Allow nesting subdiagnostics in #[derive(Subdiagnostic)]

compiler/rustc_ast_lowering/src/errors.rs

@@ -44,7 +44,7 @@ impl Subdiagnostic for InvalidAbiReason {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        _: F,
+        _: &F,
     ) {
         #[allow(rustc::untranslatable_diagnostic)]
         diag.note(self.0);

compiler/rustc_ast_passes/src/errors.rs

@@ -382,7 +382,7 @@ impl Subdiagnostic for EmptyLabelManySpans {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        _: F,
+        _: &F,
     ) {
         diag.span_labels(self.0, "");
     }
@@ -751,7 +751,7 @@ impl Subdiagnostic for StableFeature {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        _: F,
+        _: &F,
     ) {
         diag.arg("name", self.name);
         diag.arg("since", self.since);

compiler/rustc_builtin_macros/src/errors.rs

@@ -601,7 +601,7 @@ impl Subdiagnostic for FormatUnusedArg {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        f: F,
+        f: &F,
     ) {
         diag.arg("named", self.named);
         let msg = f(diag, crate::fluent_generated::builtin_macros_format_unused_arg.into());

compiler/rustc_errors/src/diagnostic.rs

@@ -177,15 +177,15 @@ where
 {
     /// Add a subdiagnostic to an existing diagnostic.
     fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
-        self.add_to_diag_with(diag, |_, m| m);
+        self.add_to_diag_with(diag, &|_, m| m);
     }
 
     /// Add a subdiagnostic to an existing diagnostic where `f` is invoked on every message used
     /// (to optionally perform eager translation).
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        f: F,
+        f: &F,
     );
 }
 
@@ -1197,7 +1197,7 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
         dcx: &crate::DiagCtxt,
         subdiagnostic: impl Subdiagnostic,
     ) -> &mut Self {
-        subdiagnostic.add_to_diag_with(self, |diag, msg| {
+        subdiagnostic.add_to_diag_with(self, &|diag, msg| {
             let args = diag.args.iter();
             let msg = diag.subdiagnostic_message_to_diagnostic_message(msg);
             dcx.eagerly_translate(msg, args)

compiler/rustc_errors/src/diagnostic_impls.rs

@@ -227,6 +227,36 @@ impl IntoDiagArg for rustc_lint_defs::Level {
     }
 }
 
+impl<Id> IntoDiagArg for hir::def::Res<Id> {
+    fn into_diag_arg(self) -> DiagArgValue {
+        DiagArgValue::Str(Cow::Borrowed(self.descr()))
+    }
+}
+
+impl IntoDiagArg for DiagLocation {
+    fn into_diag_arg(self) -> DiagArgValue {
+        DiagArgValue::Str(Cow::from(self.to_string()))
+    }
+}
+
+impl IntoDiagArg for Backtrace {
+    fn into_diag_arg(self) -> DiagArgValue {
+        DiagArgValue::Str(Cow::from(self.to_string()))
+    }
+}
+
+impl IntoDiagArg for Level {
+    fn into_diag_arg(self) -> DiagArgValue {
+        DiagArgValue::Str(Cow::from(self.to_string()))
+    }
+}
+
+impl IntoDiagArg for type_ir::ClosureKind {
+    fn into_diag_arg(self) -> DiagArgValue {
+        DiagArgValue::Str(self.as_str().into())
+    }
+}
+
 #[derive(Clone)]
 pub struct DiagSymbolList(Vec<Symbol>);
 
@@ -244,12 +274,6 @@ impl IntoDiagArg for DiagSymbolList {
     }
 }
 
-impl<Id> IntoDiagArg for hir::def::Res<Id> {
-    fn into_diag_arg(self) -> DiagArgValue {
-        DiagArgValue::Str(Cow::Borrowed(self.descr()))
-    }
-}
-
 impl<G: EmissionGuarantee> Diagnostic<'_, G> for TargetDataLayoutErrors<'_> {
     fn into_diag(self, dcx: &DiagCtxt, level: Level) -> Diag<'_, G> {
         match self {
@@ -302,7 +326,7 @@ impl Subdiagnostic for SingleLabelManySpans {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        _: F,
+        _: &F,
     ) {
         diag.span_labels(self.spans, self.label);
     }
@@ -316,24 +340,6 @@ pub struct ExpectedLifetimeParameter {
     pub count: usize,
 }
 
