Option to reject implicit merges when pushing changes for review

An implicit merge is a case where by submitting an open change one also
merges a branch into the target branch. Typically, this happens when a
change is done on top of master and, by mistake, pushed to stable
branch. Merging this change would also implicitly merge master into
stable.

Example 1:

  o < change pushed for stable
  |
  o < master
  |
  o < stable

  Submitting this change will implicitly merge master into stable:

  o < change pushed for stable, stable
  |
  o < master
  |
  o

Example 2:

           o < change pushed for stable
           |
  master > o   o < stable
            \ /
             o

  Submitting this change will implicitly merge master into stable:

               o < stable
              /|
            /  |
           o < change pushed for stable
           |   |
  master > o   o
            \ /
             o

A new project property receive.rejectImplicitMerges controls whether an
implicit merge will be rejected. When an implicit merge is detected
Gerrit will print error(s) to the user:

  remote: ERROR: Implicit Merge of 39adddb Commit message subject
  remote: ERROR: Implicit Merge of ...

and will reject the push.

Bug: issue 1107
Change-Id: I0b14c64bebe28ea5579fc11f6beedacf5982e5aa

Documentation/config-project-config.txt

@@ -173,6 +173,22 @@ configuration] for details.
 Default is `INHERIT`, which means that this property is inherited from
 the parent project.
 
+[[receive.rejectImplicitMerges]]receive.rejectImplicitMerges::
++
+Controls whether a check for implicit merges will be performed when changes are
+pushed for review. An implicit merge is a case where merging an open change
+would implicitly merge another branch into the target branch. Typically, this
+happens when a change is done on master and, by mistake, pushed to a stable branch
+for review. When submitting such change, master would be implicitly merged into
+stable without anyone noticing that. When this option is set to 'true' Gerrit
+will reject the push if an implicit merge is detected.
++
+This check is only done for non-merge commits, merge commits are not subject of
+the implicit merge check.
++
+Default is `INHERIT`, which means that this property is inherited from
+the parent project.
+
 [[submit-section]]
 === Submit section
 

Documentation/rest-api-projects.txt

@@ -733,6 +733,7 @@ link:#config-input[ConfigInput] entity.
     "create_new_change_for_all_not_in_target": "INHERIT",
     "enable_signed_push": "INHERIT",
     "require_signed_push": "INHERIT",
+    "reject_implicit_merges": "INHERIT",
     "require_change_id": "TRUE",
     "max_object_size_limit": "10m",
     "submit_type": "REBASE_IF_NECESSARY",
@@ -786,6 +787,11 @@ ConfigInfo] entity.
       "configured_value": "INHERIT",
       "inherited_value": false
     },
+    "reject_implicit_merges": {
+      "value": false,
+      "configured_value": "INHERIT",
+      "inherited_value": false
+    },
     "max_object_size_limit": {
       "value": "10m",
       "configured_value": "10m",
@@ -2305,6 +2311,9 @@ signed push validation is enabled on the project.
 |`require_signed_push`|optional, not set if signed push is disabled|
 link:#inherited-boolean-info[InheritedBooleanInfo] that tells whether
 signed push validation is required on the project.
+|`reject_implicit_merges`|optional|
+link:#inherited-boolean-info[InheritedBooleanInfo] that tells whether
+implicit merges should be rejected on changes pushed to the project.
 |`max_object_size_limit`     ||
 The link:config-gerrit.html#receive.maxObjectSizeLimit[max object size
 limit] of this project as a link:#max-object-size-limit-info[
@@ -2373,6 +2382,11 @@ uploaded for review is required. This does not apply to commits pushed
 directly to a branch or tag. +
 Can be `TRUE`, `FALSE` or `INHERIT`. +
 If not set, this setting is not updated.
+|`reject_implicit_merges`                  |optional|
+Whether a check for implicit merges will be performed when changes
+are pushed for review. +
+Can be `TRUE`, `FALSE` or `INHERIT`. +
+If not set, this setting is not updated.
 |`max_object_size_limit`                   |optional|
 The link:config-gerrit.html#receive.maxObjectSizeLimit[max object size
 limit] of this project as a link:#max-object-size-limit-info[

gerrit-acceptance-framework/src/test/java/com/google/gerrit/acceptance/PushOneCommit.java

