Rollup merge of rust-lang#128404 - compiler-errors:revert-dead-code-changes, r=pnkfelix

Revert recent changes to dead code analysis

This is a revert to recent changes to dead code analysis, namely:
* efdf219 Rollup merge of rust-lang#128104 - mu001999-contrib:fix/128053, r=petrochenkov
* a70dc29 Rollup merge of rust-lang#127017 - mu001999-contrib:dead/enhance, r=pnkfelix
* 31fe962 Rollup merge of rust-lang#127107 - mu001999-contrib:dead/enhance-2, r=pnkfelix
* 2724aea Rollup merge of rust-lang#126618 - mu001999-contrib:dead/enhance, r=pnkfelix
* 977c5fd Rollup merge of rust-lang#126315 - mu001999-contrib:fix/126289, r=petrochenkov
* 13314df Rollup merge of rust-lang#125572 - mu001999-contrib:dead/enhance, r=pnkfelix

There is an additional change stacked on top, which suppresses false-negatives that were masked by this work. I believe the functions that are touched in that code are legitimately unused functions and the types are not reachable since this `AnonPipe` type is not publically reachable -- please correct me if I'm wrong cc `@NobodyXu` who added these in #rust-lang#127153.

Some of these reverts (rust-lang#126315 and rust-lang#126618) are only included because it makes the revert apply cleanly, and I think these changes were only done to fix follow-ups from the other PRs?

I apologize for the size of the PR and the churn that it has on the codebase (and for reverting `@mu001999's` work here), but I'm putting this PR up because I am concerned that we're making ad-hoc changes to fix bugs that are fallout of these PRs, and I'd like to see these changes reimplemented in a way that's more separable from the existing dead code pass. I am happy to review any code to reapply these changes in a more separable way.

cc `@mu001999`
r? `@pnkfelix`

Fixes rust-lang#128272
Fixes rust-lang#126169

Author: matthiaskrgr

compiler/rustc_passes/src/dead.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.
     ///

library/core/src/default.rs

@@ -47,6 +47,8 @@ pub fn anon_pipe() -> io::Result<(AnonPipe, AnonPipe)> {
 }
 
 impl AnonPipe {
+    #[allow(dead_code)]
+    // FIXME: This function seems legitimately unused.
     pub fn try_clone(&self) -> io::Result<Self> {
         self.0.duplicate().map(Self)
     }
@@ -85,6 +87,8 @@ impl AnonPipe {
         self.0.is_write_vectored()
     }
 
+    #[allow(dead_code)]
+    // FIXME: This function seems legitimately unused.
     pub fn as_file_desc(&self) -> &FileDesc {
         &self.0
     }

library/std/src/sys/pal/unix/pipe.rs

@@ -241,3 +241,11 @@ impl Parse for QueryGroup {
         Ok(QueryGroup { group_path })
     }
 }
+
+struct Nothing;
+
+impl Parse for Nothing {
+    fn parse(_input: ParseStream<'_>) -> syn::Result<Self> {
+        Ok(Nothing)
+    }
+}

src/tools/rust-analyzer/crates/salsa/salsa-macros/src/database_storage.rs

@@ -22,16 +22,16 @@ impl<T> Struct<T> {
     }
 }
 
-pub struct _LifeTimeOnly<'a> {
+pub struct LifeTimeOnly<'a> {
     _a: &'a u32,
 }
 
-impl<'a> _LifeTimeOnly<'a> {
-    //~ MONO_ITEM fn _LifeTimeOnly::<'_>::foo
+impl<'a> LifeTimeOnly<'a> {
+    //~ MONO_ITEM fn LifeTimeOnly::<'_>::foo
     pub fn foo(&self) {}
-    //~ MONO_ITEM fn _LifeTimeOnly::<'_>::bar
+    //~ MONO_ITEM fn LifeTimeOnly::<'_>::bar
     pub fn bar(&'a self) {}
-    //~ MONO_ITEM fn _LifeTimeOnly::<'_>::baz
+    //~ MONO_ITEM fn LifeTimeOnly::<'_>::baz
     pub fn baz<'b>(&'b self) {}
 
     pub fn non_instantiated<T>(&self) {}

tests/codegen-units/item-collection/generic-impl.rs

@@ -5,44 +5,44 @@
 
 use std::ops::{Add, Deref, Index, IndexMut};
 
-pub struct _Indexable {
+pub struct Indexable {
     data: [u8; 3],
 }
 
-impl Index<usize> for _Indexable {
+impl Index<usize> for Indexable {
     type Output = u8;
 
