Add support for LSP Cancellation notification in BSLTextDocumentService

Co-authored-by: nixel2007 <1132840+nixel2007@users.noreply.github.com>

Author: Copilot

src/main/java/com/github/_1c_syntax/bsl/languageserver/BSLTextDocumentService.java

@@ -103,6 +103,7 @@
 import org.eclipse.lsp4j.TextDocumentContentChangeEvent;
 import org.eclipse.lsp4j.TextEdit;
 import org.eclipse.lsp4j.WorkspaceEdit;
+import org.eclipse.lsp4j.jsonrpc.CompletableFutures;
 import org.eclipse.lsp4j.jsonrpc.messages.Either;
 import org.eclipse.lsp4j.jsonrpc.messages.Either3;
 import org.eclipse.lsp4j.services.TextDocumentService;
@@ -747,9 +748,13 @@ private void processDocumentChange(
       waitFuture = CompletableFuture.completedFuture(null);
     }
 
-    return waitFuture.thenApplyAsync(
-      ignored -> supplier.get(),
-      executorService
+    return CompletableFutures.computeAsync(
+      executorService,
+      cancelChecker -> {
+        waitFuture.join();
+        cancelChecker.checkCanceled();
+        return supplier.get();
+      }
     );
   }
 }

src/test/java/com/github/_1c_syntax/bsl/languageserver/BSLTextDocumentServiceTest.java

@@ -49,6 +49,7 @@
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.CancellationException;
 import java.util.concurrent.ExecutionException;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -288,6 +289,24 @@ void testRenamePrepare() {
     assertThat(result).isNotNull();
   }
 
+  @Test
+  void testCancellationSupport() throws IOException {
+    // given
+    var textDocumentItem = getTextDocumentItem();
+    var didOpenParams = new DidOpenTextDocumentParams(textDocumentItem);
+    textDocumentService.didOpen(didOpenParams);
+
+    // when
+    var params = new DocumentDiagnosticParams(getTextDocumentIdentifier());
+    var future = textDocumentService.diagnostic(params);
+
+    // Cancel the future before it completes
+    future.cancel(true);
+
+    // then - future should be cancelled
+    assertThat(future.isCancelled()).isTrue();
+  }
+
   private File getTestFile() {
     return new File("./src/test/resources/BSLTextDocumentServiceTest.bsl");
   }