Add "zero_copy_pod" feature.

The default "zero_copy" feature unsafe impls the bytemuck::Pod trait.

The new account(zero_copy_pod) and zero_copy_pod macros derive it
instead, which adds desired sanity checks like "has no padding".

lang/attribute/account/src/lib.rs

@@ -66,6 +66,7 @@ pub fn account(
 ) -> proc_macro::TokenStream {
     let mut namespace = "".to_string();
     let mut is_zero_copy = false;
+    let mut is_zero_copy_pod = false;
     let args_str = args.to_string();
     let args: Vec<&str> = args_str.split(',').collect();
     if args.len() > 2 {
@@ -80,6 +81,8 @@ pub fn account(
             .collect();
         if ns == "zero_copy" {
             is_zero_copy = true;
+        } else if ns == "zero_copy_pod" {
+            is_zero_copy_pod = true;
         } else {
             namespace = ns;
         }
@@ -123,17 +126,7 @@ pub fn account(
         }
     };
 
-    proc_macro::TokenStream::from({
-        if is_zero_copy {
-            quote! {
-                #[zero_copy]
-                #account_strct
-
-                #[automatically_derived]
-                unsafe impl #impl_gen anchor_lang::__private::bytemuck::Pod for #account_name #type_gen #where_clause {}
-                #[automatically_derived]
-                unsafe impl #impl_gen anchor_lang::__private::bytemuck::Zeroable for #account_name #type_gen #where_clause {}
-
+    let zero_copy_common = quote! {
                 #[automatically_derived]
                 impl #impl_gen anchor_lang::ZeroCopy for #account_name #type_gen #where_clause {}
 
@@ -169,6 +162,27 @@ pub fn account(
                 }
 
                 #owner_impl
+            };
+
+    proc_macro::TokenStream::from({
+        if is_zero_copy {
+            quote! {
+                #[zero_copy]
+                #account_strct
+
+                #[automatically_derived]
+                unsafe impl #impl_gen anchor_lang::__private::bytemuck::Pod for #account_name #type_gen #where_clause {}
+                #[automatically_derived]
+                unsafe impl #impl_gen anchor_lang::__private::bytemuck::Zeroable for #account_name #type_gen #where_clause {}
+
+                #zero_copy_common
+            }
+        } else if is_zero_copy_pod {
+            quote! {
+                #[zero_copy_pod]
+                #account_strct
+
+                #zero_copy_common
             }
         } else {
             quote! {
@@ -313,6 +327,20 @@ pub fn zero_copy(
     })
 }
 
+#[proc_macro_attribute]
+pub fn zero_copy_pod(
+    _args: proc_macro::TokenStream,
+    item: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    let account_strct = parse_macro_input!(item as syn::ItemStruct);
+
+    proc_macro::TokenStream::from(quote! {
+        #[derive(anchor_lang::__private::ZeroCopyAccessor, Copy, Clone, bytemuck::Pod, bytemuck::Zeroable)]
+        #[repr(C)]
+        #account_strct
+    })
+}
+
 /// Defines the program's ID. This should be used at the root of all Anchor
 /// based programs.
 #[proc_macro]

lang/src/lib.rs

@@ -45,7 +45,7 @@ pub mod system_program;
 mod vec;
 pub use crate::bpf_upgradeable_state::*;
 pub use anchor_attribute_access_control::access_control;
-pub use anchor_attribute_account::{account, declare_id, zero_copy};
+pub use anchor_attribute_account::{account, declare_id, zero_copy, zero_copy_pod};
 pub use anchor_attribute_constant::constant;
 pub use anchor_attribute_error::*;
 pub use anchor_attribute_event::{emit, event};
@@ -241,7 +241,7 @@ pub mod prelude {
         context::Context, context::CpiContext, declare_id, emit, err, error, event, interface,
         program, require, require_eq, require_gt, require_gte, require_keys_eq, require_keys_neq,
         require_neq, solana_program::bpf_loader_upgradeable::UpgradeableLoaderState, source, state,
-        system_program::System, zero_copy, AccountDeserialize, AccountSerialize, Accounts,
+        system_program::System, zero_copy, zero_copy_pod, AccountDeserialize, AccountSerialize, Accounts,
         AccountsExit, AnchorDeserialize, AnchorSerialize, Id, Key, Owner, ProgramData, Result,
         ToAccountInfo, ToAccountInfos, ToAccountMetas,
     };