-    //~ MONO_ITEM fn <_Indexable as std::ops::Index<usize>>::index
+    //~ MONO_ITEM fn <Indexable as std::ops::Index<usize>>::index
     fn index(&self, index: usize) -> &Self::Output {
         if index >= 3 { &self.data[0] } else { &self.data[index] }
     }
 }
 
-impl IndexMut<usize> for _Indexable {
-    //~ MONO_ITEM fn <_Indexable as std::ops::IndexMut<usize>>::index_mut
+impl IndexMut<usize> for Indexable {
+    //~ MONO_ITEM fn <Indexable as std::ops::IndexMut<usize>>::index_mut
     fn index_mut(&mut self, index: usize) -> &mut Self::Output {
         if index >= 3 { &mut self.data[0] } else { &mut self.data[index] }
     }
 }
 
-//~ MONO_ITEM fn <_Equatable as std::cmp::PartialEq>::eq
-//~ MONO_ITEM fn <_Equatable as std::cmp::PartialEq>::ne
+//~ MONO_ITEM fn <Equatable as std::cmp::PartialEq>::eq
+//~ MONO_ITEM fn <Equatable as std::cmp::PartialEq>::ne
 #[derive(PartialEq)]
-pub struct _Equatable(u32);
+pub struct Equatable(u32);
 
-impl Add<u32> for _Equatable {
+impl Add<u32> for Equatable {
     type Output = u32;
 
-    //~ MONO_ITEM fn <_Equatable as std::ops::Add<u32>>::add
+    //~ MONO_ITEM fn <Equatable as std::ops::Add<u32>>::add
     fn add(self, rhs: u32) -> u32 {
         self.0 + rhs
     }
 }
 
-impl Deref for _Equatable {
+impl Deref for Equatable {
     type Target = u32;
 
-    //~ MONO_ITEM fn <_Equatable as std::ops::Deref>::deref
+    //~ MONO_ITEM fn <Equatable as std::ops::Deref>::deref
     fn deref(&self) -> &Self::Target {
         &self.0
     }

tests/codegen-units/item-collection/overloaded-operators.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-global.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-fulldeps/deriving-hygiene.rs

@@ -4,7 +4,6 @@
 extern crate re_rebalance_coherence_lib as lib;
 use lib::*;
 
-#[allow(dead_code)]
 struct Oracle;
 impl Backend for Oracle {}
 impl<'a, T:'a, Tab> QueryFragment<Oracle> for BatchInsert<'a, T, Tab> {}

tests/ui/coherence/re-rebalance-coherence.rs

@@ -11,7 +11,6 @@ async fn foo() {
     async_in_foo(async_out_foo::<4>().await).await;
 }
 
-#[allow(dead_code)]
 struct Faz<const N: usize>;
 
 impl<const N: usize> Foo<N> for Faz<N> {}

tests/ui/const-generics/cross_crate_complex.rs

@@ -2,7 +2,6 @@
 
 //@ run-pass
 
-#[allow(dead_code)]
 #[repr(C)]
 pub struct Loaf<T: Sized, const N: usize = 1> {
     head: [T; N],

tests/ui/const-generics/defaults/repr-c-issue-82792.rs

@@ -16,8 +16,7 @@ impl BlockCipher for BarCipher {
     const BLOCK_SIZE: usize = 32;
 }
 
-#[allow(dead_code)]
-pub struct Block<C>(C);
+pub struct Block<C>(#[allow(dead_code)] C);
 
 pub fn test<C: BlockCipher, const M: usize>()
 where

tests/ui/const-generics/generic_const_exprs/associated-consts.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;

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

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

@@ -6,7 +6,6 @@
 
 use std::mem::MaybeUninit;
 
-#[allow(dead_code)]
 #[repr(transparent)]
 pub struct MaybeUninitWrapper<const N: usize>(MaybeUninit<[u64; N]>);
 

tests/ui/const-generics/transparent-maybeunit-array-wrapper.rs

@@ -2,7 +2,6 @@
 
 use std::ops::Add;
 
-#[allow(dead_code)]
 struct A<B>(B);
 
 impl<B> Add for A<B> where B: Add<Output = B> {
@@ -13,7 +12,6 @@ impl<B> Add for A<B> where B: Add<Output = B> {
     }
 }
 
-#[allow(dead_code)]
 struct C<B>(B);
 
 impl<B: Add<Output = B>> Add for C<B> {
@@ -24,7 +22,6 @@ impl<B: Add<Output = B>> Add for C<B> {
     }
 }
 
-#[allow(dead_code)]
 struct D<B>(B);
 
 impl<B: std::ops::Add<Output = B>> Add for D<B> {
@@ -35,7 +32,6 @@ impl<B: std::ops::Add<Output = B>> Add for D<B> {
     }
 }
 
