Add public API function pytest.match_markexpr for marker expression evaluation

- Introduced match_markexpr to match marker expressions against markers or pytest Items.
- Updated documentation to reflect the new function.
- Added comprehensive tests to ensure functionality and error handling.

Closes #13737

Author: gomri15

changelog/13759.feature.rst

@@ -0,0 +1,3 @@
+Added public API function `pytest.match_markexpr` to match marker expressions against a set of markers or a pytest Item.
+This function is useful for plugins and test code that need to evaluate marker expressions without relying on internal APIs.
+Insuring that the public API is properly tested and documented.

doc/en/how-to/mark.rst

@@ -91,3 +91,27 @@ enforce this validation in your project by adding ``--strict-markers`` to ``addo
     markers =
         slow: marks tests as slow (deselect with '-m "not slow"')
         serial
+
+
+Check if marks match an expression
+----------------------------------
+
+You can check if a set of marks or a pytest Item matches a marker expression
+using the public API function :func:`pytest.match_markexpr`.
+
+.. code-block:: python
+
+    import pytest
+
+
+    def test_example():
+        item = ...  # some pytest Item
+        assert pytest.match_markexpr("smoke and not slow", item)
+
+
+    def test_example2():
+        marks = ["smoke", "fast"]
+        assert pytest.match_markexpr("smoke and not slow", marks)
+
+This function is useful for plugins and test code that need to evaluate marker expressions
+without relying on internal APIs.

src/_pytest/mark/__init__.py

@@ -41,6 +41,7 @@
     "MarkGenerator",
     "ParameterSet",
     "get_empty_parameterset_mark",
+    "match_markexpr",
 ]
 
 
@@ -298,3 +299,28 @@ def pytest_configure(config: Config) -> None:
 
 def pytest_unconfigure(config: Config) -> None:
     MARK_GEN._config = config.stash.get(old_mark_config_key, None)
+
+
+def match_markexpr(expr: str, mark: str | Iterable[str] | object) -> bool:
+    try:
+        compiled = Expression.compile(expr)
+    except ParseError as e:
+        raise e
+
+    # Build an iterable of Mark objects for the matcher
+    if isinstance(mark, object) and hasattr(mark, "iter_markers"):
+        markers_iter = mark.iter_markers()
+    elif isinstance(mark, str):
+        markers_iter = (Mark(mark, (), {}, _ispytest=True),)
+    elif isinstance(mark, Iterable) and not isinstance(mark, (str, bytes, bytearray)):
+        markers_iter = (Mark(name, (), {}, _ispytest=True) for name in mark)
+
+    else:
+        raise UsageError(
+            "target must be an Item-like object, a marker name string, "
+            "or an iterable of marker names"
+        )
+
+    # MarkMatcher is defined in this module (_pytest.mark)
+    matcher = MarkMatcher.from_markers(markers_iter)
+    return compiled.evaluate(matcher)

src/pytest/__init__.py

@@ -38,6 +38,7 @@
 from _pytest.mark import MARK_GEN as mark
 from _pytest.mark import MarkDecorator
 from _pytest.mark import MarkGenerator
+from _pytest.mark import match_markexpr
 from _pytest.mark import param
 from _pytest.monkeypatch import MonkeyPatch
 from _pytest.nodes import Collector
@@ -170,6 +171,7 @@
     "importorskip",
     "main",
     "mark",
+    "match_markexpr",
     "param",
     "raises",
     "register_assert_rewrite",

testing/test_match_markexpr.py

@@ -0,0 +1,53 @@
+# testing/test_match_markexpr.py
+from __future__ import annotations
+
+from _pytest.config.exceptions import UsageError
+from _pytest.mark.expression import ParseError
+import pytest
+
+
+def test_public_api_present_match_markexpr() -> None:
+    assert hasattr(pytest, "match_markexpr")
+    assert callable(pytest.match_markexpr)
+
+
+def test_strings_markexpr() -> None:
+    assert pytest.match_markexpr("smoke or slow", "slow")
+    assert not pytest.match_markexpr("smoke and slow", "smoke")
+
+
+def test_iterables_markexpr() -> None:
+    assert pytest.match_markexpr("smoke and not slow", ["smoke"])
+    assert not pytest.match_markexpr("smoke and not slow", ["smoke", "slow"])
+    assert pytest.match_markexpr("a and b", ["a", "b"])
+    assert not pytest.match_markexpr("a and b", ["a"])
+
+
+def test_invalid_expression_raises() -> None:
+    with pytest.raises(
+        ParseError, match="expected not OR left parenthesis OR identifier; got and"
+    ):
+        pytest.match_markexpr("smoke and and slow", ["smoke"])
+
+
+def test_type_error_for_unsupported_target() -> None:
+    with pytest.raises(
+        UsageError,
+        match="target must be an Item-like object, a marker name string, or an iterable of marker names",
+    ):
+        pytest.match_markexpr("smoke", 123)
+
+
+def test_item_matching_with_request_node(request: pytest.FixtureRequest) -> None:
+    request.config.addinivalue_line("markers", "smoke: test marker")
+    request.config.addinivalue_line("markers", "slow: test marker")
+
+    # Use the current test item; add/remove marks dynamically.
+    request.node.add_marker("smoke")
+    assert pytest.match_markexpr("smoke and not slow", request.node)
+    assert not pytest.match_markexpr("slow", request.node)
+
+    # Add another mark and re-check
+    request.node.add_marker("slow")
+    assert not pytest.match_markexpr("smoke and not slow", request.node)
+    assert pytest.match_markexpr("smoke and slow", request.node)