Remove RWLock from check watcher.

@matklad mentioned this might be a good idea.

So the general idea is that we don't really need the lock, as we can
just clone the check watcher state when creating a snapshot. We can then
use `Arc::get_mut` to get mutable access to the state from `WorldState`
when needed.

Running with this it seems to improve responsiveness a bit while cargo
is running, but I have no hard numbers to prove it. In any case, a
serialization point less is always better when we're trying to be
responsive.

crates/ra_cargo_watch/src/conv.rs

@@ -117,7 +117,7 @@ fn is_deprecated(rd: &RustDiagnostic) -> bool {
     }
 }
 
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 pub struct SuggestedFix {
     pub title: String,
     pub location: Location,

crates/ra_cargo_watch/src/lib.rs

@@ -7,7 +7,6 @@ use lsp_types::{
     Diagnostic, Url, WorkDoneProgress, WorkDoneProgressBegin, WorkDoneProgressEnd,
     WorkDoneProgressReport,
 };
-use parking_lot::RwLock;
 use std::{
     collections::HashMap,
     path::PathBuf,
@@ -38,7 +37,7 @@ pub struct CheckOptions {
 #[derive(Debug)]
 pub struct CheckWatcher {
     pub task_recv: Receiver<CheckTask>,
-    pub state: Arc<RwLock<CheckState>>,
+    pub state: Arc<CheckState>,
     cmd_send: Option<Sender<CheckCommand>>,
     handle: Option<JoinHandle<()>>,
 }
@@ -46,7 +45,7 @@ pub struct CheckWatcher {
 impl CheckWatcher {
     pub fn new(options: &CheckOptions, workspace_root: PathBuf) -> CheckWatcher {
         let options = options.clone();
-        let state = Arc::new(RwLock::new(CheckState::new()));
+        let state = Arc::new(CheckState::new());
 
         let (task_send, task_recv) = unbounded::<CheckTask>();
         let (cmd_send, cmd_recv) = unbounded::<CheckCommand>();
@@ -59,7 +58,7 @@ impl CheckWatcher {
 
     /// Returns a CheckWatcher that doesn't actually do anything
     pub fn dummy() -> CheckWatcher {
-        let state = Arc::new(RwLock::new(CheckState::new()));
+        let state = Arc::new(CheckState::new());
         CheckWatcher { task_recv: never(), cmd_send: None, handle: None, state }
     }
 
@@ -87,7 +86,7 @@ impl std::ops::Drop for CheckWatcher {
     }
 }
 
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 pub struct CheckState {
     diagnostic_collection: HashMap<Url, Vec<Diagnostic>>,
     suggested_fix_collection: HashMap<Url, Vec<SuggestedFix>>,

crates/ra_lsp_server/src/main_loop.rs

@@ -586,12 +586,14 @@ fn on_notification(
 
 fn on_check_task(
     task: CheckTask,
-    world_state: &WorldState,
+    world_state: &mut WorldState,
     task_sender: &Sender<Task>,
 ) -> Result<()> {
     match task {
         CheckTask::ClearDiagnostics => {
-            let cleared_files = world_state.check_watcher.state.write().clear();
+            let state = Arc::get_mut(&mut world_state.check_watcher.state)
+                .expect("couldn't get check watcher state as mutable");
+            let cleared_files = state.clear();
 
             // Send updated diagnostics for each cleared file
             for url in cleared_files {
@@ -600,11 +602,9 @@ fn on_check_task(
         }
 
         CheckTask::AddDiagnostic(url, diagnostic) => {
-            world_state
-                .check_watcher
-                .state
-                .write()
-                .add_diagnostic_with_fixes(url.clone(), diagnostic);
+            let state = Arc::get_mut(&mut world_state.check_watcher.state)
+                .expect("couldn't get check watcher state as mutable");
+            state.add_diagnostic_with_fixes(url.clone(), diagnostic);
 
             // We manually send a diagnostic update when the watcher asks
             // us to, to avoid the issue of having to change the file to

crates/ra_lsp_server/src/main_loop/handlers.rs

@@ -674,8 +674,7 @@ pub fn handle_code_action(
         res.push(action.into());
     }
 
-    for fix in world.check_watcher.read().fixes_for(&params.text_document.uri).into_iter().flatten()
-    {
+    for fix in world.check_watcher.fixes_for(&params.text_document.uri).into_iter().flatten() {
         let fix_range = fix.location.range.conv_with(&line_index);
         if fix_range.intersection(&range).is_none() {
             continue;
@@ -895,7 +894,7 @@ pub fn publish_diagnostics(
             tags: None,
         })
         .collect();
-    if let Some(check_diags) = world.check_watcher.read().diagnostics_for(&uri) {
+    if let Some(check_diags) = world.check_watcher.diagnostics_for(&uri) {
         diagnostics.extend(check_diags.iter().cloned());
     }
     Ok(req::PublishDiagnosticsParams { uri, diagnostics, version: None })

crates/ra_lsp_server/src/world.rs

@@ -63,7 +63,7 @@ pub struct WorldSnapshot {
     pub workspaces: Arc<Vec<ProjectWorkspace>>,
     pub analysis: Analysis,
     pub latest_requests: Arc<RwLock<LatestRequests>>,
-    pub check_watcher: Arc<RwLock<CheckState>>,
+    pub check_watcher: CheckState,
     vfs: Arc<RwLock<Vfs>>,
 }
 
@@ -220,7 +220,7 @@ impl WorldState {
             analysis: self.analysis_host.analysis(),
             vfs: Arc::clone(&self.vfs),
             latest_requests: Arc::clone(&self.latest_requests),
-            check_watcher: self.check_watcher.state.clone(),
+            check_watcher: (*self.check_watcher.state).clone(),
         }
     }