1 files changed, 13 insertions, 8 deletions
diff --git a/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs b/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
index e405462bbb8..12bcd939bd6 100644
--- a/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
+++ b/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
@@ -322,11 +322,7 @@ impl<'a> DiagnosticDeriveVariantBuilder<'a> {
                 let generated_code = self
                     .generate_inner_field_code(
                         attr,
-                        FieldInfo {
-                            binding: binding_info,
-                            ty: inner_ty.inner_type().unwrap_or(&field.ty),
-                            span: &field.span(),
-                        },
+                        FieldInfo { binding: binding_info, ty: inner_ty, span: &field.span() },
                         binding,
                     )
                     .unwrap_or_else(|v| v.to_compile_error());
@@ -418,9 +414,9 @@ impl<'a> DiagnosticDeriveVariantBuilder<'a> {
                 Ok(self.add_spanned_subdiagnostic(binding, &fn_ident, slug))
             }
             SubdiagnosticKind::Note | SubdiagnosticKind::Help | SubdiagnosticKind::Warn => {
-                if type_matches_path(info.ty, &["rustc_span", "Span"]) {
+                if type_matches_path(info.ty.inner_type(), &["rustc_span", "Span"]) {
                     Ok(self.add_spanned_subdiagnostic(binding, &fn_ident, slug))
-                } else if type_is_unit(info.ty) {
+                } else if type_is_unit(info.ty.inner_type()) {
                     Ok(self.add_subdiagnostic(&fn_ident, slug))
                 } else {
                     report_type_error(attr, "`Span` or `()`")?
@@ -432,6 +428,15 @@ impl<'a> DiagnosticDeriveVariantBuilder<'a> {
                 code_field,
                 code_init,
             } => {
+                if let FieldInnerTy::Vec(_) = info.ty {
+                    throw_invalid_attr!(attr, &meta, |diag| {
+                        diag
+                        .note("`#[suggestion(...)]` applied to `Vec` field is ambiguous")
+                        .help("to show a suggestion consisting of multiple parts, use a `Subdiagnostic` annotated with `#[multipart_suggestion(...)]`")
+                        .help("to show a variable set of suggestions, use a `Vec` of `Subdiagnostic`s annotated with `#[suggestion(...)]`")
+                    });
+                }
+
                 let (span_field, mut applicability) = self.span_and_applicability_of_ty(info)?;
 
                 if let Some((static_applicability, span)) = static_applicability {
@@ -489,7 +494,7 @@ impl<'a> DiagnosticDeriveVariantBuilder<'a> {
         &self,
         info: FieldInfo<'_>,
     ) -> Result<(TokenStream, SpannedOption<TokenStream>), DiagnosticDeriveError> {
-        match &info.ty {
+        match &info.ty.inner_type() {
             // If `ty` is `Span` w/out applicability, then use `Applicability::Unspecified`.
             ty @ Type::Path(..) if type_matches_path(ty, &["rustc_span", "Span"]) => {
                 let binding = &info.binding.binding;