Issue checkstyle#3: Git component

config/findbugs-exclude.xml

@@ -1,9 +1,18 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<FindBugsFilter>
-    <Match>
-        <!-- that CLI class so we need system exit code there, but only in main(...) method -->
-        <Class name="com.puppycrawl.tools.checkstyle.Main" />
-        <Method name="main" />
-        <Bug pattern="DM_EXIT" />
-    </Match>
-</FindBugsFilter>
+<?xml version="1.0" encoding="UTF-8"?>
+<FindBugsFilter>
+    <Match>
+        <!-- that CLI class so we need system exit code there, but only in main(...) method -->
+        <Class name="com.puppycrawl.tools.checkstyle.Main"/>
+        <Method name="main"/>
+        <Bug pattern="DM_EXIT"/>
+    </Match>
+    <Match>
+        <!-- This is a false positive. It is no problem to do that cast. In fact the cast is
+            in JGit library. There is no reason to raise this warning. -->
+        <Class name="com.github.checkstyle.regression.git.DiffParser"/>
+        <Or>
+            <Bug pattern="BC_UNCONFIRMED_CAST"/>
+            <Bug pattern="BC_UNCONFIRMED_CAST_OF_RETURN_VALUE"/>
+        </Or>
+    </Match>
+</FindBugsFilter>

config/import-control.xml

@@ -4,4 +4,9 @@
         "http://www.puppycrawl.com/dtds/import_control_1_1.dtd">
 
 <import-control pkg="com.github.checkstyle.regression">
+    <allow pkg="java.io"/>
+    <allow pkg="java.util"/>
+    <subpackage name="git">
+        <allow pkg="org.eclipse.jgit"/>
+    </subpackage>
 </import-control>

pom.xml

@@ -28,6 +28,18 @@
             <version>4.12</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.powermock</groupId>
+            <artifactId>powermock-api-mockito</artifactId>
+            <version>1.6.6</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.powermock</groupId>
+            <artifactId>powermock-module-junit4</artifactId>
+            <version>1.6.6</version>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.apache.maven</groupId>
             <artifactId>maven-jxr</artifactId>
@@ -146,7 +158,8 @@
                             <configLocation>
                                 https://raw.githubusercontent.com/checkstyle/checkstyle/checkstyle-${checkstyle.version}/config/checkstyle_sevntu_checks.xml
                             </configLocation>
-                            <propertyExpansion>project.basedir=${project.basedir}</propertyExpansion>
+                            <propertyExpansion>project.basedir=${project.basedir}
+                            </propertyExpansion>
                             <failOnViolation>true</failOnViolation>
                             <logViolationsToConsole>true</logViolationsToConsole>
                             <maxAllowedViolations>0</maxAllowedViolations>
@@ -205,7 +218,7 @@
                         <format>xml</format>
                         <format>html</format>
                     </formats>
-                    <check />
+                    <check/>
                 </configuration>
             </plugin>
 

src/main/java/com/github/checkstyle/regression/git/DiffParser.java

@@ -0,0 +1,110 @@
+////////////////////////////////////////////////////////////////////////////////
+// checkstyle: Checks Java source code for adherence to a set of rules.
+// Copyright (C) 2001-2017 the original author or authors.
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+////////////////////////////////////////////////////////////////////////////////
+
+package com.github.checkstyle.regression.git;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.eclipse.jgit.api.Git;
+import org.eclipse.jgit.api.errors.GitAPIException;
+import org.eclipse.jgit.diff.DiffEntry;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevTree;
+import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.storage.file.FileRepositoryBuilder;
+import org.eclipse.jgit.treewalk.AbstractTreeIterator;
+import org.eclipse.jgit.treewalk.CanonicalTreeParser;
+
+/**
+ * Parses git diff between feature branch and master for the further use.
+ * @author LuoLiangchen
+ */
+public final class DiffParser {
+    /** Prevents instantiation. */
+    private DiffParser() {
+    }
+
+    /**
+     * Parses the diff between a given branch and the master in the give repository path.
+     * @param repositoryPath the path of checkstyle repository
+     * @param branchName     the name of the branch to be compared with master
+     * @return a list of {@link GitChange} to represent the changes
+     * @throws IOException     JGit library exception
+     * @throws GitAPIException JGit library exception
+     */
+    public static List<GitChange> parse(String repositoryPath, String branchName)
+            throws IOException, GitAPIException {
+        final File gitDir = new File(repositoryPath, ".git");
+        final Repository repository = new FileRepositoryBuilder().setGitDir(gitDir)
+                .readEnvironment().findGitDir().build();
+        final Git git = new Git(repository);
+        final AbstractTreeIterator featureTreeParser =
+                prepareTreeParser(repository, Constants.R_HEADS + branchName);
+        final AbstractTreeIterator masterTreeParser =
+                prepareTreeParser(repository, Constants.R_HEADS + "master");
+        final List<GitChange> returnValue = git.diff()
+                .setOldTree(masterTreeParser)
+                .setNewTree(featureTreeParser)
+                .call()
+                .stream()
+                .map(DiffParser::convertDiffEntryToGitChange)
+                .collect(Collectors.toList());
+        git.close();
+        repository.close();
+        return returnValue;
+    }
+
+    /**
+     * Creates a tree parser from a commit, to be used by diff command.
+     * @param repository the repository to parse diff
+     * @param ref        the name of the ref to the commit; e.g., "refs/heads/master"
+     * @return the tree parser
+     * @throws IOException JGit library exception
+     */
+    private static AbstractTreeIterator prepareTreeParser(Repository repository, String ref)
+            throws IOException {
+        final Ref head = repository.exactRef(ref);
+        final RevWalk walk = new RevWalk(repository);
+        final RevCommit commit = walk.parseCommit(head.getObjectId());
+        final RevTree tree = walk.parseTree(commit.getTree().getId());
+        final CanonicalTreeParser treeParser = new CanonicalTreeParser();
+        final ObjectReader reader = repository.newObjectReader();
+        treeParser.reset(reader, tree.getId());
+        reader.close();
+        walk.dispose();
+        walk.close();
+        return treeParser;
+    }
+
+    /**
+     * Converts a {@link DiffEntry} to {@link GitChange} for the further use.
+     * @param diffEntry the {@link DiffEntry} instance to be converted
+     * @return the {@link GitChange} instance converted from the given {@link DiffEntry}
+     */
+    private static GitChange convertDiffEntryToGitChange(DiffEntry diffEntry) {
+        return new GitChange(diffEntry.getNewPath());
+    }
+}

