src/librustc/middle/lang_items.rs

   1 //! Detecting language items.
   2 //!
   3 //! Language items are items that represent concepts intrinsic to the language
   4 //! itself. Examples are:
   5 //!
   6 //! * Traits that specify "kinds"; e.g., `Sync`, `Send`.
   7 //! * Traits that represent operators; e.g., `Add`, `Sub`, `Index`.
   8 //! * Functions called by the compiler itself.
   9
  10 pub use self::LangItem::*;
  11
  12 use crate::hir::def_id::DefId;
  13 use crate::hir::check_attr::Target;
  14 use crate::ty::{self, TyCtxt};
  15 use crate::middle::weak_lang_items;
  16 use crate::middle::cstore::ExternCrate;
  17 use crate::util::nodemap::FxHashMap;
  18
  19 use syntax::ast;
  20 use syntax::symbol::{Symbol, sym};
  21 use syntax_pos::Span;
  22 use rustc_macros::HashStable;
  23 use crate::hir::itemlikevisit::ItemLikeVisitor;
  24 use crate::hir;
  25
  26 // The actual lang items defined come at the end of this file in one handy table.
  27 // So you probably just want to nip down to the end.
  28 macro_rules! language_item_table {
  29     (
  30         $( $variant:ident, $name:expr, $method:ident, $target:path; )*
  31     ) => {
  32
  33 enum_from_u32! {
  34     /// A representation of all the valid language items in Rust.
  35     #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
  36     pub enum LangItem {
  37         $($variant,)*
  38     }
  39 }
  40
  41 impl LangItem {
  42     /// Returns the `name` in `#[lang = "$name"]`.
  43     /// For example, `LangItem::EqTraitLangItem`,
  44     /// that is `#[lang = "eq"]` would result in `"eq"`.
  45     fn name(self) -> &'static str {
  46         match self {
  47             $( $variant => $name, )*
  48         }
  49     }
  50 }
  51
  52 #[derive(HashStable)]
  53 pub struct LanguageItems {
  54     /// Mappings from lang items to their possibly found `DefId`s.
  55     /// The index corresponds to the order in `LangItem`.
  56     pub items: Vec<Option<DefId>>,
  57     /// Lang items that were not found during collection.
  58     pub missing: Vec<LangItem>,
  59 }
  60
  61 impl LanguageItems {
  62     /// Construct an empty collection of lang items and no missing ones.
  63     pub fn new() -> Self {
  64         fn init_none(_: LangItem) -> Option<DefId> { None }
  65
  66         Self {
  67             items: vec![$(init_none($variant)),*],
  68             missing: Vec::new(),
  69         }
  70     }
  71
  72     /// Returns the mappings to the possibly found `DefId`s for each lang item.
  73     pub fn items(&self) -> &[Option<DefId>] {
  74         &*self.items
  75     }
  76
  77     /// Requires that a given `LangItem` was bound and returns the corresponding `DefId`.
  78     /// If it wasn't bound, e.g. due to a missing `#[lang = "<it.name()>"]`,
  79     /// returns an error message as a string.
  80     pub fn require(&self, it: LangItem) -> Result<DefId, String> {
  81         self.items[it as usize].ok_or_else(|| format!("requires `{}` lang_item", it.name()))
  82     }
  83
  84     /// Returns the kind of closure that `id`, which is one of the `Fn*` traits, corresponds to.
  85     /// If `id` is not one of the `Fn*` traits, `None` is returned.
  86     pub fn fn_trait_kind(&self, id: DefId) -> Option<ty::ClosureKind> {
  87         match Some(id) {
  88             x if x == self.fn_trait() => Some(ty::ClosureKind::Fn),
  89             x if x == self.fn_mut_trait() => Some(ty::ClosureKind::FnMut),
  90             x if x == self.fn_once_trait() => Some(ty::ClosureKind::FnOnce),
  91             _ => None
  92         }
  93     }
  94
  95     $(
  96         /// Returns the corresponding `DefId` for the lang item
  97         #[doc = $name]
  98         /// if it exists.
  99         #[allow(dead_code)]
 100         pub fn $method(&self) -> Option<DefId> {
 101             self.items[$variant as usize]
 102         }
 103     )*
 104 }
 105
 106 struct LanguageItemCollector<'tcx> {
 107     items: LanguageItems,
 108     tcx: TyCtxt<'tcx>,
 109     /// A mapping from the name of the lang item to its order and the form it must be of.
