feat: poke user when supplying faulty configurations

crates/rust-analyzer/src/main_loop.rs

@@ -9,6 +9,7 @@ use std::{
 use always_assert::always;
 use crossbeam_channel::{select, Receiver};
 use ide_db::base_db::{SourceDatabaseExt, VfsPath};
+use itertools::Itertools;
 use lsp_server::{Connection, Notification, Request};
 use lsp_types::notification::Notification as _;
 use vfs::{ChangeKind, FileId};
@@ -731,7 +732,17 @@ impl GlobalState {
                                     // Note that json can be null according to the spec if the client can't
                                     // provide a configuration. This is handled in Config::update below.
                                     let mut config = Config::clone(&*this.config);
-                                    config.update(json.take());
+                                    if let Err(errors) = config.update(json.take()) {
+                                        let errors = errors
+                                            .iter()
+                                            .format_with("\n", |(key, e),f| {
+                                                f(key)?;
+                                                f(&": ")?;
+                                                f(e)
+                                            });
+                                        let msg= format!("Failed to deserialize config key(s):\n{}", errors);
+                                        this.show_message(lsp_types::MessageType::WARNING, msg);
+                                    }
                                     this.update_configuration(config);
                                 }
                             }