Add experimental support for automatic conflict handling

Use new content merge functionality in JGit for automatic
resolution of conflicts within a file.

Change-Id: Ifae8a94709fb60f13e4c79fb6bb77a214ef5f0b7
Signed-off-by: Shawn O. Pearce <sop@google.com>

Documentation/cmd-create-project.txt

@@ -16,6 +16,7 @@ SYNOPSIS
 [\--permissions-only] \
 [\--description <DESC>] \
 [\--submit-type <TYPE>] \
+[\--use-content-merge] \
 [\--use-contributor-agreements] \
 [\--use-signed-off-by]
 
@@ -95,6 +96,13 @@ Description values containing spaces should be quoted in single quotes
 Defaults to MERGE_IF_NECESSARY.  For more details see
 link:project-setup.html#submit_type[Change Submit Actions].
 
+\--use-content-merge::
+	If enabled, Gerrit will try to perform a 3-way merge of text
+	file content when a file has been modified by both the
+	destination branch and the change being submitted.  This
+	option only takes effect if submit type is not
+	FAST_FORWARD_ONLY.  Disabled by default.
+
 \--use-contributor-agreements::
 	If enabled, authors must complete a contributor agreement
 	on the site before pushing any commits or changes to this

gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/AdminConstants.java

@@ -33,6 +33,7 @@ public interface AdminConstants extends Constants {
   String buttonAddProjectRight();
   String buttonClearProjectRight();
   String buttonSaveChanges();
+  String useContentMerge();
   String useContributorAgreements();
   String useSignedOffBy();
   String requireChangeID();

gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/AdminConstants.properties

@@ -14,6 +14,7 @@ buttonSelectGroup = Select
 buttonAddProjectRight = Add Access Right
 buttonClearProjectRight = Clear Form
 buttonSaveChanges = Save Changes
+useContentMerge = Automatically resolve conflicts
 useContributorAgreements = Require a valid contributor agreement to upload
 useSignedOffBy = Require <a href="http://gerrit.googlecode.com/svn/documentation/2.0/user-signedoffby.html#Signed-off-by" target="_blank"><code>Signed-off-by</code></a> in commit message
 requireChangeID = Require <a href="http://gerrit.googlecode.com/svn/documentation/2.0/user-changeid.html" target="_blank"><code>Change-Id</code></a> in commit message

gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/ProjectInfoScreen.java

@@ -36,6 +36,7 @@ public class ProjectInfoScreen extends ProjectScreen {
   private Panel projectOptionsPanel;
   private CheckBox requireChangeID;
   private ListBox submitType;
+  private CheckBox useContentMerge;
 
   private Panel agreementsPanel;
   private CheckBox useContributorAgreements;
@@ -88,6 +89,7 @@ public class ProjectInfoScreen extends ProjectScreen {
   private void enableForm(final boolean canModifyAgreements,
       final boolean canModifyDescription, final boolean canModifyMergeType) {
     submitType.setEnabled(canModifyMergeType);
+    useContentMerge.setEnabled(canModifyMergeType);
     descTxt.setEnabled(canModifyDescription);
     useContributorAgreements.setEnabled(canModifyAgreements);
     useSignedOffBy.setEnabled(canModifyAgreements);
@@ -119,6 +121,10 @@ public class ProjectInfoScreen extends ProjectScreen {
     saveEnabler.listenTo(submitType);
     projectOptionsPanel.add(submitType);
 
+    useContentMerge = new CheckBox(Util.C.useContentMerge(), true);
+    saveEnabler.listenTo(useContentMerge);
+    projectOptionsPanel.add(useContentMerge);
+
     requireChangeID = new CheckBox(Util.C.requireChangeID(), true);
     saveEnabler.listenTo(requireChangeID);
     projectOptionsPanel.add(requireChangeID);
@@ -166,6 +172,7 @@ public class ProjectInfoScreen extends ProjectScreen {
     descTxt.setText(project.getDescription());
     useContributorAgreements.setValue(project.isUseContributorAgreements());
     useSignedOffBy.setValue(project.isUseSignedOffBy());
+    useContentMerge.setValue(project.isUseContentMerge());
     requireChangeID.setValue(project.isRequireChangeID());
     setSubmitType(project.getSubmitType());
 
@@ -176,6 +183,7 @@ public class ProjectInfoScreen extends ProjectScreen {
     project.setDescription(descTxt.getText().trim());
     project.setUseContributorAgreements(useContributorAgreements.getValue());
     project.setUseSignedOffBy(useSignedOffBy.getValue());
+    project.setUseContentMerge(useContentMerge.getValue());
     project.setRequireChangeID(requireChangeID.getValue());
     if (submitType.getSelectedIndex() >= 0) {
       project.setSubmitType(Project.SubmitType.valueOf(submitType

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/Project.java

@@ -102,6 +102,9 @@ public final class Project {
   @Column(id = 7)
   protected boolean requireChangeID;
 
+  @Column(id = 8)
+  protected boolean useContentMerge;
+
   protected Project() {
   }
 
