diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index f320d2a..6da455d 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -6827,6 +6827,11 @@
 The source to merge from, e.g. a complete or abbreviated commit SHA-1,
 a complete reference name, a short reference name under `refs/heads`, `refs/tags`,
 or `refs/remotes` namespace, etc.
+|`source_branch`  |optional|
+A branch from which `source` is reachable. If specified,
+`source` is checked for visibility and reachability against only this
+branch. This speeds up the operation, especially for large repos with
+many branches.
 |`strategy`     |optional|
 The strategy of the merge, can be `recursive`, `resolve`,
 `simple-two-way-in-core`, `ours` or `theirs`, default will use project settings.
diff --git a/java/com/google/gerrit/extensions/common/MergeInput.java b/java/com/google/gerrit/extensions/common/MergeInput.java
index c16a551..c3cfcee 100644
--- a/java/com/google/gerrit/extensions/common/MergeInput.java
+++ b/java/com/google/gerrit/extensions/common/MergeInput.java
@@ -24,6 +24,12 @@
   public String source;
 
   /**
+   * If specified, visibility of the {@code source} commit will only be checked against {@code
+   * source_branch}, rather than all visible branches.
+   */
+  public String sourceBranch;
+
+  /**
    * {@code strategy} name of the merge strategy.
    *
    * @see org.eclipse.jgit.merge.MergeStrategy
diff --git a/java/com/google/gerrit/server/git/validators/CommitValidators.java b/java/com/google/gerrit/server/git/validators/CommitValidators.java
index 90d6b66..4159ebb 100644
--- a/java/com/google/gerrit/server/git/validators/CommitValidators.java
+++ b/java/com/google/gerrit/server/git/validators/CommitValidators.java
@@ -394,7 +394,7 @@
 
     FileCountValidator(PatchListCache patchListCache, Config config) {
       this.patchListCache = patchListCache;
-      maxFileCount = config.getInt("change", null, "maxFiles", 50_000);
+      maxFileCount = config.getInt("change", null, "maxFiles", 100_000);
     }
 
     @Override
diff --git a/java/com/google/gerrit/server/restapi/change/CreateChange.java b/java/com/google/gerrit/server/restapi/change/CreateChange.java
index c0b28d2..537993a 100644
--- a/java/com/google/gerrit/server/restapi/change/CreateChange.java
+++ b/java/com/google/gerrit/server/restapi/change/CreateChange.java
@@ -508,7 +508,13 @@
     }
 
     RevCommit sourceCommit = MergeUtil.resolveCommit(repo, rw, merge.source);
-    if (!commits.canRead(projectState, repo, sourceCommit)) {
+    if (merge.sourceBranch != null) {
+      Ref ref = repo.findRef(merge.sourceBranch);
+      logger.atFine().log("checking visibility for branch %s", merge.sourceBranch);
+      if (ref == null || !commits.canRead(projectState, repo, sourceCommit, ref)) {
+        throw new BadRequestException("do not have read permission for: " + merge.source);
+      }
+    } else if (!commits.canRead(projectState, repo, sourceCommit)) {
       throw new BadRequestException("do not have read permission for: " + merge.source);
     }
 
diff --git a/java/com/google/gerrit/server/restapi/project/CommitsCollection.java b/java/com/google/gerrit/server/restapi/project/CommitsCollection.java
index 31fa8d3..757b650 100644
--- a/java/com/google/gerrit/server/restapi/project/CommitsCollection.java
+++ b/java/com/google/gerrit/server/restapi/project/CommitsCollection.java
@@ -16,6 +16,7 @@
 
 import static com.google.common.collect.ImmutableList.toImmutableList;
 
+import com.google.common.collect.ImmutableList;
 import com.google.gerrit.entities.Project;
 import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.extensions.registration.DynamicMap;
@@ -110,6 +111,14 @@
     return views;
   }
 
+  /**
+   * @return true if {@code commit} is visible to the caller and {@code commit} is reachable from
+   *     the given branch.
+   */
+  public boolean canRead(ProjectState state, Repository repo, RevCommit commit, Ref ref) {
+    return reachable.fromRefs(state.getNameKey(), repo, commit, ImmutableList.of(ref));
+  }
+
   /** @return true if {@code commit} is visible to the caller. */
   public boolean canRead(ProjectState state, Repository repo, RevCommit commit) throws IOException {
     Project.NameKey project = state.getNameKey();
diff --git a/javatests/com/google/gerrit/acceptance/rest/change/CreateChangeIT.java b/javatests/com/google/gerrit/acceptance/rest/change/CreateChangeIT.java
index 10bae39..3f80dd1 100644
--- a/javatests/com/google/gerrit/acceptance/rest/change/CreateChangeIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/change/CreateChangeIT.java
@@ -619,6 +619,8 @@
 
     gApi.projects().name(project.get()).branch(mergeTarget).create(branchInput);
 
