Revert "Rollup merge of #127107 - mu001999-contrib:dead/enhance-2, r=pnkfelix"

This reverts commit 31fe9628cf830a08e7194a446f66c668aaea86e9, reversing
changes made to f20307851ead9fbbb9fa88bbffb3258a069230a6.

1 files changed, 28 insertions, 12 deletions

diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
index 9c475c9fbf4..78fbcc1f406 100644
--- a/compiler/rustc_passes/src/dead.rs
+++ b/compiler/rustc_passes/src/dead.rs
@@ -278,10 +278,7 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
         pats: &[hir::PatField<'_>],
     ) {
         let variant = match self.typeck_results().node_type(lhs.hir_id).kind() {
-            ty::Adt(adt, _) => {
-                self.check_def_id(adt.did());
-                adt.variant_of_res(res)
-            }
+            ty::Adt(adt, _) => adt.variant_of_res(res),
             _ => span_bug!(lhs.span, "non-ADT in struct pattern"),
         };
         for pat in pats {
@@ -301,10 +298,7 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
         dotdot: hir::DotDotPos,
     ) {
         let variant = match self.typeck_results().node_type(lhs.hir_id).kind() {
-            ty::Adt(adt, _) => {
-                self.check_def_id(adt.did());
-                adt.variant_of_res(res)
-            }
+            ty::Adt(adt, _) => adt.variant_of_res(res),
             _ => {
                 self.tcx.dcx().span_delayed_bug(lhs.span, "non-ADT in tuple struct pattern");
                 return;
@@ -409,6 +403,31 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                 return false;
             }
 
+            // don't ignore impls for Enums and pub Structs whose methods don't have self receiver,
+            // cause external crate may call such methods to construct values of these types
+            if let Some(local_impl_of) = impl_of.as_local()
+                && let Some(local_def_id) = def_id.as_local()
+                && let Some(fn_sig) =
+                    self.tcx.hir().fn_sig_by_hir_id(self.tcx.local_def_id_to_hir_id(local_def_id))
+                && matches!(fn_sig.decl.implicit_self, hir::ImplicitSelfKind::None)
+                && let TyKind::Path(hir::QPath::Resolved(_, path)) =
+                    self.tcx.hir().expect_item(local_impl_of).expect_impl().self_ty.kind
+                && let Res::Def(def_kind, did) = path.res
+            {
+                match def_kind {
+                    // for example, #[derive(Default)] pub struct T(i32);
+                    // external crate can call T::default() to construct T,
+                    // so that don't ignore impl Default for pub Enum and Structs
+                    DefKind::Struct | DefKind::Union if self.tcx.visibility(did).is_public() => {
+                        return false;
+                    }
+                    // don't ignore impl Default for Enums,
+                    // cause we don't know which variant is constructed
+                    DefKind::Enum => return false,
+                    _ => (),
+                };
+            }
+
             if let Some(trait_of) = self.tcx.trait_id_of_impl(impl_of)
                 && self.tcx.has_attr(trait_of, sym::rustc_trivial_field_reads)
             {
@@ -672,9 +691,6 @@ impl<'tcx> Visitor<'tcx> for MarkSymbolVisitor<'tcx> {
                 self.handle_field_pattern_match(pat, res, fields);
             }
             PatKind::Path(ref qpath) => {
-                if let ty::Adt(adt, _) = self.typeck_results().node_type(pat.hir_id).kind() {
-                    self.check_def_id(adt.did());
-                }
                 let res = self.typeck_results().qpath_res(qpath, pat.hir_id);
                 self.handle_res(res);
             }
@@ -830,7 +846,7 @@ fn check_item<'tcx>(
                 // mark the method live if the self_ty is public,
                 // or the method is public and may construct self
                 if tcx.visibility(local_def_id).is_public()
-                    && (ty_and_all_fields_are_public || (ty_is_public && may_construct_self))
+                    && (ty_and_all_fields_are_public || may_construct_self)
                 {
                     // if the impl item is public,
                     // and the ty may be constructed or can be constructed in foreign crates,