1 files changed, 50 insertions, 0 deletions
diff --git a/src/pallets_sphinx_themes/theme_check.py b/src/pallets_sphinx_themes/theme_check.py
new file mode 100644
index 0000000..c7c0192
--- /dev/null
+++ b/src/pallets_sphinx_themes/theme_check.py
@@ -0,0 +1,50 @@
+from functools import wraps
+
+
+def set_is_pallets_theme(app):
+    """Set the ``is_pallets_theme`` config to ``True`` if the current
+    theme is a decedent of the ``pocoo`` theme.
+    """
+    if app.config.is_pallets_theme is not None:
+        return
+
+    theme = getattr(app.builder, "theme", None)
+
+    while theme is not None:
+        if theme.name == "pocoo":
+            app.config.is_pallets_theme = True
+            break
+
+        theme = theme.base
+    else:
+        app.config.is_pallets_theme = False
+
+
+def only_pallets_theme(default=None):
+    """Create a decorator that calls a function only if the
+    ``is_pallets_theme`` config is ``True``.
+
+    Used to prevent Sphinx event callbacks from doing anything if the
+    Pallets themes are installed but not used. ::
+
+        @only_pallets_theme()
+        def inject_value(app):
+            ...
+
+        app.connect("builder-inited", inject_value)
+
+    :param default: Value to return if a Pallets theme is not in use.
+    :return: A decorator.
+    """
+
+    def decorator(f):
+        @wraps(f)
+        def wrapped(app, *args, **kwargs):
+            if not app.config.is_pallets_theme:
+                return default
+
+            return f(app, *args, **kwargs)
+
+        return wrapped
+
+    return decorator