Black removes tabs from within docstrings and thus not equivalent to the source

[d0ugal]

Describe the bug

I got this error when formatting MAAS code.

error: cannot format src/provisioningserver/drivers/pod/virsh.py: INTERNAL ERROR: Black produced code that is not equivalent to the source.  Please report a bug on https://github.com/psf/black/issues.  This diff might be helpful: /tmp/blk__oj12ra3.log
Oh no! 💥 💔 💥
1 file failed to reformat.

The diff contains...

--- src
+++ dst
@@ -17834,11 +17834,11 @@
           body=
             Expr(
               value=
                 Constant(
                   value=
-                    'Calculate a block name based on the `idx`.\n\nDrive#  Name\n0\t    vda\n25\t    vdz\n26\t    vdaa\n27\t    vdab\n51\t    vdaz\n52\t    vdba\n53\t    vdbb\n701\t    vdzz\n702\t    vdaaa\n703\t    vdaab\n18277   vdzzz',  # str
+                    'Calculate a block name based on the `idx`.\n\nDrive#  Name\n0           vda\n25          vdz\n26          vdaa\n27          vdab\n51          vdaz\n52          vdba\n53          vdbb\n701         vdzz\n702         vdaaa\n703         vdaab\n18277   vdzzz',  # str
                 )  # /Constant
             )  # /Expr
             Assign(
               targets=
                 Name(

To Reproduce Steps to reproduce the behavior:

1. Take this file https://github.com/maas/maas/blob/6620973/src/provisioningserver/drivers/pod/virsh.py
   1.1. wget https://raw.githubusercontent.com/maas/maas/6620973567f4081a4c5ada8ea2720dc079c0f23d/src/provisioningserver/drivers/pod/virsh.py
2. Run Black on it with just the filename
   2.1 black virsh.py
3. See error above

Expected behavior

It looks like black is changing tabs within the docstring, I wouldn't expect this to happen.

Environment (please complete the following information):

• Version: 20.8.b1 (and tested on master which was 2b75f88 at the time)
• OS and Python version: Ubuntu and Python 3.8.4 (and also tested 3.8.2 on another ubuntu box)

Does this bug also happen on master?

Yes, confirmed with pip install git+https://github.com/psf/black in a virtualenv

[d0ugal]

@sparkiegeek pointed out to me that this might be a dupe of #1601

[ichard26]

@d0ugal yeah this is a duplicate of #1601. Thank you for the bug report, perhaps +1 the original issue?