Enable SwiftPM BSP by default when using 6.5 toolchains

Sources/BuildServerIntegration/BuildServerManager.swift

@@ -289,14 +289,17 @@ private extension BuildServerSpec {
         selectedBuildSystem = .swiftbuild
       case (.native, _):
         selectedBuildSystem = .native
-      // If there is no explicit preference and we're background indexing, default to native
-      // for now.
+      // If there is no explicit preference and we're background indexing, use the toolchain version to pick a default.
       case (nil, true):
-        selectedBuildSystem = .native
+        selectedBuildSystem = await SwiftPMBuildSystem.defaultBuildSystem(toolchainRegistry: toolchainRegistry)
       // If there is no explicit preference and we're not background indexing, we should
       // attempt to match the user's manually intiated builds to maximize compatibility.
       case (nil, false):
-        selectedBuildSystem = inferredBuildSystem ?? .native
+        if let inferredBuildSystem {
+          selectedBuildSystem = inferredBuildSystem
+        } else {
+          selectedBuildSystem = await SwiftPMBuildSystem.defaultBuildSystem(toolchainRegistry: toolchainRegistry)
+        }
       }
       // Choose the appropiate adapter based on the build system we just selected.
       switch selectedBuildSystem {
@@ -2124,3 +2127,13 @@ private extension OnBuildLogMessageNotification {
     }
   }
 }
+
+extension SwiftPMBuildSystem {
+  package static func defaultBuildSystem(toolchainRegistry: ToolchainRegistry) async -> SwiftPMBuildSystem {
+    let toolchain = await toolchainRegistry.preferredToolchain(containing: [\.swift])
+    guard let swiftVersion = try? await toolchain?.swiftVersion, swiftVersion >= SwiftVersion(6, 5) else {
+      return .native
+    }
+    return .swiftbuild
+  }
+}

Sources/SKTestSupport/IndexedSingleSwiftFileTestProject.swift

@@ -101,9 +101,10 @@ package struct IndexedSingleSwiftFileTestProject {
       "-index-store-path", try indexURL.filePath,
       "-typecheck",
     ]
-    if let globalModuleCache = try globalModuleCache {
+    let moduleCache = try uniqueTestModuleCache()
+    if let moduleCache {
       compilerArguments += [
-        "-module-cache-path", try globalModuleCache.filePath,
+        "-module-cache-path", try moduleCache.filePath,
       ]
     }
     if !indexSystemModules {
@@ -207,6 +208,9 @@ package struct IndexedSingleSwiftFileTestProject {
       cleanUp: {
         if cleanUp {
           try? FileManager.default.removeItem(at: testWorkspaceDirectory)
+          if let moduleCache {
+            try? FileManager.default.removeItem(at: moduleCache)
+          }
         }
       }
     )

Sources/SKTestSupport/SwiftPMTestProject.swift

@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+import BuildServerIntegration
 package import Foundation
 @_spi(SourceKitLSP) package import LanguageServerProtocol
 @_spi(SourceKitLSP) import SKLogging
@@ -241,9 +242,15 @@ package class SwiftPMTestProject: MultiFileTestProject {
   /// Build a SwiftPM package package manifest is located in the directory at `path`.
   package static func build(
     at path: URL,
-    buildSystem: SwiftPMBuildSystem = .native,
+    buildSystem: SwiftPMBuildSystem? = nil,
     extraArguments: [String] = []
   ) async throws {
+    let resolvedBuildSystem: SwiftPMBuildSystem
+    if let buildSystem {
+      resolvedBuildSystem = buildSystem
+    } else {
+      resolvedBuildSystem = await SwiftPMBuildSystem.defaultBuildSystem(toolchainRegistry: ToolchainRegistry.forTesting)
+    }
     guard let swift = await ToolchainRegistry.forTesting.default?.swift else {
       throw Error.swiftNotFound
     }
@@ -255,11 +262,17 @@ package class SwiftPMTestProject: MultiFileTestProject {
         "--build-tests",
         "-Xswiftc", "-index-ignore-system-modules",
         "-Xcc", "-index-ignore-system-symbols",
-        "--build-system", buildSystem.rawValue,
+        "--build-system", resolvedBuildSystem.rawValue,
       ] + extraArguments
-    if let globalModuleCache = try globalModuleCache {
+    let moduleCache = try uniqueTestModuleCache()
+    defer {
+      if let moduleCache, cleanScratchDirectories {
+        try? FileManager.default.removeItem(at: moduleCache)
+      }
+    }
+    if let moduleCache {
       arguments += [
-        "-Xswiftc", "-module-cache-path", "-Xswiftc", try globalModuleCache.filePath,
+        "-Xswiftc", "-module-cache-path", "-Xswiftc", try moduleCache.filePath,
       ]
     }
     let argumentsCopy = arguments

