1 files changed, 278 insertions, 0 deletions
diff --git a/compiler/rustc_passes/src/lang_items.rs b/compiler/rustc_passes/src/lang_items.rs
new file mode 100644
index 000000000..79900a90a
--- /dev/null
+++ b/compiler/rustc_passes/src/lang_items.rs
@@ -0,0 +1,278 @@
+//! Detecting language items.
+//!
+//! Language items are items that represent concepts intrinsic to the language
+//! itself. Examples are:
+//!
+//! * Traits that specify "kinds"; e.g., `Sync`, `Send`.
+//! * Traits that represent operators; e.g., `Add`, `Sub`, `Index`.
+//! * Functions called by the compiler itself.
+
+use crate::check_attr::target_from_impl_item;
+use crate::weak_lang_items;
+
+use rustc_errors::{pluralize, struct_span_err};
+use rustc_hir as hir;
+use rustc_hir::def::DefKind;
+use rustc_hir::def_id::DefId;
+use rustc_hir::lang_items::{extract, GenericRequirement, ITEM_REFS};
+use rustc_hir::{HirId, LangItem, LanguageItems, Target};
+use rustc_middle::ty::TyCtxt;
+use rustc_session::cstore::ExternCrate;
+use rustc_span::Span;
+
+use rustc_middle::ty::query::Providers;
+
+struct LanguageItemCollector<'tcx> {
+    items: LanguageItems,
+    tcx: TyCtxt<'tcx>,
+}
+
+impl<'tcx> LanguageItemCollector<'tcx> {
+    fn new(tcx: TyCtxt<'tcx>) -> LanguageItemCollector<'tcx> {
+        LanguageItemCollector { tcx, items: LanguageItems::new() }
+    }
+
+    fn check_for_lang(&mut self, actual_target: Target, hir_id: HirId) {
+        let attrs = self.tcx.hir().attrs(hir_id);
+        if let Some((value, span)) = extract(&attrs) {
+            match ITEM_REFS.get(&value).cloned() {
+                // Known lang item with attribute on correct target.
+                Some((item_index, expected_target)) if actual_target == expected_target => {
+                    self.collect_item_extended(item_index, hir_id, span);
+                }
+                // Known lang item with attribute on incorrect target.
+                Some((_, expected_target)) => {
+                    struct_span_err!(
+                        self.tcx.sess,
+                        span,
+                        E0718,
+                        "`{}` language item must be applied to a {}",
+                        value,
+                        expected_target,
+                    )
+                    .span_label(
+                        span,
+                        format!(
+                            "attribute should be applied to a {}, not a {}",
+                            expected_target, actual_target,
+                        ),
+                    )
+                    .emit();
+                }
+                // Unknown lang item.
+                _ => {
+                    struct_span_err!(
+                        self.tcx.sess,
+                        span,
+                        E0522,
+                        "definition of an unknown language item: `{}`",
+                        value
+                    )
+                    .span_label(span, format!("definition of unknown language item `{}`", value))
+                    .emit();
+                }
+            }
+        }
+    }
+
+    fn collect_item(&mut self, item_index: usize, item_def_id: DefId) {
+        // Check for duplicates.
+        if let Some(original_def_id) = self.items.items[item_index] {
+            if original_def_id != item_def_id {
+                let lang_item = LangItem::from_u32(item_index as u32).unwrap();
+                let name = lang_item.name();
+                let mut err = match self.tcx.hir().span_if_local(item_def_id) {
+                    Some(span) => struct_span_err!(
+                        self.tcx.sess,
+                        span,
+                        E0152,
+                        "found duplicate lang item `{}`",
+                        name
+                    ),
+                    None => match self.tcx.extern_crate(item_def_id) {
+                        Some(ExternCrate { dependency_of, .. }) => {
+                            self.tcx.sess.struct_err(&format!(
+                                "duplicate lang item in crate `{}` (which `{}` depends on): `{}`.",
+                                self.tcx.crate_name(item_def_id.krate),
+                                self.tcx.crate_name(*dependency_of),
+                                name
+                            ))
+                        }
+                        _ => self.tcx.sess.struct_err(&format!(
+                            "duplicate lang item in crate `{}`: `{}`.",
+                            self.tcx.crate_name(item_def_id.krate),
+                            name
+                        )),
+                    },
+                };
+                if let Some(span) = self.tcx.hir().span_if_local(original_def_id) {
+                    err.span_note(span, "the lang item is first defined here");
+                } else {
+                    match self.tcx.extern_crate(original_def_id) {
+                        Some(ExternCrate { dependency_of, .. }) => {
+                            err.note(&format!(
+                                "the lang item is first defined in crate `{}` (which `{}` depends on)",
+                                self.tcx.crate_name(original_def_id.krate),
+                                self.tcx.crate_name(*dependency_of)
+                            ));
+                        }
+                        _ => {
+                            err.note(&format!(
+                                "the lang item is first defined in crate `{}`.",
+                                self.tcx.crate_name(original_def_id.krate)
+                            ));
+                        }
+                    }
+                    let mut note_def = |which, def_id: DefId| {
+                        let crate_name = self.tcx.crate_name(def_id.krate);
+                        let note = if def_id.is_local() {
+                            format!("{} definition in the local crate (`{}`)", which, crate_name)
+                        } else {
+                            let paths: Vec<_> = self
+                                .tcx
+                                .crate_extern_paths(def_id.krate)
+                                .iter()
+                                .map(|p| p.display().to_string())
+                                .collect();
+                            format!(
+                                "{} definition in `{}` loaded from {}",
+                                which,
+                                crate_name,
+                                paths.join(", ")
+                            )
+                        };
+                        err.note(&note);
+                    };
+                    note_def("first", original_def_id);
+                    note_def("second", item_def_id);
+                }
+                err.emit();
+            }
+        }
+
+        // Matched.
