From 3c59412ad64926852d763a027926f22d8bf1eef5 Mon Sep 17 00:00:00 2001
From: Mike Eltsufin <meltsufin@google.com>
Date: Fri, 17 Apr 2026 21:54:26 -0400
Subject: [PATCH 1/4] build: fall back to previous image version on release PRs

The library generation pipeline fails on release PRs because it attempts to pull a Docker image version that has not yet been built or pushed to the registry.

This PR adds a fallback mechanism in hermetic_library_generation.sh to use the previous version of the image from the main branch if the requested version fails to pull on a release PR.

To verify this in CI, this branch is named with the prefix 'release-please--' to simulate a release PR.

Fixes #12825
---
 .../scripts/hermetic_library_generation.sh        | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/sdk-platform-java/.github/scripts/hermetic_library_generation.sh b/sdk-platform-java/.github/scripts/hermetic_library_generation.sh
index fc991aa3e94d..439c03c17155 100755
--- a/sdk-platform-java/.github/scripts/hermetic_library_generation.sh
+++ b/sdk-platform-java/.github/scripts/hermetic_library_generation.sh
@@ -123,6 +123,21 @@ 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: $current_branch"
+  if ! docker pull gcr.io/cloud-devrel-public-resources/java-library-generation:"${image_tag}"; then
+    echo "Image not found for version ${image_tag}. Falling back to previous version from ${target_branch}."
+    previous_tag=$(git show "${target_branch}":.github/workflows/hermetic_library_generation.yaml | grep "image_tag:" | cut -d ':' -f 2 | cut -d '#' -f 1 | xargs)
+    if [ -n "$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)" \

From 5fa7830dd283820ac3b9cc5fd4b4ba834e6a57fa Mon Sep 17 00:00:00 2001
From: Mike Eltsufin <meltsufin@google.com>
Date: Fri, 17 Apr 2026 22:07:04 -0400
Subject: [PATCH 2/4] build: extract image name to variable in hermetic script

---
 .../.github/scripts/hermetic_library_generation.sh           | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/sdk-platform-java/.github/scripts/hermetic_library_generation.sh b/sdk-platform-java/.github/scripts/hermetic_library_generation.sh
index 439c03c17155..06e0f9cb7f46 100755
--- a/sdk-platform-java/.github/scripts/hermetic_library_generation.sh
+++ b/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
@@ -126,7 +127,7 @@ echo "Changed libraries are: ${changed_libraries:-"No changed library"}."
 # Attempt to pull the image to see if it exists on release PRs.
 if [[ "$current_branch" =~ ^release-please-- ]]; then
   echo "Detected release PR branch: $current_branch"
-  if ! docker pull gcr.io/cloud-devrel-public-resources/java-library-generation:"${image_tag}"; then
+  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 "${target_branch}":.github/workflows/hermetic_library_generation.yaml | grep "image_tag:" | cut -d ':' -f 2 | cut -d '#' -f 1 | xargs)
     if [ -n "$previous_tag" ]; then
@@ -144,7 +145,7 @@ docker run \
   -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"

From 823b98cc5348341ab37b22c556e4042137bd75b0 Mon Sep 17 00:00:00 2001
From: Mike Eltsufin <meltsufin@google.com>
Date: Fri, 17 Apr 2026 22:10:12 -0400
Subject: [PATCH 3/4] build: improve robustness of fallback version extraction

---
 .../.github/scripts/hermetic_library_generation.sh              | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sdk-platform-java/.github/scripts/hermetic_library_generation.sh b/sdk-platform-java/.github/scripts/hermetic_library_generation.sh
index 06e0f9cb7f46..879c7e2bb056 100755
--- a/sdk-platform-java/.github/scripts/hermetic_library_generation.sh
+++ b/sdk-platform-java/.github/scripts/hermetic_library_generation.sh
@@ -129,7 +129,7 @@ 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 "${target_branch}":.github/workflows/hermetic_library_generation.yaml | grep "image_tag:" | cut -d ':' -f 2 | cut -d '#' -f 1 | xargs)
+    previous_tag=$(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"

From c1395d2cc9685fd8c00b770e8ac4ead613c004eb Mon Sep 17 00:00:00 2001
From: Mike Eltsufin <meltsufin@google.com>
Date: Fri, 17 Apr 2026 22:42:33 -0400
Subject: [PATCH 4/4] build: prevent script termination on empty fallback match

---
 .../.github/scripts/hermetic_library_generation.sh              | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sdk-platform-java/.github/scripts/hermetic_library_generation.sh b/sdk-platform-java/.github/scripts/hermetic_library_generation.sh
index 879c7e2bb056..a17e7d6fcafc 100755
--- a/sdk-platform-java/.github/scripts/hermetic_library_generation.sh
+++ b/sdk-platform-java/.github/scripts/hermetic_library_generation.sh
@@ -129,7 +129,7 @@ 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 "${target_branch}":.github/workflows/hermetic_library_generation.yaml | grep -m 1 "^[[:space:]]*image_tag:" | cut -d ':' -f 2- | cut -d '#' -f 1 | xargs)
+    previous_tag=$(git show "${target_branch}":.github/workflows/hermetic_library_generation.yaml | grep -m 1 "^[[:space:]]*image_tag:" | cut -d ':' -f 2- | cut -d '#' -f 1 | xargs || true)
     if [ -n "$previous_tag" ]; then
       echo "Using previous image version: $previous_tag"
       image_tag="$previous_tag"