Crash on concatenated string + comment

[JelleZijlstra]

Another crash on master

$ cat xxx.py 
xxxxxxx_xxxxxx_xxxxxxx = xxx(
    [
        xxxxxxxxxxxx(
            xxxxxx_xxxxxxx=(
                '((x.xxxxxxxxx = "xxxxxx.xxxxxxxxxxxxxxxxxxxxx") || (x.xxxxxxxxx = "xxxxxxxxxxxx")) && '
                # xxxxx xxxxxxxxxxxx xxxx xxx (xxxxxxxxxxxxxxxx) xx x xxxxxxxxx xx xxxxxx.
                "(x.xxxxxxxxxxxx.xxx != "
                '"xxx:xxx:xxx::xxxxxxxxxxxx:xxxxxxx-xxxx/xxxxxxxxxxx/xxxxxxxxxxxxxxxxx") && '
            )
        )
    ]
)
$ black -v xxx.py 
Using configuration from /Users/jelle/py/black/pyproject.toml.
Traceback (most recent call last):
  File "/Users/jelle/py/black/src/black/__init__.py", line 648, in reformat_one
    if changed is not Changed.CACHED and format_file_in_place(
  File "/Users/jelle/py/black/src/black/__init__.py", line 791, in format_file_in_place
    dst_contents = format_file_contents(src_contents, fast=fast, mode=mode)
  File "/Users/jelle/py/black/src/black/__init__.py", line 918, in format_file_contents
    assert_stable(src_contents, dst_contents, mode=mode)
  File "/Users/jelle/py/black/src/black/__init__.py", line 6076, in assert_stable
    newdst = format_str(dst, mode=mode)
  File "/Users/jelle/py/black/src/black/__init__.py", line 977, in format_str
    for line in transform_line(
  File "/Users/jelle/py/black/src/black/__init__.py", line 2731, in transform_line
    result.extend(
  File "/Users/jelle/py/black/src/black/__init__.py", line 2725, in transform_line
    for transformed_line in transform(line, features):
  File "/Users/jelle/py/black/src/black/__init__.py", line 2834, in __call__
    for line_result in self.do_transform(line, string_idx):
  File "/Users/jelle/py/black/src/black/__init__.py", line 2978, in do_transform
    msg_result = self.__merge_string_group(new_line, string_idx)
  File "/Users/jelle/py/black/src/black/__init__.py", line 3164, in __merge_string_group
    new_line.append(string_leaf)
  File "/Users/jelle/py/black/src/black/__init__.py", line 1421, in append
    leaf.prefix += whitespace(
  File "/Users/jelle/py/black/src/black/__init__.py", line 2152, in whitespace
    assert p is not None, f"INTERNAL ERROR: hand-made leaf without parent: {leaf!r}"
AssertionError: INTERNAL ERROR: hand-made leaf without parent: Leaf(STRING, '\'(x.xxxxxxxxxxxx.xxx != "xxx:xxx:xxx::xxxxxxxxxxxx:xxxxxxx-xxxx/xxxxxxxxxxx/xxxxxxxxxxxxxxxxx") && \'')
error: cannot format xxx.py: INTERNAL ERROR: hand-made leaf without parent: Leaf(STRING, '\'(x.xxxxxxxxxxxx.xxx != "xxx:xxx:xxx::xxxxxxxxxxxx:xxxxxxx-xxxx/xxxxxxxxxxx/xxxxxxxxxxxxxxxxx") && \'')
Oh no! 💥 💔 💥
1 file failed to reformat.

[hugovk]

git bisect also points to 544ea9c as the first bad commit, from PR #1132 "Improve String Handling".

[hugovk]

Now fine on master

$ black --check xxx.py
All done! ✨ 🍰 ✨
1 file would be left unchanged.

[JelleZijlstra]

Yes, #1609 disables the feature that caused the crash. I left the issue open because we need to fix it in order to get rid of the experimental flag.