Allow mutating BranchOrder in project.config and add a test

This allows testing different behavior of change mergeability
added in I6ab0b73.

Change-Id: Id3bc861367443651a85cd57f1bfd0bdd55fd27f2

java/com/google/gerrit/server/project/ProjectConfig.java

@@ -357,6 +357,10 @@ public class ProjectConfig extends VersionedMetaData implements ValidationError.
     return branchOrderSection;
   }
 
+  public void setBranchOrderSection(BranchOrderSection branchOrderSection) {
+    this.branchOrderSection = branchOrderSection;
+  }
+
   public Map<Project.NameKey, SubscribeSection> getSubscribeSections() {
     return subscribeSections;
   }
@@ -814,6 +818,12 @@ public class ProjectConfig extends VersionedMetaData implements ValidationError.
     }
   }
 
+  private void saveBranchOrderSection(Config rc) {
+    if (branchOrderSection != null) {
+      rc.setStringList(BRANCH_ORDER, null, BRANCH, branchOrderSection.order());
+    }
+  }
+
   private ImmutableList<String> loadPatterns(
       Config rc, String section, String subsection, String varName) {
     ImmutableList.Builder<String> patterns = ImmutableList.builder();
@@ -1176,6 +1186,7 @@ public class ProjectConfig extends VersionedMetaData implements ValidationError.
     saveLabelSections(rc);
     saveCommentLinkSections(rc);
     saveSubscribeSections(rc);
+    saveBranchOrderSection(rc);
 
     saveConfig(PROJECT_CONFIG, rc);
     saveGroupList();

javatests/com/google/gerrit/server/project/ProjectConfigTest.java

@@ -34,6 +34,7 @@ import com.google.gerrit.server.config.AllProjectsName;
 import com.google.gerrit.server.config.PluginConfig;
 import com.google.gerrit.server.config.SitePaths;
 import com.google.gerrit.server.extensions.events.GitReferenceUpdated;
+import com.google.gerrit.server.git.BranchOrderSection;
 import com.google.gerrit.server.git.ValidationError;
 import com.google.gerrit.server.git.meta.MetaDataUpdate;
 import com.google.gerrit.server.project.testing.TestLabels;
@@ -360,6 +361,31 @@ public class ProjectConfigTest {
                 + "\tvalue = +1 Positive\n");
   }
 
+  @Test
+  public void readExistingBranchOrder() throws Exception {
+    RevCommit rev =
+        tr.commit()
+            .add("project.config", "[branchOrder]\n" + "\tbranch = foo\n" + "\tbranch = bar\n")
+            .create();
+    update(rev);
+
+    ProjectConfig cfg = read(rev);
+    assertThat(cfg.getBranchOrderSection())
+        .isEqualTo(BranchOrderSection.create(ImmutableList.of("foo", "bar")));
+  }
+
+  @Test
+  public void editBranchOrder() throws Exception {
+    RevCommit rev = tr.commit().create();
+    update(rev);
+
+    ProjectConfig cfg = read(rev);
+    cfg.setBranchOrderSection(BranchOrderSection.create(ImmutableList.of("foo", "bar")));
+    rev = commit(cfg);
+    assertThat(text(rev, "project.config"))
+        .isEqualTo("[branchOrder]\n" + "\tbranch = foo\n" + "\tbranch = bar\n");
+  }
+
   @Test
   public void addCommentLink() throws Exception {
     RevCommit rev = tr.commit().create();