Include a README.md in the java tools release with instructions on how  to re-create from source the same release.

Closes #8040.

PiperOrigin-RevId: 243789723

src/upload_all_java_tools.sh

diff --git a/src/upload_all_java_tools.sh b/src/upload_all_java_tools.sh
new file mode 100755
index 0000000..b560e08
--- /dev/null
+++ b/src/upload_all_java_tools.sh
@@ -0,0 +1,45 @@
+#!/bin/bash
+
+# Copyright 2019 The Bazel Authors. All rights reserved.
+#
+# 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.
+
+# A script to upload a given java_tools zip on GCS. Used by the java_tools_binaries
+# Buildkite pipeline. It is not recommended to run this script manually.
+#
+# Mandatory flags:
+# --java_tools_zip       The workspace-relative path of a java_tools zip.
+# --gcs_java_tools_dir   The directory under bazel_java_tools on GCS where the zip is uploaded.
+# --java_version         The version of the javac the given zip embeds.
+# --platform             The name of the platform where the zip was built.
+
+# Script used by the "java_tools binaries" Buildkite pipeline to build the java tools archives
+# and upload them on GCS.
+#
+# The script has to be executed directly without invoking bazel:
+# $ src/upload_all_java_tools.sh
+#
+# The script cannot be invoked through a sh_binary using bazel because git
+# cannot be used through a sh_binary.
+
+commit_hash=$(git rev-parse HEAD)
+timestamp=$(date +%s)
+bazel_version=$(bazel info release | cut -d' ' -f2)
+
+# Passing the same commit_hash and timestamp to all targets to mark all the artifacts
+# uploaded on GCS with the same identifier.
+for java_version in 9 10; do
+  for target in src:upload_java_tools_java${java_version} src:upload_java_tools_dist_java${java_version}; do
+    bazel run ${target} -- --commit_hash ${commit_hash} --timestamp ${timestamp} --bazel_version ${bazel_version}
+  done
+done

src/upload_java_tools.sh

diff --git a/src/upload_java_tools.sh b/src/upload_java_tools.sh
index 64d344a..5dc0712 100755
--- a/src/upload_java_tools.sh
+++ b/src/upload_java_tools.sh
@@ -55,16 +55,46 @@
     "--gcs_java_tools_dir") gcs_java_tools_dir="$val" ;;
     "--java_version") java_version="$val" ;;
     "--platform") platform="$val" ;;
+    "--commit_hash") commit_hash="$val" ;;
+    "--timestamp") timestamp="$val" ;;
+    "--bazel_version") bazel_version="$val" ;;
     *) echo "Flag $arg is not recognized." && exit 1 ;;
   esac
 done
 
 java_tools_zip=$(rlocation io_bazel/${java_tools_zip_name})
 
+# Create a temp directory and a writable temp zip file to add a README.md file to
+# the initial zip.
+tmp_dir=$(mktemp -d -t 'tmp_bazel_zip_files_XXXXX')
+trap "rm -fr $tmp_dir" EXIT
+tmp_zip="$tmp_dir/archive.zip"
+
+# Copy the initial zip to the temp zip and make it writable to be able to add
+# the README.md file.
+cp $java_tools_zip $tmp_zip
+chmod +w $tmp_zip
+
+# Create the README.md file and add the re-build java tools instructions.
+readme_file="README.md"
+cat >${readme_file} <<EOF
+This Java tools version was built from the bazel repository at commit hash ${commit_hash}
+using bazel version ${bazel_version}.
+To build from source the same zip run the commands:
+
+$ git clone https://github.com/bazelbuild/bazel.git
+$ git checkout ${commit_hash}
+$ bazel build //src:java_tools_java${java_version}.zip
+EOF
+
+# Add the README.md file to the temp zip.
+zip -rv "${tmp_zip}" "${readme_file}"
+
 gsutil_cmd="gsutil"
 if [[ "$platform" == "windows" ]]; then
   gsutil_cmd="gsutil.cmd"
 fi
 
-"$gsutil_cmd" cp "$java_tools_zip" \
- "gs://bazel-mirror/bazel_java_tools/${gcs_java_tools_dir}/java_tools_javac${java_version}_${platform}-$(date +%s).zip"
+# Upload the zip that contains the README.md to GCS.
+"$gsutil_cmd" cp "$tmp_zip" \
+ "gs://bazel-mirror/bazel_java_tools/${gcs_java_tools_dir}/java_tools_javac${java_version}_${platform}-${commit_hash}-${timestamp}.zip"