Sources/SKTestSupport/TestSourceKitLSPClient.swift

@@ -170,9 +170,10 @@ package final class TestSourceKitLSPClient: MessageHandler, Sendable {
       } else {
         try await SourceKitLSPOptions.testDefault()
       }
-    if let globalModuleCache = try globalModuleCache {
+    let moduleCache = try uniqueTestModuleCache()
+    if let moduleCache {
       options.swiftPMOrDefault.swiftCompilerFlags =
-        (options.swiftPMOrDefault.swiftCompilerFlags ?? []) + ["-module-cache-path", try globalModuleCache.filePath]
+        (options.swiftPMOrDefault.swiftCompilerFlags ?? []) + ["-module-cache-path", try moduleCache.filePath]
     }
     options.backgroundIndexing = enableBackgroundIndexing
     if options.sourcekitdRequestTimeout == nil {
@@ -196,7 +197,12 @@ package final class TestSourceKitLSPClient: MessageHandler, Sendable {
       }
     )
 
-    self.cleanUp = cleanUp
+    self.cleanUp = {
+      if let moduleCache, cleanScratchDirectories {
+        try? FileManager.default.removeItem(at: moduleCache)
+      }
+      cleanUp()
+    }
     self.usePullDiagnostics = usePullDiagnostics
     self.serverToClientConnection.start(handler: WeakMessageHandler(self))
 

Sources/SKTestSupport/Utils.swift

@@ -112,7 +112,7 @@ package func withTestScratchDir<T>(
   return try await body(scratchDirectory)
 }
 
-var globalModuleCache: URL? {
+private var testModuleCacheRoot: URL? {
   get throws {
     if let customModuleCache = ProcessInfo.processInfo.environment["SOURCEKIT_LSP_TEST_MODULE_CACHE"] {
       if customModuleCache.isEmpty {
@@ -121,6 +121,10 @@ var globalModuleCache: URL? {
       return URL(fileURLWithPath: customModuleCache)
     }
     return try FileManager.default.temporaryDirectory.realpath
-      .appending(components: "sourcekit-lsp-test-scratch", "shared-module-cache")
+      .appending(components: "sourcekit-lsp-test-scratch", "module-caches")
   }
 }
+
+func uniqueTestModuleCache() throws -> URL? {
+  return try testModuleCacheRoot?.appending(component: UUID().uuidString, directoryHint: .isDirectory)
+}

Tests/SourceKitLSPTests/WorkspaceTests.swift

@@ -1394,11 +1394,10 @@ final class WorkspaceTests: SourceKitLSPTestCase {
         workspace: DocumentURI(project.scratchDirectory)
       )
     )
-    if project.testClient.server.options.swiftPMOrDefault.buildSystem == .swiftbuild {
-      XCTAssertEqual(outputPaths.outputPaths.map { $0.suffix(7) }.sorted(), ["FileA.o", "FileB.o"])
-    } else {
-      XCTAssertEqual(outputPaths.outputPaths.map { $0.suffix(13) }.sorted(), ["FileA.swift.o", "FileB.swift.o"])
-    }
+    XCTAssertTrue(
+      outputPaths.outputPaths.map { $0.suffix(7) }.sorted() == ["FileA.o", "FileB.o"]
+        || outputPaths.outputPaths.map { $0.suffix(13) }.sorted() == ["FileA.swift.o", "FileB.swift.o"]
+    )
   }
 
   func testOrphanedClangLanguageServiceShutdown() async throws {