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::weak_lang_items;
12 use rustc_middle::middle::cstore::ExternCrate;
13 use rustc_middle::ty::TyCtxt;
15 use rustc_errors::struct_span_err;
17 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
18 use rustc_hir::itemlikevisit::ItemLikeVisitor;
19 use rustc_hir::lang_items::{extract, ITEM_REFS};
20 use rustc_hir::{LangItem, LanguageItems, Target};
22 use rustc_middle::ty::query::Providers;
24 struct LanguageItemCollector<'tcx> {
29 impl ItemLikeVisitor<'v> for LanguageItemCollector<'tcx> {
30 fn visit_item(&mut self, item: &hir::Item<'_>) {
31 if let Some((value, span)) = extract(&item.attrs) {
32 let actual_target = Target::from_item(item);
33 match ITEM_REFS.get(&*value.as_str()).cloned() {
34 // Known lang item with attribute on correct target.
35 Some((item_index, expected_target)) if actual_target == expected_target => {
36 let def_id = self.tcx.hir().local_def_id(item.hir_id);
37 self.collect_item(item_index, def_id.to_def_id());
39 // Known lang item with attribute on incorrect target.
40 Some((_, expected_target)) => {
45 "`{}` language item must be applied to a {}",
52 "attribute should be applied to a {}, not a {}",
53 expected_target, actual_target,
64 "definition of an unknown language item: `{}`",
67 .span_label(span, format!("definition of unknown language item `{}`", value))
74 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem<'_>) {
75 // At present, lang items are always items, not trait items.
78 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {
79 // At present, lang items are always items, not impl items.
83 impl LanguageItemCollector<'tcx> {
84 fn new(tcx: TyCtxt<'tcx>) -> LanguageItemCollector<'tcx> {
85 LanguageItemCollector { tcx, items: LanguageItems::new() }
88 fn collect_item(&mut self, item_index: usize, item_def_id: DefId) {
89 // Check for duplicates.
90 if let Some(original_def_id) = self.items.items[item_index] {
91 if original_def_id != item_def_id {
92 let name = LangItem::from_u32(item_index as u32).unwrap().name();
93 let mut err = match self.tcx.hir().span_if_local(item_def_id) {
94 Some(span) => struct_span_err!(
98 "found duplicate lang item `{}`",
101 None => match self.tcx.extern_crate(item_def_id) {
102 Some(ExternCrate { dependency_of, .. }) => {
103 self.tcx.sess.struct_err(&format!(
104 "duplicate lang item in crate `{}` (which `{}` depends on): `{}`.",
105 self.tcx.crate_name(item_def_id.krate),
106 self.tcx.crate_name(*dependency_of),
110 _ => self.tcx.sess.struct_err(&format!(
111 "duplicate lang item in crate `{}`: `{}`.",
112 self.tcx.crate_name(item_def_id.krate),
117 if let Some(span) = self.tcx.hir().span_if_local(original_def_id) {
118 err.span_note(span, "the lang item is first defined here");
120 match self.tcx.extern_crate(original_def_id) {
121 Some(ExternCrate { dependency_of, .. }) => {
123 "the lang item is first defined in crate `{}` (which `{}` depends on)",
124 self.tcx.crate_name(original_def_id.krate),
125 self.tcx.crate_name(*dependency_of)
130 "the lang item is first defined in crate `{}`.",
131 self.tcx.crate_name(original_def_id.krate)
141 self.items.items[item_index] = Some(item_def_id);
145 /// Traverses and collects all the lang items in all crates.
146 fn collect(tcx: TyCtxt<'_>) -> LanguageItems {
147 // Initialize the collector.
148 let mut collector = LanguageItemCollector::new(tcx);
150 // Collect lang items in other crates.
151 for &cnum in tcx.crates().iter() {
152 for &(def_id, item_index) in tcx.defined_lang_items(cnum).iter() {
153 collector.collect_item(item_index, def_id);
157 // Collect lang items in this crate.
158 tcx.hir().krate().visit_all_item_likes(&mut collector);
160 // Extract out the found lang items.
161 let LanguageItemCollector { mut items, .. } = collector;
163 // Find all required but not-yet-defined lang items.
164 weak_lang_items::check_crate(tcx, &mut items);
169 pub fn provide(providers: &mut Providers<'_>) {
170 providers.get_lang_items = |tcx, id| {
171 assert_eq!(id, LOCAL_CRATE);
172 tcx.arena.alloc(collect(tcx))