Mark local install as xfail

src/pip/_internal/resolution/resolvelib/candidates.py

@@ -405,6 +405,8 @@ class ExtrasCandidate(Candidate):
         ]
         # Add a dependency on the exact base.
         # (See note 2b in the class docstring)
+        # FIXME: This does not work if the base candidate is specified by
+        # link, e.g. "pip install .[dev]" will fail.
         spec = "{}=={}".format(self.base.name, self.base.version)
         deps.append(factory.make_requirement_from_spec(spec, self.base._ireq))
         return deps

tests/functional/test_new_resolver.py

@@ -573,7 +573,13 @@ class TestExtraMerge(object):
 
     @pytest.mark.parametrize(
         "pkg_builder",
-        [_local_with_setup, _direct_wheel, _wheel_from_index],
+        [
+            pytest.param(
+                _local_with_setup, marks=pytest.mark.xfail(strict=True),
+            ),
+            _direct_wheel,
+            _wheel_from_index,
+        ],
     )
     def test_new_resolver_extra_merge_in_package(
         self, monkeypatch, script, pkg_builder,