Revert "Rollup merge of rust-lang#126302 - mu001999-contrib:ignore/default, r=michaelwoerister"

This reverts commit 58bbade, reversing
changes made to c290e9d.

Author: compiler-errors

Diff for: compiler/rustc_passes/src/dead.rs

@@ -403,31 +403,6 @@ 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)
             {

Diff for: library/alloc/src/sync/tests.rs

@@ -396,7 +396,7 @@ fn show_arc() {
 
 // Make sure deriving works with Arc<T>
 #[derive(Eq, Ord, PartialEq, PartialOrd, Clone, Debug, Default)]
-struct _Foo {
+struct Foo {
     inner: Arc<i32>,
 }
 

Diff for: library/core/src/default.rs

@@ -103,7 +103,6 @@ use crate::ascii::Char as AsciiChar;
 /// ```
 #[cfg_attr(not(test), rustc_diagnostic_item = "Default")]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[cfg_attr(not(bootstrap), rustc_trivial_field_reads)]
 pub trait Default: Sized {
     /// Returns the "default value" for a type.
     ///

Diff for: tests/ui/deriving/deriving-default-enum.rs

@@ -22,6 +22,6 @@ enum MyOption<T> {
 }
 
 fn main() {
-    assert!(matches!(Foo::default(), Foo::Alpha));
+    assert_eq!(Foo::default(), Foo::Alpha);
     assert!(matches!(MyOption::<NotDefault>::default(), MyOption::None));
 }

Diff for: tests/ui/issues/issue-68696-catch-during-unwind.rs

@@ -7,7 +7,6 @@
 
 use std::panic::catch_unwind;
 
-#[allow(dead_code)]
 #[derive(Default)]
 struct Guard;