feat(xcm): support json schema (for CosmWasm VM support) (#1454)

# Description

- What does this PR do? Allows to generate JSON schema for subset of XCM
in std builds
- Why are these changes needed? To support XCM messages in CosmWasm
contracts which require Schemars to generate contract clients
- How were these changes implemented and what do they affect? We will
use schema feature flag to build XCM pallet with JSON schema enabled

# Checklist

- [x] My PR includes a detailed description as outlined in the
"Description" section above
- [x] My PR follows the [labeling requirements](CONTRIBUTING.md#Process)
of this project (at minimum one label for `T`
  required)
- [x] I have made corresponding changes to the documentation (if
applicable)
- [x] I have added tests that prove my fix is effective or that my
feature works (if applicable)
- [x] If this PR alters any external APIs or interfaces used by
Polkadot, the corresponding Polkadot PR is ready as well
  as the corresponding Cumulus PR (optional)

polkadot/xcm/src/double_encoded.rs

@@ -25,6 +25,7 @@ use parity_scale_codec::{Decode, DecodeLimit, Encode};
 #[codec(decode_bound())]
 #[scale_info(bounds(), skip_type_params(T))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub struct DoubleEncoded<T> {
 	encoded: Vec<u8>,
 	#[codec(skip)]

polkadot/xcm/src/v2/mod.rs

@@ -82,6 +82,7 @@ pub use traits::{Error, ExecuteXcm, GetWeight, Outcome, Result, SendError, SendR
 /// Basically just the XCM (more general) version of `ParachainDispatchOrigin`.
 #[derive(Copy, Clone, Eq, PartialEq, Encode, Decode, Debug, TypeInfo)]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub enum OriginKind {
 	/// Origin should just be the native dispatch origin representation for the sender in the
 	/// local runtime framework. For Cumulus/Frame chains this is the `Parachain` or `Relay` origin

polkadot/xcm/src/v3/junction.rs

@@ -49,6 +49,7 @@ use serde::{Deserialize, Serialize};
 	Serialize,
 	Deserialize,
 )]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub enum NetworkId {
 	/// Network specified by the first 32 bytes of its genesis block.
@@ -119,6 +120,7 @@ impl TryFrom<OldNetworkId> for NetworkId {
 	Serialize,
 	Deserialize,
 )]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub enum BodyId {
 	/// The only body in its context.
@@ -190,6 +192,7 @@ impl TryFrom<OldBodyId> for BodyId {
 	Serialize,
 	Deserialize,
 )]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub enum BodyPart {
 	/// The body's declaration, under whatever means it decides.
@@ -266,6 +269,7 @@ impl TryFrom<OldBodyPart> for BodyPart {
 	Serialize,
 	Deserialize,
 )]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub enum Junction {
 	/// An indexed parachain belonging to and operated by the context.

polkadot/xcm/src/v3/junctions.rs

@@ -44,6 +44,7 @@ pub(crate) const MAX_JUNCTIONS: usize = 8;
 	serde::Serialize,
 	serde::Deserialize,
 )]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub enum Junctions {
 	/// The interpreting consensus system.

polkadot/xcm/src/v3/mod.rs

@@ -69,6 +69,7 @@ pub type QueryId = u64;
 #[codec(encode_bound())]
 #[scale_info(bounds(), skip_type_params(Call))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub struct Xcm<Call>(pub Vec<Instruction<Call>>);
 
 /// The maximal number of instructions in an XCM before decoding fails.
@@ -232,15 +233,19 @@ pub mod prelude {
 }
 
 parameter_types! {
+	#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 	pub MaxPalletNameLen: u32 = 48;
 	/// Maximum size of the encoded error code coming from a `Dispatch` result, used for
 	/// `MaybeErrorCode`. This is not (yet) enforced, so it's just an indication of expectation.
+	#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 	pub MaxDispatchErrorLen: u32 = 128;
+	#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 	pub MaxPalletsInfo: u32 = 64;
 }
 
 #[derive(Clone, Eq, PartialEq, Encode, Decode, Debug, TypeInfo, MaxEncodedLen)]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub struct PalletInfo {
 	#[codec(compact)]
 	pub index: u32,
@@ -272,6 +277,7 @@ impl PalletInfo {
 
