compiler/rustc_hir/src/lang_items.rs

   1 //! Defines 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 use crate::def_id::DefId;
  11 use crate::{MethodKind, Target};
  12
  13 use rustc_ast as ast;
  14 use rustc_data_structures::fx::FxHashMap;
  15 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
  16 use rustc_macros::HashStable_Generic;
  17 use rustc_span::symbol::{kw, sym, Symbol};
  18 use rustc_span::Span;
  19
  20 use std::lazy::SyncLazy;
  21
  22 pub enum LangItemGroup {
  23     Op,
  24     Fn,
  25 }
  26
  27 const NUM_GROUPS: usize = 2;
  28
  29 macro_rules! expand_group {
  30     () => {
  31         None
  32     };
  33     ($group:expr) => {
  34         Some($group)
  35     };
  36 }
  37
  38 // The actual lang items defined come at the end of this file in one handy table.
  39 // So you probably just want to nip down to the end.
  40 macro_rules! language_item_table {
  41     (
  42         $( $(#[$attr:meta])* $variant:ident $($group:expr)?, $module:ident :: $name:ident, $method:ident, $target:expr, $generics:expr; )*
  43     ) => {
  44
  45         enum_from_u32! {
  46             /// A representation of all the valid language items in Rust.
  47             #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, Encodable, Decodable)]
  48             pub enum LangItem {
  49                 $(
  50                     #[doc = concat!("The `", stringify!($name), "` lang item.")]
  51                     ///
  52                     $(#[$attr])*
  53                     $variant,
  54                 )*
  55             }
  56         }
  57
  58         impl LangItem {
  59             /// Returns the `name` symbol in `#[lang = "$name"]`.
  60             /// For example, [`LangItem::PartialEq`]`.name()`
  61             /// would result in [`sym::eq`] since it is `#[lang = "eq"]`.
  62             pub fn name(self) -> Symbol {
  63                 match self {
  64                     $( LangItem::$variant => $module::$name, )*
  65                 }
  66             }
  67
  68             /// The [group](LangItemGroup) that this lang item belongs to,
  69             /// or `None` if it doesn't belong to a group.
  70             pub fn group(self) -> Option<LangItemGroup> {
  71                 use LangItemGroup::*;
  72                 match self {
  73                     $( LangItem::$variant => expand_group!($($group)*), )*
  74                 }
  75             }
  76
  77             pub fn required_generics(&self) -> GenericRequirement {
  78                 match self {
  79                     $( LangItem::$variant => $generics, )*
  80                 }
  81             }
  82         }
  83
  84         /// All of the language items, defined or not.
  85         /// Defined lang items can come from the current crate or its dependencies.
  86         #[derive(HashStable_Generic, Debug)]
  87         pub struct LanguageItems {
  88             /// Mappings from lang items to their possibly found [`DefId`]s.
  89             /// The index corresponds to the order in [`LangItem`].
  90             pub items: Vec<Option<DefId>>,
  91             /// Lang items that were not found during collection.
  92             pub missing: Vec<LangItem>,
  93             /// Mapping from [`LangItemGroup`] discriminants to all
  94             /// [`DefId`]s of lang items in that group.
  95             pub groups: [Vec<DefId>; NUM_GROUPS],
  96         }
  97
  98         impl LanguageItems {
  99             /// Construct an empty collection of lang items and no missing ones.
 100             pub fn new() -> Self {
 101                 fn init_none(_: LangItem) -> Option<DefId> { None }
 102                 const EMPTY: Vec<DefId> = Vec::new();
 103
 104                 Self {
 105                     items: vec![$(init_none(LangItem::$variant)),*],
 106                     missing: Vec::new(),
 107                     groups: [EMPTY; NUM_GROUPS],
 108                 }
 109             }
 110
 111             /// Returns the mappings to the possibly found `DefId`s for each lang item.
 112             pub fn items(&self) -> &[Option<DefId>] {
 113                 &*self.items
 114             }
 115
 116             /// Requires that a given `LangItem` was bound and returns the corresponding `DefId`.
 117             /// If it wasn't bound, e.g. due to a missing `#[lang = "<it.name()>"]`,
 118             /// returns an error message as a string.