-impl IntoDiagArg for DiagLocation {
-    fn into_diag_arg(self) -> DiagArgValue {
-        DiagArgValue::Str(Cow::from(self.to_string()))
-    }
-}
-
-impl IntoDiagArg for Backtrace {
-    fn into_diag_arg(self) -> DiagArgValue {
-        DiagArgValue::Str(Cow::from(self.to_string()))
-    }
-}
-
-impl IntoDiagArg for Level {
-    fn into_diag_arg(self) -> DiagArgValue {
-        DiagArgValue::Str(Cow::from(self.to_string()))
-    }
-}
-
 #[derive(Subdiagnostic)]
 #[suggestion(errors_indicate_anonymous_lifetime, code = "{suggestion}", style = "verbose")]
 pub struct IndicateAnonymousLifetime {
@@ -343,8 +349,10 @@ pub struct IndicateAnonymousLifetime {
     pub suggestion: String,
 }
 
-impl IntoDiagArg for type_ir::ClosureKind {
-    fn into_diag_arg(self) -> DiagArgValue {
-        DiagArgValue::Str(self.as_str().into())
-    }
+#[derive(Subdiagnostic)]
+pub struct ElidedLifetimeInPathSubdiag {
+    #[subdiagnostic]
+    pub expected: ExpectedLifetimeParameter,
+    #[subdiagnostic]
+    pub indicate: Option<IndicateAnonymousLifetime>,
 }

compiler/rustc_errors/src/lib.rs

@@ -41,8 +41,8 @@ pub use diagnostic::{
     SubdiagMessageOp, Subdiagnostic,
 };
 pub use diagnostic_impls::{
-    DiagArgFromDisplay, DiagSymbolList, ExpectedLifetimeParameter, IndicateAnonymousLifetime,
-    SingleLabelManySpans,
+    DiagArgFromDisplay, DiagSymbolList, ElidedLifetimeInPathSubdiag, ExpectedLifetimeParameter,
+    IndicateAnonymousLifetime, SingleLabelManySpans,
 };
 pub use emitter::ColorConfig;
 pub use rustc_error_messages::{
@@ -1912,27 +1912,24 @@ impl Level {
 }
 
 // FIXME(eddyb) this doesn't belong here AFAICT, should be moved to callsite.
-pub fn add_elided_lifetime_in_path_suggestion<G: EmissionGuarantee>(
+pub fn elided_lifetime_in_path_suggestion(
     source_map: &SourceMap,
-    diag: &mut Diag<'_, G>,
     n: usize,
     path_span: Span,
     incl_angl_brckt: bool,
     insertion_span: Span,
-) {
-    diag.subdiagnostic(diag.dcx, ExpectedLifetimeParameter { span: path_span, count: n });
-    if !source_map.is_span_accessible(insertion_span) {
-        // Do not try to suggest anything if generated by a proc-macro.
-        return;
-    }
-    let anon_lts = vec!["'_"; n].join(", ");
-    let suggestion =
-        if incl_angl_brckt { format!("<{anon_lts}>") } else { format!("{anon_lts}, ") };
-
-    diag.subdiagnostic(
-        diag.dcx,
-        IndicateAnonymousLifetime { span: insertion_span.shrink_to_hi(), count: n, suggestion },
-    );
+) -> ElidedLifetimeInPathSubdiag {
+    let expected = ExpectedLifetimeParameter { span: path_span, count: n };
+    // Do not try to suggest anything if generated by a proc-macro.
+    let indicate = source_map.is_span_accessible(insertion_span).then(|| {
+        let anon_lts = vec!["'_"; n].join(", ");
+        let suggestion =
+            if incl_angl_brckt { format!("<{anon_lts}>") } else { format!("{anon_lts}, ") };
+
+        IndicateAnonymousLifetime { span: insertion_span.shrink_to_hi(), count: n, suggestion }
+    });
+
+    ElidedLifetimeInPathSubdiag { expected, indicate }
 }
 
 pub fn report_ambiguity_error<'a, G: EmissionGuarantee>(

compiler/rustc_hir_typeck/src/errors.rs

@@ -191,7 +191,7 @@ impl Subdiagnostic for TypeMismatchFruTypo {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        _f: F,
+        _f: &F,
     ) {
         diag.arg("expr", self.expr.as_deref().unwrap_or("NONE"));
 
