docs: [Python] 型エイリアス系へのリンクについてワークアラウンド (#952)

Sphinx AutoAPIが`NewType`や`TypeAlias`へのリンクを張ってくれないという
問題について、`missing-reference`から宛先を張りなおすというワークアラウ
ンドを入れる。

以下が要課題。
#952 (review)

Resolves: #951

docs/ghpages/apis/python_api/conf.py

@@ -6,6 +6,14 @@
 # -- Project information -----------------------------------------------------
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#project-information
 
+import typing
+
+import sphinx.util.logging
+from docutils.nodes import TextElement, reference
+from sphinx.addnodes import pending_xref
+from sphinx.application import Sphinx
+from sphinx.environment import BuildEnvironment
+
 project = "voicevox_core_python_api"
 # copyright = '2022, _'
 # author = '_'
@@ -40,3 +48,37 @@
 
 html_theme = "pydata_sphinx_theme"
 # html_static_path = ['_static']
+
+
+def setup(sphinx: Sphinx) -> None:
+    sphinx.connect("missing-reference", _on_missing_reference)
+
+
+def _on_missing_reference(
+    app: Sphinx, env: BuildEnvironment, node: pending_xref, contnode: TextElement
+) -> reference | None:
+    """
+    ``NewType`` や ``TypeAlias`` について ``class``
+    宛てにリンクしようとしてmissingになったものを、 ``data`` 宛てに修正する。
+    """
+    # 参考: https://github.com/sphinx-doc/sphinx/issues/10785#issue-1348601826
+    TARGETS = {
+        "CharacterVersion",
+        "StyleId",
+        "VoiceModelId",
+    }
+    if (
+        node["refdomain"] == "py"
+        and node["reftype"] == "class"
+        and node["reftarget"].split(".")[-1] in TARGETS
+    ):
+        xref = app.env.get_domain("py").resolve_xref(
+            env, node["refdoc"], app.builder, "data", node["reftarget"], node, contnode
+        )
+        xref = typing.cast(reference | None, xref)  # ?
+        if not xref:
+            _logger.error("unresolved link to `%s`", node["reftarget"])
+        return xref
+
+
+_logger = sphinx.util.logging.getLogger(__name__)