Disable caching when evaluating expressions in marks (#7373)

changelog/7360.bugfix.rst

@@ -0,0 +1,2 @@
+Fix possibly incorrect evaluation of string expressions passed to ``pytest.mark.skipif`` and ``pytest.mark.xfail``,
+in rare circumstances where the exact same string is used but refers to different global values.

src/_pytest/mark/evaluate.py

@@ -10,25 +10,14 @@ from typing import Optional
 from ..outcomes import fail
 from ..outcomes import TEST_OUTCOME
 from .structures import Mark
-from _pytest.config import Config
 from _pytest.nodes import Item
-from _pytest.store import StoreKey
 
 
-evalcache_key = StoreKey[Dict[str, Any]]()
-
-
-def cached_eval(config: Config, expr: str, d: Dict[str, object]) -> Any:
-    default = {}  # type: Dict[str, object]
-    evalcache = config._store.setdefault(evalcache_key, default)
-    try:
-        return evalcache[expr]
-    except KeyError:
+def compiled_eval(expr: str, d: Dict[str, object]) -> Any:
     import _pytest._code
 
     exprcode = _pytest._code.compile(expr, mode="eval")
-        evalcache[expr] = x = eval(exprcode, d)
-        return x
+    return eval(exprcode, d)
 
 
 class MarkEvaluator:
@@ -98,7 +87,7 @@ class MarkEvaluator:
                     self.expr = expr
                     if isinstance(expr, str):
                         d = self._getglobals()
-                        result = cached_eval(self.item.config, expr, d)
+                        result = compiled_eval(expr, d)
                     else:
                         if "reason" not in mark.kwargs:
                             # XXX better be checked at collection time

testing/test_mark.py

@@ -706,6 +706,36 @@ class TestFunctional:
         reprec = testdir.inline_run()
         reprec.assertoutcome(skipped=1)
 
+    def test_reevaluate_dynamic_expr(self, testdir):
+        """#7360"""
+        py_file1 = testdir.makepyfile(
+            test_reevaluate_dynamic_expr1="""
+            import pytest
+
+            skip = True
+
+            @pytest.mark.skipif("skip")
+            def test_should_skip():
+                assert True
+        """
+        )
+        py_file2 = testdir.makepyfile(
+            test_reevaluate_dynamic_expr2="""
+            import pytest
+
+            skip = False
+
+            @pytest.mark.skipif("skip")
+            def test_should_not_skip():
+                assert True
+        """
+        )
+
+        file_name1 = os.path.basename(py_file1.strpath)
+        file_name2 = os.path.basename(py_file2.strpath)
+        reprec = testdir.inline_run(file_name1, file_name2)
+        reprec.assertoutcome(passed=1, skipped=1)
+
 
 class TestKeywordSelection:
     def test_select_simple(self, testdir):