_adapters: replace DegenerateFiles with CompatibilityFiles

Signed-off-by: Filipe Laíns <lains@riseup.net>

importlib_resources/_adapters.py

@@ -25,32 +25,59 @@ def __init__(self, spec):
         self.spec = spec
 
     def get_resource_reader(self, name):
-        return DegenerateFiles(self.spec)._native()
+        return CompatibilityFiles(self.spec)._native()
 
 
-class DegenerateFiles:
+class CompatibilityFiles:
     """
     Adapter for an existing or non-existant resource reader
-    to provide a degenerate .files().
+    to provide a compability .files().
     """
 
     class Path(abc.Traversable):
+        def __init__(self, spec, reader, name=None):
+            if not spec and not name:
+                raise ValueError('Need at least a module spec or a resource name')
+            self._spec = spec
+            self._reader = reader
+            self._name = name
+
         def iterdir(self):
-            return iter(())
+            if not self._spec or not self._reader:
+                return iter(())
+            return iter(
+                [
+                    CompatibilityFiles.Path(None, self._reader, path)
+                    for path in self._reader.contents()
+                ]
+            )
 
         def is_dir(self):
-            return False
+            raise FileNotFoundError("Can't access resource {}".format(self.name))
 
         is_file = exists = is_dir  # type: ignore
 
         def joinpath(self, other):
-            return DegenerateFiles.Path()
-
+            if not self._spec:
+                raise FileNotFoundError(
+                    'Orphan resource {} has no sub-resources'.format(other)
+                )
+            if not self._reader or other not in list(self._reader.contents()):
+                raise FileNotFoundError(
+                    'Module {} does not have resource {}'.format(self._spec.name, other)
+                )
+            return CompatibilityFiles.Path(None, self._reader, other)
+
+        @property
         def name(self):
-            return ''
+            return self._name if self._name is not None else self._spec.name
 
         def open(self):
-            raise ValueError()
+            if self._name is None:
+                raise FileNotFoundError(
+                    "Can't open module {} as a resource".format(self._spec.name)
+                )
+            return self._reader.open_resource(self.name)
 
     def __init__(self, spec):
         self.spec = spec
@@ -71,7 +98,7 @@ def __getattr__(self, attr):
         return getattr(self._reader, attr)
 
     def files(self):
-        return DegenerateFiles.Path()
+        return CompatibilityFiles.Path(self.spec, self._reader)
 
 
 def wrap_spec(package):

importlib_resources/_compat.py

@@ -73,7 +73,7 @@ def _file_reader(spec):
             or
             # local FileReader
             _file_reader(self.spec)
-            or _adapters.DegenerateFiles(self.spec)
+            or _adapters.CompatibilityFiles(self.spec)
         )