Add provenance information in coverage_output_generator upload script

Includes a README.md file to the final .zip file providing the commit
hash, timestamp, and build command to produce the file.

Fixes bazelbuild#15459

tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/build_and_upload.sh

@@ -14,8 +14,40 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# A script to build, package, and upload a copy of
+# coverage_output_generator.zip to bazel-mirror.
+#
+# To make a "release" of the coverage tools, it should be then copied to
+# bazel_coverage_output_generator/release/coverage_output_generator-v[major].[minor].zip
+
+commit_hash=$(git rev-parse HEAD)
+timestamp=$(date +%s)
+bazel_version=$(bazel info release | cut -d' ' -f2)
+
+readme_file="README.md"
+cat >${readme_file} <<EOF
+This coverage_output_generator version was built from the Bazel repository
+at commit hash ${commit_hash} using Bazel version ${bazel_version}.
+To build the same zip from source, run the commands:
+
+$ git clone https://github.com/bazelbuild/bazel.git
+$ git checkout ${commit_hash}
+$ bazel build //tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:coverage_output_generator.zip
+EOF
+
 bazel build //tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:coverage_output_generator.zip
-DEST=bazel_coverage_output_generator/coverage_output_generator-$(git rev-parse HEAD)-$(date +%s).zip
-gsutil cp "tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/coverage_output_generator.zip" \
-  "gs://bazel-mirror/${DEST}"
-echo "Uploaded to $DEST"
+
+cov_gen_zip="bazel-bin/tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/coverage_output_generator.zip"
+
+# copy the built zip to a temp location so we can add the README.md file
+tmp_dir=$(mktemp -d -t "tmp_bazel_cov_gen_XXXXXX")
+trap "rm -rf ${tmp_dir}" EXIT
+tmp_zip="${tmp_dir}/coverage_output_generator.zip"
+cp "${cov_gen_zip}" "${tmp_zip}"
+chmod +w "${tmp_zip}"
+
+zip -rv "${tmp_zip}" "${readme_file}"
+
+DEST="bazel_coverage_output_generator/coverage_output_generator-${commit_hash}-${timestamp}.zip"
+gsutil cp ${tmp_zip} "gs://bazel-mirror/${DEST}"
+echo "Uploaded to ${DEST}"