settings: Show notification when user/project settings fail to parse (#18122)

Closes #16876

We only ever showed parsing errors, but not if something failed to
deserialize.

Basically, if you had a stray `,` somewhere, we'd show a notification
for user errors, but only squiggly lines if you had a `[]` instead of a
`{}`.

The squiggly lines would only show up when there were schema errors.

In the case of `formatter` settings, for example, if someone put in a
`{}` instead of `[]`, we'd never show anything.

With this change we always show a notification if parsing user or
project settings fails.

(Right now, the error message might still be bad, but that's a separate
change)


Release Notes:

- Added a notification to warn users if their user settings or
project-local settings failed to deserialize.

Demo:


https://github.com/user-attachments/assets/e5c48165-f2f7-4b5c-9c6d-6ea74f678683

crates/project/src/project_settings.rs

@@ -1,11 +1,11 @@
 use collections::HashMap;
 use fs::Fs;
-use gpui::{AppContext, AsyncAppContext, BorrowAppContext, Model, ModelContext};
+use gpui::{AppContext, AsyncAppContext, BorrowAppContext, EventEmitter, Model, ModelContext};
 use paths::local_settings_file_relative_path;
 use rpc::{proto, AnyProtoClient, TypedEnvelope};
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
-use settings::{Settings, SettingsSources, SettingsStore};
+use settings::{InvalidSettingsError, Settings, SettingsSources, SettingsStore};
 use std::{
     path::{Path, PathBuf},
     sync::Arc,
@@ -176,6 +176,13 @@ pub enum SettingsObserverMode {
     Remote,
 }
 
+#[derive(Clone, Debug, PartialEq)]
+pub enum SettingsObserverEvent {
+    LocalSettingsUpdated(Result<(), InvalidSettingsError>),
+}
+
+impl EventEmitter<SettingsObserverEvent> for SettingsObserver {}
+
 pub struct SettingsObserver {
     mode: SettingsObserverMode,
     downstream_client: Option<AnyProtoClient>,
@@ -415,11 +422,16 @@ impl SettingsObserver {
     ) {
         let worktree_id = worktree.read(cx).id();
         let remote_worktree_id = worktree.read(cx).id();
-        cx.update_global::<SettingsStore, _>(|store, cx| {
+
+        let result = cx.update_global::<SettingsStore, anyhow::Result<()>>(|store, cx| {
             for (directory, file_content) in settings_contents {
-                store
-                    .set_local_settings(worktree_id, directory.clone(), file_content.as_deref(), cx)
-                    .log_err();
+                store.set_local_settings(
+                    worktree_id,
+                    directory.clone(),
+                    file_content.as_deref(),
+                    cx,
+                )?;
+
                 if let Some(downstream_client) = &self.downstream_client {
                     downstream_client
                         .send(proto::UpdateWorktreeSettings {
@@ -431,6 +443,25 @@ impl SettingsObserver {
                         .log_err();
                 }
             }
-        })
+            anyhow::Ok(())
+        });
+
+        match result {
+            Err(error) => {
+                if let Ok(error) = error.downcast::<InvalidSettingsError>() {
+                    if let InvalidSettingsError::LocalSettings {
+                        ref path,
+                        ref message,
+                    } = error
+                    {
+                        log::error!("Failed to set local settings in {:?}: {:?}", path, message);
+                        cx.emit(SettingsObserverEvent::LocalSettingsUpdated(Err(error)));
+                    }
+                }
+            }
+            Ok(()) => {
+                cx.emit(SettingsObserverEvent::LocalSettingsUpdated(Ok(())));
+            }
+        }
     }
 }