chore: add support for librarian release init (googleapis#14327)

This PR adds support for the librarian language specific `release-init`
commit following
https://github.com/googleapis/librarian/blob/main/doc/language-onboarding.md

Towards googleapis/librarian#886

Author: parthea

.generator/cli.py

@@ -36,13 +36,15 @@
 
 logger = logging.getLogger()
 
-LIBRARIAN_DIR = "librarian"
+BUILD_REQUEST_FILE = "build-request.json"
 GENERATE_REQUEST_FILE = "generate-request.json"
+RELEASE_INIT_REQUEST_FILE = "release-init-request.json"
+
 INPUT_DIR = "input"
-BUILD_REQUEST_FILE = "build-request.json"
-SOURCE_DIR = "source"
+LIBRARIAN_DIR = "librarian"
 OUTPUT_DIR = "output"
 REPO_DIR = "repo"
+SOURCE_DIR = "source"
 
 
 def _read_json_file(path: str) -> Dict:
@@ -371,7 +373,6 @@ def handle_generate(
     except Exception as e:
         raise ValueError("Generation failed.") from e
 
-    # TODO(https://github.com/googleapis/librarian/issues/448): Implement generate command and update docstring.
     logger.info("'generate' command executed.")
 
 
@@ -433,23 +434,91 @@ def handle_build(librarian: str = LIBRARIAN_DIR, repo: str = REPO_DIR):
     logger.info("'build' command executed.")
 
 
+def _get_libraries_to_prepare_for_release(library_entries: Dict) -> List[dict]:
+    """Get libraries which should be prepared for release. Only libraries
+    which have the `release_triggered` field set to `True` will be returned.
+
+    Args:
+        library_entries(Dict): Dictionary containing all of the libraries to
+        evaluate.
+
+    Returns:
+        List[dict]: List of all libraries which should be prepared for release,
+        along with the corresponding information for the release.
+    """
+    return [
+        library
+        for library in library_entries["libraries"]
+        if library.get("release_triggered")
+    ]
+
+
+def handle_release_init(
+    librarian: str = LIBRARIAN_DIR, repo: str = REPO_DIR, output: str = OUTPUT_DIR
+):
+    """The main coordinator for the release preparation process.
+
+    This function prepares for the release of client libraries by reading a
+    `librarian/release-init-request.json` file. The primary responsibility is
+    to update all required files with the new version and commit information
+    for libraries that have the `release_triggered` field set to `True`.
+
+    See https://github.com/googleapis/librarian/blob/main/doc/container-contract.md#generate-container-command
+
+    Args:
+        librarian(str): Path to the directory in the container which contains
+            the `release-init-request.json` file.
+        repo(str): This directory will contain all directories that make up a
+            library, the .librarian folder, and any global file declared in
+            the config.yaml.
+        output(str): Path to the directory in the container where modified
+            code should be placed.
+    """
+
+    try:
+        # Read a release-init-request.json file
+        request_data = _read_json_file(f"{librarian}/{RELEASE_INIT_REQUEST_FILE}")
+        libraries_to_prep_for_release = _get_libraries_to_prepare_for_release(
+            request_data
+        )
+
+        # TODO(https://github.com/googleapis/google-cloud-python/pull/14349):
+        # Update library global changelog file.
+
+        # Prepare the release for each library by updating the
+        # library specific version files and library specific changelog.
+        for library_release_data in libraries_to_prep_for_release:
+            # TODO(https://github.com/googleapis/google-cloud-python/pull/14350):
+            # Update library specific version files.
+            # TODO(https://github.com/googleapis/google-cloud-python/pull/14351):
+            # Conditionally update the library specific CHANGELOG if there is a change.
+            pass
+
+    except Exception as e:
+        raise ValueError(f"Release init failed: {e}") from e
+
+    logger.info("'release-init' command executed.")
+
+
 if __name__ == "__main__":  # pragma: NO COVER
     parser = argparse.ArgumentParser(description="A simple CLI tool.")
     subparsers = parser.add_subparsers(
         dest="command", required=True, help="Available commands"
     )
 