@@ -374,6 +374,11 @@ public class PushOneCommit {
         .contains(expectedMessage.toLowerCase());
     }
 
+    public String getMessage() {
+      RemoteRefUpdate refUpdate = result.getRemoteUpdate(ref);
+      return message(refUpdate);
+    }
+
     private String message(RemoteRefUpdate refUpdate) {
       StringBuilder b = new StringBuilder();
       if (refUpdate.getMessage() != null) {

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/git/ImplicitMergeCheckIT.java

@@ -0,0 +1,98 @@
+// Copyright (C) 2015 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.acceptance.git;
+
+import static com.google.common.truth.Truth.assertThat;
+import static com.google.gerrit.acceptance.GitUtil.pushHead;
+
+import com.google.gerrit.acceptance.AbstractDaemonTest;
+import com.google.gerrit.acceptance.PushOneCommit;
+import com.google.gerrit.extensions.client.InheritableBoolean;
+import com.google.gerrit.server.git.ProjectConfig;
+
+import org.eclipse.jgit.lib.ObjectId;
+import org.junit.Test;
+
+public class ImplicitMergeCheckIT extends AbstractDaemonTest {
+
+  @Test
+  public void implicitMergeViaFastForward() throws Exception {
+    setRejectImplicitMerges();
+
+    pushHead(testRepo, "refs/heads/stable", false);
+    PushOneCommit.Result m = push("refs/heads/master", "0", "file", "0");
+    PushOneCommit.Result c = push("refs/for/stable", "1", "file", "1");
+
+    c.assertMessage(implicitMergeOf(m.getCommit()));
+    c.assertErrorStatus();
+  }
+
+  @Test
+  public void implicitMergeViaRealMerge() throws Exception {
+    setRejectImplicitMerges();
+
+    ObjectId base = repo().exactRef("HEAD").getObjectId();
+    push("refs/heads/stable", "0", "f", "0");
+    testRepo.reset(base);
+    PushOneCommit.Result m = push("refs/heads/master", "1", "f", "1");
+    PushOneCommit.Result c = push("refs/for/stable", "2", "f", "2");
+
+    c.assertMessage(implicitMergeOf(m.getCommit()));
+    c.assertErrorStatus();
+  }
+
+  @Test
+  public void implicitMergeCheckOff() throws Exception {
+    ObjectId base = repo().exactRef("HEAD").getObjectId();
+    push("refs/heads/stable", "0", "f", "0");
+    testRepo.reset(base);
+    PushOneCommit.Result m = push("refs/heads/master", "1", "f", "1");
+    PushOneCommit.Result c = push("refs/for/stable", "2", "f", "2");
+
+    assertThat(c.getMessage().toLowerCase()).doesNotContain(
+        implicitMergeOf(m.getCommit()));
+  }
+
+  @Test
+  public void notImplicitMerge_noWarning() throws Exception {
+    setRejectImplicitMerges();
+
+    ObjectId base = repo().exactRef("HEAD").getObjectId();
+    push("refs/heads/stable", "0", "f", "0");
+    testRepo.reset(base);
+    PushOneCommit.Result m = push("refs/heads/master", "1", "f", "1");
+    PushOneCommit.Result c = push("refs/for/master", "2", "f", "2");
+
+    assertThat(c.getMessage().toLowerCase()).doesNotContain(
+        implicitMergeOf(m.getCommit()));
+  }
+
+  private static String implicitMergeOf(ObjectId commit) {
+    return "implicit merge of " + commit.abbreviate(7).name();
+  }
+
+  private void setRejectImplicitMerges() throws Exception {
+    ProjectConfig cfg = projectCache.checkedGet(project).getConfig();
+    cfg.getProject().setRejectImplicitMerges(InheritableBoolean.TRUE);
+    saveProjectConfig(project, cfg);
+  }
+
+  private PushOneCommit.Result push(String ref, String subject,
+      String fileName, String content) throws Exception {
+    PushOneCommit push = pushFactory.create(db, admin.getIdent(), testRepo,
+        subject, fileName, content);
+    return push.to(ref);
+  }
+}

