Backslash-escaped non-printable character in double-quoted string throws exception when quoted-strings are only-when-needed

[jmknoble]

The following line of YAML:

  echo_format: "\u001b[1;34m+ {command}\u001b[0m"

with the following .yamllint config:

  quoted-strings:
    quote-type: any
    required: only-when-needed

Throws an exception (shown below).

Yamllint version: yamllint 1.35.1
Python version: Python 3.12.7

Dependency versions:

└── yamllint v1.35.1 (group: dev)
    ├── pathspec v0.12.1
    └── pyyaml v6.0.2

Reproducible problem documented at https://github.com/jmknoble/yamllint-quoted-escaped-nonprintable-char-problem .

The problem seems to be in yamllint.rules.quoted_strings._quotes_are_needed() . My hunch is that the already-decoded string is being passed, which yaml.reader.check_printable() interprets as unprintable.

Traceback:

Traceback (most recent call last):
  File "/Users/jmknoble/.local/bin/yamllint", line 8, in <module>
    sys.exit(run())
             ^^^^^
  File "/Users/jmknoble/.local/share/uv/tools/yamllint/lib/python3.12/site-packages/yamllint/cli.py", line 227, in run
    prob_level = show_problems(problems, file, args_format=args.format,
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jmknoble/.local/share/uv/tools/yamllint/lib/python3.12/site-packages/yamllint/cli.py", line 102, in show_problems
    for problem in problems:
                   ^^^^^^^^
  File "/Users/jmknoble/.local/share/uv/tools/yamllint/lib/python3.12/site-packages/yamllint/linter.py", line 199, in _run
    for problem in get_cosmetic_problems(buffer, conf, filepath):
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jmknoble/.local/share/uv/tools/yamllint/lib/python3.12/site-packages/yamllint/linter.py", line 136, in get_cosmetic_problems
    for problem in rule.check(rule_conf,
                   ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jmknoble/.local/share/uv/tools/yamllint/lib/python3.12/site-packages/yamllint/rules/quoted_strings.py", line 301, in check
    not _quotes_are_needed(token.value,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jmknoble/.local/share/uv/tools/yamllint/lib/python3.12/site-packages/yamllint/rules/quoted_strings.py", line 212, in _quotes_are_needed
    loader = yaml.BaseLoader('key: ' + string)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jmknoble/.local/share/uv/tools/yamllint/lib/python3.12/site-packages/yaml/loader.py", line 14, in __init__
    Reader.__init__(self, stream)
  File "/Users/jmknoble/.local/share/uv/tools/yamllint/lib/python3.12/site-packages/yaml/reader.py", line 74, in __init__
    self.check_printable(stream)
  File "/Users/jmknoble/.local/share/uv/tools/yamllint/lib/python3.12/site-packages/yaml/reader.py", line 143, in check_printable
    raise ReaderError(self.name, position, ord(character),
yaml.reader.ReaderError: unacceptable character #x001b: special characters are not allowed
  in "<unicode string>", position 5

[adrienverge]

Hello @jmknoble,

Thanks for the report!

I confirm the bug, reproducable with:

$ yamllint -d 'rules: {quoted-strings: {required: only-when-needed}}' - <<<'key: "\u001b"'
…
yaml.reader.ReaderError: unacceptable character #x001b: special characters are not allowed
  in "<unicode string>", position 5

A contribution to fix this would be welcome 👍

[jmknoble]

A contribution to fix this would be welcome

@adrienverge, let me know whether anything else is needed for the contributed fix in #703.