Add feature for enabling decoding (#59)

* Add feature for enabling decoding

* Fmt

* Fix up no_std test errors and warnings

* Only derive Decode when decode feature enabled

* Fix ununsed import warnings for scale::Decode on --no-default-features

* Apply conditional Decode derive to TypeDefCompact

Cargo.toml

@@ -28,6 +28,8 @@ std = [
 derive = [
     "scale-info-derive"
 ]
+# enables decoding and deserialization of portable scale-info type metadata
+decode = []
 
 [workspace]
 members = [

src/form.rs

@@ -32,8 +32,6 @@
 use crate::prelude::{
     any::TypeId,
     fmt::Debug,
-    marker::PhantomData,
-    string::String,
 };
 
 use crate::{
@@ -53,18 +51,9 @@ pub trait Form {
     /// The type representing the type.
     type Type: PartialEq + Eq + PartialOrd + Ord + Clone + Debug;
     /// The string type.
-    type String: FormString;
+    type String: AsRef<str> + PartialEq + Eq + PartialOrd + Ord + Clone + Debug;
 }
 
-/// Trait for types which can be used to represent strings in type definitions.
-pub trait FormString:
-    AsRef<str> + PartialEq + Eq + PartialOrd + Ord + Clone + Debug
-{
-}
-
-impl FormString for &'static str {}
-impl FormString for String {}
-
 /// A meta meta-type.
 ///
 /// Allows to be converted into other forms such as portable form
@@ -85,16 +74,21 @@ impl Form for MetaForm {
 /// This resolves some lifetime issues with self-referential structs (such as
 /// the registry itself) but can no longer be used to resolve to the original
 /// underlying data.
-///
-/// `type String` is owned in order to enable decoding
 #[cfg_attr(feature = "serde", derive(Serialize))]
 #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Debug)]
-pub struct PortableForm<S = &'static str>(PhantomData<S>);
+pub enum PortableForm {}
 
-impl<S> Form for PortableForm<S>
-where
-    S: FormString,
-{
-    type Type = UntrackedSymbol<TypeId>;
-    type String = S;
+cfg_if::cfg_if! {
+    if #[cfg(any(feature = "std", feature = "decode"))] {
+        impl Form for PortableForm {
+            type Type = UntrackedSymbol<TypeId>;
+            // Owned string required for decoding/deserialization
+            type String = crate::prelude::string::String;
+        }
+    } else {
+        impl Form for PortableForm {
+            type Type = UntrackedSymbol<TypeId>;
+            type String = &'static str;
+        }
+    }
 }

src/registry.rs

@@ -34,7 +34,6 @@ use crate::prelude::{
 use crate::{
     form::{
         Form,
-        FormString,
         PortableForm,
     },
     interner::{
@@ -44,13 +43,9 @@ use crate::{
     meta_type::MetaType,
     Type,
 };
-use scale::{
-    Decode,
-    Encode,
-};
+use scale::Encode;
 #[cfg(feature = "serde")]
 use serde::{
-    de::DeserializeOwned,
     Deserialize,
     Serialize,
 };
@@ -68,7 +63,7 @@ impl IntoPortable for &'static str {
     type Output = <PortableForm as Form>::String;
 
     fn into_portable(self, _registry: &mut Registry) -> Self::Output {
-        self
+        self.into()
     }
 }
 
@@ -171,16 +166,10 @@ impl Registry {
 
 /// A read-only registry containing types in their portable form for serialization.
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
-#[derive(Clone, Debug, PartialEq, Eq, Encode, Decode)]
-#[cfg_attr(
-    feature = "serde",
-    serde(bound(serialize = "S: Serialize", deserialize = "S: DeserializeOwned"))
-)]
-pub struct PortableRegistry<S = &'static str>
-where
-    S: FormString,
-{
-    types: Vec<Type<PortableForm<S>>>,
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(Clone, Debug, PartialEq, Eq, Encode)]
+pub struct PortableRegistry {
+    types: Vec<Type<PortableForm>>,
 }
 
 impl From<Registry> for PortableRegistry {
@@ -191,19 +180,14 @@ impl From<Registry> for PortableRegistry {
     }
 }
 
-impl<S> PortableRegistry<S>
-where
-    S: FormString,
-{
+impl PortableRegistry {
     /// Returns the type definition for the given identifier, `None` if no type found for that ID.
-    pub fn resolve(&self, id: NonZeroU32) -> Option<&Type<PortableForm<S>>> {
+    pub fn resolve(&self, id: NonZeroU32) -> Option<&Type<PortableForm>> {
         self.types.get((id.get() - 1) as usize)
     }
 
     /// Returns an iterator for all types paired with their associated NonZeroU32 identifier.
-    pub fn enumerate(
-        &self,
-    ) -> impl Iterator<Item = (NonZeroU32, &Type<PortableForm<S>>)> {
+    pub fn enumerate(&self) -> impl Iterator<Item = (NonZeroU32, &Type<PortableForm>)> {
         self.types.iter().enumerate().map(|(i, ty)| {
             let id = NonZeroU32::new(i as u32 + 1).expect("i + 1 > 0; qed");
             (id, ty)

src/ty/composite.rs

@@ -25,10 +25,7 @@ use crate::{
     Registry,
 };
 use derive_more::From;
-use scale::{
-    Decode,
-    Encode,
-};
+use scale::Encode;
 #[cfg(feature = "serde")]
 use serde::{
     de::DeserializeOwned,
@@ -71,7 +68,8 @@ use serde::{
     ))
 )]
 #[cfg_attr(feature = "serde", serde(rename_all = "lowercase"))]
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, From, Encode, Decode)]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, From, Encode)]
 pub struct TypeDefComposite<T: Form = MetaForm> {
     /// The fields of the composite type.
     #[cfg_attr(

src/ty/fields.rs

@@ -24,7 +24,6 @@ use crate::{
     TypeInfo,
 };
 use scale::{
-    Decode,
     Encode,
     HasCompact,
 };
@@ -66,7 +65,8 @@ use serde::{
 /// may change.
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "serde", serde(rename_all = "camelCase"))]
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Encode, Decode)]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Encode)]
 pub struct Field<T: Form = MetaForm> {
     /// The name of the field. None for unnamed fields.
     #[cfg_attr(

src/ty/mod.rs

@@ -30,10 +30,7 @@ use crate::{
     TypeInfo,
 };
 use derive_more::From;
-use scale::{
-    Decode,
-    Encode,
-};
+use scale::Encode;
 #[cfg(feature = "serde")]
 use serde::{
     de::DeserializeOwned,
@@ -63,7 +60,8 @@ pub use self::{
     ))
 )]
 #[cfg_attr(feature = "serde", serde(rename_all = "lowercase"))]
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, From, Debug, Encode, Decode)]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, From, Debug, Encode)]
 pub struct Type<T: Form = MetaForm> {
     /// The unique path to the type. Can be empty for built-in types
     #[cfg_attr(
@@ -162,7 +160,8 @@ where
     ))
 )]
 #[cfg_attr(feature = "serde", serde(rename_all = "lowercase"))]
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, From, Debug, Encode, Decode)]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, From, Debug, Encode)]
 pub enum TypeDef<T: Form = MetaForm> {
     /// A composite type (e.g. a struct or a tuple)
     Composite(TypeDefComposite<T>),
@@ -200,9 +199,10 @@ impl IntoPortable for TypeDef {
 }
 
 /// A primitive Rust type.
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Decode, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "serde", serde(rename_all = "lowercase"))]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Debug)]
 pub enum TypeDefPrimitive {
     /// `bool` type
     Bool,
@@ -237,8 +237,9 @@ pub enum TypeDefPrimitive {
 }
 
 /// An array type.
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Decode, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Debug)]
 pub struct TypeDefArray<T: Form = MetaForm> {
     /// The length of the array type.
     len: u32,
@@ -291,7 +292,8 @@ where
     ))
 )]
 #[cfg_attr(feature = "serde", serde(transparent))]
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Decode, Debug)]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Debug)]
 pub struct TypeDefTuple<T: Form = MetaForm> {
     /// The types of the tuple fields.
     fields: Vec<T::Type>,
@@ -336,7 +338,8 @@ where
 