@@ -139,6 +142,10 @@ public final class Project {
     return useSignedOffBy;
   }
 
+  public boolean isUseContentMerge() {
+    return useContentMerge;
+  }
+
   public boolean isRequireChangeID() {
     return requireChangeID;
   }
@@ -147,6 +154,10 @@ public final class Project {
     useSignedOffBy = sbo;
   }
 
+  public void setUseContentMerge(final boolean cm) {
+    useContentMerge = cm;
+  }
+
   public void setRequireChangeID(final boolean cid) {
     requireChangeID = cid;
   }
@@ -163,6 +174,7 @@ public final class Project {
     description = update.description;
     useContributorAgreements = update.useContributorAgreements;
     useSignedOffBy = update.useSignedOffBy;
+    useContentMerge = update.useContentMerge;
     requireChangeID = update.requireChangeID;
     submitType = update.submitType;
   }

gerrit-server/src/main/java/com/google/gerrit/server/git/GitProjectImporter.java

@@ -102,6 +102,7 @@ public class GitProjectImporter {
         p.setSubmitType(SubmitType.MERGE_IF_NECESSARY);
         p.setUseContributorAgreements(false);
         p.setUseSignedOffBy(false);
+        p.setUseContentMerge(false);
         p.setRequireChangeID(false);
         db.projects().insert(Collections.singleton(p));
 

gerrit-server/src/main/java/com/google/gerrit/server/git/MergeOp.java

@@ -436,7 +436,18 @@ public class MergeOp {
   }
 
   private void mergeOneCommit(final CodeReviewCommit n) throws MergeException {
-    final Merger m = MergeStrategy.SIMPLE_TWO_WAY_IN_CORE.newMerger(db);
+    final ThreeWayMerger m;
+    if (destProject.isUseContentMerge()) {
+      // Settings for this project allow us to try and
+      // automatically resolve conflicts within files if needed.
+      // Use ResolveMerge and instruct to operate in core.
+      m = MergeStrategy.RESOLVE.newMerger(db, true);
+    } else {
+      // No auto conflict resolving allowed. If any of the
+      // affected files was modified, merge will fail.
+      m = MergeStrategy.SIMPLE_TWO_WAY_IN_CORE.newMerger(db);
+    }
+
     try {
       if (m.merge(new AnyObjectId[] {mergeTip, n})) {
         writeMergeCommit(m, n);
@@ -606,7 +617,17 @@ public class MergeOp {
       final CodeReviewCommit n = toMerge.remove(0);
       final ThreeWayMerger m;
 
-      m = MergeStrategy.SIMPLE_TWO_WAY_IN_CORE.newMerger(db);
+      if (destProject.isUseContentMerge()) {
+        // Settings for this project allow us to try and
+        // automatically resolve conflicts within files if needed.
+        // Use ResolveMerge and instruct to operate in core.
+        m = MergeStrategy.RESOLVE.newMerger(db, true);
+      } else {
+        // No auto conflict resolving allowed. If any of the
+        // affected files was modified, merge will fail.
+        m = MergeStrategy.SIMPLE_TWO_WAY_IN_CORE.newMerger(db);
+      }
+
       try {
         if (mergeTip == null) {
           // The branch is unborn. Take a fast-forward resolution to

gerrit-server/src/main/java/com/google/gerrit/server/schema/SchemaVersion.java

@@ -32,7 +32,7 @@ import java.util.List;
 /** A version of the database schema. */
 public abstract class SchemaVersion {
   /** The current schema version. */
-  private static final Class<? extends SchemaVersion> C = Schema_46.class;
+  private static final Class<? extends SchemaVersion> C = Schema_47.class;
 
   public static class Module extends AbstractModule {
     @Override

gerrit-server/src/main/java/com/google/gerrit/server/schema/Schema_47.java

@@ -0,0 +1,25 @@
+// Copyright (C) 2010 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.schema;
+
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+
+public class Schema_47 extends SchemaVersion {
+  @Inject
+  Schema_47(Provider<Schema_46> prior) {
+    super(prior);
+  }
+}

gerrit-sshd/src/main/java/com/google/gerrit/sshd/commands/CreateProject.java

@@ -71,6 +71,9 @@ final class CreateProject extends BaseCommand {
   @Option(name = "--use-signed-off-by", aliases = {"--so"}, usage = "if signed-off-by is required")
   private boolean signedOffBy;
 
+  @Option(name = "--use-content-merge", usage = "allow automatic conflict resolving within files")
+  private boolean contentMerge;
+
   @Option(name = "--require-change-id", aliases = {"--id"}, usage = "if change-id is required")
   private boolean requireChangeID;
 
@@ -159,6 +162,7 @@ final class CreateProject extends BaseCommand {
     newProject.setSubmitType(submitType);
     newProject.setUseContributorAgreements(contributorAgreements);
     newProject.setUseSignedOffBy(signedOffBy);
+    newProject.setUseContentMerge(contentMerge);
     newProject.setRequireChangeID(requireChangeID);
     if (newParent != null) {
       newProject.setParent(newParent.getProject().getNameKey());