Set up Eclipse to work with Java 9 and later

To create .classpath with java 9, run:

  $ tools/eclipse/project.py --java 9

Start Eclipse, and follow the instructions provided in dev-eclipse.txt to
switch to Java 9 or later.

To run gerrit from Eclipse, the system classpath is cast to
URLClassLoader to retrieve the needed JARs. In Java 9 system classpath
cannot be cast to URLClassLoader. To rectify, extract the classpath from
Bazel.

Change-Id: Ie341cd4dfee5520f689fc50f34aa5395b74b5e7d

Documentation/dev-eclipse.txt

@@ -3,7 +3,7 @@
 This document is about configuring Gerrit Code Review into an
 Eclipse workspace for development and debugging with GWT.
 
-Java 6 or later SDK is also required to run GWT's compiler and
+Java 8 or later SDK is also required to run GWT's compiler and
 runtime debugging environment.
 
 
@@ -49,6 +49,19 @@ the same way you would when
 link:dev-build-plugins.html#_bundle_custom_plugin_in_release_war[bundling in release.war]
 and run `tools/eclipse/project.py`.
 
+[[Newer Java versions]]
+
+Java 9 and later are supported, but some adjustments must be done, because
+Java 8 is still the default:
+
+* Add JRE, e.g.: directory: /usr/lib64/jvm/java-9-openjdk, name: java-9-openjdk-9
+* Change execution environemnt for gerrit project to: JavaSE-9 (java-9-openjdk-9)
+* Check that compiler compliance level in gerrit project is set to: 9
+* Add this parameter to VM argument for gerrit_daemin launcher:
+----
+  --add-modules java.activation \
+  --add-opens=jdk.management/com.sun.management.internal=ALL-UNNAMED
+----
 
 [[Formatting]]
 == Code Formatter Settings

java/com/google/gerrit/httpd/raw/BazelBuild.java

@@ -23,14 +23,15 @@ import com.google.common.flogger.FluentLogger;
 import com.google.common.html.HtmlEscapers;
 import com.google.common.io.ByteStreams;
 import com.google.gerrit.common.TimeUtil;
+import com.google.gerrit.launcher.GerritLauncher;
 import com.google.gerrit.util.http.CacheHeaders;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InterruptedIOException;
 import java.io.PrintWriter;
-import java.nio.file.Files;
-import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Properties;
 import javax.servlet.http.HttpServletResponse;
 import org.eclipse.jgit.util.RawParseUtils;
@@ -122,20 +123,19 @@ public class BazelBuild {
     }
   }
 
-  private Properties loadBuildProperties(Path propPath) throws IOException {
-    Properties properties = new Properties();
-    try (InputStream in = Files.newInputStream(propPath)) {
-      properties.load(in);
-    } catch (NoSuchFileException e) {
-      // Ignore; will be run from PATH, with a descriptive error if it fails.
-    }
-    return properties;
-  }
-
   private ProcessBuilder newBuildProcess(Label label) throws IOException {
-    Properties properties = loadBuildProperties(sourceRoot.resolve(".bazel_path"));
+    Properties properties = GerritLauncher.loadBuildProperties(sourceRoot.resolve(".bazel_path"));
     String bazel = firstNonNull(properties.getProperty("bazel"), "bazel");
-    ProcessBuilder proc = new ProcessBuilder(bazel, "build", label.fullName());
+    List<String> cmd = new ArrayList<>();
+    cmd.add(bazel);
+    cmd.add("build");
+    if (GerritLauncher.isJdk9OrLater()) {
+      String v = GerritLauncher.getJdkVersionPostJdk8();
+      cmd.add("--host_java_toolchain=@bazel_tools//tools/jdk:toolchain_java" + v);
+      cmd.add("--java_toolchain=@bazel_tools//tools/jdk:toolchain_java" + v);
+    }
+    cmd.add(label.fullName());
+    ProcessBuilder proc = new ProcessBuilder(cmd);
     if (properties.containsKey("PATH")) {
       proc.environment().put("PATH", properties.getProperty("PATH"));
     }

java/com/google/gerrit/launcher/GerritLauncher.java

@@ -34,6 +34,7 @@ import java.net.URLClassLoader;
 import java.nio.file.FileSystem;
 import java.nio.file.FileSystems;
 import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.security.CodeSource;
@@ -44,6 +45,7 @@ import java.util.Enumeration;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Properties;
 import java.util.Scanner;
 import java.util.SortedMap;
 import java.util.TreeMap;
@@ -644,6 +646,25 @@ public final class GerritLauncher {
     return resolveInSourceRoot("eclipse-out");
   }
 
