Fix race condition in "Format edited lines" causing StringIndexOutOfBoundsException

org.eclipse.jdt.text.tests/src/org/eclipse/jdt/text/tests/DocumentDirtyTrackerTest.java

@@ -0,0 +1,311 @@
+/*******************************************************************************
+ * Copyright (c) 2025 Carsten Hammer and others.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Carsten Hammer - initial API and implementation (with assistance from GitHub Copilot)
+ *******************************************************************************/
+package org.eclipse.jdt.text.tests;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import org.eclipse.jface.text.Document;
+import org.eclipse.jface.text.IDocument;
+import org.eclipse.jface.text.IRegion;
+
+import org.eclipse.jdt.internal.ui.javaeditor.DocumentDirtyTracker;
+
+/**
+ * Tests for DocumentDirtyTracker to ensure it correctly tracks dirty lines
+ * and prevents race conditions in format-on-save operations.
+ */
+public class DocumentDirtyTrackerTest {
+
+	private IDocument document;
+	private DocumentDirtyTracker tracker;
+
+	@BeforeEach
+	public void setUp() {
+		document = new Document();
+		tracker = DocumentDirtyTracker.get(document);
+	}
+
+	@AfterEach
+	public void tearDown() {
+		if (tracker != null) {
+			tracker.dispose();
+		}
+	}
+
+	@Test
+	public void testInitiallyNoDirtyRegions() {
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNull(regions, "Should have no dirty regions initially");
+	}
+
+	@Test
+	public void testSingleLineEdit() {
+		document.set("line1\nline2\nline3\n");
+		tracker.clearDirtyLines(); // Clear initial dirty marks
+
+		// Edit line 1
+		document.set("modified1\nline2\nline3\n");
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should have dirty regions after edit");
+		assertEquals(1, regions.length, "Should have 1 dirty region");
+	}
+
+	@Test
+	public void testMultipleConsecutiveLines() {
+		document.set("line1\nline2\nline3\nline4\n");
+		tracker.clearDirtyLines();
+
+		// Edit lines 1 and 2
+		document.set("modified1\nmodified2\nline3\nline4\n");
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should have dirty regions");
+		assertEquals(1, regions.length, "Should merge consecutive lines into 1 region");
+	}
+
+	@Test
+	public void testNonConsecutiveLines() {
+		document.set("line1\nline2\nline3\nline4\n");
+		tracker.clearDirtyLines();
+
+		// Mark lines 0 and 2 as dirty manually
+		tracker.markLinesDirty(0, 2);
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should have dirty regions");
+		assertEquals(2, regions.length, "Should have 2 separate regions");
+	}
+
+	@Test
+	public void testLineInsertion() {
+		document.set("line1\nline2\nline3\n");
+		tracker.clearDirtyLines();
+
+		// Mark line 1 as dirty
+		tracker.markLinesDirty(1);
+
+		// Insert a line before line 1
+		document.set("line1\ninserted\nline2\nline3\n");
+
+		// The dirty line should have shifted from 1 to 2
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should still have dirty regions after insertion");
+	}
+
+	@Test
+	public void testLineDeletion() {
+		document.set("line1\nline2\nline3\nline4\n");
+		tracker.clearDirtyLines();
+
+		// Mark line 2 as dirty
+		tracker.markLinesDirty(2);
+
+		// Delete line 1
+		document.set("line1\nline3\nline4\n");
+
+		// The dirty line should have shifted from 2 to 1
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should still have dirty regions after deletion");
+	}
+
+	@Test
+	public void testClearDirtyLines() {
+		document.set("line1\nline2\nline3\n");
+		tracker.clearDirtyLines();
+
+		// Edit a line
+		document.set("modified1\nline2\nline3\n");
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should have dirty regions before clear");
+
+		// Clear dirty lines
+		tracker.clearDirtyLines();
+
+		regions = tracker.getDirtyRegions();
+		assertNull(regions, "Should have no dirty regions after clear");
+	}
+
+	@Test
+	public void testUTF8Characters() {
+		// Test with UTF-8 characters including emojis
+		document.set("Hello 世界\n你好 World\nEmoji 😀🎉\n");
+		tracker.clearDirtyLines();
+
+		// Edit the emoji line
+		document.set("Hello 世界\n你好 World\nModified 🚀✨\n");
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should handle UTF-8 characters correctly");
+		assertEquals(1, regions.length, "Should have 1 dirty region");
+	}
+
+	@Test
+	public void testRapidSuccessiveEdits() {
+		document.set("line1\nline2\nline3\n");
+		tracker.clearDirtyLines();
+
+		// Simulate rapid successive edits on different lines
+		document.set("mod1\nline2\nline3\n");
+		document.set("mod1\nmod2\nline3\n");
+		document.set("mod1\nmod2\nmod3\n");
