🐛 fix(frontend): clear stale fallback metadata

docs/changelog.d/+fallback-stale-metadata.bugfix.rst

@@ -0,0 +1 @@
+Clear stale files from reused ``.dist-info`` directories when building wheel or editable metadata.

src/pyproject_api/_frontend.py

@@ -499,9 +499,15 @@ def metadata_from_built(
             with ZipFile(str(wheel), "r") as zip_file:
                 for name in zip_file.namelist():  # pragma: no branch
                     root = Path(name).parts[0]
-                    if root.endswith(".dist-info"):
-                        basename = root
-                        zip_file.extract(name, extract_to)
+                    if not root.endswith(".dist-info"):
+                        continue
+                    if basename is None:
+                        destination: Final[Path] = metadata_directory / root
+                        if destination.is_symlink():  # pragma: win32 no cover
+                            destination.unlink()
+                        ensure_empty_dir(destination)
+                    basename = root
+                    zip_file.extract(name, extract_to)
         if basename is None:  # pragma: no branch
             msg = f"no .dist-info found inside generated wheel {wheel}"
             raise RuntimeError(msg)

tests/test_frontend.py

@@ -610,6 +610,43 @@ def test_metadata_from_built_wheel(
     assert not err
 
 
+@pytest.mark.parametrize("target", [pytest.param("wheel", id="wheel"), pytest.param("editable", id="editable")])
+def test_metadata_from_built_removes_stale_files(
+    demo_pkg_inline: Path, tmp_path: Path, target: Literal["wheel", "editable"]
+) -> None:
+    metadata: Final[Path] = tmp_path / "demo_pkg_inline-1.0.0.dist-info"
+    metadata.mkdir()
+    (metadata / "entry_points.txt").write_text("obsolete entry points")
+    (tmp_path / "unrelated.txt").write_text("keep")
+
+    metadata_path: Final[Path] = SubprocessFrontend(
+        *SubprocessFrontend.create_args_from_folder(demo_pkg_inline)[:-1]
+    ).metadata_from_built(tmp_path, target)[0]
+
+    assert {entry.name for entry in metadata_path.iterdir()} == {"top_level.txt", "WHEEL", "RECORD", "METADATA"}
+    assert (tmp_path / "unrelated.txt").read_text() == "keep"
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="Creating symlinks requires privileges")
+def test_metadata_from_built_replaces_directory_symlink(
+    demo_pkg_inline: Path, tmp_path: Path
+) -> None:  # pragma: win32 no cover
+    external: Final[Path] = tmp_path / "external"
+    external.mkdir()
+    (external / "keep.txt").write_text("keep")
+    output: Final[Path] = tmp_path / "metadata"
+    output.mkdir()
+    (output / "demo_pkg_inline-1.0.0.dist-info").symlink_to(external, target_is_directory=True)
+
+    metadata_path: Final[Path] = SubprocessFrontend(
+        *SubprocessFrontend.create_args_from_folder(demo_pkg_inline)[:-1]
+    ).metadata_from_built(output, "wheel")[0]
+
+    assert not metadata_path.is_symlink()
+    assert (metadata_path / "METADATA").is_file()
+    assert {entry.name: entry.read_text() for entry in external.iterdir()} == {"keep.txt": "keep"}
+
+
 def test_bad_wheel_metadata_from_built_wheel(local_builder: Callable[[str], Path]) -> None:
     txt = """
     import sys