+    // To create a merge commit, create two changes from the same parent,
+    // and submit them one after the other.
     PushOneCommit.Result result1 =
         pushFactory
             .create(
@@ -668,6 +670,39 @@
     gApi.changes().create(in);
   }
 
+  @Test
+  public void createChangeWithSourceBranch() throws Exception {
+    changeInTwoBranches("branchA", "a.txt", "branchB", "b.txt");
+
+    // create a merge change from branchA to master in gerrit
+    ChangeInput in = new ChangeInput();
+    in.project = project.get();
+    in.branch = "branchA";
+    in.subject = "message";
+    in.status = ChangeStatus.NEW;
+    MergeInput mergeInput = new MergeInput();
+
+    String mergeRev = gApi.projects().name(project.get()).branch("branchB").get().revision;
+    mergeInput.source = mergeRev;
+    in.merge = mergeInput;
+
+    assertCreateSucceeds(in);
+
+    // Succeeds with a visible branch
+    in.merge.sourceBranch = "refs/heads/branchB";
+    gApi.changes().create(in);
+
+    // Make it invisible
+    projectOperations
+        .project(project)
+        .forUpdate()
+        .add(block(READ).ref(in.merge.sourceBranch).group(REGISTERED_USERS))
+        .update();
+
+    // Now it fails.
+    assertThrows(BadRequestException.class, () -> gApi.changes().create(in));
+  }
+
   private ChangeInput newChangeInput(ChangeStatus status) {
     ChangeInput in = new ChangeInput();
     in.project = project.get();
diff --git a/lib/guava.bzl b/lib/guava.bzl
index 18a8355..86060d4 100644
--- a/lib/guava.bzl
+++ b/lib/guava.bzl
@@ -1,5 +1,5 @@
-GUAVA_VERSION = "28.1-jre"
+GUAVA_VERSION = "28.2-jre"
 
-GUAVA_BIN_SHA1 = "b0e91dcb6a44ffb6221b5027e12a5cb34b841145"
+GUAVA_BIN_SHA1 = "8ec9ed76528425762174f0011ce8f74ad845b756"
 
 GUAVA_DOC_URL = "https://google.github.io/guava/releases/" + GUAVA_VERSION + "/api/docs/"
diff --git a/lib/lucene/BUILD b/lib/lucene/BUILD
index 5ca9580..93eeccb 100644
--- a/lib/lucene/BUILD
+++ b/lib/lucene/BUILD
@@ -1,5 +1,4 @@
 load("@rules_java//java:defs.bzl", "java_binary", "java_import", "java_library")
-load("//tools/bzl:maven.bzl", "merge_maven_jars")
 
 package(default_visibility = ["//visibility:public"])
 
diff --git a/plugins/delete-project b/plugins/delete-project
index 39dd25c..7885a9f 160000
--- a/plugins/delete-project
+++ b/plugins/delete-project
@@ -1 +1 @@
-Subproject commit 39dd25c822be14a69282d38e5205f0ca4f2902c1
+Subproject commit 7885a9fa8d262b6127a7a3aa294108d6aac47a4d
diff --git a/polygerrit-ui/app/behaviors/gr-change-table-behavior/gr-change-table-behavior.html b/polygerrit-ui/app/behaviors/gr-change-table-behavior/gr-change-table-behavior.html
index d3cd940..d03316a 100644
--- a/polygerrit-ui/app/behaviors/gr-change-table-behavior/gr-change-table-behavior.html
+++ b/polygerrit-ui/app/behaviors/gr-change-table-behavior/gr-change-table-behavior.html
@@ -55,6 +55,9 @@
      * @return {boolean}
      */
     isColumnHidden(columnToCheck, columnsToDisplay) {
+      if ([columnsToDisplay, columnToCheck].some(arg => arg === undefined)) {
+        return false;
+      }
       return !columnsToDisplay.includes(columnToCheck);
     },
 
diff --git a/polygerrit-ui/app/elements/change-list/gr-change-list/gr-change-list.js b/polygerrit-ui/app/elements/change-list/gr-change-list/gr-change-list.js
index 2d6b440..8fd4214 100644
--- a/polygerrit-ui/app/elements/change-list/gr-change-list/gr-change-list.js
+++ b/polygerrit-ui/app/elements/change-list/gr-change-list/gr-change-list.js
@@ -187,8 +187,13 @@
       if (account) {
         this.showNumber = !!(preferences &&
             preferences.legacycid_in_change_table);
-        this.visibleChangeTableColumns = preferences.change_table.length > 0 ?
-          this.getVisibleColumns(preferences.change_table) : this.columnNames;
+        if (preferences.change_table &&
+            preferences.change_table.length > 0) {
+          this.visibleChangeTableColumns =
+            this.getVisibleColumns(preferences.change_table);
+        } else {
+          this.visibleChangeTableColumns = this.columnNames;
+        }
       } else {
         // Not logged in.
         this.showNumber = false;
diff --git a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.js b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.js
index d5eeee8..53c5ef5 100644
--- a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.js
+++ b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.js
@@ -305,7 +305,8 @@
       if (!account) { return; }
 
