compiler/rustc_passes/src/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 use crate::check_attr::target_from_impl_item;
  11 use crate::weak_lang_items;
  12
  13 use rustc_middle::middle::cstore::ExternCrate;
  14 use rustc_middle::ty::TyCtxt;
  15
  16 use rustc_errors::{pluralize, struct_span_err};
  17 use rustc_hir as hir;
  18 use rustc_hir::def_id::DefId;
  19 use rustc_hir::itemlikevisit::ItemLikeVisitor;
  20 use rustc_hir::lang_items::{extract, ITEM_REFS};
  21 use rustc_hir::{HirId, LangItem, LanguageItems, Target};
  22 use rustc_span::Span;
  23
  24 use rustc_middle::ty::query::Providers;
  25
  26 struct LanguageItemCollector<'tcx> {
  27     items: LanguageItems,
  28     tcx: TyCtxt<'tcx>,
  29 }
  30
  31 impl ItemLikeVisitor<'v> for LanguageItemCollector<'tcx> {
  32     fn visit_item(&mut self, item: &hir::Item<'_>) {
  33         self.check_for_lang(Target::from_item(item), item.hir_id());
  34
  35         if let hir::ItemKind::Enum(def, ..) = &item.kind {
  36             for variant in def.variants {
  37                 self.check_for_lang(Target::Variant, variant.id);
  38             }
  39         }
  40     }
  41
  42     fn visit_trait_item(&mut self, trait_item: &hir::TraitItem<'_>) {
  43         self.check_for_lang(Target::from_trait_item(trait_item), trait_item.hir_id())
  44     }
  45
  46     fn visit_impl_item(&mut self, impl_item: &hir::ImplItem<'_>) {
  47         self.check_for_lang(target_from_impl_item(self.tcx, impl_item), impl_item.hir_id())
  48     }
  49
  50     fn visit_foreign_item(&mut self, _: &hir::ForeignItem<'_>) {}
  51 }
  52
  53 impl LanguageItemCollector<'tcx> {
  54     fn new(tcx: TyCtxt<'tcx>) -> LanguageItemCollector<'tcx> {
  55         LanguageItemCollector { tcx, items: LanguageItems::new() }
  56     }
  57
  58     fn check_for_lang(&mut self, actual_target: Target, hir_id: HirId) {
  59         let attrs = self.tcx.hir().attrs(hir_id);
  60         let check_name = |attr, sym| self.tcx.sess.check_name(attr, sym);
  61         if let Some((value, span)) = extract(check_name, &attrs) {
  62             match ITEM_REFS.get(&value).cloned() {
  63                 // Known lang item with attribute on correct target.
  64                 Some((item_index, expected_target)) if actual_target == expected_target => {
  65                     self.collect_item_extended(item_index, hir_id, span);
  66                 }
  67                 // Known lang item with attribute on incorrect target.
  68                 Some((_, expected_target)) => {
  69                     struct_span_err!(
  70                         self.tcx.sess,
  71                         span,
  72                         E0718,
  73                         "`{}` language item must be applied to a {}",
  74                         value,
  75                         expected_target,
  76                     )
  77                     .span_label(
  78                         span,
  79                         format!(
  80                             "attribute should be applied to a {}, not a {}",
  81                             expected_target, actual_target,
  82                         ),
  83                     )
  84                     .emit();
  85                 }
  86                 // Unknown lang item.
  87                 _ => {
  88                     struct_span_err!(
  89                         self.tcx.sess,
  90                         span,
  91                         E0522,
  92                         "definition of an unknown language item: `{}`",
  93                         value
  94                     )
  95                     .span_label(span, format!("definition of unknown language item `{}`", value))
  96                     .emit();
  97                 }
  98             }
  99         }
 100     }
 101
 102     fn collect_item(&mut self, item_index: usize, item_def_id: DefId) {
 103         // Check for duplicates.
