Avoid setuptools_wheel fixture to create recursively nested build/lib/build/lib/... directories

Based on the test introduced in b4d3e83, we can see that when none of
`PRE_BUILT_SETUPTOOLS_SDIST` or `PRE_BUILT_SETUPTOOLS_WHEEL` is set,
the `setuptools_wheel` fixture keeps recursively creating
`build/lib/build/lib/...` directories which slows down the tests and
creates a huge amount of unnecessary files.

This change tries to target that.

Author: abravalheri

setuptools/tests/fixtures.py

@@ -63,73 +63,56 @@ def sample_project(tmp_path):
 # sdist and wheel artifacts should be stable across a round of tests
 # so we can build them once per session and use the files as "readonly"
 
+# In the case of setuptools, building the wheel without sdist may cause
+# it to contain the `build` directory, and therefore create situations with
+# `setuptools/build/lib/build/lib/...`. To avoid that, build both artifacts at once.
 
-@pytest.fixture(scope="session")
-def setuptools_sdist(tmp_path_factory, request):
-    prebuilt = os.getenv("PRE_BUILT_SETUPTOOLS_SDIST")
-    if prebuilt and os.path.exists(prebuilt):  # pragma: no cover
-        return Path(prebuilt).resolve()
 
+def _build_distributions(tmp_path_factory, request):
     with contexts.session_locked_tmp_dir(
-        request, tmp_path_factory, "sdist_build"
+        request, tmp_path_factory, "dist_build"
     ) as tmp:  # pragma: no cover
-        dist = next(tmp.glob("*.tar.gz"), None)
-        if dist:
-            return dist
+        sdist = next(tmp.glob("*.tar.gz"), None)
+        wheel = next(tmp.glob("*.whl"), None)
+        if sdist and wheel:
+            return (sdist, wheel)
 
-        # Sanity check
-        # Building should not create recursive `setuptools/build/lib/build/lib/...`
+        # Sanity check: should not create recursive setuptools/build/lib/build/lib/...
         assert not Path(request.config.rootdir, "build/lib/build").exists()
 
         subprocess.check_output([
             sys.executable,
             "-m",
             "build",
-            "--sdist",
             "--outdir",
             str(tmp),
             str(request.config.rootdir),
         ])
 
-        # Sanity check
-        # Building should not create recursive `setuptools/build/lib/build/lib/...`
+        # Sanity check: should not create recursive setuptools/build/lib/build/lib/...
         assert not Path(request.config.rootdir, "build/lib/build").exists()
 
-        return next(tmp.glob("*.tar.gz"))
+        return next(tmp.glob("*.tar.gz")), next(tmp.glob("*.whl"))
 
 
 @pytest.fixture(scope="session")
-def setuptools_wheel(tmp_path_factory, request):
-    prebuilt = os.getenv("PRE_BUILT_SETUPTOOLS_WHEEL")
+def setuptools_sdist(tmp_path_factory, request):
+    prebuilt = os.getenv("PRE_BUILT_SETUPTOOLS_SDIST")
     if prebuilt and os.path.exists(prebuilt):  # pragma: no cover
         return Path(prebuilt).resolve()
 
-    with contexts.session_locked_tmp_dir(
-        request, tmp_path_factory, "wheel_build"
-    ) as tmp:  # pragma: no cover
-        dist = next(tmp.glob("*.whl"), None)
-        if dist:
-            return dist
+    sdist, _ = _build_distributions(tmp_path_factory, request)
+    return sdist
 
-        # Sanity check
-        # Building should not create recursive `setuptools/build/lib/build/lib/...`
-        assert not Path(request.config.rootdir, "build/lib/build").exists()
 
-        subprocess.check_output([
-            sys.executable,
-            "-m",
-            "build",
-            "--wheel",
-            "--outdir",
-            str(tmp),
-            str(request.config.rootdir),
-        ])
-
-        # Sanity check
-        # Building should not create recursive `setuptools/build/lib/build/lib/...`
-        assert not Path(request.config.rootdir, "build/lib/build").exists()
+@pytest.fixture(scope="session")
+def setuptools_wheel(tmp_path_factory, request):
+    prebuilt = os.getenv("PRE_BUILT_SETUPTOOLS_WHEEL")
+    if prebuilt and os.path.exists(prebuilt):  # pragma: no cover
+        return Path(prebuilt).resolve()
 
-        return next(tmp.glob("*.whl"))
+    _, wheel = _build_distributions(tmp_path_factory, request)
+    return wheel
 
 
 @pytest.fixture