Google first-line is being wrapped 2 chars shorter than the rest

[AgentRev]

The following docstring

class FooBar:
    """Abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc.

    Abcabc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc.
    """
    pass

strangely gets formatted to

class FooBar:
    """Abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc
    abc.

    Abcabc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc abc.
    """
    pass

The problem appears to come from

format-docstring/format_docstring/line_wrap_google.py

Lines 32 to 35 in ac5aab2

	# Google docstrings can preserve string prefixes such as ``rf`` when rebuilt,
	# so first-line wrapping reserves two prefix characters plus opening quotes.
	GOOGLE_OPENING_QUOTES_WIDTH: Final[int] = 5
	GOOGLE_COMPACT_OPENING_QUOTES_WIDTH: Final[int] = 5

which contradicts

format-docstring/format_docstring/docstring_rewriter.py

Line 580 in ac5aab2

if isinstance(val, ast.Constant) and isinstance(val.value, str):

because f prefixed strings are of type ast.JoinedStr and not ast.Constant, and thus never satisfy the condition to count as docstrings.

b and u prefixed strings, while of ast.Constant type, do not seem to get formatted either, albeit for a different reason.

---

Easy solution, just sweep prefixed docstrings under the rug, and change the constants to:

# First-line wrapping reserves 3 opening quotes. 
GOOGLE_OPENING_QUOTES_WIDTH: Final[int] = 3
GOOGLE_COMPACT_OPENING_QUOTES_WIDTH: Final[int] = 3

[jsh9]

Thanks for the report. I dug back through the code/history, and your diagnosis is basically right.

The reason this was 5 is that I originally reserved space for 2 possible string-prefix chars (such as rf"""...""") plus the 3 opening quotes, because rebuild_literal() preserves prefixes. But in the current AST-based Python path, f"""...""" and rf"""...""" are ast.JoinedStr, so they do not pass the docstring detection path. b"""...""" is bytes and also is not treated as a docstring. The only prefixed literals that actually matter here are string-valued constants like r"""...""" and u"""...""".

So a flat 5 is too conservative for normal """...""" docstrings and causes exactly the two-character-short wrap you found. I don’t think a flat 3 is quite right either, because raw/unicode-prefixed docstrings are still rewritten and the prefix is preserved.

The better fix is probably to reserve the actual opener width from the source literal: 3 + len(prefix) for rebuilt Python literals, with 3 as the default where the wrapper is called without source-literal context. That should fix the plain triple-quote case without letting r"""...""" exceed the configured line length.

Thanks again for catching this.