1 //! Detecting language items.
3 //! Language items are items that represent concepts intrinsic to the language
4 //! itself. Examples are:
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.
10 use crate::check_attr::target_from_impl_item;
11 use crate::weak_lang_items;
13 use rustc_ast::Attribute;
14 use rustc_errors::{pluralize, struct_span_err};
16 use rustc_hir::def_id::DefId;
17 use rustc_hir::itemlikevisit::ItemLikeVisitor;
18 use rustc_hir::lang_items::{extract, GenericRequirement, ITEM_REFS};
19 use rustc_hir::{HirId, LangItem, LanguageItems, Target};
20 use rustc_middle::ty::TyCtxt;
21 use rustc_session::cstore::ExternCrate;
24 use rustc_middle::ty::query::Providers;
26 struct LanguageItemCollector<'tcx> {
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());
35 if let hir::ItemKind::Enum(def, ..) = &item.kind {
36 for variant in def.variants {
37 self.check_for_lang(Target::Variant, variant.id);
42 fn visit_trait_item(&mut self, trait_item: &hir::TraitItem<'_>) {
43 self.check_for_lang(Target::from_trait_item(trait_item), trait_item.hir_id())
46 fn visit_impl_item(&mut self, impl_item: &hir::ImplItem<'_>) {
47 self.check_for_lang(target_from_impl_item(self.tcx, impl_item), impl_item.hir_id())
50 fn visit_foreign_item(&mut self, _: &hir::ForeignItem<'_>) {}
53 impl LanguageItemCollector<'tcx> {
54 fn new(tcx: TyCtxt<'tcx>) -> LanguageItemCollector<'tcx> {
55 LanguageItemCollector { tcx, items: LanguageItems::new() }
58 fn check_for_lang(&mut self, actual_target: Target, hir_id: HirId) {
59 let attrs = self.tcx.hir().attrs(hir_id);
60 let check_name = |attr: &Attribute, sym| attr.has_name(sym);
61 if let Some((value, span)) = extract(check_name, &attrs) {
62 match ITEM_REFS.get(&value).cloned() {
63 // Known lang item with attribute on correct target.
64 Some((item_index, expected_target)) if actual_target == expected_target => {
65 self.collect_item_extended(item_index, hir_id, span);
67 // Known lang item with attribute on incorrect target.
68 Some((_, expected_target)) => {
73 "`{}` language item must be applied to a {}",
80 "attribute should be applied to a {}, not a {}",
81 expected_target, actual_target,
92 "definition of an unknown language item: `{}`",
95 .span_label(span, format!("definition of unknown language item `{}`", value))
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!(
113 "found duplicate lang item `{}`",
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),
125 _ => self.tcx.sess.struct_err(&format!(
126 "duplicate lang item in crate `{}`: `{}`.",
127 self.tcx.crate_name(item_def_id.krate),
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");
135 match self.tcx.extern_crate(original_def_id) {
136 Some(ExternCrate { dependency_of, .. }) => {
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)
145 "the lang item is first defined in crate `{}`.",
146 self.tcx.crate_name(original_def_id.krate)
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)
155 let paths: Vec<_> = self
157 .crate_extern_paths(def_id.krate)
159 .map(|p| p.display().to_string())
162 "{} definition in `{}` loaded from {}",
170 note_def("first", original_def_id);
171 note_def("second", item_def_id);
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);
184 // Like collect_item() above, but also checks whether the lang item is declared
185 // with the right number of generic arguments.
186 fn collect_item_extended(&mut self, item_index: usize, hir_id: HirId, span: Span) {
187 let item_def_id = self.tcx.hir().local_def_id(hir_id).to_def_id();
188 let lang_item = LangItem::from_u32(item_index as u32).unwrap();
189 let name = lang_item.name();
191 // Now check whether the lang_item has the expected number of generic
192 // arguments. Generally speaking, binary and indexing operations have
193 // one (for the RHS/index), unary operations have none, the closure
194 // traits have one for the argument list, generators have one for the
195 // resume argument, and ordering/equality relations have one for the RHS
196 // Some other types like Box and various functions like drop_in_place
197 // have minimum requirements.
199 if let hir::Node::Item(hir::Item { kind, span: item_span, .. }) = self.tcx.hir().get(hir_id)
201 let (actual_num, generics_span) = match kind.generics() {
202 Some(generics) => (generics.params.len(), generics.span),
203 None => (0, *item_span),
206 let required = match lang_item.required_generics() {
207 GenericRequirement::Exact(num) if num != actual_num => {
208 Some((format!("{}", num), pluralize!(num)))
210 GenericRequirement::Minimum(num) if actual_num < num => {
211 Some((format!("at least {}", num), pluralize!(num)))
213 // If the number matches, or there is no requirement, handle it normally
217 if let Some((range_str, pluralized)) = required {
218 // We are issuing E0718 "incorrect target" here, because while the
219 // item kind of the target is correct, the target is still wrong
220 // because of the wrong number of generic arguments.
225 "`{}` language item must be applied to a {} with {} generic argument{}",
234 "this {} has {} generic argument{}",
237 pluralize!(actual_num),
242 // return early to not collect the lang item
247 self.collect_item(item_index, item_def_id);
251 /// Traverses and collects all the lang items in all crates.
252 fn get_lang_items(tcx: TyCtxt<'_>, (): ()) -> LanguageItems {
253 // Initialize the collector.
254 let mut collector = LanguageItemCollector::new(tcx);
256 // Collect lang items in other crates.
257 for &cnum in tcx.crates(()).iter() {
258 for &(def_id, item_index) in tcx.defined_lang_items(cnum).iter() {
259 collector.collect_item(item_index, def_id);
263 // Collect lang items in this crate.
264 tcx.hir().visit_all_item_likes(&mut collector);
266 // Extract out the found lang items.
267 let LanguageItemCollector { mut items, .. } = collector;
269 // Find all required but not-yet-defined lang items.
270 weak_lang_items::check_crate(tcx, &mut items);
275 pub fn provide(providers: &mut Providers) {
276 providers.get_lang_items = get_lang_items;