src/main/java/com/github/checkstyle/regression/git/GitChange.java

@@ -0,0 +1,45 @@
+////////////////////////////////////////////////////////////////////////////////
+// checkstyle: Checks Java source code for adherence to a set of rules.
+// Copyright (C) 2001-2017 the original author or authors.
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+////////////////////////////////////////////////////////////////////////////////
+
+package com.github.checkstyle.regression.git;
+
+/**
+ * Represents git changes of a file.
+ * @author LuoLiangchen
+ */
+public class GitChange {
+    /** The path of the changed file. */
+    private final String path;
+
+    /**
+     * Creates a new {@link GitChange} instance.
+     * @param path the path of the changed file
+     */
+    GitChange(String path) {
+        this.path = path;
+    }
+
+    /**
+     * Gets the path of the changed file.
+     * @return the path of the changed file
+     */
+    public String getPath() {
+        return path;
+    }
+}

src/main/java/com/github/checkstyle/regression/git/package-info.java

@@ -0,0 +1,23 @@
+////////////////////////////////////////////////////////////////////////////////
+// checkstyle: Checks Java source code for adherence to a set of rules.
+// Copyright (C) 2001-2017 the original author or authors.
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Contains git related classes.
+ */
+package com.github.checkstyle.regression.git;

src/test/java/com/github/checkstyle/regression/git/DiffParserTest.java

@@ -0,0 +1,66 @@
+////////////////////////////////////////////////////////////////////////////////
+// checkstyle: Checks Java source code for adherence to a set of rules.
+// Copyright (C) 2001-2017 the original author or authors.
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+////////////////////////////////////////////////////////////////////////////////
+
+package com.github.checkstyle.regression.git;
+
+import static com.github.checkstyle.regression.internal.TestUtils.assertUtilsClassHasPrivateConstructor;
+import static org.junit.Assert.assertEquals;
+
+import java.io.File;
+import java.nio.file.Files;
+import java.nio.file.StandardOpenOption;
+import java.util.List;
+
+import org.eclipse.jgit.lib.Repository;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import com.github.checkstyle.regression.internal.GitUtils;
+
+public class DiffParserTest {
+    private Repository repository;
+
+    @Before
+    public void setUp() throws Exception {
+        repository = GitUtils.createNewRepository();
+        final File helloWorld = GitUtils.addAnEmptyFileAndCommit(repository, "HelloWorld");
+        GitUtils.createNewBranchAndCheckout(repository, "foo");
+        Files.write(helloWorld.toPath(), "hello world!".getBytes(), StandardOpenOption.APPEND);
+        GitUtils.addAllAndCommit(repository, "append text to HelloWorld");
+    }
+
+    @After
+    public void tearDown() throws Exception {
+        repository.close();
+    }
+
+    @Test
+    public void testIsProperUtilsClass() throws Exception {
+        assertUtilsClassHasPrivateConstructor(DiffParser.class);
+    }
+
+    @Test
+    public void testParse() throws Exception {
+        final List<GitChange> changes = DiffParser.parse(
+                repository.getDirectory().getParent(), "foo");
+        assertEquals(1, changes.size());
+        assertEquals("HelloWorld", changes.iterator().next().getPath());
+    }
+}