Revert "Rollup merge of rust-lang#128104 - mu001999-contrib:fix/128053, r=petrochenkov"

This reverts commit 91b18a0, reversing
changes made to 9aedec9.

Author: compiler-errors

compiler/rustc_passes/src/dead.rs

@@ -73,26 +73,24 @@ fn adt_of<'tcx>(ty: &hir::Ty<'tcx>) -> Option<(LocalDefId, DefKind)> {
 }
 
 fn struct_all_fields_are_public(tcx: TyCtxt<'_>, id: LocalDefId) -> bool {
-    let adt_def = tcx.adt_def(id);
-
-    // skip types contain fields of unit and never type,
-    // it's usually intentional to make the type not constructible
-    let not_require_constructor = adt_def.all_fields().any(|field| {
+    // treat PhantomData and positional ZST as public,
+    // we don't want to lint types which only have them,
+    // cause it's a common way to use such types to check things like well-formedness
+    tcx.adt_def(id).all_fields().all(|field| {
         let field_type = tcx.type_of(field.did).instantiate_identity();
-        field_type.is_unit() || field_type.is_never()
-    });
-
-    not_require_constructor
-        || adt_def.all_fields().all(|field| {
-            let field_type = tcx.type_of(field.did).instantiate_identity();
-            // skip fields of PhantomData,
-            // cause it's a common way to check things like well-formedness
-            if field_type.is_phantom_data() {
-                return true;
-            }
-
-            field.vis.is_public()
-        })
+        if field_type.is_phantom_data() {
+            return true;
+        }
+        let is_positional = field.name.as_str().starts_with(|c: char| c.is_ascii_digit());
+        if is_positional
+            && tcx
+                .layout_of(tcx.param_env(field.did).and(field_type))
+                .map_or(true, |layout| layout.is_zst())
+        {
+            return true;
+        }
+        field.vis.is_public()
+    })
 }
 
 /// check struct and its fields are public or not,

tests/ui/derives/clone-debug-dead-code-in-the-same-struct.rs

@@ -1,9 +1,9 @@
 #![forbid(dead_code)]
 
 #[derive(Debug)]
-pub struct Whatever {
+pub struct Whatever { //~ ERROR struct `Whatever` is never constructed
     pub field0: (),
-    field1: (), //~ ERROR fields `field1`, `field2`, `field3`, and `field4` are never read
+    field1: (),
     field2: (),
     field3: (),
     field4: (),

tests/ui/derives/clone-debug-dead-code-in-the-same-struct.stderr

@@ -1,19 +1,9 @@
-error: fields `field1`, `field2`, `field3`, and `field4` are never read
-  --> $DIR/clone-debug-dead-code-in-the-same-struct.rs:6:5
+error: struct `Whatever` is never constructed
+  --> $DIR/clone-debug-dead-code-in-the-same-struct.rs:4:12
    |
 LL | pub struct Whatever {
-   |            -------- fields in this struct
-LL |     pub field0: (),
-LL |     field1: (),
-   |     ^^^^^^
-LL |     field2: (),
-   |     ^^^^^^
-LL |     field3: (),
-   |     ^^^^^^
-LL |     field4: (),
-   |     ^^^^^^
+   |            ^^^^^^^^
    |
-   = note: `Whatever` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis
 note: the lint level is defined here
   --> $DIR/clone-debug-dead-code-in-the-same-struct.rs:1:11
    |