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should track all rapid edits");
+		// All lines should be marked as dirty
+		assertEquals(1, regions.length, "All consecutive lines should be in 1 region");
+	}
+
+	@Test
+	public void testEmptyDocument() {
+		document.set("");
+		tracker.clearDirtyLines();
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNull(regions, "Empty document should have no dirty regions");
+	}
+
+	@Test
+	public void testSingleLineDocument() {
+		document.set("single line");
+		tracker.clearDirtyLines();
+
+		// Edit the single line
+		document.set("modified line");
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should have dirty regions for single line edit");
+		assertEquals(1, regions.length, "Should have 1 dirty region");
+	}
+
+	@Test
+	public void testRegionBounds() {
+		document.set("line1\nline2\nline3\n");
+		tracker.clearDirtyLines();
+
+		// Edit line 1
+		document.set("modified1\nline2\nline3\n");
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should have regions");
+
+		// Verify region is within document bounds
+		for (IRegion region : regions) {
+			int offset = region.getOffset();
+			int length = region.getLength();
+			int docLength = document.getLength();
+
+			assertTrue(offset >= 0, "Offset should be non-negative");
+			assertTrue(length >= 0, "Length should be non-negative");
+			assertTrue(offset + length <= docLength, "Region should be within document bounds");
+		}
+	}
+
+	@Test
+	public void testMultipleDocuments() {
+		// Test that different documents have independent trackers
+		IDocument doc1 = new Document("doc1 line1\ndoc1 line2\n");
+		IDocument doc2 = new Document("doc2 line1\ndoc2 line2\n");
+
+		DocumentDirtyTracker tracker1 = DocumentDirtyTracker.get(doc1);
+		DocumentDirtyTracker tracker2 = DocumentDirtyTracker.get(doc2);
+
+		tracker1.clearDirtyLines();
+		tracker2.clearDirtyLines();
+
+		// Edit only doc1
+		doc1.set("doc1 modified\ndoc1 line2\n");
+
+		IRegion[] regions1 = tracker1.getDirtyRegions();
+		IRegion[] regions2 = tracker2.getDirtyRegions();
+
+		assertNotNull(regions1, "Doc1 should have dirty regions");
+		assertNull(regions2, "Doc2 should not have dirty regions");
+
+		tracker1.dispose();
+		tracker2.dispose();
+	}
+
+	@Test
+	public void testSameDocumentReturnsSameTracker() {
+		DocumentDirtyTracker tracker1 = DocumentDirtyTracker.get(document);
+		DocumentDirtyTracker tracker2 = DocumentDirtyTracker.get(document);
+
+		assertEquals(tracker1, tracker2, "Same document should return same tracker instance");
+	}
+
+	@Test
+	public void testIncrementalSingleLineEdit() throws Exception {
+		document.set("line1\nline2\nline3\n");
+		tracker.clearDirtyLines();
+
+		// Incremental edit on line 0: replace "line1" with "modified1"
+		document.replace(0, 5, "modified1");
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should have dirty regions after incremental edit");
+		assertEquals(1, regions.length, "Should have 1 dirty region");
+	}
+
+	@Test
+	public void testIncrementalInsertNewLine() throws Exception {
+		document.set("line1\nline2\nline3\n");
+		tracker.clearDirtyLines();
+
+		// Insert a new line after "line1\n" (offset 6)
+		document.replace(6, 0, "inserted\n");
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should have dirty regions after line insertion");
+	}
+
+	@Test
+	public void testIncrementalDeleteLine() throws Exception {
+		document.set("line1\nline2\nline3\n");
+		tracker.clearDirtyLines();
+
+		// Mark line 2 as dirty first
+		tracker.markLinesDirty(2);
+
+		// Delete "line2\n" (offset 6, length 6)
+		document.replace(6, 6, "");
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should still have dirty regions after deletion");
+	}
+
+	@Test
+	public void testIncrementalMultipleEditsOnDifferentLines() throws Exception {
+		document.set("line1\nline2\nline3\nline4\n");
+		tracker.clearDirtyLines();
+
+		// Edit line 0
+		document.replace(0, 5, "mod1");
+		// Edit line 2 (offsets shifted because line 0 is now shorter)
+		int line2Offset = document.getLineOffset(2);
+		document.replace(line2Offset, 5, "mod3");
+
+		IRegion[] regions = tracker.getDirtyRegions();
+		assertNotNull(regions, "Should have dirty regions");
+		assertEquals(2, regions.length, "Should have 2 separate dirty regions for non-consecutive edits");
+	}
+}

org.eclipse.jdt.text.tests/src/org/eclipse/jdt/text/tests/JdtTextTestSuite.java

@@ -35,6 +35,7 @@
 @SelectClasses({
 	PluginsNotLoadedTest.class,
 	CompilationUnitDocumentProviderTest.class,
+	DocumentDirtyTrackerTest.class,
 	JavaHeuristicScannerTest.class,
 	JavaAutoIndentStrategyTest.class,
 	JavaBreakIteratorTest.class,