ci: Speed up Protobuf Compatibility checks by running specific modules in Google-Cloud-Java (#3683)

Run from this speed-up for google-cloud-java:
https://github.com/googleapis/sdk-platform-java/actions/runs/13845404432/job/38742611238

Google-cloud-java is able to run linkage checker on the handwritten
modules in ~4 min. Slowest is now bigquerystorage that runs in ~10 min

Author: lqiu96

.kokoro/nightly/common.sh

@@ -13,6 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# For google-cloud-java, only test specific handwritten libraries included in the monorepo. This is to
+# help speed up the execution as building the entire repo is an expensive operation. Specify the nested
+# `google-cloud-*` path (except for grafeas as it doesn't have one) because maven -pl will only build the
+# specified folder (i.e. parent folder) and ignore all the related sub-modules inside
+google_cloud_java_handwritten_maven_args="java-grafeas,java-vertexai/google-cloud-vertexai,java-resourcemanager/google-cloud-resourcemanager,java-translate/google-cloud-translate"
+
 # Checks that the protobuf compatibility scripts provide non-empty input
 function validate_protobuf_compatibility_script_inputs {
   # Comma-delimited list of repos to test

.kokoro/nightly/downstream-protobuf-binary-compatibility.sh

@@ -76,8 +76,16 @@ for repo in ${REPOS_UNDER_TEST//,/ }; do # Split on comma
   # Perform testing on main (with latest changes). Shallow copy as history is not important
   git clone "https://github.com/googleapis/${repo}.git" --depth=1
   pushd "${repo}"
-  # Install all repo modules to ~/.m2 (there can be multiple relevant artifacts to test i.e. core, admin, control)
-  mvn -B -ntp install -T 1C -DskipTests -Dclirr.skip -Denforcer.skip
+
+  if [ "${repo}" == "google-cloud-java" ]; then
+    # The `-am` command also builds anything these libraries depend on (i.e. proto-* and grpc-* sub modules)
+    mvn clean install -B -V -ntp -T 1C -DskipTests -Dclirr.skip -Denforcer.skip -Dmaven.javadoc.skip \
+      -pl "${google_cloud_java_handwritten_maven_args}" -am
+  else
+    # Install all repo modules to ~/.m2 (there can be multiple relevant artifacts to test i.e. core, admin, control)
+    mvn clean install -B -V -ntp -T 1C -DskipTests -Dclirr.skip -Denforcer.skip -Dmaven.javadoc.skip
+  fi
+
 
   linkage_checker_arguments=""
   build_program_arguments "${repo}"

.kokoro/nightly/downstream-protobuf-source-compatibility.sh

@@ -30,11 +30,25 @@ for repo in ${REPOS_UNDER_TEST//,/ }; do # Split on comma
 
   # Compile the Handwritten Library with the Protobuf-Java version to test source compatibility
   # Run unit tests to help check for any behavior differences (dependant on coverage)
-  mvn clean test -B -V -ntp \
-      -Dclirr.skip=true \
-      -Denforcer.skip=true \
-      -Dmaven.javadoc.skip=true \
+  if [ "${repo}" == "google-cloud-java" ]; then
+    # The `-am` command also builds anything these libraries depend on (i.e. proto-* and grpc-* sub modules)
+    mvn clean test -B -V -ntp \
+      -Dclirr.skip \
+      -Denforcer.skip \
+      -Dmaven.javadoc.skip \
+      -Denforcer.skip \
       -Dprotobuf.version=${PROTOBUF_RUNTIME_VERSION} \
+      -pl "${google_cloud_java_handwritten_maven_args}" -am \
       -T 1C
+  else
+    mvn clean test -B -V -ntp \
+      -Dclirr.skip \
+      -Denforcer.skip \
+      -Dmaven.javadoc.skip \
+      -Denforcer.skip \
+      -Dprotobuf.version=${PROTOBUF_RUNTIME_VERSION} \
+      -T 1C
+  fi
+
   popd
 done