Unpacking int arguments to datetime.datetime gives a complaint about tzinfo

Bug Report

mypy complains about this line of code. First I don't understand why and second I cannot bring it to accept it, even when including tzinfo=None in the parameter list.

# error: "datetime" gets multiple values for keyword argument "tzinfo"
dt.datetime(*split_int_string(date, 4, 6, 8), *split_int_string(time, 2, 4))

# or

# error: "datetime" gets multiple values for keyword argument "tzinfo"
dt.datetime(*split_int_string(date, 4, 6, 8), *split_int_string(time, 2, 4), tzinfo=None)

Why does mypy think tzinfo would already be used, it cannot be from a List[int]. The behavior when running is as expected.

The helper function is annotated like this:

def split_int_string(digits: str, *at: int) -> List[int]:
    """
    Split a string at given indices and parse the parts to int.
    """
    # Make a canonical representation.
    split: List[int] = sorted(at)
    if not split or split[0] != 0:
        split.insert(0, 0)
    if split[-1] != len(digits):
        split.append(len(digits))
    return [int(digits[split[i - 1] : split[i]]) for i in range(1, len(split))]

To Reproduce

(Write your steps here:)

1. Paste from here into a file.
2. Run with python3, it works.
3. Pass to mypy to see the error.

Expected Behavior

I expect not to get a typing error for that line.

Actual Behavior

It prints

error: Argument 1 to "datetime" has incompatible type "*List[int]"; expected "Optional[tzinfo]"

or

error: "datetime" gets multiple values for keyword argument "tzinfo"

depending on whether one also adds the tzinfo=None or not.

Your Environment

• Mypy version used: 0.812
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.8.6
• Operating system and version: Linux CL003356 4.19.128-microsoft-standard #1 SMP Tue Jun 23 12:58:10 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

Issue にリンクされた貼り付け済みの再現コードから始め、複数の展開された List[int] 引数を指定した datetime.datetime の呼び出しを mypy がどのように解析するかを調べます。tzinfo に関する診断を確認し、その後、報告に示された実行時の挙動と比較します。有効な呼び出しで誤った型エラーが発生しなくなり、実際の引数の競合については引き続き診断されれば完了です。