Add CI workflow to check for missing image version bumps

.github/scripts/check_docker_image_versions.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+
+echoerr() { printf "%s\n" "$*" >&2; }
+
+WORKFLOW_FILE=./.github/workflows/custom_docker_builds.yml
+
+# Set to 1 if any of the checks fail
+FAILED=0
+
+# What gets fed into the $image var is defined at the end of the loop
+while read image; do
+    DOCKER_IMAGE_DIR=$(echo $image | jq '."docker-image"' -r | sed 's/^\.\///')
+    IMAGE_TAG=$(echo $image | jq '."image-tags"' -r)
+
+    # Skip if the directory was not modified at all
+    if ! git diff --name-only | grep $DOCKER_IMAGE_DIR > /dev/null; then
+        continue
+    fi
+
+    # Is the found tag in the added lines of the diff? If so, don't error just yet.
+    # If not, error, as that means the tag we're looking at is the old tag
+    if ! git diff -- $WORKFLOW_FILE | grep "^+[^+].\+$IMAGE_TAG" > /dev/null; then
+        FAILED=1
+        echoerr "ERROR: Directory '$DOCKER_IMAGE_DIR' modified, but image tag $IMAGE_TAG not incremented!"
+        continue
+    fi
+
+    # Find the old tag from the diff and search for it. If it exists, error, as that means it hasn't been bumped
+    BASE_IMAGE_TAG=$(echo $IMAGE_TAG | cut -d ":" -f1)
+    BASE_IMAGE_TAG_PATTERN=$(echo $BASE_IMAGE_TAG | sed 's/[.\/]/\\&/g')
+    OLD_TAG=$(git diff -- $WORKFLOW_FILE | sed -nr s"/^-[^-].+($BASE_IMAGE_TAG_PATTERN)/\1/p")
+
+    NEW_TAG_VERSION=$(echo $IMAGE_TAG | cut -d ":" -f2)
+    OLD_TAG_VERSION=$(echo $OLD_TAG | cut -d ":" -f2)
+
+    # Search for this old tag. If found error, as we should only find the new tag
+    if git grep $OLD_TAG > /dev/null; then
+        FAILED=1
+        echoerr "ERROR: Image $BASE_IMAGE_TAG incremented to $NEW_TAG_VERSION, found remaining occurances of $OLD_TAG_VERSION!"
+    fi
+
+# This is where the input to the while loop variable $image comes in. This is called a "here string" and
+# circumvents the issue with subshells setting global variables.
+# https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#Here-Strings
+done <<< $(cat $WORKFLOW_FILE | yq ".jobs.build.strategy.matrix.include" -o json | jq -c ".[]")
+
+if [ "$FAILED" -eq "1" ]; then
+    exit 1
+fi

.github/workflows/check_docker_image_versions.yml

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+name: Check Docker Image Versions
+
+on:
+  pull_request:
+
+jobs:
+  check-image:
+    if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-image-bump') }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Check for modified directories that need an image bump
+        run: ./.github/scripts/check_docker_image_versions.sh