[formatter] Add "preserve" quote-style to mimic Black's skip-string-n…

…ormalization

Fixes #7525

crates/ruff_python_formatter/src/expression/string/docstring.rs

@@ -436,7 +436,9 @@ impl<'ast, 'buf, 'fmt, 'src> DocstringLinePrinter<'ast, 'buf, 'fmt, 'src> {
         // `docstring_code_examples.py` for when this check is relevant.
         let wrapped = match self.quote_style {
             QuoteStyle::Single => std::format!("'''{}'''", printed.as_code()),
-            QuoteStyle::Double => std::format!(r#""""{}""""#, printed.as_code()),
+            QuoteStyle::Double | QuoteStyle::Preserve => {
+                std::format!(r#""""{}""""#, printed.as_code())
+            }
         };
         let result = ruff_python_parser::parse(
             &wrapped,

crates/ruff_python_formatter/src/expression/string/mod.rs

@@ -386,7 +386,9 @@ impl StringPart {
         let quotes = match quoting {
             Quoting::Preserve => self.quotes,
             Quoting::CanChange => {
-                if self.prefix.is_raw_string() {
+                if preferred_style == QuoteStyle::Preserve {
+                    self.quotes
+                } else if self.prefix.is_raw_string() {
                     choose_quotes_raw(raw_content, self.quotes, preferred_style)
                 } else {
                     choose_quotes(raw_content, self.quotes, preferred_style)
@@ -665,7 +667,7 @@ fn choose_quotes(input: &str, quotes: StringQuotes, preferred_style: QuoteStyle)
                     QuoteStyle::Single
                 }
             }
-            QuoteStyle::Double => {
+            QuoteStyle::Double | QuoteStyle::Preserve => {
                 if double_quotes > single_quotes {
                     QuoteStyle::Single
                 } else {
@@ -717,8 +719,8 @@ impl Format<PyFormatContext<'_>> for StringQuotes {
         let quotes = match (self.style, self.triple) {
             (QuoteStyle::Single, false) => "'",
             (QuoteStyle::Single, true) => "'''",
-            (QuoteStyle::Double, false) => "\"",
-            (QuoteStyle::Double, true) => "\"\"\"",
+            (QuoteStyle::Double | QuoteStyle::Preserve, false) => "\"",
+            (QuoteStyle::Double | QuoteStyle::Preserve, true) => "\"\"\"",
         };
 
         token(quotes).fmt(f)

crates/ruff_python_formatter/src/options.rs

@@ -207,13 +207,15 @@ pub enum QuoteStyle {
     Single,
     #[default]
     Double,
+    Preserve,
 }
 
 impl QuoteStyle {
     pub const fn as_char(self) -> char {
         match self {
             QuoteStyle::Single => '\'',
             QuoteStyle::Double => '"',
+            QuoteStyle::Preserve => '"', // not used
         }
     }
 
@@ -222,6 +224,7 @@ impl QuoteStyle {
         match self {
             QuoteStyle::Single => QuoteStyle::Double,
             QuoteStyle::Double => QuoteStyle::Single,
+            QuoteStyle::Preserve => QuoteStyle::Preserve,
         }
     }
 }
@@ -245,6 +248,7 @@ impl FromStr for QuoteStyle {
         match s {
             "\"" | "double" | "Double" => Ok(Self::Double),
             "'" | "single" | "Single" => Ok(Self::Single),
+            "preserve" | "Preserve" => Ok(Self::Preserve),
             // TODO: replace this error with a diagnostic
             _ => Err("Value not supported for QuoteStyle"),
         }