test: Release please simulation testing #12848

.github/workflows/hermetic_library_generation.yaml

@@ -44,4 +44,4 @@ jobs:
         head_ref: ${{ github.head_ref }}
         token: ${{ secrets.CLOUD_JAVA_BOT_GITHUB_TOKEN }}
         force_regenerate_all: ${{ github.event.pull_request.head.ref == 'generate-libraries-main' }}
-        image_tag: 2.71.0  # {x-version-update:gapic-generator-java:current}
+        image_tag: 9.99.9

sdk-platform-java/.github/scripts/hermetic_library_generation.sh

@@ -27,6 +27,7 @@ set -exo pipefail
 # the default value is generation_config.yaml in the repository root.
 # 5. [optional] showcase_mode, true if we wish to download the showcase api
 # definitions, which are necessary for generating the showcase library.
+IMAGE_NAME="gcr.io/cloud-devrel-public-resources/java-library-generation"
 while [[ $# -gt 0 ]]; do
 key="$1"
 case "${key}" in
@@ -123,13 +124,28 @@ changed_libraries="$(cat "${changed_libraries_file}")"
 echo "Changed libraries are: ${changed_libraries:-"No changed library"}."
 
 # run hermetic code generation docker image.
+# Attempt to pull the image to see if it exists on release PRs.
+if [[ "$current_branch" =~ ^release-please-- ]]; then
+  echo "Detected release PR branch: $current_branch"
+  if ! docker pull "${IMAGE_NAME}:${image_tag}"; then
+    echo "Image not found for version ${image_tag}. Falling back to previous version from ${target_branch}."
+    previous_tag=$(git show "${target_branch}":.github/workflows/hermetic_library_generation.yaml | grep -m 1 "^[[:space:]]*image_tag:" | cut -d ':' -f 2- | cut -d '#' -f 1 | xargs)
+    if [ -n "$previous_tag" ]; then
+      echo "Using previous image version: $previous_tag"
+      image_tag="$previous_tag"
+    else
+      echo "Failed to extract previous version from ${target_branch}. Proceeding with original tag."
+    fi
+  fi
+fi
+
 docker run \
   --rm \
   -u "$(id -u):$(id -g)" \
   -v "$(pwd):${workspace_name}" \
   -v "${api_def_dir}:${workspace_name}/googleapis" \
   -e GENERATOR_VERSION="${image_tag}" \
-  gcr.io/cloud-devrel-public-resources/java-library-generation:"${image_tag}" \
+  "${IMAGE_NAME}:${image_tag}" \
   --generation-config-path="${workspace_name}/${generation_config}" \
   --library-names="${changed_libraries}" \
   --api-definitions-path="${workspace_name}/googleapis"