+  public static boolean isJdk9OrLater() {
+    return Double.parseDouble(System.getProperty("java.class.version")) >= 53.0;
+  }
+
+  public static String getJdkVersionPostJdk8() {
+    // 9.0.4 => 9
+    return System.getProperty("java.version").substring(0, 1);
+  }
+
+  public static Properties loadBuildProperties(Path propPath) throws IOException {
+    Properties properties = new Properties();
+    try (InputStream in = Files.newInputStream(propPath)) {
+      properties.load(in);
+    } catch (NoSuchFileException e) {
+      // Ignore; will be run from PATH, with a descriptive error if it fails.
+    }
+    return properties;
+  }
+
   static final String SOURCE_ROOT_RESOURCE = "/com/google/gerrit/launcher/workspace-root.txt";
 
   /**
@@ -708,23 +729,47 @@ public final class GerritLauncher {
     return ret;
   }
 
-  private static ClassLoader useDevClasspath() throws MalformedURLException, FileNotFoundException {
+  private static ClassLoader useDevClasspath() throws IOException {
     Path out = getDeveloperEclipseOut();
     List<URL> dirs = new ArrayList<>();
     dirs.add(out.resolve("classes").toUri().toURL());
     ClassLoader cl = GerritLauncher.class.getClassLoader();
+
+    if (isJdk9OrLater()) {
+      Path rootPath = resolveInSourceRoot(".").normalize();
+
+      Properties properties = loadBuildProperties(rootPath.resolve(".bazel_path"));
+      Path outputBase = Paths.get(properties.getProperty("output_base"));
+
+      Path runtimeClasspath =
+          rootPath.resolve("bazel-bin/tools/eclipse/main_classpath_collect.runtime_classpath");
+      for (String f : Files.readAllLines(runtimeClasspath, UTF_8)) {
+        URL url;
+        if (f.startsWith("external")) {
+          url = outputBase.resolve(f).toUri().toURL();
+        } else {
+          url = rootPath.resolve(f).toUri().toURL();
+        }
+        if (includeJar(url)) {
+          dirs.add(url);
+        }
+      }
+    } else {
       for (URL u : ((URLClassLoader) cl).getURLs()) {
         if (includeJar(u)) {
           dirs.add(u);
         }
       }
+    }
     return URLClassLoader.newInstance(
         dirs.toArray(new URL[dirs.size()]), ClassLoader.getSystemClassLoader().getParent());
   }
 
   private static boolean includeJar(URL u) {
     String path = u.getPath();
-    return path.endsWith(".jar") && !path.endsWith("-src.jar");
+    return path.endsWith(".jar")
+        && !path.endsWith("-src.jar")
+        && !path.contains("/com/google/gerrit");
   }
 
   private GerritLauncher() {}

tools/eclipse/project.py

@@ -32,7 +32,7 @@ AUTO = '//lib/auto:auto-value'
 JRE = '/'.join([
     'org.eclipse.jdt.launching.JRE_CONTAINER',
     'org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType',
-    'JavaSE-1.8',
+    'JavaSE-9',
 ])
 # Map of targets to corresponding classpath collector rules
 cp_targets = {
@@ -52,10 +52,12 @@ opts.add_option('--name', help='name of the generated project',
                 action='store', default='gerrit', dest='project_name')
 opts.add_option('-b', '--batch', action='store_true',
                 dest='batch', help='Bazel batch option')
+opts.add_option('-j', '--java', action='store',
+                dest='java', help='Post Java 8 support (9|10|11|...)')
 args, _ = opts.parse_args()
 
 batch_option = '--batch' if args.batch else None
-
+custom_java = args.java
 
 def _build_bazel_cmd(*args):
     cmd = ['bazel']
@@ -63,6 +65,9 @@ def _build_bazel_cmd(*args):
         cmd.append('--batch')
     for arg in args:
         cmd.append(arg)
+    if custom_java:
+        cmd.append('--host_java_toolchain=@bazel_tools//tools/jdk:toolchain_java%s' % custom_java)
+        cmd.append('--java_toolchain=@bazel_tools//tools/jdk:toolchain_java%s' % custom_java)
     return cmd
 
 
@@ -70,9 +75,10 @@ def retrieve_ext_location():
     return check_output(_build_bazel_cmd('info', 'output_base')).strip()
 
 
-def gen_bazel_path():
+def gen_bazel_path(ext_location):
     bazel = check_output(['which', 'bazel']).strip().decode('UTF-8')
     with open(path.join(ROOT, ".bazel_path"), 'w') as fd:
+        fd.write("output_base=%s\n" % ext_location)
         fd.write("bazel=%s\n" % bazel)
         fd.write("PATH=%s\n" % environ["PATH"])
 
@@ -301,7 +307,7 @@ try:
     gen_project(args.project_name)
     gen_classpath(ext_location)
     gen_factorypath(ext_location)
-    gen_bazel_path()
+    gen_bazel_path(ext_location)
 
     # TODO(davido): Remove this when GWT gone
     gwt_working_dir = ".gwt_work_dir"