 /// A type to refer to a sequence of elements of the same type.
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Decode, Debug)]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Debug)]
 pub struct TypeDefSequence<T: Form = MetaForm> {
     /// The element type of the sequence type.
     #[cfg_attr(feature = "serde", serde(rename = "type"))]
@@ -384,8 +387,9 @@ where
 }
 
 /// A type wrapped in [`Compact`].
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Decode, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Debug)]
 pub struct TypeDefCompact<T: Form = MetaForm> {
     /// The type wrapped in [`Compact`], i.e. the `T` in `Compact<T>`.
     #[cfg_attr(feature = "serde", serde(rename = "type"))]
@@ -429,7 +433,8 @@ where
 /// required to explicitly skip fields that cannot be represented in SCALE
 /// encoding, using the `#[codec(skip)]` attribute.
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Decode, Debug)]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Debug)]
 pub struct TypeDefPhantom<T: Form = MetaForm> {
     /// The PhantomData type parameter
     #[cfg_attr(feature = "serde", serde(rename = "type"))]

src/ty/path.rs

@@ -32,10 +32,7 @@ use crate::{
     IntoPortable,
     Registry,
 };
-use scale::{
-    Decode,
-    Encode,
-};
+use scale::Encode;
 #[cfg(feature = "serde")]
 use serde::{
     de::DeserializeOwned,
@@ -50,7 +47,6 @@ use serde::{
 /// has been defined. The last
 ///
 /// Rust prelude type may have an empty namespace definition.
-#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Encode, Decode)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(
     feature = "serde",
@@ -60,6 +56,8 @@ use serde::{
     ))
 )]
 #[cfg_attr(feature = "serde", serde(transparent))]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Encode)]
 pub struct Path<T: Form = MetaForm> {
     /// The segments of the namespace.
     segments: Vec<T::String>,

src/ty/variant.rs

@@ -26,10 +26,7 @@ use crate::{
     Registry,
 };
 use derive_more::From;
-use scale::{
-    Decode,
-    Encode,
-};
+use scale::Encode;
 #[cfg(feature = "serde")]
 use serde::{
     de::DeserializeOwned,
@@ -84,7 +81,8 @@ use serde::{
     ))
 )]
 #[cfg_attr(feature = "serde", serde(rename_all = "lowercase"))]
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, From, Encode, Decode)]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, From, Encode)]
 pub struct TypeDefVariant<T: Form = MetaForm> {
     /// The variants of a variant type
     #[cfg_attr(
@@ -149,7 +147,8 @@ where
         deserialize = "T::Type: DeserializeOwned, T::String: DeserializeOwned",
     ))
 )]
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Encode, Decode)]
+#[cfg_attr(any(feature = "std", feature = "decode"), derive(scale::Decode))]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Encode)]
 pub struct Variant<T: Form = MetaForm> {
     /// The name of the variant.
     name: T::String,

test_suite/tests/codec.rs

@@ -62,7 +62,7 @@ fn scale_encode_then_decode_to_readonly() {
     let mut encoded = registry.encode();
     let original_serialized = serde_json::to_value(registry).unwrap();
 
-    let readonly_decoded = PortableRegistry::<String>::decode(&mut &encoded[..]).unwrap();
+    let readonly_decoded = PortableRegistry::decode(&mut &encoded[..]).unwrap();
     assert!(readonly_decoded
         .resolve(NonZeroU32::new(1).unwrap())
         .is_some());
@@ -79,7 +79,7 @@ fn json_serialize_then_deserialize_to_readonly() {
     let registry: PortableRegistry = registry.into();
     let original_serialized = serde_json::to_value(registry).unwrap();
     // assert_eq!(original_serialized, serde_json::Value::Null);
-    let readonly_deserialized: PortableRegistry<String> =
+    let readonly_deserialized: PortableRegistry =
         serde_json::from_value(original_serialized.clone()).unwrap();
     assert!(readonly_deserialized
         .resolve(NonZeroU32::new(1).unwrap())