 110     item_refs: FxHashMap<&'static str, (usize, Target)>,
 111 }
 112
 113 impl ItemLikeVisitor<'v> for LanguageItemCollector<'tcx> {
 114     fn visit_item(&mut self, item: &hir::Item) {
 115         if let Some((value, span)) = extract(&item.attrs) {
 116             let actual_target = Target::from_item(item);
 117             match self.item_refs.get(&*value.as_str()).cloned() {
 118                 // Known lang item with attribute on correct target.
 119                 Some((item_index, expected_target)) if actual_target == expected_target => {
 120                     let def_id = self.tcx.hir().local_def_id(item.hir_id);
 121                     self.collect_item(item_index, def_id);
 122                 },
 123                 // Known lang item with attribute on incorrect target.
 124                 Some((_, expected_target)) => {
 125                     struct_span_err!(
 126                         self.tcx.sess, span, E0718,
 127                         "`{}` language item must be applied to a {}",
 128                         value, expected_target,
 129                     ).span_label(
 130                         span,
 131                         format!(
 132                             "attribute should be applied to a {}, not a {}",
 133                             expected_target, actual_target,
 134                         ),
 135                     ).emit();
 136                 },
 137                 // Unknown lang item.
 138                 _ => {
 139                     struct_span_err!(
 140                         self.tcx.sess, span, E0522,
 141                         "definition of an unknown language item: `{}`",
 142                         value
 143                     ).span_label(
 144                         span,
 145                         format!("definition of unknown language item `{}`", value)
 146                     ).emit();
 147                 },
 148             }
 149         }
 150     }
 151
 152     fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem) {
 153         // At present, lang items are always items, not trait items.
 154     }
 155
 156     fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem) {
 157         // At present, lang items are always items, not impl items.
 158     }
 159 }
 160
 161 impl LanguageItemCollector<'tcx> {
 162     fn new(tcx: TyCtxt<'tcx>) -> LanguageItemCollector<'tcx> {
 163         let mut item_refs = FxHashMap::default();
 164
 165         $( item_refs.insert($name, ($variant as usize, $target)); )*
 166
 167         LanguageItemCollector {
 168             tcx,
 169             items: LanguageItems::new(),
 170             item_refs,
 171         }
 172     }
 173
 174     fn collect_item(&mut self, item_index: usize, item_def_id: DefId) {
 175         // Check for duplicates.
 176         if let Some(original_def_id) = self.items.items[item_index] {
 177             if original_def_id != item_def_id {
 178                 let name = LangItem::from_u32(item_index as u32).unwrap().name();
 179                 let mut err = match self.tcx.hir().span_if_local(item_def_id) {
 180                     Some(span) => struct_span_err!(
 181                         self.tcx.sess,
 182                         span,
 183                         E0152,
 184                         "duplicate lang item found: `{}`.",
 185                         name),
 186                     None => {
 187                         match self.tcx.extern_crate(item_def_id) {
 188                             Some(ExternCrate {dependency_of, ..}) => {
 189                                 self.tcx.sess.struct_err(&format!(
 190                                 "duplicate lang item in crate `{}` (which `{}` depends on): `{}`.",
 191                                 self.tcx.crate_name(item_def_id.krate),
 192                                 self.tcx.crate_name(*dependency_of),
 193                                 name))
 194                             },
 195                             _ => {
 196                                 self.tcx.sess.struct_err(&format!(
 197                                 "duplicate lang item in crate `{}`: `{}`.",
 198                                 self.tcx.crate_name(item_def_id.krate),
 199                                 name))
 200                             }
 201                         }
 202                     },
 203                 };
 204                 if let Some(span) = self.tcx.hir().span_if_local(original_def_id) {
 205                     span_note!(&mut err, span, "first defined here.");
 206                 } else {
 207                     match self.tcx.extern_crate(original_def_id) {
 208                         Some(ExternCrate {dependency_of, ..}) => {
 209                             err.note(&format!(
 210                             "first defined in crate `{}` (which `{}` depends on).",
 211                                       self.tcx.crate_name(original_def_id.krate),
 212                                       self.tcx.crate_name(*dependency_of)));
 213                         },
 214                         _ => {
 215                             err.note(&format!("first defined in crate `{}`.",
 216                                       self.tcx.crate_name(original_def_id.krate)));
 217                         }
 218                     }
 219                 }
 220                 err.emit();
 221             }
 222         }
 223
 224         // Matched.
