Add signposts for background preparation and indexing

Sources/LSPLogging/NonDarwinLogging.swift

@@ -394,5 +394,6 @@ public struct NonDarwinSignposter: Sendable {
 
   public func emitEvent(_ name: StaticString, id: NonDarwinSignpostID, _ message: NonDarwinLogMessage = "") {}
 
-  public func endInterval(_ name: StaticString, _ state: NonDarwinSignpostIntervalState, _ message: StaticString) {}
+  public func endInterval(_ name: StaticString, _ state: NonDarwinSignpostIntervalState, _ message: StaticString = "") {
+  }
 }

Sources/SemanticIndex/PreparationTaskDescription.swift

@@ -74,7 +74,10 @@ public struct PreparationTaskDescription: IndexTaskDescription {
     // Only use the last two digits of the preparation ID for the logging scope to avoid creating too many scopes.
     // See comment in `withLoggingScope`.
     // The last 2 digits should be sufficient to differentiate between multiple concurrently running preparation operations
-    await withLoggingScope("preparation-\(id % 100)") {
+    await withLoggingSubsystemAndScope(
+      subsystem: "org.swift.sourcekit-lsp.indexing",
+      scope: "preparation-\(id % 100)"
+    ) {
       await testHooks.preparationTaskDidStart?(self)
       let targetsToPrepare = await targetsToPrepare.asyncFilter {
         await !preparationUpToDateStatus.isUpToDate($0)
@@ -92,6 +95,12 @@ public struct PreparationTaskDescription: IndexTaskDescription {
       logger.log(
         "Starting preparation with priority \(Task.currentPriority.rawValue, privacy: .public): \(targetsToPrepareDescription)"
       )
+      let signposter = Logger(subsystem: LoggingScope.subsystem, category: "preparation").makeSignposter()
+      let signpostID = signposter.makeSignpostID()
+      let state = signposter.beginInterval("Preparing", id: signpostID, "Preparing \(targetsToPrepareDescription)")
+      defer {
+        signposter.endInterval("Preparing", state)
+      }
       let startDate = Date()
       do {
         try await buildSystemManager.prepare(

Sources/SemanticIndex/SemanticIndexManager.swift

@@ -186,6 +186,12 @@ public final actor SemanticIndexManager {
   /// This method is intended to initially update the index of a project after it is opened.
   public func scheduleBuildGraphGenerationAndBackgroundIndexAllFiles() async {
     generateBuildGraphTask = Task(priority: .low) {
+      let signposter = Logger(subsystem: LoggingScope.subsystem, category: "preparation").makeSignposter()
+      let signpostID = signposter.makeSignpostID()
+      let state = signposter.beginInterval("Preparing", id: signpostID, "Generating build graph")
+      defer {
+        signposter.endInterval("Preparing", state)
+      }
       await orLog("Generating build graph") { try await self.buildSystemManager.generateBuildGraph() }
       let index = index.checked(for: .modifiedFiles)
       let filesToIndex = await self.buildSystemManager.sourceFiles().lazy.map(\.uri)

Sources/SemanticIndex/UpdateIndexStoreTaskDescription.swift

@@ -310,6 +310,16 @@ public struct UpdateIndexStoreTaskDescription: IndexTaskDescription {
       return
     }
     let start = ContinuousClock.now
+    let signposter = Logger(subsystem: LoggingScope.subsystem, category: "indexing").makeSignposter()
+    let signpostID = signposter.makeSignpostID()
+    let state = signposter.beginInterval(
+      "Indexing",
+      id: signpostID,
+      "Indexing \(indexFile.fileURL?.lastPathComponent ?? indexFile.pseudoPath)"
+    )
+    defer {
+      signposter.endInterval("Indexing", state)
+    }
     let process = try Process.launch(
       arguments: processArguments,
       workingDirectory: workingDirectory