Use WorkDoneProgress LSP API for initial load

Addresses #3283

Rather than using custom UI for showing the loaded state. Rely
on the WorkDoneProgress API in 3.15.0
https://microsoft.github.io/language-server-protocol/specification#workDoneProgress.

No client-side work was necessary. The UI is not exactly what is
described in the issue but afaict that's how VS Code implements the LSP
API.

- The WorkDoneProgressEnd does not appear to display its message
  contents (controlled by vscode)

crates/rust-analyzer/src/main_loop.rs

@@ -16,7 +16,10 @@ use std::{
 
 use crossbeam_channel::{select, unbounded, RecvError, Sender};
 use lsp_server::{Connection, ErrorCode, Message, Notification, Request, RequestId, Response};
-use lsp_types::{ClientCapabilities, NumberOrString};
+use lsp_types::{
+    ClientCapabilities, NumberOrString, WorkDoneProgress, WorkDoneProgressBegin,
+    WorkDoneProgressCreateParams, WorkDoneProgressEnd, WorkDoneProgressReport,
+};
 use ra_cargo_watch::{url_from_path_with_drive_lowercasing, CheckOptions, CheckTask};
 use ra_ide::{Canceled, FileId, InlayHintsOptions, LibraryData, SourceRootId};
 use ra_prof::profile;
@@ -329,6 +332,7 @@ struct LoopState {
     in_flight_libraries: usize,
     pending_libraries: Vec<(SourceRootId, Vec<(FileId, RelativePathBuf, Arc<String>)>)>,
     workspace_loaded: bool,
+    roots_scanned_progress: Option<usize>,
 }
 
 impl LoopState {
@@ -428,11 +432,6 @@ fn loop_turn(
         && loop_state.in_flight_libraries == 0
     {
         loop_state.workspace_loaded = true;
-        let n_packages: usize = world_state.workspaces.iter().map(|it| it.n_packages()).sum();
-        if world_state.feature_flags.get("notifications.workspace-loaded") {
-            let msg = format!("workspace loaded, {} rust packages", n_packages);
-            show_message(req::MessageType::Info, msg, &connection.sender);
-        }
         world_state.check_watcher.update();
         pool.execute({
             let subs = loop_state.subscriptions.subscriptions();
@@ -440,6 +439,7 @@ fn loop_turn(
             move || snap.analysis().prime_caches(subs).unwrap_or_else(|_: Canceled| ())
         });
     }
+    send_startup_progress(&connection.sender, loop_state, world_state);
 
     if state_changed {
         update_file_notifications_on_threadpool(
@@ -703,6 +703,65 @@ fn on_diagnostic_task(task: DiagnosticTask, msg_sender: &Sender<Message>, state:
     }
 }
 
+fn send_startup_progress(
+    sender: &Sender<Message>,
+    loop_state: &mut LoopState,
+    world_state: &WorldState,
+) {
+    if !world_state.feature_flags.get("notifications.workspace-loaded") {
+        return;
+    }
+    let total: usize = world_state.workspaces.iter().map(|it| it.n_packages()).sum();
+    let progress = total - world_state.roots_to_scan;
+    if loop_state.roots_scanned_progress == Some(progress) {
+        return;
+    }
+    loop_state.roots_scanned_progress = Some(progress);
+
+    match (progress, loop_state.workspace_loaded) {
+        (0, false) => {
+            let work_done_progress_create = request_new::<req::WorkDoneProgressCreate>(
+                loop_state.next_request_id(),
+                WorkDoneProgressCreateParams {
+                    token: req::ProgressToken::String("rustAnalyzer/startup".into()),
+                },
+            );
+            sender.send(work_done_progress_create.into()).unwrap();
+            send_startup_progress_notif(
+                sender,
+                WorkDoneProgress::Begin(WorkDoneProgressBegin {
+                    title: "rust-analyzer".into(),
+                    cancellable: None,
+                    message: Some(format!("{}/{} packages", progress, total)),
+                    percentage: Some(100 as f64 * progress as f64 / total as f64),
+                }),
+            );
+        }
+        (_, false) => send_startup_progress_notif(
+            sender,
+            WorkDoneProgress::Report(WorkDoneProgressReport {
+                cancellable: None,
+                message: Some(format!("{}/{} packages", progress, total)),
+                percentage: Some(100 as f64 * progress as f64 / total as f64),
+            }),
+        ),
+        (_, true) => send_startup_progress_notif(
+            sender,
+            WorkDoneProgress::End(WorkDoneProgressEnd {
+                message: Some(format!("rust-analyzer loaded, {} packages", progress)),
+            }),
+        ),
+    }
+}
+
+fn send_startup_progress_notif(sender: &Sender<Message>, work_done_progress: WorkDoneProgress) {
+    let notif = notification_new::<req::Progress>(req::ProgressParams {
+        token: req::ProgressToken::String("rustAnalyzer/startup".into()),
+        value: req::ProgressParamsValue::WorkDone(work_done_progress),
+    });
+    sender.send(notif.into()).unwrap();
+}
+
 struct PoolDispatcher<'a> {
     req: Option<Request>,
     pool: &'a ThreadPool,