use files() api in is_resource()

The files() api makes the identification of resources blury. Here we
re-implement is_resource() by mirroring the previous logic to the best
extent we can. This is not fully correct, as the files() api is not
fully compatible with the legacy api, but it is pretty close and as
correct as we can get. The semantics for what constitutes resources have
always been blurry in the first place.

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

importlib_resources/__init__.py

@@ -8,12 +8,12 @@
     read_binary,
     open_text,
     read_text,
+    is_resource,
 )
 
 from importlib_resources._py3 import (
     Package,
     Resource,
-    is_resource,
     path,
 )
 from importlib_resources.abc import ResourceReader

importlib_resources/_common.py

@@ -165,3 +165,15 @@ def contents(package: Package) -> Iterable[str]:
     to check if it is a resource or not.
     """
     return [path.name for path in files(package).iterdir()]
+
+
+def is_resource(package: Package, name: str) -> bool:
+    """True if `name` is a resource inside `package`.
+
+    Directories are *not* resources.
+    """
+    resource = normalize_path(name)
+    for traversable in files(package).iterdir():
+        if traversable.name == resource:
+            return traversable.is_file()
+    return False

importlib_resources/_py3.py

@@ -51,22 +51,6 @@ def _path_from_open_resource(reader, resource):
     return _common._tempfile(saved.read, suffix=resource)
 
 
-def is_resource(package: Package, name: str) -> bool:
-    """True if `name` is a resource inside `package`.
-
-    Directories are *not* resources.
-    """
-    package = _common.get_package(package)
-    _common.normalize_path(name)
-    reader = _common.get_resource_reader(package)
-    if reader is not None:
-        return reader.is_resource(name)
-    package_contents = set(_common.contents(package))
-    if name not in package_contents:
-        return False
-    return (_common.from_package(package) / name).is_file()
-
-
 @singledispatch
 def _ensure_sequence(iterable):
     return list(iterable)