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::errors::{
  12     DuplicateLangItem, IncorrectTarget, LangItemOnIncorrectTarget, UnknownLangItem,
  13 };
  14 use crate::weak_lang_items;
  15
  16 use rustc_hir as hir;
  17 use rustc_hir::def::DefKind;
  18 use rustc_hir::def_id::{DefId, LocalDefId};
  19 use rustc_hir::lang_items::{extract, GenericRequirement};
  20 use rustc_hir::{LangItem, LanguageItems, Target};
  21 use rustc_middle::ty::TyCtxt;
  22 use rustc_session::cstore::ExternCrate;
  23 use rustc_span::symbol::kw::Empty;
  24 use rustc_span::{sym, Span};
  25
  26 use rustc_middle::query::Providers;
  27
  28 pub(crate) enum Duplicate {
  29     Plain,
  30     Crate,
  31     CrateDepends,
  32 }
  33
  34 struct LanguageItemCollector<'tcx> {
  35     items: LanguageItems,
  36     tcx: TyCtxt<'tcx>,
  37 }
  38
  39 impl<'tcx> LanguageItemCollector<'tcx> {
  40     fn new(tcx: TyCtxt<'tcx>) -> LanguageItemCollector<'tcx> {
  41         LanguageItemCollector { tcx, items: LanguageItems::new() }
  42     }
  43
  44     fn check_for_lang(&mut self, actual_target: Target, def_id: LocalDefId) {
  45         let attrs = self.tcx.hir().attrs(self.tcx.hir().local_def_id_to_hir_id(def_id));
  46         if let Some((name, span)) = extract(&attrs) {
  47             match LangItem::from_name(name) {
  48                 // Known lang item with attribute on correct target.
  49                 Some(lang_item) if actual_target == lang_item.target() => {
  50                     self.collect_item_extended(lang_item, def_id, span);
  51                 }
  52                 // Known lang item with attribute on incorrect target.
  53                 Some(lang_item) => {
  54                     self.tcx.sess.emit_err(LangItemOnIncorrectTarget {
  55                         span,
  56                         name,
  57                         expected_target: lang_item.target(),
  58                         actual_target,
  59                     });
  60                 }
  61                 // Unknown lang item.
  62                 _ => {
  63                     self.tcx.sess.emit_err(UnknownLangItem { span, name });
  64                 }
  65             }
  66         }
  67     }
  68
  69     fn collect_item(&mut self, lang_item: LangItem, item_def_id: DefId) {
  70         // Check for duplicates.
  71         if let Some(original_def_id) = self.items.get(lang_item) {
  72             if original_def_id != item_def_id {
  73                 let local_span = self.tcx.hir().span_if_local(item_def_id);
  74                 let lang_item_name = lang_item.name();
  75                 let crate_name = self.tcx.crate_name(item_def_id.krate);
  76                 let mut dependency_of = Empty;
  77                 let is_local = item_def_id.is_local();
  78                 let path = if is_local {
  79                     String::new()
  80                 } else {
  81                     self.tcx
  82                         .crate_extern_paths(item_def_id.krate)
  83                         .iter()
  84                         .map(|p| p.display().to_string())
  85                         .collect::<Vec<_>>()
  86                         .join(", ")
  87                 };
  88                 let first_defined_span = self.tcx.hir().span_if_local(original_def_id);
  89                 let mut orig_crate_name = Empty;
  90                 let mut orig_dependency_of = Empty;
  91                 let orig_is_local = original_def_id.is_local();
  92                 let orig_path = if orig_is_local {
  93                     String::new()
  94                 } else {
  95                     self.tcx
  96                         .crate_extern_paths(original_def_id.krate)
  97                         .iter()
  98                         .map(|p| p.display().to_string())
  99                         .collect::<Vec<_>>()
 100                         .join(", ")
 101                 };
 102                 if first_defined_span.is_none() {
 103                     orig_crate_name = self.tcx.crate_name(original_def_id.krate);
 104                     if let Some(ExternCrate { dependency_of: inner_dependency_of, .. }) =
 105                         self.tcx.extern_crate(original_def_id)
 106                     {
 107                         orig_dependency_of = self.tcx.crate_name(*inner_dependency_of);
 108                     }
 109                 }
 110
 111                 let duplicate = if local_span.is_some() {
 112                     Duplicate::Plain
 113                 } else {
 114                     match self.tcx.extern_crate(item_def_id) {
 115                         Some(ExternCrate { dependency_of: inner_dependency_of, .. }) => {
 116                             dependency_of = self.tcx.crate_name(*inner_dependency_of);
 117                             Duplicate::CrateDepends
 118                         }
 119                         _ => Duplicate::Crate,
 120                     }
 121                 };
 122
 123                 self.tcx.sess.emit_err(DuplicateLangItem {
 124                     local_span,
 125                     lang_item_name,
 126                     crate_name,
 127                     dependency_of,
 128                     is_local,
 129                     path,
 130                     first_defined_span,
 131                     orig_crate_name,
 132                     orig_dependency_of,
 133                     orig_is_local,
 134                     orig_path,
 135                     duplicate,
 136                 });
 137             }
 138         }
 139
 140         // Matched.