 119             pub fn require(&self, it: LangItem) -> Result<DefId, String> {
 120                 self.items[it as usize].ok_or_else(|| format!("requires `{}` lang_item", it.name()))
 121             }
 122
 123             /// Returns the [`DefId`]s of all lang items in a group.
 124             pub fn group(&self, group: LangItemGroup) -> &[DefId] {
 125                 self.groups[group as usize].as_ref()
 126             }
 127
 128             $(
 129                 #[doc = concat!("Returns the [`DefId`] of the `", stringify!($name), "` lang item if it is defined.")]
 130                 pub fn $method(&self) -> Option<DefId> {
 131                     self.items[LangItem::$variant as usize]
 132                 }
 133             )*
 134         }
 135
 136         /// A mapping from the name of the lang item to its order and the form it must be of.
 137         pub static ITEM_REFS: SyncLazy<FxHashMap<Symbol, (usize, Target)>> = SyncLazy::new(|| {
 138             let mut item_refs = FxHashMap::default();
 139             $( item_refs.insert($module::$name, (LangItem::$variant as usize, $target)); )*
 140             item_refs
 141         });
 142
 143 // End of the macro
 144     }
 145 }
 146
 147 impl<CTX> HashStable<CTX> for LangItem {
 148     fn hash_stable(&self, _: &mut CTX, hasher: &mut StableHasher) {
 149         ::std::hash::Hash::hash(self, hasher);
 150     }
 151 }
 152
 153 /// Extracts the first `lang = "$name"` out of a list of attributes.
 154 /// The attributes `#[panic_handler]` and `#[alloc_error_handler]`
 155 /// are also extracted out when found.
 156 pub fn extract(attrs: &[ast::Attribute]) -> Option<(Symbol, Span)> {
 157     attrs.iter().find_map(|attr| {
 158         Some(match attr {
 159             _ if attr.has_name(sym::lang) => (attr.value_str()?, attr.span),
 160             _ if attr.has_name(sym::panic_handler) => (sym::panic_impl, attr.span),
 161             _ if attr.has_name(sym::alloc_error_handler) => (sym::oom, attr.span),
 162             _ => return None,
 163         })
 164     })
 165 }
 166
 167 language_item_table! {
 168 //  Variant name,            Name,                     Method name,                Target                  Generic requirements;
 169     Bool,                    sym::bool,                bool_impl,                  Target::Impl,           GenericRequirement::None;
 170     Char,                    sym::char,                char_impl,                  Target::Impl,           GenericRequirement::None;
 171     Str,                     sym::str,                 str_impl,                   Target::Impl,           GenericRequirement::None;
 172     Array,                   sym::array,               array_impl,                 Target::Impl,           GenericRequirement::None;
 173     Slice,                   sym::slice,               slice_impl,                 Target::Impl,           GenericRequirement::None;
 174     SliceU8,                 sym::slice_u8,            slice_u8_impl,              Target::Impl,           GenericRequirement::None;
 175     StrAlloc,                sym::str_alloc,           str_alloc_impl,             Target::Impl,           GenericRequirement::None;
 176     SliceAlloc,              sym::slice_alloc,         slice_alloc_impl,           Target::Impl,           GenericRequirement::None;
 177     SliceU8Alloc,            sym::slice_u8_alloc,      slice_u8_alloc_impl,        Target::Impl,           GenericRequirement::None;
 178     ConstPtr,                sym::const_ptr,           const_ptr_impl,             Target::Impl,           GenericRequirement::None;
 179     MutPtr,                  sym::mut_ptr,             mut_ptr_impl,               Target::Impl,           GenericRequirement::None;
