Add helper to run a containerized build environment (#2292)

Using `make container` or, if you don't have automake/gmake on your host
system, `./scripts/container.sh` will build an image for the current
branch your are on and drop you into a shell running inside a container
using that image.

From there all tooling required to work on Gluon is available.

Supports both podman (preferred) and docker.

Makefile

@@ -186,6 +186,10 @@ config: $(LUA) FORCE
 	$(GLUON_ENV) $(LUA) scripts/target_config_check.lua
 
 
+container: FORCE
+	@scripts/container.sh
+
+
 all: config
 	+@
 	$(GLUON_ENV) $(LUA) scripts/clean_output.lua

docs/user/getting_started.rst

@@ -40,6 +40,12 @@ freshly installed Debian Stretch system the following packages are required:
 * `time` (built-in `time` doesn't work)
 * `qemu-utils`
 
+We also provide a container environment that already tracks all these dependencies. It quickly gets you up and running, if you already have either Docker or Podman installed locally.
+
+::
+
+   ./scripts/container.sh
+
 Building the images
 -------------------
 

scripts/container.sh

+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# move into base directory, in case this script is not executed via `make container`
+cd "$(dirname "$0")/.."
+
+# normalize branch name to reflect a valid image name
+BRANCH=$(git branch --show-current | sed 's/[^a-z0-9-]/_/ig')
+TAG=gluon:${BRANCH}
+
+if [ "$(command -v podman)" ]
+then
+	podman build -t "${TAG}" contrib/docker
+	podman run -it --rm --userns=keep-id --volume="$(pwd):/gluon" "${TAG}"
+elif [ "$(command -v docker)" ]
+then
+	docker build -t "${TAG}" contrib/docker
+	docker run -it --rm --volume="$(pwd):/gluon" "${TAG}"
+else
+	1>&2 echo "Please install either podman or docker. Exiting" >/dev/null
+	exit 1
+fi
+