Better error messages when the proc-macro-server fails to start

crates/rust-analyzer/src/cli/load_cargo.rs

@@ -60,9 +60,9 @@ pub fn load_workspace(
 
     let proc_macro_client = if load_config.with_proc_macro {
         let path = AbsPathBuf::assert(std::env::current_exe()?);
-        Some(ProcMacroServer::spawn(path, &["proc-macro"]).unwrap())
+        Ok(ProcMacroServer::spawn(path, &["proc-macro"]).unwrap())
     } else {
-        None
+        Err("proc macro server not started".to_owned())
     };
 
     let crate_graph = ws.to_crate_graph(
@@ -89,7 +89,7 @@ pub fn load_workspace(
     if load_config.prefill_caches {
         host.analysis().parallel_prime_caches(1, |_| {})?;
     }
-    Ok((host, vfs, proc_macro_client))
+    Ok((host, vfs, proc_macro_client.ok()))
 }
 
 fn load_crate_graph(