Adds FilteredRevCommit that can overwrites its parents in the DAG.

Change-Id: I2df9843dde0f589f5fea6cedaaff52e313eea6de

2 files changed, 118 insertions, 3 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/FilteredRevCommit.java b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/FilteredRevCommit.java
new file mode 100644
index 0000000000..be6e57fd5f
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/FilteredRevCommit.java
@@ -0,0 +1,115 @@
+/*
+ * Copyright (C) 2022, Google LLC.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.revwalk;
+
+import org.eclipse.jgit.lib.ObjectId;
+
+/** A filtered commit reference that overrides its parent in the DAG. */
+public class FilteredRevCommit extends RevCommit {
+	private RevCommit[] overriddenParents;
+
+	/**
+	 * Create a new commit reference for the given id.
+	 *
+	 * @param id
+	 *            object name for the commit.
+	 */
+	public FilteredRevCommit(ObjectId id) {
+		this(id, NO_PARENTS);
+	}
+
+	/**
+	 * Create a new commit reference wrapping an underlying commit reference.
+	 *
+	 * @param commit
+	 *            commit that is being wrapped
+	 */
+	public FilteredRevCommit(RevCommit commit) {
+		this(commit, NO_PARENTS);
+	}
+
+	/**
+	 * Create a new commit reference wrapping an underlying commit reference.
+	 *
+	 * @param commit
+	 *            commit that is being wrapped
+	 * @param parents
+	 *            overridden parents for the commit
+	 */
+	public FilteredRevCommit(RevCommit commit, RevCommit... parents) {
+		this(commit.getId(), parents);
+	}
+
+	/**
+	 * Create a new commit reference wrapping an underlying commit reference.
+	 *
+	 * @param id
+	 *            object name for the commit.
+	 * @param parents
+	 *            overridden parents for the commit
+	 */
+	public FilteredRevCommit(ObjectId id, RevCommit... parents) {
+		super(id);
+		this.overriddenParents = parents;
+	}
+
+	/**
+	 * Update parents on the commit
+	 *
+	 * @param overriddenParents
+	 *            parents to be overwritten
+	 */
+	public void setParents(RevCommit... overriddenParents) {
+		this.overriddenParents = overriddenParents;
+	}
+
+	/**
+	 * Get the number of parent commits listed in this commit.
+	 *
+	 * @return number of parents; always a positive value but can be 0 if it has
+	 *         no parents.
+	 */
+	@Override
+	public int getParentCount() {
+		return overriddenParents.length;
+	}
+
+	/**
+	 * Get the nth parent from this commit's parent list.
+	 *
+	 * @param nth
+	 *            parent index to obtain. Must be in the range 0 through
+	 *            {@link #getParentCount()}-1.
+	 * @return the specified parent.
+	 * @throws java.lang.ArrayIndexOutOfBoundsException
+	 *             an invalid parent index was specified.
+	 */
+	@Override
+	public RevCommit getParent(int nth) {
+		return overriddenParents[nth];
+	}
+
+	/**
+	 * Obtain an array of all parents (<b>NOTE - THIS IS NOT A COPY</b>).
+	 *
+	 * <p>
+	 * This method is exposed only to provide very fast, efficient access to
+	 * this commit's parent list. Applications relying on this list should be
+	 * very careful to ensure they do not modify its contents during their use
+	 * of it.
+	 *
+	 * @return the array of parents.
+	 */
+	@Override
+	public RevCommit[] getParents() {
+		return overriddenParents;
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RewriteGenerator.java b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RewriteGenerator.java
index 2c88bb872e..3318a97a3f 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RewriteGenerator.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RewriteGenerator.java
@@ -79,9 +79,9 @@ class RewriteGenerator extends Generator {
 			final RevCommit newp = rewrite(oldp);
 			if (firstParent) {
 				if (newp == null) {
-					c.parents = RevCommit.NO_PARENTS;
+					c = new FilteredRevCommit(c.getId());
 				} else {
-					c.parents = new RevCommit[] { newp };
+					c = new FilteredRevCommit(c.getId(), newp);
 				}
 				return c;
 			}
@@ -91,7 +91,7 @@ class RewriteGenerator extends Generator {
 			}
 		}
 		if (rewrote) {
-			c.parents = cleanup(pList);
+			c = new FilteredRevCommit(c.getId(), cleanup(pList));
 		}
 		return c;
 	}