black mishandles magic comma in context managers

[graingert]

Black fa6caa

Playground link

Options

--line-length=88
--safe

Input

@gen_test()
async def test_eq():
    async with Cluster(
        asynchronous=True,
        name="A",
    ) as clusterA, Cluster(
        asynchronous=True,
        name="A2",
    ) as clusterA2, Cluster(
        asynchronous=True,
        name="B",
    ) as clusterB:
        assert clusterA != "A"
        assert not (clusterA == "A")
        assert clusterA == clusterA
        assert not (clusterA != clusterA)
        assert clusterA != clusterA2
        assert not (clusterA == clusterA2)
        assert clusterA != clusterB
        assert not (clusterA == clusterB)

Output

@gen_test()
async def test_eq():
    async with Cluster(asynchronous=True, name="A",) as clusterA, Cluster(
        asynchronous=True,
        name="A2",
    ) as clusterA2, Cluster(
        asynchronous=True,
        name="B",
    ) as clusterB:
        assert clusterA != "A"
        assert not (clusterA == "A")
        assert clusterA == clusterA
        assert not (clusterA != clusterA)
        assert clusterA != clusterA2
        assert not (clusterA == clusterA2)
        assert clusterA != clusterB
        assert not (clusterA == clusterB)

Expected

idempotency

[graingert]

I think black should emit an internal error if it emits a ,) outside a tuple, or a ,] or ,}

[JelleZijlstra]

Feels similar to #1671.