Implement diff between two changesets for git

scm-plugins/scm-git-plugin/src/main/java/sonia/scm/repository/GitUtil.java

@@ -48,6 +48,7 @@ import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.revwalk.filter.RevFilter;
 import org.eclipse.jgit.storage.file.FileRepositoryBuilder;
 import org.eclipse.jgit.transport.FetchResult;
 import org.eclipse.jgit.transport.RefSpec;
@@ -716,6 +717,18 @@ public final class GitUtil
     return (id != null) &&!id.equals(ObjectId.zeroId());
   }
 
+  /**
+   * Computes the first common ancestor of two revisions, aka merge base.
+   */
+  public static ObjectId computeCommonAncestor(org.eclipse.jgit.lib.Repository repository, ObjectId revision1, ObjectId revision2) throws IOException {
+    try (RevWalk mergeBaseWalk = new RevWalk(repository)) {
+      mergeBaseWalk.setRevFilter(RevFilter.MERGE_BASE);
+      mergeBaseWalk.markStart(mergeBaseWalk.lookupCommit(revision1));
+      mergeBaseWalk.markStart(mergeBaseWalk.parseCommit(revision2));
+      return mergeBaseWalk.next().getId();
+    }
+  }
+
   //~--- methods --------------------------------------------------------------
 
   /**

scm-plugins/scm-git-plugin/src/main/java/sonia/scm/repository/spi/GitDiffCommand.java

@@ -34,27 +34,25 @@ package sonia.scm.repository.spi;
 
 //~--- non-JDK imports --------------------------------------------------------
 
+import com.google.common.base.Strings;
 import org.eclipse.jgit.diff.DiffEntry;
 import org.eclipse.jgit.diff.DiffFormatter;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevTree;
 import org.eclipse.jgit.revwalk.RevWalk;
 import org.eclipse.jgit.treewalk.EmptyTreeIterator;
 import org.eclipse.jgit.treewalk.TreeWalk;
 import org.eclipse.jgit.treewalk.filter.PathFilter;
-
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-
 import sonia.scm.repository.GitUtil;
 import sonia.scm.repository.Repository;
 import sonia.scm.util.Util;
 
-//~--- JDK imports ------------------------------------------------------------
-
 import java.io.BufferedOutputStream;
+import java.io.IOException;
 import java.io.OutputStream;
-
 import java.util.List;
 
 /**
@@ -107,7 +105,8 @@ public class GitDiffCommand extends AbstractGitCommand implements DiffCommand
 
       walk = new RevWalk(gr);
 
-      RevCommit commit = walk.parseCommit(gr.resolve(request.getRevision()));
+      ObjectId revision = gr.resolve(request.getRevision());
+      RevCommit commit = walk.parseCommit(revision);
 
       walk.markStart(commit);
       commit = walk.next();
@@ -120,7 +119,15 @@ public class GitDiffCommand extends AbstractGitCommand implements DiffCommand
         treeWalk.setFilter(PathFilter.create(request.getPath()));
       }
 
-      if (commit.getParentCount() > 0)
+
+      if (!Strings.isNullOrEmpty(request.getAncestorChangeset()))
+      {
+        ObjectId otherRevision = gr.resolve(request.getAncestorChangeset());
+        ObjectId ancestorId = computeCommonAncestor(gr, revision, otherRevision);
+        RevTree tree = walk.parseCommit(ancestorId).getTree();
+        treeWalk.addTree(tree);
+      }
+      else if (commit.getParentCount() > 0)
       {
         RevTree tree = commit.getParent(0).getTree();
 
@@ -156,7 +163,6 @@ public class GitDiffCommand extends AbstractGitCommand implements DiffCommand
     }
     catch (Exception ex)
     {
-
       // TODO throw exception
       logger.error("could not create diff", ex);
     }
@@ -167,4 +173,9 @@ public class GitDiffCommand extends AbstractGitCommand implements DiffCommand
       GitUtil.release(formatter);
     }
   }
+
+  private ObjectId computeCommonAncestor(org.eclipse.jgit.lib.Repository repository, ObjectId revision1, ObjectId revision2) throws IOException {
+    return GitUtil.computeCommonAncestor(repository, revision1, revision2);
+  }
+
 }

scm-plugins/scm-git-plugin/src/test/java/sonia/scm/repository/spi/GitDiffCommandTest.java

@@ -42,4 +42,28 @@ public class GitDiffCommandTest extends AbstractGitCommandTestBase {
     gitDiffCommand.getDiffResult(diffCommandRequest, output);
     assertEquals(DIFF_LATEST_COMMIT_TEST_BRANCH, output.toString());
   }
+
+  @Test
+  public void diffBetweenTwoBranchesShouldCreateDiff() {
+    GitDiffCommand gitDiffCommand = new GitDiffCommand(createContext(), repository);
+    DiffCommandRequest diffCommandRequest = new DiffCommandRequest();
+    diffCommandRequest.setRevision("master");
+    diffCommandRequest.setAncestorChangeset("test-branch");
+    ByteArrayOutputStream output = new ByteArrayOutputStream();
+    gitDiffCommand.getDiffResult(diffCommandRequest, output);
+    assertEquals("diff --git a/a.txt b/a.txt\n" +
+      "index 7898192..2f8bc28 100644\n" +
+      "--- a/a.txt\n" +
+      "+++ b/a.txt\n" +
+      "@@ -1 +1,2 @@\n" +
+      " a\n" +
+      "+line for blame\n" +
+      "diff --git a/f.txt b/f.txt\n" +
+      "new file mode 100644\n" +
+      "index 0000000..6a69f92\n" +
+      "--- /dev/null\n" +
+      "+++ b/f.txt\n" +
+      "@@ -0,0 +1 @@\n" +
+      "+f\n", output.toString());
+  }
 }