Adding a comment on its own line in a list comprehension introduces line breaks in the code.

[bersbersbers]

Describe the bug
A clear and concise description of what the bug is the title:

Adding a comment on its own line in a list comprehension introduces line breaks in the code.

To Reproduce

1. Take the code below
2. Run Black on it
3. Notice that in the second block, ** 2 for i in some_long_var_name is - unnecessarily - broken in two lines.

Expected behavior
i ** 2 for i in some_long_var_name should not be broken in two lines.

Environment

• Version: 19.10b0
• OS and Python version: Windows 10, 3.8.2

Does this bug also happen on master?

Yes.

"""Bug."""
if True and True:
    if True and True:
        if True and True:
            if True and True:
                print(
                    list(
                        map(
                            lambda some_long_var_name: [
                                i ** 2 for i in some_long_var_name
                            ],
                            [[1, 2, 3], [4, 5, 6]],
                        )
                    )
                )

                print(
                    list(
                        map(
                            lambda some_long_var_name: [
                                # Why does this comment force the next line into two?
                                i ** 2 for i in some_long_var_name
                            ],
                            [[1, 2, 3], [4, 5, 6]],
                        )
                    )
                )