Merge pull request #2018 from ahoppen/output-paths-lsp-request

Add an experimental LSP request to return the output paths for all files in a target

Author: ahoppen

Contributor Documentation/LSP Extensions.md

@@ -678,6 +678,40 @@ export interface SourceKitOptionsResult {
 }
 ```
 
+## `workspace/_outputPaths`
+
+New request from the client to the server to retrieve the output paths of a target (see the `buildTarget/outputPaths` BSP request).
+
+This request will only succeed if the build server supports the `buildTarget/outputPaths` request.
+
+> [!IMPORTANT]
+> This request is experimental, guarded behind the `output-paths-request` experimental feature, and may be modified or removed in future versions of SourceKit-LSP without notice. Do not rely on it.
+
+
+- params: `OutputPathsRequest`
+- result: `OutputPathsResult`
+
+```ts
+export interface OutputPathsRequest {
+  /**
+   * The target whose output file paths to get.
+   */
+  target: DocumentURI;
+
+  /**
+   * The URI of the workspace to which the target belongs.
+   */
+  workspace: DocumentURI;
+}
+
+export interface OutputPathsResult {
+  /**
+   * The output paths for all source files in the target
+   */
+  outputPaths: string[];
+}
+```
+
 ## `workspace/getReferenceDocument`
 
 Request from the client to the server asking for contents of a URI having a custom scheme.

Documentation/Configuration File.md

@@ -53,7 +53,7 @@ The structure of the file is currently not guaranteed to be stable. Options may
   - `noLazy`: Prepare a target without generating object files but do not do lazy type checking and function body skipping. This uses SwiftPM's `--experimental-prepare-for-indexing-no-lazy` flag.
   - `enabled`: Prepare a target without generating object files.
 - `cancelTextDocumentRequestsOnEditAndClose: boolean`: Whether sending a `textDocument/didChange` or `textDocument/didClose` notification for a document should cancel all pending requests for that document.
-- `experimentalFeatures: ("on-type-formatting"|"set-options-request"|"sourcekit-options-request"|"is-indexing-request"|"structured-logs")[]`: Experimental features that are enabled.
+- `experimentalFeatures: ("on-type-formatting"|"set-options-request"|"sourcekit-options-request"|"is-indexing-request"|"structured-logs"|"output-paths-request")[]`: Experimental features that are enabled.
 - `swiftPublishDiagnosticsDebounceDuration: number`: The time that `SwiftLanguageService` should wait after an edit before starting to compute diagnostics and sending a `PublishDiagnosticsNotification`.
 - `workDoneProgressDebounceDuration: number`: When a task is started that should be displayed to the client as a work done progress, how many milliseconds to wait before actually starting the work done progress. This prevents flickering of the work done progress in the client for short-lived index tasks which end within this duration.
 - `sourcekitdRequestTimeout: number`: The maximum duration that a sourcekitd request should be allowed to execute before being declared as timed out. In general, editors should cancel requests that they are no longer interested in, but in case editors don't cancel requests, this ensures that a long-running non-cancelled request is not blocking sourcekitd and thus most semantic functionality. In particular, VS Code does not cancel the semantic tokens request, which can cause a long-running AST build that blocks sourcekitd.

Sources/LanguageServerProtocol/CMakeLists.txt

@@ -70,6 +70,7 @@ add_library(LanguageServerProtocol STATIC
   Requests/IsIndexingRequest.swift
   Requests/LinkedEditingRangeRequest.swift
   Requests/MonikersRequest.swift
+  Requests/OutputPathsRequest.swift
   Requests/PeekDocumentsRequest.swift
   Requests/PollIndexRequest.swift
   Requests/PrepareRenameRequest.swift

Sources/LanguageServerProtocol/Messages.swift

@@ -61,6 +61,7 @@ public let builtinRequests: [_RequestType.Type] = [
   IsIndexingRequest.self,
   LinkedEditingRangeRequest.self,
   MonikersRequest.self,
+  OutputPathsRequest.self,
   PeekDocumentsRequest.self,
   PollIndexRequest.self,
   PrepareRenameRequest.self,

Sources/LanguageServerProtocol/Requests/OutputPathsRequest.swift

@@ -0,0 +1,39 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+/// Request from the client to the server to retrieve the output paths of a target (see the `buildTarget/outputPaths`
+/// BSP request).
+///
+/// **(LSP Extension)**.
+public struct OutputPathsRequest: RequestType, Hashable {
+  public static let method: String = "workspace/_outputPaths"
+  public typealias Response = OutputPathsResponse
+
+  /// The target whose output file paths to get.
+  public var target: DocumentURI
+
+  /// The URI of the workspace to which the target belongs.
