build: improve release script to create tarball directly (#429)

Improves the release script to create the tarball directly. This
makes it easier to cut new releases as a few manual steps are
now automated. This change also includes some fallback logic
for finding Copybara for Googlers (like it was done previously),
and no longer relies on a release directory to be specified as `$1`
argument to the Bash script.

.gitignore

@@ -6,3 +6,4 @@ bazel-*
 user.bazelrc
 
 .idea/
+dist/

tools/copy.bara.sky

@@ -47,7 +47,7 @@ core.workflow(
             "bazel-bin/go/wsl/main/main_*",
             "bazel-bin/go/wtl/main/main_*",
         ],
-        exclude = ["go/metadata/main/**", "**/*.runfiles_manifest"],
+        exclude = [".bazelrc", "go/metadata/main/**", "**/*.runfiles_manifest"],
     ),
     transformations = [
         core.move("bazel-bin/go/metadata/main", "go/metadata/main"),

tools/releaser.sh

@@ -16,6 +16,17 @@
 
 # Shell script for creating a release directory.
 
+copybaraBin=$(which copybara)
+
+# If Copybara is not available in the `PATH`, we try using Copybara
+# from a path where it is supposed to exist (Googlers-only).
+if [[ -z "${copybaraBin}" ]]; then
+  copybaraBin=/google/data/ro/teams/copybara/copybara
+fi
+
+cd "$(dirname $0)/.."
+pwd
+
 bazel build -c opt --stamp \
     --platforms=@io_bazel_rules_go//go/toolchain:darwin_amd64 \
     //go/metadata/main \
@@ -40,4 +51,19 @@ bazel build -c opt --stamp \
     //go/wsl/main \
     //go/wtl/main
 
-copybara --folder-dir="$1" migrate tools/copy.bara.sky release .
+tmpDir="$PWD/dist"
+outputDir="${tmpDir}/release-artifact"
+archiveDir="${tmpDir}/rules_webtesting.tar.gz"
+
+# Create a temporary directory for storing the release artifacts.
+rm -Rf ${tmpDir}
+mkdir -p ${tmpDir}
+
+# Build the release artifact directory using the Copybara `release` workflow.
+${copybaraBin} --folder-dir="${outputDir}" migrate tools/copy.bara.sky "release" $PWD
+
+# Create the release output tarball.
+tar -cvzf ${archiveDir} -C ${outputDir} .
+
+echo "Release tarball has been stored in: ${archiveDir}"
+echo "Attach this tarball to the Github release entry."