Bazel: Add support for Java 10

Bazel@HEAD doesn't support Java 10 any more. The tool chain is extended
to support building with Java 10 using host_javabase option and vanilla
java builder. To use --host_javabase option we have to provide absolute
path to the JDK 10. To keep that non-portable part out of the build file
we use variable that is substitued during build invocation. Say, the
location of the JDK 10 is: /usr/lib64/jvm/java-10, then the build is
invoked with:

  $ bazel build --host_javabase=:absolute_javabase \
    --define=ABSOLUTE_JAVABASE=/usr/lib64/jvm/java-10 ...

Given that absolute_javabase rule is not a part of released Bazel yet,
but will be only included in future Bazel releases, we have to add it in
our own build file:

  java_runtime(
      name = "absolute_javabase",
      java_home = "$(ABSOLUTE_JAVABASE)",
      visibility = ["//visibility:public"],
  )

While this works, it fails the Gerrit-CI, because recently it was
changed to exercise //... rule, and cannot resolve ABSOLUTE_JAVABASE
variable, because it wasn't provided in the CI environment. CI is still
using Java 8.

One approach to address that problem would be to use "manual" tag for a
rule that would exclude it from generic targets like //..., but
unfortunately, java_runtime rule doesn't expose tag attribute.

The next workaround is to hide that variable behind a select statement.
This is a harmless hack:

  config_setting(
      name = "use_absolute_javabase",
      values = {"define": "USE_ABSOLUTE_JAVABASE=true"},
  )

  java_runtime(
      name = "absolute_javabase",
      java_home = select({
          ":use_absolute_javabase": "$(ABSOLUTE_JAVABASE)",
          "//conditions:default": "",
      }),
      visibility = ["//visibility:public"],
  )

Now from the CI the rule: //:absolute_javabase would produce non working
java_runtime, because java_home wasn't specified, but given that this
java_runtime is not used during the build, it doesn't matter. Add also
a TODO comment to replace that interim solution when absolute_javabase
is supported in released Bazel version. As the consequence for hiding
that rule behind a condition, we need to provide additional variable so
that Bazel can correctly resolve java_home in java_runtime rule:

  $ bazel build --host_javabase=:absolute_javabase \
    --define=ABSOLUTE_JAVABASE=/usr/lib64/jvm/java-10 \
    --define=USE_ABSOLUTE_JAVABASE=true [...]

Also extend tools/eclipse/project.py to accept Java 10 specific options.
There is already --java <jdk number> option that was added recently to
support Eclipse .classpath generation when JDK 9 is used, but this can
not be used, because for Java 10 we have to provide absolute path to the
Java 10 location. Add new option --edge_java where all Java 10 specific
options can be passed:

  $ tools/eclipse/project.py --edge_java \
    "--host_javabase=:absolute_javabase \
    --define=ABSOLUTE_JAVABASE=/usr/lib64/jvm/java-10 \
    --define=USE_ABSOLUTE_JAVABASE=true \
    --host_java_toolchain=//:toolchain_vanilla \
    --java_toolchain=//:toolchain_vanilla"

Alternative approach would be to add those options to Bazel resource
file.

Test Plan:

  $ bazel build --host_javabase=:absolute_javabase \
    --define=ABSOLUTE_JAVABASE=/usr/lib64/jvm/java-10 \
    --define=USE_ABSOLUTE_JAVABASE=true \
    --host_java_toolchain=//:toolchain_vanilla \
    --java_toolchain=//:toolchain_vanilla \
    :release

and replace ABSOLUTE_JAVABASE variable with the location of JDK 10.

To verify that major version of generated classes is 54, use:

  $ $JAVA_HOME/bin/javap -verbose \
    -cp bazel-bin/java/com/google/gerrit/common/libserver.jar \
     com.google.gerrit.common.data.ProjectAccess | grep "major version"
  54

[1] https://github.com/bazelbuild/bazel/issues/6012
Change-Id: I5e652f7a19afbcf3607febd9a7a165dc07918bd0

BUILD

@@ -2,6 +2,10 @@ package(default_visibility = ["//visibility:public"])
 
 load("//tools/bzl:genrule2.bzl", "genrule2")
 load("//tools/bzl:pkg_war.bzl", "pkg_war")
+load(
+    "@bazel_tools//tools/jdk:default_java_toolchain.bzl",
+    "default_java_toolchain",
+)
 
 config_setting(
     name = "java9",
@@ -10,6 +14,43 @@ config_setting(
     },
 )
 