 #[derive(Clone, Eq, PartialEq, Encode, Decode, Debug, TypeInfo, MaxEncodedLen)]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub enum MaybeErrorCode {
 	Success,
 	Error(BoundedVec<u8, MaxDispatchErrorLen>),
@@ -296,6 +302,7 @@ impl Default for MaybeErrorCode {
 /// Response data to a query.
 #[derive(Clone, Eq, PartialEq, Encode, Decode, Debug, TypeInfo, MaxEncodedLen)]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub enum Response {
 	/// No response. Serves as a neutral default.
 	Null,
@@ -320,6 +327,7 @@ impl Default for Response {
 /// Information regarding the composition of a query response.
 #[derive(Clone, Eq, PartialEq, Encode, Decode, Debug, TypeInfo)]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub struct QueryResponseInfo {
 	/// The destination to which the query response message should be send.
 	pub destination: MultiLocation,
@@ -333,6 +341,7 @@ pub struct QueryResponseInfo {
 /// An optional weight limit.
 #[derive(Clone, Eq, PartialEq, Encode, Decode, Debug, TypeInfo)]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub enum WeightLimit {
 	/// No weight limit imposed.
 	Unlimited,
@@ -417,6 +426,7 @@ impl XcmContext {
 #[codec(decode_bound())]
 #[scale_info(bounds(), skip_type_params(Call))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub enum Instruction<Call> {
 	/// Withdraw asset(s) (`assets`) from the ownership of `origin` and place them into the Holding
 	/// Register.

polkadot/xcm/src/v3/multiasset.rs

@@ -47,6 +47,7 @@ use scale_info::TypeInfo;
 	Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Encode, Decode, Debug, TypeInfo, MaxEncodedLen,
 )]
 #[cfg_attr(feature = "std", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub enum AssetInstance {
 	/// Undefined - used if the non-fungible asset class has only one instance.
@@ -243,6 +244,7 @@ impl TryFrom<AssetInstance> for u128 {
 /// instance.
 #[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Encode, TypeInfo, MaxEncodedLen)]
 #[cfg_attr(feature = "std", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub enum Fungibility {
 	/// A fungible asset; we record a number of units, as a `u128` in the inner item.
@@ -313,6 +315,7 @@ impl TryFrom<OldFungibility> for Fungibility {
 	Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Encode, Decode, TypeInfo, MaxEncodedLen,
 )]
 #[cfg_attr(feature = "std", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub enum WildFungibility {
 	/// The asset is fungible.
@@ -337,6 +340,7 @@ impl TryFrom<OldWildFungibility> for WildFungibility {
 	Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Encode, Decode, TypeInfo, MaxEncodedLen,
 )]
 #[cfg_attr(feature = "std", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub enum AssetId {
 	/// A specific location identifying an asset.
@@ -412,6 +416,7 @@ impl AssetId {
 /// Either an amount of a single fungible asset, or a single well-identified non-fungible asset.
 #[derive(Clone, Eq, PartialEq, Debug, Encode, Decode, TypeInfo, MaxEncodedLen)]
 #[cfg_attr(feature = "std", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub struct MultiAsset {
 	/// The overall asset identity (aka *class*, in the case of a non-fungible).
@@ -510,6 +515,7 @@ impl TryFrom<OldMultiAsset> for MultiAsset {
 /// - The number of items should grow no larger than `MAX_ITEMS_IN_MULTIASSETS`.
 #[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Encode, TypeInfo, Default)]
 #[cfg_attr(feature = "std", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub struct MultiAssets(Vec<MultiAsset>);
 
@@ -710,6 +716,7 @@ impl MultiAssets {
 /// A wildcard representing a set of assets.
 #[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Encode, Decode, TypeInfo, MaxEncodedLen)]
 #[cfg_attr(feature = "std", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub enum WildMultiAsset {
 	/// All assets in Holding.
@@ -823,6 +830,7 @@ impl<A: Into<AssetId>, B: Into<WildFungibility>> From<(A, B)> for WildMultiAsset
 /// `MultiAsset` collection, defined either by a number of `MultiAssets` or a single wildcard.
 #[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Encode, Decode, TypeInfo, MaxEncodedLen)]
 #[cfg_attr(feature = "std", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub enum MultiAssetFilter {
 	/// Specify the filter as being everything contained by the given `MultiAssets` inner.

polkadot/xcm/src/v3/multilocation.rs

@@ -66,6 +66,7 @@ use scale_info::TypeInfo;
 	serde::Serialize,
 	serde::Deserialize,
 )]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub struct MultiLocation {
 	/// The number of parent junctions at the beginning of this `MultiLocation`.
 	pub parents: u8,

polkadot/xcm/src/v3/traits.rs

@@ -30,6 +30,7 @@ use super::*;
 /// they will retain the same index over time.
 #[derive(Copy, Clone, Encode, Decode, Eq, PartialEq, Debug, TypeInfo)]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub enum Error {
 	// Errors that happen due to instructions being executed. These alone are defined in the
 	// XCM specification.