Add "show first parent only" button to the history view

This includes:
 - action in GitHistoryPage
 - allow the setting to be sticky to one repository
 - add getter and setter for GitHistoryPage.currentRepo
 	-> so a repo change can be detected
 - add the action to the menu and toolbar
 - add corresponding preference to the preference page
    -> "Team -> Git -> History"
 - add a new icon for the action
 - based on the preference do a first-parent-only RevWalk
 - create some new helper methods in RepositoryUtil

Bug: 549424
Change-Id: I548ef25f8c13661fadf725952bc25d2f481c7a43
Signed-off-by: Tim Neumann <Tim.Neumann@advantest.com>
Also-by: Tetiana Pliekhova <tetiana.pliekhova@advantest.com>
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>

12 files changed, 458 insertions, 38 deletions

diff --git a/icons/org.eclipse.egit.ui/icons/obj16/first_parent_only.svg b/icons/org.eclipse.egit.ui/icons/obj16/first_parent_only.svg
new file mode 100644
index 0000000000..c7c439d263
--- /dev/null
+++ b/icons/org.eclipse.egit.ui/icons/obj16/first_parent_only.svg
@@ -0,0 +1,165 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!-- Created with Inkscape (http://www.inkscape.org/) -->
+
+<svg
+   xmlns:dc="http://purl.org/dc/elements/1.1/"
+   xmlns:cc="http://creativecommons.org/ns#"
+   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+   xmlns:svg="http://www.w3.org/2000/svg"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:xlink="http://www.w3.org/1999/xlink"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   width="16"
+   height="16"
+   id="svg2"
+   version="1.1"
+   inkscape:version="0.92.2 (5c3e80d, 2017-08-06)"
+   sodipodi:docname="first_parent_only.svg">
+  <defs
+     id="defs4">
+    <linearGradient
+       id="linearGradient3861">
+      <stop
+         style="stop-color:#caf3f6;stop-opacity:1;"
+         offset="0"
+         id="stop3863" />
+      <stop
+         style="stop-color:#ffffff;stop-opacity:1;"
+         offset="1"
+         id="stop3865" />
+    </linearGradient>
+    <linearGradient
+       inkscape:collect="always"
+       xlink:href="#linearGradient3861"
+       id="linearGradient3867"
+       x1="-11"
+       y1="1054.3622"
+       x2="-11"
+       y2="1029.3622"
+       gradientUnits="userSpaceOnUse"
+       gradientTransform="matrix(0.5,0,0,0.5,13.03125,521.1811)" />
+    <linearGradient
+       id="linearGradient4844-4">
+      <stop
+         id="stop4846-8"
+         offset="0"
+         style="stop-color:#414141;stop-opacity:1;" />
+      <stop
+         id="stop4848-8"
+         offset="1"
+         style="stop-color:#535353;stop-opacity:1;" />
+    </linearGradient>
+    <linearGradient
+       gradientTransform="matrix(0.47199644,0,0,0.47199414,7.4742532,550.36311)"
+       gradientUnits="userSpaceOnUse"
+       y2="1038.5814"
+       x2="4.7528968"
+       y1="1051.0466"
+       x1="4.7528968"
+       id="x-bg"
+       xlink:href="#x-bg-3"
+       inkscape:collect="always" />
+    <linearGradient
+       id="x-bg-3"
+       inkscape:collect="always">
+      <stop
+         id="x-bg-stop0"
+         offset="0"
+         style="stop-color:#df2c33;stop-opacity:1" />
+      <stop
+         id="x-bg-stop1"
+         offset="1"
+         style="stop-color:#f5817d;stop-opacity:1" />
+    </linearGradient>
+    <linearGradient
+       gradientTransform="matrix(0.47199644,0,0,0.47199414,7.4742532,550.36311)"
+       gradientUnits="userSpaceOnUse"
+       y2="1037.7"
+       x2="8.6566515"
+       y1="1050.7386"
+       x1="8.6566515"
+       id="x-stroke"
+       xlink:href="#x-stroke-6"
+       inkscape:collect="always" />
+    <linearGradient
+       id="x-stroke-6"
