chore: make the showcase scripts to automatically prepare the generat…

…or jar (#3171)

The recent changes in the hermetic library generation workflow make it necessary for the environment to have a well-known folder where the generator jar is assumed to be located.

This PR sets up the generator jar in such location when running showcase golden tests or using the `-Pupdate` profile.

More details in the [development guide](https://togithub.com/googleapis/sdk-platform-java/blob/main/library_generation/DEVELOPMENT.md#the-hermetic-builds-well-known-folder)

.github/workflows/ci.yaml

@@ -232,17 +232,6 @@ jobs:
       - name: Showcase golden tests
         working-directory: showcase
         run: |
-          # The golden test directly calls
-          # library_generation/generate_library.sh, which expects the jar to be
-          # located in its well-known location. More info in
-          # library_generation/DEVELOPMENT.md
-          # Here we prepare the jar in such location
-          generator_version=$(grep "gapic-generator-java:" "../versions.txt" \
-            | cut -d: -f3) # the 3rd field is the snapshot version
-          mkdir -p "${HOME}/.library_generation"
-          cp \
-            "${HOME}/.m2/repository/com/google/api/gapic-generator-java/${generator_version}/gapic-generator-java-${generator_version}.jar" \
-            "${HOME}/.library_generation/gapic-generator-java.jar"
           mvn test \
             -P enable-golden-tests \
             --batch-mode \

showcase/README.md

@@ -77,6 +77,11 @@ Note:
 ## Update the Golden Showcase Files
 
 Open a new terminal window in the root project directory.
+Note that the underlying scripts will modify your `$HOME` folder by creating a
+`.library_generation` folder.
+This is the well-known location of the artifacts the generation scripts use.
+For more details see the
+[development guide](https://github.com/googleapis/sdk-platform-java/blob/main/library_generation/DEVELOPMENT.md#the-hermetic-builds-well-known-folder)
 
 ```shell
 # In repository's root directory

showcase/scripts/generate_showcase.sh

@@ -6,9 +6,9 @@
 set -ex
 
 readonly SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
-lib_gen_scripts_dir="${SCRIPT_DIR}/../../library_generation/"
-source "${lib_gen_scripts_dir}/test/test_utilities.sh"
-source "${lib_gen_scripts_dir}/utils/utilities.sh"
+readonly LIB_GEN_SCRIPTS_DIR="${SCRIPT_DIR}/../../library_generation/"
+source "${LIB_GEN_SCRIPTS_DIR}/test/test_utilities.sh"
+source "${LIB_GEN_SCRIPTS_DIR}/utils/utilities.sh"
 readonly perform_cleanup=$1
 
 cd "${SCRIPT_DIR}"
@@ -21,6 +21,14 @@ get_version_from_pom() {
   grep -e "<${key}>" "${target_pom}" | cut -d'>' -f2 | cut -d'<' -f1
 }
 
+# gets the latest version of the specified artifact from versions.txt
+get_version_from_versions_txt() {
+  readonly VERSIONS_TXT_PATH="${SCRIPT_DIR}/../../versions.txt"
+  target_artifact="$1"
+  # prints the result to stdout
+  grep -e "${target_artifact}" "${VERSIONS_TXT_PATH}" | cut -d: -f3
+}
+
 # clone gapic-showcase
 if [ ! -d schema ]; then
   if [ -d gapic-showcase ]; then
@@ -47,6 +55,30 @@ if [ ! -d google ];then
   rm -rdf googleapis
 fi
 
+# copy the generator into its well-known location. For more details,
+# refer to library_generation/DEVELOPMENT.md
+well_known_folder="${HOME}/.library_generation"
+well_known_generator_jar_location="${well_known_folder}/gapic-generator-java.jar"
+if [[ ! -d "${well_known_folder}" ]]; then
+  mkdir "${well_known_folder}"
+fi
+if [[ -f "${well_known_generator_jar_location}" ]]; then
+  echo "replacing well-known generator jar with the latest one"
+  rm "${well_known_generator_jar_location}"
+fi
+maven_repository="$(mvn help:evaluate -Dexpression=settings.localRepository -q -DforceStdout)"
+generator_version=$(get_version_from_versions_txt "gapic-generator-java")
+source_jar_path="${maven_repository}/com/google/api/gapic-generator-java/${generator_version}/gapic-generator-java-${generator_version}.jar"
+
+if [[ ! -f "${source_jar_path}" ]]; then
+  echo "generator jar not found in its assumed location"
+  echo "in the local repository: ${source_jar_path}"
+  echo "(did you run mvn install in this repository's root?)"
+  exit 1
+fi
+# transfer the snapshot jar into its well-known location
+cp "${source_jar_path}" "${well_known_generator_jar_location}"
+
 gapic_additional_protos="google/iam/v1/iam_policy.proto google/cloud/location/locations.proto"
 
 path_to_generator_parent_pom="${SCRIPT_DIR}/../../gapic-generator-java-pom-parent/pom.xml"