Merge the two diagnostics.

compiler/rustc_passes/locales/en-US.ftl

@@ -402,9 +402,6 @@ passes_invalid_attr_at_crate_level =
     `{$name}` attribute cannot be used at crate level
     .suggestion = perhaps you meant to use an outer attribute
 
-passes_duplicate_diagnostic_item =
-    duplicate diagnostic item found: `{$name}`.
-
 passes_duplicate_diagnostic_item_in_crate =
     duplicate diagnostic item in crate `{$crate_name}`: `{$name}`.
     .note = the diagnostic item is first defined in crate `{$orig_crate_name}`.

compiler/rustc_passes/src/diagnostic_items.rs

@@ -15,9 +15,9 @@ use rustc_hir::OwnerId;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::TyCtxt;
 use rustc_span::def_id::{CrateNum, DefId, LOCAL_CRATE};
-use rustc_span::symbol::{kw::Empty, sym, Symbol};
+use rustc_span::symbol::{sym, Symbol};
 
-use crate::errors::{DuplicateDiagnosticItem, DuplicateDiagnosticItemInCrate};
+use crate::errors::DuplicateDiagnosticItemInCrate;
 
 fn observe_item<'tcx>(tcx: TyCtxt<'tcx>, diagnostic_items: &mut DiagnosticItems, owner: OwnerId) {
     let attrs = tcx.hir().attrs(owner.into());
@@ -42,20 +42,16 @@ fn report_duplicate_item(
     original_def_id: DefId,
     item_def_id: DefId,
 ) {
-    let (orig_span, orig_crate_name, have_orig_crate_name) = match original_def_id.as_local() {
-        Some(local_original) => (Some(tcx.def_span(local_original)), Empty, None),
-        None => (None, tcx.crate_name(original_def_id.krate), Some(())),
-    };
-    match tcx.hir().span_if_local(item_def_id) {
-        Some(span) => tcx.sess.emit_err(DuplicateDiagnosticItem { span, name }),
-        None => tcx.sess.emit_err(DuplicateDiagnosticItemInCrate {
-            span: orig_span,
-            orig_crate_name,
-            have_orig_crate_name,
-            crate_name: tcx.crate_name(item_def_id.krate),
-            name,
-        }),
-    };
+    let orig_span = tcx.hir().span_if_local(original_def_id);
+    let duplicate_span = tcx.hir().span_if_local(item_def_id);
+    tcx.sess.emit_err(DuplicateDiagnosticItemInCrate {
+        duplicate_span,
+        orig_span,
+        crate_name: tcx.crate_name(item_def_id.krate),
+        orig_crate_name: tcx.crate_name(original_def_id.krate),
+        different_crates: (item_def_id.krate != original_def_id.krate).then_some(()),
+        name,
+    });
 }
 
 /// Extract the first `rustc_diagnostic_item = "$name"` out of a list of attributes.

compiler/rustc_passes/src/errors.rs

@@ -809,23 +809,17 @@ impl IntoDiagnostic<'_> for InvalidAttrAtCrateLevel {
     }
 }
 
-#[derive(Diagnostic)]
-#[diag(passes_duplicate_diagnostic_item)]
-pub struct DuplicateDiagnosticItem {
-    #[primary_span]
-    pub span: Span,
-    pub name: Symbol,
-}
-
 #[derive(Diagnostic)]
 #[diag(passes_duplicate_diagnostic_item_in_crate)]
 pub struct DuplicateDiagnosticItemInCrate {
+    #[primary_span]
+    pub duplicate_span: Option<Span>,
     #[note(passes_diagnostic_item_first_defined)]
-    pub span: Option<Span>,
-    pub orig_crate_name: Symbol,
+    pub orig_span: Option<Span>,
     #[note]
-    pub have_orig_crate_name: Option<()>,
+    pub different_crates: Option<()>,
     pub crate_name: Symbol,
+    pub orig_crate_name: Symbol,
     pub name: Symbol,
 }
 

tests/ui/tool-attributes/duplicate-diagnostic.rs

@@ -9,5 +9,5 @@ extern crate p1;
 extern crate p2;
 
 #[rustc_diagnostic_item = "Foo"]
-pub struct Foo {} //~ ERROR duplicate diagnostic item found
+pub struct Foo {} //~ ERROR duplicate diagnostic item in crate `duplicate_diagnostic`: `Foo`
 fn main() {}

tests/ui/tool-attributes/duplicate-diagnostic.stderr

@@ -2,11 +2,13 @@ error: duplicate diagnostic item in crate `p2`: `Foo`.
    |
    = note: the diagnostic item is first defined in crate `p1`.
 
-error: duplicate diagnostic item found: `Foo`.
+error: duplicate diagnostic item in crate `duplicate_diagnostic`: `Foo`.
   --> $DIR/duplicate-diagnostic.rs:12:1
    |
 LL | pub struct Foo {}
    | ^^^^^^^^^^^^^^
+   |
+   = note: the diagnostic item is first defined in crate `p2`.
 
 error: aborting due to 2 previous errors