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

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

20 files changed, 52 insertions, 164 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,
diff --git a/library/core/src/default.rs b/library/core/src/default.rs
index 4524b352ec8..5cacedcb241 100644
--- a/library/core/src/default.rs
+++ b/library/core/src/default.rs
@@ -103,6 +103,7 @@ 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 --git a/tests/ui-fulldeps/deriving-global.rs b/tests/ui-fulldeps/deriving-global.rs
index 0ba149c9ad6..7783010be44 100644
--- a/tests/ui-fulldeps/deriving-global.rs
+++ b/tests/ui-fulldeps/deriving-global.rs
@@ -17,21 +17,18 @@ mod submod {
     // if any of these are implemented without global calls for any
     // function calls, then being in a submodule will (correctly)
     // cause errors about unrecognised module `std` (or `extra`)
-    #[allow(dead_code)]
     #[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone, Debug, Encodable, Decodable)]
     enum A {
         A1(usize),
         A2(isize),
     }
 
-    #[allow(dead_code)]
     #[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone, Debug, Encodable, Decodable)]
     struct B {
         x: usize,
         y: isize,
     }
 
-    #[allow(dead_code)]
     #[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone, Debug, Encodable, Decodable)]
     struct C(usize, isize);
 }
diff --git a/tests/ui-fulldeps/deriving-hygiene.rs b/tests/ui-fulldeps/deriving-hygiene.rs
index f948d6ac544..a3a6f9e022e 100644
--- a/tests/ui-fulldeps/deriving-hygiene.rs
+++ b/tests/ui-fulldeps/deriving-hygiene.rs
@@ -20,7 +20,6 @@ pub const s: u8 = 1;
 pub const state: u8 = 1;
 pub const cmp: u8 = 1;
 
-#[allow(dead_code)]
 #[derive(Ord, Eq, PartialOrd, PartialEq, Debug, Decodable, Encodable, Hash)]
 struct Foo {}
 
diff --git a/tests/ui/const-generics/issues/issue-86535-2.rs b/tests/ui/const-generics/issues/issue-86535-2.rs
index ab68c6b78df..8d064f3eeb1 100644
--- a/tests/ui/const-generics/issues/issue-86535-2.rs
+++ b/tests/ui/const-generics/issues/issue-86535-2.rs
@@ -9,7 +9,6 @@ pub trait Foo {
         [(); Self::ASSOC_C]:;
 }
 
-#[allow(dead_code)]
 struct Bar<const N: &'static ()>;
 impl<const N: &'static ()> Foo for Bar<N> {
     const ASSOC_C: usize = 3;
diff --git a/tests/ui/const-generics/issues/issue-86535.rs b/tests/ui/const-generics/issues/issue-86535.rs
index 9aaf7ddc9e8..62454f4a388 100644
--- a/tests/ui/const-generics/issues/issue-86535.rs
+++ b/tests/ui/const-generics/issues/issue-86535.rs
@@ -2,7 +2,6 @@
 #![feature(adt_const_params, unsized_const_params, generic_const_exprs)]
 #![allow(incomplete_features, unused_variables)]
 
-#[allow(dead_code)]
 struct F<const S: &'static str>;
 impl<const S: &'static str> X for F<{ S }> {
     const W: usize = 3;
diff --git a/tests/ui/impl-trait/extra-impl-in-trait-impl.fixed b/tests/ui/impl-trait/extra-impl-in-trait-impl.fixed
index 3c4499f0173..886fc1d0058 100644
--- a/tests/ui/impl-trait/extra-impl-in-trait-impl.fixed
+++ b/tests/ui/impl-trait/extra-impl-in-trait-impl.fixed
@@ -1,8 +1,6 @@
 //@ run-rustfix
 
-#[allow(dead_code)]
 struct S<T>(T);
-#[allow(dead_code)]
 struct S2;
 
 impl<T: Default> Default for S<T> {
diff --git a/tests/ui/impl-trait/extra-impl-in-trait-impl.rs b/tests/ui/impl-trait/extra-impl-in-trait-impl.rs
index ac078329524..f3271993867 100644
--- a/tests/ui/impl-trait/extra-impl-in-trait-impl.rs
+++ b/tests/ui/impl-trait/extra-impl-in-trait-impl.rs
@@ -1,8 +1,6 @@
 //@ run-rustfix
 
