Sentinel instance is not assignable to `Sentinel` type

[sobolevn]

When I write:

from typing_extensions import Sentinel 

X = Sentinel("X")

def inspect_sentinel(arg: Sentinel) -> None:
    ...

inspect_sentinel(arg=X)

I get:

Argument of type "X" cannot be assigned to parameter "arg" of type "Sentinel" in function "inspect_sentinel"
  "X" is not assignable to "Sentinel"  (reportArgumentType)

But, X is an instance of a Sentinel type. It should be possible to pass any sentinel where Sentinel type is expected. For example: for type inspection, as I do here.

Playground: https://pyright-play.net/?strict=true&locale=en&code=GYJw9gtgBALgngBwJYDsDmB9ApgDxllAZyTCKiQgTBBigGUCZUsAbKAKHYA0oBeexsxYAKAERdRASk4ATLMHJEEWAMYwMhQSlbCAhiDQAuASibaWkqAFoAfFABypLIfZQ3UAHRfOqQsrUaWjr6aLxckkA

[bram-tv]

It appears this got broken in pyright v1.1.410;
Extending your example slightly with reveal_type added:

from typing_extensions import Sentinel

X = Sentinel("X")


def inspect_sentinel(arg: Sentinel) -> None: ...


reveal_type(X)
reveal_type(inspect_sentinel)
inspect_sentinel(arg=X)

Output with pyright v1.1.409:

.../gh-11529.py
  .../gh-11529.py:9:13 - information: Type of "X" is "Sentinel"
  .../gh-11529.py:10:13 - information: Type of "inspect_sentinel" is "(arg: Sentinel) -> None"
0 errors, 0 warnings, 2 informations

Output with pyright v1.1.410 (and v1.1.411):

.../gh-11529.py
  .../gh-11529.py:9:13 - information: Type of "X" is "X"
  .../gh-11529.py:10:13 - information: Type of "inspect_sentinel" is "(arg: Sentinel) -> None"
  .../gh-11529.py:11:22 - error: Argument of type "X" cannot be assigned to parameter "arg" of type "Sentinel" in function "inspect_sentinel"
    "X" is not assignable to "Sentinel" (reportArgumentType)
1 error, 0 warnings, 2 informations

Looking at the list of changes https://github.com/microsoft/pyright/releases/tag/1.1.410 there is not an obvious commit that triggered it.
My best guess it's somewhere in the Push pylance changes to pyright...
(In my opinion that is not a very useful message or even commit, it includes too much in a single commit to be able to narrow down why the behavior changed)

For completness: output of mypy v1.20.2 and mypy v2.1.0:

gh-11529.py:9: note: Revealed type is "typing_extensions.Sentinel"
gh-11529.py:10: note: Revealed type is "def (arg: typing_extensions.Sentinel)"
Success: no issues found in 1 source file

[bram-tv]

I guess this change was made to conform to PEP 661.

Its example contains:

MISSING = sentinel('MISSING')

def foo(value: int | MISSING = MISSING) -> int:
    ...

Note that it uses: int | MISSING and not int | sentinel.

Possible related discussion of typing extensions: python/typing_extensions#742

So I guess the work-around for now is to use something like:

def inspect_sentinel(arg: X | Sentinel) -> None: