Make the more restrictive behavior the default, add changelog

CHANGELOG.md

@@ -21,6 +21,12 @@ The minor version will be incremented upon a breaking change and the patch versi
 ### Breaking
 
 - lang: Remove `state` and `interface` attributes ([#2285](https://github.com/coral-xyz/anchor/pull/2285)).
+- lang: `account(zero_copy)` now derives the `bytemuck::Pod` and `Zeroable` traits instead of using `unsafe impl` ([#2330](https://github.com/coral-xyz/anchor/pull/2330)).
+
+  This imposes useful restrictions on the type, like not having padding bytes and all fields being `Pod` themselves.
+  See [bytemuck::Pod](https://docs.rs/bytemuck/latest/bytemuck/trait.Pod.html) for details.
+
+  Legacy applications can use `account(zero_copy(unsafe_bytemuck_impls))` for the old behavior.
 
 ## [0.26.0] - 2022-12-15
 

lang/attribute/account/src/lib.rs

@@ -66,7 +66,7 @@ pub fn account(
 ) -> proc_macro::TokenStream {
     let mut namespace = "".to_string();
     let mut is_zero_copy = false;
-    let mut safe_bytemuck = false;
+    let mut unsafe_bytemuck = false;
     let args_str = args.to_string();
     let args: Vec<&str> = args_str.split(',').collect();
     if args.len() > 2 {
@@ -81,10 +81,10 @@ pub fn account(
             .collect();
         if ns == "zero_copy" {
             is_zero_copy = true;
-            safe_bytemuck = false;
-        } else if ns == "zero_copy(safe_bytemuck_derives)" {
+            unsafe_bytemuck = false;
+        } else if ns == "zero_copy(unsafe_bytemuck_impls)" {
             is_zero_copy = true;
-            safe_bytemuck = true;
+            unsafe_bytemuck = true;
         } else {
             namespace = ns;
         }
@@ -129,7 +129,7 @@ pub fn account(
     };
 
     let unsafe_bytemuck_impl = {
-        if !safe_bytemuck {
+        if unsafe_bytemuck {
             quote! {
                 #[automatically_derived]
                 unsafe impl #impl_gen anchor_lang::__private::bytemuck::Pod for #account_name #type_gen #where_clause {}
@@ -142,7 +142,7 @@ pub fn account(
     };
 
     let safe_bytemuck_derives = {
-        if safe_bytemuck {
+        if !unsafe_bytemuck {
             quote! {
                 #[derive(bytemuck::Pod, bytemuck::Zeroable)]
             }

lang/tests/generics_test.rs

@@ -22,7 +22,7 @@ where
     pub associated: Account<'info, Associated<U>>,
 }
 
-#[account(zero_copy)]
+#[account(zero_copy(unsafe_bytemuck_impls))]
 pub struct FooAccount<const N: usize> {
     pub data: WrappedU8Array<N>,
 }