Allow tests to build pkgutil legacy namespaces

setuptools/tests/namespaces.py

@@ -1,3 +1,5 @@
+import ast
+import json
 import textwrap
 
 
@@ -7,33 +9,44 @@ def iter_namespace_pkgs(namespace):
         yield ".".join(parts[:i+1])
 
 
-def build_namespace_package(tmpdir, name, version="1.0"):
+def build_namespace_package(tmpdir, name, version="1.0", impl="pkg_resources"):
     src_dir = tmpdir / name
     src_dir.mkdir()
     setup_py = src_dir / 'setup.py'
     namespace, _, rest = name.rpartition('.')
     namespaces = list(iter_namespace_pkgs(namespace))
+    setup_args = {
+        "name": name,
+        "version": version,
+        "packages": namespaces,
+    }
+
+    if impl == "pkg_resources":
+        tmpl = '__import__("pkg_resources").declare_namespace(__name__)'
+        setup_args["namespace_packages"] = namespaces
+    elif impl == "pkgutil":
+        tmpl = '__path__ = __import__("pkgutil").extend_path(__path__, __name__)'
+    else:
+        raise ValueError(f"Cannot recognise {impl=} when creating namespaces")
+
+    args = json.dumps(setup_args, indent=4)
+    assert ast.literal_eval(args)  # ensure it is valid Python
+
     script = textwrap.dedent(
-        """
+        """\
         import setuptools
-        setuptools.setup(
-            name={name!r},
-            version={version!r},
-            namespace_packages={namespaces!r},
-            packages={namespaces!r},
-        )
+        args = {args}
+        setuptools.setup(**args)
         """
-    ).format(**locals())
+    ).format(args=args)
     setup_py.write_text(script, encoding='utf-8')
 
     ns_pkg_dir = src_dir / namespace.replace(".", "/")
     ns_pkg_dir.mkdir(parents=True)
 
     for ns in namespaces:
         pkg_init = src_dir / ns.replace(".", "/") / '__init__.py'
-        tmpl = '__import__("pkg_resources").declare_namespace(__name__)'
-        decl = tmpl.format(**locals())
-        pkg_init.write_text(decl, encoding='utf-8')
+        pkg_init.write_text(tmpl, encoding='utf-8')
 
     pkg_mod = ns_pkg_dir / (rest + '.py')
     some_functionality = 'name = {rest!r}'.format(**locals())

setuptools/tests/test_editable_install.py

@@ -261,8 +261,17 @@ def test_nspkg_file_is_unique(self, tmp_path, monkeypatch):
         files = list(installation_dir.glob("*-nspkg.pth"))
         assert len(files) == len(examples)
 
+    @pytest.mark.parametrize(
+        "impl",
+        (
+            "pkg_resources",
+            #  "pkgutil",  => does not work
+        )
+    )
     @pytest.mark.parametrize("ns", ("myns.n",))
-    def test_namespace_package_importable(self, venv, tmp_path, ns, editable_opts):
+    def test_namespace_package_importable(
+        self, venv, tmp_path, ns, impl, editable_opts
+    ):
         """
         Installing two packages sharing the same namespace, one installed
         naturally using pip or `--single-version-externally-managed`
@@ -275,8 +284,8 @@ def test_namespace_package_importable(self, venv, tmp_path, ns, editable_opts):
         requires = ["setuptools"]
         build-backend = "setuptools.build_meta"
         """
-        pkg_A = namespaces.build_namespace_package(tmp_path, f"{ns}.pkgA")
-        pkg_B = namespaces.build_namespace_package(tmp_path, f"{ns}.pkgB")
+        pkg_A = namespaces.build_namespace_package(tmp_path, f"{ns}.pkgA", impl=impl)
+        pkg_B = namespaces.build_namespace_package(tmp_path, f"{ns}.pkgB", impl=impl)
         (pkg_A / "pyproject.toml").write_text(build_system, encoding="utf-8")
         (pkg_B / "pyproject.toml").write_text(build_system, encoding="utf-8")
         # use pip to install to the target directory