crates/syntax/src/ast/token_ext.rs

   1 //! There are many AstNodes, but only a few tokens, so we hand-write them here.
   2
   3 use std::{
   4     borrow::Cow,
   5     convert::{TryFrom, TryInto},
   6 };
   7
   8 use rustc_lexer::unescape::{unescape_literal, Mode};
   9
  10 use crate::{
  11     ast::{self, AstToken},
  12     TextRange, TextSize,
  13 };
  14
  15 impl ast::Comment {
  16     pub fn kind(&self) -> CommentKind {
  17         CommentKind::from_text(self.text())
  18     }
  19
  20     pub fn is_inner(&self) -> bool {
  21         self.kind().doc == Some(CommentPlacement::Inner)
  22     }
  23
  24     pub fn is_outer(&self) -> bool {
  25         self.kind().doc == Some(CommentPlacement::Outer)
  26     }
  27
  28     pub fn prefix(&self) -> &'static str {
  29         let &(prefix, _kind) = CommentKind::BY_PREFIX
  30             .iter()
  31             .find(|&(prefix, kind)| self.kind() == *kind && self.text().starts_with(prefix))
  32             .unwrap();
  33         prefix
  34     }
  35
  36     /// Returns the textual content of a doc comment node as a single string with prefix and suffix
  37     /// removed.
  38     pub fn doc_comment(&self) -> Option<&str> {
  39         let kind = self.kind();
  40         match kind {
  41             CommentKind { shape, doc: Some(_) } => {
  42                 let prefix = kind.prefix();
  43                 let text = &self.text()[prefix.len()..];
  44                 let text = if shape == CommentShape::Block {
  45                     text.strip_suffix("*/").unwrap_or(text)
  46                 } else {
  47                     text
  48                 };
  49                 Some(text)
  50             }
  51             _ => None,
  52         }
  53     }
  54 }
  55
  56 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
  57 pub struct CommentKind {
  58     pub shape: CommentShape,
  59     pub doc: Option<CommentPlacement>,
  60 }
  61
  62 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
  63 pub enum CommentShape {
  64     Line,
  65     Block,
  66 }
  67
  68 impl CommentShape {
  69     pub fn is_line(self) -> bool {
  70         self == CommentShape::Line
  71     }
  72
  73     pub fn is_block(self) -> bool {
  74         self == CommentShape::Block
  75     }
  76 }
  77
  78 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
  79 pub enum CommentPlacement {
  80     Inner,
  81     Outer,
  82 }
  83
  84 impl CommentKind {
  85     const BY_PREFIX: [(&'static str, CommentKind); 9] = [
  86         ("/**/", CommentKind { shape: CommentShape::Block, doc: None }),
  87         ("/***", CommentKind { shape: CommentShape::Block, doc: None }),
  88         ("////", CommentKind { shape: CommentShape::Line, doc: None }),
  89         ("///", CommentKind { shape: CommentShape::Line, doc: Some(CommentPlacement::Outer) }),
  90         ("//!", CommentKind { shape: CommentShape::Line, doc: Some(CommentPlacement::Inner) }),
  91         ("/**", CommentKind { shape: CommentShape::Block, doc: Some(CommentPlacement::Outer) }),
  92         ("/*!", CommentKind { shape: CommentShape::Block, doc: Some(CommentPlacement::Inner) }),
  93         ("//", CommentKind { shape: CommentShape::Line, doc: None }),
  94         ("/*", CommentKind { shape: CommentShape::Block, doc: None }),
  95     ];
  96
  97     pub(crate) fn from_text(text: &str) -> CommentKind {
  98         let &(_prefix, kind) = CommentKind::BY_PREFIX
  99             .iter()
 100             .find(|&(prefix, _kind)| text.starts_with(prefix))
 101             .unwrap();
 102         kind
 103     }
 104
 105     fn prefix(&self) -> &'static str {
 106         let &(prefix, _) = CommentKind::BY_PREFIX.iter().find(|(_, kind)| kind == self).unwrap();
 107         prefix
 108     }
 109 }
 110
 111 impl ast::Whitespace {
 112     pub fn spans_multiple_lines(&self) -> bool {
 113         let text = self.text();
 114         text.find('\n').map_or(false, |idx| text[idx + 1..].contains('\n'))
 115     }
 116 }
 117
 118 pub struct QuoteOffsets {
 119     pub quotes: (TextRange, TextRange),
 120     pub contents: TextRange,
 121 }
 122
 123 impl QuoteOffsets {
 124     fn new(literal: &str) -> Option<QuoteOffsets> {
 125         let left_quote = literal.find('"')?;
 126         let right_quote = literal.rfind('"')?;
 127         if left_quote == right_quote {
 128             // `literal` only contains one quote
 129             return None;
 130         }
 131
 132         let start = TextSize::from(0);
 133         let left_quote = TextSize::try_from(left_quote).unwrap() + TextSize::of('"');
 134         let right_quote = TextSize::try_from(right_quote).unwrap();
 135         let end = TextSize::of(literal);
 136
 137         let res = QuoteOffsets {
 138             quotes: (TextRange::new(start, left_quote), TextRange::new(right_quote, end)),
 139             contents: TextRange::new(left_quote, right_quote),
 140         };
 141         Some(res)
 142     }
 143 }
 144
 145 impl ast::String {
