Consider raw pointers fields as normalizable

This is only used to determine the layout, and the layout of a raw
pointer is known, whatever the designated type is. As a side effect,
this makes the layout of `Box<T>` known, even inside `T`, and enables
recursive types.

Author: samueltardieu

clippy_utils/src/ty/mod.rs

@@ -375,6 +375,7 @@ fn is_normalizable_helper<'tcx>(
                     .iter()
                     .all(|field| is_normalizable_helper(cx, param_env, field.ty(cx.tcx, args), cache))
             }),
+            ty::RawPtr(..) => true,
             _ => ty.walk().all(|generic_arg| match generic_arg.unpack() {
                 GenericArgKind::Type(inner_ty) if inner_ty != ty => {
                     is_normalizable_helper(cx, param_env, inner_ty, cache)

tests/ui/large_enum_variant.64bit.stderr

@@ -283,14 +283,30 @@ LL | / enum WithRecursion {
 LL | |     Large([u64; 64]),
    | |     ---------------- the largest variant contains at least 512 bytes
 LL | |     Recursive(Box<WithRecursion>),
-   | |     ----------------------------- the second-largest variant contains at least 0 bytes
+   | |     ----------------------------- the second-largest variant contains at least 8 bytes
 LL | | }
-   | |_^ the entire enum is at least 0 bytes
+   | |_^ the entire enum is at least 520 bytes
    |
 help: consider boxing the large fields to reduce the total size of the enum
    |
 LL |     Large(Box<[u64; 64]>),
    |           ~~~~~~~~~~~~~~
 
-error: aborting due to 17 previous errors
+error: large size difference between variants
+  --> tests/ui/large_enum_variant.rs:168:1
+   |
+LL | / enum LargeEnumWithGenericsAndRecursive {
+LL | |     Ok(),
+   | |     ---- the second-largest variant carries no data at all
+LL | |     Error(WithRecursionAndGenerics<u64>),
+   | |     ------------------------------------ the largest variant contains at least 520 bytes
+LL | | }
+   | |_^ the entire enum is at least 520 bytes
+   |
+help: consider boxing the large fields to reduce the total size of the enum
+   |
+LL |     Error(Box<WithRecursionAndGenerics<u64>>),
+   |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to 18 previous errors