Keep the prior behavior of overwriting File.page (#3381)

unless the page value is a *strict* subclass of Page
mkdocs · Sep 10, 2023 · 759e1e3 · 759e1e3
1 parent 3db7b8c
commit 759e1e3
Showing 1 changed file with 14 additions and 4 deletions.
diff --git a/mkdocs/structure/nav.py b/mkdocs/structure/nav.py
@@ -201,12 +201,22 @@ def _data_to_navigation(data, files: Files, config: MkDocsConfig):
                 f"A reference to '{file.src_path}' is included in the 'nav' "
                 "configuration, but this file is excluded from the built site.",
             )
-        if file.page is not None:
-            if not isinstance(file.page, Page):
+        page = file.page
+        if page is not None:
+            if isinstance(page, Page):
+                if type(page) is not Page:  # Strict subclass
+                    return page
+                warnings.warn(
+                    "A plugin has set File.page to an instance of Page and it got overwritten. "
+                    "The behavior of this will change in MkDocs 1.6.",
+                    DeprecationWarning,
+                )
+            else:
                 warnings.warn(  # type: ignore[unreachable]
-                    "File.page should not be set to any type other than Page", DeprecationWarning
+                    "A plugin has set File.page to a type other than Page. "
+                    "This will be an error in MkDocs 1.6.",
+                    DeprecationWarning,
                 )
-            return file.page
         return Page(title, file, config)
     return Link(title, path)