Introduce CI with GitHub Actionsethomson/github_actions

Add CI using GitHub Actions and GitHub Packages:

* This moves our Linux build containers into GitHub Packages; we will
  identify the most recent commit that updated the docker descriptions,
  and then look for a docker image in libgit2's GitHub Packages registry
  for a container with the tag corresponding to that description.  If
  there is not one, we will build the container and then push it to
  GitHub Packages.

* We no longer need to manage authentication with our own credentials or
  PAT tokens.  GitHub Actions provides a GITHUB_TOKEN that can publish
  artifacts, packages and commits to our repository within a workflow
  run.

* We will use a matrix to build our various CI steps.  This allows us
  to keep configuration in a single place without multiple YAML files.

1 files changed, 45 insertions, 0 deletions

diff --git a/azure-pipelines/getcontainer.sh b/azure-pipelines/getcontainer.sh
new file mode 100755
index 000000000..bc93f4919
--- /dev/null
+++ b/azure-pipelines/getcontainer.sh
@@ -0,0 +1,45 @@
+#!/bin/bash
+
+set -e
+
+DOCKERFILE_PATH=$1
+
+if [ "${DOCKERFILE_PATH}" = "" ]; then
+	echo "usage: $0 dockerfile"
+	exit 1
+fi
+
+if [ "${DOCKER_REGISTRY}" = "" ]; then
+	echo "DOCKER_REGISTRY environment variable is unset."
+	echo "Not running inside GitHub Actions or misconfigured?"
+	exit 1
+fi
+
+DOCKER_CONTAINER="${GITHUB_REPOSITORY}/$(basename ${DOCKERFILE_PATH})"
+DOCKER_REGISTRY_CONTAINER="${DOCKER_REGISTRY}/${DOCKER_CONTAINER}"
+
+echo "::set-env name=docker-container::${DOCKER_CONTAINER}"
+echo "::set-env name=docker-registry-container::${DOCKER_REGISTRY_CONTAINER}"
+
+# Identify the last git commit that touched the Dockerfiles
+# Use this as a hash to identify the resulting docker containers
+DOCKER_SHA=$(git log -1 --pretty=format:"%h" -- "${DOCKERFILE_PATH}")
+echo "::set-env name=docker-sha::${DOCKER_SHA}"
+
+DOCKER_REGISTRY_CONTAINER_SHA="${DOCKER_REGISTRY_CONTAINER}:${DOCKER_SHA}"
+
+echo "::set-env name=docker-registry-container-sha::${DOCKER_REGISTRY_CONTAINER_SHA}"
+echo "::set-env name=docker-registry-container-latest::${DOCKER_REGISTRY_CONTAINER}:latest"
+
+exists="true"
+docker login https://${DOCKER_REGISTRY} -u ${GITHUB_ACTOR} -p ${GITHUB_TOKEN} || exists="false"
+
+if [ "${exists}" != "false" ]; then
+	docker pull ${DOCKER_REGISTRY_CONTAINER_SHA} || exists="false"
+fi
+
+if [ "${exists}" = "true" ]; then
+	echo "::set-env name=docker-container-exists::true"
+else
+	echo "::set-env name=docker-container-exists::false"
+fi