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_ast::Attribute;
  14 use rustc_errors::{pluralize, struct_span_err};
  15 use rustc_hir as hir;
  16 use rustc_hir::def_id::DefId;
  17 use rustc_hir::itemlikevisit::ItemLikeVisitor;
  18 use rustc_hir::lang_items::{extract, GenericRequirement, ITEM_REFS};
  19 use rustc_hir::{HirId, LangItem, LanguageItems, Target};
  20 use rustc_middle::ty::TyCtxt;
  21 use rustc_session::cstore::ExternCrate;
  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: &Attribute, sym| attr.has_name(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.
 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         // Now check whether the lang_item has the expected number of generic
 192         // arguments. Generally speaking, binary and indexing operations have
 193         // one (for the RHS/index), unary operations have none, the closure
 194         // traits have one for the argument list, generators have one for the
 195         // resume argument, and ordering/equality relations have one for the RHS
 196         // Some other types like Box and various functions like drop_in_place
 197         // have minimum requirements.
 198
 199         if let hir::Node::Item(hir::Item { kind, span: item_span, .. }) = self.tcx.hir().get(hir_id)
 200         {
 201             let (actual_num, generics_span) = match kind.generics() {
 202                 Some(generics) => (generics.params.len(), generics.span),
 203                 None => (0, *item_span),
 204             };
 205
 206             let required = match lang_item.required_generics() {
 207                 GenericRequirement::Exact(num) if num != actual_num => {
 208                     Some((format!("{}", num), pluralize!(num)))
 209                 }
 210                 GenericRequirement::Minimum(num) if actual_num < num => {
 211                     Some((format!("at least {}", num), pluralize!(num)))
 212                 }
 213                 // If the number matches, or there is no requirement, handle it normally
 214                 _ => None,
 215             };
 216
 217             if let Some((range_str, pluralized)) = required {
 218                 // We are issuing E0718 "incorrect target" here, because while the
 219                 // item kind of the target is correct, the target is still wrong
 220                 // because of the wrong number of generic arguments.
 221                 struct_span_err!(
 222                     self.tcx.sess,
 223                     span,
 224                     E0718,
 225                     "`{}` language item must be applied to a {} with {} generic argument{}",
 226                     name,
 227                     kind.descr(),
 228                     range_str,
 229                     pluralized,
 230                 )
 231                 .span_label(
 232                     generics_span,
 233                     format!(
 234                         "this {} has {} generic argument{}",
 235                         kind.descr(),
 236                         actual_num,
 237                         pluralize!(actual_num),
 238                     ),
 239                 )
 240                 .emit();
 241
 242                 // return early to not collect the lang item
 243                 return;
 244             }
 245         }
 246
 247         self.collect_item(item_index, item_def_id);
 248     }
 249 }
 250
 251 /// Traverses and collects all the lang items in all crates.
 252 fn get_lang_items(tcx: TyCtxt<'_>, (): ()) -> LanguageItems {
 253     // Initialize the collector.
 254     let mut collector = LanguageItemCollector::new(tcx);
 255
 256     // Collect lang items in other crates.
 257     for &cnum in tcx.crates(()).iter() {
 258         for &(def_id, item_index) in tcx.defined_lang_items(cnum).iter() {
 259             collector.collect_item(item_index, def_id);
 260         }
 261     }
 262
 263     // Collect lang items in this crate.
 264     tcx.hir().visit_all_item_likes(&mut collector);
 265
 266     // Extract out the found lang items.
 267     let LanguageItemCollector { mut items, .. } = collector;
 268
 269     // Find all required but not-yet-defined lang items.
 270     weak_lang_items::check_crate(tcx, &mut items);
 271
 272     items
 273 }
 274
 275 pub fn provide(providers: &mut Providers) {
 276     providers.get_lang_items = get_lang_items;
 277 }