Fix UnifiedDiffReader to use correct DeltaType

aparmet-toast · aparmet-toast · commit 3966413ecae1 · 2026-05-05T17:22:40.000-04:00
finalizeChunk() previously always created ChangeDelta regardless of whether the hunk contained only insertions, only deletions, or only context lines. This made it impossible for consumers to determine the actual type of change from the delta alone. Now uses InsertDelta when a hunk contains only additions (no context), DeleteDelta when only deletions (no context), EqualDelta when only context, and ChangeDelta otherwise. Hunks with context lines still use ChangeDelta to preserve backward-compatible applyTo behavior. Fixes #201
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
@@ -15,8 +15,12 @@
  */
 package com.github.difflib.unifieddiff;
 
+import com.github.difflib.patch.AbstractDelta;
 import com.github.difflib.patch.ChangeDelta;
 import com.github.difflib.patch.Chunk;
+import com.github.difflib.patch.DeleteDelta;
+import com.github.difflib.patch.EqualDelta;
+import com.github.difflib.patch.InsertDelta;
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStream;
@@ -298,23 +302,41 @@ private void processSimilarityIndex(MatchResult match, String line) {
 		private int delLineIdx = 0;
 		private int addLineIdx = 0;
 
-		private void finalizeChunk() {
-				if (!originalTxt.isEmpty() || !revisedTxt.isEmpty()) {
-						actualFile
-										.getPatch()
-										.addDelta(new ChangeDelta<>(
-														new Chunk<>(old_ln - 1, originalTxt, delLineIdxList),
-														new Chunk<>(new_ln - 1, revisedTxt, addLineIdxList)));
-						old_ln = 0;
-						new_ln = 0;
-						originalTxt.clear();
-						revisedTxt.clear();
-						addLineIdxList.clear();
-						delLineIdxList.clear();
-						delLineIdx = 0;
-						addLineIdx = 0;
-				}
-		}
+	private void finalizeChunk() {
+			if (!originalTxt.isEmpty() || !revisedTxt.isEmpty()) {
+					boolean hasDeletes = !delLineIdxList.isEmpty();
+					boolean hasInserts = !addLineIdxList.isEmpty();
+					boolean hasContext = originalTxt.size() != delLineIdxList.size()
+								|| revisedTxt.size() != addLineIdxList.size();
+					AbstractDelta<String> delta;
+					if (hasContext || (hasDeletes && hasInserts)) {
+							delta = new ChangeDelta<>(
+										new Chunk<>(old_ln - 1, originalTxt, delLineIdxList),
+										new Chunk<>(new_ln - 1, revisedTxt, addLineIdxList));
+					} else if (hasDeletes) {
+							delta = new DeleteDelta<>(
+										new Chunk<>(old_ln - 1, originalTxt, delLineIdxList),
+										new Chunk<>(new_ln - 1, revisedTxt, addLineIdxList));
+					} else if (hasInserts) {
+							delta = new InsertDelta<>(
+										new Chunk<>(old_ln - 1, originalTxt, delLineIdxList),
+										new Chunk<>(new_ln - 1, revisedTxt, addLineIdxList));
+					} else {
+							delta = new EqualDelta<>(
+										new Chunk<>(old_ln - 1, originalTxt, delLineIdxList),
+										new Chunk<>(new_ln - 1, revisedTxt, addLineIdxList));
+					}
+					actualFile.getPatch().addDelta(delta);
+					old_ln = 0;
+					new_ln = 0;
+					originalTxt.clear();
+					revisedTxt.clear();
+					addLineIdxList.clear();
+					delLineIdxList.clear();
+					delLineIdx = 0;
+					addLineIdx = 0;
+			}
+	}
 
 		private void processNormalLine(MatchResult match, String line) {
 				String cline = line.substring(1);
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
@@ -275,7 +275,7 @@ public void testParseIssue104() throws IOException {
 				assertThat(file.getToFile()).isEqualTo("doc/samba_data_tool_path.xml.in");
 
 				assertThat(file.getPatch().toString())
-								.isEqualTo("Patch{deltas=[[ChangeDelta, position: 0, lines: [] to [@SAMBA_DATA_TOOL@]]]}");
+								.isEqualTo("Patch{deltas=[[InsertDelta, position: 0, lines: [@SAMBA_DATA_TOOL@]]]}");
 
 				assertThat(diff.getTail()).isEqualTo("2.14.4");
 		}

Original file line number	Diff line number	Diff line change
`@@ -275,7 +275,7 @@ public void testParseIssue104() throws IOException {`
`275`	`275`	`assertThat(file.getToFile()).isEqualTo("doc/samba_data_tool_path.xml.in");`
`276`	`276`
`277`	`277`	`assertThat(file.getPatch().toString())`
`278`		`- .isEqualTo("Patch{deltas=[[ChangeDelta, position: 0, lines: [] to [@SAMBA_DATA_TOOL@]]]}");`
	`278`	`+ .isEqualTo("Patch{deltas=[[InsertDelta, position: 0, lines: [@SAMBA_DATA_TOOL@]]]}");`
`279`	`279`
`280`	`280`	`assertThat(diff.getTail()).isEqualTo("2.14.4");`
`281`	`281`	`}`