empty lines at end of file trimmed even with fmt: off

[matejcik]

Operating system: Linux Mint
Python version: 3.6.6
Black version: latest
Does also happen on master: yes

The following file:

# fmt: off

print("hello")

gets trimmed to:

# fmt: off

print("hello")

IOW, if the file ends with empty lines, they are removed.

[zsol]

Sounds like a bug. Want to take a look at fixing it?

[scolby33]

The problem here appears to happen in convert_one_fmt_off_pair, where the node enters as # fmt: off\n\nprint("hello")\n\n and exits as # fmt: off\n\nprint("hello")\n. I am continuing to investigate.

[scolby33]

The function generate_ignored_nodes creates a list of nodes that is just # fmt: off\n\nprint("hello")\n. This is where the final newline is lost.

Unfortunately, I've reached the end of my experience/time to look at this today. I hope this has given someone more versed in the project a better starting place for fixing this bug.

EDIT: also, because of how test files are read in read_data in test_black.py, it will be difficult to write a test for this since the final \n will be removed.

[felix-hilden]

At least our documentation states that fmt: off should be followed by a fmt: on, but supporting a single off switch is a reasonable request.