 146     pub fn is_raw(&self) -> bool {
 147         self.text().starts_with('r')
 148     }
 149     pub fn map_range_up(&self, range: TextRange) -> Option<TextRange> {
 150         let contents_range = self.text_range_between_quotes()?;
 151         assert!(TextRange::up_to(contents_range.len()).contains_range(range));
 152         Some(range + contents_range.start())
 153     }
 154
 155     pub fn value(&self) -> Option<Cow<'_, str>> {
 156         if self.is_raw() {
 157             let text = self.text();
 158             let text =
 159                 &text[self.text_range_between_quotes()? - self.syntax().text_range().start()];
 160             return Some(Cow::Borrowed(text));
 161         }
 162
 163         let text = self.text();
 164         let text = &text[self.text_range_between_quotes()? - self.syntax().text_range().start()];
 165
 166         let mut buf = String::new();
 167         let mut text_iter = text.chars();
 168         let mut has_error = false;
 169         unescape_literal(text, Mode::Str, &mut |char_range, unescaped_char| match (
 170             unescaped_char,
 171             buf.capacity() == 0,
 172         ) {
 173             (Ok(c), false) => buf.push(c),
 174             (Ok(c), true) if char_range.len() == 1 && Some(c) == text_iter.next() => (),
 175             (Ok(c), true) => {
 176                 buf.reserve_exact(text.len());
 177                 buf.push_str(&text[..char_range.start]);
 178                 buf.push(c);
 179             }
 180             (Err(_), _) => has_error = true,
 181         });
 182
 183         match (has_error, buf.capacity() == 0) {
 184             (true, _) => None,
 185             (false, true) => Some(Cow::Borrowed(text)),
 186             (false, false) => Some(Cow::Owned(buf)),
 187         }
 188     }
 189
 190     pub fn quote_offsets(&self) -> Option<QuoteOffsets> {
 191         let text = self.text();
 192         let offsets = QuoteOffsets::new(text)?;
 193         let o = self.syntax().text_range().start();
 194         let offsets = QuoteOffsets {
 195             quotes: (offsets.quotes.0 + o, offsets.quotes.1 + o),
 196             contents: offsets.contents + o,
 197         };
 198         Some(offsets)
 199     }
 200     pub fn text_range_between_quotes(&self) -> Option<TextRange> {
 201         self.quote_offsets().map(|it| it.contents)
 202     }
 203     pub fn open_quote_text_range(&self) -> Option<TextRange> {
 204         self.quote_offsets().map(|it| it.quotes.0)
 205     }
 206     pub fn close_quote_text_range(&self) -> Option<TextRange> {
 207         self.quote_offsets().map(|it| it.quotes.1)
 208     }
 209 }
 210
 211 impl ast::ByteString {
 212     pub fn is_raw(&self) -> bool {
 213         self.text().starts_with("br")
 214     }
 215 }
 216
 217 #[derive(Debug)]
 218 pub enum FormatSpecifier {
 219     Open,
 220     Close,
 221     Integer,
 222     Identifier,
 223     Colon,
 224     Fill,
 225     Align,
 226     Sign,
 227     NumberSign,
 228     Zero,
 229     DollarSign,
 230     Dot,
 231     Asterisk,
 232     QuestionMark,
 233 }
 234
 235 pub trait HasFormatSpecifier: AstToken {
 236     fn char_ranges(
 237         &self,
 238     ) -> Option<Vec<(TextRange, Result<char, rustc_lexer::unescape::EscapeError>)>>;
 239
 240     fn lex_format_specifier<F>(&self, mut callback: F)
 241     where
 242         F: FnMut(TextRange, FormatSpecifier),
 243     {
 244         let char_ranges = if let Some(char_ranges) = self.char_ranges() {
 245             char_ranges
 246         } else {
 247             return;
 248         };
 249         let mut chars = char_ranges.iter().peekable();
 250
 251         while let Some((range, first_char)) = chars.next() {
 252             match first_char {
 253                 Ok('{') => {
 254                     // Format specifier, see syntax at https://doc.rust-lang.org/std/fmt/index.html#syntax
 255                     if let Some((_, Ok('{'))) = chars.peek() {
 256                         // Escaped format specifier, `{{`
 257                         chars.next();
 258                         continue;
 259                     }
 260
 261                     callback(*range, FormatSpecifier::Open);
 262
 263                     // check for integer/identifier
 264                     match chars
 265                         .peek()
 266                         .and_then(|next| next.1.as_ref().ok())
 267                         .copied()
 268                         .unwrap_or_default()
 269                     {
 270                         '0'..='9' => {
 271                             // integer
 272                             read_integer(&mut chars, &mut callback);
 273                         }
 274                         c if c == '_' || c.is_alphabetic() => {
 275                             // identifier
 276                             read_identifier(&mut chars, &mut callback);
 277                         }
 278                         _ => {}
 279                     }
 280
