Make Node.warn support two forms, new and deprecated

As suggested during review, it now accepts two forms:

Node.warn(warning_instance)  (recommended)

Node.warn(code, message)  (deprecated)

changelog/2452.removal.rst

@@ -1,5 +1,12 @@
-The functions ``Node.warn`` and ``Config.warn`` have been deprecated. Instead of ``Node.warn`` users should now use
-``Node.std_warn``, while ``Config.warn`` should be replaced by the standard ``warnings.warn``.
+``Config.warn`` has been deprecated, it should be replaced by calls to the standard ``warnings.warn``.
+
+``Node.warn`` now supports two signatures:
+
+* ``node.warn(PytestWarning("some message"))``: is now the recommended way to call this function. The warning
+  instance must be a ``PytestWarning`` or subclass  instance.
+
+* ``node.warn("CI", "some message")``: this code/message form is now deprecated and should be converted to
+  the warning instance form above.
 
 ``RemovedInPytest4Warning`` and ``PytestExperimentalApiWarning`` are now part of the public API and should be accessed
 using ``pytest.RemovedInPytest4Warning`` and ``pytest.PytestExperimentalApiWarning``.

src/_pytest/deprecated.py

@@ -54,7 +54,7 @@ MARK_PARAMETERSET_UNPACKING = RemovedInPytest4Warning(
 )
 
 NODE_WARN = RemovedInPytest4Warning(
-    "Node.warn has been deprecated, use Node.std_warn instead"
+    "Node.warn(code, message) form has been deprecated, use Node.warn(warning_instance) instead."
 )
 
 RECORD_XML_PROPERTY = RemovedInPytest4Warning(

src/_pytest/junitxml.py

@@ -262,7 +262,7 @@ def record_xml_property(record_property, request):
     """(Deprecated) use record_property."""
     from _pytest import deprecated
 
-    request.node.std_warn(deprecated.RECORD_XML_PROPERTY)
+    request.node.warn(deprecated.RECORD_XML_PROPERTY)
 
     return record_property
 
@@ -275,9 +275,7 @@ def record_xml_attribute(request):
     """
     from _pytest.warning_types import PytestWarning
 
-    request.node.std_warn(
-        PytestWarning("record_xml_attribute is an experimental feature")
-    )
+    request.node.warn(PytestWarning("record_xml_attribute is an experimental feature"))
     xml = getattr(request.config, "_xml", None)
     if xml is not None:
         node_reporter = xml.node_reporter(request.node.nodeid)

src/_pytest/mark/structures.py

@@ -95,7 +95,7 @@ class ParameterSet(namedtuple("ParameterSet", "values, marks, id")):
             argval = (argval,)
 
         if newmarks and belonging_definition is not None:
-            belonging_definition.std_warn(MARK_PARAMETERSET_UNPACKING)
+            belonging_definition.warn(MARK_PARAMETERSET_UNPACKING)
 
         return cls(argval, marks=newmarks, id=None)
 

src/_pytest/nodes.py

@@ -136,7 +136,42 @@ class Node(object):
     def __repr__(self):
         return "<%s %r>" % (self.__class__.__name__, getattr(self, "name", None))
 
-    def warn(self, code, message):
+    def warn(self, code_or_warning, message=None):
+        """Issue a warning for this item.
+
+        Warnings will be displayed after the test session, unless explicitly suppressed.
+
+        This can be called in two forms:
+
+        **Warning instance**
+
+        This was introduced in pytest 3.8 and uses the standard warning mechanism to issue warnings.
+
+        .. code-block:: python
+
+            node.warn(PytestWarning("some message"))
+
+        The warning instance must be a subclass of :class:`pytest.PytestWarning`.
+
+        **code/message (deprecated)**
+
+        This form was used in pytest prior to 3.8 and is considered deprecated. Using this form will emit another
+        warning about the deprecation:
+
+        .. code-block:: python
+
+            node.warn("CI", "some message")
+
+        :param Union[Warning,str] code_or_warning: warning instance or warning code (legacy).
+        :param Union[str,None] message: message to display when called in the legacy form.
+        :return:
+        """
+        if message is None:
+            self._std_warn(code_or_warning)
+        else:
+            self._legacy_warn(code_or_warning, message)
+
+    def _legacy_warn(self, code, message):
         """
         .. deprecated:: 3.8
 
@@ -146,7 +181,7 @@ class Node(object):
         """
         from _pytest.deprecated import NODE_WARN
 
-        self.std_warn(NODE_WARN)
+        self._std_warn(NODE_WARN)
 
         assert isinstance(code, str)
         fslocation = get_fslocation_from_item(self)
@@ -156,7 +191,7 @@ class Node(object):
             )
         )
 
-    def std_warn(self, warning):
+    def _std_warn(self, warning):
         """Issue a warning for this item.
 
