bpo-42129: Add support for resources in namespaces (GH-24670)

* Unify behavior in ResourceReaderDefaultsTests and align with the behavior found in importlib_resources.
* Equip NamespaceLoader with a NamespaceReader.
* Apply changes from importlib_resources 5.0.4

1 files changed, 61 insertions, 49 deletions

diff --git a/Lib/importlib/resources.py b/Lib/importlib/resources.py
index 4169171..db0e0c0 100644
--- a/Lib/importlib/resources.py
+++ b/Lib/importlib/resources.py
@@ -3,8 +3,10 @@ import io
 
 from . import _common
 from ._common import as_file, files
+from .abc import ResourceReader
 from contextlib import suppress
 from importlib.abc import ResourceLoader
+from importlib.machinery import ModuleSpec
 from io import BytesIO, TextIOWrapper
 from pathlib import Path
 from types import ModuleType
@@ -18,6 +20,7 @@ from functools import singledispatch
 __all__ = [
     'Package',
     'Resource',
+    'ResourceReader',
     'as_file',
     'contents',
     'files',
@@ -27,7 +30,7 @@ __all__ = [
     'path',
     'read_binary',
     'read_text',
-    ]
+]
 
 
 Package = Union[str, ModuleType]
@@ -41,36 +44,45 @@ def open_binary(package: Package, resource: Resource) -> BinaryIO:
     reader = _common.get_resource_reader(package)
     if reader is not None:
         return reader.open_resource(resource)
-    absolute_package_path = os.path.abspath(
-        package.__spec__.origin or 'non-existent file')
-    package_path = os.path.dirname(absolute_package_path)
-    full_path = os.path.join(package_path, resource)
-    try:
-        return open(full_path, mode='rb')
-    except OSError:
-        # Just assume the loader is a resource loader; all the relevant
-        # importlib.machinery loaders are and an AttributeError for
-        # get_data() will make it clear what is needed from the loader.
-        loader = cast(ResourceLoader, package.__spec__.loader)
-        data = None
-        if hasattr(package.__spec__.loader, 'get_data'):
-            with suppress(OSError):
-                data = loader.get_data(full_path)
-        if data is None:
-            package_name = package.__spec__.name
-            message = '{!r} resource not found in {!r}'.format(
-                resource, package_name)
-            raise FileNotFoundError(message)
-        return BytesIO(data)
-
-
-def open_text(package: Package,
-              resource: Resource,
-              encoding: str = 'utf-8',
-              errors: str = 'strict') -> TextIO:
+    spec = cast(ModuleSpec, package.__spec__)
+    # Using pathlib doesn't work well here due to the lack of 'strict'
+    # argument for pathlib.Path.resolve() prior to Python 3.6.
+    if spec.submodule_search_locations is not None:
+        paths = spec.submodule_search_locations
+    elif spec.origin is not None:
+        paths = [os.path.dirname(os.path.abspath(spec.origin))]
+
+    for package_path in paths:
+        full_path = os.path.join(package_path, resource)
+        try:
+            return open(full_path, mode='rb')
+        except OSError:
+            # Just assume the loader is a resource loader; all the relevant
+            # importlib.machinery loaders are and an AttributeError for
+            # get_data() will make it clear what is needed from the loader.
+            loader = cast(ResourceLoader, spec.loader)
+            data = None
+            if hasattr(spec.loader, 'get_data'):
+                with suppress(OSError):
+                    data = loader.get_data(full_path)
+            if data is not None:
+                return BytesIO(data)
+
+    raise FileNotFoundError(
+        '{!r} resource not found in {!r}'.format(resource, spec.name)
+    )
+
+
+def open_text(
+    package: Package,
+    resource: Resource,
+    encoding: str = 'utf-8',
+    errors: str = 'strict',
+) -> TextIO:
     """Return a file-like object opened for text reading of the resource."""
     return TextIOWrapper(
-        open_binary(package, resource), encoding=encoding, errors=errors)
+        open_binary(package, resource), encoding=encoding, errors=errors
+    )
 
 
 def read_binary(package: Package, resource: Resource) -> bytes:
@@ -79,10 +91,12 @@ def read_binary(package: Package, resource: Resource) -> bytes:
         return fp.read()
 
 
-def read_text(package: Package,
-              resource: Resource,
-              encoding: str = 'utf-8',
-              errors: str = 'strict') -> str:
+def read_text(
+    package: Package,
+    resource: Resource,
+    encoding: str = 'utf-8',
+    errors: str = 'strict',
+) -> str:
     """Return the decoded string of the resource.
 
     The decoding-related arguments have the same semantics as those of
@@ -93,8 +107,9 @@ def read_text(package: Package,
 
 
 def path(
-        package: Package, resource: Resource,
-        ) -> 'ContextManager[Path]':
+    package: Package,
+    resource: Resource,
+) -> 'ContextManager[Path]':
     """A context manager providing a file path object to the resource.
 
     If the resource does not already exist on its own on the file system,
@@ -106,15 +121,17 @@ def path(
     reader = _common.get_resource_reader(_common.get_package(package))
     return (
         _path_from_reader(reader, _common.normalize_path(resource))
-        if reader else
-        _common.as_file(
-            _common.files(package).joinpath(_common.normalize_path(resource)))
+        if reader
+        else _common.as_file(
+            _common.files(package).joinpath(_common.normalize_path(resource))
         )
+    )
 
 
 def _path_from_reader(reader, resource):
-    return _path_from_resource_path(reader, resource) or \
-        _path_from_open_resource(reader, resource)
+    return _path_from_resource_path(reader, resource) or _path_from_open_resource(
+        reader, resource
+    )
 
 
 def _path_from_resource_path(reader, resource):
@@ -154,15 +171,10 @@ def contents(package: Package) -> Iterable[str]:
     reader = _common.get_resource_reader(package)
     if reader is not None:
         return _ensure_sequence(reader.contents())
-    # Is the package a namespace package?  By definition, namespace packages
-    # cannot have resources.
-    namespace = (
-        package.__spec__.origin is None or
-        package.__spec__.origin == 'namespace'
-        )
-    if namespace or not package.__spec__.has_location:
-        return ()
-    return list(item.name for item in _common.from_package(package).iterdir())
+    transversable = _common.from_package(package)
+    if transversable.is_dir():
+        return list(item.name for item in transversable.iterdir())
+    return []
 
 
 @singledispatch