       this.$.restAPI.getPreferences().then(prefs => {
-        this._userLinks = prefs.my.map(this._fixCustomMenuItem);
+        this._userLinks = prefs && prefs.my ?
+          prefs.my.map(this._fixCustomMenuItem) : [];
       });
     }
 
diff --git a/polygerrit-ui/app/styles/themes/app-theme.html b/polygerrit-ui/app/styles/themes/app-theme.html
index 0dec63f..369af2b 100644
--- a/polygerrit-ui/app/styles/themes/app-theme.html
+++ b/polygerrit-ui/app/styles/themes/app-theme.html
@@ -59,17 +59,15 @@
   --view-background-color: var(--background-color-primary);
   /* unique background colors */
   --assignee-highlight-color: #fcfad6;
+  --comment-background-color: #fcfad6;
+  --robot-comment-background-color: #e8f0fe;
   --edit-mode-background-color: #ebf5fb;
   --emphasis-color: #fff9c4;
   --hover-background-color: rgba(161, 194, 250, 0.2);
   --primary-button-background-color: #2a66d9;
   --selection-background-color: rgba(161, 194, 250, 0.1);
   --tooltip-background-color: #333;
-  /* comment background colors */
-  --comment-background-color: #fef7f0;
-  --robot-comment-background-color: #e8f0fe;
-  --unresolved-comment-background-color: #e8eaed;
-  /* vote background colors */
+  --unresolved-comment-background-color: #fcfaa6;
   --vote-color-approved: #9fcc6b;
   --vote-color-disliked: #f7c4cb;
   --vote-color-neutral: #ebf5fb;
diff --git a/polygerrit-ui/app/styles/themes/dark-theme.html b/polygerrit-ui/app/styles/themes/dark-theme.html
index 57ceb32..80243dc 100644
--- a/polygerrit-ui/app/styles/themes/dark-theme.html
+++ b/polygerrit-ui/app/styles/themes/dark-theme.html
@@ -49,17 +49,15 @@
       /*   empty, because inheriting from app-theme is just fine
       /* unique background colors */
       --assignee-highlight-color: #3a361c;
+      --comment-background-color: #0b162b;
+      --robot-comment-background-color: rgba(232, 234, 237, 0.08);
       --edit-mode-background-color: #5c0a36;
       --emphasis-color: #383f4a;
       --hover-background-color: rgba(161, 194, 250, 0.2);
       --primary-button-background-color: var(--link-color);
       --selection-background-color: rgba(161, 194, 250, 0.1);
       --tooltip-background-color: #111;
-      /* comment background colors */
-      --comment-background-color: #303134;
-      --robot-comment-background-color: #40454e;
-      --unresolved-comment-background-color: #4b463a;
-      /* vote background colors */
+      --unresolved-comment-background-color: #385a9a;
       --vote-color-approved: #7fb66b;
       --vote-color-disliked: #bf6874;
       --vote-color-neutral: #597280;
diff --git a/tools/bzl/maven.bzl b/tools/bzl/maven.bzl
deleted file mode 100644
index 36e3084e..0000000
--- a/tools/bzl/maven.bzl
+++ /dev/null
@@ -1,34 +0,0 @@
-# Copyright (C) 2016 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.
-
-# Merge maven files
-
-load("@rules_java//java:defs.bzl", "java_import")
-
-def cmd(jars):
-    return ("$(location //tools:merge_jars) $@ " +
-            " ".join(["$(location %s)" % j for j in jars]))
-
-def merge_maven_jars(name, srcs, **kwargs):
-    native.genrule(
-        name = "%s__merged_bin" % name,
-        cmd = cmd(srcs),
-        tools = srcs + ["//tools:merge_jars"],
-        outs = ["%s__merged.jar" % name],
-    )
-    java_import(
-        name = name,
-        jars = [":%s__merged_bin" % name],
-        **kwargs
-    )
diff --git a/tools/eclipse/project.py b/tools/eclipse/project.py
index 7f0e88b..9915a6e 100755
--- a/tools/eclipse/project.py
+++ b/tools/eclipse/project.py
@@ -239,7 +239,7 @@
             if p.endswith('libquery_parser.jar') or \
                p.endswith('libgerrit-prolog-common.jar') or \
                p.endswith('com_google_protobuf/libprotobuf_java.jar') or \
-               p.endswith('lucene-core-and-backward-codecs__merged.jar'):
+               p.endswith('lucene-core-and-backward-codecs-merged_deploy.jar'):
                 lib.add(p)
             if proto_library.match(p) :
                 proto.add(p)