feat(gapic-generator): add pure-python package initialization and versioning codegen

packages/gapic-generator/gapic/codegen/components/package_init.py

@@ -0,0 +1,34 @@
+# Copyright 2026 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
+#
+#     https://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.
+
+from gapic.codegen.writer import CodeWriter
+from gapic.schema.api import API
+
+
+class PackageInitGenerator:
+    """Pure Python generator for package initialization files (__init__.py, gapic_version.py, py.typed)."""
+
+    @staticmethod
+    def generate_gapic_version(api_schema: API) -> str:
+        """Generates gapic_version.py content."""
+        writer = CodeWriter()
+        writer.write_license_header()
+        writer.write_line(f'__version__ = "{api_schema.gapic_version}"  # {{x-release-please-version}}')
+        return writer.dump()
+
+    @staticmethod
+    def generate_py_typed(api_schema: API) -> str:
+        """Generates py.typed file (PEP 561 marker)."""
+        pkg_name = api_schema.naming.warehouse_package_name
+        return f"# Marker file for PEP 561.\n# The {pkg_name} package uses inline types.\n"

packages/gapic-generator/gapic/codegen/engine.py

@@ -0,0 +1,39 @@
+# Copyright 2026 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
+#
+#     https://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.
+
+from typing import Any, Optional
+from gapic.codegen.components.package_init import PackageInitGenerator
+
+
+class PurePythonEngine:
+    """Pure-Python template-free code generation engine."""
+
+    @staticmethod
+    def render(template_name: str, context: dict[str, Any]) -> Optional[str]:
+        """Dispatches template rendering to pure-Python component generators.
+
+        Returns None to fall back to Jinja rendering if the template is not yet migrated.
+        """
+        api_schema = context.get("api")
+        if not api_schema:
+            return None
+
+        # Package Init & Versioning Component
+        if template_name.endswith("gapic_version.py.j2"):
+            return PackageInitGenerator.generate_gapic_version(api_schema)
+        if template_name.endswith("py.typed.j2"):
+            return PackageInitGenerator.generate_py_typed(api_schema)
+
+        # Fallback to Jinja for un-migrated templates
+        return None

packages/gapic-generator/gapic/generator/generator.py

@@ -22,6 +22,7 @@
 from typing import Any, DefaultDict, Dict, Mapping, Optional, Tuple
 from hashlib import sha256
 from collections import OrderedDict, defaultdict
+from gapic.codegen.engine import PurePythonEngine
 from gapic.samplegen_utils.utils import (
     coerce_response_name,
     is_valid_sample_cfg,
@@ -402,12 +403,16 @@ def _get_file(
         )
 
         # Render the file contents.
+        rendered = PurePythonEngine.render(
+            template_name, {"api": api_schema, "opts": opts, **context}
+        )
+        if rendered is None:
+            rendered = self._env.get_template(template_name).render(
+                api=api_schema, opts=opts, **context
+            )
+
         cgr_file = CodeGeneratorResponse.File(
-            content=formatter.fix_whitespace(
-                self._env.get_template(template_name).render(
-                    api=api_schema, opts=opts, **context
-                ),
-            ),
+            content=formatter.fix_whitespace(rendered),
             name=fn,
         )
 

packages/gapic-generator/tests/unit/codegen/test_package_init.py

@@ -0,0 +1,51 @@
+# Copyright 2026 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
+#
+#     https://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.
+
+from unittest.mock import MagicMock
+from gapic.codegen.components.package_init import PackageInitGenerator
+
+
+def test_generate_gapic_version():
+    mock_api = MagicMock()
+    mock_api.gapic_version = "0.1.0"
+    content = PackageInitGenerator.generate_gapic_version(mock_api)
+
+    assert "# Copyright 2026 Google LLC" in content
+    assert '__version__ = "0.1.0"  # {x-release-please-version}' in content
+
+
+def test_generate_py_typed():
+    mock_api = MagicMock()
+    mock_api.naming.warehouse_package_name = "google-iam-credentials"
+    content = PackageInitGenerator.generate_py_typed(mock_api)
+    assert "# Marker file for PEP 561." in content
+    assert "google-iam-credentials" in content
+
+
+def test_pure_python_engine_render():
+    from gapic.codegen.engine import PurePythonEngine
+
+    assert PurePythonEngine.render("gapic_version.py.j2", {}) is None
+
+    mock_api = MagicMock()
+    mock_api.gapic_version = "0.1.0"
+    mock_api.naming.warehouse_package_name = "google-iam-credentials"
+
+    v_out = PurePythonEngine.render("gapic_version.py.j2", {"api": mock_api})
+    assert '__version__ = "0.1.0"' in v_out
+
+    t_out = PurePythonEngine.render("py.typed.j2", {"api": mock_api})
+    assert "google-iam-credentials" in t_out
+
+    assert PurePythonEngine.render("other_file.py.j2", {"api": mock_api}) is None