Use TYPE_CHECKING instead of False

This allows for e.g. Jedi to infer types (it checks the name).

It was only used to support Python 3.5.0/3.5.1, where this is is not
available in the `typing` module.

Ref: davidhalter/jedi#1472

Put at the top to work around circular import.

Author: blueyed

.coveragerc

@@ -24,3 +24,5 @@ exclude_lines =
     \#\s*pragma: no cover
     ^\s*raise NotImplementedError\b
     ^\s*return NotImplemented\b
+
+    ^\s*if TYPE_CHECKING:

changelog/6435.trivial.rst

@@ -0,0 +1 @@
+Added ``typing_extensions`` as dependency on Python 3.5.1 or lower.

doc/en/conf.py

@@ -19,8 +19,9 @@
 import sys
 
 from _pytest import __version__ as version
+from _pytest.compat import TYPE_CHECKING
 
-if False:  # TYPE_CHECKING
+if TYPE_CHECKING:
     import sphinx.application
 
 

src/_pytest/_code/code.py

@@ -32,8 +32,9 @@
 from _pytest._io.saferepr import safeformat
 from _pytest._io.saferepr import saferepr
 from _pytest.compat import overload
+from _pytest.compat import TYPE_CHECKING
 
-if False:  # TYPE_CHECKING
+if TYPE_CHECKING:
     from typing import Type
     from typing_extensions import Literal
     from weakref import ReferenceType  # noqa: F401

src/_pytest/compat.py

@@ -1,12 +1,18 @@
 """
 python version compatibility code
 """
+import sys  # isort:skip
+
+if sys.version_info < (3, 5, 2):
+    TYPE_CHECKING = False  # type: bool
+else:
+    from typing import TYPE_CHECKING
+
 import functools
 import inspect
 import io
 import os
 import re
-import sys
 from contextlib import contextmanager
 from inspect import Parameter
 from inspect import signature
@@ -28,7 +34,8 @@
 from _pytest.outcomes import fail
 from _pytest.outcomes import TEST_OUTCOME
 
-if False:  # TYPE_CHECKING
+
+if TYPE_CHECKING:
     from typing import Type  # noqa: F401 (used in type string)
 
 

src/_pytest/config/__init__.py

@@ -37,12 +37,13 @@
 from _pytest._code import ExceptionInfo
 from _pytest._code import filter_traceback
 from _pytest.compat import importlib_metadata
+from _pytest.compat import TYPE_CHECKING
 from _pytest.outcomes import fail
 from _pytest.outcomes import Skipped
 from _pytest.pathlib import Path
 from _pytest.warning_types import PytestConfigWarning
 
-if False:  # TYPE_CHECKING
+if TYPE_CHECKING:
     from typing import Type
 
     from .argparsing import Argument

src/_pytest/config/argparsing.py

@@ -15,9 +15,10 @@
 
 import py
 
+from _pytest.compat import TYPE_CHECKING
 from _pytest.config.exceptions import UsageError
 
-if False:  # TYPE_CHECKING
+if TYPE_CHECKING:
     from typing import NoReturn
     from typing_extensions import Literal  # noqa: F401
 

src/_pytest/config/findpaths.py

@@ -5,9 +5,10 @@
 import py
 
 from .exceptions import UsageError
+from _pytest.compat import TYPE_CHECKING
 from _pytest.outcomes import fail
 
-if False:
+if TYPE_CHECKING:
     from . import Config  # noqa: F401
 
 

src/_pytest/doctest.py

@@ -19,12 +19,13 @@
 from _pytest._code.code import ReprFileLocation
 from _pytest._code.code import TerminalRepr
 from _pytest.compat import safe_getattr
+from _pytest.compat import TYPE_CHECKING
 from _pytest.fixtures import FixtureRequest
 from _pytest.outcomes import Skipped
 from _pytest.python_api import approx
 from _pytest.warning_types import PytestWarning
 
-if False:  # TYPE_CHECKING
+if TYPE_CHECKING:
     import doctest
     from typing import Type
 

src/_pytest/fixtures.py

@@ -27,12 +27,13 @@
 from _pytest.compat import is_generator
 from _pytest.compat import NOTSET
 from _pytest.compat import safe_getattr
+from _pytest.compat import TYPE_CHECKING
 from _pytest.deprecated import FIXTURE_POSITIONAL_ARGUMENTS
 from _pytest.deprecated import FUNCARGNAMES
 from _pytest.outcomes import fail
 from _pytest.outcomes import TEST_OUTCOME
 
-if False:  # TYPE_CHECKING
+if TYPE_CHECKING:
     from typing import Type
 
     from _pytest import nodes