-#[allow(dead_code)]
 struct S<T>(T);
-#[allow(dead_code)]
 struct S2;
 
 impl<T: Default> impl Default for S<T> {
diff --git a/tests/ui/impl-trait/extra-impl-in-trait-impl.stderr b/tests/ui/impl-trait/extra-impl-in-trait-impl.stderr
index 91c7da5a04f..5aafc8b64d4 100644
--- a/tests/ui/impl-trait/extra-impl-in-trait-impl.stderr
+++ b/tests/ui/impl-trait/extra-impl-in-trait-impl.stderr
@@ -1,23 +1,23 @@
 error: unexpected `impl` keyword
-  --> $DIR/extra-impl-in-trait-impl.rs:8:18
+  --> $DIR/extra-impl-in-trait-impl.rs:6:18
    |
 LL | impl<T: Default> impl Default for S<T> {
    |                  ^^^^^ help: remove the extra `impl`
    |
 note: this is parsed as an `impl Trait` type, but a trait is expected at this position
-  --> $DIR/extra-impl-in-trait-impl.rs:8:18
+  --> $DIR/extra-impl-in-trait-impl.rs:6:18
    |
 LL | impl<T: Default> impl Default for S<T> {
    |                  ^^^^^^^^^^^^
 
 error: unexpected `impl` keyword
-  --> $DIR/extra-impl-in-trait-impl.rs:14:6
+  --> $DIR/extra-impl-in-trait-impl.rs:12:6
    |
 LL | impl impl Default for S2 {
    |      ^^^^^ help: remove the extra `impl`
    |
 note: this is parsed as an `impl Trait` type, but a trait is expected at this position
-  --> $DIR/extra-impl-in-trait-impl.rs:14:6
+  --> $DIR/extra-impl-in-trait-impl.rs:12:6
    |
 LL | impl impl Default for S2 {
    |      ^^^^^^^^^^^^
diff --git a/tests/ui/lint/dead-code/issue-59003.rs b/tests/ui/lint/dead-code/issue-59003.rs
index 319cf2db149..e3dcaca5778 100644
--- a/tests/ui/lint/dead-code/issue-59003.rs
+++ b/tests/ui/lint/dead-code/issue-59003.rs
@@ -4,8 +4,8 @@
 
 #![deny(dead_code)]
 
