Issue checkstyle#18: Implemented Diff generation with build

Author: Anmol202005

.github/workflows/ci.yml

@@ -7,29 +7,7 @@ on:
     branches: [ main ]
 
 jobs:
-  diff-check:
-    strategy:
-      matrix:
-        platform: [ubuntu-latest, macos-latest, windows-latest]
-    runs-on: ${{ matrix.platform }}
-
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Generate diffs
-        shell: bash
-        run: ./scripts/generate-diffs.sh
-
-      - name: Check diff validity
-        shell: bash
-        run: |
-          git diff --exit-code || (
-            echo "::error::Generated diffs are not valid - please regenerate"
-            exit 1
-          )
-
   build:
-    needs: diff-check
     strategy:
       matrix:
         platform: [ubuntu-latest, macos-latest, windows-latest]

config/import-control-test.xml

@@ -12,5 +12,6 @@
     <allow pkg="java.nio"/>
     <allow pkg="java.lang"/>
     <allow pkg="javax.xml.stream"/>
+    <allow pkg="org.eclipse.jgit.diff"/>
     <allow pkg="com.puppycrawl.tools.checkstyle"/>
 </import-control>

pom.xml

@@ -64,6 +64,13 @@
             <version>${rewrite.version}</version>
         </dependency>
 
+        <!-- JGit for generating diffs without external Git dependency -->
+        <dependency>
+            <groupId>org.eclipse.jgit</groupId>
+            <artifactId>org.eclipse.jgit</artifactId>
+            <version>7.3.0.202506031305-r</version>
+        </dependency>
+
         <!-- Test dependencies -->
         <dependency>
             <groupId>com.google.truth</groupId>

scripts/generate-diffs.sh

@@ -0,0 +1,89 @@
+///////////////////////////////////////////////////////////////////////////////////////////////
+// checkstyle-openrewrite-recipes: Automatically fix Checkstyle violations with OpenRewrite.
+// Copyright (C) 2025 The Checkstyle OpenRewrite Recipes Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+///////////////////////////////////////////////////////////////////////////////////////////////
+
+package org.checkstyle.autofix.generator;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.List;
+import java.util.logging.Logger;
+import java.util.stream.Stream;
+
+import org.eclipse.jgit.diff.DiffFormatter;
+import org.eclipse.jgit.diff.HistogramDiff;
+import org.eclipse.jgit.diff.RawText;
+import org.eclipse.jgit.diff.RawTextComparator;
+import org.junit.jupiter.api.Test;
+
+public class GenerateDiffFilesTest {
+
+    private static final Logger LOGGER = Logger.getLogger(GenerateDiffFilesTest.class.getName());
+    private static final String RESOURCES_DIR = "src/test/resources/org/checkstyle/autofix/recipe";
+
+    @Test
+    void generateDiffs() throws IOException, InterruptedException {
+        LOGGER.info("Generating diffs for recipe tests....");
+
+        try (Stream<Path> pathStream = Files.walk(Paths.get(RESOURCES_DIR))) {
+            final List<Path> inputFiles = pathStream
+                    .filter(Files::isRegularFile)
+                    .filter(path -> path.getFileName().toString().startsWith("Input"))
+                    .toList();
+
+            for (Path inputFile : inputFiles) {
+                createDiff(inputFile);
+            }
+        }
+        LOGGER.info("Files generated successfully.");
+    }
+
+    private void createDiff(Path inputFile) throws IOException, InterruptedException {
+        final String inputFileName = inputFile.getFileName().toString();
+        final String suffix = inputFileName.substring(5);
+
+        final Path outputFile = inputFile.getParent().resolve("Output" + suffix);
+        final String diffFileName = "Diff" + suffix.replaceFirst("\\.[^.]*$", ".diff");
+        final Path diffFile = inputFile.getParent().resolve(diffFileName);
+
+        if (!Files.exists(outputFile)) {
+            throw new IOException("Output file does not exist: " + outputFile);
+        }
+
+        final ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        final String oldPath = inputFile.toString().replace('\\', '/');
+        final String newPath = outputFile.toString().replace('\\', '/');
+        out.write(String.format("--- %s%n", oldPath).getBytes());
+        out.write(String.format("+++ %s%n", newPath).getBytes());
+
+        try (DiffFormatter formatter = new DiffFormatter(out)) {
+
+            final RawText oldText = new RawText(Files.readAllBytes(inputFile));
+            final RawText newText = new RawText(Files.readAllBytes(outputFile));
+
+            formatter.format(
+                    new HistogramDiff().diff(RawTextComparator.DEFAULT, oldText, newText),
+                    oldText, newText);
+        }
+
+        final String diff = out.toString();
+        Files.writeString(diffFile, diff);
+    }
+}

src/test/java/org/checkstyle/autofix/generator/GenerateDiffFilesTest.java

@@ -1,8 +1,6 @@
-diff --git src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/classfieldtest/InputClassFieldTest.java src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/classfieldtest/OutputClassFieldTest.java
-index ac06187..74b379e 100644
 --- src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/classfieldtest/InputClassFieldTest.java
 +++ src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/classfieldtest/OutputClassFieldTest.java
-@@ -14,7 +14,7 @@ import java.util.HashMap;
+@@ -14,7 +14,7 @@
  import java.util.List;
  import java.util.Map;
 
