chore(librarian): update release init changelog (#14799)

This PR ensures that both `CHANGELOG.md` and `docs/CHANGELOG.md` files
are updated during release init.

Author: ohmayr

.generator/cli.py

@@ -1345,7 +1345,7 @@ def _update_changelog_for_library(
     version: str,
     previous_version: str,
     library_id: str,
-    relative_path: str,
+    is_mono_repo: bool,
 ):
     """Prepends a new release entry with multiple, grouped changes, to a changelog.
 
@@ -1361,7 +1361,15 @@ def _update_changelog_for_library(
         previous_version(str): The version in state.yaml for a given library
         library_id(str): The id of the library where the changelog should
             be updated.
+        is_mono_repo(bool): True if the current repository is a mono-repo.
     """
+    if is_mono_repo:
+        relative_path = f"packages/{library_id}/CHANGELOG.md"
+        docs_relative_path = f"packages/{library_id}/docs/CHANGELOG.md"
+    else:
+        relative_path = "CHANGELOG.md"
+        docs_relative_path = f"docs/CHANGELOG.md"
+
     changelog_src = f"{repo}/{relative_path}"
     changelog_dest = f"{output}/{relative_path}"
     updated_content = _process_changelog(
@@ -1373,6 +1381,11 @@ def _update_changelog_for_library(
     )
     _write_text_file(changelog_dest, updated_content)
 
+    docs_changelog_src = f"{repo}/{docs_relative_path}"
+    if os.path.lexists(docs_changelog_src):
+        docs_changelog_dst = f"{output}/{docs_relative_path}"
+        _write_text_file(docs_changelog_dst, updated_content)
+
 
 def _is_mono_repo(repo: str) -> bool:
     """Determines if a library is generated or handwritten.
@@ -1424,7 +1437,6 @@ def handle_release_init(
         )
 
         if is_mono_repo:
-
             # only a mono repo has a global changelog
             _update_global_changelog(
                 f"{repo}/CHANGELOG.md",
@@ -1449,10 +1461,8 @@ def handle_release_init(
 
             if is_mono_repo:
                 path_to_library = f"packages/{library_id}"
-                changelog_relative_path = f"packages/{library_id}/CHANGELOG.md"
             else:
                 path_to_library = "."
-                changelog_relative_path = "CHANGELOG.md"
 
             _update_version_for_library(repo, output, path_to_library, version)
             _update_changelog_for_library(
@@ -1462,7 +1472,7 @@ def handle_release_init(
                 version,
                 previous_version,
                 library_id,
-                relative_path=changelog_relative_path,
+                is_mono_repo=is_mono_repo,
             )
 
     except Exception as e:

.generator/test_cli.py

@@ -312,6 +312,7 @@ def test_handle_configure_no_new_library(mocker):
     with pytest.raises(ValueError, match="Configuring a new library failed."):
         handle_configure()
 
+
 def test_create_new_changelog_for_library(mocker):
     """Tests that the changelog files are created correctly."""
     library_id = "google-cloud-language"
@@ -325,7 +326,9 @@ def test_create_new_changelog_for_library(mocker):
     docs_changelog_path = f"{output}/packages/{library_id}/docs/CHANGELOG.md"
 
     # Check that makedirs was called for both parent directories
-    mock_makedirs.assert_any_call(os.path.dirname(package_changelog_path), exist_ok=True)
+    mock_makedirs.assert_any_call(
+        os.path.dirname(package_changelog_path), exist_ok=True
+    )
     mock_makedirs.assert_any_call(os.path.dirname(docs_changelog_path), exist_ok=True)
     assert mock_makedirs.call_count == 2
 
@@ -1141,29 +1144,60 @@ def test_get_previous_version_failure(mock_state_file):
         _get_previous_version("google-cloud-does-not-exist", LIBRARIAN_DIR)
 
 
-def test_update_changelog_for_library_success(mocker):
-    m = mock_open()
-
+def test_update_changelog_for_library_writes_both_changelogs(mocker):
+    """Tests that _update_changelog_for_library writes to both changelogs."""
     mock_content = """# Changelog
 
 [PyPI History][1]
 
 [1]: https://pypi.org/project/google-cloud-language/#history
+"""
+    mock_read = mocker.patch("cli._read_text_file", return_value=mock_content)
+    mock_write = mocker.patch("cli._write_text_file")
+    mock_path_exists = mocker.patch("cli.os.path.lexists", return_value=True)
+    _update_changelog_for_library(
+        "repo",
+        "output",
+        _MOCK_LIBRARY_CHANGES,
+        "1.2.3",
+        "1.2.2",
+        "google-cloud-language",
+        is_mono_repo=True,
+    )
 
-## [2.17.2](https://github.com/googleapis/google-cloud-python/compare/google-cloud-language-v2.17.1...google-cloud-language-v2.17.2) (2025-06-11)
+    assert mock_write.call_count == 2
+    mock_write.assert_any_call(
+        "output/packages/google-cloud-language/CHANGELOG.md", mocker.ANY
+    )
+    mock_write.assert_any_call(
+        "output/packages/google-cloud-language/docs/CHANGELOG.md", mocker.ANY
+    )
 
+
+def test_update_changelog_for_library_single_repo(mocker):
+    """Tests that _update_changelog_for_library writes to both changelogs in a single repo."""
+    mock_content = """# Changelog
+
+[PyPI History][1]
+
+[1]: https://pypi.org/project/google-cloud-language/#history
 """
-    with unittest.mock.patch("cli.open", m):
-        mocker.patch("cli._read_text_file", return_value=mock_content)
-        _update_changelog_for_library(
-            "repo",
-            "output",
-            _MOCK_LIBRARY_CHANGES,
-            "1.2.3",
-            "1.2.2",
-            "google-cloud-language",
-            "CHANGELOG.md",
-        )
+    mock_read = mocker.patch("cli._read_text_file", return_value=mock_content)
+    mock_write = mocker.patch("cli._write_text_file")
+    mock_path_exists = mocker.patch("cli.os.path.lexists", return_value=True)
+    _update_changelog_for_library(
+        "repo",
+        "output",
+        _MOCK_LIBRARY_CHANGES,
+        "1.2.3",
+        "1.2.2",
+        "google-cloud-language",
+        is_mono_repo=False,
+    )
+
+    assert mock_write.call_count == 2
+    mock_write.assert_any_call("output/CHANGELOG.md", mocker.ANY)
+    mock_write.assert_any_call("output/docs/CHANGELOG.md", mocker.ANY)
 
 
 def test_process_changelog_success():