From 9a0d277803d54383a7ae40348856e390c322ae25 Mon Sep 17 00:00:00 2001
From: Jack Wrenn <jswrenn@google.com>
Date: Wed, 27 May 2026 10:42:24 +0000
Subject: [PATCH] [wip] Introduce unstable `derive(most_traits)`

gherrit-pr-id: G713b9f3eb6365b11e4e1777ee69e75a6fae758d3
---
 zerocopy-derive/src/derive/mod.rs |  6 +++---
 zerocopy-derive/src/lib.rs        | 32 +++++++++++++++++++++++++++++++
 zerocopy-derive/src/util.rs       |  5 +++++
 3 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/zerocopy-derive/src/derive/mod.rs b/zerocopy-derive/src/derive/mod.rs
index a3d066ed2b..943658ff56 100644
--- a/zerocopy-derive/src/derive/mod.rs
+++ b/zerocopy-derive/src/derive/mod.rs
@@ -13,8 +13,8 @@ use crate::{
     util::{Ctx, DataExt, FieldBounds, ImplBlockBuilder, Trait},
 };
 
-pub(crate) fn derive_immutable(ctx: &Ctx, _top_level: Trait) -> TokenStream {
-    match &ctx.ast.data {
+pub(crate) fn derive_immutable(ctx: &Ctx, _top_level: Trait) -> Result<TokenStream, Error> {
+    Ok(match &ctx.ast.data {
         Data::Struct(strct) => {
             ImplBlockBuilder::new(ctx, strct, Trait::Immutable, FieldBounds::ALL_SELF).build()
         }
@@ -24,7 +24,7 @@ pub(crate) fn derive_immutable(ctx: &Ctx, _top_level: Trait) -> TokenStream {
         Data::Union(unn) => {
             ImplBlockBuilder::new(ctx, unn, Trait::Immutable, FieldBounds::ALL_SELF).build()
         }
-    }
+    })
 }
 
 pub(crate) fn derive_hash(ctx: &Ctx, _top_level: Trait) -> Result<TokenStream, Error> {
diff --git a/zerocopy-derive/src/lib.rs b/zerocopy-derive/src/lib.rs
index a1d10a2ada..fcc070d13c 100644
--- a/zerocopy-derive/src/lib.rs
+++ b/zerocopy-derive/src/lib.rs
@@ -127,6 +127,38 @@ derive!(ByteHash => derive_hash => crate::derive::derive_hash);
 derive!(ByteEq => derive_eq => crate::derive::derive_eq);
 derive!(SplitAt => derive_split_at => crate::derive::derive_split_at);
 
+#[cfg(not(zerocopy_unstable_derive_on_error))]
+#[proc_macro_derive(most_traits, attributes(zerocopy))]
+pub fn most_traits(ts: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let ast = syn::parse_macro_input!(ts as DeriveInput);
+    let ctx = match Ctx::try_from_derive_input(ast) {
+        Ok(ctx) => ctx,
+        Err(e) => return e.into_compile_error().into(),
+    }
+    .skip_on_error();
+
+    // top-level traits for which to attempt a derive
+    let derives: [(fn(&Ctx, Trait) -> _, _); 4] = [
+        (crate::derive::known_layout::derive, Trait::KnownLayout),
+        (crate::derive::derive_immutable, Trait::Immutable),
+        (crate::derive::try_from_bytes::derive_try_from_bytes, Trait::FromBytes),
+        (crate::derive::into_bytes::derive_into_bytes, Trait::IntoBytes),
+    ];
+
+    let mut tokens = proc_macro2::TokenStream::new();
+    for (derive, t) in derives {
+        tokens.extend(derive(&ctx, t))
+    }
+
+    // We wrap in `const_block` as a backstop in case any derive fails
+    // to wrap its output in `const_block` (and thus fails to annotate)
+    // with the full set of `#[allow(...)]` attributes).
+    let ts = const_block([Some(tokens)]);
+    #[cfg(test)]
+    crate::util::testutil::check_hygiene(ts.clone());
+    ts.into()
+}
+
 /// Deprecated: prefer [`FromZeros`] instead.
 #[deprecated(since = "0.8.0", note = "`FromZeroes` was renamed to `FromZeros`")]
 #[doc(hidden)]
diff --git a/zerocopy-derive/src/util.rs b/zerocopy-derive/src/util.rs
index 4ec28bf957..146d33bf97 100644
--- a/zerocopy-derive/src/util.rs
+++ b/zerocopy-derive/src/util.rs
@@ -96,6 +96,11 @@ impl Ctx {
         }
     }
 
+    pub(crate) fn skip_on_error(mut self) -> Self {
+        self.skip_on_error = true;
+        self
+    }
+
     pub(crate) fn core_path(&self) -> TokenStream {
         let zerocopy_crate = &self.zerocopy_crate;
         quote!(#zerocopy_crate::util::macro_util::core_reexport)