@@ -11,7 +9,7 @@ index ac06187..74b379e 100644
      private String instanceField = "instance";
      private int counter = 0;
      private List<String> dataList = new ArrayList<>();
-@@ -25,10 +25,9 @@ public class InputClassFieldTest {
+@@ -25,10 +25,9 @@
      private static int globalCounter = 0;
 
      public void FieldsParametersLocalsTest(String name, int initialValue, boolean autoStart) {
@@ -25,7 +23,7 @@ index ac06187..74b379e 100644
 
          this.instanceField = normalizedName;
          this.counter = validatedValue;
-@@ -37,14 +36,11 @@ public class InputClassFieldTest {
+@@ -37,14 +36,11 @@
 
      public void complexMethod(String param1, int param2, List<String> param3,
                                Map<String, Object> param4, boolean param5) {

src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/classfieldtest/DiffClassFieldTest.diff

@@ -1,8 +1,6 @@
-diff --git src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/edgecasetest/InputEdgeCaseTest.java src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/edgecasetest/OutputEdgeCaseTest.java
-index bb10884..651244a 100644
 --- src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/edgecasetest/InputEdgeCaseTest.java
 +++ src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/edgecasetest/OutputEdgeCaseTest.java
-@@ -17,67 +17,64 @@ import java.util.Arrays;
+@@ -17,67 +17,64 @@
  import java.util.HashMap;
  import java.util.List;
 
@@ -13,15 +11,14 @@ index bb10884..651244a 100644
 -        var autoNumber = 42;                                // violation, "should be declared final"
 -        var autoList = new ArrayList<String>();             // violation, "should be declared final"
 -        var autoMap = new HashMap<String, Integer>();       // violation, "should be declared final"
--
--        String regularString = "explicit type";             // violation, "should be declared final"
--        var anotherAuto = "mixed with regular";             // violation, "should be declared final"
--        int regularInt = 100;                               // violation, "should be declared final"
 +        final var autoString = "inferred string";
 +        final var autoNumber = 42;
 +        final var autoList = new ArrayList<String>();
 +        final var autoMap = new HashMap<String, Integer>();
-+
+ 
+-        String regularString = "explicit type";             // violation, "should be declared final"
+-        var anotherAuto = "mixed with regular";             // violation, "should be declared final"
+-        int regularInt = 100;                               // violation, "should be declared final"
 +        final String regularString = "explicit type";
 +        final var anotherAuto = "mixed with regular";
 +        final int regularInt = 100;

src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/edgecasetest/DiffEdgeCaseTest.diff

@@ -1,5 +1,3 @@
-diff --git src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/enhancedforloop/InputEnhancedForLoop.java src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/enhancedforloop/OutputEnhancedForLoop.java
-index af3995c..cad8af0 100644
 --- src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/enhancedforloop/InputEnhancedForLoop.java
 +++ src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/enhancedforloop/OutputEnhancedForLoop.java
 @@ -12,28 +12,26 @@

src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/enhancedforloop/DiffEnhancedForLoop.diff

@@ -1,8 +1,6 @@
-diff --git src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/singlelocaltest/InputSingleLocalTest.java src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/singlelocaltest/OutputSingleLocalTest.java
-index 357b8f9..163d0a6 100644
 --- src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/singlelocaltest/InputSingleLocalTest.java
 +++ src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/singlelocaltest/OutputSingleLocalTest.java
-@@ -15,36 +15,35 @@ import java.util.Date;
+@@ -15,36 +15,35 @@
  import java.util.HashMap;
  import java.util.List;
 

src/test/resources/org/checkstyle/autofix/recipe/finallocalvariable/singlelocaltest/DiffSingleLocalTest.diff

@@ -1,5 +1,3 @@
-diff --git src/test/resources/org/checkstyle/autofix/recipe/header/headerblanklines/InputHeaderBlankLines.java src/test/resources/org/checkstyle/autofix/recipe/header/headerblanklines/OutputHeaderBlankLines.java
-index c095e1d..4ebba0c 100644
 --- src/test/resources/org/checkstyle/autofix/recipe/header/headerblanklines/InputHeaderBlankLines.java
 +++ src/test/resources/org/checkstyle/autofix/recipe/header/headerblanklines/OutputHeaderBlankLines.java
 @@ -1,4 +1,11 @@