Support the importlib.resources files API in rewritten files (#9173)

changelog/9169.bugfix.rst

@@ -0,0 +1 @@
+Support for the ``files`` API from ``importlib.resources`` within rewritten files.

src/_pytest/assertion/rewrite.py

@@ -64,7 +64,7 @@ class AssertionRewritingHook(importlib.abc.MetaPathFinder, importlib.abc.Loader)
         except ValueError:
             self.fnpats = ["test_*.py", "*_test.py"]
         self.session: Optional[Session] = None
-        self._rewritten_names: Set[str] = set()
+        self._rewritten_names: Dict[str, Path] = {}
         self._must_rewrite: Set[str] = set()
         # flag to guard against trying to rewrite a pyc file while we are already writing another pyc file,
         # which might result in infinite recursion (#3506)
@@ -134,7 +134,7 @@ class AssertionRewritingHook(importlib.abc.MetaPathFinder, importlib.abc.Loader)
         fn = Path(module.__spec__.origin)
         state = self.config.stash[assertstate_key]
 
-        self._rewritten_names.add(module.__name__)
+        self._rewritten_names[module.__name__] = fn
 
         # The requested module looks like a test file, so rewrite it. This is
         # the most magical part of the process: load the source, rewrite the
@@ -276,6 +276,14 @@ class AssertionRewritingHook(importlib.abc.MetaPathFinder, importlib.abc.Loader)
         with open(pathname, "rb") as f:
             return f.read()
 
+    if sys.version_info >= (3, 9):
+
+        def get_resource_reader(self, name: str) -> importlib.abc.TraversableResources:  # type: ignore
+            from types import SimpleNamespace
+            from importlib.readers import FileReader
+
+            return FileReader(SimpleNamespace(path=self._rewritten_names[name]))
+
 
 def _write_pyc_fp(
     fp: IO[bytes], source_stat: os.stat_result, co: types.CodeType

testing/test_assertrewrite.py

@@ -795,6 +795,35 @@ class TestRewriteOnImport:
         )
         assert pytester.runpytest().ret == ExitCode.NO_TESTS_COLLECTED
 
+    @pytest.mark.skipif(
+        sys.version_info < (3, 9),
+        reason="importlib.resources.files was introduced in 3.9",
+    )
+    def test_load_resource_via_files_with_rewrite(self, pytester: Pytester) -> None:
+        example = pytester.path.joinpath("demo") / "example"
+        init = pytester.path.joinpath("demo") / "__init__.py"
+        pytester.makepyfile(
+            **{
+                "demo/__init__.py": """
+                from importlib.resources import files
+
+                def load():
+                    return files(__name__)
+                """,
+                "test_load": f"""
+                pytest_plugins = ["demo"]
+
+                def test_load():
+                    from demo import load
+                    found = {{str(i) for i in load().iterdir() if i.name != "__pycache__"}}
+                    assert found == {{{str(example)!r}, {str(init)!r}}}
+                """,
+            }
+        )
+        example.mkdir()
+
+        assert pytester.runpytest("-vv").ret == ExitCode.OK
+
     def test_readonly(self, pytester: Pytester) -> None:
         sub = pytester.mkdir("testing")
         sub.joinpath("test_readonly.py").write_bytes(