feat: generate selected libraries (#2598)

In this PR:
- Generate a selected list of libraries based on `library_name`

This PR is a preparation for improve nightly generation.

Note that we need to change the [new library generation
workflow](https://github.com/googleapis/google-cloud-java/blob/main/.github/workflows/generate_new_client_hermetic_build.yaml)
in google-cloud-java to accommodate this change because
`library_generation/generate_repo.py` has replaced
`--target-library-api-shortname` with `--target-library-names`.

library_generation/generate_repo.py

@@ -13,11 +13,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import click
 import library_generation.utilities as util
+import click
 import os
 from library_generation.generate_composed_library import generate_composed_library
+from library_generation.model.generation_config import GenerationConfig
 from library_generation.model.generation_config import from_yaml
+from library_generation.model.library_config import LibraryConfig
 from library_generation.utils.monorepo_postprocessor import monorepo_postprocessing
 
 
@@ -39,13 +41,22 @@ def main(ctx):
     """,
 )
 @click.option(
-    "--target-library-api-shortname",
+    "--target-library-names",
     required=False,
+    default=None,
     type=str,
     help="""
-    If specified, only the `library` whose api_shortname equals to
-    target-library-api-shortname will be generated.
+    A list of libraries will be generated.
+    
+    If specified, only the `library` whose library_name is in
+    target-library-names will be generated.
     If not specified, all libraries in the configuration yaml will be generated.
+    
+    The input string will be parsed to a list of string with comma as the
+    separator.
+    
+    For example, apigeeconnect,alloydb-connectors will be parsed as a
+    list of two strings, apigeeconnect and alloydb-connectors.
     """,
 )
 @click.option(
@@ -61,39 +72,46 @@ def main(ctx):
 )
 def generate(
     generation_config_yaml: str,
-    target_library_api_shortname: str,
+    target_library_names: str,
     repository_path: str,
 ):
     generate_from_yaml(
         generation_config_yaml=generation_config_yaml,
         repository_path=repository_path,
-        target_library_api_shortname=target_library_api_shortname,
+        target_library_names=target_library_names.split(",")
+        if target_library_names is not None
+        else target_library_names,
     )
 
 
 def generate_from_yaml(
     generation_config_yaml: str,
     repository_path: str,
-    target_library_api_shortname: str = None,
+    target_library_names: list[str] = None,
 ) -> None:
     """
     Parses a config yaml and generates libraries via
     generate_composed_library.py
+    :param generation_config_yaml: Path to generation_config.yaml that contains
+    the metadata about library generation
+    :param repository_path: If specified, the generated files will be sent to
+    this location. If not specified, the repository will be generated to the
+    current working directory.
+    :param target_library_names: a list of libraries to be generated.
+    If specified, only the library whose library_name is in
+    target-library-names will be generated.
+    If specified with an empty list, then no library will be generated.
+    If not specified, all libraries in the configuration yaml will be generated.
     """
-    # convert paths to absolute paths so they can be correctly referenced in
+    # convert paths to absolute paths, so they can be correctly referenced in
     # downstream scripts
     generation_config_yaml = os.path.abspath(generation_config_yaml)
     repository_path = os.path.abspath(repository_path)
 
     config = from_yaml(generation_config_yaml)
-    target_libraries = config.libraries
-    if target_library_api_shortname is not None:
-        target_libraries = [
-            library
-            for library in config.libraries
-            if library.api_shortname == target_library_api_shortname
-        ]
-
+    target_libraries = get_target_libraries(
+        config=config, target_library_names=target_library_names
+    )
     repo_config = util.prepare_repo(
         gen_config=config, library_config=target_libraries, repo_path=repository_path
     )
@@ -118,5 +136,22 @@ def generate_from_yaml(
     )
 
 
-if __name__ == "__main__":
-    main()
+def get_target_libraries(
+    config: GenerationConfig, target_library_names: list[str] = None
+) -> list[LibraryConfig]:
+    """
+    Returns LibraryConfig objects whose library_name is in target_library_names.
+
+    :param config: a GenerationConfig object.
+    :param target_library_names: library_name of target libraries.
+    If not specified, all libraries in the given config will be returned.
+    :return: LibraryConfig objects.
+    """
+    if target_library_names is None:
+        return config.libraries
+    target_libraries = set(target_library_names)
+    return [
+        library
+        for library in config.libraries
+        if library.get_library_name() in target_libraries
+    ]

library_generation/test/generate_repo_unit_tests.py

@@ -0,0 +1,63 @@
+#!/usr/bin/env python3
+#  Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import unittest
+
+from library_generation.generate_repo import get_target_libraries
+from library_generation.model.generation_config import GenerationConfig
+from library_generation.model.library_config import LibraryConfig
+
+
+class GenerateRepoTest(unittest.TestCase):
+    def test_get_target_library_returns_selected_libraries(self):
+        one_library = GenerateRepoTest.__get_an_empty_library_config()
+        one_library.api_shortname = "one_library"
+        another_library = GenerateRepoTest.__get_an_empty_library_config()
+        another_library.api_shortname = "another_library"
+        config = GenerateRepoTest.__get_an_empty_generation_config()
+        config.libraries.extend([one_library, another_library])
+        target_libraries = get_target_libraries(config, ["another_library"])
+        self.assertEqual([another_library], target_libraries)
+
+    def test_get_target_library_given_null_returns_all_libraries(self):
+        one_library = GenerateRepoTest.__get_an_empty_library_config()
+        one_library.api_shortname = "one_library"
+        another_library = GenerateRepoTest.__get_an_empty_library_config()
+        another_library.api_shortname = "another_library"
+        config = GenerateRepoTest.__get_an_empty_generation_config()
+        config.libraries.extend([one_library, another_library])
+        target_libraries = get_target_libraries(config)
+        self.assertEqual([one_library, another_library], target_libraries)
+
+    @staticmethod
+    def __get_an_empty_generation_config() -> GenerationConfig:
+        return GenerationConfig(
+            gapic_generator_version="",
+            googleapis_commitish="",
+            synthtool_commitish="",
+            owlbot_cli_image="",
+            template_excludes=[],
+            path_to_yaml="",
+            libraries=[],
+        )
+
+    @staticmethod
+    def __get_an_empty_library_config() -> LibraryConfig:
+        return LibraryConfig(
+            api_shortname="",
+            name_pretty="",
+            api_description="",
+            product_documentation="",
+            gapic_configs=[],
+        )

library_generation/utilities.py

@@ -131,11 +131,7 @@ def prepare_repo(
     os.makedirs(output_folder, exist_ok=True)
     libraries = {}
     for library in library_config:
-        library_name = (
-            f"{language}-{library.library_name}"
-            if library.library_name
-            else f"{language}-{library.api_shortname}"
-        )
+        library_name = f"{language}-{library.get_library_name()}"
         library_path = (
             f"{repo_path}/{library_name}" if gen_config.is_monorepo else f"{repo_path}"
         )