Add --derive-for-type to cli (#708)

* Add `--derive-for-type` to cli

* Remove clippy warnings

cli/src/commands/codegen.rs

@@ -28,14 +28,27 @@ pub struct Opts {
     /// Additional derives
     #[clap(long = "derive")]
     derives: Vec<String>,
+    /// Additional derives for a given type.
+    ///
+    /// Example `--derive-for-type my_module::my_type=serde::Serialize`.
+    #[clap(long = "derive-for-type", value_parser = derive_for_type_parser)]
+    derives_for_type: Vec<(String, String)>,
     /// The `subxt` crate access path in the generated code.
     /// Defaults to `::subxt`.
     #[clap(long = "crate")]
     crate_path: Option<String>,
 }
 
+fn derive_for_type_parser(src: &str) -> Result<(String, String), String> {
+    let (ty, derive) = src
+        .split_once('=')
+        .ok_or_else(|| String::from("Invalid pattern for `derive-for-type`. It should be `type=derive`, like `my_type=serde::Serialize`"))?;
+
+    Ok((ty.to_string(), derive.to_string()))
+}
+
 pub async fn run(opts: Opts) -> color_eyre::Result<()> {
-    if let Some(file) = opts.file.as_ref() {
+    let bytes = if let Some(file) = opts.file.as_ref() {
         if opts.url.is_some() {
             eyre::bail!("specify one of `--url` or `--file` but not both")
         };
@@ -43,23 +56,24 @@ pub async fn run(opts: Opts) -> color_eyre::Result<()> {
         let mut file = fs::File::open(file)?;
         let mut bytes = Vec::new();
         file.read_to_end(&mut bytes)?;
-        codegen(&bytes, opts.derives, opts.crate_path)?;
-        return Ok(())
-    }
+        bytes
+    } else {
+        let url = opts.url.unwrap_or_else(|| {
+            "http://localhost:9933"
+                .parse::<Uri>()
+                .expect("default url is valid")
+        });
+        subxt_codegen::utils::fetch_metadata_bytes(&url).await?
+    };
 
-    let url = opts.url.unwrap_or_else(|| {
-        "http://localhost:9933"
-            .parse::<Uri>()
-            .expect("default url is valid")
-    });
-    let bytes = subxt_codegen::utils::fetch_metadata_bytes(&url).await?;
-    codegen(&bytes, opts.derives, opts.crate_path)?;
+    codegen(&bytes, opts.derives, opts.derives_for_type, opts.crate_path)?;
     Ok(())
 }
 
 fn codegen(
     metadata_bytes: &[u8],
     raw_derives: Vec<String>,
+    derives_for_type: Vec<(String, String)>,
     crate_path: Option<String>,
 ) -> color_eyre::Result<()> {
     let item_mod = syn::parse_quote!(
@@ -75,6 +89,12 @@ fn codegen(
     let mut derives = DerivesRegistry::new(&crate_path);
     derives.extend_for_all(p.into_iter());
 
+    for (ty, derive) in derives_for_type.into_iter() {
+        let ty = syn::parse_str(&ty)?;
+        let derive = syn::parse_str(&derive)?;
+        derives.extend_for_type(ty, std::iter::once(derive), &crate_path)
+    }
+
     let runtime_api = subxt_codegen::generate_runtime_api_from_bytes(
         item_mod,
         metadata_bytes,