Build with Buck

Implement a new build system using Buck[1], Facebook's
open source clone of Google's internal build system.

  Pros:
  - Concise build language
  - Test and build output is concise
  - Test failures and stack traces show on terminal
  - Reliable incrementals; clean is unnecessary
  - Extensible with simple blocks of Python
  - Fast
      buck: clean: 0.452s, full 1m21.083s [*], no-op:  7.145s,
      mvn:  clean: 4.596s, full 2m53.776s,     no-op: 59.108s,

      [*] full build includes downloading all dependencies,
          time can vary due to remote server performance.

  Cons:
  - No Windows support
  - No native Maven Central support (added by macros)
  - No native GWT, Prolog, or WAR support (added by macros)
  - Bootstrap of buck requires Ant

Getting started:

  git clone https://gerrit.googlesource.com/buck
  cd buck
  ant

  Mac OS X:
    PATH="`pwd`/bin:/System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands:$PATH"

  Linux:
    PATH="`pwd`/bin:$PATH"

Importing into Eclipse:

  $ time buck build :eclipse
  0m48.949s

  Import existing project from `pwd`
  Import 'gerrit' (do not import other Maven based projects)
  Expand 'gerrit'
  Right click 'buck-out' > Properties
  Under Attributes check 'Derived'

  If the code doesn't currently compile but an updated classpath
  is needed, refresh the configs and obtain missing JARs:

  $ buck build :eclipse_project :download

Running JUnit tests:

  $ time buck test --all -e slow  # skip slow tests
  0m19.320s

  $ time buck test --all          # includes acceptance tests
  5m17.517s

Building WAR:

  $ buck build :gerrit
  $ java -jar buck-out/gen/gerrit.war

Building release:

  $ buck test --all && buck build :api :release
  $ java -jar buck-out/gen/release.war
  $ ls -lh buck-out/gen/{extension,plugin}-api.jar

Downloading dependencies:

  Dependencies are normally downloaded automatically, but Buck can
  inspect its graph and download missing dependencies so future
  compiles can run without the network:

  $ buck build :download

[1] http://facebook.github.io/buck/

Change-Id: I40853b108bd8e153cefa0896a5280a9a5ff81655

gerrit-gwtdebug/src/main/java/com/google/gerrit/gwtdebug/GerritDebugLauncher.java

@@ -381,9 +381,15 @@ public class GerritDebugLauncher extends ServletContainerLauncher {
     Server server = new Server();
     server.addConnector(connector);
 
-    // warDir is "$top/gerrit-gwtui/target/gwt-hosted-mode"
-    //
-    File top = warDir.getParentFile().getParentFile().getParentFile();
+    File top;
+    String root = System.getProperty("gerrit.source_root");
+    if (root != null) {
+      top = new File(root);
+    } else {
+      // Under Maven warDir is "$top/gerrit-gwtui/target/gwt-hosted-mode"
+      top = warDir.getParentFile().getParentFile().getParentFile();
+    }
+
     File app = new File(top, "gerrit-war/src/main/webapp");
     File webxml = new File(app, "WEB-INF/web.xml");