Empty-context add-only patches were applied in the wrong place

java-diff-utils-lib/src/main/java/difflib/DiffUtils.java

@@ -204,25 +204,8 @@ public static Patch<String> parseUnifiedDiff(List<String> diff) {
             Matcher m = unifiedDiffChunkRe.matcher(line);
             if (m.find()) {
                 // Process the lines in the previous chunk
-                if (rawChunk.size() != 0) {
-                    List<String> oldChunkLines = new ArrayList<String>();
-                    List<String> newChunkLines = new ArrayList<String>();
-
-                    for (String[] raw_line : rawChunk) {
-                        tag = raw_line[0];
-                        rest = raw_line[1];
-                        if (tag.equals(" ") || tag.equals("-")) {
-                            oldChunkLines.add(rest);
-                        }
-                        if (tag.equals(" ") || tag.equals("+")) {
-                            newChunkLines.add(rest);
-                        }
-                    }
-                    patch.addDelta(new ChangeDelta<String>(new Chunk<String>(
-                            old_ln - 1, oldChunkLines), new Chunk<String>(
-                            new_ln - 1, newChunkLines)));
-                    rawChunk.clear();
-                }
+                processRawChunk(rawChunk, patch, old_ln, new_ln);
+
                 // Parse the @@ header
                 old_ln = m.group(1) == null ? 1 : Integer.parseInt(m.group(1));
                 new_ln = m.group(3) == null ? 1 : Integer.parseInt(m.group(3));
@@ -247,6 +230,15 @@ public static Patch<String> parseUnifiedDiff(List<String> diff) {
         }
 
         // Process the lines in the last chunk
+        processRawChunk(rawChunk, patch, old_ln, new_ln);
+
+        return patch;
+    }
+
+    public static void processRawChunk(List<String[]> rawChunk, Patch patch, int old_ln, int new_ln) {
+        String tag;
+        String rest;
+
         if (rawChunk.size() != 0) {
             List<String> oldChunkLines = new ArrayList<String>();
             List<String> newChunkLines = new ArrayList<String>();
@@ -262,13 +254,18 @@ public static Patch<String> parseUnifiedDiff(List<String> diff) {
                 }
             }
 
-            patch.addDelta(new ChangeDelta<String>(new Chunk<String>(
-                    old_ln - 1, oldChunkLines), new Chunk<String>(new_ln - 1,
-                    newChunkLines)));
+            if (oldChunkLines.isEmpty()) {
+                patch.addDelta(new InsertDelta<String>(new Chunk<String>(old_ln, oldChunkLines),
+                        new Chunk<String>(new_ln - 1, newChunkLines)));
+            } else if (newChunkLines.isEmpty()) {
+                patch.addDelta(new DeleteDelta<String>(new Chunk<String>(old_ln - 1, oldChunkLines),
+                        new Chunk<String>(new_ln, newChunkLines)));
+            } else {
+                patch.addDelta(new ChangeDelta<String>(new Chunk<String>(old_ln - 1, oldChunkLines),
+                        new Chunk<String>(new_ln - 1, newChunkLines)));
+            }
             rawChunk.clear();
         }
-
-        return patch;
     }
 
     /**
@@ -416,6 +413,14 @@ private static List<String> processDeltas(List<String> origLines,
             revTotal++;
         }
 
+        // In case of empty chunk and context
+        if (origTotal == 0 && origStart > 1)
+                --origStart;
+
+        // In case of empty chunk and context
+        if (revTotal == 0 && revStart > 1)
+                --revStart;
+
         // Create and insert the block header, conforming to the Unified Diff
         // standard
         StringBuffer header = new StringBuffer();

