src/librustc_passes/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::ast::Attribute;
  17 use rustc_errors::struct_span_err;
  18 use rustc_hir as hir;
  19 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
  20 use rustc_hir::itemlikevisit::ItemLikeVisitor;
  21 use rustc_hir::lang_items::{extract, ITEM_REFS};
  22 use rustc_hir::{HirId, LangItem, LanguageItems, Target};
  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, item.attrs)
  34     }
  35
  36     fn visit_trait_item(&mut self, trait_item: &hir::TraitItem<'_>) {
  37         self.check_for_lang(
  38             Target::from_trait_item(trait_item),
  39             trait_item.hir_id,
  40             trait_item.attrs,
  41         )
  42     }
  43
  44     fn visit_impl_item(&mut self, impl_item: &hir::ImplItem<'_>) {
  45         self.check_for_lang(
  46             target_from_impl_item(self.tcx, impl_item),
  47             impl_item.hir_id,
  48             impl_item.attrs,
  49         )
  50     }
  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, attrs: &[Attribute]) {
  59         if let Some((value, span)) = extract(&attrs) {
  60             match ITEM_REFS.get(&*value.as_str()).cloned() {
  61                 // Known lang item with attribute on correct target.
  62                 Some((item_index, expected_target)) if actual_target == expected_target => {
  63                     let def_id = self.tcx.hir().local_def_id(hir_id);
  64                     self.collect_item(item_index, def_id.to_def_id());
  65                 }
  66                 // Known lang item with attribute on incorrect target.
  67                 Some((_, expected_target)) => {
  68                     struct_span_err!(
  69                         self.tcx.sess,
  70                         span,
  71                         E0718,
  72                         "`{}` language item must be applied to a {}",
  73                         value,
  74                         expected_target,
  75                     )
  76                     .span_label(
  77                         span,
  78                         format!(
  79                             "attribute should be applied to a {}, not a {}",
  80                             expected_target, actual_target,
  81                         ),
  82                     )
  83                     .emit();
  84                 }
  85                 // Unknown lang item.
  86                 _ => {
  87                     struct_span_err!(
  88                         self.tcx.sess,
  89                         span,
  90                         E0522,
  91                         "definition of an unknown language item: `{}`",
  92                         value
  93                     )
  94                     .span_label(span, format!("definition of unknown language item `{}`", value))
  95                     .emit();
  96                 }
  97             }
  98         }
  99     }
 100
 101     fn collect_item(&mut self, item_index: usize, item_def_id: DefId) {
 102         // Check for duplicates.
 103         if let Some(original_def_id) = self.items.items[item_index] {
 104             if original_def_id != item_def_id {
 105                 let lang_item = LangItem::from_u32(item_index as u32).unwrap();
 106                 let name = lang_item.name();
 107                 let mut err = match self.tcx.hir().span_if_local(item_def_id) {
 108                     Some(span) => struct_span_err!(
 109                         self.tcx.sess,
 110                         span,
 111                         E0152,
 112                         "found duplicate lang item `{}`",
 113                         name
 114                     ),
 115                     None => match self.tcx.extern_crate(item_def_id) {
 116                         Some(ExternCrate { dependency_of, .. }) => {
 117                             self.tcx.sess.struct_err(&format!(
 118                                 "duplicate lang item in crate `{}` (which `{}` depends on): `{}`.",
 119                                 self.tcx.crate_name(item_def_id.krate),
 120                                 self.tcx.crate_name(*dependency_of),
 121                                 name
 122                             ))
 123                         }
 124                         _ => self.tcx.sess.struct_err(&format!(
 125                             "duplicate lang item in crate `{}`: `{}`.",
 126                             self.tcx.crate_name(item_def_id.krate),
 127                             name
 128                         )),
 129                     },
 130                 };
 131                 if let Some(span) = self.tcx.hir().span_if_local(original_def_id) {
 132                     err.span_note(span, "the lang item is first defined here");
 133                 } else {
 134                     match self.tcx.extern_crate(original_def_id) {
 135                         Some(ExternCrate { dependency_of, .. }) => {
 136                             err.note(&format!(
 137                                 "the lang item is first defined in crate `{}` (which `{}` depends on)",
 138                                 self.tcx.crate_name(original_def_id.krate),
 139                                 self.tcx.crate_name(*dependency_of)
 140                             ));
 141                         }
 142                         _ => {
 143                             err.note(&format!(
 144                                 "the lang item is first defined in crate `{}`.",
 145                                 self.tcx.crate_name(original_def_id.krate)
 146                             ));
 147                         }
 148                     }
 149                     let mut note_def = |which, def_id: DefId| {
 150                         let crate_name = self.tcx.crate_name(def_id.krate);
 151                         let note = if def_id.is_local() {
 152                             format!("{} definition in the local crate (`{}`)", which, crate_name)
 153                         } else {
 154                             let paths: Vec<_> = self
 155                                 .tcx
 156                                 .crate_extern_paths(def_id.krate)
 157                                 .iter()
 158                                 .map(|p| p.display().to_string())
 159                                 .collect();
 160                             format!(
 161                                 "{} definition in `{}` loaded from {}",
 162                                 which,
 163                                 crate_name,
 164                                 paths.join(", ")
 165                             )
 166                         };
 167                         err.note(&note);
 168                     };
 169                     note_def("first", original_def_id);
 170                     note_def("second", item_def_id);
 171                 }
 172                 err.emit();
 173             }
 174         }
 175
 176         // Matched.
 177         self.items.items[item_index] = Some(item_def_id);
 178         if let Some(group) = LangItem::from_u32(item_index as u32).unwrap().group() {
 179             self.items.groups[group as usize].push(item_def_id);
 180         }
 181     }
 182 }
 183
 184 /// Traverses and collects all the lang items in all crates.
 185 fn collect(tcx: TyCtxt<'_>) -> LanguageItems {
 186     // Initialize the collector.
 187     let mut collector = LanguageItemCollector::new(tcx);
 188
 189     // Collect lang items in other crates.
 190     for &cnum in tcx.crates().iter() {
 191         for &(def_id, item_index) in tcx.defined_lang_items(cnum).iter() {
 192             collector.collect_item(item_index, def_id);
 193         }
 194     }
 195
 196     // Collect lang items in this crate.
 197     tcx.hir().krate().visit_all_item_likes(&mut collector);
 198
 199     // Extract out the found lang items.
 200     let LanguageItemCollector { mut items, .. } = collector;
 201
 202     // Find all required but not-yet-defined lang items.
 203     weak_lang_items::check_crate(tcx, &mut items);
 204
 205     items
 206 }
 207
 208 pub fn provide(providers: &mut Providers<'_>) {
 209     providers.get_lang_items = |tcx, id| {
 210         assert_eq!(id, LOCAL_CRATE);
 211         collect(tcx)
 212     };
 213 }