 180     ConstSlicePtr,           sym::const_slice_ptr,     const_slice_ptr_impl,       Target::Impl,           GenericRequirement::None;
 181     MutSlicePtr,             sym::mut_slice_ptr,       mut_slice_ptr_impl,         Target::Impl,           GenericRequirement::None;
 182     I8,                      sym::i8,                  i8_impl,                    Target::Impl,           GenericRequirement::None;
 183     I16,                     sym::i16,                 i16_impl,                   Target::Impl,           GenericRequirement::None;
 184     I32,                     sym::i32,                 i32_impl,                   Target::Impl,           GenericRequirement::None;
 185     I64,                     sym::i64,                 i64_impl,                   Target::Impl,           GenericRequirement::None;
 186     I128,                    sym::i128,                i128_impl,                  Target::Impl,           GenericRequirement::None;
 187     Isize,                   sym::isize,               isize_impl,                 Target::Impl,           GenericRequirement::None;
 188     U8,                      sym::u8,                  u8_impl,                    Target::Impl,           GenericRequirement::None;
 189     U16,                     sym::u16,                 u16_impl,                   Target::Impl,           GenericRequirement::None;
 190     U32,                     sym::u32,                 u32_impl,                   Target::Impl,           GenericRequirement::None;
 191     U64,                     sym::u64,                 u64_impl,                   Target::Impl,           GenericRequirement::None;
 192     U128,                    sym::u128,                u128_impl,                  Target::Impl,           GenericRequirement::None;
 193     Usize,                   sym::usize,               usize_impl,                 Target::Impl,           GenericRequirement::None;
 194     F32,                     sym::f32,                 f32_impl,                   Target::Impl,           GenericRequirement::None;
 195     F64,                     sym::f64,                 f64_impl,                   Target::Impl,           GenericRequirement::None;
 196     F32Runtime,              sym::f32_runtime,         f32_runtime_impl,           Target::Impl,           GenericRequirement::None;
 197     F64Runtime,              sym::f64_runtime,         f64_runtime_impl,           Target::Impl,           GenericRequirement::None;
 198
 199     Sized,                   sym::sized,               sized_trait,                Target::Trait,          GenericRequirement::Exact(0);
 200     Unsize,                  sym::unsize,              unsize_trait,               Target::Trait,          GenericRequirement::Minimum(1);
 201     /// Trait injected by `#[derive(PartialEq)]`, (i.e. "Partial EQ").
 202     StructuralPeq,           sym::structural_peq,      structural_peq_trait,       Target::Trait,          GenericRequirement::None;
 203     /// Trait injected by `#[derive(Eq)]`, (i.e. "Total EQ"; no, I will not apologize).
 204     StructuralTeq,           sym::structural_teq,      structural_teq_trait,       Target::Trait,          GenericRequirement::None;
 205     Copy,                    sym::copy,                copy_trait,                 Target::Trait,          GenericRequirement::Exact(0);
 206     Clone,                   sym::clone,               clone_trait,                Target::Trait,          GenericRequirement::None;
 207     Sync,                    sym::sync,                sync_trait,                 Target::Trait,          GenericRequirement::Exact(0);
 208     DiscriminantKind,        sym::discriminant_kind,   discriminant_kind_trait,    Target::Trait,          GenericRequirement::None;
 209     /// The associated item of the [`DiscriminantKind`] trait.
