[sys] Add the 3.14 _jit 'module' (#15692)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Author: lambda-abstraction

stdlib/@tests/stubtest_allowlists/py314.txt

@@ -132,6 +132,7 @@ importlib.metadata.DeprecatedNonAbstract.__new__
 importlib.resources._common.files
 
 sys._monitoring  # Doesn't really exist. See comments in the stub.
+sys.__jit        # Similar to sys._monitoring
 sys.last_exc  # not always defined
 
 # These only exist to give a better error message if you try to subclass an instance

stdlib/@tests/test_cases/sys/check_jit.py

@@ -0,0 +1,12 @@
+import sys
+from typing_extensions import assert_type
+
+if sys.version_info >= (3, 14):
+    assert_type(sys._jit.is_available(), bool)
+    assert_type(sys._jit.is_enabled(), bool)
+    assert_type(sys._jit.is_active(), bool)
+
+    def sys_is_not_a_package() -> None:
+        # This has to be put into a function, because otherwise the presence
+        # of this import statement causes errors on the above usages of `sys._jit`.
+        import sys._jit  # type: ignore

stdlib/VERSIONS

@@ -295,6 +295,7 @@ sunau: 3.0-3.12
 symbol: 3.0-3.9
 symtable: 3.0-
 sys: 3.0-
+sys.__jit: 3.14-        # Similar to sys._monitoring
 sys._monitoring: 3.12-  # Doesn't actually exist. See comments in the stub.
 sysconfig: 3.0-
 syslog: 3.0-

stdlib/sys/__init__.pyi

@@ -518,3 +518,7 @@ if sys.version_info >= (3, 14):
     def is_remote_debug_enabled() -> bool: ...
     def remote_exec(pid: int, script: StrOrBytesPath) -> None: ...
     def _is_immortal(op: object, /) -> bool: ...
+
+    from . import __jit
+
+    _jit = __jit

stdlib/sys/__jit.pyi

@@ -0,0 +1,11 @@
+# This py314+ module provides annotations for `sys._jit`.
+# It's named `sys.__jit` in typeshed,
+# because trying to import `sys._jit` will fail at runtime!
+# At runtime, `sys._jit` has the unusual status
+# of being a `types.ModuleType` instance that cannot be directly imported,
+# (same as sys.monitoring)
+# and exists in the `sys`-module namespace despite `sys` not being a package.
+
+def is_available() -> bool: ...
+def is_enabled() -> bool: ...
+def is_active() -> bool: ...

stdlib/sys/_monitoring.pyi

@@ -1,8 +1,9 @@
 # This py312+ module provides annotations for `sys.monitoring`.
 # It's named `sys._monitoring` in typeshed,
 # because trying to import `sys.monitoring` will fail at runtime!
-# At runtime, `sys.monitoring` has the unique status
+# At runtime, `sys.monitoring` has the unusual status
 # of being a `types.ModuleType` instance that cannot be directly imported,
+# (same as sys._jit)
 # and exists in the `sys`-module namespace despite `sys` not being a package.
 
 import sys