use a smarter tagging scheme and allow parametrising the channel

.travis.yml

@@ -1,16 +1,23 @@
 services:
 - docker
 script:
+- export RUST_CHANNEL="nightly"
 - docker login -e="$DOCKER_EMAIL" -u="$DOCKER_USERNAME" -p="$DOCKER_PASSWORD"
-- docker build -t clux/muslrust .
-- export DOCKER_TAG="$(docker run -it clux/muslrust rustc --version | awk '{print $2}')-$(date +%Y-%m-%d)"
+- docker build --build-arg CHANNEL=${RUST_CHANNEL} -t clux/muslrust .
+- export RUST_DATE=$(docker run -it clux/muslrust rustc --version | grep -oE "[[:digit:]]{4}-[[:digit:]]{2}-[[:digit:]]{2}")
+- export RUST_VER=$(docker run -it clux/muslrust rustc --version | grep -oE "[[:digit:]]+\.[[:digit:]]+\.[[:digit:]]")
+- export FULL_TAG="${RUST_VER}-${RUST_CHANNEL}-${RUST_DATE}"
+- export MEDIUM_TAG="${RUST_CHANNEL}-${RUST_DATE}"
+- export SHORT_TAG="${RUST_CHANNEL}"
 - make test
 after_success:
 - docker push clux/muslrust
-- docker tag clux/muslrust clux/muslrust:$DOCKER_TAG
-- docker push clux/muslrust:$DOCKER_TAG
-- docker tag clux/muslrust clux/muslrust:nightly
-- docker push clux/muslrust:nightly
+- docker tag clux/muslrust clux/muslrust:$FULL_TAG
+- docker push clux/muslrust:$FULL_TAG
+- docker tag clux/muslrust clux/muslrust:$MEDIUM_TAG
+- docker push clux/muslrust:$MEDIUM_TAG
+- docker tag clux/muslrust clux/muslrust:$SHORT_TAG
+- docker push clux/muslrust:$SHORT_TAG
 notifications:
   email:
     on_success: change

Dockerfile

@@ -30,14 +30,15 @@ RUN apt-get update && apt-get install -y \
 
 
 # Install rust (old fashioned way to avoid unnecessary rustup.rs shenanigans)
+ARG CHANNEL="nightly"
 ARG NIGHTLY_SNAPSHOT=""
 RUN if test "${NIGHTLY_SNAPSHOT}"; then DATEARG="--date=${NIGHTLY_SNAPSHOT}"; fi &&\
   curl https://static.rust-lang.org/rustup.sh | sh -s -- \
   --with-target=x86_64-unknown-linux-musl \
   --yes \
   --disable-sudo \
   ${DATEARG} \
-  --channel=nightly && \
+  --channel=${CHANNEL} && \
   mkdir /.cargo && \
   echo "[build]\ntarget = \"x86_64-unknown-linux-musl\"" > /.cargo/config