Merge #135

135: Forbid custom Unpin/Drop impl if trait has Pin<&mut self> receiver r=taiki-e a=taiki-e

If a user creates their own `Unpin` or `Drop` implementation, trait implementations with `Pin<&mut self>` receiver can cause unsoundness.

This was not a problem in `#[auto_enum]` attribute where enums are anonymized, but it becomes a problem when users have access to enums (i.e., when using `#[enum_derive]`).

This is essentially a problem of `derive_utils`, the backend of the derive implementation of this crate, and I was investigating ways to fix it on the `derive_utils` side, but finally decided it would be difficult and removed support for the `Pin<&mut self>` receiver from `derive_utils`. (taiki-e/derive_utils#41)

So, we ensure safety here by an `Unpin` implementation that implements `Unpin` only if all fields are `Unpin` (this also forbids custom `Unpin` implementation), and a hack that forbids custom `Drop` implementation. (Both are what `pin-project` does by default.) The `repr(packed)` check is unnecessary since `repr(packed)` is unavailable on enum.

This would make it impossible to use together with `#[pin_project]` or `pin_project!`, or to create custom `Drop` or `Unpin` implementations -- If someone needs it, it is possible to add an option like use_pin_project to support them, so please leave a comment.

Co-authored-by: Taiki Endo <te316e89@gmail.com>

Cargo.toml

@@ -84,7 +84,7 @@ trusted_len = []
 
 # Note: futures, tokio, serde, and rayon are public dependencies.
 [dependencies]
-derive_utils = { version = "0.11" }
+derive_utils = { version = "0.12" }
 proc-macro2 = "1"
 quote = "1"
 syn = { version = "1.0.56", features = ["full", "visit-mut"] }

src/derive/core/convert.rs

@@ -3,7 +3,7 @@ pub(crate) mod as_ref {
 
     pub(crate) const NAME: &[&str] = &["AsRef"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(data, parse_quote!(::core::convert::AsRef), None, parse_quote! {
             trait AsRef<__T: ?Sized> {
                 #[inline]
@@ -18,7 +18,7 @@ pub(crate) mod as_mut {
 
     pub(crate) const NAME: &[&str] = &["AsMut"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(data, parse_quote!(::core::convert::AsMut), None, parse_quote! {
             trait AsMut<__T: ?Sized> {
                 #[inline]

src/derive/core/fmt.rs

@@ -5,7 +5,7 @@ macro_rules! derive_fmt {
 
             pub(crate) const NAME: &[&str] = &[$($name),*];
 
-            pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+            pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
                 Ok(derive_trait(data, parse_quote!(::core::fmt::$Trait), None, parse_quote! {
                     trait $Trait {
                         #[inline]
@@ -40,7 +40,7 @@ pub(crate) mod write {
 
     pub(crate) const NAME: &[&str] = &["fmt::Write"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(data, parse_quote!(::core::fmt::Write), None, parse_quote! {
             trait Write {
                 #[inline]

src/derive/core/future.rs

@@ -1,16 +1,36 @@
+use quote::ToTokens;
+
 use crate::derive::*;
 
 pub(crate) const NAME: &[&str] = &["Future"];
 
-pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
-    Ok(derive_trait(data, parse_quote!(::core::future::Future), None, parse_quote! {
+pub(crate) fn derive(cx: &Context, data: &Data) -> Result<TokenStream> {
+    cx.needs_pin_projection();
+
+    let ident = &data.ident;
+    let pin = quote!(::core::pin::Pin);
+    let trait_: syn::Path = parse_quote!(::core::future::Future);
+    let mut impl_ = EnumImpl::from_trait(data, trait_.clone(), None, parse_quote! {
         trait Future {
             type Output;
-            #[inline]
-            fn poll(
-                self: ::core::pin::Pin<&mut Self>,
-                cx: &mut ::core::task::Context<'_>,
-            ) -> ::core::task::Poll<Self::Output>;
         }
-    }))
+    })
+    .build_impl();
+
+    let poll = data
+        .variant_idents()
+        .map(|v| quote!(#ident::#v(x) => #trait_::poll(#pin::new_unchecked(x), cx)));
+    impl_.items.push(parse_quote! {
+        #[inline]
+        fn poll(
+            self: #pin<&mut Self>,
+            cx: &mut ::core::task::Context<'_>,
+        ) -> ::core::task::Poll<Self::Output> {
+            unsafe {
+                match self.get_unchecked_mut() { #(#poll,)* }
+            }
+        }
+    });
+
+    Ok(impl_.into_token_stream())
 }

src/derive/core/iter.rs

@@ -3,7 +3,7 @@ pub(crate) mod iterator {
 
     pub(crate) const NAME: &[&str] = &["Iterator"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         // TODO: When `try_trait` stabilized, add `try_fold` and remove `fold`, `find` etc. conditionally.
 
         // It is equally efficient if `try_fold` can be used.
@@ -47,7 +47,7 @@ pub(crate) mod double_ended_iterator {
 
     pub(crate) const NAME: &[&str] = &["DoubleEndedIterator"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         // TODO: When `try_trait` stabilized, add `try_rfold` and remove `rfold` and `rfind` conditionally.
 
         // It is equally efficient if `try_rfold` can be used.
@@ -82,7 +82,7 @@ pub(crate) mod exact_size_iterator {
 
     pub(crate) const NAME: &[&str] = &["ExactSizeIterator"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         // TODO: When `exact_size_is_empty` stabilized, add `is_empty` conditionally.
 
