Fix ButlerURI inheritance

This change inserts ButlerURI into the ResourcePath class
inheritance by repointing the base class.

.github/workflows/mypy.yaml

@@ -23,7 +23,7 @@ jobs:
         run: pip install "mypy==0.910" pydantic
 
       - name: Install third party stubs
-        run: pip install types-requests types-PyYAML types-click types-pkg_resources
+        run: pip install types-requests types-PyYAML types-click types-pkg_resources types-Deprecated
 
       - name: Install lsst.utils
         run: |

python/lsst/daf/butler/core/_butlerUri.py

@@ -1,8 +1,31 @@
 # Temporarily alias ResourcePath as ButlerURI.
-from typing import Any
+from typing import Any, Type
 
 from deprecated.sphinx import deprecated
 from lsst.resources import ResourcePath, ResourcePathExpression
+from lsst.resources.file import FileResourcePath
+
+
+def _add_base(cls: Type) -> None:
+    """Update the class to use ButlerURI as the base.
+
+    Notes
+    -----
+    Care must be taken with SchemelessResourcePath since that class inherits
+    from FileResourcePath.
+    """
+    if cls.__bases__ == (ResourcePath,):
+        cls.__bases__ = (ButlerURI,)
+    elif cls.__bases__ == (FileResourcePath,) and FileResourcePath.__bases__ == (ResourcePath,):
+        FileResourcePath.__bases__ = (ButlerURI,)
+
+
+def _reset_base(cls: Type) -> None:
+    """Reset the base class to be ResourcePath."""
+    if cls.__bases__ == (ButlerURI,):
+        cls.__bases__ = (ResourcePath,)
+    elif issubclass(cls, FileResourcePath) and FileResourcePath.__bases__ == (ButlerURI,):
+        FileResourcePath.__bases__ = (ResourcePath,)
 
 
 @deprecated(
@@ -17,4 +40,21 @@ class ButlerURI(ResourcePath):
     """
 
     def __new__(cls, uri: ResourcePathExpression, **kwargs: Any) -> ResourcePath:  # type: ignore
-        return ResourcePath(uri, **kwargs)
+        if cls is not ButlerURI:
+            # This is a subclass trying to create an updated version of
+            # itself without wanting to change the class. The ButlerURI
+            # __new__ forces ResourcePath() to be used every time and so
+            # the knowledge of the subclass is lost. This can result in a
+            # Schemeless becoming a File URI. The simplest approach is to
+            # remove ButlerURI from the class hierarchy and add it back again.
+            # This seems inefficient but without it the subclass will
+            # always try to call ButlerURI.__new__.
+            _reset_base(cls)
+            new = cls(uri, **kwargs)
+            _add_base(cls)
+            return new
+
+        new = ResourcePath(uri, **kwargs)
+        _add_base(type(new))
+
+        return new

tests/test_uri.py

@@ -49,6 +49,7 @@ def tearDown(self):
     def testFile(self):
         file = os.path.join(self.tmpdir, "test.txt")
         uri = ButlerURI(file)
+        self.assertIsInstance(uri, ButlerURI)
         self.assertFalse(uri.exists(), f"{uri} should not exist")
         self.assertEqual(uri.ospath, file)