+        self.items.items[item_index] = Some(item_def_id);
+        if let Some(group) = LangItem::from_u32(item_index as u32).unwrap().group() {
+            self.items.groups[group as usize].push(item_def_id);
+        }
+    }
+
+    // Like collect_item() above, but also checks whether the lang item is declared
+    // with the right number of generic arguments.
+    fn collect_item_extended(&mut self, item_index: usize, hir_id: HirId, span: Span) {
+        let item_def_id = self.tcx.hir().local_def_id(hir_id).to_def_id();
+        let lang_item = LangItem::from_u32(item_index as u32).unwrap();
+        let name = lang_item.name();
+
+        // Now check whether the lang_item has the expected number of generic
+        // arguments. Generally speaking, binary and indexing operations have
+        // one (for the RHS/index), unary operations have none, the closure
+        // traits have one for the argument list, generators have one for the
+        // resume argument, and ordering/equality relations have one for the RHS
+        // Some other types like Box and various functions like drop_in_place
+        // have minimum requirements.
+
+        if let hir::Node::Item(hir::Item { kind, span: item_span, .. }) = self.tcx.hir().get(hir_id)
+        {
+            let (actual_num, generics_span) = match kind.generics() {
+                Some(generics) => (generics.params.len(), generics.span),
+                None => (0, *item_span),
+            };
+
+            let required = match lang_item.required_generics() {
+                GenericRequirement::Exact(num) if num != actual_num => {
+                    Some((format!("{}", num), pluralize!(num)))
+                }
+                GenericRequirement::Minimum(num) if actual_num < num => {
+                    Some((format!("at least {}", num), pluralize!(num)))
+                }
+                // If the number matches, or there is no requirement, handle it normally
+                _ => None,
+            };
+
+            if let Some((range_str, pluralized)) = required {
+                // We are issuing E0718 "incorrect target" here, because while the
+                // item kind of the target is correct, the target is still wrong
+                // because of the wrong number of generic arguments.
+                struct_span_err!(
+                    self.tcx.sess,
+                    span,
+                    E0718,
+                    "`{}` language item must be applied to a {} with {} generic argument{}",
+                    name,
+                    kind.descr(),
+                    range_str,
+                    pluralized,
+                )
+                .span_label(
+                    generics_span,
+                    format!(
+                        "this {} has {} generic argument{}",
+                        kind.descr(),
+                        actual_num,
+                        pluralize!(actual_num),
+                    ),
+                )
+                .emit();
+
+                // return early to not collect the lang item
+                return;
+            }
+        }
+
+        self.collect_item(item_index, item_def_id);
+    }
+}
+
+/// Traverses and collects all the lang items in all crates.
+fn get_lang_items(tcx: TyCtxt<'_>, (): ()) -> LanguageItems {
+    // Initialize the collector.
+    let mut collector = LanguageItemCollector::new(tcx);
+
+    // Collect lang items in other crates.
+    for &cnum in tcx.crates(()).iter() {
+        for &(def_id, item_index) in tcx.defined_lang_items(cnum).iter() {
+            collector.collect_item(item_index, def_id);
+        }
+    }
+
+    // Collect lang items in this crate.
+    let crate_items = tcx.hir_crate_items(());
+
+    for id in crate_items.items() {
+        collector.check_for_lang(Target::from_def_kind(tcx.def_kind(id.def_id)), id.hir_id());
+
+        if matches!(tcx.def_kind(id.def_id), DefKind::Enum) {
+            let item = tcx.hir().item(id);
+            if let hir::ItemKind::Enum(def, ..) = &item.kind {
+                for variant in def.variants {
+                    collector.check_for_lang(Target::Variant, variant.id);
+                }
+            }
+        }
+    }
+
+    // FIXME: avoid calling trait_item() when possible
+    for id in crate_items.trait_items() {
+        let item = tcx.hir().trait_item(id);
+        collector.check_for_lang(Target::from_trait_item(item), item.hir_id())
+    }
+
+    // FIXME: avoid calling impl_item() when possible
+    for id in crate_items.impl_items() {
+        let item = tcx.hir().impl_item(id);
+        collector.check_for_lang(target_from_impl_item(tcx, item), item.hir_id())
+    }
+
+    // Extract out the found lang items.
+    let LanguageItemCollector { mut items, .. } = collector;
+
+    // Find all required but not-yet-defined lang items.
+    weak_lang_items::check_crate(tcx, &mut items);
+
+    items
+}
+
+pub fn provide(providers: &mut Providers) {
+    providers.get_lang_items = get_lang_items;
+}