java-diff-utils-lib/src/test/java/diffutils/EmptyContextUnifiedDiffTest.java

@@ -0,0 +1,90 @@
+package diffutils;
+
+import java.io.BufferedReader;
+import java.io.FileReader;
+import java.io.IOException;
+import java.util.LinkedList;
+import java.util.List;
+
+import difflib.DiffUtils;
+import difflib.Patch;
+import difflib.PatchFailedException;
+
+import junit.framework.TestCase;
+
+public class EmptyContextUnifiedDiffTest extends TestCase {
+
+	public List<String> fileToLines(String filename) {
+		List<String> lines = new LinkedList<String>();
+		String line = "";
+		BufferedReader in = null;
+		try {
+			in = new BufferedReader(new FileReader(filename));
+			while ((line = in.readLine()) != null) {
+				lines.add(line);
+			}
+		} catch (IOException e) {
+			e.printStackTrace();
+			fail(e.getMessage());
+		} finally {
+			if (in != null) {
+				try {
+					in.close();
+				} catch (IOException e) {
+					// ignore ... any errors should already have been
+					// reported via an IOException from the final flush.
+				}
+			}
+		}
+		return lines;
+	}
+
+	public void testEmptyUnifiedContextPatch() {
+		List<String> origLines = fileToLines(TestConstants.MOCK_FOLDER + "unified_empty_context_original.txt");
+		List<String> revLines = fileToLines(TestConstants.MOCK_FOLDER + "unified_empty_context_revised.txt");
+		List<String> unifiedDiff = fileToLines(TestConstants.MOCK_FOLDER + "unified_empty_context_patch.txt");
+
+		List<String> patchedLines = null;
+		Patch patch = DiffUtils.parseUnifiedDiff(unifiedDiff);
+
+		try {
+			patchedLines = (List<String>) patch.applyTo(origLines);
+		} catch (PatchFailedException e) {
+			fail(e.getMessage());
+		}
+
+		verifyLinesEqual(patchedLines, revLines);
+	}
+
+	public void testEmptyUnifiedContextDiff() {
+		List<String> origLines = fileToLines(TestConstants.MOCK_FOLDER + "unified_empty_context_original.txt");
+		List<String> revLines = fileToLines(TestConstants.MOCK_FOLDER + "unified_empty_context_revised.txt");
+
+		List<String> patchedLines = null;
+
+		// Generate a 0-context diff then reapply
+		Patch generatedPatch = DiffUtils.diff(origLines, revLines);
+		List<String> generatedDiff = DiffUtils.generateUnifiedDiff("original", "revised", origLines, generatedPatch, 0);
+		Patch newPatch = DiffUtils.parseUnifiedDiff(generatedDiff);
+
+		try {
+			patchedLines = (List<String>) newPatch.applyTo(origLines);
+		} catch (PatchFailedException e) {
+			fail(e.getMessage());
+		}
+
+		verifyLinesEqual(patchedLines, revLines);
+	}
+
+	public void verifyLinesEqual(List<String> patchedLines, List<String> revLines) {
+		assertTrue(revLines.size() == patchedLines.size());
+		for (int i = 0; i < revLines.size(); i++) {
+			String l1 = revLines.get(i);
+			String l2 = patchedLines.get(i);
+			if (!l1.equals(l2)) {
+				fail("Line " + (i + 1) + " of the patched file did not match the revised original");
+			}
+		}
+	}
+
+}

java-diff-utils-lib/src/test/resources/mocks/unified_empty_context_original.txt

@@ -0,0 +1,5 @@
+This
+is
+a
+test
+file

java-diff-utils-lib/src/test/resources/mocks/unified_empty_context_patch.txt

@@ -0,0 +1,6 @@
+--- uc_original.txt	2011-06-14 16:21:56.578627000 +0300
++++ uc_insert_revised.txt	2011-06-14 16:20:37.654820000 +0300
+@@ -2,0 +3 @@
++not
+@@ -5 +5,0 @@
+-file

java-diff-utils-lib/src/test/resources/mocks/unified_empty_context_revised.txt

@@ -0,0 +1,5 @@
+This
+is
+not
+a
+test