Revert "Rollup merge of rust-lang#127107 - mu001999-contrib:dead/enha…

…nce-2, r=pnkfelix"

This reverts commit 31fe962, reversing
changes made to f203078.

compiler/rustc_passes/src/dead.rs

@@ -277,10 +277,7 @@ 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 {
@@ -300,10 +297,7 @@ 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;
@@ -408,6 +402,31 @@ 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)
             {
@@ -671,9 +690,6 @@ 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);
             }
@@ -829,7 +845,7 @@ 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,

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.
     ///

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);
 }

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 {}
 

tests/ui/const-generics/issues/issue-86535-2.rs

@@ -7,7 +7,6 @@ pub trait Foo {
     fn foo() where [(); Self::ASSOC_C]:;
 }
 
-#[allow(dead_code)]
 struct Bar<const N: &'static ()>;
 impl<const N: &'static ()> Foo for Bar<N> {
     const ASSOC_C: usize = 3;

tests/ui/const-generics/issues/issue-86535.rs

@@ -2,7 +2,6 @@
 #![feature(adt_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;

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> {

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> {

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 {
    |      ^^^^^^^^^^^^

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,
 }
 

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() {}

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
 

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();
 }

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
    |