+       inkscape:collect="always">
+      <stop
+         id="x-stroke-stop0"
+         offset="0"
+         style="stop-color:#c51325;stop-opacity:1;" />
+      <stop
+         id="x-stroke-stop1"
+         offset="1"
+         style="stop-color:#ca5d49;stop-opacity:1" />
+    </linearGradient>
+  </defs>
+  <sodipodi:namedview
+     id="base"
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1.0"
+     inkscape:pageopacity="0.0"
+     inkscape:pageshadow="2"
+     inkscape:zoom="45.254834"
+     inkscape:cx="4.621357"
+     inkscape:cy="9.1963964"
+     inkscape:document-units="px"
+     inkscape:current-layer="g6616"
+     showgrid="true"
+     inkscape:window-width="1920"
+     inkscape:window-height="1082"
+     inkscape:window-x="-4"
+     inkscape:window-y="-4"
+     inkscape:window-maximized="1"
+     showguides="true"
+     inkscape:guide-bbox="true"
+     inkscape:snap-global="false">
+    <inkscape:grid
+       type="xygrid"
+       id="grid4000" />
+  </sodipodi:namedview>
+  <metadata
+     id="metadata7">
+    <rdf:RDF>
+      <cc:Work
+         rdf:about="">
+        <dc:format>image/svg+xml</dc:format>
+        <dc:type
+           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
+        <dc:title></dc:title>
+      </cc:Work>
+    </rdf:RDF>
+  </metadata>
+  <g
+     inkscape:label="Layer 1"
+     inkscape:groupmode="layer"
+     id="layer1"
+     style="display:inline"
+     transform="translate(0,-1036.3622)">
+    <g
+       id="g6616">
+      <path
+         style="fill:url(#linearGradient3867);fill-opacity:1;stroke:#679093;stroke-width:1;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:4;stroke-opacity:1;stroke-dasharray:none"
+         d="m 6.53125,1037.3622 0,4.5 -2,0 c -1,0 -2,1 -2,2 l 0,2 -2,0 0,1 3,3 3,-3 0,-1 -2,0 0,-1 c 0,-0.5 0.5,-1 1,-1 l 4,0 c 0.5,0 1,0.5 1,1 l 0,1 -2,0 0,1 3,3 3,-3 0,-1 -2,0 0,-2 c 0,-1 -1,-2 -2,-2 l -2,0 0,-4.5"
+         id="path3091"
+         inkscape:connector-curvature="0"
+         sodipodi:nodetypes="cccccccccccccccccccccccccc" />
+      <g
+         style="display:inline"
+         id="layer1-4"
+         inkscape:label="Layer 1"
+         transform="matrix(0.60535164,0,0,0.60535164,6.3760192,414.27492)" />
+      <path
+         sodipodi:nodetypes="sccccccccssccsccsccss"
+         inkscape:connector-curvature="0"
+         id="x-0"
+         d="m 13.808113,1040.6023 c -0.220982,-0.2209 -0.576769,-0.2209 -0.797739,0 l -1.469229,1.4694 -1.469216,-1.4694 c -0.2209502,-0.2209 -0.5767696,-0.2209 -0.7977394,0 l -0.4059426,0.4059 c -0.2209596,0.2211 -0.2209544,0.5769 1.74e-5,0.7979 l 1.4691946,1.4692 -1.4691976,1.4691 c -0.2209914,0.221 -0.2209873,0.5768 -6.2e-6,0.7978 l 0.4059652,0.4058 c 0.2209564,0.2212 0.5767434,0.2212 0.7977376,0 l 1.46922,-1.4691 1.479428,1.4794 c 0.220958,0.2212 0.576745,0.2212 0.797739,0 l 0.405941,-0.4058 c 0.220971,-0.221 0.218752,-0.5746 -1.5e-5,-0.7977 l -1.47943,-1.4795 1.469221,-1.4692 c 0.220978,-0.221 0.220972,-0.5768 1.4e-5,-0.7979 z"
+         style="display:inline;fill:url(#x-bg);fill-opacity:1;stroke:url(#x-stroke);stroke-width:0.46284017;stroke-linecap:round;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0;stroke-opacity:1">
+        <title
+           id="title3202-1">x</title>
+      </path>
+    </g>
+  </g>
+</svg>
diff --git a/org.eclipse.egit.core/src/org/eclipse/egit/core/RepositoryUtil.java b/org.eclipse.egit.core/src/org/eclipse/egit/core/RepositoryUtil.java
index 15a3964dd9..e3172fb0fc 100644
--- a/org.eclipse.egit.core/src/org/eclipse/egit/core/RepositoryUtil.java
+++ b/org.eclipse.egit.core/src/org/eclipse/egit/core/RepositoryUtil.java
@@ -557,14 +557,27 @@ public class RepositoryUtil {
 	}
 
