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