 281                     if let Some((_, Ok(':'))) = chars.peek() {
 282                         skip_char_and_emit(&mut chars, FormatSpecifier::Colon, &mut callback);
 283
 284                         // check for fill/align
 285                         let mut cloned = chars.clone().take(2);
 286                         let first = cloned
 287                             .next()
 288                             .and_then(|next| next.1.as_ref().ok())
 289                             .copied()
 290                             .unwrap_or_default();
 291                         let second = cloned
 292                             .next()
 293                             .and_then(|next| next.1.as_ref().ok())
 294                             .copied()
 295                             .unwrap_or_default();
 296                         match second {
 297                             '<' | '^' | '>' => {
 298                                 // alignment specifier, first char specifies fillment
 299                                 skip_char_and_emit(
 300                                     &mut chars,
 301                                     FormatSpecifier::Fill,
 302                                     &mut callback,
 303                                 );
 304                                 skip_char_and_emit(
 305                                     &mut chars,
 306                                     FormatSpecifier::Align,
 307                                     &mut callback,
 308                                 );
 309                             }
 310                             _ => match first {
 311                                 '<' | '^' | '>' => {
 312                                     skip_char_and_emit(
 313                                         &mut chars,
 314                                         FormatSpecifier::Align,
 315                                         &mut callback,
 316                                     );
 317                                 }
 318                                 _ => {}
 319                             },
 320                         }
 321
 322                         // check for sign
 323                         match chars
 324                             .peek()
 325                             .and_then(|next| next.1.as_ref().ok())
 326                             .copied()
 327                             .unwrap_or_default()
 328                         {
 329                             '+' | '-' => {
 330                                 skip_char_and_emit(
 331                                     &mut chars,
 332                                     FormatSpecifier::Sign,
 333                                     &mut callback,
 334                                 );
 335                             }
 336                             _ => {}
 337                         }
 338
 339                         // check for `#`
 340                         if let Some((_, Ok('#'))) = chars.peek() {
 341                             skip_char_and_emit(
 342                                 &mut chars,
 343                                 FormatSpecifier::NumberSign,
 344                                 &mut callback,
 345                             );
 346                         }
 347
 348                         // check for `0`
 349                         let mut cloned = chars.clone().take(2);
 350                         let first = cloned.next().and_then(|next| next.1.as_ref().ok()).copied();
 351                         let second = cloned.next().and_then(|next| next.1.as_ref().ok()).copied();
 352
 353                         if first == Some('0') && second != Some('$') {
 354                             skip_char_and_emit(&mut chars, FormatSpecifier::Zero, &mut callback);
 355                         }
 356
 357                         // width
 358                         match chars
 359                             .peek()
 360                             .and_then(|next| next.1.as_ref().ok())
 361                             .copied()
 362                             .unwrap_or_default()
 363                         {
 364                             '0'..='9' => {
 365                                 read_integer(&mut chars, &mut callback);
 366                                 if let Some((_, Ok('$'))) = chars.peek() {
 367                                     skip_char_and_emit(
 368                                         &mut chars,
 369                                         FormatSpecifier::DollarSign,
 370                                         &mut callback,
 371                                     );
 372                                 }
 373                             }
 374                             c if c == '_' || c.is_alphabetic() => {
 375                                 read_identifier(&mut chars, &mut callback);
 376
 377                                 if chars.peek().and_then(|next| next.1.as_ref().ok()).copied()
 378                                     == Some('?')
