Add PolyGerrit site theme file url to REST API

Change-Id: If25d0850f92f90aa4eabdf9aa74f0d3bc6307392

Documentation/rest-api-config.txt

@@ -1801,6 +1801,9 @@ the first matched group, `$2` for the second matched group, etc.
 Information about the configuration from the
 link:config-gerrit.html#user[user] section as link:#user-config-info[
 UserConfigInfo] entity.
+|`default_theme`           |optional|
+URL to a default PolyGerrit UI theme plugin, if available.
+Located in `/static/gerrit-theme.html` by default.
 |=======================================
 
 [[sshd-info]]

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/common/ServerInfo.java

@@ -28,4 +28,5 @@ public class ServerInfo {
   public Map<String, String> urlAliases;
   public UserConfigInfo user;
   public ReceiveInfo receive;
+  public String defaultTheme;
 }

gerrit-server/src/main/java/com/google/gerrit/server/config/GetServerInfo.java

@@ -53,6 +53,7 @@ import com.google.gerrit.server.notedb.NotesMigration;
 import com.google.gerrit.server.project.ProjectCache;
 import com.google.inject.Inject;
 import java.net.MalformedURLException;
+import java.nio.file.Files;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.EnumSet;
@@ -86,6 +87,7 @@ public class GetServerInfo implements RestReadView<ConfigResource> {
   private final AgreementJson agreementJson;
   private final GerritOptions gerritOptions;
   private final ChangeIndexCollection indexes;
+  private final SitePaths sitePaths;
 
   @Inject
   public GetServerInfo(
@@ -107,7 +109,8 @@ public class GetServerInfo implements RestReadView<ConfigResource> {
       ProjectCache projectCache,
       AgreementJson agreementJson,
       GerritOptions gerritOptions,
-      ChangeIndexCollection indexes) {
+      ChangeIndexCollection indexes,
+      SitePaths sitePaths) {
     this.config = config;
     this.authConfig = authConfig;
     this.realm = realm;
@@ -127,6 +130,7 @@ public class GetServerInfo implements RestReadView<ConfigResource> {
     this.agreementJson = agreementJson;
     this.gerritOptions = gerritOptions;
     this.indexes = indexes;
+    this.sitePaths = sitePaths;
   }
 
   @Override
@@ -139,6 +143,9 @@ public class GetServerInfo implements RestReadView<ConfigResource> {
     info.gerrit = getGerritInfo(config, allProjectsName, allUsersName);
     info.noteDbEnabled = toBoolean(isNoteDbEnabled());
     info.plugin = getPluginInfo();
+    if (Files.exists(sitePaths.site_theme)) {
+      info.defaultTheme = "/static/" + SitePaths.THEME_FILENAME;
+    }
     info.sshd = getSshdInfo(config);
     info.suggest = getSuggestInfo(config);
 

gerrit-server/src/main/java/com/google/gerrit/server/config/SitePaths.java

@@ -29,6 +29,7 @@ public final class SitePaths {
   public static final String CSS_FILENAME = "GerritSite.css";
   public static final String HEADER_FILENAME = "GerritSiteHeader.html";
   public static final String FOOTER_FILENAME = "GerritSiteFooter.html";
+  public static final String THEME_FILENAME = "gerrit-theme.html";
 
   public final Path site_path;
   public final Path bin_dir;
@@ -67,6 +68,8 @@ public final class SitePaths {
   public final Path site_css;
   public final Path site_header;
   public final Path site_footer;
+  // For PolyGerrit UI only.
+  public final Path site_theme;
   public final Path site_gitweb;
 
   /** {@code true} if {@link #site_path} has not been initialized. */
@@ -115,6 +118,9 @@ public final class SitePaths {
     site_footer = etc_dir.resolve(FOOTER_FILENAME);
     site_gitweb = etc_dir.resolve("gitweb_config.perl");
 
+    // For PolyGerrit UI.
+    site_theme = static_dir.resolve(THEME_FILENAME);
+
     boolean isNew;
     try (DirectoryStream<Path> files = Files.newDirectoryStream(site_path)) {
       isNew = Iterables.isEmpty(files);