-#[allow(dead_code)]
 struct Foo {
+    #[allow(dead_code)]
     inner: u32,
 }
 
diff --git a/tests/ui/lint/dead-code/lint-unused-adt-appeared-in-pattern.rs b/tests/ui/lint/dead-code/lint-unused-adt-appeared-in-pattern.rs
deleted file mode 100644
index 25777438456..00000000000
--- a/tests/ui/lint/dead-code/lint-unused-adt-appeared-in-pattern.rs
+++ /dev/null
@@ -1,37 +0,0 @@
-#![deny(dead_code)]
-
-struct Foo(u8); //~ ERROR struct `Foo` is never constructed
-
-enum Bar { //~ ERROR enum `Bar` is never used
-    Var1(u8),
-    Var2(u8),
-}
-
-pub trait Tr1 {
-    fn f1() -> Self;
-}
-
-impl Tr1 for Foo {
-    fn f1() -> Foo {
-        let f = Foo(0);
-        let Foo(tag) = f;
-        Foo(tag)
-    }
-}
-
-impl Tr1 for Bar {
-    fn f1() -> Bar {
-        let b = Bar::Var1(0);
-        let b = if let Bar::Var1(_) = b {
-            Bar::Var1(0)
-        } else {
-            Bar::Var2(0)
-        };
-        match b {
-            Bar::Var1(_) => Bar::Var2(0),
-            Bar::Var2(_) => Bar::Var1(0),
-        }
-    }
-}
-
-fn main() {}
diff --git a/tests/ui/lint/dead-code/lint-unused-adt-appeared-in-pattern.stderr b/tests/ui/lint/dead-code/lint-unused-adt-appeared-in-pattern.stderr
deleted file mode 100644
index 7c1a4b45977..00000000000
--- a/tests/ui/lint/dead-code/lint-unused-adt-appeared-in-pattern.stderr
+++ /dev/null
@@ -1,20 +0,0 @@
-error: struct `Foo` is never constructed
-  --> $DIR/lint-unused-adt-appeared-in-pattern.rs:3:8
-   |
-LL | struct Foo(u8);
-   |        ^^^
-   |
-note: the lint level is defined here
-  --> $DIR/lint-unused-adt-appeared-in-pattern.rs:1:9
-   |
-LL | #![deny(dead_code)]
-   |         ^^^^^^^^^
-
-error: enum `Bar` is never used
-  --> $DIR/lint-unused-adt-appeared-in-pattern.rs:5:6
-   |
-LL | enum Bar {
-   |      ^^^
-
-error: aborting due to 2 previous errors
-
diff --git a/tests/ui/lint/dead-code/not-lint-used-adt-appeared-in-pattern.rs b/tests/ui/lint/dead-code/not-lint-used-adt-appeared-in-pattern.rs
deleted file mode 100644
index 43a2e431904..00000000000
--- a/tests/ui/lint/dead-code/not-lint-used-adt-appeared-in-pattern.rs
+++ /dev/null
@@ -1,32 +0,0 @@
-//@ check-pass
-
-#![deny(dead_code)]
-
-#[repr(u8)]
-#[derive(Copy, Clone, Debug)]
-pub enum RecordField {
-    Target = 1,
-    Level,
-    Module,
-    File,
-    Line,
-    NumArgs,
-}
-
-unsafe trait Pod {}
-
-#[repr(transparent)]
-struct RecordFieldWrapper(RecordField);
-
-unsafe impl Pod for RecordFieldWrapper {}
-
-fn try_read<T: Pod>(buf: &[u8]) -> T {
-    unsafe { std::ptr::read_unaligned(buf.as_ptr() as *const T) }
-}
-
-pub fn foo(buf: &[u8]) -> RecordField {
-    let RecordFieldWrapper(tag) = try_read(buf);
-    tag
-}
-
-fn main() {}
diff --git a/tests/ui/lint/dead-code/unused-adt-impl-pub-trait-with-assoc-const.rs b/tests/ui/lint/dead-code/unused-adt-impl-pub-trait-with-assoc-const.rs
index 658cc3d6c61..bf2fc243e81 100644
--- a/tests/ui/lint/dead-code/unused-adt-impl-pub-trait-with-assoc-const.rs
+++ b/tests/ui/lint/dead-code/unused-adt-impl-pub-trait-with-assoc-const.rs
@@ -1,9 +1,8 @@
 #![deny(dead_code)]
 
 struct T1; //~ ERROR struct `T1` is never constructed
-struct T2; //~ ERROR struct `T2` is never constructed
-pub struct T3(i32); //~ ERROR struct `T3` is never constructed
-pub struct T4(i32); //~ ERROR field `0` is never read
+pub struct T2(i32); //~ ERROR struct `T2` is never constructed
+struct T3;
 
 trait Trait1 { //~ ERROR trait `Trait1` is never used
     const UNUSED: i32;
@@ -12,13 +11,13 @@ trait Trait1 { //~ ERROR trait `Trait1` is never used
 }
 
 pub trait Trait2 {
-    const MAY_USED: i32;
-    fn may_used(&self) {}
+    const USED: i32;
+    fn used(&self) {}
 }
 
 pub trait Trait3 {
-    const MAY_USED: i32;
-    fn may_used() -> Self;
+    const USED: i32;
+    fn construct_self() -> Self;
 }
 
 impl Trait1 for T1 {
@@ -31,34 +30,23 @@ impl Trait1 for T1 {
 impl Trait1 for T2 {
     const UNUSED: i32 = 0;
     fn construct_self() -> Self {
-        Self
+        T2(0)
     }
 }
 
 impl Trait2 for T1 {
-    const MAY_USED: i32 = 0;
+    const USED: i32 = 0;
 }
 
 impl Trait2 for T2 {
-    const MAY_USED: i32 = 0;
-}
-
-impl Trait2 for T3 {
-    const MAY_USED: i32 = 0;
+    const USED: i32 = 0;
 }
 
-impl Trait3 for T2 {
-    const MAY_USED: i32 = 0;
-    fn may_used() -> Self {
+impl Trait3 for T3 {
+    const USED: i32 = 0;
+    fn construct_self() -> Self {
         Self
     }
 }
 
