Refactor default_could_be_derived

Author: camsteffen

compiler/rustc_lint/src/default_could_be_derived.rs

@@ -1,14 +1,12 @@
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{Applicability, Diag};
 use rustc_hir as hir;
-use rustc_hir::attrs::AttributeKind;
-use rustc_hir::find_attr;
 use rustc_middle::ty;
 use rustc_middle::ty::TyCtxt;
-use rustc_session::{declare_lint, impl_lint_pass};
-use rustc_span::Symbol;
+use rustc_session::{declare_lint, declare_lint_pass};
 use rustc_span::def_id::DefId;
 use rustc_span::symbol::sym;
+use rustc_span::{Span, Symbol};
 
 use crate::{LateContext, LateLintPass};
 
@@ -52,27 +50,24 @@ declare_lint! {
     @feature_gate = default_field_values;
 }
 
-#[derive(Default)]
-pub(crate) struct DefaultCouldBeDerived;
-
-impl_lint_pass!(DefaultCouldBeDerived => [DEFAULT_OVERRIDES_DEFAULT_FIELDS]);
+declare_lint_pass!(DefaultCouldBeDerived => [DEFAULT_OVERRIDES_DEFAULT_FIELDS]);
 
 impl<'tcx> LateLintPass<'tcx> for DefaultCouldBeDerived {
     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
         // Look for manual implementations of `Default`.
-        let Some(default_def_id) = cx.tcx.get_diagnostic_item(sym::Default) else { return };
-        let hir::ImplItemKind::Fn(_sig, body_id) = impl_item.kind else { return };
-        let parent = cx.tcx.parent(impl_item.owner_id.to_def_id());
-        if find_attr!(cx.tcx.get_all_attrs(parent), AttributeKind::AutomaticallyDerived(..)) {
-            // We don't care about what `#[derive(Default)]` produces in this lint.
+        let hir::ImplItemImplKind::Trait { trait_item_def_id, .. } = impl_item.impl_kind else {
+            return;
+        };
+        if !trait_item_def_id.is_ok_and(|id| cx.tcx.is_diagnostic_item(sym::default_fn, id)) {
             return;
         }
-        let Some(trait_ref) = cx.tcx.impl_trait_ref(parent) else { return };
-        let trait_ref = trait_ref.instantiate_identity();
-        if trait_ref.def_id != default_def_id {
+        let hir::ImplItemKind::Fn(_sig, body_id) = impl_item.kind else { return };
+        let impl_id = cx.tcx.local_parent(impl_item.owner_id.def_id);
+        if cx.tcx.is_automatically_derived(impl_id.to_def_id()) {
+            // We don't care about what `#[derive(Default)]` produces in this lint.
             return;
         }
-        let ty = trait_ref.self_ty();
+        let ty = cx.tcx.type_of(impl_id).instantiate_identity();
         let ty::Adt(def, _) = ty.kind() else { return };
 
         // We now know we have a manually written definition of a `<Type as Default>::default()`.
@@ -150,11 +145,10 @@ impl<'tcx> LateLintPass<'tcx> for DefaultCouldBeDerived {
             return;
         }
 
-        let Some(local) = parent.as_local() else { return };
-        let hir_id = cx.tcx.local_def_id_to_hir_id(local);
-        let hir::Node::Item(item) = cx.tcx.hir_node(hir_id) else { return };
-        cx.tcx.node_span_lint(DEFAULT_OVERRIDES_DEFAULT_FIELDS, hir_id, item.span, |diag| {
-            mk_lint(cx.tcx, diag, type_def_id, parent, orig_fields, fields);
+        let hir_id = cx.tcx.local_def_id_to_hir_id(impl_id);
+        let span = cx.tcx.hir_span_with_body(hir_id);
+        cx.tcx.node_span_lint(DEFAULT_OVERRIDES_DEFAULT_FIELDS, hir_id, span, |diag| {
+            mk_lint(cx.tcx, diag, type_def_id, orig_fields, fields, span);
         });
     }
 }
@@ -163,9 +157,9 @@ fn mk_lint(
     tcx: TyCtxt<'_>,
     diag: &mut Diag<'_, ()>,
     type_def_id: DefId,
-    impl_def_id: DefId,
     orig_fields: FxHashMap<Symbol, &hir::FieldDef<'_>>,
     fields: &[hir::ExprField<'_>],
+    impl_span: Span,
 ) {
     diag.primary_message("`Default` impl doesn't use the declared default field values");
 
@@ -186,18 +180,14 @@ fn mk_lint(
     if removed_all_fields {
         let msg = "to avoid divergence in behavior between `Struct { .. }` and \
                    `<Struct as Default>::default()`, derive the `Default`";
-        if let Some(hir::Node::Item(impl_)) = tcx.hir_get_if_local(impl_def_id) {
-            diag.multipart_suggestion_verbose(
-                msg,
-                vec![
-                    (tcx.def_span(type_def_id).shrink_to_lo(), "#[derive(Default)] ".to_string()),
-                    (impl_.span, String::new()),
-                ],
-                Applicability::MachineApplicable,
-            );
-        } else {
-            diag.help(msg);
-        }
+        diag.multipart_suggestion_verbose(
+            msg,
+            vec![
+                (tcx.def_span(type_def_id).shrink_to_lo(), "#[derive(Default)] ".to_string()),
+                (impl_span, String::new()),
+            ],
+            Applicability::MachineApplicable,
+        );
     } else {
         let msg = "use the default values in the `impl` with `Struct { mandatory_field, .. }` to \
                    avoid them diverging over time";

compiler/rustc_lint/src/lib.rs

@@ -191,7 +191,7 @@ late_lint_methods!(
         BuiltinCombinedModuleLateLintPass,
         [
             ForLoopsOverFallibles: ForLoopsOverFallibles,
-            DefaultCouldBeDerived: DefaultCouldBeDerived::default(),
+            DefaultCouldBeDerived: DefaultCouldBeDerived,
             DerefIntoDynSupertrait: DerefIntoDynSupertrait,
             DropForgetUseless: DropForgetUseless,
             ImproperCTypesLint: ImproperCTypesLint,