pvf-precheck: teach runtime-api to work with versions (#4510)

As part of #3211 we will need to add a couple of runtime APIs. That
change is coming in a following PR.

The runtime API for pre-checking will be introduced with a version bump
for `ParachainHost`. This commit prepares the ground for that change,
by introducing a error condition that signals that the given API is not
supported.

polkadot/node/subsystem-types/src/errors.rs

@@ -19,23 +19,27 @@
 use crate::JaegerError;
 
 /// A description of an error causing the runtime API request to be unservable.
-#[derive(Debug, Clone)]
-pub struct RuntimeApiError(String);
+#[derive(thiserror::Error, Debug, Clone)]
+pub enum RuntimeApiError {
+	/// The runtime API cannot be executed due to a
+	#[error("The runtime API '{runtime_api_name}' cannot be executed")]
+	Execution {
+		/// The runtime API being called
+		runtime_api_name: &'static str,
+		/// The wrapped error. Marked as source for tracking the error chain.
+		#[source]
+		source: std::sync::Arc<dyn 'static + std::error::Error + Send + Sync>,
+	},
 
-impl From<String> for RuntimeApiError {
-	fn from(s: String) -> Self {
-		RuntimeApiError(s)
-	}
+	/// The runtime API request in question cannot be executed because the runtime at the requested
+	/// relay-parent is an old version.
+	#[error("The API is not supported by the runtime at the relay-parent")]
+	NotSupported {
+		/// The runtime API being called
+		runtime_api_name: &'static str,
+	},
 }
 
-impl core::fmt::Display for RuntimeApiError {
-	fn fmt(&self, f: &mut core::fmt::Formatter) -> Result<(), core::fmt::Error> {
-		write!(f, "{}", self.0)
-	}
-}
-
-impl std::error::Error for RuntimeApiError {}
-
 /// A description of an error causing the chain API request to be unservable.
 #[derive(Debug, Clone)]
 pub struct ChainApiError {