+  public var workspace: DocumentURI
+
+  public init(target: DocumentURI, workspace: DocumentURI) {
+    self.target = target
+    self.workspace = workspace
+  }
+}
+public struct OutputPathsResponse: ResponseType, Hashable {
+  /// The output paths for all source files in the target
+  public var outputPaths: [String]
+
+  public init(outputPaths: [String]) {
+    self.outputPaths = outputPaths
+  }
+}

Sources/SKOptions/ExperimentalFeatures.swift

@@ -28,4 +28,7 @@ public enum ExperimentalFeature: String, Codable, Sendable, CaseIterable {
 
   /// Indicate that the client can handle the experimental `structure` field in the `window/logMessage` notification.
   case structuredLogs = "structured-logs"
+
+  /// Enable the `workspace/_outputPaths` request.
+  case outputPathsRequest = "output-paths-request"
 }

Sources/SourceKitLSP/MessageHandlingDependencyTracker.swift

@@ -63,7 +63,7 @@ package enum MessageHandlingDependencyTracker: QueueBasedMessageHandlerDependenc
     case (.globalConfigurationChange, _): return true
     case (_, .globalConfigurationChange): return true
 
-    // globalDocumentState
+    // workspaceRequest
     case (.workspaceRequest, .workspaceRequest): return false
     case (.documentUpdate, .workspaceRequest): return true
     case (.workspaceRequest, .documentUpdate): return true
@@ -208,6 +208,8 @@ package enum MessageHandlingDependencyTracker: QueueBasedMessageHandlerDependenc
       self = .freestanding
     case is IsIndexingRequest:
       self = .freestanding
+    case is OutputPathsRequest:
+      self = .freestanding
     case is PollIndexRequest:
       self = .globalConfigurationChange
     case is RenameRequest:

Sources/SourceKitLSP/SourceKitLSPServer.swift

@@ -830,6 +830,8 @@ extension SourceKitLSPServer: QueueBasedMessageHandler {
       await self.handleRequest(for: request, requestHandler: self.inlayHint)
     case let request as RequestAndReply<IsIndexingRequest>:
       await request.reply { try await self.isIndexing(request.params) }
+    case let request as RequestAndReply<OutputPathsRequest>:
+      await request.reply { try await outputPaths(request.params) }
     case let request as RequestAndReply<PollIndexRequest>:
       await request.reply { try await pollIndex(request.params) }
     case let request as RequestAndReply<PrepareRenameRequest>:
@@ -1559,6 +1561,22 @@ extension SourceKitLSPServer {
     )
   }
 
+  func outputPaths(_ request: OutputPathsRequest) async throws -> OutputPathsResponse {
+    guard options.hasExperimentalFeature(.outputPathsRequest) else {
+      throw ResponseError.unknown("\(OutputPathsRequest.method) is an experimental request")
+    }
+    guard let workspace = self.workspaces.first(where: { $0.rootUri == request.workspace }) else {
+      throw ResponseError.unknown("No workspace with URI \(request.workspace.forLogging) found")
+    }
+    guard await workspace.buildSystemManager.initializationData?.outputPathsProvider ?? false else {
+      throw ResponseError.unknown("Build server for \(request.workspace.forLogging) does not support output paths")
+    }
+    let outputPaths = try await workspace.buildSystemManager.outputPaths(in: [
+      BuildTargetIdentifier(uri: request.target)
+    ])
+    return OutputPathsResponse(outputPaths: outputPaths)
+  }
+
   // MARK: - Language features
 
   func completion(

Sources/SourceKitLSP/Workspace.swift

@@ -105,6 +105,8 @@ package final class Workspace: Sendable, BuildSystemManagerDelegate {
   }
 
   /// The root directory of the workspace.
+  ///
+  /// `nil` when SourceKit-LSP is launched without a workspace (ie. no workspace folder or rootURI).
   package let rootUri: DocumentURI?
 
   /// Tracks dynamically registered server capabilities as well as the client's capabilities.

Tests/SourceKitLSPTests/WorkspaceTests.swift

@@ -1380,6 +1380,25 @@ final class WorkspaceTests: XCTestCase {
     )
     XCTAssert(options.compilerArguments.contains("-DHAVE_SETTINGS"))
   }
+
+  func testOutputPaths() async throws {
+    let project = try await SwiftPMTestProject(
+      files: [
+        "FileA.swift": "",
+        "FileB.swift": "",
+      ],
+      options: .testDefault(experimentalFeatures: [.outputPathsRequest]),
+      enableBackgroundIndexing: true
+    )
+
+    let outputPaths = try await project.testClient.send(
+      OutputPathsRequest(
+        target: BuildTargetIdentifier(target: "MyLibrary", destination: .target).uri,
+        workspace: DocumentURI(project.scratchDirectory)
+      )
+    )
+    XCTAssertEqual(outputPaths.outputPaths.map { $0.suffix(13) }.sorted(), ["FileA.swift.o", "FileB.swift.o"])
+  }
 }
 
 fileprivate let defaultSDKArgs: String = {