History: show diffs for merges in first-parent mode

When the history is filtered to show only first parents of merges,
use a simple file diff against that single first merge parent to
show the list of changes files, and make sure the diff is shown when
a file is selected.

Change-Id: If2f5f2a7cdd86515190b7d1619c58bd6883520b4
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

3 files changed, 33 insertions, 10 deletions

diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/CommitFileDiffViewer.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/CommitFileDiffViewer.java
index 7b5f8dfc06..d6be435af6 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/CommitFileDiffViewer.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/CommitFileDiffViewer.java
@@ -509,6 +509,8 @@ public class CommitFileDiffViewer extends TableViewer {
 					FileDiffInput newInput = (FileDiffInput) input;
 					if (!Objects.equals(realInput.getRepository(),
 							newInput.getRepository())
+							|| realInput.isFirstParentOnly() != newInput
+									.isFirstParentOnly()
 							|| !realInput.getCommit()
 									.equals(newInput.getCommit())) {
 						setSelection(StructuredSelection.EMPTY);
@@ -744,9 +746,17 @@ public class CommitFileDiffViewer extends TableViewer {
 				if (monitor.isCanceled()) {
 					return Status.CANCEL_STATUS;
 				}
-				diffs = FileDiff.compute(input.getRepository(),
-						input.getTreeWalk(), input.getCommit(), monitor,
-						filter);
+				if (input.isFirstParentOnly()
+						&& input.getCommit().getParentCount() > 1) {
+					RevCommit[] parents = { input.getCommit().getParent(0) };
+					diffs = FileDiff.compute(input.getRepository(),
+							input.getTreeWalk(), input.getCommit(), parents,
+							monitor, filter);
+				} else {
+					diffs = FileDiff.compute(input.getRepository(),
+							input.getTreeWalk(), input.getCommit(), monitor,
+							filter);
+				}
 			} catch (IOException err) {
 				Activator.handleError(MessageFormat.format(
 						UIText.CommitFileDiffViewer_errorGettingDifference,
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/FileDiffInput.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/FileDiffInput.java
index 4a0004d1c8..14fe989f65 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/FileDiffInput.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/FileDiffInput.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (C) 2018, Thomas Wolf <thomas.wolf@paranor.ch>
+ * Copyright (C) 2018, 2019 Thomas Wolf <thomas.wolf@paranor.ch>
  *
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -33,6 +33,8 @@ public class FileDiffInput {
 
 	private final boolean selectMarked;
 
+	private final boolean firstParentOnly;
+
 	/**
 	 * Creates a new {@link FileDiffInput}.
 	 *
@@ -41,11 +43,14 @@ public class FileDiffInput {
 	 * @param commit
 	 * @param interestingPaths
 	 * @param selectMarked
+	 * @param firstParentOnly
 	 */
 	public FileDiffInput(Repository repository, TreeWalk walk, RevCommit commit,
-			Collection<String> interestingPaths, boolean selectMarked) {
+			Collection<String> interestingPaths, boolean selectMarked,
+			boolean firstParentOnly) {
 		this.commit = commit;
 		this.selectMarked = selectMarked;
+		this.firstParentOnly = firstParentOnly;
 		this.repository = repository;
 		this.walk = walk;
 		this.interestingPaths = interestingPaths;
@@ -59,6 +64,13 @@ public class FileDiffInput {
 	}
 
 	/**
+	 * @return whether the diffs shall be computed against the first parent only
+	 */
+	public boolean isFirstParentOnly() {
+		return firstParentOnly;
+	}
+
+	/**
 	 * @return whether the first marked entry shall be selected
 	 */
 	public boolean isSelectMarked() {
@@ -88,7 +100,7 @@ public class FileDiffInput {
 
 	/**
 	 * Sets the interesting paths.
-	 * 
+	 *
 	 * @param interestingPaths
 	 *            to set; may be {@code null} or empty
 	 */
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/GitHistoryPage.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/GitHistoryPage.java
index 1e33ac4c36..8d5519a5ca 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/GitHistoryPage.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/GitHistoryPage.java
@@ -8,7 +8,7 @@
  * Copyright (C) 2012-2013 Robin Stocker <robin@nibor.org>
  * Copyright (C) 2012, François Rey <eclipse.org_@_francois_._rey_._name>
  * Copyright (C) 2015, IBM Corporation (Dani Megert <daniel_megert@ch.ibm.com>)
- * Copyright (C) 2015-2018 Thomas Wolf <thomas.wolf@paranor.ch>
+ * Copyright (C) 2015-2019 Thomas Wolf <thomas.wolf@paranor.ch>
  * Copyright (C) 2015-2017, Stefan Dirix <sdirix@eclipsesource.com>
  *
  * All rights reserved. This program and the accompanying materials
@@ -1620,6 +1620,7 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 					return;
 				}
 				commentViewer.setInput(c);
+				boolean firstParentOnly = isShowFirstParentOnly();
 				try (RevWalk walk = new RevWalk(input.getRepository())) {
 					final RevCommit unfilteredCommit = walk.parseCommit(c);
 					for (RevCommit parent : unfilteredCommit.getParents())
@@ -1627,11 +1628,11 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 					fileViewer.newInput(new FileDiffInput(input.getRepository(),
 							fileDiffWalker, unfilteredCommit,
 							fileViewerInterestingPaths,
-							input.getSingleFile() != null));
+							input.getSingleFile() != null, firstParentOnly));
 				} catch (IOException e) {
 					fileViewer.newInput(new FileDiffInput(input.getRepository(),
 							fileDiffWalker, c, fileViewerInterestingPaths,
-							input.getSingleFile() != null));
+							input.getSingleFile() != null, firstParentOnly));
 				}
 			}
 		});
@@ -2797,7 +2798,7 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 							diffs.size());
 					for (FileDiff diff : diffs) {
 						if (progress.isCanceled()
-								|| diff.getCommit().getParentCount() > 1
+								|| diff.getBlobs().length > 2
 								|| document.getNumberOfLines() > maxLines) {
 							break;
 						}