wrong inference with nested unpacking

Bug Report

Unpacking a list into multiple variables when the list itself is (partially) created by unpacking another iterable the type inference is faulty

To Reproduce

from typing import reveal_type
text = "some\nstuff"
version, desc, *_ = [*text.split(sep="\n", maxsplit=1), None, None]
reveal_type(version)  # str
reveal_type(desc)      # None

Expected Behavior

Mypy infers version and desc and str | None (if you want to go very far you can even infer version as str because str.split never returns an empty list, but that is not my expectation)

Actual Behavior

Mypy infers version as str and desc as None

Your Environment

Mypy playground: https://mypy-play.net/?mypy=latest&python=3.12&flags=strict%2Cstrict-bytes%2Ccheck-untyped-defs%2Cdisallow-any-decorated%2Cdisallow-any-expr%2Cdisallow-any-explicit%2Cdisallow-any-generics%2Cdisallow-any-unimported%2Cdisallow-incomplete-defs%2Cdisallow-subclassing-any%2Cdisallow-untyped-calls%2Cdisallow-untyped-decorators%2Cdisallow-untyped-defs%2Cno-implicit-reexport%2Cno-strict-optional%2Cstrict-equality%2Cstrict-equality-for-none%2Cwarn-incomplete-stub%2Cwarn-redundant-casts%2Cwarn-return-any%2Cwarn-unreachable%2Cwarn-unused-configs%2Cwarn-unused-ignores%2Cextra-checks

Inizia con il riproduttore di nested unpacking nel mypy playground e verifica come reveal_type riporta version e desc. Segui l’inferenza dei tipi per l’espressione di lista con asterisco e l’unpacking della tupla; il lavoro è completato quando entrambe le variabili vengono inferite come str | None nell’esempio riportato.