Return fileHandlingCapability.handled for all files that SwiftPMBuildSystem has build settings for

Previously, `SwiftPMBuildSystem` would report `.unhandled` as the file handling capability for `Package.swift`. In single workspace-folder setups, this was not an issue because we would always default to using the build system of the first/only workspace folder, which was the only `SwiftPMBuildSystem` and then returned compiler arguments despite saying that it couldn’t handle `Package.swift`.

This, however, breaks if you have a setup with multi workspace folders, where we can’t rely on the first workspace folder being able to provide build settings for the package manifest.

To fix this, report `.handled` file handling capability for all files that `SwiftPMBuildSystem` can compute build settings for.

Fixes #1210
rdar://127351614

Author: ahoppen

Sources/SKSwiftPMWorkspace/SwiftPMBuildSystem.swift

@@ -315,6 +315,11 @@ extension SwiftPMBuildSystem: SKCore.BuildSystem {
   public var indexPrefixMappings: [PathPrefixMapping] { return [] }
 
   public func buildSettings(for uri: DocumentURI, language: Language) throws -> FileBuildSettings? {
+    // SwiftPMBuildSystem doesn't respect the langue specified by the editor.
+    return try buildSettings(for: uri)
+  }
+
+  private func buildSettings(for uri: DocumentURI) throws -> FileBuildSettings? {
     guard let url = uri.fileURL else {
       // We can't determine build settings for non-file URIs.
       return nil
@@ -335,7 +340,7 @@ extension SwiftPMBuildSystem: SKCore.BuildSystem {
     }
 
     if path.extension == "h" {
-      return try settings(forHeader: path, language)
+      return try settings(forHeader: path)
     }
 
     return nil
@@ -432,14 +437,10 @@ extension SwiftPMBuildSystem: SKCore.BuildSystem {
   }
 
   public func fileHandlingCapability(for uri: DocumentURI) -> FileHandlingCapability {
-    guard let fileUrl = uri.fileURL else {
-      return .unhandled
-    }
-    if (try? buildTarget(for: AbsolutePath(validating: fileUrl.path))) != nil {
+    if (try? buildSettings(for: uri)) != nil {
       return .handled
-    } else {
-      return .unhandled
     }
+    return .unhandled
   }
 
   public func sourceFiles() -> [SourceFileInfo] {
@@ -491,7 +492,7 @@ extension SwiftPMBuildSystem {
   /// file.
   /// This is safe because all files within one target have the same build settings except for reference to the file
   /// itself, which we are replacing.
-  private func settings(forHeader path: AbsolutePath, _ language: Language) throws -> FileBuildSettings? {
+  private func settings(forHeader path: AbsolutePath) throws -> FileBuildSettings? {
     func impl(_ path: AbsolutePath) throws -> FileBuildSettings? {
       var dir = path.parentDirectory
       while !dir.isRoot {

Tests/SourceKitLSPTests/WorkspaceTests.swift

@@ -161,6 +161,39 @@ final class WorkspaceTests: XCTestCase {
     )
   }
 
+  func testOpenPackageManifestInMultiSwiftPMWorkspaceSetup() async throws {
+    let project = try await MultiFileTestProject(
+      files: [
+        // PackageA
+        "PackageA/Sources/MyLibrary/libA.swift": "",
+        "PackageA/Package.swift": SwiftPMTestProject.defaultPackageManifest,
+
+        // PackageB
+        "PackageB/Sources/MyLibrary/libB.swift": "",
+        "PackageB/Package.swift": SwiftPMTestProject.defaultPackageManifest,
+      ],
+      workspaces: { scratchDir in
+        return [
+          WorkspaceFolder(uri: DocumentURI(scratchDir)),
+          WorkspaceFolder(uri: DocumentURI(scratchDir.appendingPathComponent("PackageA"))),
+          WorkspaceFolder(uri: DocumentURI(scratchDir.appendingPathComponent("PackageB"))),
+        ]
+      }
+    )
+
+    let bPackageManifestUri = DocumentURI(
+      project.scratchDirectory.appendingPathComponent("PackageB").appendingPathComponent("Package.swift")
+    )
+
+    project.testClient.openDocument(SwiftPMTestProject.defaultPackageManifest, uri: bPackageManifestUri)
+
+    // Ensure that we get proper build settings for Package.swift and no error about `No such module: PackageDescription`
+    let diags = try await project.testClient.send(
+      DocumentDiagnosticsRequest(textDocument: TextDocumentIdentifier(bPackageManifestUri))
+    )
+    XCTAssertEqual(diags, .full(RelatedFullDocumentDiagnosticReport(items: [])))
+  }
+
   func testSwiftPMPackageInSubfolder() async throws {
     try await SkipUnless.swiftpmStoresModulesInSubdirectory()