_stable_hash_key(&self, _: &CTX) -> SymbolStr {