Allow to resolve a conflict by checking out a file

DirCacheEditor unconditionally applied a PathEdit to all stages in the
index. This gives wrong results if one wants to check out a file from
some commit to resolve a conflict: JGit would update the working tree
file multiple times (once per stage), and set all stages to point to
the checked-out blob.

C git replaces the stages by the entry for the checked-out file.

To support this, add a DirCacheEntry.setStage() method so that
CheckoutCommand can force the stage to zero. In DirCacheEditor, keep
only the zero stage if the PathEdit re-set the stage.

Bug: 568038
Change-Id: Ic7c635bb5aaa06ffaaeed50bc5e45702c56fc6d1
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

3 files changed, 50 insertions, 7 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/CheckoutCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/CheckoutCommand.java
index 0dc5d5e7f7..847ab0a9a8 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/CheckoutCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/CheckoutCommand.java
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2010, Chris Aniszczyk <caniszczyk@gmail.com>
- * Copyright (C) 2011, Matthias Sohn <matthias.sohn@sap.com> and others
+ * Copyright (C) 2011, 2020 Matthias Sohn <matthias.sohn@sap.com> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -503,6 +503,11 @@ public class CheckoutCommand extends GitCommand<Ref> {
 			editor.add(new PathEdit(path) {
 				@Override
 				public void apply(DirCacheEntry ent) {
+					if (ent.getStage() != DirCacheEntry.STAGE_0) {
+						// A checkout on a conflicting file stages the checked
+						// out file and resolves the conflict.
+						ent.setStage(DirCacheEntry.STAGE_0);
+					}
 					ent.setObjectId(blobId);
 					ent.setFileMode(mode);
 					checkoutPath(ent, r,
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEditor.java b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEditor.java
index 73d2807eaf..8c342e267d 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEditor.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEditor.java
@@ -1,6 +1,6 @@
 /*
- * Copyright (C) 2008-2009, Google Inc.
- * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2009, Google Inc.
+ * Copyright (C) 2008, 2020 Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -139,10 +139,28 @@ public class DirCacheEditor extends BaseDirCacheEditor {
 					: eIdx;
 				fastAdd(ent);
 			} else {
-				// Apply to all entries of the current path (different stages)
 				lastIdx = cache.nextEntry(eIdx);
-				for (int i = eIdx; i < lastIdx; i++) {
-					final DirCacheEntry ent = cache.getEntry(i);
+				if (lastIdx > eIdx + 1) {
+					// Apply to all entries of the current path (different
+					// stages). If any apply() resets the stage to STAGE_0, take
+					// only that entry and omit all others.
+					DirCacheEntry[] tmp = new DirCacheEntry[lastIdx - eIdx];
+					int n = 0;
+					for (int i = eIdx; i < lastIdx; i++) {
+						DirCacheEntry ent = cache.getEntry(i);
+						e.apply(ent);
+						if (ent.getStage() == DirCacheEntry.STAGE_0) {
+							fastAdd(ent);
+							n = 0;
+							break;
+						}
+						tmp[n++] = ent;
+					}
+					for (int i = 0; i < n; i++) {
+						fastAdd(tmp[i]);
+					}
+				} else {
+					DirCacheEntry ent = cache.getEntry(eIdx);
 					e.apply(ent);
 					fastAdd(ent);
 				}
@@ -257,7 +275,9 @@ public class DirCacheEditor extends BaseDirCacheEditor {
 	 * {@link #apply(DirCacheEntry)} method. The editor will invoke apply once
 	 * for each record in the index which matches the path name. If there are
 	 * multiple records (for example in stages 1, 2 and 3), the edit instance
-	 * will be called multiple times, once for each stage.
+	 * will be called multiple times, once for each stage. If any of these calls
+	 * resets the stage to 0, only this entry will be taken and entries for
+	 * other stages are discarded.
 	 */
 	public abstract static class PathEdit {
 		final byte[] path;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java
index dcb84825fe..67edf50f44 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheEntry.java
@@ -542,6 +542,24 @@ public class DirCacheEntry {
 	}
 
 	/**
+	 * Sets the stage of an entry.
+	 *
+	 * @param stage
+	 *            to set, in the range [0..3]
+	 * @throws IllegalArgumentException
+	 *             if the stage is outside the range [0..3]
+	 * @since 5.10
+	 */
+	public void setStage(int stage) {
+		if ((stage & ~0x3) != 0) {
+			throw new IllegalArgumentException(
+					"Invalid stage, must be in range [0..3]"); //$NON-NLS-1$
+		}
+		byte flags = info[infoOffset + P_FLAGS];
+		info[infoOffset + P_FLAGS] = (byte) ((flags & 0xCF) | (stage << 4));
+	}
+
+	/**
 	 * Returns whether this entry should be skipped from the working tree.
 	 *
 	 * @return true if this entry should be skipepd.