Add extra paths to the pth file

Author: vyasr

src/scikit_build_core/build/wheel.py

@@ -325,9 +325,19 @@ def _build_wheel_impl(
                     f"_{normalized_name}_editable.py",
                     editable_txt.encode("utf-8"),
                 )
+                # Support Cython by adding the source directory directly to the path.
+                # This is necessary because Cython does not support sys.meta_path for
+                # cimports (as of 3.0.5).
+                pth_import_paths = (
+                    f"import _{normalized_name}_editable\n"
+                    + "\n".join(
+                        os.fspath(Path(pkg).parent.resolve()) for pkg in packages
+                    )
+                    + "\n"
+                )
                 wheel.writestr(
                     f"_{normalized_name}_editable.pth",
-                    f"import _{normalized_name}_editable\n".encode(),
+                    pth_import_paths.encode(),
                 )
 
     if metadata_directory is not None: