Add broken NoReturn check

Author: cdce8p

ChangeLog

@@ -33,6 +33,7 @@ Release date: TBA
 * Properly identify parameters with no documentation and add new message called ``missing-any-param-doc``
 
   Closes #3799
+
 * Add checkers ``overridden-final-method`` & ``subclassed-final-class``
 
   Closes #3197
@@ -182,6 +183,15 @@ Release date: TBA
 
 * Make yn validator case insensitive, to allow for ``True`` and ``False`` in config files.
 
+* ``TypingChecker``
+
+  * Fix false-negative for ``deprecated-typing-alias`` and ``consider-using-alias``
+    with ``typing.Type`` + ``typing.Callable``.
+
+  * Added new check ``broken-noreturn`` to detect broken uses of ``typing.NoReturn``
+    if ``py-version`` is set to Python ``3.7.1`` or below.
+    https://bugs.python.org/issue34921
+
 
 What's New in Pylint 2.11.2?
 ============================
@@ -260,11 +270,6 @@ Release date: TBA
   Closes #3507
   Closes #5087
 
-* ``TypingChecker``
-
-  * Fix false-negative for ``deprecated-typing-alias`` and ``consider-using-alias``
-    with ``typing.Type`` + ``typing.Callable``.
-
 
 What's New in Pylint 2.11.1?
 ============================

doc/whatsnew/2.12.rst

@@ -69,6 +69,7 @@ Removed checkers
 
 Extensions
 ==========
+
 * Added an optional extension ``consider-using-any-or-all``: Emitted when a ``for`` loop only
   produces a boolean and could be replaced by ``any`` or ``all`` using a generator. Also suggests
   a suitable any/all statement if it is concise.
@@ -81,6 +82,15 @@ Extensions
 
   Closes #1064
 
+* ``TypingChecker``
+
+  * Fix false-negative for ``deprecated-typing-alias`` and ``consider-using-alias``
+    with ``typing.Type`` + ``typing.Callable``.
+
+  * Added new check ``broken-noreturn`` to detect broken uses of ``typing.NoReturn``
+    if ``py-version`` is set to Python ``3.7.1`` or below.
+    https://bugs.python.org/issue34921
+
 Other Changes
 =============
 

pylint/extensions/typing.py

@@ -66,6 +66,12 @@ class TypingAlias(NamedTuple):
 
 ALIAS_NAMES = frozenset(key.split(".")[1] for key in DEPRECATED_TYPING_ALIASES)
 UNION_NAMES = ("Optional", "Union")
+TYPING_NORETURN = frozenset(
+    (
+        "typing.NoReturn",
+        "typing_extensions.NoReturn",
+    )
+)
 
 
 class DeprecatedTypingAliasMsg(NamedTuple):
@@ -101,6 +107,14 @@ class TypingChecker(BaseChecker):
             "Emitted when 'typing.Union' or 'typing.Optional' is used "
             "instead of the alternative Union syntax 'int | None'.",
         ),
+        "E6004": (
+            "'NoReturn' inside compound types is broken in 3.7.0 / 3.7.1",
+            "broken-noreturn",
+            "``typing.NoReturn`` inside compound types is broken in "
+            "Python 3.7.0 and 3.7.1. If not dependend on runtime introspection, "
+            "use string annotation instead. E.g. "
+            "``Callable[..., 'NoReturn']``. https://bugs.python.org/issue34921",
+        ),
     }
     options = (
         (
@@ -151,6 +165,8 @@ def open(self) -> None:
             self._py37_plus and self.config.runtime_typing is False
         )
 
