ruff/crates/ruff_python_formatter/src/other/string_literal.rs

use ruff_formatter::FormatRuleWithOptions;
use ruff_python_ast::StringLiteral;

use crate::prelude::*;
use crate::string::{docstring, StringNormalizer};
use crate::QuoteStyle;

#[derive(Default)]
pub struct FormatStringLiteral {
    layout: StringLiteralKind,
}

impl FormatRuleWithOptions<StringLiteral, PyFormatContext<'_>> for FormatStringLiteral {
    type Options = StringLiteralKind;

    fn with_options(mut self, layout: StringLiteralKind) -> Self {
        self.layout = layout;
        self
    }
}

/// The kind of a string literal.
#[derive(Copy, Clone, Debug, Default)]
pub enum StringLiteralKind {
    /// A normal string literal e.g., `"foo"`.
    #[default]
    String,
    /// A string literal used as a docstring.
    Docstring,
}

impl StringLiteralKind {
    /// Checks if this string literal is a docstring.
    pub(crate) const fn is_docstring(self) -> bool {
        matches!(self, StringLiteralKind::Docstring)
    }
}

impl FormatNodeRule<StringLiteral> for FormatStringLiteral {
    fn fmt_fields(&self, item: &StringLiteral, f: &mut PyFormatter) -> FormatResult<()> {
        let quote_style = f.options().quote_style();
        let quote_style = if self.layout.is_docstring() && !quote_style.is_preserve() {
            // Per PEP 8 and PEP 257, always prefer double quotes for docstrings,
            // except when using quote-style=preserve
            QuoteStyle::Double
        } else {
            quote_style
        };

        let normalized = StringNormalizer::from_context(f.context())
            .with_preferred_quote_style(quote_style)
            .normalize(item.into());

        if self.layout.is_docstring() {
            docstring::format(&normalized, f)
        } else {
            normalized.fmt(f)
        }
    }
}