Implement a version of Schema types that are owned, using the heap, a…

…nd can be

punned or converted with existing typed or serialized schema types

source/postcard/src/lib.rs

@@ -81,6 +81,11 @@ pub mod experimental {
         pub use crate::schema::{NamedType, NamedValue, NamedVariant, Schema, SdmTy, Varint};
         // NOTE: ...and this is the derive macro
         pub use postcard_derive::Schema;
+
+        #[cfg(any(feature = "use-std", feature = "alloc"))]
+        pub use crate::schema::owned::{
+            OwnedNamedType, OwnedNamedValue, OwnedNamedVariant, OwnedSdmTy,
+        };
     }
 }
 

source/postcard/src/schema.rs

@@ -1,7 +1,7 @@
-use serde::Serialize;
+use serde::{Deserialize, Serialize};
 
 /// A schema type representing a variably encoded integer
-#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub enum Varint {
     /// A variably encoded i16
     I16,
@@ -26,7 +26,7 @@ pub enum Varint {
 }
 
 /// Serde Data Model Types (and friends)
-#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize)]
 pub enum SdmTy {
     /// The `bool` Serde Data Model Type
     Bool,
@@ -104,7 +104,7 @@ pub enum SdmTy {
 }
 
 /// A data type with a name - e.g. a field of a Struct
-#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize)]
 pub struct NamedValue {
     /// The name of this value
     pub name: &'static str,
@@ -113,7 +113,7 @@ pub struct NamedValue {
 }
 
 /// A data type - e.g. a custom `struct Foo{ ... }` type
-#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize)]
 pub struct NamedType {
     /// The name of this type
     pub name: &'static str,
@@ -122,7 +122,7 @@ pub struct NamedType {
 }
 
 /// An enum variant with a name, e.g. `T::Bar(...)`
-#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize)]
 pub struct NamedVariant {
     /// The name of this variant
     pub name: &'static str,
@@ -278,3 +278,189 @@ impl Schema for alloc::string::String {
         ty: &SdmTy::String,
     };
 }
+
+#[cfg(any(feature = "use-std", feature = "alloc"))]
+pub(crate) mod owned {
+    use super::*;
+
+    #[cfg(feature = "use-std")]
+    use std::{boxed::Box, string::String, vec::Vec};
+
+    #[cfg(all(not(feature = "use-std"), feature = "alloc"))]
+    use alloc::{
+        boxed::Box,
+        string::{String, ToString},
+        vec::Vec,
+    };
+
+    /// Serde Data Model Types (and friends)
+    #[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
+    pub enum OwnedSdmTy {
+        /// The `bool` Serde Data Model Type
+        Bool,
+
+        /// The `i8` Serde Data Model Type
+        I8,
+
+        /// The `u8` Serde Data Model Type
+        U8,
+
+        /// The Serde Data Model Type for variably length encoded integers
+        Varint(Varint),
+
+        /// The `f32` Serde Data Model Type
+        F32,
+
+        /// The `f64 Serde Data Model Type
+        F64,
+
+        /// The `char` Serde Data Model Type
+        Char,
+
+        /// The `String` Serde Data Model Type
+        String,
+
+        /// The `[u8; N]` Serde Data Model Type
+        ByteArray,
+
+        /// The `Option<T>` Serde Data Model Type
+        Option(Box<OwnedNamedType>),
+
+        /// The `()` Serde Data Model Type
+        Unit,
+
+        /// The "unit struct" Serde Data Model Type
+        UnitStruct,
+
+        /// The "unit variant" Serde Data Model Type
+        UnitVariant,
+
+        /// The "newtype struct" Serde Data Model Type
+        NewtypeStruct(Box<OwnedNamedType>),
+
+        /// The "newtype variant" Serde Data Model Type
+        NewtypeVariant(Box<OwnedNamedType>),
+
+        /// The "Sequence" Serde Data Model Type
+        Seq(Box<OwnedNamedType>),
+
+        /// The "Tuple" Serde Data Model Type
+        Tuple(Vec<OwnedNamedType>),
+
+        /// The "Tuple Struct" Serde Data Model Type
+        TupleStruct(Vec<OwnedNamedType>),
+
+        /// The "Tuple Variant" Serde Data Model Type
+        TupleVariant(Vec<OwnedNamedType>),
+
+        /// The "Map" Serde Data Model Type
+        Map {
+            /// The map "Key" type
+            key: Box<OwnedNamedType>,
+            /// The map "Value" type
+            val: Box<OwnedNamedType>,
+        },
+
+        /// The "Struct" Serde Data Model Type
+        Struct(Vec<OwnedNamedValue>),
+
+        /// The "Struct Variant" Serde Data Model Type
+        StructVariant(Vec<OwnedNamedValue>),
+
+        /// The "Enum" Serde Data Model Type (which contains any of the "Variant" types)
+        Enum(Vec<OwnedNamedVariant>),
+    }
+
+    impl From<&SdmTy> for OwnedSdmTy {
+        fn from(other: &SdmTy) -> Self {
+            match other {
+                SdmTy::Bool => Self::Bool,
+                SdmTy::I8 => Self::I8,
+                SdmTy::U8 => Self::U8,
+                SdmTy::Varint(v) => Self::Varint(*v),
+                SdmTy::F32 => Self::F32,
+                SdmTy::F64 => Self::F64,
+                SdmTy::Char => Self::Char,
+                SdmTy::String => Self::String,
+                SdmTy::ByteArray => Self::ByteArray,
+                SdmTy::Option(o) => Self::Option(Box::new((*o).into())),
+                SdmTy::Unit => Self::Unit,
+                SdmTy::UnitStruct => Self::UnitStruct,
+                SdmTy::UnitVariant => Self::UnitVariant,
+                SdmTy::NewtypeStruct(nts) => Self::NewtypeStruct(Box::new((*nts).into())),
+                SdmTy::NewtypeVariant(ntv) => Self::NewtypeVariant(Box::new((*ntv).into())),
+                SdmTy::Seq(s) => Self::Seq(Box::new((*s).into())),
+                SdmTy::Tuple(t) => Self::Tuple(t.iter().map(|i| (*i).into()).collect()),
+                SdmTy::TupleStruct(ts) => {
+                    Self::TupleStruct(ts.iter().map(|i| (*i).into()).collect())
+                }
+                SdmTy::TupleVariant(tv) => {
+                    Self::TupleVariant(tv.iter().map(|i| (*i).into()).collect())
+                }
+                SdmTy::Map { key, val } => Self::Map {
+                    key: Box::new((*key).into()),
+                    val: Box::new((*val).into()),
+                },
+                SdmTy::Struct(s) => Self::Struct(s.iter().map(|i| (*i).into()).collect()),
+                SdmTy::StructVariant(sv) => {
+                    Self::StructVariant(sv.iter().map(|i| (*i).into()).collect())
+                }
+                SdmTy::Enum(e) => Self::Enum(e.iter().map(|i| (*i).into()).collect()),
+            }
+        }
+    }
+
+    /// A data type with a name - e.g. a field of a Struct
+    #[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
+    pub struct OwnedNamedValue {
+        /// The name of this value
+        pub name: String,
+        /// The type of this value
+        pub ty: OwnedNamedType,
+    }
+
+    impl From<&NamedValue> for OwnedNamedValue {
+        fn from(value: &NamedValue) -> Self {
+            Self {
+                name: value.name.to_string(),
+                ty: value.ty.into(),
+            }
+        }
+    }
+
+    /// A data type - e.g. a custom `struct Foo{ ... }` type
+    #[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
+    pub struct OwnedNamedType {
+        /// The name of this type
+        pub name: String,
+        /// The type
+        pub ty: OwnedSdmTy,
+    }
+
+    impl From<&NamedType> for OwnedNamedType {
+        fn from(value: &NamedType) -> Self {
+            Self {
+                name: value.name.to_string(),
+                ty: value.ty.into(),
+            }
+        }
+    }
+
+    /// An enum variant with a name, e.g. `T::Bar(...)`
+    #[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
+    pub struct OwnedNamedVariant {
+        /// The name of this variant
+        pub name: String,
+        /// The type of this variant
+        pub ty: OwnedSdmTy,
+    }
+
+    impl From<&NamedVariant> for OwnedNamedVariant {
+        fn from(value: &NamedVariant) -> Self {
+            Self {
+                name: value.name.to_string(),
+                ty: value.ty.into(),
+            }
+        }
+    }
+}