 225         self.items.items[item_index] = Some(item_def_id);
 226     }
 227 }
 228
 229 /// Extracts the first `lang = "$name"` out of a list of attributes.
 230 /// The attributes `#[panic_handler]` and `#[alloc_error_handler]`
 231 /// are also extracted out when found.
 232 pub fn extract(attrs: &[ast::Attribute]) -> Option<(Symbol, Span)> {
 233     attrs.iter().find_map(|attr| Some(match attr {
 234         _ if attr.check_name(sym::lang) => (attr.value_str()?, attr.span),
 235         _ if attr.check_name(sym::panic_handler) => (sym::panic_impl, attr.span),
 236         _ if attr.check_name(sym::alloc_error_handler) => (sym::oom, attr.span),
 237         _ => return None,
 238     }))
 239 }
 240
 241 /// Traverses and collects all the lang items in all crates.
 242 pub fn collect<'tcx>(tcx: TyCtxt<'tcx>) -> LanguageItems {
 243     // Initialize the collector.
 244     let mut collector = LanguageItemCollector::new(tcx);
 245
 246     // Collect lang items in other crates.
 247     for &cnum in tcx.crates().iter() {
 248         for &(def_id, item_index) in tcx.defined_lang_items(cnum).iter() {
 249             collector.collect_item(item_index, def_id);
 250         }
 251     }
 252
 253     // Collect lang items in this crate.
 254     tcx.hir().krate().visit_all_item_likes(&mut collector);
 255
 256     // Extract out the found lang items.
 257     let LanguageItemCollector { mut items, .. } = collector;
 258
 259     // Find all required but not-yet-defined lang items.
 260     weak_lang_items::check_crate(tcx, &mut items);
 261
 262     items
 263 }
 264
 265 // End of the macro
 266     }
 267 }
 268
 269 language_item_table! {
 270 //  Variant name,                Name,                 Method name,             Target;
 271     BoolImplItem,                "bool",               bool_impl,               Target::Impl;
 272     CharImplItem,                "char",               char_impl,               Target::Impl;
 273     StrImplItem,                 "str",                str_impl,                Target::Impl;
 274     SliceImplItem,               "slice",              slice_impl,              Target::Impl;
 275     SliceU8ImplItem,             "slice_u8",           slice_u8_impl,           Target::Impl;
 276     StrAllocImplItem,            "str_alloc",          str_alloc_impl,          Target::Impl;
 277     SliceAllocImplItem,          "slice_alloc",        slice_alloc_impl,        Target::Impl;
 278     SliceU8AllocImplItem,        "slice_u8_alloc",     slice_u8_alloc_impl,     Target::Impl;
 279     ConstPtrImplItem,            "const_ptr",          const_ptr_impl,          Target::Impl;
 280     MutPtrImplItem,              "mut_ptr",            mut_ptr_impl,            Target::Impl;
 281     I8ImplItem,                  "i8",                 i8_impl,                 Target::Impl;
 282     I16ImplItem,                 "i16",                i16_impl,                Target::Impl;
 283     I32ImplItem,                 "i32",                i32_impl,                Target::Impl;
 284     I64ImplItem,                 "i64",                i64_impl,                Target::Impl;
 285     I128ImplItem,                "i128",               i128_impl,               Target::Impl;
 286     IsizeImplItem,               "isize",              isize_impl,              Target::Impl;
 287     U8ImplItem,                  "u8",                 u8_impl,                 Target::Impl;
 288     U16ImplItem,                 "u16",                u16_impl,                Target::Impl;
 289     U32ImplItem,                 "u32",                u32_impl,                Target::Impl;
 290     U64ImplItem,                 "u64",                u64_impl,                Target::Impl;
 291     U128ImplItem,                "u128",               u128_impl,               Target::Impl;
 292     UsizeImplItem,               "usize",              usize_impl,              Target::Impl;
 293     F32ImplItem,                 "f32",                f32_impl,                Target::Impl;
 294     F64ImplItem,                 "f64",                f64_impl,                Target::Impl;
 295     F32RuntimeImplItem,          "f32_runtime",        f32_runtime_impl,        Target::Impl;
 296     F64RuntimeImplItem,          "f64_runtime",        f64_runtime_impl,        Target::Impl;
 297
 298     SizedTraitLangItem,          "sized",              sized_trait,             Target::Trait;
 299     UnsizeTraitLangItem,         "unsize",             unsize_trait,            Target::Trait;
 300     // trait injected by #[derive(PartialEq)], (i.e. "Partial EQ").