 	/**
+	 * Relativize the given absolute path.
+	 * <p>
+	 * The result is the path of {@code pathString} relative to the workspace
+	 * root if the given {@code pathString} is under the workspace root,
+	 * otherwise the absolute path {@code pathString}.
+	 * </p>
+	 * <p>
+	 * This enables moving or copying the workspace, when saving this path and
+	 * later resolving it relative to the workspace path.
+	 * </p>
+	 * <p>
+	 * It is required, that the given pathString is absolute
+	 * </p>
+	 *
 	 * @param pathString
-	 *            an absolute path String
-	 * @return if the given {@code pathString} is under the workspace root the
-	 *         relative path of {@code pathString} relative to the workspace
-	 *         root, otherwise the absolute path {@code pathString}. This
-	 *         enables moving or copying the workspace.
+	 *            an absolute path String. Must be absolute.
+	 * @return the relativized path String
+	 * @throws java.nio.file.InvalidPathException
+	 *             if the path string cannot be converted to a Path
 	 */
-	private String relativizeToWorkspace(String pathString) {
+	public @NonNull String relativizeToWorkspace(@NonNull String pathString) {
 		java.nio.file.Path p = java.nio.file.Paths.get(pathString);
 		if (p.startsWith(workspacePath)) {
 			return workspacePath.relativize(p).toString();
@@ -574,6 +587,27 @@ public class RepositoryUtil {
 	}
 
 	/**
+	 * Get the relativized path of the given repository.
+	 * <p>
+	 * If the repository is not local this method will return null.
+	 * </p>
+	 *
+	 * @param repository
+	 *            The repository to get the path String of
+	 * @return the relativized path String
+	 * @see #relativizeToWorkspace(String)
+	 */
+	@Nullable
+	public String getRelativizedRepositoryPath(
+			final @NonNull Repository repository) {
+		File dir = repository.getDirectory();
+		if (dir == null) {
+			return null;
+		}
+		return relativizeToWorkspace(dir.getAbsolutePath());
+	}
+
+	/**
 	 * Does the collection of repository returned by
 	 * {@link #getConfiguredRepositories()} contain the given repository?
 	 *
diff --git a/org.eclipse.egit.ui/icons/obj16/first_parent_only.png b/org.eclipse.egit.ui/icons/obj16/first_parent_only.png
new file mode 100644
index 0000000000..1ceb1ed3cc
--- /dev/null
+++ b/org.eclipse.egit.ui/icons/obj16/first_parent_only.png
diff --git a/org.eclipse.egit.ui/icons/obj16/first_parent_only@2x.png b/org.eclipse.egit.ui/icons/obj16/first_parent_only@2x.png
new file mode 100644
index 0000000000..746da3dc7b
--- /dev/null
+++ b/org.eclipse.egit.ui/icons/obj16/first_parent_only@2x.png
diff --git a/org.eclipse.egit.ui/plugin.properties b/org.eclipse.egit.ui/plugin.properties
index 22cce65ccd..3130ebb806 100644
--- a/org.eclipse.egit.ui/plugin.properties
+++ b/org.eclipse.egit.ui/plugin.properties
@@ -82,7 +82,7 @@ CommittingPreferencePage_keywords = git egit committing staging stage untracked
 StagingViewPreferencePage_keywords = git egit staging stage
 DialogsPreferencePage_keywords = git egit confirmation dialog configuration rebase checkout detached launch branch clone lfs fetch push log home
 SynchronizePreferencePage_keywords = git egit synchronize fetch commit models merge
-HistoryPreferencePage_keywords = git egit history branches tags refs notes rename revision comment date author committer diff
+HistoryPreferencePage_keywords = git egit history branches tags refs notes rename revision comment date author committer diff first parent
 HistoryColumnsPreferencePage_keywords = git egit history columns id author committer date
 