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/api/projects/ConfigInfo.java

@@ -31,6 +31,7 @@ public class ConfigInfo {
   public InheritedBooleanInfo requireChangeId;
   public InheritedBooleanInfo enableSignedPush;
   public InheritedBooleanInfo requireSignedPush;
+  public InheritedBooleanInfo rejectImplicitMerges;
   public MaxObjectSizeLimitInfo maxObjectSizeLimit;
   public SubmitType submitType;
   public ProjectState state;

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/api/projects/ConfigInput.java

@@ -29,6 +29,7 @@ public class ConfigInput {
   public InheritableBoolean requireChangeId;
   public InheritableBoolean enableSignedPush;
   public InheritableBoolean requireSignedPush;
+  public InheritableBoolean rejectImplicitMerges;
   public String maxObjectSizeLimit;
   public SubmitType submitType;
   public ProjectState state;

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

@@ -45,6 +45,7 @@ public interface AdminConstants extends Constants {
   String enableSignedPush();
   String requireSignedPush();
   String requireChangeID();
+  String rejectImplicitMerges();
   String headingMaxObjectSizeLimit();
   String headingGroupOptions();
   String isVisibleToAll();

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

@@ -27,6 +27,7 @@ createNewChangeForAllNotInTarget = Create a new change for every commit not in t
 enableSignedPush = Enable signed push
 requireSignedPush = Require signed push
 requireChangeID = Require <code>Change-Id</code> in commit message
+rejectImplicitMerges = Reject implicit merges when changes are pushed for review
 headingMaxObjectSizeLimit = Maximum Git object size limit
 headingGroupOptions = Group Options
 isVisibleToAll = Make group visible to all registered users.

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

@@ -85,6 +85,7 @@ public class ProjectInfoScreen extends ProjectScreen {
   private ListBox newChangeForAllNotInTarget;
   private ListBox enableSignedPush;
   private ListBox requireSignedPush;
+  private ListBox rejectImplicitMerges;
   private NpTextBox maxObjectSizeLimit;
   private Label effectiveMaxObjectSizeLimit;
   private Map<String, Map<String, HasEnabled>> pluginConfigWidgets;
@@ -184,6 +185,7 @@ public class ProjectInfoScreen extends ProjectScreen {
     contributorAgreements.setEnabled(isOwner);
     signedOffBy.setEnabled(isOwner);
     requireChangeID.setEnabled(isOwner);
+    rejectImplicitMerges.setEnabled(isOwner);
     maxObjectSizeLimit.setEnabled(isOwner);
 
     if (pluginConfigWidgets != null) {
@@ -253,6 +255,10 @@ public class ProjectInfoScreen extends ProjectScreen {
       grid.add(Util.C.requireSignedPush(), requireSignedPush);
     }
 
+    rejectImplicitMerges = newInheritedBooleanBox();
+    saveEnabler.listenTo(rejectImplicitMerges);
+    grid.addHtml(Util.C.rejectImplicitMerges(), rejectImplicitMerges);
+
     maxObjectSizeLimit = new NpTextBox();
     saveEnabler.listenTo(maxObjectSizeLimit);
     effectiveMaxObjectSizeLimit = new Label();
@@ -383,6 +389,7 @@ public class ProjectInfoScreen extends ProjectScreen {
       setBool(enableSignedPush, result.enableSignedPush());
       setBool(requireSignedPush, result.requireSignedPush());
     }
+    setBool(rejectImplicitMerges, result.rejectImplicitMerges());
     setSubmitType(result.submitType());
     setState(result.state());
     maxObjectSizeLimit.setText(result.maxObjectSizeLimit().configuredValue());
@@ -659,7 +666,7 @@ public class ProjectInfoScreen extends ProjectScreen {
     ProjectApi.setConfig(getProjectKey(), descTxt.getText().trim(),
         getBool(contributorAgreements), getBool(contentMerge),
         getBool(signedOffBy), getBool(newChangeForAllNotInTarget), getBool(requireChangeID),
-        esp, rsp,
+        esp, rsp, getBool(rejectImplicitMerges),
         maxObjectSizeLimit.getText().trim(),
         SubmitType.valueOf(submitType.getValue(submitType.getSelectedIndex())),
         ProjectState.valueOf(state.getValue(state.getSelectedIndex())),

gerrit-gwtui/src/main/java/com/google/gerrit/client/projects/ConfigInfo.java

@@ -56,6 +56,9 @@ public class ConfigInfo extends JavaScriptObject {
   public final native InheritedBooleanInfo requireSignedPush()
   /*-{ return this.require_signed_push; }-*/;
 