 301     StructuralPeqTraitLangItem,  "structural_peq",     structural_peq_trait,    Target::Trait;
 302     // trait injected by #[derive(Eq)], (i.e. "Total EQ"; no, I will not apologize).
 303     StructuralTeqTraitLangItem,  "structural_teq",     structural_teq_trait,    Target::Trait;
 304     CopyTraitLangItem,           "copy",               copy_trait,              Target::Trait;
 305     CloneTraitLangItem,          "clone",              clone_trait,             Target::Trait;
 306     SyncTraitLangItem,           "sync",               sync_trait,              Target::Trait;
 307     FreezeTraitLangItem,         "freeze",             freeze_trait,            Target::Trait;
 308
 309     DropTraitLangItem,           "drop",               drop_trait,              Target::Trait;
 310
 311     CoerceUnsizedTraitLangItem,  "coerce_unsized",     coerce_unsized_trait,    Target::Trait;
 312     DispatchFromDynTraitLangItem,"dispatch_from_dyn",  dispatch_from_dyn_trait, Target::Trait;
 313
 314     AddTraitLangItem,            "add",                add_trait,               Target::Trait;
 315     SubTraitLangItem,            "sub",                sub_trait,               Target::Trait;
 316     MulTraitLangItem,            "mul",                mul_trait,               Target::Trait;
 317     DivTraitLangItem,            "div",                div_trait,               Target::Trait;
 318     RemTraitLangItem,            "rem",                rem_trait,               Target::Trait;
 319     NegTraitLangItem,            "neg",                neg_trait,               Target::Trait;
 320     NotTraitLangItem,            "not",                not_trait,               Target::Trait;
 321     BitXorTraitLangItem,         "bitxor",             bitxor_trait,            Target::Trait;
 322     BitAndTraitLangItem,         "bitand",             bitand_trait,            Target::Trait;
 323     BitOrTraitLangItem,          "bitor",              bitor_trait,             Target::Trait;
 324     ShlTraitLangItem,            "shl",                shl_trait,               Target::Trait;
 325     ShrTraitLangItem,            "shr",                shr_trait,               Target::Trait;
 326     AddAssignTraitLangItem,      "add_assign",         add_assign_trait,        Target::Trait;
 327     SubAssignTraitLangItem,      "sub_assign",         sub_assign_trait,        Target::Trait;
 328     MulAssignTraitLangItem,      "mul_assign",         mul_assign_trait,        Target::Trait;
 329     DivAssignTraitLangItem,      "div_assign",         div_assign_trait,        Target::Trait;
 330     RemAssignTraitLangItem,      "rem_assign",         rem_assign_trait,        Target::Trait;
 331     BitXorAssignTraitLangItem,   "bitxor_assign",      bitxor_assign_trait,     Target::Trait;
 332     BitAndAssignTraitLangItem,   "bitand_assign",      bitand_assign_trait,     Target::Trait;
 333     BitOrAssignTraitLangItem,    "bitor_assign",       bitor_assign_trait,      Target::Trait;
 334     ShlAssignTraitLangItem,      "shl_assign",         shl_assign_trait,        Target::Trait;
 335     ShrAssignTraitLangItem,      "shr_assign",         shr_assign_trait,        Target::Trait;
 336     IndexTraitLangItem,          "index",              index_trait,             Target::Trait;
 337     IndexMutTraitLangItem,       "index_mut",          index_mut_trait,         Target::Trait;
 338
 339     UnsafeCellTypeLangItem,      "unsafe_cell",        unsafe_cell_type,        Target::Struct;
 340     VaListTypeLangItem,          "va_list",            va_list,                 Target::Struct;
 341
 342     DerefTraitLangItem,          "deref",              deref_trait,             Target::Trait;
 343     DerefMutTraitLangItem,       "deref_mut",          deref_mut_trait,         Target::Trait;
 344     ReceiverTraitLangItem,       "receiver",           receiver_trait,          Target::Trait;
 345
 346     FnTraitLangItem,             "fn",                 fn_trait,                Target::Trait;
 347     FnMutTraitLangItem,          "fn_mut",             fn_mut_trait,            Target::Trait;
 348     FnOnceTraitLangItem,         "fn_once",            fn_once_trait,           Target::Trait;
 349
 350     FutureTraitLangItem,         "future_trait",       future_trait,            Target::Trait;
 351     GeneratorStateLangItem,      "generator_state",    gen_state,               Target::Enum;
 352     GeneratorTraitLangItem,      "generator",          gen_trait,               Target::Trait;
 353     UnpinTraitLangItem,          "unpin",              unpin_trait,             Target::Trait;
 354     PinTypeLangItem,             "pin",                pin_type,                Target::Struct;
 355
 356     // Don't be fooled by the naming here: this lang item denotes `PartialEq`, not `Eq`.