 GitActions_label=Git
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/PluginPreferenceInitializer.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/PluginPreferenceInitializer.java
index 9ef7e469bd..79208d709f 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/PluginPreferenceInitializer.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/PluginPreferenceInitializer.java
@@ -60,6 +60,8 @@ public class PluginPreferenceInitializer extends AbstractPreferenceInitializer {
 		store.setDefault(UIPreferences.RESOURCEHISTORY_SHOW_REV_COMMENT, true);
 		store.setDefault(UIPreferences.RESOURCEHISTORY_SHOW_TOOLTIPS, false);
 		store.setDefault(UIPreferences.RESOURCEHISTORY_SHOW_ALL_BRANCHES, false);
+		store.setDefault(UIPreferences.RESOURCEHISTORY_SHOW_FIRST_PARENT_ONLY_DEFAULT,
+				false);
 		store.setDefault(UIPreferences.RESOURCEHISTORY_SHOW_ADDITIONAL_REFS,
 				false);
 		store.setDefault(UIPreferences.RESOURCEHISTORY_FOLLOW_RENAMES, true);
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/UIPreferences.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/UIPreferences.java
index cf161b712e..61b9069f6d 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/UIPreferences.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/UIPreferences.java
@@ -50,6 +50,8 @@ public class UIPreferences {
 	/** */
 	public final static String RESOURCEHISTORY_SHOW_ALL_BRANCHES = "resourcehistory_show_all_branches"; //$NON-NLS-1$
 	/** */
+	public final static String RESOURCEHISTORY_SHOW_FIRST_PARENT_ONLY_DEFAULT = "resourcehistory_show_first_parent_only"; //$NON-NLS-1$
+	/** */
 	public final static String RESOURCEHISTORY_SHOW_ADDITIONAL_REFS = "resourcehistory_show_additionalrefs"; //$NON-NLS-1$
 	/** */
 	public static final String RESOURCEHISTORY_FOLLOW_RENAMES = "resourcehistory_follow_renames"; //$NON-NLS-1$
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/UIIcons.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/UIIcons.java
index a217e0280f..effd4247f4 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/UIIcons.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/UIIcons.java
@@ -268,6 +268,9 @@ public class UIIcons {
 	/** Merge icon */
 	public final static ImageDescriptor MERGE;
 
+	/** First parent only icon */
+	public final static ImageDescriptor FIRST_PARENT_ONLY;
+
 	/** Annotated tag icon */
 	public final static ImageDescriptor TAG_ANNOTATED;
 
@@ -452,6 +455,7 @@ public class UIIcons {
 		REBASE_PROCESS_STEPS = map("elcl16/start.png"); //$NON-NLS-1$
 		OVR_ERROR = map("ovr/error.png"); //$NON-NLS-1$
 		MERGE = map("obj16/merge.png"); //$NON-NLS-1$
+		FIRST_PARENT_ONLY = map("obj16/first_parent_only.png"); //$NON-NLS-1$
 		TAG_ANNOTATED = map("obj16/annotated-tag.png"); //$NON-NLS-1$
 		CREATE_REPOSITORY = map("etool16/createRepository.png"); //$NON-NLS-1$
 		SUBMODULES = map("obj16/submodules.png"); //$NON-NLS-1$
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/UIText.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/UIText.java
index 4f7e617fdc..63fdde843b 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/UIText.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/UIText.java
@@ -475,6 +475,9 @@ public class UIText extends NLS {
 	public static String GitHistoryPage_showAllBranches;
 
 	/** */
+	public static String GitHistoryPage_showFirstParentOnly;
+
+	/** */
 	public static String GitHistoryPage_squashMenuItem;
 
 	/** */
@@ -625,6 +628,9 @@ public class UIText extends NLS {
 	public static String GitHistoryPage_ShowAllBranchesMenuLabel;
 
 	/** */
+	public static String GitHistoryPage_ShowFirstParentOnlyMenuLabel;
+
+	/** */
 	public static String GitHistoryPage_FollowRenames;
 
 	/** */
@@ -2131,6 +2137,9 @@ public class UIText extends NLS {
 	public static String HistoryPreferencePage_toggleAllBranches;
 
 	/** */
+	public static String HistoryPreferencePage_showFirstParentOnlyDefault;
+
+	/** */
 	public static String HistoryPreferencePage_toggleEmailAddresses;
 
 	/** */
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 d9c53516d0..1e33ac4c36 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
@@ -23,8 +23,10 @@ package org.eclipse.egit.ui.internal.history;
 import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Objects;
 import java.util.Set;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -87,6 +89,7 @@ import org.eclipse.jface.bindings.keys.SWTKeySupport;
 import org.eclipse.jface.layout.GridDataFactory;
 import org.eclipse.jface.layout.GridLayoutFactory;
 import org.eclipse.jface.preference.IPersistentPreferenceStore;
+import org.eclipse.jface.preference.IPreferenceStore;
 import org.eclipse.jface.preference.PreferenceDialog;
 import org.eclipse.jface.resource.ImageDescriptor;
 import org.eclipse.jface.resource.JFaceResources;
@@ -189,6 +192,8 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 
 	private static final int INITIAL_ITEM = -1;
 
+	private static final String P_REPOSITORY = "GitHistoryPage.Repository"; //$NON-NLS-1$
+
 	/** actions used in GitHistoryPage **/
 	private static class GitHistoryPageActions {
 