+  public final native InheritedBooleanInfo rejectImplicitMerges()
+  /*-{ return this.reject_implicit_merges; }-*/;
+
   public final SubmitType submitType() {
     return SubmitType.valueOf(submitTypeRaw());
   }

gerrit-gwtui/src/main/java/com/google/gerrit/client/projects/ProjectApi.java

@@ -118,6 +118,7 @@ public class ProjectApi {
       InheritableBoolean requireChangeId,
       InheritableBoolean enableSignedPush,
       InheritableBoolean requireSignedPush,
+      InheritableBoolean rejectImplicitMerges,
       String maxObjectSizeLimit,
       SubmitType submitType, ProjectState state,
       Map<String, Map<String, ConfigParameterValue>> pluginConfigValues,
@@ -135,6 +136,7 @@ public class ProjectApi {
     if (requireSignedPush != null) {
       in.setRequireSignedPush(requireSignedPush);
     }
+    in.setRejectImplicitMerges(rejectImplicitMerges);
     in.setMaxObjectSizeLimit(maxObjectSizeLimit);
     in.setSubmitType(submitType);
     in.setState(state);
@@ -267,6 +269,12 @@ public class ProjectApi {
     private native void setRequireSignedPushRaw(String v)
     /*-{ if(v)this.require_signed_push=v; }-*/;
 
+    final void setRejectImplicitMerges(InheritableBoolean v) {
+      setRejectImplicitMergesRaw(v.name());
+    }
+    private native void setRejectImplicitMergesRaw(String v)
+    /*-{ if(v)this.reject_implicit_merges=v; }-*/;
+
     final native void setMaxObjectSizeLimit(String l)
     /*-{ if(l)this.max_object_size_limit=l; }-*/;
 

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

@@ -99,6 +99,8 @@ public final class Project {
   protected InheritableBoolean enableSignedPush;
   protected InheritableBoolean requireSignedPush;
 
+  protected InheritableBoolean rejectImplicitMerges;
+
   protected Project() {
   }
 
@@ -151,6 +153,10 @@ public final class Project {
     return maxObjectSizeLimit;
   }
 
+  public InheritableBoolean getRejectImplicitMerges() {
+    return rejectImplicitMerges;
+  }
+
   public void setUseContributorAgreements(final InheritableBoolean u) {
     useContributorAgreements = u;
   }
@@ -196,6 +202,10 @@ public final class Project {
     maxObjectSizeLimit = limit;
   }
 
+  public void setRejectImplicitMerges(InheritableBoolean check) {
+    rejectImplicitMerges = check;
+  }
+
   public SubmitType getSubmitType() {
     return submitType;
   }

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

@@ -125,6 +125,7 @@ public class ProjectConfig extends VersionedMetaData implements ValidationError.
   private static final String KEY_CHECK_RECEIVED_OBJECTS = "checkReceivedObjects";
   private static final String KEY_ENABLE_SIGNED_PUSH = "enableSignedPush";
   private static final String KEY_REQUIRE_SIGNED_PUSH = "requireSignedPush";
+  private static final String KEY_REJECT_IMPLICIT_MERGES = "rejectImplicitMerges";
 
   private static final String SUBMIT = "submit";
   private static final String KEY_ACTION = "action";
@@ -491,6 +492,8 @@ public class ProjectConfig extends VersionedMetaData implements ValidationError.
     p.setRequireSignedPush(getEnum(rc, RECEIVE, null,
           KEY_REQUIRE_SIGNED_PUSH, InheritableBoolean.INHERIT));
     p.setMaxObjectSizeLimit(rc.getString(RECEIVE, null, KEY_MAX_OBJECT_SIZE_LIMIT));
+    p.setRejectImplicitMerges(getEnum(rc, RECEIVE, null,
+        KEY_REJECT_IMPLICIT_MERGES, InheritableBoolean.INHERIT));
 
