feat: impl BorshSchema for Rc and Arc; add doc for rc feature

.github/test.sh

@@ -8,14 +8,14 @@ cargo test
 cargo test --features unstable__schema,ascii --test test_ascii_strings
 cargo test --features derive
 cargo test --features unstable__schema
-cargo test --test test_rc --features rc
+cargo test --test test_rc --features unstable__schema,rc
 cargo test --test test_hash_map --test test_btree_map --features de_strict_order
 
 cargo test --no-default-features
 cargo test --no-default-features --features unstable__schema,ascii --test test_ascii_strings
 cargo test --no-default-features --features derive
 cargo test --no-default-features --features unstable__schema
-cargo test --no-default-features --test test_rc --features rc
+cargo test --no-default-features --test test_rc --features unstable__schema,rc
 cargo test --no-default-features --features hashbrown
 popd
 pushd borsh-derive

borsh/Cargo.toml

@@ -45,13 +45,16 @@ borsh = { path = ".", default_features = false, features = ["bytes", "bson"] }
 insta = "1.29.0"
 
 [package.metadata.docs.rs]
-features = ["derive", "unstable__schema"]
+features = ["derive", "unstable__schema", "rc"]
 targets = ["x86_64-unknown-linux-gnu"]
 
 [features]
 default = ["std"]
 derive = ["borsh-derive"]
 unstable__schema = ["derive", "borsh-derive/schema"]
 std = []
+# Opt into impls for Rc<T> and Arc<T>. Serializing and deserializing these types
+# does not preserve identity and may result in multiple copies of the same data.
+# Be sure that this is what you want before enabling this feature.
 rc = []
 de_strict_order = []

borsh/src/de/mod.rs

@@ -19,8 +19,6 @@ use crate::__private::maybestd::{
 };
 use crate::io::{Error, ErrorKind, Read, Result};
 
-#[cfg(feature = "rc")]
-use crate::__private::maybestd::{rc::Rc, sync::Arc};
 use crate::error::check_zst;
 
 mod hint;
@@ -883,23 +881,42 @@ impl_range!(RangeFrom, start.., start);
 impl_range!(RangeTo, ..end, end);
 impl_range!(RangeToInclusive, ..=end, end);
 
+/// Module is available if borsh is built with `features = ["rc"]`.
 #[cfg(feature = "rc")]
-impl<T: ?Sized> BorshDeserialize for Rc<T>
-where
-    Box<T>: BorshDeserialize,
-{
-    fn deserialize_reader<R: Read>(reader: &mut R) -> Result<Self> {
-        Ok(Box::<T>::deserialize_reader(reader)?.into())
+pub mod rc {
+    //!
+    //! Module defines [BorshDeserialize] implementation for
+    //! [alloc::rc::Rc](std::rc::Rc) and [alloc::sync::Arc](std::sync::Arc).
+    use crate::__private::maybestd::{boxed::Box, rc::Rc, sync::Arc};
+    use crate::io::{Read, Result};
+    use crate::BorshDeserialize;
+
+    /// This impl requires the [`"rc"`] Cargo feature of borsh.
+    ///
+    /// Deserializing a data structure containing `Rc` will not attempt to
+    /// deduplicate `Rc` references to the same data. Every deserialized `Rc`
+    /// will end up with a strong count of 1.
+    impl<T: ?Sized> BorshDeserialize for Rc<T>
+    where
+        Box<T>: BorshDeserialize,
+    {
+        fn deserialize_reader<R: Read>(reader: &mut R) -> Result<Self> {
+            Ok(Box::<T>::deserialize_reader(reader)?.into())
+        }
     }
-}
 