@@ -206,12 +211,7 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 			@Override
 			public void run() {
 				historyPage.store.setValue(prefName, isChecked());
-				if (historyPage.store.needsSaving())
-					try {
-						historyPage.store.save();
-					} catch (IOException e) {
-						Activator.handleError(e.getMessage(), e, false);
-					}
+				historyPage.saveStoreIfNeeded();
 			}
 
 			abstract void apply(boolean value);
@@ -319,6 +319,8 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 
 		IWorkbenchAction showAllBranchesAction;
 
+		IWorkbenchAction showFirstParentOnlyAction;
+
 		IWorkbenchAction showAdditionalRefsAction;
 
 		BooleanPrefAction followRenamesAction;
@@ -356,6 +358,7 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 			createCompareModeAction();
 			createReuseCompareEditorAction();
 			createShowAllBranchesAction();
+			createShowFirstParentOnlyAction();
 			createShowAdditionalRefsAction();
 			createShowCommentAction();
 			createShowFilesAction();
@@ -374,9 +377,9 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 
 		private void createRepositorySwitchAction() {
 			switchRepositoryAction = new RepositoryToolbarAction(true,
-					() -> historyPage.currentRepo,
+					() -> historyPage.getCurrentRepo(),
 					repo -> {
-						Repository current = historyPage.currentRepo;
+						Repository current = historyPage.getCurrentRepo();
 						if (current != null && repo.getDirectory()
 								.equals(current.getDirectory())) {
 							HistoryPageInput currentInput = historyPage
@@ -406,13 +409,7 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 					historyPage.store.setValue(
 							UIPreferences.RESOURCEHISTORY_SHOW_FINDTOOLBAR,
 							isChecked());
-					if (historyPage.store.needsSaving()) {
-						try {
-							historyPage.store.save();
-						} catch (IOException e) {
-							Activator.handleError(e.getMessage(), e, false);
-						}
-					}
+					historyPage.saveStoreIfNeeded();
 					historyPage.searchBar.setVisible(isChecked());
 				}
 
@@ -520,6 +517,100 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 			actionsToDispose.add(showAllBranchesAction);
 		}
 
+		private class ShowFirstParentOnlyPrefAction extends Action
+				implements IPropertyChangeListener, IWorkbenchAction {
+
+			ShowFirstParentOnlyPrefAction() {
+				super(UIText.GitHistoryPage_ShowFirstParentOnlyMenuLabel);
+				historyPage.addPropertyChangeListener(this);
+				historyPage.store.addPropertyChangeListener(this);
+				setChecked(historyPage.isShowFirstParentOnly());
+				setImageDescriptor(UIIcons.FIRST_PARENT_ONLY);
+				setToolTipText(UIText.GitHistoryPage_showFirstParentOnly);
+			}
+
+			@Override
+			public void run() {
+				final String prefKey = UIPreferences.RESOURCEHISTORY_SHOW_FIRST_PARENT_ONLY_DEFAULT;
+				Repository repo = historyPage.getCurrentRepo();
+				if (repo != null) {
+					String repoSpecificKey = getRepoSpecificKey(repo, prefKey);
+					boolean newBoolean = isChecked();
+					if (newBoolean == historyPage.store.getBoolean(prefKey)) {
+						historyPage.store.setToDefault(repoSpecificKey);
+					} else {
+						String newValue = newBoolean ? IPreferenceStore.TRUE
+								: IPreferenceStore.FALSE;
+						historyPage.store.putValue(repoSpecificKey, newValue);
+					}
+
+					historyPage.saveStoreIfNeeded();
+				}
+				historyPage.refresh();
+			}
+
+			/**
+			 * Applies the new boolean state to the checkbox and refreshes the
+			 * historyPage if the state was changed.
+			 *
+			 * @param newState
+			 *            the new state to apply.
+			 */
+			private void applyNewState(boolean newState) {
+				Control control = historyPage.getControl();
+				if (control != null && !control.isDisposed()) {
+					control.getDisplay().asyncExec(() -> {
+						if (!control.isDisposed()) {
+							setChecked(newState);
+						}
+					});
+				}
+				historyPage.refresh();
+			}
+
+			@Override
+			public void propertyChange(PropertyChangeEvent event) {
+				Repository repo = historyPage.getCurrentRepo();
+
+				final String prefKey = UIPreferences.RESOURCEHISTORY_SHOW_FIRST_PARENT_ONLY_DEFAULT;
+
+				if (repo == null) {
+					if (prefKey.equals(event.getProperty())) {
+						// global first parent preference changed and we have no
+						// current repo. Apply the new global preference
+						applyNewState(historyPage.store.getBoolean(prefKey));
+					}
+					return;
+				}
+
+				String repoSpecificKey = getRepoSpecificKey(repo, prefKey);
+
+				if (prefKey.equals(event.getProperty())) {
+					// global first parent preference changed, if this repo does
+					// not have a repo specific one apply the global one
+					if (!historyPage.store.contains(repoSpecificKey)) {
+						applyNewState(historyPage.store.getBoolean(prefKey));
+					}
+				}
+
+				if (P_REPOSITORY.equals(event.getProperty())) {
+					// The repository was switched. Apply that correct state.
+					applyNewState(historyPage.isShowFirstParentOnly());
+				}
+			}
+
+			@Override
+			public void dispose() {
+				historyPage.removePropertyChangeListener(this);
+				historyPage.store.removePropertyChangeListener(this);
+			}
+		}
+
+		private void createShowFirstParentOnlyAction() {
+			showFirstParentOnlyAction = new ShowFirstParentOnlyPrefAction();
+			actionsToDispose.add(showFirstParentOnlyAction);
+		}
+
 		private void createShowAdditionalRefsAction() {
 			showAdditionalRefsAction = new BooleanPrefAction(
 					UIPreferences.RESOURCEHISTORY_SHOW_ADDITIONAL_REFS,
@@ -818,6 +909,8 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 
 	private boolean currentShowAllBranches;
 
