Improve interop with importlib.metadata: variation without importlib_metadata

src/pyproject_hooks/_in_process/_in_process.py

@@ -106,6 +106,15 @@ def find_spec(self, fullname, _path, _target=None):
 
         return spec
 
+    if sys.version_info >= (3, 8):
+
+        def find_distributions(self, context=None):
+            # Delayed import: Python 3.7 does not contain importlib.metadata
+            from importlib.metadata import DistributionFinder, MetadataPathFinder
+
+            context = DistributionFinder.Context(path=self.backend_path)
+            return MetadataPathFinder.find_distributions(context=context)
+
 
 def _supported_features():
     """Return the list of options features supported by the backend.

tests/samples/pkg_intree_metadata/backend/_test_boostrap-0.0.1.dist-info/METADATA

@@ -0,0 +1,2 @@
+Name: _test_bootstrap
+Version: 0.0.1

tests/samples/pkg_intree_metadata/backend/_test_boostrap-0.0.1.dist-info/entry_points.txt

@@ -0,0 +1,2 @@
+[_test_backend.importlib_metadata]
+hello = world

tests/samples/pkg_intree_metadata/backend/intree_backend.py

@@ -0,0 +1,7 @@
+from importlib.metadata import distribution
+
+
+def get_requires_for_build_sdist(config_settings):
+    dist = distribution("_test_bootstrap")  # discovered in backend-path
+    ep = next(iter(dist.entry_points))
+    return [ep.group, ep.name, ep.value]

tests/samples/pkg_intree_metadata/pyproject.toml

@@ -0,0 +1,3 @@
+[build-system]
+build-backend = 'intree_backend'
+backend-path = ['backend']

tests/test_inplace_hooks.py

@@ -89,6 +89,17 @@ def test_intree_backend_loaded_from_correct_backend_path():
     assert res == ["intree_backend_called"]
 
 
+def test_intree_backend_importlib_metadata_interoperation():
+    pytest.importorskip("importlib.metadata")
+
+    hooks = get_hooks("pkg_intree_metadata", backend="intree_backend")
+    assert hooks.get_requires_for_build_sdist({}) == [
+        "_test_backend.importlib_metadata",
+        "hello",
+        "world",
+    ]
+
+
 def install_finder_with_sitecustomize(directory, mapping):
     finder = f"""
         import sys