@@ -370,7 +370,7 @@ impl Subdiagnostic for RemoveSemiForCoerce {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        _f: F,
+        _f: &F,
     ) {
         let mut multispan: MultiSpan = self.semi.into();
         multispan.push_span_label(self.expr, fluent::hir_typeck_remove_semi_for_coerce_expr);
@@ -546,7 +546,7 @@ impl rustc_errors::Subdiagnostic for CastUnknownPointerSub {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        f: F,
+        f: &F,
     ) {
         match self {
             CastUnknownPointerSub::To(span) => {

compiler/rustc_infer/src/errors/mod.rs

@@ -239,7 +239,7 @@ impl Subdiagnostic for RegionOriginNote<'_> {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        _f: F,
+        _f: &F,
     ) {
         let mut label_or_note = |span, msg: DiagMessage| {
             let sub_count = diag.children.iter().filter(|d| d.span.is_dummy()).count();
@@ -304,7 +304,7 @@ impl Subdiagnostic for LifetimeMismatchLabels {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        _f: F,
+        _f: &F,
     ) {
         match self {
             LifetimeMismatchLabels::InRet { param_span, ret_span, span, label_var1 } => {
@@ -352,7 +352,7 @@ impl Subdiagnostic for AddLifetimeParamsSuggestion<'_> {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        _f: F,
+        _f: &F,
     ) {
         let mut mk_suggestion = || {
             let (
@@ -454,7 +454,7 @@ impl Subdiagnostic for IntroducesStaticBecauseUnmetLifetimeReq {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         mut self,
         diag: &mut Diag<'_, G>,
-        _f: F,
+        _f: &F,
     ) {
         self.unmet_requirements
             .push_span_label(self.binding_span, fluent::infer_msl_introduces_static);
@@ -773,7 +773,7 @@ impl Subdiagnostic for ConsiderBorrowingParamHelp {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        f: F,
+        f: &F,
     ) {
         let mut type_param_span: MultiSpan = self.spans.clone().into();
         for &span in &self.spans {
@@ -818,7 +818,7 @@ impl Subdiagnostic for DynTraitConstraintSuggestion {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        f: F,
+        f: &F,
     ) {
         let mut multi_span: MultiSpan = vec![self.span].into();
         multi_span.push_span_label(self.span, fluent::infer_dtcs_has_lifetime_req_label);
@@ -865,7 +865,7 @@ impl Subdiagnostic for ReqIntroducedLocations {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         mut self,
         diag: &mut Diag<'_, G>,
-        f: F,
+        f: &F,
     ) {
         for sp in self.spans {
             self.span.push_span_label(sp, fluent::infer_ril_introduced_here);
@@ -888,7 +888,7 @@ impl Subdiagnostic for MoreTargeted {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        _f: F,
+        _f: &F,
     ) {
         diag.code(E0772);
         diag.primary_message(fluent::infer_more_targeted);
@@ -1293,7 +1293,7 @@ impl Subdiagnostic for SuggestTuplePatternMany {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        f: F,
+        f: &F,
     ) {
         diag.arg("path", self.path);
         let message = f(diag, crate::fluent_generated::infer_stp_wrap_many.into());

compiler/rustc_infer/src/errors/note_and_explain.rs

@@ -163,7 +163,7 @@ impl Subdiagnostic for RegionExplanation<'_> {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        f: F,
+        f: &F,
     ) {
         diag.arg("pref_kind", self.prefix);
         diag.arg("suff_kind", self.suffix);

compiler/rustc_lint/src/context/diagnostics.rs

@@ -2,7 +2,7 @@
 #![allow(rustc::untranslatable_diagnostic)]
 
 use rustc_ast::util::unicode::TEXT_FLOW_CONTROL_CHARS;
-use rustc_errors::{add_elided_lifetime_in_path_suggestion, Diag};
+use rustc_errors::{elided_lifetime_in_path_suggestion, Diag};
 use rustc_errors::{Applicability, SuggestionStyle};
 use rustc_middle::middle::stability;
 use rustc_session::lint::BuiltinLintDiag;
@@ -74,13 +74,15 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
             diag.span_note(span_def, "the macro is defined here");
         }
         BuiltinLintDiag::ElidedLifetimesInPaths(n, path_span, incl_angl_brckt, insertion_span) => {
-            add_elided_lifetime_in_path_suggestion(
-                sess.source_map(),
-                diag,
-                n,
-                path_span,
-                incl_angl_brckt,
-                insertion_span,
+            diag.subdiagnostic(
+                sess.dcx(),
+                elided_lifetime_in_path_suggestion(
+                    sess.source_map(),
+                    n,
+                    path_span,
+                    incl_angl_brckt,
+                    insertion_span,
+                ),
             );
         }
         BuiltinLintDiag::UnknownCrateTypes(span, note, sugg) => {

compiler/rustc_lint/src/errors.rs

@@ -27,7 +27,7 @@ impl Subdiagnostic for OverruledAttributeSub {
     fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
         self,
         diag: &mut Diag<'_, G>,
-        _f: F,
+        _f: &F,
     ) {
         match self {
             OverruledAttributeSub::DefaultSource { id } => {