Internal Error when formatting bracketed return annotations

[AntObr]

Describe the bug

When formatting a *.py file with bracketed returns annotations the error below is returned:

error: cannot format test.py: INTERNAL ERROR: Black produced code that is not equivalent to the source on pass 1.  Please report a bug on https://github.com/psf/black/issues.  This diff might be helpful: /var/folders/9m/cps802s92k77tpy3z1w56hxr0000gn/T/blk_fu7q8w3k.log

To Reproduce

For example:
test.py

returning_a_deeply_nested_import_of_a_type = str

def some_method_with_a_really_long_name() -> (
    returning_a_deeply_nested_import_of_a_type
):
    pass

run black -l 79 on the above file

Expected behavior

The file is formatted and the bracketed form is maintained.

Environment (please complete the following information):

• Version: main
• OS and Python version: macOS v11.4/Python 3.9.4

Does this bug also happen on main?

[felix-hilden]

Hi, thanks for the report! Just for easy inspection, I've reproduced this on the playground.

[ichard26]

Yeah thanks for the report, that trailing comma Black tries to add actually changes the type annotation's type to a tuple ... good thing the AST equivalence check caught that :)

This should be fixed by this PR: #2384.