Forward all errors that translate to .cancelled from document diagnostics request

We were only forwarding `CancellationError` but depending on when cancellation happens, we would get `SKDError.cancelled`, which we would translate to empty diagnostics, causing the test to fail.

Author: ahoppen

Sources/SourceKitLSP/Swift/SwiftLanguageService.swift

@@ -888,12 +888,15 @@ extension SwiftLanguageService {
         buildSettings: buildSettings
       )
       return .full(diagnosticReport)
-    } catch let error as CancellationError {
-      throw error
     } catch {
       // VS Code does not request diagnostics again for a document if the diagnostics request failed.
       // Since sourcekit-lsp usually recovers from failures (e.g. after sourcekitd crashes), this is undesirable.
       // Instead of returning an error, return empty results.
+      // Do forward cancellation because we don't want to clear diagnostics in the client if they cancel the diagnostic
+      // request.
+      if ResponseError(error) == .cancelled {
+        throw error
+      }
       logger.error(
         """
         Loading diagnostic failed with the following error. Returning empty diagnostics.

Tests/SourceKitLSPTests/PullDiagnosticsTests.swift

@@ -337,7 +337,7 @@ final class PullDiagnosticsTests: XCTestCase {
     let requestID = project.testClient.send(
       DocumentDiagnosticsRequest(textDocument: TextDocumentIdentifier(uri))
     ) { result in
-      XCTAssertEqual(result.failure?.code, .cancelled)
+      XCTAssertEqual(result, .failure(ResponseError.cancelled))
       diagnosticResponseReceived.fulfill()
     }
     project.testClient.send(CancelRequestNotification(id: requestID))