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_ast::Attribute;
  17 use rustc_errors::{pluralize, struct_span_err};
  18 use rustc_hir as hir;
  19 use rustc_hir::def_id::DefId;
  20 use rustc_hir::itemlikevisit::ItemLikeVisitor;
  21 use rustc_hir::lang_items::{extract, GenericRequirement, ITEM_REFS};
  22 use rustc_hir::{HirId, LangItem, LanguageItems, Target};
  23 use rustc_span::Span;
  24
  25 use rustc_middle::ty::query::Providers;
  26
  27 struct LanguageItemCollector<'tcx> {
  28     items: LanguageItems,
  29     tcx: TyCtxt<'tcx>,
  30 }
  31
  32 impl ItemLikeVisitor<'v> for LanguageItemCollector<'tcx> {
  33     fn visit_item(&mut self, item: &hir::Item<'_>) {
  34         self.check_for_lang(Target::from_item(item), item.hir_id());
  35
  36         if let hir::ItemKind::Enum(def, ..) = &item.kind {
  37             for variant in def.variants {
  38                 self.check_for_lang(Target::Variant, variant.id);
  39             }
  40         }
  41     }
  42
  43     fn visit_trait_item(&mut self, trait_item: &hir::TraitItem<'_>) {
  44         self.check_for_lang(Target::from_trait_item(trait_item), trait_item.hir_id())
  45     }
  46
  47     fn visit_impl_item(&mut self, impl_item: &hir::ImplItem<'_>) {
  48         self.check_for_lang(target_from_impl_item(self.tcx, impl_item), impl_item.hir_id())
  49     }
  50
  51     fn visit_foreign_item(&mut self, _: &hir::ForeignItem<'_>) {}
  52 }
  53
  54 impl LanguageItemCollector<'tcx> {
  55     fn new(tcx: TyCtxt<'tcx>) -> LanguageItemCollector<'tcx> {
  56         LanguageItemCollector { tcx, items: LanguageItems::new() }
  57     }
  58
  59     fn check_for_lang(&mut self, actual_target: Target, hir_id: HirId) {
  60         let attrs = self.tcx.hir().attrs(hir_id);
  61         let check_name = |attr: &Attribute, sym| attr.has_name(sym);
  62         if let Some((value, span)) = extract(check_name, &attrs) {
  63             match ITEM_REFS.get(&value).cloned() {
  64                 // Known lang item with attribute on correct target.
  65                 Some((item_index, expected_target)) if actual_target == expected_target => {
  66                     self.collect_item_extended(item_index, hir_id, span);
  67                 }
  68                 // Known lang item with attribute on incorrect target.
  69                 Some((_, expected_target)) => {
  70                     struct_span_err!(
  71                         self.tcx.sess,
  72                         span,
  73                         E0718,
  74                         "`{}` language item must be applied to a {}",
  75                         value,
  76                         expected_target,
  77                     )
  78                     .span_label(
  79                         span,
  80                         format!(
  81                             "attribute should be applied to a {}, not a {}",
  82                             expected_target, actual_target,
  83                         ),
  84                     )
  85                     .emit();
  86                 }
  87                 // Unknown lang item.
  88                 _ => {
  89                     struct_span_err!(
  90                         self.tcx.sess,
  91                         span,
  92                         E0522,
  93                         "definition of an unknown language item: `{}`",
  94                         value
  95                     )
  96                     .span_label(span, format!("definition of unknown language item `{}`", value))
  97                     .emit();
  98                 }
  99             }
 100         }
 101     }
 102
 103     fn collect_item(&mut self, item_index: usize, item_def_id: DefId) {
 104         // Check for duplicates.
 105         if let Some(original_def_id) = self.items.items[item_index] {
 106             if original_def_id != item_def_id {
 107                 let lang_item = LangItem::from_u32(item_index as u32).unwrap();
 108                 let name = lang_item.name();
 109                 let mut err = match self.tcx.hir().span_if_local(item_def_id) {
 110                     Some(span) => struct_span_err!(
 111                         self.tcx.sess,
 112                         span,
 113                         E0152,
 114                         "found duplicate lang item `{}`",
 115                         name
 116                     ),
 117                     None => match self.tcx.extern_crate(item_def_id) {
 118                         Some(ExternCrate { dependency_of, .. }) => {
 119                             self.tcx.sess.struct_err(&format!(
 120                                 "duplicate lang item in crate `{}` (which `{}` depends on): `{}`.",
 121                                 self.tcx.crate_name(item_def_id.krate),
 122                                 self.tcx.crate_name(*dependency_of),
 123                                 name
 124                             ))
 125                         }
 126                         _ => self.tcx.sess.struct_err(&format!(
 127                             "duplicate lang item in crate `{}`: `{}`.",
 128                             self.tcx.crate_name(item_def_id.krate),
 129                             name
 130                         )),
 131                     },
 132                 };
 133                 if let Some(span) = self.tcx.hir().span_if_local(original_def_id) {
 134                     err.span_note(span, "the lang item is first defined here");
 135                 } else {
 136                     match self.tcx.extern_crate(original_def_id) {
 137                         Some(ExternCrate { dependency_of, .. }) => {
 138                             err.note(&format!(
 139                                 "the lang item is first defined in crate `{}` (which `{}` depends on)",
 140                                 self.tcx.crate_name(original_def_id.krate),
 141                                 self.tcx.crate_name(*dependency_of)
 142                             ));
 143                         }
 144                         _ => {
 145                             err.note(&format!(
 146                                 "the lang item is first defined in crate `{}`.",
 147                                 self.tcx.crate_name(original_def_id.krate)
 148                             ));
 149                         }
 150                     }
 151                     let mut note_def = |which, def_id: DefId| {
 152                         let crate_name = self.tcx.crate_name(def_id.krate);
 153                         let note = if def_id.is_local() {
 154                             format!("{} definition in the local crate (`{}`)", which, crate_name)
 155                         } else {
 156                             let paths: Vec<_> = self
 157                                 .tcx
 158                                 .crate_extern_paths(def_id.krate)
 159                                 .iter()
 160                                 .map(|p| p.display().to_string())
 161                                 .collect();
 162                             format!(
 163                                 "{} definition in `{}` loaded from {}",
 164                                 which,
 165                                 crate_name,
 166                                 paths.join(", ")
 167                             )
 168                         };
 169                         err.note(&note);
 170                     };
 171                     note_def("first", original_def_id);
 172                     note_def("second", item_def_id);
 173                 }
 174                 err.emit();
 175             }
 176         }
 177
 178         // Matched.
