allow 'latest' metadata to be returned from the fallback code (#1127)

cli/src/utils.rs

@@ -24,15 +24,11 @@ pub struct FileOrUrl {
     pub file: Option<PathBuf>,
     /// Specify the metadata version.
     ///
-    ///  - unstable:
+    ///  - "latest": Use the latest stable version available.
+    ///  - "unstable": Use the unstable metadata, if present.
+    ///  - a number: Use a specific metadata version.
     ///
-    ///    Use the latest unstable metadata of the node.
-    ///
-    ///  - number
-    ///
-    ///    Use this specific metadata version.
-    ///
-    /// Defaults to 14.
+    /// Defaults to asking for the latest stable metadata version.
     #[clap(long)]
     pub version: Option<MetadataVersion>,
 }

codegen/src/utils/fetch_metadata.rs

@@ -201,14 +201,18 @@ async fn fetch_metadata(
         client: &impl ClientT,
         version: MetadataVersion,
     ) -> Result<Vec<u8>, FetchMetadataError> {
-        if !matches!(version, MetadataVersion::Version(14)) {
+        // If the user specifically asks for anything other than version 14 or "latest", error.
+        if !matches!(
+            version,
+            MetadataVersion::Latest | MetadataVersion::Version(14)
+        ) {
             return Err(FetchMetadataError::Other(
                 "The node can only return version 14 metadata using the legacy API but you've asked for something else"
                     .to_string(),
             ));
         }
 
-        // Fetch the metadata at that version:
+        // Fetch the metadata.
         let metadata_string: String = client
             .request("state_call", rpc_params!["Metadata_metadata", "0x"])
             .await?;