+	private boolean currentShowFirstParentOnly;
+
 	private boolean currentShowAdditionalRefs;
 
 	private boolean currentShowNotes;
@@ -860,6 +953,29 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 				});
 			}
 		}
+
+		Object oldValue = event.getOldValue();
+		String pathSep = File.pathSeparator;
+
+		if (oldValue != null) {
+			String[] oldPaths = oldValue.toString().split(pathSep);
+			List<String> removedPaths = new ArrayList<>(
+					Arrays.asList(oldPaths));
+
+			Object newValue = event.getNewValue();
+			if (newValue != null) {
+				String[] newPaths = newValue.toString().split(pathSep);
+				for (String path : newPaths) {
+					removedPaths.remove(path);
+				}
+			}
+
+			for (String path : removedPaths) {
+				unsetRepoSpecificPreference(path,
+						UIPreferences.RESOURCEHISTORY_SHOW_FIRST_PARENT_ONLY_DEFAULT);
+			}
+			saveStoreIfNeeded();
+		}
 	};
 
 	/** Tracks the selection to display the correct input when linked with editors. */
@@ -1425,12 +1541,7 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 			public void widgetDisposed(DisposeEvent e) {
 				final int[] w = sf.getWeights();
 				store.putValue(key, UIPreferences.intArrayToString(w));
-				if (store.needsSaving())
-					try {
-						store.save();
-					} catch (IOException e1) {
-						Activator.handleError(e1.getMessage(), e1, false);
-					}
+				saveStoreIfNeeded();
 
 			}
 		});
@@ -1572,6 +1683,7 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 		mgr.add(new Separator());
 		mgr.add(actions.compareModeAction);
 		mgr.add(actions.showAllBranchesAction);
+		mgr.add(actions.showFirstParentOnlyAction);
 	}
 
 	private class ColumnAction extends Action implements IUpdate {
@@ -1618,6 +1730,7 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 				UIText.GitHistoryPage_ShowSubMenuLabel);
 		viewMenuMgr.add(showSubMenuMgr);
 		showSubMenuMgr.add(actions.showAllBranchesAction);
+		showSubMenuMgr.add(actions.showFirstParentOnlyAction);
 		showSubMenuMgr.add(actions.showAdditionalRefsAction);
 		showSubMenuMgr.add(actions.showNotesAction);
 		showSubMenuMgr.add(actions.followRenamesAction);
@@ -1693,14 +1806,14 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 		}
 		renameTracker.reset(null);
 		Job.getJobManager().cancel(JobFamilies.HISTORY_DIFF);
-		currentRepo = null;
+		setCurrentRepo(null);
 		selectedObj = null;
 		super.dispose();
 	}
 