-impl Trait3 for T4 {
-    const MAY_USED: i32 = 0;
-    fn may_used() -> Self {
-        T4(0)
-    }
-}
-
 fn main() {}
diff --git a/tests/ui/lint/dead-code/unused-adt-impl-pub-trait-with-assoc-const.stderr b/tests/ui/lint/dead-code/unused-adt-impl-pub-trait-with-assoc-const.stderr
index 08c7a5cb4b0..174096d9398 100644
--- a/tests/ui/lint/dead-code/unused-adt-impl-pub-trait-with-assoc-const.stderr
+++ b/tests/ui/lint/dead-code/unused-adt-impl-pub-trait-with-assoc-const.stderr
@@ -11,32 +11,16 @@ LL | #![deny(dead_code)]
    |         ^^^^^^^^^
 
 error: struct `T2` is never constructed
-  --> $DIR/unused-adt-impl-pub-trait-with-assoc-const.rs:4:8
+  --> $DIR/unused-adt-impl-pub-trait-with-assoc-const.rs:4:12
    |
-LL | struct T2;
-   |        ^^
-
-error: struct `T3` is never constructed
-  --> $DIR/unused-adt-impl-pub-trait-with-assoc-const.rs:5:12
-   |
-LL | pub struct T3(i32);
+LL | pub struct T2(i32);
    |            ^^
 
-error: field `0` is never read
-  --> $DIR/unused-adt-impl-pub-trait-with-assoc-const.rs:6:15
-   |
-LL | pub struct T4(i32);
-   |            -- ^^^
-   |            |
-   |            field in this struct
-   |
-   = help: consider removing this field
-
 error: trait `Trait1` is never used
-  --> $DIR/unused-adt-impl-pub-trait-with-assoc-const.rs:8:7
+  --> $DIR/unused-adt-impl-pub-trait-with-assoc-const.rs:7:7
    |
 LL | trait Trait1 {
    |       ^^^^^^
 
-error: aborting due to 5 previous errors
+error: aborting due to 3 previous errors
 
diff --git a/tests/ui/lint/dead-code/unused-struct-derive-default.rs b/tests/ui/lint/dead-code/unused-struct-derive-default.rs
index f20b7cb66ee..330ad32dd57 100644
--- a/tests/ui/lint/dead-code/unused-struct-derive-default.rs
+++ b/tests/ui/lint/dead-code/unused-struct-derive-default.rs
@@ -22,5 +22,4 @@ pub struct T2 {
 
 fn main() {
     let _x: Used = Default::default();
-    let _e: E = Default::default();
 }
diff --git a/tests/ui/lint/dead-code/unused-struct-derive-default.stderr b/tests/ui/lint/dead-code/unused-struct-derive-default.stderr
index 7422f9a39f3..bbb0bd7be70 100644
--- a/tests/ui/lint/dead-code/unused-struct-derive-default.stderr
+++ b/tests/ui/lint/dead-code/unused-struct-derive-default.stderr
@@ -4,6 +4,7 @@ error: struct `T` is never constructed
 LL | struct T;
    |        ^
    |
+   = note: `T` has a derived impl for the trait `Default`, but this is intentionally ignored during dead code analysis
 note: the lint level is defined here
   --> $DIR/unused-struct-derive-default.rs:1:9
    |
diff --git a/tests/ui/parser/issues/issue-105366.fixed b/tests/ui/parser/issues/issue-105366.fixed
index 95419dc07f2..7157b647524 100644
--- a/tests/ui/parser/issues/issue-105366.fixed
+++ b/tests/ui/parser/issues/issue-105366.fixed
@@ -1,6 +1,5 @@
 //@ run-rustfix
 
-#[allow(dead_code)]
 struct Foo;
 
 impl From<i32> for Foo {
diff --git a/tests/ui/parser/issues/issue-105366.rs b/tests/ui/parser/issues/issue-105366.rs
index 3278b737991..dc3cb8b343d 100644
--- a/tests/ui/parser/issues/issue-105366.rs
+++ b/tests/ui/parser/issues/issue-105366.rs
@@ -1,6 +1,5 @@
 //@ run-rustfix
 
-#[allow(dead_code)]
 struct Foo;
 
 fn From<i32> for Foo {
diff --git a/tests/ui/parser/issues/issue-105366.stderr b/tests/ui/parser/issues/issue-105366.stderr
index 195305a2ec8..18c04dfaf20 100644
--- a/tests/ui/parser/issues/issue-105366.stderr
+++ b/tests/ui/parser/issues/issue-105366.stderr
@@ -1,5 +1,5 @@
 error: you might have meant to write `impl` instead of `fn`
-  --> $DIR/issue-105366.rs:6:1
+  --> $DIR/issue-105366.rs:5:1
    |
 LL | fn From<i32> for Foo {
    | ^^