-#[cfg(feature = "rc")]
-impl<T: ?Sized> BorshDeserialize for Arc<T>
-where
-    Box<T>: BorshDeserialize,
-{
-    fn deserialize_reader<R: Read>(reader: &mut R) -> Result<Self> {
-        Ok(Box::<T>::deserialize_reader(reader)?.into())
+    /// This impl requires the [`"rc"`] Cargo feature of borsh.
+    ///
+    /// Deserializing a data structure containing `Arc` will not attempt to
+    /// deduplicate `Arc` references to the same data. Every deserialized `Arc`
+    /// will end up with a strong count of 1.
+    impl<T: ?Sized> BorshDeserialize for Arc<T>
+    where
+        Box<T>: BorshDeserialize,
+    {
+        fn deserialize_reader<R: Read>(reader: &mut R) -> Result<Self> {
+            Ok(Box::<T>::deserialize_reader(reader)?.into())
+        }
     }
 }
 

borsh/src/lib.rs

@@ -35,6 +35,9 @@
   Gates implementation of [BorshSerialize] and [BorshDeserialize]
   for [`Rc<T>`](std::rc::Rc)/[`Arc<T>`](std::sync::Arc) respectively.
   In `no_std` setting `Rc`/`Arc` are pulled from `alloc` crate.
+  Serializing and deserializing these types
+  does not preserve identity and may result in multiple copies of the same data.
+  Be sure that this is what you want before enabling this feature.
 * **hashbrown** -
   Pulls in [HashMap](std::collections::HashMap)/[HashSet](std::collections::HashSet) when no `std` is available.
   This feature is set to be mutually exclusive with **std** feature.

borsh/src/schema.rs

@@ -317,6 +317,44 @@ where
         T::declaration()
     }
 }
+/// Module is available if borsh is built with `features = ["rc"]`.
+#[cfg(feature = "rc")]
+pub mod rc {
+    //!
+    //! Module defines [BorshSchema] implementation for
+    //! [alloc::rc::Rc](std::rc::Rc) and [alloc::sync::Arc](std::sync::Arc).
+    use crate::BorshSchema;
+
+    use super::{Declaration, Definition};
+    use crate::__private::maybestd::collections::BTreeMap;
+    use crate::__private::maybestd::{rc::Rc, sync::Arc};
+
+    impl<T> BorshSchema for Rc<T>
+    where
+        T: BorshSchema + ?Sized,
+    {
+        fn add_definitions_recursively(definitions: &mut BTreeMap<Declaration, Definition>) {
+            T::add_definitions_recursively(definitions);
+        }
+
+        fn declaration() -> Declaration {
+            T::declaration()
+        }
+    }
+
+    impl<T> BorshSchema for Arc<T>
+    where
+        T: BorshSchema + ?Sized,
+    {
+        fn add_definitions_recursively(definitions: &mut BTreeMap<Declaration, Definition>) {
+            T::add_definitions_recursively(definitions);
+        }
+
+        fn declaration() -> Declaration {
+            T::declaration()
+        }
+    }
+}
 
 macro_rules! impl_for_renamed_primitives {
     ($($ty: ty : $name: ident => $size: expr);+) => {

borsh/src/ser/mod.rs

@@ -11,9 +11,6 @@ use crate::__private::maybestd::{
 use crate::error::check_zst;
 use crate::io::{Error, ErrorKind, Result, Write};
 
-#[cfg(feature = "rc")]
-use crate::__private::maybestd::{rc::Rc, sync::Arc};
-
 pub(crate) mod helpers;
 
 const FLOAT_NAN_ERR: &str = "For portability reasons we do not allow to serialize NaNs.";
@@ -600,17 +597,38 @@ impl_range!(RangeFrom, this, &this.start);
 impl_range!(RangeTo, this, &this.end);
 impl_range!(RangeToInclusive, this, &this.end);
 
+/// Module is available if borsh is built with `features = ["rc"]`.
 #[cfg(feature = "rc")]
-impl<T: BorshSerialize + ?Sized> BorshSerialize for Rc<T> {
-    fn serialize<W: Write>(&self, writer: &mut W) -> Result<()> {
-        (**self).serialize(writer)
+pub mod rc {
+    //!
+    //! Module defines [BorshSerialize] implementation for
+    //! [alloc::rc::Rc](std::rc::Rc) and [alloc::sync::Arc](std::sync::Arc).
+    use crate::__private::maybestd::{rc::Rc, sync::Arc};
+    use crate::io::{Result, Write};
+    use crate::BorshSerialize;
+
+    /// This impl requires the [`"rc"`] Cargo feature of borsh.
+    ///
+    /// Serializing a data structure containing `Rc` will serialize a copy of
+    /// the contents of the `Rc` each time the `Rc` is referenced within the
+    /// data structure. Serialization will not attempt to deduplicate these
+    /// repeated data.
+    impl<T: BorshSerialize + ?Sized> BorshSerialize for Rc<T> {
+        fn serialize<W: Write>(&self, writer: &mut W) -> Result<()> {
+            (**self).serialize(writer)
+        }
     }
-}
 