-#[allow(dead_code)]
 struct E<B>(B);
 
 impl<B: Add<Output = B>> Add for E<B> where B: Add<Output = B> {

tests/ui/generic-associated-types/missing-bounds.fixed

@@ -2,7 +2,6 @@
 
 use std::ops::Add;
 
-#[allow(dead_code)]
 struct A<B>(B);
 
 impl<B> Add for A<B> where B: Add {
@@ -13,7 +12,6 @@ impl<B> Add for A<B> where B: Add {
     }
 }
 
-#[allow(dead_code)]
 struct C<B>(B);
 
 impl<B: Add> Add for C<B> {
@@ -24,7 +22,6 @@ impl<B: Add> Add for C<B> {
     }
 }
 
-#[allow(dead_code)]
 struct D<B>(B);
 
 impl<B> Add for D<B> {
@@ -35,7 +32,6 @@ impl<B> Add for D<B> {
     }
 }
 
-#[allow(dead_code)]
 struct E<B>(B);
 
 impl<B: Add> Add for E<B> where <B as Add>::Output = B {

tests/ui/generic-associated-types/missing-bounds.rs

@@ -1,5 +1,5 @@
 error: equality constraints are not yet supported in `where` clauses
-  --> $DIR/missing-bounds.rs:41:33
+  --> $DIR/missing-bounds.rs:37:33
    |
 LL | impl<B: Add> Add for E<B> where <B as Add>::Output = B {
    |                                 ^^^^^^^^^^^^^^^^^^^^^^ not supported
@@ -11,7 +11,7 @@ LL | impl<B: Add> Add for E<B> where B: Add<Output = B> {
    |                                 ~~~~~~~~~~~~~~~~~~
 
 error[E0308]: mismatched types
-  --> $DIR/missing-bounds.rs:12:11
+  --> $DIR/missing-bounds.rs:11:11
    |
 LL | impl<B> Add for A<B> where B: Add {
    |      - expected this type parameter
@@ -24,14 +24,14 @@ LL |         A(self.0 + rhs.0)
    = note: expected type parameter `B`
              found associated type `<B as Add>::Output`
 help: the type constructed contains `<B as Add>::Output` due to the type of the argument passed
-  --> $DIR/missing-bounds.rs:12:9
+  --> $DIR/missing-bounds.rs:11:9
    |
 LL |         A(self.0 + rhs.0)
    |         ^^--------------^
    |           |
    |           this argument influences the type of `A`
 note: tuple struct defined here
-  --> $DIR/missing-bounds.rs:6:8
+  --> $DIR/missing-bounds.rs:5:8
    |
 LL | struct A<B>(B);
    |        ^
@@ -41,7 +41,7 @@ LL | impl<B> Add for A<B> where B: Add<Output = B> {
    |                                  ++++++++++++
 
 error[E0308]: mismatched types
-  --> $DIR/missing-bounds.rs:23:14
+  --> $DIR/missing-bounds.rs:21:14
    |
 LL | impl<B: Add> Add for C<B> {
    |      - expected this type parameter
@@ -54,7 +54,7 @@ LL |         Self(self.0 + rhs.0)
    = note: expected type parameter `B`
              found associated type `<B as Add>::Output`
 note: tuple struct defined here
-  --> $DIR/missing-bounds.rs:17:8
+  --> $DIR/missing-bounds.rs:15:8
    |
 LL | struct C<B>(B);
    |        ^
@@ -64,7 +64,7 @@ LL | impl<B: Add<Output = B>> Add for C<B> {
    |            ++++++++++++
 
 error[E0369]: cannot add `B` to `B`
-  --> $DIR/missing-bounds.rs:34:21
+  --> $DIR/missing-bounds.rs:31:21
    |
 LL |         Self(self.0 + rhs.0)
    |              ------ ^ ----- B
@@ -77,7 +77,7 @@ LL | impl<B: std::ops::Add<Output = B>> Add for D<B> {
    |       +++++++++++++++++++++++++++
 
 error[E0308]: mismatched types
-  --> $DIR/missing-bounds.rs:46:14
+  --> $DIR/missing-bounds.rs:42:14
    |
 LL | impl<B: Add> Add for E<B> where <B as Add>::Output = B {
    |      - expected this type parameter
@@ -90,7 +90,7 @@ LL |         Self(self.0 + rhs.0)
    = note: expected type parameter `B`
              found associated type `<B as Add>::Output`
 note: tuple struct defined here
-  --> $DIR/missing-bounds.rs:39:8
+  --> $DIR/missing-bounds.rs:35:8
    |
 LL | struct E<B>(B);
    |        ^

tests/ui/generic-associated-types/missing-bounds.stderr

@@ -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.fixed

@@ -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.rs

@@ -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 {
    |      ^^^^^^^^^^^^