Report the note when specified in diagnostic::on_unimplemented

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1317,7 +1317,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 let actual_prefix = rcvr_ty.prefix_string(self.tcx);
                 info!("unimplemented_traits.len() == {}", unimplemented_traits.len());
                 let mut long_ty_file = None;
-                let (primary_message, label) = if unimplemented_traits.len() == 1
+                let (primary_message, label, notes) = if unimplemented_traits.len() == 1
                     && unimplemented_traits_only
                 {
                     unimplemented_traits
@@ -1327,16 +1327,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             if trait_ref.self_ty().references_error() || rcvr_ty.references_error()
                             {
                                 // Avoid crashing.
-                                return (None, None);
+                                return (None, None, Vec::new());
                             }
-                            let OnUnimplementedNote { message, label, .. } = self
+                            let OnUnimplementedNote { message, label, notes, .. } = self
                                 .err_ctxt()
                                 .on_unimplemented_note(trait_ref, &obligation, &mut long_ty_file);
-                            (message, label)
+                            (message, label, notes)
                         })
                         .unwrap()
                 } else {
-                    (None, None)
+                    (None, None, Vec::new())
                 };
                 let primary_message = primary_message.unwrap_or_else(|| {
                     format!(
@@ -1363,6 +1363,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         "the following trait bounds were not satisfied:\n{bound_list}"
                     ));
                 }
+                for note in notes {
+                    err.note(note);
+                }
+
                 suggested_derive = self.suggest_derive(&mut err, unsatisfied_predicates);
 
                 unsatisfied_bounds = true;

tests/ui/methods/suggest-convert-ptr-to-ref.stderr

@@ -11,6 +11,7 @@ note: the method `to_string` exists on the type `&u8`
    = note: the following trait bounds were not satisfied:
            `*const u8: std::fmt::Display`
            which is required by `*const u8: ToString`
+   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 
 error[E0599]: `*mut u8` doesn't implement `std::fmt::Display`
   --> $DIR/suggest-convert-ptr-to-ref.rs:8:22
@@ -25,6 +26,7 @@ note: the method `to_string` exists on the type `&&mut u8`
    = note: the following trait bounds were not satisfied:
            `*mut u8: std::fmt::Display`
            which is required by `*mut u8: ToString`
+   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 
 error[E0599]: no method named `make_ascii_lowercase` found for raw pointer `*mut u8` in the current scope
   --> $DIR/suggest-convert-ptr-to-ref.rs:9:7

tests/ui/traits/custom-on-unimplemented-diagnostic.rs

@@ -0,0 +1,19 @@
+#[diagnostic::on_unimplemented(message = "my message", label = "my label", note = "my note")]
+pub trait ProviderLt {}
+
+pub trait ProviderExt {
+    fn request<R>(&self) {
+        todo!()
+    }
+}
+
+impl<T: ?Sized + ProviderLt> ProviderExt for T {}
+
+struct B;
+
+fn main() {
+    B.request();
+    //~^ my message [E0599]
+    //~| my label
+    //~| my note
+}

tests/ui/traits/custom-on-unimplemented-diagnostic.stderr

@@ -0,0 +1,32 @@
+error[E0599]: my message
+  --> $DIR/custom-on-unimplemented-diagnostic.rs:15:7
+   |
+LL | struct B;
+   | -------- method `request` not found for this struct because it doesn't satisfy `B: ProviderExt` or `B: ProviderLt`
+...
+LL |     B.request();
+   |       ^^^^^^^ my label
+   |
+note: trait bound `B: ProviderLt` was not satisfied
+  --> $DIR/custom-on-unimplemented-diagnostic.rs:10:18
+   |
+LL | impl<T: ?Sized + ProviderLt> ProviderExt for T {}
+   |                  ^^^^^^^^^^  -----------     -
+   |                  |
+   |                  unsatisfied trait bound introduced here
+   = note: my note
+note: the trait `ProviderLt` must be implemented
+  --> $DIR/custom-on-unimplemented-diagnostic.rs:2:1
+   |
+LL | pub trait ProviderLt {}
+   | ^^^^^^^^^^^^^^^^^^^^
+   = help: items from traits can only be used if the trait is implemented and in scope
+note: `ProviderExt` defines an item `request`, perhaps you need to implement it
+  --> $DIR/custom-on-unimplemented-diagnostic.rs:4:1
+   |
+LL | pub trait ProviderExt {
+   | ^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0599`.