message: [lang] Add initial unfinished instantiation code gen for messages
diff: @@ -75,6 +75,47 @@ fn codegen_for_instantiate(tokens: &mut TokenStream, contract: &hir::Contract) {
  let messages_toks = {
  let mut content = quote! {};
  + for message in &contract.messages {
  + let msg_ident = &message.sig.ident;
  +
  + use crate::ident_ext::IdentExt as _;
  + use heck::CamelCase as _;
  + let camelcase_msg_ident = Ident::new(
  + &message.sig.ident.to_owned_string().to_camel_case(),
  + message.sig.ident.span(),
  + );
  +
  + let msg_fn_args = quote! {};
  + let msg_call_args = quote! {};
  + let mut_msg = {
  + let self_arg = message.sig.decl.inputs.iter().next().unwrap();
  + if let ast::FnArg::SelfRef(syn::ArgSelfRef {
  + mutability: Some(_),
  + ..
  + }) = self_arg
  + {
  + true
  + } else {
  + false
  + }
  + };
  + let msg_toks = if mut_msg {
  + quote! {
  + .on_msg_mut::< #camelcase_msg_ident >(|env, #msg_fn_args| {
  + let (handler, state) = env.split_mut();
  + state. #msg_ident (handler, #msg_call_args)
  + })
  + }
  + } else {
  + quote! {
  + .on_msg::< #camelcase_msg_ident >(|env, #msg_fn_args| {
  + let (handler, state) = env.split();
  + state. #msg_ident (handler, #msg_call_args)
  + })
  + }
  + };
  + msg_toks.to_tokens(&mut content)
  + }
  content
  };
  