 104         if let Some(original_def_id) = self.items.items[item_index] {
 105             if original_def_id != item_def_id {
 106                 let lang_item = LangItem::from_u32(item_index as u32).unwrap();
 107                 let name = lang_item.name();
 108                 let mut err = match self.tcx.hir().span_if_local(item_def_id) {
 109                     Some(span) => struct_span_err!(
 110                         self.tcx.sess,
 111                         span,
 112                         E0152,
 113                         "found duplicate lang item `{}`",
 114                         name
 115                     ),
 116                     None => match self.tcx.extern_crate(item_def_id) {
 117                         Some(ExternCrate { dependency_of, .. }) => {
 118                             self.tcx.sess.struct_err(&format!(
 119                                 "duplicate lang item in crate `{}` (which `{}` depends on): `{}`.",
 120                                 self.tcx.crate_name(item_def_id.krate),
 121                                 self.tcx.crate_name(*dependency_of),
 122                                 name
 123                             ))
 124                         }
 125                         _ => self.tcx.sess.struct_err(&format!(
 126                             "duplicate lang item in crate `{}`: `{}`.",
 127                             self.tcx.crate_name(item_def_id.krate),
 128                             name
 129                         )),
 130                     },
 131                 };
 132                 if let Some(span) = self.tcx.hir().span_if_local(original_def_id) {
 133                     err.span_note(span, "the lang item is first defined here");
 134                 } else {
 135                     match self.tcx.extern_crate(original_def_id) {
 136                         Some(ExternCrate { dependency_of, .. }) => {
 137                             err.note(&format!(
 138                                 "the lang item is first defined in crate `{}` (which `{}` depends on)",
 139                                 self.tcx.crate_name(original_def_id.krate),
 140                                 self.tcx.crate_name(*dependency_of)
 141                             ));
 142                         }
 143                         _ => {
 144                             err.note(&format!(
 145                                 "the lang item is first defined in crate `{}`.",
 146                                 self.tcx.crate_name(original_def_id.krate)
 147                             ));
 148                         }
 149                     }
 150                     let mut note_def = |which, def_id: DefId| {
 151                         let crate_name = self.tcx.crate_name(def_id.krate);
 152                         let note = if def_id.is_local() {
 153                             format!("{} definition in the local crate (`{}`)", which, crate_name)
 154                         } else {
 155                             let paths: Vec<_> = self
 156                                 .tcx
 157                                 .crate_extern_paths(def_id.krate)
 158                                 .iter()
 159                                 .map(|p| p.display().to_string())
 160                                 .collect();
 161                             format!(
 162                                 "{} definition in `{}` loaded from {}",
 163                                 which,
 164                                 crate_name,
 165                                 paths.join(", ")
 166                             )
 167                         };
 168                         err.note(&note);
 169                     };
 170                     note_def("first", original_def_id);
 171                     note_def("second", item_def_id);
 172                 }
 173                 err.emit();
 174             }
 175         }
 176
 177         // Matched.
 178         self.items.items[item_index] = Some(item_def_id);
 179         if let Some(group) = LangItem::from_u32(item_index as u32).unwrap().group() {
 180             self.items.groups[group as usize].push(item_def_id);
 181         }
 182     }
 183
 184     // Like collect_item() above, but also checks whether the lang item is declared
 185     // with the right number of generic arguments if it is a trait.
 186     fn collect_item_extended(&mut self, item_index: usize, hir_id: HirId, span: Span) {
 187         let item_def_id = self.tcx.hir().local_def_id(hir_id).to_def_id();
 188         let lang_item = LangItem::from_u32(item_index as u32).unwrap();
 189         let name = lang_item.name();
 190
 191         self.collect_item(item_index, item_def_id);
 192
 193         // Now check whether the lang_item has the expected number of generic
 194         // arguments if it is a trait. Generally speaking, binary and indexing
 195         // operations have one (for the RHS/index), unary operations have none,
 196         // and the rest also have none except for the closure traits (one for
 197         // the argument list), generators (one for the resume argument),
 198         // ordering/equality relations (one for the RHS), and various conversion
 199         // traits.