         Ok(derive_trait(
@@ -104,7 +104,7 @@ pub(crate) mod fused_iterator {
 
     pub(crate) const NAME: &[&str] = &["FusedIterator"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(
             data,
             parse_quote!(::core::iter::FusedIterator),
@@ -122,7 +122,7 @@ pub(crate) mod trusted_len {
 
     pub(crate) const NAME: &[&str] = &["TrustedLen"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(
             data,
             parse_quote!(::core::iter::TrustedLen),
@@ -139,7 +139,7 @@ pub(crate) mod extend {
 
     pub(crate) const NAME: &[&str] = &["Extend"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(data, parse_quote!(::core::iter::Extend), None, parse_quote! {
             trait Extend<__A> {
                 #[inline]

src/derive/core/ops.rs

@@ -4,7 +4,7 @@ pub(crate) mod deref {
 
     pub(crate) const NAME: &[&str] = &["Deref"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(data, parse_quote!(::core::ops::Deref), None, parse_quote! {
             trait Deref {
                 type Target;
@@ -21,7 +21,7 @@ pub(crate) mod deref_mut {
 
     pub(crate) const NAME: &[&str] = &["DerefMut"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(
             data,
             parse_quote!(::core::ops::DerefMut),
@@ -42,7 +42,7 @@ pub(crate) mod index {
 
     pub(crate) const NAME: &[&str] = &["Index"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(data, parse_quote!(::core::ops::Index), None, parse_quote! {
             trait Index<__Idx> {
                 type Output;
@@ -59,7 +59,7 @@ pub(crate) mod index_mut {
 
     pub(crate) const NAME: &[&str] = &["IndexMut"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(
             data,
             parse_quote!(::core::ops::IndexMut),
@@ -80,7 +80,7 @@ pub(crate) mod range_bounds {
 
     pub(crate) const NAME: &[&str] = &["RangeBounds"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(data, parse_quote!(::core::ops::RangeBounds), None, parse_quote! {
             trait RangeBounds<__T: ?Sized> {
                 #[inline]
@@ -94,22 +94,42 @@ pub(crate) mod range_bounds {
 
 #[cfg(feature = "generator_trait")]
 pub(crate) mod generator {
+    use quote::ToTokens;
+
     use crate::derive::*;
 
     pub(crate) const NAME: &[&str] = &["Generator"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
-        Ok(derive_trait(data, parse_quote!(::core::ops::Generator), None, parse_quote! {
+    pub(crate) fn derive(cx: &Context, data: &Data) -> Result<TokenStream> {
+        cx.needs_pin_projection();
+
+        let ident = &data.ident;
+        let pin = quote!(::core::pin::Pin);
+        let trait_: syn::Path = parse_quote!(::core::ops::Generator);
+        let mut impl_ = EnumImpl::from_trait(data, trait_.clone(), None, parse_quote! {
             trait Generator<R> {
                 type Yield;
                 type Return;
-                #[inline]
-                fn resume(
-                    self: ::core::pin::Pin<&mut Self>,
-                    arg: R,
-                ) -> ::core::ops::GeneratorState<Self::Yield, Self::Return>;
             }
-        }))
+        })
+        .build_impl();
+
+        let resume = data
+            .variant_idents()
+            .map(|v| quote!(#ident::#v(x) => #trait_::resume(#pin::new_unchecked(x), arg)));
+        impl_.items.push(parse_quote! {
+            #[inline]
+            fn resume(
+                self: #pin<&mut Self>,
+                arg: R,
+            ) -> ::core::ops::GeneratorState<Self::Yield, Self::Return> {
+                unsafe {
+                    match self.get_unchecked_mut() { #(#resume,)* }
+                }
+            }
+        });
+
+        Ok(impl_.into_token_stream())
     }
 }
 
@@ -122,7 +142,7 @@ pub(crate) mod fn_ {
 
     pub(crate) const NAME: &[&str] = &["Fn"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         let trait_path = quote!(::core::ops::Fn);
         let trait_ = quote!(#trait_path(__T) -> __U);
         let fst = data.field_types().next();
@@ -155,7 +175,7 @@ pub(crate) mod fn_mut {
 
     pub(crate) const NAME: &[&str] = &["FnMut"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         let trait_path = quote!(::core::ops::FnMut);
         let trait_ = quote!(#trait_path(__T) -> __U);
         let fst = data.field_types().next();
@@ -188,7 +208,7 @@ pub(crate) mod fn_once {
 
     pub(crate) const NAME: &[&str] = &["FnOnce"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         let trait_path = quote!(::core::ops::FnOnce);
         let trait_ = quote!(#trait_path(__T) -> __U);
         let fst = data.field_types().next();

src/derive/external/futures01.rs

@@ -3,7 +3,7 @@ pub(crate) mod future {
 
     pub(crate) const NAME: &[&str] = &["futures01::Future"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(data, parse_quote!(::futures::future::Future), None, parse_quote! {
             trait Future {
                 type Item;
@@ -20,7 +20,7 @@ pub(crate) mod stream {
 
     pub(crate) const NAME: &[&str] = &["futures01::Stream"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(data, parse_quote!(::futures::stream::Stream), None, parse_quote! {
             trait Stream {
                 type Item;
@@ -39,7 +39,7 @@ pub(crate) mod sink {
 
     pub(crate) const NAME: &[&str] = &["futures01::Sink"];
 
-    pub(crate) fn derive(data: &Data) -> Result<TokenStream> {
+    pub(crate) fn derive(_cx: &Context, data: &Data) -> Result<TokenStream> {
         Ok(derive_trait(data, parse_quote!(::futures::sink::Sink), None, parse_quote! {
             trait Sink {
                 type SinkItem;