     p.setSubmitType(getEnum(rc, SUBMIT, null, KEY_ACTION, defaultSubmitAction));
     p.setUseContentMerge(getEnum(rc, SUBMIT, null, KEY_MERGE_CONTENT, InheritableBoolean.INHERIT));
@@ -940,6 +943,8 @@ public class ProjectConfig extends VersionedMetaData implements ValidationError.
         p.getEnableSignedPush(), InheritableBoolean.INHERIT);
     set(rc, RECEIVE, null, KEY_REQUIRE_SIGNED_PUSH,
         p.getRequireSignedPush(), InheritableBoolean.INHERIT);
+    set(rc, RECEIVE, null, KEY_REJECT_IMPLICIT_MERGES,
+        p.getRejectImplicitMerges(), InheritableBoolean.INHERIT);
 
     set(rc, SUBMIT, null, KEY_ACTION, p.getSubmitType(), defaultSubmitAction);
     set(rc, SUBMIT, null, KEY_MERGE_CONTENT, p.getUseContentMerge(), InheritableBoolean.INHERIT);

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

@@ -1608,8 +1608,8 @@ public class ReceiveCommits {
     rp.getRevWalk().sort(RevSort.TOPO);
     rp.getRevWalk().sort(RevSort.REVERSE, true);
     try {
-      rp.getRevWalk().markStart(
+      RevCommit start = rp.getRevWalk().parseCommit(magicBranch.cmd.getNewId());
-          rp.getRevWalk().parseCommit(magicBranch.cmd.getNewId()));
+      rp.getRevWalk().markStart(start);
       if (magicBranch.baseCommit != null) {
         logDebug("Marking {} base commits uninteresting",
             magicBranch.baseCommit.size());
@@ -1635,6 +1635,15 @@ public class ReceiveCommits {
           receiveConfig.getEffectiveMaxBatchChangesLimit(user);
       int total = 0;
       int alreadyTracked = 0;
+      boolean rejectImplicitMerges = start.getParentCount() == 1
+          && projectCache.get(project.getNameKey()).isRejectImplicitMerges();
+      Set<RevCommit> mergedParents;
+      if (rejectImplicitMerges) {
+        mergedParents = new HashSet<>();
+      } else {
+        mergedParents = null;
+      }
+
       for (;;) {
         RevCommit c = rp.getRevWalk().next();
         if (c == null) {
@@ -1644,6 +1653,14 @@ public class ReceiveCommits {
         String name = c.name();
         groupCollector.visit(c);
         Collection<Ref> existingRefs = existing.get(c);
+
+        if (rejectImplicitMerges) {
+          for (RevCommit p : c.getParents()) {
+            mergedParents.add(p);
+          }
+          mergedParents.remove(c);
+        }
+
         if (!existingRefs.isEmpty()) { // Commit is already tracked.
           alreadyTracked++;
           // Corner cases where an existing commit might need a new group:
@@ -1717,6 +1734,10 @@ public class ReceiveCommits {
           + " lookups", total, alreadyTracked, newChanges.size(),
           pending.size());
 
+      if (rejectImplicitMerges) {
+        rejectImplicitMerges(mergedParents);
+      }
+
       for (Iterator<ChangeLookup> itr = pending.iterator(); itr.hasNext();) {
         ChangeLookup p = itr.next();
         if (newChangeIds.contains(p.changeKey)) {
@@ -1833,6 +1854,38 @@ public class ReceiveCommits {
     }
   }
 
