Bazel: add java_doc rule

Add javadoc rules for plugin API:

* gerrit-extension-api
* gerrit-plugin-api
* gerrit-acceptance-framework

Note that GWT UI is not covered by Bazel build yet, so that we cannot
offer gerrit-plugin-gwtui:plugin-gwtui-javadoc rule in this change.

TEST PLAN:

  bazel build gerrit-acceptance-framework:acceptance-framework-javadoc
  bazel build gerrit-extension-api:extension-api-javadoc
  bazel build gerrit-plugin-api:plugin-api-javadoc

Change-Id: I60832752010118e33eb6a06529032d86f169ee44

tools/bzl/javadoc.bzl

@@ -0,0 +1,71 @@
+# Copyright (C) 2016 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.
+
+# Javadoc rule.
+
+def _impl(ctx):
+  zip_output = ctx.outputs.zip
+
+  transitive_jar_set = set()
+  source_jars = set()
+  for l in ctx.attr.libs:
+    source_jars += l.java.source_jars
+    transitive_jar_set += l.java.transitive_deps
+
+  transitive_jar_paths = [j.path for j in transitive_jar_set]
+  dir = ctx.outputs.zip.path + ".dir"
+  source = ctx.outputs.zip.path + ".source"
+  cmd = [
+      "mkdir %s" % source,
+      " && ".join(["unzip -qud %s %s" % (source, j.path) for j in source_jars]),
+      "mkdir %s" % dir,
+      " ".join([
+        ctx.file._javadoc.path,
+        "-protected",
+        "-encoding UTF-8",
+        "-charset UTF-8",
+        "-notimestamp",
+        "-quiet",
+        "-windowtitle '%s'" % ctx.attr.title,
+        "-link", "http://docs.oracle.com/javase/7/docs/api",
+        "-sourcepath %s" % source,
+        "-subpackages ",
+        ":".join(ctx.attr.pkgs),
+        " -classpath ",
+        ":".join(transitive_jar_paths),
+        "-d %s" % dir]),
+    "find %s -exec touch -t 198001010000 '{}' ';'" % dir,
+    "(cd %s && zip -qr ../%s *)" % (dir, ctx.outputs.zip.basename),
+  ]
+  ctx.action(
+      inputs = list(transitive_jar_set) + list(source_jars) + ctx.files._jdk,
+      outputs = [zip_output],
+      command = " && ".join(cmd))
+
+java_doc = rule(
+    attrs = {
+      "libs": attr.label_list(allow_files = False),
+      "pkgs": attr.string_list(),
+      "title": attr.string(),
+      "_javadoc": attr.label(
+        default = Label("@local_jdk//:bin/javadoc"),
+        single_file = True,
+        allow_files = True),
+      "_jdk": attr.label(
+        default = Label("@local_jdk//:jdk-default"),
+        allow_files = True),
+    },
+    implementation = _impl,
+    outputs = {"zip" : "%{name}.zip"},
+)