Add #[derive(Clone, Copy)] to anonymous adts

Fix the `AssertBoundIsClone` error for anonymous adts.

Author: frank-king

Diff for: compiler/rustc_ast/src/ast.rs

@@ -2161,6 +2161,10 @@ impl TyKind {
             None
         }
     }
+
+    pub fn is_anon_adt(&self) -> bool {
+        matches!(self, TyKind::AnonStruct(..) | TyKind::AnonUnion(..))
+    }
 }
 
 /// Syntax used to declare a trait object.

Diff for: compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -110,7 +110,9 @@ fn cs_clone_simple(
                 && !seen_type_names.insert(name)
             {
                 // Already produced an assertion for this type.
-            } else {
+                // Anonymous structs or unions must be eliminated as they cannot be
+                // type parameters.
+            } else if !field.ty.kind.is_anon_adt() {
                 // let _: AssertParamIsClone<FieldTy>;
                 super::assert_ty_bounds(
                     cx,

Diff for: compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -123,6 +123,8 @@ fn assert_ty_bounds(
     span: Span,
     assert_path: &[Symbol],
 ) {
+    // Deny anonymous structs or unions to avoid wierd errors.
+    assert!(!ty.kind.is_anon_adt(), "Anonymous structs or unions cannot be type parameters");
     // Generate statement `let _: assert_path<ty>;`.
     let span = cx.with_def_site_ctxt(span);
     let assert_path = cx.path_all(span, true, cx.std_path(assert_path), vec![GenericArg::Type(ty)]);

Diff for: tests/ui/union/unnamed-fields/field_uniqueness_check.rs

@@ -1,11 +1,13 @@
 #![allow(incomplete_features)]
 #![feature(unnamed_fields)]
 
+#[derive(Clone, Copy)]
 #[repr(C)]
 struct Foo {
     a: u8,
 }
 
+#[derive(Clone, Copy)]
 #[repr(C)]
 struct Bar {
     _: union {
@@ -15,6 +17,7 @@ struct Bar {
 
 
 // duplicated with a normal field
+#[derive(Clone, Copy)]
 #[repr(C)]
 union A {
     // referent field
@@ -44,6 +47,7 @@ union A {
 }
 
 // duplicated with a nested field
+#[derive(Clone, Copy)]
 #[repr(C)]
 struct B {
     _: union {
@@ -95,6 +99,7 @@ struct B {
 }
 
 // duplicated with a more nested field
+#[derive(Clone, Copy)]
 #[repr(C)]
 union C {
     _: struct {
@@ -168,6 +173,7 @@ union C {
 }
 
 // duplicated with a nested field in a named adt
+#[derive(Clone, Copy)]
 #[repr(C)]
 struct D {
     // referent field `a`
@@ -196,6 +202,7 @@ struct D {
 }
 
 // duplicated with a nested field in a nested field of a named adt
+#[derive(Clone, Copy)]
 #[repr(C)]
 union D2 {
     // referent field `a`
@@ -224,6 +231,7 @@ union D2 {
 }
 
 // duplicated with a nested field in a named adt in an anonymous adt
+#[derive(Clone, Copy)]
 #[repr(C)]
 struct E {
     _: struct {
@@ -276,6 +284,7 @@ struct E {
 
 // duplicated with a nested field in a named adt in an anonymous adt
 #[repr(C)]
+#[derive(Clone, Copy)]
 union E2 {
     _: struct {
         // referent field `a`