Auto-disable auto gc in jgit

By JGit's default, git-receive-pack will run auto gc after receiving
data from git-push and updating refs.

Disable this behavior in Gerrit init to avoid the additional load it
creates: gc should be configured in gc config section or run as a
separate process.

Change-Id: I9450f8edbade7b6e789387645cfe70daa0949aff

Documentation/config-gerrit.txt

@@ -5604,10 +5604,12 @@ Supported versions:
 
 [[receive.autogc]]receive.autogc::
 +
-By default, `git-receive-pack` will run auto gc after receiving data from git-push and updating refs.
+By default, up to Gerrit 3.2 `git-receive-pack` will run auto gc after receiving data from git-push and updating refs.
 You can stop it by setting this variable to `false`. This is recommended in gerrit to avoid the
 additional load this creates. Instead schedule gc using link:cmd-gc.html#gc.startTime[gc.startTime]
 and link:cmd-gc.html#gc.interval[gc.interval] or e.g. in a cron job that runs gc in a separate process.
+Since Gerrit 3.3 the init command will auto-configure `git-receive-pack = false` in `etc/jgit.config` if
+it wasn't set manually and show a warning if it was set to `true` manually.
 
 GERRIT
 ------

java/com/google/gerrit/pgm/init/InitJGitConfig.java

@@ -0,0 +1,71 @@
+// Copyright (C) 2020 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.pgm.init;
+
+import static com.google.gerrit.pgm.init.api.InitUtil.die;
+
+import com.google.gerrit.pgm.init.api.ConsoleUI;
+import com.google.gerrit.pgm.init.api.InitStep;
+import com.google.gerrit.server.config.SitePaths;
+import com.google.inject.Inject;
+import com.google.inject.Singleton;
+import java.io.IOException;
+import org.eclipse.jgit.errors.ConfigInvalidException;
+import org.eclipse.jgit.lib.ConfigConstants;
+import org.eclipse.jgit.storage.file.FileBasedConfig;
+import org.eclipse.jgit.util.FS;
+
+/** Initialize the JGit configuration. */
+@Singleton
+class InitJGitConfig implements InitStep {
+  private final ConsoleUI ui;
+  private final SitePaths sitePaths;
+
+  @Inject
+  InitJGitConfig(ConsoleUI ui, SitePaths sitePaths) {
+    this.ui = ui;
+    this.sitePaths = sitePaths;
+  }
+
+  @Override
+  public void run() {
+    ui.header("JGit Configuration");
+    FileBasedConfig jgitConfig = new FileBasedConfig(sitePaths.jgit_config.toFile(), FS.DETECTED);
+    try {
+      jgitConfig.load();
+      if (!jgitConfig
+          .getNames(ConfigConstants.CONFIG_RECEIVE_SECTION)
+          .contains(ConfigConstants.CONFIG_KEY_AUTOGC)) {
+        jgitConfig.setBoolean(
+            ConfigConstants.CONFIG_RECEIVE_SECTION, null, ConfigConstants.CONFIG_KEY_AUTOGC, false);
+        jgitConfig.save();
+        ui.error(
+            "Auto-configured \"receive.autogc = false\" to disable auto-gc after git-receive-pack.");
+      } else if (jgitConfig.getBoolean(
+          ConfigConstants.CONFIG_RECEIVE_SECTION, ConfigConstants.CONFIG_KEY_AUTOGC, true)) {
+        ui.error(
+            "WARNING: JGit option \"receive.autogc = true\". This is not recommended in Gerrit.\n"
+                + "git-receive-pack will run auto gc after receiving data from "
+                + "git-push and updating refs.\n"
+                + "Disable this behavior to avoid the additional load it creates: "
+                + "gc should be configured in gc config section or run as a separate process.");
+      }
+    } catch (IOException e) {
+      throw die(String.format("Handling JGit configuration %s failed", sitePaths.jgit_config), e);
+    } catch (ConfigInvalidException e) {
+      throw die(String.format("Invalid JGit configuration %s", sitePaths.jgit_config), e);
+    }
+  }
+}

java/com/google/gerrit/pgm/init/InitModule.java

@@ -40,6 +40,7 @@ public class InitModule extends FactoryModule {
     // Steps are executed in the order listed here.
     //
     step().to(InitGitManager.class);
+    step().to(InitJGitConfig.class);
     step().to(InitLogging.class);
     step().to(InitIndex.class);
     step().to(InitAuth.class);