False-positive with multiple *args splats in a function call

Bug Report

mypy falsely(?) reports a type error when the *args syntax is used more than once in a function call.

To Reproduce

mypy --no-incremental --config /dev/null -c '
def foobar(a: int, b: str, c: int) -> None:
    ...


foo = (1,)
bar = ("b", 3)

foobar(*foo, *bar)
'

Expected Behavior

Success: no issues found in 1 source file

Actual Behavior

<string>:9: error: Argument 2 to "foobar" has incompatible type "*Tuple[str, int]"; expected "str"
<string>:9: error: Argument 2 to "foobar" has incompatible type "*Tuple[str, int]"; expected "int"

This error goes away if I:

• make foo an int instead of Tuple[int], and remove the splat when foobar() is called.
• make bar two ints and make foobar() take three int arguments.
• make foo a Tuple[str, int] and make foobar() take str, int, str, int arguments.
• make bar just a Tuple[str] and make foobar() take int, str arguments.

Your Environment

This occurs with the standard version of mypy in Debian Testing:

$ /usr/bin/mypy --version
mypy 0.812

...as well as with the latest git revision:

$ ~/.local/pipx/venvs/mypy/bin/mypy --version
mypy 0.820+dev.8642b351cff94c471333256f9cd6867807384f01

In both cases, I'm using the Debian-provided Python 3.9.2,
on up-to-date Debian Testing.

Start by running the supplied mypy command and confirming the two diagnostics for the call with multiple tuple splats. Trace the call argument checking and tuple-splat handling, then add coverage for this reproducer; done means the command reports no issues without regressing the listed variations.