 357     EqTraitLangItem,             "eq",                 eq_trait,                Target::Trait;
 358     PartialOrdTraitLangItem,     "partial_ord",        partial_ord_trait,       Target::Trait;
 359     OrdTraitLangItem,            "ord",                ord_trait,               Target::Trait;
 360
 361     // A number of panic-related lang items. The `panic` item corresponds to
 362     // divide-by-zero and various panic cases with `match`. The
 363     // `panic_bounds_check` item is for indexing arrays.
 364     //
 365     // The `begin_unwind` lang item has a predefined symbol name and is sort of
 366     // a "weak lang item" in the sense that a crate is not required to have it
 367     // defined to use it, but a final product is required to define it
 368     // somewhere. Additionally, there are restrictions on crates that use a weak
 369     // lang item, but do not have it defined.
 370     PanicFnLangItem,             "panic",              panic_fn,                Target::Fn;
 371     PanicBoundsCheckFnLangItem,  "panic_bounds_check", panic_bounds_check_fn,   Target::Fn;
 372     PanicInfoLangItem,           "panic_info",         panic_info,              Target::Struct;
 373     PanicLocationLangItem,       "panic_location",     panic_location,          Target::Struct;
 374     PanicImplLangItem,           "panic_impl",         panic_impl,              Target::Fn;
 375     // Libstd panic entry point. Necessary for const eval to be able to catch it
 376     BeginPanicFnLangItem,        "begin_panic",        begin_panic_fn,          Target::Fn;
 377
 378     ExchangeMallocFnLangItem,    "exchange_malloc",    exchange_malloc_fn,      Target::Fn;
 379     BoxFreeFnLangItem,           "box_free",           box_free_fn,             Target::Fn;
 380     DropInPlaceFnLangItem,       "drop_in_place",      drop_in_place_fn,        Target::Fn;
 381     OomLangItem,                 "oom",                oom,                     Target::Fn;
 382     AllocLayoutLangItem,         "alloc_layout",       alloc_layout,            Target::Struct;
 383
 384     StartFnLangItem,             "start",              start_fn,                Target::Fn;
 385
 386     EhPersonalityLangItem,       "eh_personality",     eh_personality,          Target::Fn;
 387     EhUnwindResumeLangItem,      "eh_unwind_resume",   eh_unwind_resume,        Target::Fn;
 388     EhCatchTypeinfoLangItem,     "eh_catch_typeinfo",  eh_catch_typeinfo,       Target::Static;
 389
 390     OwnedBoxLangItem,            "owned_box",          owned_box,               Target::Struct;
 391
 392     PhantomDataItem,             "phantom_data",       phantom_data,            Target::Struct;
 393
 394     ManuallyDropItem,            "manually_drop",      manually_drop,           Target::Struct;
 395
 396     MaybeUninitLangItem,         "maybe_uninit",       maybe_uninit,            Target::Union;
 397
 398     // Align offset for stride != 1; must not panic.
 399     AlignOffsetLangItem,         "align_offset",       align_offset_fn,         Target::Fn;
 400
 401     TerminationTraitLangItem,    "termination",        termination,             Target::Trait;
 402
 403     Arc,                         "arc",                arc,                     Target::Struct;
 404     Rc,                          "rc",                 rc,                      Target::Struct;
 405 }
 406
 407 impl<'tcx> TyCtxt<'tcx> {
 408     /// Returns the `DefId` for a given `LangItem`.
 409     /// If not found, fatally aborts compilation.
 410     pub fn require_lang_item(&self, lang_item: LangItem, span: Option<Span>) -> DefId {
 411         self.lang_items().require(lang_item).unwrap_or_else(|msg| {
 412             if let Some(span) = span {
 413                 self.sess.span_fatal(span, &msg)
 414             } else {
 415                 self.sess.fatal(&msg)
 416             }
 417         })
 418     }
 419 }