 179         self.items.items[item_index] = Some(item_def_id);
 180         if let Some(group) = LangItem::from_u32(item_index as u32).unwrap().group() {
 181             self.items.groups[group as usize].push(item_def_id);
 182         }
 183     }
 184
 185     // Like collect_item() above, but also checks whether the lang item is declared
 186     // with the right number of generic arguments.
 187     fn collect_item_extended(&mut self, item_index: usize, hir_id: HirId, span: Span) {
 188         let item_def_id = self.tcx.hir().local_def_id(hir_id).to_def_id();
 189         let lang_item = LangItem::from_u32(item_index as u32).unwrap();
 190         let name = lang_item.name();
 191
 192         // Now check whether the lang_item has the expected number of generic
 193         // arguments. Generally speaking, binary and indexing operations have
 194         // one (for the RHS/index), unary operations have none, the closure
 195         // traits have one for the argument list, generators have one for the
 196         // resume argument, and ordering/equality relations have one for the RHS
 197         // Some other types like Box and various functions like drop_in_place
 198         // have minimum requirements.
 199
 200         if let hir::Node::Item(hir::Item { kind, span: item_span, .. }) = self.tcx.hir().get(hir_id)
 201         {
 202             let (actual_num, generics_span) = match kind.generics() {
 203                 Some(generics) => (generics.params.len(), generics.span),
 204                 None => (0, *item_span),
 205             };
 206
 207             let required = match lang_item.required_generics() {
 208                 GenericRequirement::Exact(num) if num != actual_num => {
 209                     Some((format!("{}", num), pluralize!(num)))
 210                 }
 211                 GenericRequirement::Minimum(num) if actual_num < num => {
 212                     Some((format!("at least {}", num), pluralize!(num)))
 213                 }
 214                 // If the number matches, or there is no requirement, handle it normally
 215                 _ => None,
 216             };
 217
 218             if let Some((range_str, pluralized)) = required {
 219                 // We are issuing E0718 "incorrect target" here, because while the
 220                 // item kind of the target is correct, the target is still wrong
 221                 // because of the wrong number of generic arguments.
 222                 struct_span_err!(
 223                     self.tcx.sess,
 224                     span,
 225                     E0718,
 226                     "`{}` language item must be applied to a {} with {} generic argument{}",
 227                     name,
 228                     kind.descr(),
 229                     range_str,
 230                     pluralized,
 231                 )
 232                 .span_label(
 233                     generics_span,
 234                     format!(
 235                         "this {} has {} generic argument{}",
 236                         kind.descr(),
 237                         actual_num,
 238                         pluralize!(actual_num),
 239                     ),
 240                 )
 241                 .emit();
 242
 243                 // return early to not collect the lang item
 244                 return;
 245             }
 246         }
 247
 248         self.collect_item(item_index, item_def_id);
 249     }
 250 }
 251
 252 /// Traverses and collects all the lang items in all crates.
 253 fn get_lang_items(tcx: TyCtxt<'_>, (): ()) -> LanguageItems {
 254     // Initialize the collector.
 255     let mut collector = LanguageItemCollector::new(tcx);
 256
 257     // Collect lang items in other crates.
 258     for &cnum in tcx.crates(()).iter() {
 259         for &(def_id, item_index) in tcx.defined_lang_items(cnum).iter() {
 260             collector.collect_item(item_index, def_id);
 261         }
 262     }
 263
 264     // Collect lang items in this crate.
 265     tcx.hir().krate().visit_all_item_likes(&mut collector);
 266
 267     // Extract out the found lang items.
 268     let LanguageItemCollector { mut items, .. } = collector;
 269
 270     // Find all required but not-yet-defined lang items.
 271     weak_lang_items::check_crate(tcx, &mut items);
 272
 273     items
 274 }
 275
 276 pub fn provide(providers: &mut Providers) {
 277     providers.get_lang_items = get_lang_items;
 278 }