resolve: Do not show deprecated helper attributes in typo recommendations

Remove one FIXME, addressing it does not reduce the hacky-ness much, and the logic is going to be removed anyway together with the `legacy_derive_helpers` deprecation lint.

Author: petrochenkov

compiler/rustc_resolve/src/diagnostics.rs

@@ -1041,28 +1041,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     }
                 }
                 Scope::DeriveHelpersCompat => {
-                    let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat);
-                    if filter_fn(res) {
-                        for derive in parent_scope.derives {
-                            let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
-                            let Ok((Some(ext), _)) = this.reborrow().resolve_macro_path(
-                                derive,
-                                MacroKind::Derive,
-                                parent_scope,
-                                false,
-                                false,
-                                None,
-                                None,
-                            ) else {
-                                continue;
-                            };
-                            suggestions.extend(
-                                ext.helper_attrs
-                                    .iter()
-                                    .map(|name| TypoSuggestion::typo_from_name(*name, res)),
-                            );
-                        }
-                    }
+                    // Never recommend deprecated helper attributes.
                 }
                 Scope::MacroRules(macro_rules_scope) => {
                     if let MacroRulesScope::Binding(macro_rules_binding) = macro_rules_scope.get() {

compiler/rustc_resolve/src/ident.rs

@@ -448,11 +448,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         }
                     }
                     Scope::DeriveHelpersCompat => {
-                        // FIXME: Try running this logic earlier, to allocate name bindings for
-                        // legacy derive helpers when creating an attribute invocation with
-                        // following derives. Legacy derive helpers are not common, so it shouldn't
-                        // affect performance. It should also allow to remove the `derives`
-                        // component from `ParentScope`.
                         let mut result = Err(Determinacy::Determined);
                         for derive in parent_scope.derives {
                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };

tests/ui/proc-macro/proc-macro-attributes.stderr

@@ -2,7 +2,13 @@ error: cannot find attribute `C` in this scope
   --> $DIR/proc-macro-attributes.rs:9:3
    |
 LL | #[C]
-   |   ^ help: a derive helper attribute with a similar name exists: `B`
+   |   ^
+   |
+help: the derive macro `B` accepts the similarly named `B` attribute
+   |
+LL - #[C]
+LL + #[B]
+   |
 
 error[E0659]: `B` is ambiguous
   --> $DIR/proc-macro-attributes.rs:6:3