Unexpected space in docstring near escaped quote

[vincent0426]

Summary

Description

Ruff formatter modifies the spacing in a string within a docstring when the string contains an escaped quote. Specifically, it adds an unwanted space between the escaped quote and the closing triple quotes of the docstring.

Steps to Reproduce

1. Create a Python class with the following content:

   class Sample:
       """Hello "World\""""
   
       def __init__(self, name):
           self.name = name

2. Run ruff format on the file
3. Observe that the formatter modifies the docstring to:

   class Sample:
       """Hello "World\" """
   
       def __init__(self, name):
           self.name = name

Expected Behavior

Docstring remain unchanged after formatting as its escaped already

"""Hello "World\""""

Version

ruff 0.9.10 (0dfa810 2025-03-07)

[MichaReiser]

Our formatting matches black's and the extra space is required for non-escaped quotes at the end of a docstring. But this does seem to be unintentional in the escaped case and is, arguably, a bug because it changes the docstring.

[InSyncWithFoo]

@vincent0426 This seems to have been incorrectly closed. Was it?

[vincent0426]

@InSyncWithFoo ah yeah, I reopened it!

[maxmynter]

I think the culprit is around this function in crates/ruff_python_formatter/src/string/docstring.rs:1599ff.

/// If the last line of the docstring is `content" """` or `content\ """`, we need a chaperone space
/// that avoids `content""""` and `content\"""`. This does only applies to un-escaped backslashes,
/// so `content\\ """` doesn't need a space while `content\\\ """` does.
pub(super) fn needs_chaperone_space(flags: AnyStringFlags, trim_end: &str) -> bool {
    if trim_end.chars().rev().take_while(|c| *c == '\\').count() % 2 == 1 {
        true
    } else {
        flags.is_triple_quoted() && trim_end.ends_with(flags.quote_style().as_char())
    }
}

I'll tinker around to see if I can come up for a fix + tests.