 	@Override
 	public void setFocus() {
-		if (repoHasBeenRemoved(currentRepo)) {
+		if (repoHasBeenRemoved(getCurrentRepo())) {
 			clearHistoryPage();
 			graph.getControl().setFocus();
 		} else {
@@ -1718,7 +1831,7 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 	}
 
 	private void clearHistoryPage() {
-		currentRepo = null;
+		setCurrentRepo(null);
 		selectedObj = null;
 		name = ""; //$NON-NLS-1$
 		input = null;
@@ -1741,7 +1854,7 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 
 	@Override
 	public void refresh() {
-		if (repoHasBeenRemoved(currentRepo)) {
+		if (repoHasBeenRemoved(getCurrentRepo())) {
 			clearHistoryPage();
 		}
 		this.input = null;
@@ -2243,6 +2356,19 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 		return getInputInternal();
 	}
 
+	private Repository getCurrentRepo() {
+		return currentRepo;
+	}
+
+	private void setCurrentRepo(Repository newRepo) {
+		Repository old = getCurrentRepo();
+		this.currentRepo = newRepo;
+
+		if (!Objects.equals(old, newRepo)) {
+			this.firePropertyChange(this, P_REPOSITORY, old, newRepo);
+		}
+	}
+
 	void setWarningTextInUIThread(final Job j) {
 		graph.getControl().getDisplay().asyncExec(new Runnable() {
 			@Override
@@ -2356,7 +2482,7 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 				currentHeadId = null;
 				currentFetchHeadId = null;
 				selectedObj = null;
-				currentRepo = db;
+				setCurrentRepo(db);
 				clearViewers();
 				return;
 			}
@@ -2366,9 +2492,9 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 					.getFileList(), db);
 
 			boolean repoChanged = false;
-			if (!db.equals(currentRepo)) {
+			if (!db.equals(getCurrentRepo())) {
 				repoChanged = true;
-				currentRepo = db;
+				setCurrentRepo(db);
 			}
 
 			boolean objChanged = false;
@@ -2417,6 +2543,10 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 		currentShowAllBranches = store
 			.getBoolean(UIPreferences.RESOURCEHISTORY_SHOW_ALL_BRANCHES);
 
+		boolean isShowFirstParentOnly = isShowFirstParentOnly();
+		boolean firstParentOnlyChanged = currentShowFirstParentOnly != isShowFirstParentOnly;
+		currentShowFirstParentOnly = isShowFirstParentOnly;
+
 		boolean additionalRefsChange = currentShowAdditionalRefs != store
 				.getBoolean(UIPreferences.RESOURCEHISTORY_SHOW_ADDITIONAL_REFS);
 		currentShowAdditionalRefs = store
@@ -2433,8 +2563,9 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 		currentFollowRenames = getFollowRenames();
 
 		return pathChanged || headChanged || fetchHeadChanged
-				|| allBranchesChanged || additionalRefsChange
-				|| showNotesChanged || followRenamesChanged;
+				|| allBranchesChanged || firstParentOnlyChanged
+				|| additionalRefsChange || showNotesChanged
+				|| followRenamesChanged;
 	}
 
 	/**
@@ -2550,11 +2681,76 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 		return !o.equals(n);
 	}
 
+	private static String getRepoSpecificKey(String repositoryId,
+			String key) {
+		return key + "_" + repositoryId; //$NON-NLS-1$
+	}
+
+	private static String getRepoSpecificKey(@NonNull Repository repo,
+			String key) {
+		String pathString = Activator.getDefault().getRepositoryUtil()
+				.getRelativizedRepositoryPath(repo);
+
+		if (pathString == null) {
+			return getRepoSpecificKey(repo.toString(), key);
+		}
+
+		return getRepoSpecificKey(pathString, key);
+	}
+
+	/**
+	 * Unset the repository specific preference of the given key for the
+	 * repository represented by the given repository path.
+	 * <p>
+	 * This method does not save the preference store. Call
+	 * {@link #saveStoreIfNeeded()} when appropriate.
+	 * </p>
+	 *
+	 * @param repositoryPath
+	 *            Representing the repository to remove the preference for
+	 * @param key
+	 *            The preference to remove for the given repository.
+	 */
+	private void unsetRepoSpecificPreference(String repositoryPath,
+			String key) {
+		String prefString = getRepoSpecificKey(repositoryPath, key);
+		store.setToDefault(prefString);
+	}
+
+	private void saveStoreIfNeeded() {
+		if (store.needsSaving()) {
+			try {
+				store.save();
+			} catch (IOException e) {
+				Activator.handleError(e.getMessage(), e, false);
+			}
+		}
+	}
+
+	private boolean isShowFirstParentOnly() {
+		final String prefKey = UIPreferences.RESOURCEHISTORY_SHOW_FIRST_PARENT_ONLY_DEFAULT;
+		boolean firstParent = store.getBoolean(prefKey);
+		Repository repo = getCurrentRepo();
+
+		if (repo != null) {
+			String repoSpecificKey = getRepoSpecificKey(repo, prefKey);
+			if (store.contains(repoSpecificKey)) {
+				firstParent = store.getBoolean(repoSpecificKey);
+			}
+		}
+		return firstParent;
+	}
+
 	private @NonNull SWTWalk createNewWalk(Repository db, AnyObjectId headId,
 			AnyObjectId fetchHeadId) {
 		currentHeadId = headId;
 		currentFetchHeadId = fetchHeadId;
 		SWTWalk walk = new GitHistoryWalk(db, headId, selectedObj);
+
+		if (isShowFirstParentOnly()) {
+			walk.setFirstParent(true);
+		}
+
 		try {
 			if (store
 					.getBoolean(UIPreferences.RESOURCEHISTORY_SHOW_ADDITIONAL_REFS))
@@ -2731,7 +2927,8 @@ public class GitHistoryPage extends HistoryPage implements RefsChangedListener,
 		if (paths == null || paths.isEmpty())
 			throw new IllegalArgumentException("paths must not be null nor empty"); //$NON-NLS-1$
 