 210     Discriminant,            sym::discriminant_type,   discriminant_type,          Target::AssocTy,        GenericRequirement::None;
 211
 212     PointeeTrait,            sym::pointee_trait,       pointee_trait,              Target::Trait,          GenericRequirement::None;
 213     Metadata,                sym::metadata_type,       metadata_type,              Target::AssocTy,        GenericRequirement::None;
 214     DynMetadata,             sym::dyn_metadata,        dyn_metadata,               Target::Struct,         GenericRequirement::None;
 215
 216     Freeze,                  sym::freeze,              freeze_trait,               Target::Trait,          GenericRequirement::Exact(0);
 217
 218     Drop,                    sym::drop,                drop_trait,                 Target::Trait,          GenericRequirement::None;
 219
 220     CoerceUnsized,           sym::coerce_unsized,      coerce_unsized_trait,       Target::Trait,          GenericRequirement::Minimum(1);
 221     DispatchFromDyn,         sym::dispatch_from_dyn,   dispatch_from_dyn_trait,    Target::Trait,          GenericRequirement::Minimum(1);
 222
 223     Add(Op),                 sym::add,                 add_trait,                  Target::Trait,          GenericRequirement::Exact(1);
 224     Sub(Op),                 sym::sub,                 sub_trait,                  Target::Trait,          GenericRequirement::Exact(1);
 225     Mul(Op),                 sym::mul,                 mul_trait,                  Target::Trait,          GenericRequirement::Exact(1);
 226     Div(Op),                 sym::div,                 div_trait,                  Target::Trait,          GenericRequirement::Exact(1);
 227     Rem(Op),                 sym::rem,                 rem_trait,                  Target::Trait,          GenericRequirement::Exact(1);
 228     Neg(Op),                 sym::neg,                 neg_trait,                  Target::Trait,          GenericRequirement::Exact(0);
 229     Not(Op),                 sym::not,                 not_trait,                  Target::Trait,          GenericRequirement::Exact(0);
 230     BitXor(Op),              sym::bitxor,              bitxor_trait,               Target::Trait,          GenericRequirement::Exact(1);
 231     BitAnd(Op),              sym::bitand,              bitand_trait,               Target::Trait,          GenericRequirement::Exact(1);
 232     BitOr(Op),               sym::bitor,               bitor_trait,                Target::Trait,          GenericRequirement::Exact(1);
 233     Shl(Op),                 sym::shl,                 shl_trait,                  Target::Trait,          GenericRequirement::Exact(1);
 234     Shr(Op),                 sym::shr,                 shr_trait,                  Target::Trait,          GenericRequirement::Exact(1);
 235     AddAssign(Op),           sym::add_assign,          add_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
 236     SubAssign(Op),           sym::sub_assign,          sub_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
 237     MulAssign(Op),           sym::mul_assign,          mul_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
 238     DivAssign(Op),           sym::div_assign,          div_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
 239     RemAssign(Op),           sym::rem_assign,          rem_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
 240     BitXorAssign(Op),        sym::bitxor_assign,       bitxor_assign_trait,        Target::Trait,          GenericRequirement::Exact(1);
 241     BitAndAssign(Op),        sym::bitand_assign,       bitand_assign_trait,        Target::Trait,          GenericRequirement::Exact(1);
 242     BitOrAssign(Op),         sym::bitor_assign,        bitor_assign_trait,         Target::Trait,          GenericRequirement::Exact(1);
 243     ShlAssign(Op),           sym::shl_assign,          shl_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
 244     ShrAssign(Op),           sym::shr_assign,          shr_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
 245     Index(Op),               sym::index,               index_trait,                Target::Trait,          GenericRequirement::Exact(1);
 246     IndexMut(Op),            sym::index_mut,           index_mut_trait,            Target::Trait,          GenericRequirement::Exact(1);
 247
 248     UnsafeCell,              sym::unsafe_cell,         unsafe_cell_type,           Target::Struct,         GenericRequirement::None;
 249     VaList,                  sym::va_list,             va_list,                    Target::Struct,         GenericRequirement::None;
 250
 251     Deref,                   sym::deref,               deref_trait,                Target::Trait,          GenericRequirement::Exact(0);
 252     DerefMut,                sym::deref_mut,           deref_mut_trait,            Target::Trait,          GenericRequirement::Exact(0);
 253     DerefTarget,             sym::deref_target,        deref_target,               Target::AssocTy,        GenericRequirement::None;
 254     Receiver,                sym::receiver,            receiver_trait,             Target::Trait,          GenericRequirement::None;
 255
 256     Fn(Fn),                  kw::Fn,                   fn_trait,                   Target::Trait,          GenericRequirement::Exact(1);
 257     FnMut(Fn),               sym::fn_mut,              fn_mut_trait,               Target::Trait,          GenericRequirement::Exact(1);
 258     FnOnce(Fn),              sym::fn_once,             fn_once_trait,              Target::Trait,          GenericRequirement::Exact(1);
 259
 260     FnOnceOutput,            sym::fn_once_output,      fn_once_output,             Target::AssocTy,        GenericRequirement::None;
 261
 262     Future,                  sym::future_trait,        future_trait,               Target::Trait,          GenericRequirement::Exact(0);
 263     GeneratorState,          sym::generator_state,     gen_state,                  Target::Enum,           GenericRequirement::None;
 264     Generator,               sym::generator,           gen_trait,                  Target::Trait,          GenericRequirement::Minimum(1);
 265     GeneratorReturn,         sym::generator_return,    generator_return,           Target::AssocTy,        GenericRequirement::None;
 266     Unpin,                   sym::unpin,               unpin_trait,                Target::Trait,          GenericRequirement::None;
 267     Pin,                     sym::pin,                 pin_type,                   Target::Struct,         GenericRequirement::None;
 268
 269     PartialEq(Op),           sym::eq,                  eq_trait,                   Target::Trait,          GenericRequirement::Exact(1);
 270     PartialOrd(Op),          sym::partial_ord,         partial_ord_trait,          Target::Trait,          GenericRequirement::Exact(1);
 271
 272     // A number of panic-related lang items. The `panic` item corresponds to divide-by-zero and
 273     // various panic cases with `match`. The `panic_bounds_check` item is for indexing arrays.
