Add a setup file context manager in sdist builder

A temporary setup file is required for various scenarios
at the moment. This change introduces a context manager
such that generates a temporary setup.py file and handles
cleanup on exiting the context.

poetry/core/masonry/builders/sdist.py

@@ -6,13 +6,16 @@
 import time
 
 from collections import defaultdict
+from contextlib import contextmanager
 from copy import copy
 from gzip import GzipFile
 from io import BytesIO
 from posixpath import join as pjoin
 from pprint import pformat
+from typing import Iterator
 
 from poetry.core.utils._compat import Path
+from poetry.core.utils._compat import decode
 from poetry.core.utils._compat import encode
 from poetry.core.utils._compat import to_str
 
@@ -198,6 +201,24 @@ def build_setup(self):  # type: () -> bytes
             )
         )
 
+    @contextmanager
+    def setup_py(self):  # type: () -> Iterator[Path]
+        setup = self._path / "setup.py"
+        has_setup = setup.exists()
+
+        if has_setup:
+            logger.info(
+                " - <warning>A setup.py file already exists. Using it.</warning>"
+            )
+        else:
+            with setup.open("w", encoding="utf-8") as f:
+                f.write(decode(self.build_setup()))
+
+        yield setup
+
+        if not has_setup:
+            setup.unlink()
+
     def build_pkg_info(self):
         return encode(self.get_metadata_content())
 

tests/masonry/builders/test_sdist.py

@@ -14,6 +14,7 @@
 from poetry.core.packages.dependency import Dependency
 from poetry.core.packages.vcs_dependency import VCSDependency
 from poetry.core.utils._compat import Path
+from poetry.core.utils._compat import encode
 from poetry.core.utils._compat import to_str
 
 
@@ -247,6 +248,29 @@ def test_package():
         assert "my-package-1.2.3/LICENSE" in tar.getnames()
 
 
+def test_setup_py_context():
+    poetry = Factory().create_poetry(project("complete"))
+
+    builder = SdistBuilder(poetry)
+
+    project_setup_py = poetry.file.parent / "setup.py"
+
+    assert not project_setup_py.exists()
+
+    try:
+        with builder.setup_py() as setup:
+            assert setup.exists()
+            assert project_setup_py == setup
+
+            with open(str(setup), "r") as f:
+                assert encode(f.read()) == builder.build_setup()
+
+        assert not project_setup_py.exists()
+    finally:
+        if project_setup_py.exists():
+            project_setup_py.unlink()
+
+
 def test_module():
     poetry = Factory().create_poetry(project("module1"))