-#[cfg(feature = "rc")]
-impl<T: BorshSerialize + ?Sized> BorshSerialize for Arc<T> {
-    fn serialize<W: Write>(&self, writer: &mut W) -> Result<()> {
-        (**self).serialize(writer)
+    /// This impl requires the [`"rc"`] Cargo feature of borsh.
+    ///
+    /// Serializing a data structure containing `Arc` will serialize a copy of
+    /// the contents of the `Arc` each time the `Arc` is referenced within the
+    /// data structure. Serialization will not attempt to deduplicate these
+    /// repeated data.
+    impl<T: BorshSerialize + ?Sized> BorshSerialize for Arc<T> {
+        fn serialize<W: Write>(&self, writer: &mut W) -> Result<()> {
+            (**self).serialize(writer)
+        }
     }
 }
 

borsh/tests/test_rc.rs

@@ -4,7 +4,6 @@
 #[cfg(feature = "std")]
 pub use std::{rc, sync};
 
-#[cfg(not(feature = "std"))]
 extern crate alloc;
 #[cfg(not(feature = "std"))]
 pub use alloc::{rc, sync};
@@ -44,3 +43,75 @@ fn test_slice_arc() {
     let deserialized = from_slice::<sync::Arc<[i32]>>(&serialized).unwrap();
     assert_eq!(original, &*deserialized);
 }
+
+#[cfg(feature = "unstable__schema")]
+mod schema {
+    use super::{rc, sync};
+    use alloc::{
+        collections::BTreeMap,
+        string::{String, ToString},
+    };
+    use borsh::schema::{BorshSchema, Definition};
+    macro_rules! map(
+        () => { BTreeMap::new() };
+        { $($key:expr => $value:expr),+ } => {
+            {
+                let mut m = BTreeMap::new();
+                $(
+                    m.insert($key.to_string(), $value);
+                )+
+                m
+            }
+         };
+        );
+    fn common_map_i32() -> BTreeMap<String, Definition> {
+        map! {
+
+            "i32" => Definition::Primitive(4)
+        }
+    }
+
+    fn common_map_slice_i32() -> BTreeMap<String, Definition> {
+        map! {
+            "Vec<i32>" => Definition::Sequence {
+                length_width: Definition::DEFAULT_LENGTH_WIDTH,
+                length_range: Definition::DEFAULT_LENGTH_RANGE,
+                elements: "i32".to_string()
+            },
+            "i32" => Definition::Primitive(4)
+        }
+    }
+
+    #[test]
+    fn test_rc() {
+        assert_eq!("i32", <rc::Rc<i32> as BorshSchema>::declaration());
+
+        let mut actual_defs = map!();
+        <rc::Rc<i32> as BorshSchema>::add_definitions_recursively(&mut actual_defs);
+        assert_eq!(common_map_i32(), actual_defs);
+    }
+
+    #[test]
+    fn test_slice_rc() {
+        assert_eq!("Vec<i32>", <rc::Rc<[i32]> as BorshSchema>::declaration());
+        let mut actual_defs = map!();
+        <rc::Rc<[i32]> as BorshSchema>::add_definitions_recursively(&mut actual_defs);
+        assert_eq!(common_map_slice_i32(), actual_defs);
+    }
+
+    #[test]
+    fn test_arc() {
+        assert_eq!("i32", <sync::Arc<i32> as BorshSchema>::declaration());
+        let mut actual_defs = map!();
+        <sync::Arc<i32> as BorshSchema>::add_definitions_recursively(&mut actual_defs);
+        assert_eq!(common_map_i32(), actual_defs);
+    }
+
+    #[test]
+    fn test_slice_arc() {
+        assert_eq!("Vec<i32>", <sync::Arc<[i32]> as BorshSchema>::declaration());
+        let mut actual_defs = map!();
+        <sync::Arc<[i32]> as BorshSchema>::add_definitions_recursively(&mut actual_defs);
+        assert_eq!(common_map_slice_i32(), actual_defs);
+    }
+}