Fix issue with editable install and single module distributions

3 files changed, 31 insertions, 1 deletions

diff --git a/changelog.d/3502.misc.rst b/changelog.d/3502.misc.rst
new file mode 100644
index 00000000..ecc98334
--- /dev/null
+++ b/changelog.d/3502.misc.rst
@@ -0,0 +1 @@
+Fix issue with editable install and single module packages.
diff --git a/setuptools/command/editable_wheel.py b/setuptools/command/editable_wheel.py
index eb79608b..1bb7ddfb 100644
--- a/setuptools/command/editable_wheel.py
+++ b/setuptools/command/editable_wheel.py
@@ -439,7 +439,7 @@ class _TopLevelFinder:
         roots = _find_package_roots(top_level, package_dir, src_root)
 
         namespaces_: Dict[str, List[str]] = dict(chain(
-            _find_namespaces(self.dist.packages, roots),
+            _find_namespaces(self.dist.packages or [], roots),
             ((ns, []) for ns in _find_virtual_namespaces(roots)),
         ))
 
diff --git a/setuptools/tests/test_editable_install.py b/setuptools/tests/test_editable_install.py
index 40a35f65..8ab17b3c 100644
--- a/setuptools/tests/test_editable_install.py
+++ b/setuptools/tests/test_editable_install.py
@@ -163,6 +163,35 @@ def test_editable_with_flat_layout(tmp_path, venv, editable_opts):
     assert subprocess.check_output(cmd).strip() == b"4 2"
 
 
+def test_editable_with_single_module(tmp_path, venv, editable_opts):
+    files = {
+        "mypkg": {
+            "pyproject.toml": dedent("""\
+                [build-system]
+                requires = ["setuptools", "wheel"]
+                build-backend = "setuptools.build_meta"
+
+                [project]
+                name = "mod"
+                version = "3.14159"
+
+                [tool.setuptools]
+                py-modules = ["mod"]
+                """),
+            "mod.py": "b = 2",
+        },
+    }
+    jaraco.path.build(files, prefix=tmp_path)
+    project = tmp_path / "mypkg"
+
+    cmd = [venv.exe(), "-m", "pip", "install",
+           "--no-build-isolation",  # required to force current version of setuptools
+           "-e", str(project), *editable_opts]
+    print(str(subprocess.check_output(cmd), "utf-8"))
+    cmd = [venv.exe(), "-c", "import mod; print(mod.b)"]
+    assert subprocess.check_output(cmd).strip() == b"2"
+
+
 class TestLegacyNamespaces:
     """Ported from test_develop"""