Enable background indexing by default

Author: ahoppen

Documentation/Enable Experimental Background Indexing.md

@@ -1,24 +1,22 @@
 # Enable Experimental Background Indexing
 
-Background indexing in SourceKit-LSP is available as an experimental feature. This guide shows how to set up background indexing and which caveats to expect.
+> [!IMPORTANT]
+> Background indexing is enabled by default in Swift 6.1 toolchains and above. This guide only refers to Swift 6.0 toolchains.
+
+Background indexing in SourceKit-LSP is enabled by default in Swift 6.1 toolchains and is available as an experimental feature for Swift 6.0 toolchains.
 
 ## Behavior Without Background Indexing
 
-By default SourceKit-LSP does not update its global index in the background or build Swift modules in the background. Thus, a lot of cross-module or global functionality is limited if the project hasn't been built recently. For example consider two modules: `Lib` and `Exec`, where `Exec` depends on `Lib`: Without background indexing, if a function is added to `Lib`, completion/jump to definition/etc in `Exec` would not be able to see that function until after a build. Background indexing solves that issue.
+With background indexing disabled SourceKit-LSP does not update its global index in the background or build Swift modules in the background. Thus, a lot of cross-module or global functionality is limited if the project hasn't been built recently. For example consider two modules: `Lib` and `Exec`, where `Exec` depends on `Lib`: Without background indexing, if a function is added to `Lib`, completion/jump to definition/etc in `Exec` would not be able to see that function until after a build. Background indexing solves that issue.
 
 ## Set Up
 
-1. Install a `main` or `release/6.0` Swift Development Snapshot from https://www.swift.org/install or install the [Xcode 16 beta](https://developer.apple.com/xcode/).
-2. Point your editor to the newly installed toolchain.
-   - In VS Code on macOS this can be done by adding the following to your `settings.json`:
-     - For open source toolchains `"swift.path": "/Library/Developer/Toolchains/swift-latest.xctoolchain/usr/bin"`
-     - When installing the Xcode 16 beta `"swift.path": "/Applications/Xcode-beta.app/Library/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin"`
-   - In VS Code on other platforms, you need to set the `swift.path` to the `usr/bin` directory of your toolchain’s install location.
-   - Other editors likely also have a way to pick the Swift toolchain, the exact steps vary by your setup.
+1. Install the Swift 6.0 toolchain or install [Xcode 16](https://developer.apple.com/xcode/).
 3. Enable the experimental `background-indexing` feature by creating a [configuration file](Configuration%20File.md) with the following contents at `~/.sourcekit-lsp/config.json` with the following contents:
 ```json
 {
-  "backgroundIndexing": true
+  "backgroundIndexing": true,
+  "backgroundPreparationMode": "enabled"
 }
 ```
 

Sources/SKOptions/SourceKitLSPOptions.swift

@@ -288,7 +288,7 @@ public struct SourceKitLSPOptions: Sendable, Codable, Equatable {
   public var backgroundIndexing: Bool?
 
   public var backgroundIndexingOrDefault: Bool {
-    return backgroundIndexing ?? false
+    return backgroundIndexing ?? true
   }
 
   public var backgroundPreparationMode: String?
@@ -297,7 +297,7 @@ public struct SourceKitLSPOptions: Sendable, Codable, Equatable {
     if let backgroundPreparationMode, let parsed = BackgroundPreparationMode(rawValue: backgroundPreparationMode) {
       return parsed
     }
-    return .build
+    return .enabled
   }
 
   /// Whether sending a `textDocument/didChange` or `textDocument/didClose` notification for a document should cancel

Sources/SKTestSupport/SkipUnless.swift

@@ -450,7 +450,10 @@ package actor SkipUnless {
           ],
           manifest: SwiftPMTestProject.macroPackageManifest
         )
-        try await SwiftPMTestProject.build(at: project.scratchDirectory)
+        try await SwiftPMTestProject.build(
+          at: project.scratchDirectory,
+          extraArguments: ["--experimental-prepare-for-indexing"]
+        )
         return .featureSupported
       } catch {
         return .featureUnsupported(

Sources/SKTestSupport/SwiftPMTestProject.swift

@@ -223,18 +223,19 @@ package class SwiftPMTestProject: MultiFileTestProject {
   }
 
   /// Build a SwiftPM package package manifest is located in the directory at `path`.
-  package static func build(at path: URL) async throws {
+  package static func build(at path: URL, extraArguments: [String] = []) async throws {
     guard let swift = await ToolchainRegistry.forTesting.default?.swift?.asURL else {
       throw Error.swiftNotFound
     }
-    var arguments = [
-      try swift.filePath,
-      "build",
-      "--package-path", try path.filePath,
-      "--build-tests",
-      "-Xswiftc", "-index-ignore-system-modules",
-      "-Xcc", "-index-ignore-system-symbols",
-    ]
+    var arguments =
+      [
+        try swift.filePath,
+        "build",
+        "--package-path", try path.filePath,
+        "--build-tests",
+        "-Xswiftc", "-index-ignore-system-modules",
+        "-Xcc", "-index-ignore-system-symbols",
+      ] + extraArguments
     if let globalModuleCache = try globalModuleCache {
       arguments += [
         "-Xswiftc", "-module-cache-path", "-Xswiftc", try globalModuleCache.filePath,

Tests/BuildSystemIntegrationTests/SwiftPMBuildSystemTests.swift

@@ -1030,6 +1030,7 @@ private func buildPath(
   options: SourceKitLSPOptions.SwiftPMOptions = SourceKitLSPOptions.SwiftPMOptions(),
   platform: String
 ) -> AbsolutePath {
-  let buildPath = AbsolutePath(validatingOrNil: options.scratchPath) ?? root.appending(component: ".build")
+  let buildPath =
+    AbsolutePath(validatingOrNil: options.scratchPath) ?? root.appending(components: ".build", "index-build")
   return buildPath.appending(components: platform, "\(options.configuration ?? .debug)")
 }

Tests/SourceKitLSPTests/ExpandMacroTests.swift

@@ -59,7 +59,7 @@ final class ExpandMacroTests: XCTestCase {
       """,
     ]
 
-    for (getReferenceDocument, peekDocuments) in cartesianProduct([true], [true]) {
+    for (getReferenceDocument, peekDocuments) in cartesianProduct([true, false], [true, false]) {
       let project = try await SwiftPMTestProject(
         files: files,
         manifest: SwiftPMTestProject.macroPackageManifest,