Return compiler arguments for invalid package manifests

Currently, when there‘s a syntax error in a package manifest, we don’t get any build settings from it in SourceKit-LSP and thus loose almost all semantic functionality. If we can’t parse the package manifest, fall back to providing build settings by assuming it has the current Swift tools version.

Currently, when there‘s a syntax error in a package manifest, we don’t get any build settings from it in SourceKit-LSP and thus loose almost all semantic functionality. If we can’t parse the package manifest, fall back to providing build settings by assuming it has the current Swift tools version.

Fixes #1704
rdar://136423767

Author: ahoppen

Sources/BuildSystemIntegration/SwiftPMBuildSystem.swift

@@ -783,7 +783,7 @@ package actor SwiftPMBuildSystem: BuiltInBuildSystem {
 
   /// Retrieve settings for a package manifest (Package.swift).
   private func settings(forPackageManifest path: AbsolutePath) throws -> TextDocumentSourceKitOptionsResponse? {
-    let compilerArgs = swiftPMWorkspace.interpreterFlags(for: path.parentDirectory) + [path.pathString]
+    let compilerArgs = try swiftPMWorkspace.interpreterFlags(for: path) + [path.pathString]
     return TextDocumentSourceKitOptionsResponse(compilerArguments: compilerArgs)
   }
 }

Tests/BuildSystemIntegrationTests/SwiftPMBuildSystemTests.swift

@@ -1148,6 +1148,39 @@ final class SwiftPMBuildSystemTests: XCTestCase {
       XCTAssert(compilerArgs.contains(try versionSpecificManifestURL.filePath))
     }
   }
+
+  func testBuildSettingsForInvalidManifest() async throws {
+    try await withTestScratchDir { tempDir in
+      try FileManager.default.createFiles(
+        root: tempDir,
+        files: [
+          "pkg/Sources/lib/a.swift": "",
+          "pkg/Package.swift": """
+          // swift-tools-version: 4.2
+          import PackageDescription
+          """,
+        ]
+      )
+      let packageRoot = try tempDir.appendingPathComponent("pkg").realpath
+      let manifestURL = packageRoot.appendingPathComponent("Package.swift")
+      let buildSystemManager = await BuildSystemManager(
+        buildSystemSpec: BuildSystemSpec(kind: .swiftPM, projectRoot: packageRoot),
+        toolchainRegistry: .forTesting,
+        options: SourceKitLSPOptions(),
+        connectionToClient: DummyBuildSystemManagerConnectionToClient(),
+        buildSystemTestHooks: BuildSystemTestHooks()
+      )
+      await buildSystemManager.waitForUpToDateBuildGraph()
+      let settings = await buildSystemManager.buildSettingsInferredFromMainFile(
+        for: DocumentURI(manifestURL),
+        language: .swift,
+        fallbackAfterTimeout: false
+      )
+      let compilerArgs = try XCTUnwrap(settings?.compilerArguments)
+      XCTAssert(compilerArgs.contains("-package-description-version"))
+      XCTAssert(compilerArgs.contains(try manifestURL.filePath))
+    }
+  }
 }
 
 private func assertArgumentsDoNotContain(