Remove rustc_trivial_field_reads from trait Default

Author: estebank

library/core/src/default.rs

@@ -105,7 +105,6 @@ use crate::ascii::Char as AsciiChar;
 #[stable(feature = "rust1", since = "1.0.0")]
 #[const_trait]
 #[rustc_const_unstable(feature = "const_default", issue = "none")]
-#[rustc_trivial_field_reads]
 pub trait Default: Sized {
     /// Returns the "default value" for a type.
     ///

src/tools/clippy/clippy_utils/src/hir_utils.rs

@@ -26,7 +26,6 @@ type SpanlessEqCallback<'a> = dyn FnMut(&Expr<'_>, &Expr<'_>) -> bool + 'a;
 
 /// Determines how paths are hashed and compared for equality.
 #[derive(Copy, Clone, Debug, Default)]
-#[allow(dead_code)]
 pub enum PathCheck {
     /// Paths must match exactly and are hashed by their exact HIR tree.
     ///

tests/ui/deriving/deriving-default-enum.rs

@@ -1,5 +1,4 @@
 //@ run-pass
-#![allow(dead_code)]
 
 // nb: does not impl Default
 #[derive(Debug, PartialEq)]
@@ -9,6 +8,7 @@ struct NotDefault;
 enum Foo {
     #[default]
     Alpha,
+    #[allow(dead_code)]
     Beta(NotDefault),
 }
 
@@ -17,6 +17,7 @@ enum Foo {
 enum MyOption<T> {
     #[default]
     None,
+    #[allow(dead_code)]
     Some(T),
 }
 

tests/ui/lint/dead-code/unused-struct-derive-default.rs

@@ -9,9 +9,8 @@ struct Used;
 #[derive(Default)]
 enum E { //~ NOTE variants in this enum
     #[default]
-    A, //~ ERROR variants `A` and `B` are never constructed
-    //~^ NOTE `E` has a derived impl for the trait `Default`, but this is intentionally ignored during dead code analysis
-    B,
+    A,
+    B, //~ ERROR variant `B` is never constructed
 }
 
 // external crate can call T2::default() to construct T2,

tests/ui/lint/dead-code/unused-struct-derive-default.stderr

@@ -10,19 +10,14 @@ note: the lint level is defined here
 LL | #![deny(dead_code)]
    |         ^^^^^^^^^
 
-error: variants `A` and `B` are never constructed
-  --> $DIR/unused-struct-derive-default.rs:12:5
+error: variant `B` is never constructed
+  --> $DIR/unused-struct-derive-default.rs:13:5
    |
 LL | enum E {
-   |      - variants in this enum
-LL |     #[default]
-LL |     A,
-   |     ^
-LL |
+   |      - variant in this enum
+...
 LL |     B,
    |     ^
-   |
-   = note: `E` has a derived impl for the trait `Default`, but this is intentionally ignored during dead code analysis
 
 error: aborting due to 2 previous errors