add tagged release workflow using github actions (#1452)

* first pass at setting up a release workflow

* narrow test command

* make workspace_snippet.sh executable

* set cache options explicitly on test scope

* fix cache path quoting

actions/cache#878

Author: jvandew

.github/workflows/release.yml

@@ -0,0 +1,25 @@
+# Cut a release whenever a new tag is pushed to the repo.
+# You should use an annotated tag, like `git tag -a v1.2.3`.
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v*.*.*'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Prepare workspace snippet
+        run: .github/workflows/workspace_snippet.sh > release_notes.txt
+
+      - name: Release
+        uses: softprops/action-gh-release@v1
+        with:
+          # Use GH feature to populate the changelog automatically
+          generate_release_notes: true
+          body_path: release_notes.txt

.github/workflows/workspace_snippet.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+
+set -o errexit -o nounset -o pipefail
+
+# Set by GH actions, see
+# https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables
+TAG=${GITHUB_REF_NAME}
+PREFIX="rules_scala-${TAG:1}"
+SHA=$(git archive --format=tar --prefix="${PREFIX}/" "${TAG}" | gzip | shasum -a 256 | awk '{print $1}')
+
+cat << EOF
+## Using WORKSPACE
+
+Paste this snippet into your \`WORKSPACE\` file:
+
+\`\`\`starlark
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+http_archive(
+    name = "rules_scala",
+    sha256 = "${SHA}",
+    strip_prefix = "${PREFIX}",
+    url = "https://github.com/bazelbuild/rules_scala/archive/refs/tags/${TAG}.tar.gz",
+)
+\`\`\`
+
+See https://github.com/bazelbuild/rules_scala#getting-started for full setup instructions.
+EOF

README.md

@@ -46,6 +46,7 @@ http_archive(
     url = "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/{}/bazel-skylib-{}.tar.gz".format(skylib_version, skylib_version),
 )
 
+# See https://github.com/bazelbuild/rules_scala/releases for up to date version information.
 rules_scala_version = "c711b4d1f0d1cc386c63ef748c9df14d2f3a187e"
 http_archive(
     name = "io_bazel_rules_scala",