make polkadot-parachain chain-spec extension more relaxed (#4452)

A small step towards
https://forum.polkadot.network/t/polkadot-parachain-omni-node-gathering-ideas-and-feedback/7823
and #4352.

Many parachains use `camelCase` and/or `PascalCase`ing for their chain
spec extension. Sometimes the only reason polkadot-parachain cannot sync
them is because it cannot parse the chain spec extension. This PR
relaxes the requirement for the extension to be camel case.

---------

Co-authored-by: Branislav Kontur <bkontur@gmail.com>

cumulus/polkadot-parachain/src/chain_spec/mod.rs

@@ -37,11 +37,12 @@ const SAFE_XCM_VERSION: u32 = xcm::prelude::XCM_VERSION;
 
 /// Generic extensions for Parachain ChainSpecs.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, ChainSpecGroup, ChainSpecExtension)]
-#[serde(deny_unknown_fields)]
 pub struct Extensions {
 	/// The relay chain of the Parachain.
+	#[serde(alias = "relayChain", alias = "RelayChain")]
 	pub relay_chain: String,
 	/// The id of the Parachain.
+	#[serde(alias = "paraId", alias = "ParaId")]
 	pub para_id: u32,
 }
 
@@ -78,3 +79,22 @@ where
 pub fn get_collator_keys_from_seed<AuraId: Public>(seed: &str) -> <AuraId::Pair as Pair>::Public {
 	get_from_seed::<AuraId>(seed)
 }
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn can_decode_extension_camel_and_snake_case() {
+		let camel_case = r#"{"relayChain":"relay","paraId":1}"#;
+		let snake_case = r#"{"relay_chain":"relay","para_id":1}"#;
+		let pascal_case = r#"{"RelayChain":"relay","ParaId":1}"#;
+
+		let camel_case_extension: Extensions = serde_json::from_str(camel_case).unwrap();
+		let snake_case_extension: Extensions = serde_json::from_str(snake_case).unwrap();
+		let pascal_case_extension: Extensions = serde_json::from_str(pascal_case).unwrap();
+
+		assert_eq!(camel_case_extension, snake_case_extension);
+		assert_eq!(snake_case_extension, pascal_case_extension);
+	}
+}

templates/parachain/node/src/chain_spec.rs

@@ -22,11 +22,12 @@ pub fn get_from_seed<TPublic: Public>(seed: &str) -> <TPublic::Pair as Pair>::Pu
 
 /// The extensions for the [`ChainSpec`].
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, ChainSpecGroup, ChainSpecExtension)]
-#[serde(deny_unknown_fields)]
 pub struct Extensions {
 	/// The relay chain of the Parachain.
+	#[serde(alias = "relayChain", alias = "RelayChain")]
 	pub relay_chain: String,
 	/// The id of the Parachain.
+	#[serde(alias = "paraId", alias = "ParaId")]
 	pub para_id: u32,
 }