Remove unreachable and untested suggestion for invalid span enum derive(Default)

compiler/rustc_resolve/messages.ftl

@@ -60,9 +60,6 @@ resolve_change_import_binding =
 resolve_consider_adding_a_derive =
     consider adding a derive
 
-resolve_consider_adding_a_derive_enum =
-    consider adding `#[derive(Default)]` to this enum
-
 resolve_const_not_member_of_trait =
     const `{$const_}` is not a member of trait `{$trait_}`
     .label = not a member of trait `{$trait_}`

compiler/rustc_resolve/src/diagnostics.rs

@@ -32,7 +32,7 @@
 
 use crate::errors::{
     AddedMacroUse, ChangeImportBinding, ChangeImportBindingSuggestion, ConsiderAddingADerive,
-    ConsiderAddingADeriveEnum, ExplicitUnsafeTraits,
+    ExplicitUnsafeTraits,
 };
 use crate::imports::{Import, ImportKind};
 use crate::late::{PatternSource, Rib};
@@ -1393,14 +1393,10 @@ pub(crate) fn unresolved_macro_suggestions(
             let span = self.def_span(def_id);
             let source_map = self.tcx.sess.source_map();
             let head_span = source_map.guess_head_span(span);
-            if let Ok(head) = source_map.span_to_snippet(head_span) {
-                err.subdiagnostic(ConsiderAddingADerive {
-                    span: head_span,
-                    suggestion: format!("#[derive(Default)]\n{head}")
-                });
-            } else {
-                err.subdiagnostic(ConsiderAddingADeriveEnum { span: head_span });
-            }
+            err.subdiagnostic(ConsiderAddingADerive {
+                span: head_span.shrink_to_lo(),
+                suggestion: format!("#[derive(Default)]\n")
+            });
         }
         for ns in [Namespace::MacroNS, Namespace::TypeNS, Namespace::ValueNS] {
             if let Ok(binding) = self.early_resolve_ident_in_lexical_scope(

compiler/rustc_resolve/src/errors.rs

@@ -646,10 +646,3 @@ pub(crate) struct ConsiderAddingADerive {
     pub(crate) span: Span,
     pub(crate) suggestion: String,
 }
-
-#[derive(Subdiagnostic)]
-#[help(resolve_consider_adding_a_derive_enum)]
-pub(crate) struct ConsiderAddingADeriveEnum {
-    #[primary_span]
-    pub(crate) span: Span,
-}

tests/ui/enum/suggest-default-attribute.stderr

@@ -7,7 +7,7 @@ LL |     #[default]
 help: consider adding a derive
    |
 LL + #[derive(Default)]
-LL ~ pub enum Test {
+LL | pub enum Test {
    |
 
 error: aborting due to previous error