Add more functionality and safety to build.sh

- Add --tag CLI flag to add the corresponding Git tag (useful to create
  releases without typos or copy&paste mistakes). Fails with error when
  a branch other than master is checked out, since releases should
  always be created on the master branch.
- Pass --pull to "docker build" to ensure we always base our images on
  the latest base image.
- Reject pushing images to Docker Registry if the corresponding Git tag
  already exists (i.e. image is officially released). Avoids overwriting
  released images by accident, but still allow overwriting (unreleased)
  images during development/testing phase.

Author: ubruhin

README.md

@@ -89,12 +89,19 @@ Same purpose as `windowsservercore-ltsc2019-qt5.15.0-32bit`, but with Qt 5.15.2.
 
 ## Updating Images
 
+**Important: On Linux, use the helper script `./build.sh` since it makes the
+procedure less error prone!**
+
 1. Add/modify the Dockerfiles, update this README and commit all changes.
-2. Run `./build.sh <image-tag> <version> --push` to build and push the image.
-   Make sure to pass a version number which does not yet exist on Docker Hub!
+2. Run `./build.sh <image-name> <version> --push` to build and push the image.
+   Use the next unused version number, i.e. the previous image version plus one.
    Use just a single number as version identifier, e.g. `1`, `2`, `3`. Semantic
    versioning is not needed since CI always links to one specific version.
-3. Add and push a Git tag with the exact image tag (e.g. `ubuntu-18.04-1`).
+3. Test the new image by pushing the LibrePCB repository to trigger the CI.
+4. If everything was successful, merge the changes into `master`.
+5. On the `master` branch (merge commit checked out!), create the corresponding
+   Git tag by running `./build.sh <image-name> <version> --tag` (can also be
+   combined with `--push` to push the image again).
 
 
 ## Using Images Locally

build.sh

@@ -5,19 +5,59 @@ set -eu -o pipefail
 
 # Usage:
 #
-#   ./build.sh <tag> <version> [--push]
+#   ./build.sh <name> <version> [--push] [--tag]
 #
 # Example:
 #
 #   ./build.sh ubuntu-18.04 2 --push
 
-TAG="$1"
+NAME="$1"
 VERSION="$2"
-FLAG="${3-}"
+DO_PUSH=0
+DO_TAG=0
+for i in "$@"
+do
+case $i in
+  --push)
+  DO_PUSH=1
+  shift
+  ;;
+  --tag)
+  DO_TAG=1
+  shift
+  ;;
+esac
+done
 
-docker build -t librepcb/librepcb-dev:$TAG-$VERSION $TAG
+echo "Build image $NAME-$VERSION..."
+docker build --pull -t librepcb/librepcb-dev:$NAME-$VERSION $NAME
 
-if [ "$FLAG" = "--push" ]
+if [ "$DO_PUSH" == 1 ]
 then
-  docker push librepcb/librepcb-dev:$TAG-$VERSION
+  # Fail if the corresponding Git tag exists, since this means that the
+  # image was already released and we must not overwrite released images.
+  if git rev-parse "$NAME-$VERSION" >/dev/null 2>&1
+  then
+    echo "ERROR: This image is already released (Git tag exists)!"
+    exit 1
+  fi
+
+  echo "Push image $NAME-$VERSION..."
+  docker push librepcb/librepcb-dev:$NAME-$VERSION
+fi
+
+if [ "$DO_TAG" == 1 ]
+then
+  # Fail if a branch other than master is checked out since we should create
+  # releases only from the master branch.
+  BRANCH="$(git rev-parse --abbrev-ref HEAD)"
+  if [[ "$BRANCH" != "master" ]]
+  then
+    echo "ERROR: Releases must be created on master branch, not $BRANCH!"
+    exit 1
+  fi
+
+  echo "Create Git tag $NAME-$VERSION..."
+  git tag "$NAME-$VERSION"
+  git push origin "$NAME-$VERSION"
 fi