Fix editable compatibility with distutils' build_ext (#3526)

Author: abravalheri

changelog.d/3526.misc.rst

@@ -0,0 +1,2 @@
+Fix backward compatibility of editable installs and custom ``build_ext``
+commands inheriting directly from ``distutils``.

setuptools/command/editable_wheel.py

@@ -237,6 +237,8 @@ def _set_editable_mode(self):
             cmd = dist.get_command_obj(cmd_name)
             if hasattr(cmd, "editable_mode"):
                 cmd.editable_mode = True
+            elif hasattr(cmd, "inplace"):
+                cmd.inplace = True  # backward compatibility with distutils
 
     def _collect_build_outputs(self) -> Tuple[List[str], Dict[str, str]]:
         files: List[str] = []

setuptools/tests/test_editable_install.py

@@ -5,6 +5,7 @@
 import platform
 from copy import deepcopy
 from importlib import import_module
+from importlib.machinery import EXTENSION_SUFFIXES
 from pathlib import Path
 from textwrap import dedent
 from unittest.mock import Mock
@@ -28,6 +29,7 @@
     editable_wheel,
 )
 from setuptools.dist import Distribution
+from setuptools.extension import Extension
 
 
 @pytest.fixture(params=["strict", "lenient"])
@@ -872,9 +874,40 @@ def test_access_plat_name(self, tmpdir_cwd):
         cmd = editable_wheel(dist)
         cmd.ensure_finalized()
         cmd.run()
-        wheel_file = str(next(Path().glob('dist/*')))
+        wheel_file = str(next(Path().glob('dist/*.whl')))
         assert "editable" in wheel_file
-        assert wheel_file.endswith(".whl")
+
+
+class TestCustomBuildExt:
+    def install_custom_build_ext_distutils(self, dist):
+        from distutils.command.build_ext import build_ext as build_ext_cls
+
+        class MyBuildExt(build_ext_cls):
+            pass
+
+        dist.cmdclass["build_ext"] = MyBuildExt
+
+    @pytest.mark.skipif(
+        sys.platform != "linux", reason="compilers may fail without correct setup",
+    )
+    def test_distutils_leave_inplace_files(self, tmpdir_cwd):
+        jaraco.path.build({"module.c": ""})
+        attrs = {
+            "ext_modules": [Extension("module", ["module.c"])],
+        }
+        dist = Distribution(attrs)
+        dist.script_name = "setup.py"
+        dist.set_defaults()
+        self.install_custom_build_ext_distutils(dist)
+        cmd = editable_wheel(dist)
+        cmd.ensure_finalized()
+        cmd.run()
+        wheel_file = str(next(Path().glob('dist/*.whl')))
+        assert "editable" in wheel_file
+        files = [p for p in Path().glob("module.*") if p.suffix != ".c"]
+        assert len(files) == 1
+        name = files[0].name
+        assert any(name.endswith(ext) for ext in EXTENSION_SUFFIXES)
 
 
 def install_project(name, venv, tmp_path, files, *opts):