[PATCH 5/8] rust: pin-init: internal: pin_data: move projection struct into `const _: ()` block

[Gary Guo <gary@garyguo.net>]

Most users would not need to mention the generated projection struct. With
the upcoming self-referential support, there needs to be additional
projection structs. Instead of give them publicly visible names, simply
make the name not publicly accessible.

A heavy user of pin projection outside kernel is for async programming.
I've checked tokio codebase there is a single use case and that's for
enums.

Signed-off-by: Gary Guo <gary@garyguo.net>
---
 rust/pin-init/internal/src/pin_data.rs | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/rust/pin-init/internal/src/pin_data.rs b/rust/pin-init/internal/src/pin_data.rs
index ac83f0f73e61..3acced1fe806 100644
--- a/rust/pin-init/internal/src/pin_data.rs
+++ b/rust/pin-init/internal/src/pin_data.rs
@@ -186,10 +186,10 @@ pub(crate) fn pin_data(
 
     Ok(quote! {
         #struct_
-        #projections
         // We put the rest into this const item, because it then will not be accessible to anything
         // outside.
         const _: () = {
+            #projections
             #the_pin_data
             #unpin_impl
             #drop_impl
@@ -322,7 +322,6 @@ fn generate_projections(
     let (impl_generics, ty_generics, whr) = generics.split_for_impl();
     let (_, ty_generics_with_pin_lt, _) = generics_with_pin_lt.split_for_impl();
 
-    let projection = format_ident!("{ident}Projection");
     let this = format_ident!("this");
 
     let (fields_decl, fields_proj): (Vec<_>, Vec<_>) = fields
@@ -371,13 +370,13 @@ fn generate_projections(
     let (projection_def, projection_init) = if is_tuple_struct {
         (
             quote! {
-                #vis struct #projection #generics_with_pin_lt (
+                #vis struct __Projection #generics_with_pin_lt (
                     #(#fields_decl)*
                     ::core::marker::PhantomData<&'__pin mut ()>,
                 ) #whr;
             },
             quote! {
-                #projection(
+                __Projection(
                     #(#fields_proj)*
                     ::core::marker::PhantomData,
                 )
@@ -386,7 +385,7 @@ fn generate_projections(
     } else {
         (
             quote! {
-                #vis struct #projection #generics_with_pin_lt
+                #vis struct __Projection #generics_with_pin_lt
                     #whr
                 {
                     #(#fields_decl)*
@@ -394,7 +393,7 @@ fn generate_projections(
                 }
             },
             quote! {
-                #projection {
+                __Projection {
                     #(#fields_proj)*
                     ___pin_phantom_data: ::core::marker::PhantomData,
                 }
@@ -422,7 +421,7 @@ impl #impl_generics #ident #ty_generics
             #[inline]
             #vis fn project<'__pin>(
                 self: ::core::pin::Pin<&'__pin mut Self>,
-            ) -> #projection #ty_generics_with_pin_lt {
+            ) -> __Projection #ty_generics_with_pin_lt {
                 // SAFETY: we only give access to `&mut` for fields not structurally pinned.
                 let #this = unsafe { ::core::pin::Pin::get_unchecked_mut(self) };
                 #projection_init

-- 
2.54.0