 274     //
 275     // The `begin_unwind` lang item has a predefined symbol name and is sort of a "weak lang item"
 276     // in the sense that a crate is not required to have it defined to use it, but a final product
 277     // is required to define it somewhere. Additionally, there are restrictions on crates that use
 278     // a weak lang item, but do not have it defined.
 279     Panic,                   sym::panic,               panic_fn,                   Target::Fn,             GenericRequirement::Exact(0);
 280     PanicFmt,                sym::panic_fmt,           panic_fmt,                  Target::Fn,             GenericRequirement::None;
 281     PanicDisplay,            sym::panic_display,       panic_display,              Target::Fn,             GenericRequirement::None;
 282     ConstPanicFmt,           sym::const_panic_fmt,     const_panic_fmt,            Target::Fn,             GenericRequirement::None;
 283     PanicBoundsCheck,        sym::panic_bounds_check,  panic_bounds_check_fn,      Target::Fn,             GenericRequirement::Exact(0);
 284     PanicInfo,               sym::panic_info,          panic_info,                 Target::Struct,         GenericRequirement::None;
 285     PanicLocation,           sym::panic_location,      panic_location,             Target::Struct,         GenericRequirement::None;
 286     PanicImpl,               sym::panic_impl,          panic_impl,                 Target::Fn,             GenericRequirement::None;
 287     PanicNoUnwind,           sym::panic_no_unwind,     panic_no_unwind,            Target::Fn,             GenericRequirement::Exact(0);
 288     /// libstd panic entry point. Necessary for const eval to be able to catch it
 289     BeginPanic,              sym::begin_panic,         begin_panic_fn,             Target::Fn,             GenericRequirement::None;
 290
 291     ExchangeMalloc,          sym::exchange_malloc,     exchange_malloc_fn,         Target::Fn,             GenericRequirement::None;
 292     BoxFree,                 sym::box_free,            box_free_fn,                Target::Fn,             GenericRequirement::Minimum(1);
 293     DropInPlace,             sym::drop_in_place,       drop_in_place_fn,           Target::Fn,             GenericRequirement::Minimum(1);
 294     Oom,                     sym::oom,                 oom,                        Target::Fn,             GenericRequirement::None;
 295     AllocLayout,             sym::alloc_layout,        alloc_layout,               Target::Struct,         GenericRequirement::None;
 296     ConstEvalSelect,         sym::const_eval_select,   const_eval_select,          Target::Fn,             GenericRequirement::Exact(4);
 297     ConstConstEvalSelect,    sym::const_eval_select_ct,const_eval_select_ct,       Target::Fn,             GenericRequirement::Exact(4);
 298
 299     Start,                   sym::start,               start_fn,                   Target::Fn,             GenericRequirement::Exact(1);
 300
 301     EhPersonality,           sym::eh_personality,      eh_personality,             Target::Fn,             GenericRequirement::None;
 302     EhCatchTypeinfo,         sym::eh_catch_typeinfo,   eh_catch_typeinfo,          Target::Static,         GenericRequirement::None;
 303
 304     OwnedBox,                sym::owned_box,           owned_box,                  Target::Struct,         GenericRequirement::Minimum(1);
 305
 306     PhantomData,             sym::phantom_data,        phantom_data,               Target::Struct,         GenericRequirement::Exact(1);
 307
 308     ManuallyDrop,            sym::manually_drop,       manually_drop,              Target::Struct,         GenericRequirement::None;
 309
 310     MaybeUninit,             sym::maybe_uninit,        maybe_uninit,               Target::Union,          GenericRequirement::None;
 311
 312     /// Align offset for stride != 1; must not panic.
