wumpz · Oct 9, 2026 · Sep 28, 2026 · Oct 9, 2026
diff --git a/java-diff-utils/src/main/java/com/github/difflib/UnifiedDiffUtils.java b/java-diff-utils/src/main/java/com/github/difflib/UnifiedDiffUtils.java
@@ -69,6 +69,13 @@ public static Patch<String> parseUnifiedDiff(List<String> diff) {
 								old_ln = m.group(1) == null ? 1 : Integer.parseInt(m.group(1));
 								new_ln = m.group(3) == null ? 1 : Integer.parseInt(m.group(3));
 
+								// an empty range names the line before it
+								if ("0".equals(m.group(2))) {
+										old_ln++;
+								}
+								if ("0".equals(m.group(4))) {
+										new_ln++;
+								}
 								if (old_ln == 0) {
 										old_ln = 1;
 								}
@@ -278,6 +285,14 @@ private static List<String> processDeltas(
 						revTotal++;
 				}
 
+				// an empty range names the line before it
+				if (origTotal == 0 && origStart > 0) {
+						origStart--;
+				}
+				if (revTotal == 0) {
+						revStart--;
+				}
+
 				// Create and insert the block header, conforming to the Unified Diff
 				// standard
 				StringBuilder header = new StringBuilder();

diff --git a/java-diff-utils/src/main/java/com/github/difflib/unifieddiff/UnifiedDiffReader.java b/java-diff-utils/src/main/java/com/github/difflib/unifieddiff/UnifiedDiffReader.java
@@ -366,6 +366,13 @@ private void processChunk(MatchResult match, String chunkStart) {
 				old_size = toInteger(match, 2, 1);
 				new_ln = toInteger(match, 3, 1);
 				new_size = toInteger(match, 4, 1);
+				// an empty range names the line before it
+				if (old_size == 0) {
+						old_ln++;
+				}
+				if (new_size == 0) {
+						new_ln++;
+				}
 				if (old_ln == 0) {
 						old_ln = 1;
 				}

diff --git a/java-diff-utils/src/main/java/com/github/difflib/unifieddiff/UnifiedDiffWriter.java b/java-diff-utils/src/main/java/com/github/difflib/unifieddiff/UnifiedDiffWriter.java
@@ -196,6 +196,14 @@ private static void processDeltas(
 						revTotal++;
 				}
 
+				// an empty range names the line before it
+				if (origTotal == 0 && origStart > 0) {
+						origStart--;
+				}
+				if (revTotal == 0) {
+						revStart--;
+				}
+
 				// Create and insert the block header, conforming to the Unified Diff
 				// standard
 				writer.accept("@@ -" + origStart + "," + origTotal + " +" + revStart + "," + revTotal + " @@");

diff --git a/java-diff-utils/src/test/java/com/github/difflib/GenerateUnifiedDiffTest.java b/java-diff-utils/src/test/java/com/github/difflib/GenerateUnifiedDiffTest.java
@@ -138,6 +138,35 @@ public void testNewFileCreation() {
 				UnifiedDiffUtils.parseUnifiedDiff(udiff);
 		}
 
+		@Test
+		public void testZeroContextEmptyRangeHeader() throws PatchFailedException {
+				List<String> original = Arrays.asList("a", "b", "c");
+				List<String> revised = Arrays.asList("a", "b", "X", "c");
+
+				Patch<String> patch = DiffUtils.diff(original, revised);
+				List<String> udiff = UnifiedDiffUtils.generateUnifiedDiff("original", "revised", original, patch, 0);
+
+				assertEquals("@@ -2,0 +3,1 @@", udiff.get(2));
+				assertEquals(revised, UnifiedDiffUtils.parseUnifiedDiff(udiff).applyTo(original));
+		}
+
+		@Test
+		public void testParseZeroContextEmptyRanges() throws PatchFailedException {
+				// as written by diff -U0 and git diff -U0
+				List<String> insert = Arrays.asList("--- original", "+++ revised", "@@ -2,0 +3 @@", "+X");
+				assertEquals(
+								Arrays.asList("a", "b", "X", "c"),
+								UnifiedDiffUtils.parseUnifiedDiff(insert).applyTo(Arrays.asList("a", "b", "c")));
+
+				List<String> delete = Arrays.asList("--- original", "+++ revised", "@@ -2 +1,0 @@", "-b");
+				assertEquals(
+								Arrays.asList("a", "c"),
+								UnifiedDiffUtils.parseUnifiedDiff(delete).applyTo(Arrays.asList("a", "b", "c")));
+				assertEquals(
+								Arrays.asList("a", "b", "c"),
+								UnifiedDiffUtils.parseUnifiedDiff(delete).restore(Arrays.asList("a", "c")));
+		}
+
 		/**
 		 * Issue 89
 		 */

