Remove std requirement

frame/contracts/proc-macro/src/lib.rs

@@ -641,9 +641,13 @@ fn expand_functions(def: &EnvDef, expand_blocks: bool, host_state: TokenStream2)
 			quote! {
 				if ::log::log_enabled!(target: "runtime::contracts::strace", ::log::Level::Trace) {
 					let result = #body;
-
-					#[cfg(feature = "std")]
-					ctx.ext.append_debug_buffer(&format!(#debug_buffer_fmt_str, #( #debug_buffer_fmt_args, )* result));
+					{
+						use sp_std::fmt::Write;
+						let mut w = sp_std::Writer::default();
+						let _ = ::core::write!(&mut w, #debug_buffer_fmt_str, #( #debug_buffer_fmt_args, )* result); 
+						let msg = core::str::from_utf8(&w.inner()).unwrap_or_default();
+						ctx.ext.append_debug_buffer(msg);
+					}
 					result
 
 				} else {