 141         self.items.set(lang_item, item_def_id);
 142     }
 143
 144     // Like collect_item() above, but also checks whether the lang item is declared
 145     // with the right number of generic arguments.
 146     fn collect_item_extended(&mut self, lang_item: LangItem, item_def_id: LocalDefId, span: Span) {
 147         let name = lang_item.name();
 148
 149         // Now check whether the lang_item has the expected number of generic
 150         // arguments. Generally speaking, binary and indexing operations have
 151         // one (for the RHS/index), unary operations have none, the closure
 152         // traits have one for the argument list, generators have one for the
 153         // resume argument, and ordering/equality relations have one for the RHS
 154         // Some other types like Box and various functions like drop_in_place
 155         // have minimum requirements.
 156
 157         if let hir::Node::Item(hir::Item { kind, span: item_span, .. }) =
 158             self.tcx.hir().get_by_def_id(item_def_id)
 159         {
 160             let (actual_num, generics_span) = match kind.generics() {
 161                 Some(generics) => (
 162                     generics
 163                         .params
 164                         .iter()
 165                         .filter(|p| !self.tcx.has_attr(p.def_id, sym::rustc_host))
 166                         .count(),
 167                     generics.span,
 168                 ),
 169                 None => (0, *item_span),
 170             };
 171
 172             let mut at_least = false;
 173             let required = match lang_item.required_generics() {
 174                 GenericRequirement::Exact(num) if num != actual_num => Some(num),
 175                 GenericRequirement::Minimum(num) if actual_num < num => {
 176                     at_least = true;
 177                     Some(num)}
 178                 ,
 179                 // If the number matches, or there is no requirement, handle it normally
 180                 _ => None,
 181             };
 182
 183             if let Some(num) = required {
 184                 // We are issuing E0718 "incorrect target" here, because while the
 185                 // item kind of the target is correct, the target is still wrong
 186                 // because of the wrong number of generic arguments.
 187                 self.tcx.sess.emit_err(IncorrectTarget {
 188                     span,
 189                     generics_span,
 190                     name: name.as_str(),
 191                     kind: kind.descr(),
 192                     num,
 193                     actual_num,
 194                     at_least,
 195                 });
 196
 197                 // return early to not collect the lang item
 198                 return;
 199             }
 200         }
 201
 202         self.collect_item(lang_item, item_def_id.to_def_id());
 203     }
 204 }
 205
 206 /// Traverses and collects all the lang items in all crates.
 207 fn get_lang_items(tcx: TyCtxt<'_>, (): ()) -> LanguageItems {
 208     // Initialize the collector.
 209     let mut collector = LanguageItemCollector::new(tcx);
 210
 211     // Collect lang items in other crates.
 212     for &cnum in tcx.crates(()).iter() {
 213         for &(def_id, lang_item) in tcx.defined_lang_items(cnum).iter() {
 214             collector.collect_item(lang_item, def_id);
 215         }
 216     }
 217
 218     // Collect lang items in this crate.
 219     let crate_items = tcx.hir_crate_items(());
 220
 221     for id in crate_items.items() {
 222         collector
 223             .check_for_lang(Target::from_def_kind(tcx.def_kind(id.owner_id)), id.owner_id.def_id);
 224
 225         if matches!(tcx.def_kind(id.owner_id), DefKind::Enum) {
 226             let item = tcx.hir().item(id);
 227             if let hir::ItemKind::Enum(def, ..) = &item.kind {
 228                 for variant in def.variants {
 229                     collector.check_for_lang(Target::Variant, variant.def_id);
 230                 }
 231             }
 232         }
 233     }
 234
 235     // FIXME: avoid calling trait_item() when possible
 236     for id in crate_items.trait_items() {
 237         let item = tcx.hir().trait_item(id);
 238         collector.check_for_lang(Target::from_trait_item(item), item.owner_id.def_id)
 239     }
 240
 241     // FIXME: avoid calling impl_item() when possible
 242     for id in crate_items.impl_items() {
 243         let item = tcx.hir().impl_item(id);
 244         collector.check_for_lang(target_from_impl_item(tcx, item), item.owner_id.def_id)
 245     }
 246
 247     // Extract out the found lang items.
 248     let LanguageItemCollector { mut items, .. } = collector;
 249
 250     // Find all required but not-yet-defined lang items.
 251     weak_lang_items::check_crate(tcx, &mut items);
 252
 253     items
 254 }
 255
 256 pub fn provide(providers: &mut Providers) {
 257     providers.get_lang_items = get_lang_items;
 258 }