+config_setting(
+    name = "java10",
+    values = {
+        "java_toolchain": ":toolchain_vanilla",
+    },
+)
+
+# TODO(davido): Switch to consuming it from @bazel_tool//tools/jdk:absolute_javabase
+# when new Bazel version is released with this change included:
+# https://github.com/bazelbuild/bazel/issues/6012
+# https://github.com/bazelbuild/bazel/commit/0173bdbf7bdd1874379d4dd3eb70d5321e0f1816
+# As the interim use a hack that works around it by putting the variable reference
+# behind a select
+config_setting(
+    name = "use_absolute_javabase",
+    values = {"define": "USE_ABSOLUTE_JAVABASE=true"},
+)
+
+java_runtime(
+    name = "absolute_javabase",
+    java_home = select({
+        ":use_absolute_javabase": "$(ABSOLUTE_JAVABASE)",
+        "//conditions:default": "",
+    }),
+    visibility = ["//visibility:public"],
+)
+
+# TODO(davido): Switch to consuming it from @bazel_tool//tools/jdk:toolchain_vanilla
+# when my change is included in released Bazel version:
+# https://github.com/bazelbuild/bazel/commit/0bef68e054eccecd690e5d9f46db8a0c4b2d887a
+default_java_toolchain(
+    name = "toolchain_vanilla",
+    forcibly_disable_header_compilation = True,
+    javabuilder = ["@bazel_tools//tools/jdk:VanillaJavaBuilder_deploy.jar"],
+    jvm_opts = [],
+)
+
 genrule(
     name = "gen_version",
     outs = ["version.txt"],

Documentation/dev-bazel.txt

@@ -6,7 +6,7 @@
 To build Gerrit from source, you need:
 
 * A Linux or macOS system (Windows is not supported at this time)
-* A JDK for Java 8
+* A JDK for Java 8|9|10
 * Python 2 or 3
 * Node.js
 * link:https://www.bazel.io/versions/master/docs/install.html[Bazel]
@@ -14,6 +14,30 @@ To build Gerrit from source, you need:
 * zip, unzip
 * gcc
 
+[[Java 10 support]]
+Java 10 is supported through vanilla java toolchain
+link:https://docs.bazel.build/versions/master/toolchains.html[Bazel option].
+To build Gerrit with Java 10, specify vanilla java toolchain and provide
+path to Java 10 home:
+
+```
+  $ bazel build --host_javabase=:absolute_javabase \
+    --define=ABSOLUTE_JAVABASE=<path-to-java-10> \
+    --define=USE_ABSOLUTE_JAVABASE=true \
+    --host_java_toolchain=//:toolchain_vanilla \
+    --java_toolchain=//:toolchain_vanilla \
+    :release
+```
+
+Note that the following options must be added to `container.javaOptions`
+in `$gerrit_site/etc/gerrit.config` to run Gerrit with Java 10:
+
+```
+[container]
+  javaOptions = --add-modules java.activation
+  javaOptions = --add-opens=jdk.management/com.sun.management.internal=ALL-UNNAMED
+```
+
 [[Java 9 support]]
 Java 9 is supported through alternative java toolchain
 link:https://docs.bazel.build/versions/master/toolchains.html[Bazel option].

tools/bzl/junit.bzl

@@ -64,6 +64,14 @@ _GenSuite = rule(
     implementation = _impl,
 )
 
+POST_JDK8_OPTS = [
+    # Enforce JDK 8 compatibility on Java 9, see
+    # https://docs.oracle.com/javase/9/intl/internationalization-enhancements-jdk-9.htm#JSINT-GUID-AF5AECA7-07C1-4E7D-BC10-BC7E73DC6C7F
+    "-Djava.locale.providers=COMPAT,CLDR,SPI",
+    "--add-modules java.activation",
+    "--add-opens=jdk.management/com.sun.management.internal=ALL-UNNAMED",
+]
+
 def junit_tests(name, srcs, **kwargs):
     s_name = name + "TestSuite"
     _GenSuite(
@@ -73,13 +81,8 @@ def junit_tests(name, srcs, **kwargs):
     )
     jvm_flags = kwargs.get("jvm_flags", [])
     jvm_flags = jvm_flags + select({
-        "//:java9": [
-            # Enforce JDK 8 compatibility on Java 9, see
-            # https://docs.oracle.com/javase/9/intl/internationalization-enhancements-jdk-9.htm#JSINT-GUID-AF5AECA7-07C1-4E7D-BC10-BC7E73DC6C7F
-            "-Djava.locale.providers=COMPAT,CLDR,SPI",
-            "--add-modules java.activation",
-            "--add-opens=jdk.management/com.sun.management.internal=ALL-UNNAMED",
-        ],
+        "//:java9": POST_JDK8_OPTS,
+        "//:java10": POST_JDK8_OPTS,
         "//conditions:default": [],
     })
     native.java_test(

tools/eclipse/project.py

@@ -53,21 +53,29 @@ opts.add_option('--name', help='name of the generated project',
 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|...)')
+                dest='java', help='Post Java 8 support (9)')
+opts.add_option('-e', '--edge_java', action='store',
+                dest='edge_java', help='Post Java 9 support (10|11|...)')
 args, _ = opts.parse_args()
 
 batch_option = '--batch' if args.batch else None
 custom_java = args.java
+edge_java = args.edge_java
 
 def _build_bazel_cmd(*args):
+    build = False
     cmd = ['bazel']
     if batch_option:
         cmd.append('--batch')
     for arg in args:
+        if arg == "build":
+            build = True
         cmd.append(arg)
-    if custom_java:
+    if custom_java and not edge_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)
+        if edge_java and build:
+            cmd.append(edge_java)
     return cmd