source/postcard/tests/schema.rs

@@ -1,6 +1,8 @@
 #![cfg(feature = "experimental-derive")]
 
-use postcard::experimental::schema::{NamedType, NamedValue, NamedVariant, Schema, SdmTy, Varint};
+use postcard::experimental::schema::{
+    NamedType, NamedValue, NamedVariant, OwnedNamedType, Schema, SdmTy, Varint,
+};
 
 const U8_SCHEMA: NamedType = NamedType {
     name: "u8",
@@ -161,3 +163,53 @@ fn test_slice_serialize() {
         Slice::SCHEMA
     );
 }
+
+#[allow(unused)]
+#[derive(Debug, Schema)]
+enum TestEnum<'a> {
+    Alpha,
+    Beta(u32),
+    Gamma { a: bool, b: &'a [u8] },
+    Delta(f32, Option<&'a str>),
+    Epsilon(TestStruct1),
+}
+
+#[allow(unused)]
+#[derive(Debug, Schema)]
+struct TestStruct1 {
+    a: i8,
+    b: i16,
+    c: i32,
+    d: i64,
+}
+
+#[allow(unused)]
+#[derive(Debug, Schema)]
+struct TestStruct2<'a> {
+    x: TestEnum<'a>,
+    y: TestStruct1,
+    z: Result<TestStruct1, u32>,
+}
+
+#[test]
+fn owned_punning() {
+    let borrowed_schema = TestStruct2::SCHEMA;
+    let owned_schema: OwnedNamedType = borrowed_schema.into();
+
+    // Check that they are the same on the wire when serialized
+    let ser_borrowed_schema = postcard::to_stdvec(borrowed_schema).unwrap();
+    let ser_owned_schema = postcard::to_stdvec(&owned_schema).unwrap();
+    assert_eq!(ser_borrowed_schema, ser_owned_schema);
+
+    // TODO: This is wildly repetitive, and likely could benefit from interning of
+    // repeated types, strings, etc.
+    assert_eq!(ser_borrowed_schema.len(), 282);
+
+    // Check that we round-trip correctly
+    let deser_borrowed_schema =
+        postcard::from_bytes::<OwnedNamedType>(&ser_borrowed_schema).unwrap();
+    let deser_owned_schema = postcard::from_bytes::<OwnedNamedType>(&ser_owned_schema).unwrap();
+    assert_eq!(deser_borrowed_schema, deser_owned_schema);
+    assert_eq!(deser_borrowed_schema, owned_schema);
+    assert_eq!(deser_owned_schema, owned_schema);
+}