Add `pytest_markeval_namespace` hook.

Add a new hook , `pytest_markeval_namespace` which should return a dictionary.
This dictionary will be used to augment the "global" variables available to evaluate skipif/xfail/xpass markers.

Pseudo example

``conftest.py``:

.. code-block:: python
   def pytest_markeval_namespace():
       return {"color": "red"}
``test_func.py``:

.. code-block:: python
   @pytest.mark.skipif("color == 'blue'", reason="Color is not red")
   def test_func():
       assert False

1 files changed, 158 insertions, 0 deletions

diff --git a/testing/test_skipping.py b/testing/test_skipping.py
index cfc0cdbca..fc66eb18e 100644
--- a/testing/test_skipping.py
+++ b/testing/test_skipping.py
@@ -1,4 +1,5 @@
 import sys
+import textwrap
 
 import pytest
 from _pytest.pytester import Pytester
@@ -155,6 +156,136 @@ class TestEvaluation:
         assert skipped
         assert skipped.reason == "condition: config._hackxyz"
 
+    def test_skipif_markeval_namespace(self, pytester: Pytester) -> None:
+        pytester.makeconftest(
+            """
+            import pytest
+
+            def pytest_markeval_namespace():
+                return {"color": "green"}
+            """
+        )
+        p = pytester.makepyfile(
+            """
+            import pytest
+
+            @pytest.mark.skipif("color == 'green'")
+            def test_1():
+                assert True
+
+            @pytest.mark.skipif("color == 'red'")
+            def test_2():
+                assert True
+        """
+        )
+        res = pytester.runpytest(p)
+        assert res.ret == 0
+        res.stdout.fnmatch_lines(["*1 skipped*"])
+        res.stdout.fnmatch_lines(["*1 passed*"])
+
+    def test_skipif_markeval_namespace_multiple(self, pytester: Pytester) -> None:
+        """Keys defined by ``pytest_markeval_namespace()`` in nested plugins override top-level ones."""
+        root = pytester.mkdir("root")
+        root.joinpath("__init__.py").touch()
+        root.joinpath("conftest.py").write_text(
+            textwrap.dedent(
+                """\
+            import pytest
+
+            def pytest_markeval_namespace():
+                return {"arg": "root"}
+            """
+            )
+        )
+        root.joinpath("test_root.py").write_text(
+            textwrap.dedent(
+                """\
+            import pytest
+
+            @pytest.mark.skipif("arg == 'root'")
+            def test_root():
+                assert False
+            """
+            )
+        )
+        foo = root.joinpath("foo")
+        foo.mkdir()
+        foo.joinpath("__init__.py").touch()
+        foo.joinpath("conftest.py").write_text(
+            textwrap.dedent(
+                """\
+            import pytest
+
+            def pytest_markeval_namespace():
+                return {"arg": "foo"}
+            """
+            )
+        )
+        foo.joinpath("test_foo.py").write_text(
+            textwrap.dedent(
+                """\
+            import pytest
+
+            @pytest.mark.skipif("arg == 'foo'")
+            def test_foo():
+                assert False
+            """
+            )
+        )
+        bar = root.joinpath("bar")
+        bar.mkdir()
+        bar.joinpath("__init__.py").touch()
+        bar.joinpath("conftest.py").write_text(
+            textwrap.dedent(
+                """\
+            import pytest
+
+            def pytest_markeval_namespace():
+                return {"arg": "bar"}
+            """
+            )
+        )
+        bar.joinpath("test_bar.py").write_text(
+            textwrap.dedent(
+                """\
+            import pytest
+
+            @pytest.mark.skipif("arg == 'bar'")
+            def test_bar():
+                assert False
+            """
+            )
+        )
+
+        reprec = pytester.inline_run("-vs", "--capture=no")
+        reprec.assertoutcome(skipped=3)
+
+    def test_skipif_markeval_namespace_ValueError(self, pytester: Pytester) -> None:
+        pytester.makeconftest(
+            """
+            import pytest
+
+            def pytest_markeval_namespace():
+                return True
+            """
+        )
+        p = pytester.makepyfile(
+            """
+            import pytest
+
+            @pytest.mark.skipif("color == 'green'")
+            def test_1():
+                assert True
+        """
+        )
+        res = pytester.runpytest(p)
+        assert res.ret == 1
+        res.stdout.fnmatch_lines(
+            [
+                "*ValueError: pytest_markeval_namespace() needs to return a dict, got True*"
+            ]
+        )
+
 
 class TestXFail:
     @pytest.mark.parametrize("strict", [True, False])
@@ -577,6 +708,33 @@ class TestXFail:
         result.stdout.fnmatch_lines(["*1 failed*" if strict else "*1 xpassed*"])
         assert result.ret == (1 if strict else 0)
 
+    def test_xfail_markeval_namespace(self, pytester: Pytester) -> None:
+        pytester.makeconftest(
+            """
+            import pytest
+
+            def pytest_markeval_namespace():
+                return {"color": "green"}
+            """
+        )
+        p = pytester.makepyfile(
+            """
+            import pytest
+
+            @pytest.mark.xfail("color == 'green'")
+            def test_1():
+                assert False
+
+            @pytest.mark.xfail("color == 'red'")
+            def test_2():
+                assert False
+        """
+        )
+        res = pytester.runpytest(p)
+        assert res.ret == 1
+        res.stdout.fnmatch_lines(["*1 failed*"])
+        res.stdout.fnmatch_lines(["*1 xfailed*"])
+
 
 class TestXFailwithSetupTeardown:
     def test_failing_setup_issue9(self, pytester: Pytester) -> None: