fix: exclude subpackage from setup.py if __init__.py is excluded

Fixes: python-poetry#1009

poetry/masonry/builders/sdist.py

@@ -237,7 +237,9 @@ def find_nearest_pkg(rel_path):
             if from_top_level == ".":
                 continue
 
-            is_subpkg = "__init__.py" in filenames
+            is_subpkg = "__init__.py" in filenames and not self.is_excluded(
+                Path(path, "__init__.py").relative_to(self._path)
+            )
             if is_subpkg:
                 subpkg_paths.add(from_top_level)
                 parts = from_top_level.split(os.sep)

tests/masonry/builders/test_sdist.py

@@ -465,3 +465,18 @@ def test_proper_python_requires_if_three_digits_precision_version_specified():
     parsed = p.parsestr(to_str(pkg_info))
 
     assert parsed["Requires-Python"] == "==2.7.15"
+
+
+def test_excluded_subpackage():
+    poetry = Factory().create_poetry(project("excluded_subpackage"))
+
+    builder = SdistBuilder(poetry, NullEnv(), NullIO())
+    setup = builder.build_setup()
+
+    setup_ast = ast.parse(setup)
+
+    setup_ast.body = [n for n in setup_ast.body if isinstance(n, ast.Assign)]
+    ns = {}
+    exec(compile(setup_ast, filename="setup.py", mode="exec"), ns)
+
+    assert ns["packages"] == ["example"]