Deprecate raises(..., 'code(as_a_string)') / `warns(..., 'code(as_a_string)')

src/_pytest/deprecated.py

@@ -92,6 +92,15 @@ NODE_WARN = RemovedInPytest4Warning(
     "Node.warn(code, message) form has been deprecated, use Node.warn(warning_instance) instead."
 )
 
+RAISES_EXEC = PytestDeprecationWarning(
+    "raises(..., 'code(as_a_string)') is deprecated, use the context manager form or use `exec()` directly\n\n"
+    "See https://docs.pytest.org/en/latest/deprecations.html#raises-warns-exec"
+)
+WARNS_EXEC = PytestDeprecationWarning(
+    "warns(..., 'code(as_a_string)') is deprecated, use the context manager form or use `exec()` directly.\n\n"
+    "See https://docs.pytest.org/en/latest/deprecations.html#raises-warns-exec"
+)
+
 RECORD_XML_PROPERTY = RemovedInPytest4Warning(
     'Fixture renamed from "record_xml_property" to "record_property" as user '
     "properties are now available to all reporters.\n"

src/_pytest/python_api.py

@@ -1,6 +1,9 @@
+from __future__ import absolute_import
+
 import math
 import pprint
 import sys
+import warnings
 from decimal import Decimal
 from numbers import Number
 
@@ -14,6 +17,7 @@ from _pytest.compat import isclass
 from _pytest.compat import Mapping
 from _pytest.compat import Sequence
 from _pytest.compat import STRING_TYPES
+from _pytest.deprecated import RAISES_EXEC
 from _pytest.outcomes import fail
 
 BASE_TYPE = (type, STRING_TYPES)
@@ -604,9 +608,9 @@ def raises(expected_exception, *args, **kwargs):
         >>> with raises(ValueError, match=r'must be \d+$'):
         ...     raise ValueError("value must be 42")
 
-    **Legacy forms**
+    **Legacy form**
 
-    The forms below are fully supported but are discouraged for new code because the
+    The form below is fully supported but discouraged for new code because the
     context manager form is regarded as more readable and less error-prone.
 
     It is possible to specify a callable by passing a to-be-called lambda::
@@ -623,14 +627,6 @@ def raises(expected_exception, *args, **kwargs):
         >>> raises(ZeroDivisionError, f, x=0)
         <ExceptionInfo ...>
 
-    It is also possible to pass a string to be evaluated at runtime::
-
-        >>> raises(ZeroDivisionError, "f(0)")
-        <ExceptionInfo ...>
-
-    The string will be evaluated using the same ``locals()`` and ``globals()``
-    at the moment of the ``raises`` call.
-
     .. currentmodule:: _pytest._code
 
     Consult the API of ``excinfo`` objects: :class:`ExceptionInfo`.
@@ -672,6 +668,7 @@ def raises(expected_exception, *args, **kwargs):
             raise TypeError(msg)
         return RaisesContext(expected_exception, message, match_expr)
     elif isinstance(args[0], str):
+        warnings.warn(RAISES_EXEC, stacklevel=2)
         code, = args
         assert isinstance(code, str)
         frame = sys._getframe(1)

src/_pytest/recwarn.py

@@ -11,6 +11,7 @@ import warnings
 import six
 
 import _pytest._code
+from _pytest.deprecated import WARNS_EXEC
 from _pytest.fixtures import yield_fixture
 from _pytest.outcomes import fail
 
@@ -89,6 +90,7 @@ def warns(expected_warning, *args, **kwargs):
             match_expr = kwargs.pop("match")
         return WarningsChecker(expected_warning, match_expr=match_expr)
     elif isinstance(args[0], str):
+        warnings.warn(WARNS_EXEC, stacklevel=2)
         code, = args
         assert isinstance(code, str)
         frame = sys._getframe(1)