 200
 201         let expected_num = match lang_item {
 202             // Binary operations
 203             LangItem::Add
 204             | LangItem::Sub
 205             | LangItem::Mul
 206             | LangItem::Div
 207             | LangItem::Rem
 208             | LangItem::BitXor
 209             | LangItem::BitAnd
 210             | LangItem::BitOr
 211             | LangItem::Shl
 212             | LangItem::Shr
 213             | LangItem::AddAssign
 214             | LangItem::SubAssign
 215             | LangItem::MulAssign
 216             | LangItem::DivAssign
 217             | LangItem::RemAssign
 218             | LangItem::BitXorAssign
 219             | LangItem::BitAndAssign
 220             | LangItem::BitOrAssign
 221             | LangItem::ShlAssign
 222             | LangItem::ShrAssign
 223             | LangItem::Index
 224             | LangItem::IndexMut
 225
 226             // Miscellaneous
 227             | LangItem::Unsize
 228             | LangItem::CoerceUnsized
 229             | LangItem::DispatchFromDyn
 230             | LangItem::Fn
 231             | LangItem::FnMut
 232             | LangItem::FnOnce
 233             | LangItem::Generator
 234             | LangItem::PartialEq
 235             | LangItem::PartialOrd
 236                 => Some(1),
 237
 238             // Unary operations
 239             LangItem::Neg
 240             | LangItem::Not
 241
 242             // Miscellaneous
 243             | LangItem::Deref
 244             | LangItem::DerefMut
 245             | LangItem::Sized
 246             | LangItem::StructuralPeq
 247             | LangItem::StructuralTeq
 248             | LangItem::Copy
 249             | LangItem::Clone
 250             | LangItem::Sync
 251             | LangItem::DiscriminantKind
 252             | LangItem::PointeeTrait
 253             | LangItem::Freeze
 254             | LangItem::Drop
 255             | LangItem::Receiver
 256             | LangItem::Future
 257             | LangItem::Unpin
 258             | LangItem::Termination
 259             | LangItem::Try
 260             | LangItem::Send
 261             | LangItem::UnwindSafe
 262             | LangItem::RefUnwindSafe
 263                 => Some(0),
 264
 265             // Not a trait
 266             _ => None,
 267         };
 268
 269         if let Some(expected_num) = expected_num {
 270             let (actual_num, generics_span) = match self.tcx.hir().get(hir_id) {
 271                 hir::Node::Item(hir::Item {
 272                     kind: hir::ItemKind::Trait(_, _, generics, ..),
 273                     ..
 274                 }) => (generics.params.len(), generics.span),
 275                 _ => bug!("op/index/deref lang item target is not a trait: {:?}", lang_item),
 276             };
 277
 278             if expected_num != actual_num {
 279                 // We are issuing E0718 "incorrect target" here, because while the
 280                 // item kind of the target is correct, the target is still wrong
 281                 // because of the wrong number of generic arguments.
 282                 struct_span_err!(
 283                     self.tcx.sess,
 284                     span,
 285                     E0718,
 286                     "`{}` language item must be applied to a trait with {} generic argument{}",
 287                     name,
 288                     expected_num,
 289                     pluralize!(expected_num)
 290                 )
 291                 .span_label(
 292                     generics_span,
 293                     format!(
 294                         "this trait has {} generic argument{}, not {}",
 295                         actual_num,
 296                         pluralize!(actual_num),
 297                         expected_num
 298                     ),
 299                 )
 300                 .emit();
 301             }
 302         }
 303     }
 304 }
 305
 306 /// Traverses and collects all the lang items in all crates.
 307 fn get_lang_items(tcx: TyCtxt<'_>, (): ()) -> LanguageItems {
 308     // Initialize the collector.
 309     let mut collector = LanguageItemCollector::new(tcx);
 310
 311     // Collect lang items in other crates.
 312     for &cnum in tcx.crates().iter() {
 313         for &(def_id, item_index) in tcx.defined_lang_items(cnum).iter() {
 314             collector.collect_item(item_index, def_id);
 315         }
 316     }
 317
 318     // Collect lang items in this crate.
 319     tcx.hir().krate().visit_all_item_likes(&mut collector);
 320
 321     // Extract out the found lang items.
 322     let LanguageItemCollector { mut items, .. } = collector;
 323
 324     // Find all required but not-yet-defined lang items.
 325     weak_lang_items::check_crate(tcx, &mut items);
 326
 327     items
 328 }
 329
 330 pub fn provide(providers: &mut Providers) {
 331     providers.get_lang_items = get_lang_items;
 332 }