Black adds an extra blank line to an import line that ends with # fmt: skip

[yilei]

Describe the bug

It reformats:

import os
import re  # fmt: skip
import sys

to:

import os

import re  # fmt: skip
import sys

Example: https://black.vercel.app/?version=stable&state=_Td6WFoAAATm1rRGAgAhARYAAAB0L-Wj4ACSAFtdAD2IimZxl1N_WlwxRhR7MSgE-ANVmAcXiiHH_vLVBv6H9oJYdLgh3uJSbWM1qliEV5h8ji5l4G2iqd5AHPniBCkwXU5Gi97RWyWgW8b3Yvc90k3x9wXSWeryKEAAAIvWais0zjPAAAF3kwEAAAAB02j7scRn-wIAAAAABFla

Expected behavior

# fmt: skip shouldn't make it add an extra line.

Additional context

The issue is Black internally converts the import re # fmt: skip line to a STANDALONE_COMMENT, and for other "real" STANDALONE_COMMENT lines it will add the blank line as designed. Maybe internally it needs to distinguish between real STANDALONE_COMMENT nodes v.s. converted from fmt off/skip?

[ichard26]

I didn't know we added a blank before a comment preceding imports, that's a bit surprising. Anyway, distinguishing between real and internal STANDALONE_COMMENTS sounds like a reasonable fix, but I haven't looked at the code. This also affects fmt: off/on FWIW:

--- test.py	2022-12-14 04:17:08.331940 +0000
+++ test.py	2022-12-14 04:17:22.664904 +0000
@@ -1,5 +1,6 @@
 import os
+
 # fmt: off
 import re
 # fmt: on
 import sys

[julian-west]

I have also come across this bug in the situation where I have a long import statement which black reformats across multiple lines. I tried to skip formatting on this import statement but instead an extra line is created. This causes problems with tools like isort which then tries to remove the new blank line.

For example:

from my_package.my_module import function
from my_package.my_module_with_a_very_very_long_name import function_with_a_very_very_long_name  # fmt: skip

Reformatted to:

from my_package.my_module import function

from my_package.my_module_with_a_very_very_long_name import function_with_a_very_very_long_name  # fmt: skip

---

I'm not sure if it helps solve/understand the bug better, but I also noticed that if I add # fmt: skip to all imports in the 'block', then the extra line is not created.

For example, the following:

import os
import sys  # fmt: skip
import re  # fmt: skip

import os  # fmt: skip
import sys  # fmt: skip
import re  # fmt: skip

Is reformatted to:

import os

import sys  # fmt: skip
import re  # fmt: skip

import os  # fmt: skip
import sys  # fmt: skip
import re  # fmt: skip

Playground example