+  private void rejectImplicitMerges(Set<RevCommit> mergedParents)
+      throws MissingObjectException, IncorrectObjectTypeException, IOException {
+    if (!mergedParents.isEmpty()) {
+      Ref targetRef = allRefs.get(magicBranch.ctl.getRefName());
+      if (targetRef != null) {
+        RevWalk rw = rp.getRevWalk();
+        RevCommit tip = rw.parseCommit(targetRef.getObjectId());
+        boolean containsImplicitMerges = true;
+        for (RevCommit p : mergedParents) {
+          containsImplicitMerges &= !rw.isMergedInto(p, tip);
+        }
+
+        if (containsImplicitMerges) {
+          rw.reset();
+          for (RevCommit p : mergedParents) {
+            rw.markStart(p);
+          }
+          rw.markUninteresting(tip);
+          RevCommit c;
+          while ((c = rw.next()) != null) {
+            rw.parseBody(c);
+            messages.add(new CommitValidationMessage(
+                "ERROR: Implicit Merge of " + c.abbreviate(7).name()
+                + " " + c.getShortMessage(), false));
+
+          }
+          reject(magicBranch.cmd, "implicit merges detected");
+        }
+      }
+    }
+  }
+
   private void markHeadsAsUninteresting(RevWalk rw, @Nullable String forRef) {
     int i = 0;
     for (Ref ref : allRefs.values()) {

gerrit-server/src/main/java/com/google/gerrit/server/project/ConfigInfoImpl.java

@@ -39,7 +39,6 @@ import java.util.Map;
 import java.util.TreeMap;
 
 public class ConfigInfoImpl extends ConfigInfo {
-
   public ConfigInfoImpl(boolean serverEnableSignedPush,
       ProjectControl control,
       TransferConfig config,
@@ -60,6 +59,7 @@ public class ConfigInfoImpl extends ConfigInfo {
         new InheritedBooleanInfo();
     InheritedBooleanInfo enableSignedPush = new InheritedBooleanInfo();
     InheritedBooleanInfo requireSignedPush = new InheritedBooleanInfo();
+    InheritedBooleanInfo rejectImplicitMerges = new InheritedBooleanInfo();
 
     useContributorAgreements.value = projectState.isUseContributorAgreements();
     useSignedOffBy.value = projectState.isUseSignedOffBy();
@@ -77,6 +77,7 @@ public class ConfigInfoImpl extends ConfigInfo {
         p.getCreateNewChangeForAllNotInTarget();
     enableSignedPush.configuredValue = p.getEnableSignedPush();
     requireSignedPush.configuredValue = p.getRequireSignedPush();
+    rejectImplicitMerges.configuredValue = p.getRejectImplicitMerges();
 
     ProjectState parentState = Iterables.getFirst(projectState
         .parents(), null);
@@ -90,12 +91,14 @@ public class ConfigInfoImpl extends ConfigInfo {
           parentState.isCreateNewChangeForAllNotInTarget();
       enableSignedPush.inheritedValue = projectState.isEnableSignedPush();
       requireSignedPush.inheritedValue = projectState.isRequireSignedPush();
+      rejectImplicitMerges.inheritedValue = projectState.isRejectImplicitMerges();
     }
 
     this.useContributorAgreements = useContributorAgreements;
     this.useSignedOffBy = useSignedOffBy;
     this.useContentMerge = useContentMerge;
     this.requireChangeId = requireChangeId;
+    this.rejectImplicitMerges = rejectImplicitMerges;
     this.createNewChangeForAllNotInTarget = createNewChangeForAllNotInTarget;
     if (serverEnableSignedPush) {
       this.enableSignedPush = enableSignedPush;

gerrit-server/src/main/java/com/google/gerrit/server/project/ProjectState.java

@@ -440,6 +440,15 @@ public class ProjectState {
     });
   }
 
+  public boolean isRejectImplicitMerges() {
+    return getInheritableBoolean(new Function<Project, InheritableBoolean>() {
+      @Override
+      public InheritableBoolean apply(Project input) {
+        return input.getRejectImplicitMerges();
+      }
+    });
+  }
+
   public LabelTypes getLabelTypes() {
     Map<String, LabelType> types = new LinkedHashMap<>();
     for (ProjectState s : treeInOrder()) {

gerrit-server/src/main/java/com/google/gerrit/server/project/PutConfig.java

@@ -145,6 +145,10 @@ public class PutConfig implements RestModifyView<ProjectResource, ConfigInput> {
         }
       }
 
+      if (input.rejectImplicitMerges != null) {
+        p.setRejectImplicitMerges(input.rejectImplicitMerges);
+      }
+
       if (input.maxObjectSizeLimit != null) {
         p.setMaxObjectSizeLimit(input.maxObjectSizeLimit);
       }