Enable #[diagnostic::on_const] for local impls

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -882,55 +882,46 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             let trait_name = self.tcx.item_name(trait_did);
 
             if self.tcx.is_const_trait(trait_did) && !self.tcx.is_const_trait_impl(impl_did) {
-                if let Some(impl_did) = impl_did.as_local()
-                    && let item = self.tcx.hir_expect_item(impl_did)
-                    && let hir::ItemKind::Impl(item) = item.kind
-                    && let Some(of_trait) = item.of_trait
-                {
-                    // trait is const, impl is local and not const
-                    diag.span_suggestion_verbose(
-                        of_trait.trait_ref.path.span.shrink_to_lo(),
-                        format!("make the `impl` of trait `{trait_name}` `const`"),
-                        "const ".to_string(),
-                        Applicability::MaybeIncorrect,
-                    );
-                } else {
+                if !impl_did.is_local() {
                     diag.span_note(
                         impl_span,
                         format!("trait `{trait_name}` is implemented but not `const`"),
                     );
+                }
 
-                    let (condition_options, format_args) = self.on_unimplemented_components(
+                if let Some(command) =
+                    find_attr!(self.tcx, impl_did, OnConst {directive, ..} => directive.as_deref())
+                        .flatten()
+                {
+                    let (_, format_args) = self.on_unimplemented_components(
                         trait_ref,
                         main_obligation,
                         diag.long_ty_path(),
                     );
+                    let CustomDiagnostic { message, label, notes, parent_label: _ } =
+                        command.eval(None, &format_args);
 
-                    if let Some(command) = find_attr!(self.tcx, impl_did, OnConst {directive, ..} => directive.as_deref()).flatten(){
-                        let note = command.eval(
-                            Some(&condition_options),
-                            &format_args,
-                        );
-                        let CustomDiagnostic {
-                            message,
-                            label,
-                            notes,
-                            parent_label,
-                        } = note;
-
-                        if let Some(message) = message {
-                            diag.primary_message(message);
-                        }
-                        if let Some(label) = label {
-                            diag.span_label(impl_span, label);
-                        }
-                        for note in notes {
-                            diag.note(note);
-                        }
-                        if let Some(parent_label) = parent_label {
-                            diag.span_label(impl_span, parent_label);
-                        }
+                    if let Some(message) = message {
+                        diag.primary_message(message);
+                    }
+                    if let Some(label) = label {
+                        diag.span_label(span, label);
+                    }
+                    for note in notes {
+                        diag.note(note);
                     }
+                } else if let Some(impl_did) = impl_did.as_local()
+                    && let item = self.tcx.hir_expect_item(impl_did)
+                    && let hir::ItemKind::Impl(item) = item.kind
+                    && let Some(of_trait) = item.of_trait
+                {
+                    // trait is const, impl is local and not const
+                    diag.span_suggestion_verbose(
+                        of_trait.trait_ref.path.span.shrink_to_lo(),
+                        format!("make the `impl` of trait `{trait_name}` `const`"),
+                        "const ".to_string(),
+                        Applicability::MaybeIncorrect,
+                    );
                 }
             }
         }

tests/ui/diagnostic_namespace/on_const/auxiliary/non_const_impl.rs

@@ -0,0 +1,15 @@
+#![feature(diagnostic_on_const)]
+
+pub struct X;
+
+#[diagnostic::on_const(
+    message = "their message",
+    label = "their label",
+    note = "their note",
+    note = "their other note"
+)]
+impl PartialEq for X {
+    fn eq(&self, _other: &X) -> bool {
+        true
+    }
+}

tests/ui/diagnostic_namespace/on_const/it_works_foreign.rs

@@ -0,0 +1,16 @@
+//@ aux-build: non_const_impl.rs
+#![crate_type = "lib"]
+
+extern crate non_const_impl;
+
+use non_const_impl::X;
+
+const _: () = {
+    let x = X;
+    x == x;
+    //~^ ERROR: their message
+    //~| NOTE: their label
+    //~| NOTE: trait `PartialEq` is implemented but not `const`
+    //~| NOTE: their note
+    //~| NOTE: their other note
+};

tests/ui/diagnostic_namespace/on_const/it_works_foreign.stderr

@@ -0,0 +1,17 @@
+error[E0277]: their message
+  --> $DIR/it_works_foreign.rs:10:5
+   |
+LL |     x == x;
+   |     ^^^^^^ their label
+   |
+note: trait `PartialEq` is implemented but not `const`
+  --> $DIR/auxiliary/non_const_impl.rs:11:1
+   |
+LL | impl PartialEq for X {
+   | ^^^^^^^^^^^^^^^^^^^^
+   = note: their note
+   = note: their other note
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/diagnostic_namespace/on_const/it_works_local.rs

@@ -0,0 +1,25 @@
+#![crate_type = "lib"]
+#![feature(diagnostic_on_const)]
+
+pub struct X;
+
+#[diagnostic::on_const(
+    message = "my message",
+    label = "my label",
+    note = "my note",
+    note = "my other note"
+)]
+impl PartialEq for X {
+    fn eq(&self, _other: &X) -> bool {
+        true
+    }
+}
+
+const _: () = {
+    let x = X;
+    x == x;
+    //~^ ERROR: my message
+    //~| NOTE: my label
+    //~| NOTE: my note
+    //~| NOTE: my other note
+};

tests/ui/diagnostic_namespace/on_const/it_works_local.stderr

@@ -0,0 +1,12 @@
+error[E0277]: my message
+  --> $DIR/it_works_local.rs:20:5
+   |
+LL |     x == x;
+   |     ^^^^^^ my label
+   |
+   = note: my note
+   = note: my other note
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.