Preserve backslash in raw string literal

crates/ruff_python_formatter/src/expression/string.rs

@@ -203,11 +203,17 @@ impl Format<PyFormatContext<'_>> for FormatStringPart {
  let raw_content_range = relative_raw_content_range + self.part_range.start();
 
  let raw_content = &string_content[relative_raw_content_range];
- let preferred_quotes = preferred_quotes(raw_content, quotes, f.options().quote_style());
+ let is_raw_string = prefix.is_raw_string();
+ let preferred_quotes = if is_raw_string {
+ preferred_quotes_raw(raw_content, quotes, f.options().quote_style())
+ } else {
+ preferred_quotes(raw_content, quotes, f.options().quote_style())
+ };
 
  write!(f, [prefix, preferred_quotes])?;
 
- let (normalized, contains_newlines) = normalize_string(raw_content, preferred_quotes);
+ let (normalized, contains_newlines) =
+ normalize_string(raw_content, preferred_quotes, is_raw_string);
 
  match normalized {
  Cow::Borrowed(_) => {
@@ -223,7 +229,7 @@ impl Format<PyFormatContext<'_>> for FormatStringPart {
 }
 
 bitflags! {
- #[derive(Copy, Clone, Debug)]
+ #[derive(Copy, Clone, Debug, PartialEq, Eq)]
  pub(super) struct StringPrefix: u8 {
  const UNICODE = 0b0000_0001;
  /// `r"test"`
@@ -264,6 +270,10 @@ impl StringPrefix {
  pub(super) const fn text_len(self) -> TextSize {
  TextSize::new(self.bits().count_ones())
  }
+
+ pub(super) const fn is_raw_string(self) -> bool {
+ matches!(self, StringPrefix::RAW | StringPrefix::RAW_UPPER)
+ }
 }
 
 impl Format<PyFormatContext<'_>> for StringPrefix {
@@ -290,6 +300,54 @@ impl Format<PyFormatContext<'_>> for StringPrefix {
  }
 }
 
+/// Detects the preferred quotes for raw string `input`.
+/// The configured quote style is preferred unless `input` contains unescaped quotes of the
+/// configured style. For example, `r"foo"` is preferred over `r'foo'` if the configured
+/// quote style is double quotes.
+fn preferred_quotes_raw(
+ input: &str,
+ quotes: StringQuotes,
+ configured_style: QuoteStyle,
+) -> StringQuotes {
+ let configured_quote_char = configured_style.as_char();
+ let mut chars = input.chars().peekable();
+ let contains_unescaped_configured_quotes = loop {
+ match chars.next() {
+ Some('\\') => {
+ // Ignore escaped characters
+ chars.next();
+ }
+ // `"` or `'`
+ Some(c) if c == configured_quote_char => {
+ if !quotes.triple {
+ break true;
+ }
+
+ if chars.peek() == Some(&configured_quote_char) {
+ // `""` or `''`
+ chars.next();
+
+ if chars.peek() == Some(&configured_quote_char) {
+ // `"""` or `'''`
+ break true;
+ }
+ }
+ }
+ Some(_) => continue,
+ None => break false,
+ }
+ };
+
+ StringQuotes {
+ triple: quotes.triple,
+ style: if contains_unescaped_configured_quotes {
+ quotes.style
+ } else {
+ configured_style
+ },
+ }
+}
+
 /// Detects the preferred quotes for `input`.
 /// * single quoted strings: The preferred quote style is the one that requires less escape sequences.
 /// * triple quoted strings: Use double quotes except the string contains a sequence of `"""`.
@@ -434,7 +492,11 @@ impl Format<PyFormatContext<'_>> for StringQuotes {
 /// with the provided `style`.
 ///
 /// Returns the normalized string and whether it contains new lines.
-fn normalize_string(input: &str, quotes: StringQuotes) -> (Cow<str>, ContainsNewlines) {
+fn normalize_string(
+ input: &str,
+ quotes: StringQuotes,
+ is_raw: bool,
+) -> (Cow<str>, ContainsNewlines) {
  // The normalized string if `input` is not yet normalized.
  // `output` must remain empty if `input` is already normalized.
  let mut output = String::new();
@@ -467,7 +529,7 @@ fn normalize_string(input: &str, quotes: StringQuotes) -> (Cow<str>, ContainsNew
  newlines = ContainsNewlines::Yes;
  } else if c == '\n' {
  newlines = ContainsNewlines::Yes;
- } else if !quotes.triple {
+ } else if !quotes.triple && !is_raw {
  if c == '\\' {
  if let Some(next) = input.as_bytes().get(index + 1).copied().map(char::from) {
  #[allow(clippy::if_same_then_else)]

crates/ruff_python_formatter/tests/snapshots/black_compatibility@miscellaneous__string_quotes.py.snap

@@ -82,13 +82,11 @@ f"\"{a}\"{'hello' * b}\"{c}\""
 +f"NOT_YET_IMPLEMENTED_ExprJoinedStr"
 +f"NOT_YET_IMPLEMENTED_ExprJoinedStr"
  r"raw string ftw"
--r"Date d\'expiration:(.*)"
-+r"Date d'expiration:(.*)"
+ r"Date d\'expiration:(.*)"
  r'Tricky "quote'
--r"Not-so-tricky \"quote"
+ r"Not-so-tricky \"quote"
 -rf"{yay}"
 -"\nThe \"quick\"\nbrown fox\njumps over\nthe 'lazy' dog.\n"
-+r'Not-so-tricky "quote'
 +f"NOT_YET_IMPLEMENTED_ExprJoinedStr"
 +"\n\
 +The \"quick\"\n\
@@ -147,9 +145,9 @@ f"NOT_YET_IMPLEMENTED_ExprJoinedStr"
 f"NOT_YET_IMPLEMENTED_ExprJoinedStr"
 f"NOT_YET_IMPLEMENTED_ExprJoinedStr"
 r"raw string ftw"
-r"Date d'expiration:(.*)"
+r"Date d\'expiration:(.*)"
 r'Tricky "quote'
-r'Not-so-tricky "quote'
+r"Not-so-tricky \"quote"
 f"NOT_YET_IMPLEMENTED_ExprJoinedStr"
 "\n\
 The \"quick\"\n\