-		DiffConfig diffConfig = currentRepo.getConfig().get(DiffConfig.KEY);
+		DiffConfig diffConfig = getCurrentRepo().getConfig()
+				.get(DiffConfig.KEY);
 
 		List<TreeFilter> followFilters = new ArrayList<>(paths.size());
 		for (String path : paths)
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/preferences/HistoryPreferencePage.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/preferences/HistoryPreferencePage.java
index 8c03996452..f02c06ff54 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/preferences/HistoryPreferencePage.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/preferences/HistoryPreferencePage.java
@@ -63,6 +63,10 @@ public class HistoryPreferencePage extends FieldEditorPreferencePage implements
 				UIPreferences.RESOURCEHISTORY_SHOW_ALL_BRANCHES,
 				UIText.HistoryPreferencePage_toggleAllBranches, showGroup));
 		addField(new BooleanFieldEditor(
+				UIPreferences.RESOURCEHISTORY_SHOW_FIRST_PARENT_ONLY_DEFAULT,
+				UIText.HistoryPreferencePage_showFirstParentOnlyDefault,
+				showGroup));
+		addField(new BooleanFieldEditor(
 				UIPreferences.RESOURCEHISTORY_SHOW_ADDITIONAL_REFS,
 				UIText.HistoryPreferencePage_toggleAdditionalRefs, showGroup));
 		addField(new BooleanFieldEditor(
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/uitext.properties b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/uitext.properties
index 857bcfee2c..48cb05abc1 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/uitext.properties
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/uitext.properties
@@ -187,6 +187,7 @@ GitHistoryPage_CreateTagMenuLabel=Create &Tag...
 GitHistoryPage_cherryPickMenuItem=C&herry-Pick...
 GitHistoryPage_compareMode=Compare Mode
 GitHistoryPage_showAllBranches=Show All Branches and Tags
+GitHistoryPage_showFirstParentOnly=Show First Parent Only
 GitHistoryPage_squashMenuItem=Squash
 GitHistoryPage_errorLookingUpPath=IO error looking up path {0} in {1}.
 GitHistoryPage_errorParsingHead=Cannot parse HEAD in: {0}
@@ -227,6 +228,7 @@ GitHistoryPage_editMenuItem=&Edit
 GitHistoryPage_SetAsBaselineMenuLabel=&Set as Baseline
 GitHistoryPage_ShowAdditionalRefsMenuLabel=&Additional Refs
 GitHistoryPage_ShowAllBranchesMenuLabel=All &Branches and Tags
+GitHistoryPage_ShowFirstParentOnlyMenuLabel=First &Parent Only
 GitHistoryPage_FollowRenames=&Follow Renames
 GitHistoryPage_FormatDiffJobName=Updating Diff
 GitHistoryPage_FilterSubMenuLabel=&Filter
@@ -729,6 +731,7 @@ HistoryPage_findbar_exceeded=Results limit exceeded
 HistoryPage_findbar_notFound=String not found
 HistoryPage_findbar_reference=Branch/Tag
 HistoryPreferencePage_toggleAllBranches=All &Branches and Tags
+HistoryPreferencePage_showFirstParentOnlyDefault=F&irst parent only by default
 HistoryPreferencePage_toggleAdditionalRefs=&Additional Refs
 HistoryPreferencePage_toggleEmailAddresses=&E-mail addresses in Author/Committer columns
 HistoryPreferencePage_toggleShortenAtStart=&Shorten long tag and branch names at the front