diff --git a/java-diff-utils/src/test/java/com/github/difflib/unifieddiff/UnifiedDiffReaderTest.java b/java-diff-utils/src/test/java/com/github/difflib/unifieddiff/UnifiedDiffReaderTest.java
@@ -21,7 +21,12 @@
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.github.difflib.patch.AbstractDelta;
+import com.github.difflib.patch.Patch;
+import com.github.difflib.patch.PatchFailedException;
+import java.io.ByteArrayInputStream;
 import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import org.junit.jupiter.api.Test;
@@ -503,4 +508,16 @@ public void testParseIssue193Copy() throws IOException {
 				assertThat(file1.getCopyTo())
 								.isEqualTo("modules/configuration/config/web/pcf/account/AccountContactCV.default.pcf");
 		}
+
+		@Test
+		public void testParseZeroContextEmptyRanges() throws IOException, PatchFailedException {
+				// as written by diff -U0 and git diff -U0
+				String text = "--- a/f\n+++ b/f\n@@ -2,0 +3 @@\n+X\n@@ -4 +4,0 @@\n-d\n";
+				UnifiedDiff diff =
+								UnifiedDiffReader.parseUnifiedDiff(new ByteArrayInputStream(text.getBytes(StandardCharsets.UTF_8)));
+
+				Patch<String> patch = diff.getFiles().get(0).getPatch();
+				assertThat(patch.applyTo(Arrays.asList("a", "b", "c", "d"))).containsExactly("a", "b", "X", "c");
+				assertThat(patch.restore(Arrays.asList("a", "b", "X", "c"))).containsExactly("a", "b", "c", "d");
+		}
 }
diff --git a/java-diff-utils/src/test/java/com/github/difflib/unifieddiff/UnifiedDiffWriterTest.java b/java-diff-utils/src/test/java/com/github/difflib/unifieddiff/UnifiedDiffWriterTest.java
@@ -31,6 +31,7 @@
 import java.nio.file.Files;
 import java.nio.file.Paths;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import org.junit.jupiter.api.Test;
@@ -86,6 +87,23 @@ public void testWriteWithNewFile() throws URISyntaxException, IOException {
 				assertEquals("@@ -0,0 +1,2 @@", lines[2]);
 		}
 
+		@Test
+		public void testWriteZeroContextEmptyRange() throws IOException {
+				List<String> original = Arrays.asList("a", "b", "c");
+				List<String> revised = Arrays.asList("a", "b", "X", "c");
+
+				Patch<String> patch = DiffUtils.diff(original, revised);
+				UnifiedDiff diff = new UnifiedDiff();
+				diff.addFile(UnifiedDiffFile.from("original", "revised", patch));
+
+				StringWriter writer = new StringWriter();
+				UnifiedDiffWriter.write(diff, f -> original, writer, 0);
+
+				String[] lines = writer.toString().split("\\n");
+
+				assertEquals("@@ -2,0 +3,1 @@", lines[2]);
+    }
+
 		@ParameterizedTest
 		@ValueSource(ints = {1, 2, 9, 16})
 		public void testPropagateWriterFailures(int failOnWrite) {