 313     AlignOffset,             sym::align_offset,        align_offset_fn,            Target::Fn,             GenericRequirement::None;
 314
 315     Termination,             sym::termination,         termination,                Target::Trait,          GenericRequirement::None;
 316
 317     Try,                     sym::Try,                 try_trait,                  Target::Trait,          GenericRequirement::None;
 318
 319     SliceLen,                sym::slice_len_fn,        slice_len_fn,               Target::Method(MethodKind::Inherent), GenericRequirement::None;
 320
 321     // Language items from AST lowering
 322     TryTraitFromResidual,    sym::from_residual,       from_residual_fn,           Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
 323     TryTraitFromOutput,      sym::from_output,         from_output_fn,             Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
 324     TryTraitBranch,          sym::branch,              branch_fn,                  Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
 325
 326     PollReady,               sym::Ready,               poll_ready_variant,         Target::Variant,        GenericRequirement::None;
 327     PollPending,             sym::Pending,             poll_pending_variant,       Target::Variant,        GenericRequirement::None;
 328
 329     FromGenerator,           sym::from_generator,      from_generator_fn,          Target::Fn,             GenericRequirement::None;
 330     GetContext,              sym::get_context,         get_context_fn,             Target::Fn,             GenericRequirement::None;
 331
 332     FuturePoll,              sym::poll,                future_poll_fn,             Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
 333
 334     FromFrom,                sym::from,                from_fn,                    Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
 335
 336     OptionSome,              sym::Some,                option_some_variant,        Target::Variant,        GenericRequirement::None;
 337     OptionNone,              sym::None,                option_none_variant,        Target::Variant,        GenericRequirement::None;
 338
 339     ResultOk,                sym::Ok,                  result_ok_variant,          Target::Variant,        GenericRequirement::None;
 340     ResultErr,               sym::Err,                 result_err_variant,         Target::Variant,        GenericRequirement::None;
 341
 342     ControlFlowContinue,     sym::Continue,            cf_continue_variant,        Target::Variant,        GenericRequirement::None;
 343     ControlFlowBreak,        sym::Break,               cf_break_variant,           Target::Variant,        GenericRequirement::None;
 344
 345     IntoFutureIntoFuture,    sym::into_future,         into_future_fn,             Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
 346     IntoIterIntoIter,        sym::into_iter,           into_iter_fn,               Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
 347     IteratorNext,            sym::next,                next_fn,                    Target::Method(MethodKind::Trait { body: false}), GenericRequirement::None;
 348
 349     PinNewUnchecked,         sym::new_unchecked,       new_unchecked_fn,           Target::Method(MethodKind::Inherent), GenericRequirement::None;
 350
 351     RangeFrom,               sym::RangeFrom,           range_from_struct,          Target::Struct,         GenericRequirement::None;
 352     RangeFull,               sym::RangeFull,           range_full_struct,          Target::Struct,         GenericRequirement::None;
 353     RangeInclusiveStruct,    sym::RangeInclusive,      range_inclusive_struct,     Target::Struct,         GenericRequirement::None;
 354     RangeInclusiveNew,       sym::range_inclusive_new, range_inclusive_new_method, Target::Method(MethodKind::Inherent), GenericRequirement::None;
 355     Range,                   sym::Range,               range_struct,               Target::Struct,         GenericRequirement::None;
 356     RangeToInclusive,        sym::RangeToInclusive,    range_to_inclusive_struct,  Target::Struct,         GenericRequirement::None;
 357     RangeTo,                 sym::RangeTo,             range_to_struct,            Target::Struct,         GenericRequirement::None;
 358 }
 359
 360 pub enum GenericRequirement {
 361     None,
 362     Minimum(usize),
 363     Exact(usize),
 364 }