         Warnings will be displayed after the test session, unless explicitly suppressed
@@ -175,8 +210,8 @@ class Node(object):
             )
         path, lineno = get_fslocation_from_item(self)
         warnings.warn_explicit(
-            six.text_type(warning),
-            type(warning),
+            warning,
+            category=None,
             filename=str(path),
             lineno=lineno + 1 if lineno is not None else None,
         )

src/_pytest/pytester.py

@@ -126,7 +126,7 @@ class LsofFdLeakChecker(object):
             error.append(error[0])
             error.append("*** function %s:%s: %s " % item.location)
             error.append("See issue #2366")
-            item.std_warn(pytest.PytestWarning("\n".join(error)))
+            item.warn(pytest.PytestWarning("\n".join(error)))
 
 
 # XXX copied from execnet's conftest.py - needs to be merged

src/_pytest/python.py

@@ -659,7 +659,7 @@ class Class(PyCollector):
         if not safe_getattr(self.obj, "__test__", True):
             return []
         if hasinit(self.obj):
-            self.std_warn(
+            self.warn(
                 PytestWarning(
                     "cannot collect test class %r because it has a "
                     "__init__ constructor" % self.obj.__name__
@@ -667,7 +667,7 @@ class Class(PyCollector):
             )
             return []
         elif hasnew(self.obj):
-            self.std_warn(
+            self.warn(
                 PytestWarning(
                     "cannot collect test class %r because it has a "
                     "__new__ constructor" % self.obj.__name__
@@ -799,7 +799,7 @@ class Generator(FunctionMixin, PyCollector):
                 )
             seen[name] = True
             values.append(self.Function(name, self, args=args, callobj=call))
-        self.std_warn(deprecated.YIELD_TESTS)
+        self.warn(deprecated.YIELD_TESTS)
         return values
 
     def getcallargs(self, obj):
@@ -1106,7 +1106,7 @@ class Metafunc(fixtures.FuncargnamesCompatAttr):
             invocation through the ``request.param`` attribute.
         """
         if self.config:
-            self.definition.std_warn(deprecated.METAFUNC_ADD_CALL)
+            self.definition.warn(deprecated.METAFUNC_ADD_CALL)
 
         assert funcargs is None or isinstance(funcargs, dict)
         if funcargs is not None:
@@ -1170,7 +1170,7 @@ def _idval(val, argname, idx, idfn, item, config=None):
             )
             msg += "  {}: {}\n".format(type(e).__name__, e)
             msg += "This warning will be an error error in pytest-4.0."
-            item.std_warn(RemovedInPytest4Warning(msg))
+            item.warn(RemovedInPytest4Warning(msg))
         if s:
             return ascii_escaped(s)
 

testing/test_config.py

@@ -831,7 +831,7 @@ class TestLegacyWarning(object):
             ===*warnings summary*===
             *test_warn_on_test_item_from_request.py::test_hello*
             *hello*
-            *test_warn_on_test_item_from_request.py:7:*Node.warn has been deprecated, use Node.std_warn instead*
+            *test_warn_on_test_item_from_request.py:7:*Node.warn(code, message) form has been deprecated*
         """
         )
 

testing/test_mark.py

@@ -1042,7 +1042,7 @@ class TestKeywordSelection(object):
 @pytest.mark.filterwarnings("ignore")
 def test_parameterset_extractfrom(argval, expected):
     class DummyItem:
-        def std_warn(self, warning):
+        def warn(self, warning):
             pass
 
     extracted = ParameterSet.extract_from(argval, belonging_definition=DummyItem())

testing/test_nodes.py

@@ -29,4 +29,4 @@ def test_std_warn_not_pytestwarning(testdir):
     """
     )
     with pytest.raises(ValueError, match=".*instance of PytestWarning.*"):
-        items[0].std_warn(UserWarning("some warning"))
+        items[0].warn(UserWarning("some warning"))