mark: export pytest.MarkDecorator for typing purposes

The type cannot be constructed directly, but is exported for use in type
annotations, since it is reachable through existing public API.

3 files changed, 25 insertions, 19 deletions

diff --git a/src/_pytest/fixtures.py b/src/_pytest/fixtures.py
index c24ab7069..dbb039bf2 100644
--- a/src/_pytest/fixtures.py
+++ b/src/_pytest/fixtures.py
@@ -551,7 +551,7 @@ class FixtureRequest:
         on all function invocations.
 
         :param marker:
-            A :py:class:`_pytest.mark.MarkDecorator` object created by a call
+            A :class:`pytest.MarkDecorator` object created by a call
             to ``pytest.mark.NAME(...)``.
         """
         self.node.add_marker(marker)
diff --git a/src/_pytest/mark/structures.py b/src/_pytest/mark/structures.py
index 29b958687..8bce33e68 100644
--- a/src/_pytest/mark/structures.py
+++ b/src/_pytest/mark/structures.py
@@ -268,14 +268,14 @@ class Mark:
 # A generic parameter designating an object to which a Mark may
 # be applied -- a test function (callable) or class.
 # Note: a lambda is not allowed, but this can't be represented.
-_Markable = TypeVar("_Markable", bound=Union[Callable[..., object], type])
+Markable = TypeVar("Markable", bound=Union[Callable[..., object], type])
 
 
-@attr.s
+@attr.s(init=False, auto_attribs=True)
 class MarkDecorator:
     """A decorator for applying a mark on test functions and classes.
 
-    MarkDecorators are created with ``pytest.mark``::
+    ``MarkDecorators`` are created with ``pytest.mark``::
 
         mark1 = pytest.mark.NAME              # Simple MarkDecorator
         mark2 = pytest.mark.NAME(name1=value) # Parametrized MarkDecorator
@@ -286,7 +286,7 @@ class MarkDecorator:
         def test_function():
             pass
 
-    When a MarkDecorator is called it does the following:
+    When a ``MarkDecorator`` is called, it does the following:
 
     1. If called with a single class as its only positional argument and no
        additional keyword arguments, it attaches the mark to the class so it
@@ -295,19 +295,24 @@ class MarkDecorator:
     2. If called with a single function as its only positional argument and
        no additional keyword arguments, it attaches the mark to the function,
        containing all the arguments already stored internally in the
-       MarkDecorator.
+       ``MarkDecorator``.
 
-    3. When called in any other case, it returns a new MarkDecorator instance
-       with the original MarkDecorator's content updated with the arguments
-       passed to this call.
+    3. When called in any other case, it returns a new ``MarkDecorator``
+       instance with the original ``MarkDecorator``'s content updated with
+       the arguments passed to this call.
 
-    Note: The rules above prevent MarkDecorators from storing only a single
-    function or class reference as their positional argument with no
+    Note: The rules above prevent a ``MarkDecorator`` from storing only a
+    single function or class reference as its positional argument with no
     additional keyword or positional arguments. You can work around this by
     using `with_args()`.
     """
 
-    mark = attr.ib(type=Mark, validator=attr.validators.instance_of(Mark))
+    mark: Mark
+
+    def __init__(self, mark: Mark, *, _ispytest: bool = False) -> None:
+        """:meta private:"""
+        check_ispytest(_ispytest)
+        self.mark = mark
 
     @property
     def name(self) -> str:
@@ -326,6 +331,7 @@ class MarkDecorator:
 
     @property
     def markname(self) -> str:
+        """:meta private:"""
         return self.name  # for backward-compat (2.4.1 had this attr)
 
     def __repr__(self) -> str:
@@ -336,17 +342,15 @@ class MarkDecorator:
 
         Unlike calling the MarkDecorator, with_args() can be used even
         if the sole argument is a callable/class.
-
-        :rtype: MarkDecorator
         """
         mark = Mark(self.name, args, kwargs, _ispytest=True)
-        return self.__class__(self.mark.combined_with(mark))
+        return MarkDecorator(self.mark.combined_with(mark), _ispytest=True)
 
     # Type ignored because the overloads overlap with an incompatible
     # return type. Not much we can do about that. Thankfully mypy picks
     # the first match so it works out even if we break the rules.
     @overload
-    def __call__(self, arg: _Markable) -> _Markable:  # type: ignore[misc]
+    def __call__(self, arg: Markable) -> Markable:  # type: ignore[misc]
         pass
 
     @overload
@@ -405,7 +409,7 @@ if TYPE_CHECKING:
 
     class _SkipMarkDecorator(MarkDecorator):
         @overload  # type: ignore[override,misc]
-        def __call__(self, arg: _Markable) -> _Markable:
+        def __call__(self, arg: Markable) -> Markable:
             ...
 
         @overload
@@ -423,7 +427,7 @@ if TYPE_CHECKING:
 
     class _XfailMarkDecorator(MarkDecorator):
         @overload  # type: ignore[override,misc]
-        def __call__(self, arg: _Markable) -> _Markable:
+        def __call__(self, arg: Markable) -> Markable:
             ...
 
         @overload
@@ -534,7 +538,7 @@ class MarkGenerator:
                     2,
                 )
 
-        return MarkDecorator(Mark(name, (), {}, _ispytest=True))
+        return MarkDecorator(Mark(name, (), {}, _ispytest=True), _ispytest=True)
 
 
 MARK_GEN = MarkGenerator()
diff --git a/src/pytest/__init__.py b/src/pytest/__init__.py
index 4b194e0c8..1d5b38ee0 100644
--- a/src/pytest/__init__.py
+++ b/src/pytest/__init__.py
@@ -23,6 +23,7 @@ from _pytest.logging import LogCaptureFixture
 from _pytest.main import Session
 from _pytest.mark import Mark
 from _pytest.mark import MARK_GEN as mark
+from _pytest.mark import MarkDecorator
 from _pytest.mark import param
 from _pytest.monkeypatch import MonkeyPatch
 from _pytest.nodes import Collector
@@ -91,6 +92,7 @@ __all__ = [
     "main",
     "mark",
     "Mark",
+    "MarkDecorator",
     "Module",
     "MonkeyPatch",
     "Package",