+        self._should_check_noreturn = py_version < (3, 7, 2)
+
     def _msg_postponed_eval_hint(self, node) -> str:
         """Message hint if postponed evaluation isn't enabled."""
         if self._py310_plus or "annotations" in node.root().future_imports:
@@ -161,23 +177,29 @@ def _msg_postponed_eval_hint(self, node) -> str:
         "deprecated-typing-alias",
         "consider-using-alias",
         "consider-alternative-union-syntax",
+        "broken-noreturn",
     )
     def visit_name(self, node: nodes.Name) -> None:
         if self._should_check_typing_alias and node.name in ALIAS_NAMES:
             self._check_for_typing_alias(node)
         if self._should_check_alternative_union_syntax and node.name in UNION_NAMES:
             self._check_for_alternative_union_syntax(node, node.name)
+        if self._should_check_noreturn and node.name == "NoReturn":
+            self._check_broken_noreturn(node)
 
     @check_messages(
         "deprecated-typing-alias",
         "consider-using-alias",
         "consider-alternative-union-syntax",
+        "broken-noreturn",
     )
     def visit_attribute(self, node: nodes.Attribute) -> None:
         if self._should_check_typing_alias and node.attrname in ALIAS_NAMES:
             self._check_for_typing_alias(node)
         if self._should_check_alternative_union_syntax and node.attrname in UNION_NAMES:
             self._check_for_alternative_union_syntax(node, node.attrname)
+        if self._should_check_noreturn and node.attrname == "NoReturn":
+            self._check_broken_noreturn(node)
 
     def _check_for_alternative_union_syntax(
         self,
@@ -281,6 +303,17 @@ def leave_module(self, node: nodes.Module) -> None:
         self._alias_name_collisions.clear()
         self._consider_using_alias_msgs.clear()
 
+    def _check_broken_noreturn(self, node: Union[nodes.Name, nodes.Attribute]) -> None:
+        """Check for 'NoReturn' inside compound types."""
+        for inferred in node.infer():
+            if (
+                isinstance(inferred, (nodes.FunctionDef, nodes.ClassDef))
+                and inferred.qname() in TYPING_NORETURN
+                and isinstance(node.parent, nodes.BaseContainer)
+            ):
+                self.add_message("broken-noreturn", node=node)
+                break
+
 
 def register(linter: PyLinter) -> None:
     linter.register_checker(TypingChecker(linter))

tests/functional/ext/typing/typing_broken_noreturn.py

@@ -0,0 +1,38 @@
+"""
+'typing.NoReturn' is broken inside compond types for Python 3.7.0
+https://bugs.python.org/issue34921
+
+If no runtime introspection is required, use string annotations instead.
+"""
+# pylint: disable=missing-docstring
+import sys
+import typing
+from typing import Callable, Union
+
+import typing_extensions
+
+if sys.version_info >= (3, 6, 2):
+    from typing import NoReturn
+else:
+    from typing_extensions import NoReturn
+
+
+def func1() -> NoReturn:
+    raise Exception
+
+def func2() -> Union[None, NoReturn]:  # [broken-noreturn]
+    pass
+
+def func3() -> Union[None, "NoReturn"]:
+    pass
+
+def func4() -> Union[None, typing.NoReturn]:  # [broken-noreturn]
+    pass
+
+def func5() -> Union[None, typing_extensions.NoReturn]:  # [broken-noreturn]
+    pass
+
+
+Alias1 = NoReturn
+Alias2 = Callable[..., NoReturn]  # [broken-noreturn]
+Alias3 = Callable[..., "NoReturn"]

tests/functional/ext/typing/typing_broken_noreturn.rc

@@ -0,0 +1,6 @@
+[master]
+py-version=3.7
+load-plugins=pylint.extensions.typing
+
+[testoptions]
+min_pyver=3.7

tests/functional/ext/typing/typing_broken_noreturn.txt

@@ -0,0 +1,4 @@
+broken-noreturn:23:27:func2:'NoReturn' inside compound types is broken in 3.7.0 / 3.7.1
+broken-noreturn:29:27:func4:'NoReturn' inside compound types is broken in 3.7.0 / 3.7.1
+broken-noreturn:32:27:func5:'NoReturn' inside compound types is broken in 3.7.0 / 3.7.1
+broken-noreturn:37:23::'NoReturn' inside compound types is broken in 3.7.0 / 3.7.1