Support exhaustive checking for “in” operator.

[Malika1109]

This PR attempts to fix #16093

from enum import Enum
from typing import assert_never

class MyEnum(Enum):
A = 1
B = 2
C = 3

def my_function(a: MyEnum) -> bool:
if a == MyEnum.A:
return True
elif a in (MyEnum.B, MyEnum.C):
return False
assert_never(a)

my_function(MyEnum.A)

Earlier the above code would generate the below error:
error: Argument 1 to "assert_never" has incompatible type
"Literal[MyEnum.B, MyEnum.C]"; expected "NoReturn" [arg-type]
assert_never(a)

This PR aims to fix the issue presented in #16093 because creates a separate case for “in” operator to be handled when the right hand side of a comparison expression is TupleExpr.

Through the changes of the pull request my_function passes without any mypy issues:

[JelleZijlstra]

black (https://github.com/psf/black)
+ src/black/__init__.py:530:17: error: Statement is unreachable  [unreachable]
+ src/black/__init__.py:835:17: error: Statement is unreachable  [unreachable]
+ src/black/concurrency.py:139:9: error: Statement is unreachable  [unreachable]

These are all false positives, so the PR has some bugs.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

black (https://github.com/psf/black)
+ src/black/__init__.py:530:17: error: Statement is unreachable  [unreachable]
+ src/black/__init__.py:835:17: error: Statement is unreachable  [unreachable]
+ src/black/concurrency.py:139:9: error: Statement is unreachable  [unreachable]

trio (https://github.com/python-trio/trio)
+ src/trio/_dtls.py:367: error: Need type annotation for "messages_by_seq" (hint: "messages_by_seq: Dict[<type>, <type>] = ...")  [var-annotated]

mkosi (https://github.com/systemd/mkosi)
+ mkosi/config.py:343:9: error: Statement is unreachable  [unreachable]
+ mkosi/qemu.py:428:13: error: Right operand of "or" is never evaluated  [unreachable]
+ mkosi/qemu.py:432:13: error: Statement is unreachable  [unreachable]
+ mkosi/qemu.py:551:13: error: Statement is unreachable  [unreachable]
+ mkosi/distributions/ubuntu.py:27:13: error: Statement is unreachable  [unreachable]
+ mkosi/__init__.py:1356:5: error: Statement is unreachable  [unreachable]
+ mkosi/__init__.py:1381:5: error: Statement is unreachable  [unreachable]
+ mkosi/__init__.py:2309:13: error: Statement is unreachable  [unreachable]
+ mkosi/__init__.py:2802:9: error: Statement is unreachable  [unreachable]
+ mkosi/__init__.py:2805:5: error: Statement is unreachable  [unreachable]

discord.py (https://github.com/Rapptz/discord.py)
- discord/automod.py:316: error: Argument 1 to "_from_value" of "ArrayFlags" has incompatible type "object"; expected "Sequence[int]"  [arg-type]
- discord/automod.py:316: error: Argument "allow_list" to "AutoModTrigger" has incompatible type "object"; expected "list[str] | None"  [arg-type]
- discord/automod.py:321: error: Argument "mention_limit" to "AutoModTrigger" has incompatible type "object"; expected "int | None"  [arg-type]
- discord/automod.py:322: error: Argument "mention_raid_protection" to "AutoModTrigger" has incompatible type "object"; expected "bool | None"  [arg-type]
- discord/automod.py:327: error: Missing return statement  [return]
+ discord/scheduled_event.py:466: error: Need type annotation for "metadata" (hint: "metadata: Dict[<type>, <type>] = ...")  [var-annotated]
- discord/scheduled_event.py:533: error: Incompatible types in assignment (expression has type "None", target has type "str")  [assignment]
- discord/scheduled_event.py:555: error: Incompatible types in assignment (expression has type "dict[str, str]", target has type "str")  [assignment]
+ discord/scheduled_event.py:555: error: Incompatible types in assignment (expression has type "dict[Any, Any]", target has type "str")  [assignment]
+ discord/voice_state.py:278: error: Unused "type: ignore" comment  [unused-ignore]
+ discord/voice_state.py:285: error: Unused "type: ignore" comment  [unused-ignore]
+ discord/guild.py:2400: error: Unused "type: ignore" comment  [unused-ignore]
+ discord/guild.py:3136: error: Need type annotation for "metadata" (hint: "metadata: Dict[<type>, <type>] = ...")  [var-annotated]
- discord/guild.py:3209: error: Incompatible types in assignment (expression has type "dict[str, str]", target has type "str")  [assignment]
+ discord/guild.py:3209: error: Incompatible types in assignment (expression has type "dict[Any, Any]", target has type "str")  [assignment]
+ discord/client.py:2578: error: Unused "type: ignore" comment  [unused-ignore]
- discord/app_commands/tree.py:413: error: Missing return statement  [return]
- discord/app_commands/tree.py:533: error: Missing return statement  [return]

urllib3 (https://github.com/urllib3/urllib3)
+ src/urllib3/poolmanager.py:570: error: Argument 1 to "get" of "dict" has incompatible type "str | None"; expected "str"  [arg-type]

streamlit (https://github.com/streamlit/streamlit)
+ lib/streamlit/runtime/runtime.py: note: In function "stop":
+ lib/streamlit/runtime/runtime.py:307:13: error: Statement is unreachable  [unreachable]
+ lib/streamlit/runtime/runtime.py: note: In member "connect_session" of class "Runtime":
+ lib/streamlit/runtime/runtime.py:371:9: error: Statement is unreachable  [unreachable]
+ lib/streamlit/runtime/runtime.py: note: In member "handle_backmsg" of class "Runtime":
+ lib/streamlit/runtime/runtime.py:479:9: error: Statement is unreachable  [unreachable]
+ lib/streamlit/runtime/runtime.py: note: In member "handle_backmsg_deserialization_exception" of class "Runtime":
+ lib/streamlit/runtime/runtime.py:509:9: error: Statement is unreachable  [unreachable]
+ lib/streamlit/runtime/runtime.py: note: In member "is_ready_for_browser_connection" of class "Runtime":
+ lib/streamlit/runtime/runtime.py:526:13: error: Statement is unreachable  [unreachable]

[hauntsaninja]

Thanks, this logic has been rewritten a few times since this PR, #21456 and preceding PRs fix the relevant issue