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::struct_span_err;
  17 use rustc_hir as hir;
  18 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
  19 use rustc_hir::itemlikevisit::ItemLikeVisitor;
  20 use rustc_hir::lang_items::{extract, ITEM_REFS};
  21 use rustc_hir::{HirId, LangItem, LanguageItems, Target};
  22
  23 use rustc_middle::ty::query::Providers;
  24
  25 struct LanguageItemCollector<'tcx> {
  26     items: LanguageItems,
  27     tcx: TyCtxt<'tcx>,
  28 }
  29
  30 impl ItemLikeVisitor<'v> for LanguageItemCollector<'tcx> {
  31     fn visit_item(&mut self, item: &hir::Item<'_>) {
  32         self.check_for_lang(Target::from_item(item), item.hir_id());
  33
  34         if let hir::ItemKind::Enum(def, ..) = &item.kind {
  35             for variant in def.variants {
  36                 self.check_for_lang(Target::Variant, variant.id);
  37             }
  38         }
  39     }
  40
  41     fn visit_trait_item(&mut self, trait_item: &hir::TraitItem<'_>) {
  42         self.check_for_lang(Target::from_trait_item(trait_item), trait_item.hir_id())
  43     }
  44
  45     fn visit_impl_item(&mut self, impl_item: &hir::ImplItem<'_>) {
  46         self.check_for_lang(target_from_impl_item(self.tcx, impl_item), impl_item.hir_id())
  47     }
  48
  49     fn visit_foreign_item(&mut self, _: &hir::ForeignItem<'_>) {}
  50 }
  51
  52 impl LanguageItemCollector<'tcx> {
  53     fn new(tcx: TyCtxt<'tcx>) -> LanguageItemCollector<'tcx> {
  54         LanguageItemCollector { tcx, items: LanguageItems::new() }
  55     }
  56
  57     fn check_for_lang(&mut self, actual_target: Target, hir_id: HirId) {
  58         let attrs = self.tcx.hir().attrs(hir_id);
  59         let check_name = |attr, sym| self.tcx.sess.check_name(attr, sym);
  60         if let Some((value, span)) = extract(check_name, &attrs) {
  61             match ITEM_REFS.get(&value).cloned() {
  62                 // Known lang item with attribute on correct target.
  63                 Some((item_index, expected_target)) if actual_target == expected_target => {
  64                     let def_id = self.tcx.hir().local_def_id(hir_id);
  65                     self.collect_item(item_index, def_id.to_def_id());
  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
 185 /// Traverses and collects all the lang items in all crates.
 186 fn collect(tcx: TyCtxt<'_>) -> LanguageItems {
 187     // Initialize the collector.
 188     let mut collector = LanguageItemCollector::new(tcx);
 189
 190     // Collect lang items in other crates.
 191     for &cnum in tcx.crates().iter() {
 192         for &(def_id, item_index) in tcx.defined_lang_items(cnum).iter() {
 193             collector.collect_item(item_index, def_id);
 194         }
 195     }
 196
 197     // Collect lang items in this crate.
 198     tcx.hir().krate().visit_all_item_likes(&mut collector);
 199
 200     // Extract out the found lang items.
 201     let LanguageItemCollector { mut items, .. } = collector;
 202
 203     // Find all required but not-yet-defined lang items.
 204     weak_lang_items::check_crate(tcx, &mut items);
 205
 206     items
 207 }
 208
 209 pub fn provide(providers: &mut Providers) {
 210     providers.get_lang_items = |tcx, id| {
 211         assert_eq!(id, LOCAL_CRATE);
 212         collect(tcx)
 213     };
 214 }