-    # Define commands
+    # Define commands and their corresponding handler functions
     handler_map = {
         "configure": handle_configure,
         "generate": handle_generate,
         "build": handle_build,
+        "release-init": handle_release_init,
     }
 
     for command_name, help_text in [
         ("configure", "Onboard a new library or an api path to Librarian workflow."),
         ("generate", "generate a python client for an API."),
         ("build", "Run unit tests via nox for the generated library."),
+        ("release-init", "Prepare to release a given set of libraries"),
     ]:
         parser_cmd = subparsers.add_parser(command_name, help=help_text)
         parser_cmd.set_defaults(func=handler_map[command_name])
@@ -483,6 +552,7 @@ def handle_build(librarian: str = LIBRARIAN_DIR, repo: str = REPO_DIR):
             help="Path to the directory in the container which contains google-cloud-python repository",
             default=REPO_DIR,
         )
+
     if len(sys.argv) == 1:
         parser.print_help(sys.stderr)
         sys.exit(1)
@@ -499,5 +569,7 @@ def handle_build(librarian: str = LIBRARIAN_DIR, repo: str = REPO_DIR):
         )
     elif args.command == "build":
         args.func(librarian=args.librarian, repo=args.repo)
+    elif args.command == "release-init":
+        args.func(librarian=args.librarian, repo=args.repo, output=args.output)
     else:
         args.func()

.generator/test_cli.py

@@ -23,13 +23,15 @@
 from cli import (
     GENERATE_REQUEST_FILE,
     BUILD_REQUEST_FILE,
+    RELEASE_INIT_REQUEST_FILE,
     LIBRARIAN_DIR,
     REPO_DIR,
     _build_bazel_target,
     _clean_up_files_after_post_processing,
     _copy_files_needed_for_post_processing,
     _determine_bazel_rule,
     _get_library_id,
+    _get_libraries_to_prepare_for_release,
     _locate_and_extract_artifact,
     _read_json_file,
     _run_individual_session,
@@ -38,6 +40,7 @@
     handle_build,
     handle_configure,
     handle_generate,
+    handle_release_init,
 )
 
 
@@ -92,6 +95,40 @@ def mock_generate_request_data_for_nox():
     }
 
 
+@pytest.fixture
+def mock_release_init_request_file(tmp_path, monkeypatch):
+    """Creates the mock request file at the correct path inside a temp dir."""
+    # Create the path as expected by the script: .librarian/release-request.json
+    request_path = f"{LIBRARIAN_DIR}/{RELEASE_INIT_REQUEST_FILE}"
+    request_dir = tmp_path / os.path.dirname(request_path)
+    request_dir.mkdir()
+    request_file = request_dir / os.path.basename(request_path)
+
+    request_content = {
+        "libraries": [
+            {
+                "id": "google-cloud-another-library",
+                "apis": [{"path": "google/cloud/another/library/v1"}],
+                "release_triggered": False,
+                "version": "1.2.3",
+                "changes": [],
+            },
+            {
+                "id": "google-cloud-language",
+                "apis": [{"path": "google/cloud/language/v1"}],
+                "release_triggered": True,
+                "version": "1.2.3",
+                "changes": [],
+            },
+        ]
+    }
+    request_file.write_text(json.dumps(request_content))
+
+    # Change the current working directory to the temp path for the test.
+    monkeypatch.chdir(tmp_path)
+    return request_file
+
+
 def test_get_library_id_success():
     """Tests that _get_library_id returns the correct ID when present."""
     request_data = {"id": "test-library", "name": "Test Library"}
@@ -454,3 +491,30 @@ def test_clean_up_files_after_post_processing_success(mocker):
     mock_shutil_rmtree = mocker.patch("shutil.rmtree")
     mock_os_remove = mocker.patch("os.remove")
     _clean_up_files_after_post_processing("output", "library_id")
+
+
+def test_get_libraries_to_prepare_for_release(mock_release_init_request_file):
+    """
+    Tests that only libraries with the `release_triggered` field set to `True` are
+    returned.
+    """
+    request_data = _read_json_file(f"{LIBRARIAN_DIR}/{RELEASE_INIT_REQUEST_FILE}")
+    libraries_to_prep_for_release = _get_libraries_to_prepare_for_release(request_data)
+    assert len(libraries_to_prep_for_release) == 1
+    assert "google-cloud-language" in libraries_to_prep_for_release[0]["id"]
+    assert libraries_to_prep_for_release[0]["release_triggered"]
+
+
+def test_handle_release_init_success(mock_release_init_request_file):
+    """
+    Simply tests that `handle_release_init` runs without errors.
+    """
+    handle_release_init()
+
+
+def test_handle_release_init_fail():
+    """
+    Tests that handle_release_init fails to read `librarian/release-init-request.json`.
+    """
+    with pytest.raises(ValueError):
+        handle_release_init()