1 files changed, 113 insertions, 0 deletions
diff --git a/compiler/rustc_passes/src/diagnostic_items.rs b/compiler/rustc_passes/src/diagnostic_items.rs
new file mode 100644
index 000000000..e6b69d898
--- /dev/null
+++ b/compiler/rustc_passes/src/diagnostic_items.rs
@@ -0,0 +1,113 @@
+//! Detecting diagnostic items.
+//!
+//! Diagnostic items are items that are not language-inherent, but can reasonably be expected to
+//! exist for diagnostic purposes. This allows diagnostic authors to refer to specific items
+//! directly, without having to guess module paths and crates.
+//! Examples are:
+//!
+//! * Traits like `Debug`, that have no bearing on language semantics
+//!
+//! * Compiler internal types like `Ty` and `TyCtxt`
+
+use rustc_ast as ast;
+use rustc_hir::diagnostic_items::DiagnosticItems;
+use rustc_middle::ty::query::Providers;
+use rustc_middle::ty::TyCtxt;
+use rustc_span::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
+use rustc_span::symbol::{sym, Symbol};
+
+fn observe_item<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    diagnostic_items: &mut DiagnosticItems,
+    def_id: LocalDefId,
+) {
+    let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
+    let attrs = tcx.hir().attrs(hir_id);
+    if let Some(name) = extract(attrs) {
+        // insert into our table
+        collect_item(tcx, diagnostic_items, name, def_id.to_def_id());
+    }
+}
+
+fn collect_item(tcx: TyCtxt<'_>, items: &mut DiagnosticItems, name: Symbol, item_def_id: DefId) {
+    items.id_to_name.insert(item_def_id, name);
+    if let Some(original_def_id) = items.name_to_id.insert(name, item_def_id) {
+        if original_def_id != item_def_id {
+            let mut err = match tcx.hir().span_if_local(item_def_id) {
+                Some(span) => tcx
+                    .sess
+                    .struct_span_err(span, &format!("duplicate diagnostic item found: `{name}`.")),
+                None => tcx.sess.struct_err(&format!(
+                    "duplicate diagnostic item in crate `{}`: `{}`.",
+                    tcx.crate_name(item_def_id.krate),
+                    name
+                )),
+            };
+            if let Some(span) = tcx.hir().span_if_local(original_def_id) {
+                err.span_note(span, "the diagnostic item is first defined here");
+            } else {
+                err.note(&format!(
+                    "the diagnostic item is first defined in crate `{}`.",
+                    tcx.crate_name(original_def_id.krate)
+                ));
+            }
+            err.emit();
+        }
+    }
+}
+
+/// Extract the first `rustc_diagnostic_item = "$name"` out of a list of attributes.
+fn extract(attrs: &[ast::Attribute]) -> Option<Symbol> {
+    attrs.iter().find_map(|attr| {
+        if attr.has_name(sym::rustc_diagnostic_item) { attr.value_str() } else { None }
+    })
+}
+
+/// Traverse and collect the diagnostic items in the current
+fn diagnostic_items<'tcx>(tcx: TyCtxt<'tcx>, cnum: CrateNum) -> DiagnosticItems {
+    assert_eq!(cnum, LOCAL_CRATE);
+
+    // Initialize the collector.
+    let mut diagnostic_items = DiagnosticItems::default();
+
+    // Collect diagnostic items in this crate.
+    let crate_items = tcx.hir_crate_items(());
+
+    for id in crate_items.items() {
+        observe_item(tcx, &mut diagnostic_items, id.def_id);
+    }
+
+    for id in crate_items.trait_items() {
+        observe_item(tcx, &mut diagnostic_items, id.def_id);
+    }
+
+    for id in crate_items.impl_items() {
+        observe_item(tcx, &mut diagnostic_items, id.def_id);
+    }
+
+    for id in crate_items.foreign_items() {
+        observe_item(tcx, &mut diagnostic_items, id.def_id);
+    }
+
+    diagnostic_items
+}
+
+/// Traverse and collect all the diagnostic items in all crates.
+fn all_diagnostic_items<'tcx>(tcx: TyCtxt<'tcx>, (): ()) -> DiagnosticItems {
+    // Initialize the collector.
+    let mut items = DiagnosticItems::default();
+
+    // Collect diagnostic items in other crates.
+    for &cnum in tcx.crates(()).iter().chain(std::iter::once(&LOCAL_CRATE)) {
+        for (&name, &def_id) in &tcx.diagnostic_items(cnum).name_to_id {
+            collect_item(tcx, &mut items, name, def_id);
+        }
+    }
+
+    items
+}
+
+pub fn provide(providers: &mut Providers) {
+    providers.diagnostic_items = diagnostic_items;
+    providers.all_diagnostic_items = all_diagnostic_items;
+}