 379                                 {
 380                                     skip_char_and_emit(
 381                                         &mut chars,
 382                                         FormatSpecifier::QuestionMark,
 383                                         &mut callback,
 384                                     );
 385                                 }
 386
 387                                 // can be either width (indicated by dollar sign, or type in which case
 388                                 // the next sign has to be `}`)
 389                                 let next =
 390                                     chars.peek().and_then(|next| next.1.as_ref().ok()).copied();
 391
 392                                 match next {
 393                                     Some('$') => skip_char_and_emit(
 394                                         &mut chars,
 395                                         FormatSpecifier::DollarSign,
 396                                         &mut callback,
 397                                     ),
 398                                     Some('}') => {
 399                                         skip_char_and_emit(
 400                                             &mut chars,
 401                                             FormatSpecifier::Close,
 402                                             &mut callback,
 403                                         );
 404                                         continue;
 405                                     }
 406                                     _ => continue,
 407                                 };
 408                             }
 409                             _ => {}
 410                         }
 411
 412                         // precision
 413                         if let Some((_, Ok('.'))) = chars.peek() {
 414                             skip_char_and_emit(&mut chars, FormatSpecifier::Dot, &mut callback);
 415
 416                             match chars
 417                                 .peek()
 418                                 .and_then(|next| next.1.as_ref().ok())
 419                                 .copied()
 420                                 .unwrap_or_default()
 421                             {
 422                                 '*' => {
 423                                     skip_char_and_emit(
 424                                         &mut chars,
 425                                         FormatSpecifier::Asterisk,
 426                                         &mut callback,
 427                                     );
 428                                 }
 429                                 '0'..='9' => {
 430                                     read_integer(&mut chars, &mut callback);
 431                                     if let Some((_, Ok('$'))) = chars.peek() {
 432                                         skip_char_and_emit(
 433                                             &mut chars,
 434                                             FormatSpecifier::DollarSign,
 435                                             &mut callback,
 436                                         );
 437                                     }
 438                                 }
 439                                 c if c == '_' || c.is_alphabetic() => {
 440                                     read_identifier(&mut chars, &mut callback);
 441                                     if chars.peek().and_then(|next| next.1.as_ref().ok()).copied()
 442                                         != Some('$')
 443                                     {
 444                                         continue;
 445                                     }
 446                                     skip_char_and_emit(
 447                                         &mut chars,
 448                                         FormatSpecifier::DollarSign,
 449                                         &mut callback,
 450                                     );
 451                                 }
 452                                 _ => {
 453                                     continue;
 454                                 }
 455                             }
 456                         }
 457
 458                         // type
 459                         match chars
 460                             .peek()
 461                             .and_then(|next| next.1.as_ref().ok())
 462                             .copied()
 463                             .unwrap_or_default()
 464                         {
 465                             '?' => {
 466                                 skip_char_and_emit(
 467                                     &mut chars,
 468                                     FormatSpecifier::QuestionMark,
 469                                     &mut callback,
 470                                 );
 471                             }
 472                             c if c == '_' || c.is_alphabetic() => {
 473                                 read_identifier(&mut chars, &mut callback);
 474
 475                                 if chars.peek().and_then(|next| next.1.as_ref().ok()).copied()
 476                                     == Some('?')
 477                                 {
 478                                     skip_char_and_emit(
 479                                         &mut chars,
 480                                         FormatSpecifier::QuestionMark,
 481                                         &mut callback,
 482                                     );
 483                                 }
 484                             }
 485                             _ => {}
 486                         }
 487                     }
 488
 489                     if let Some((_, Ok('}'))) = chars.peek() {
 490                         skip_char_and_emit(&mut chars, FormatSpecifier::Close, &mut callback);
 491                     } else {
 492                         continue;
 493                     }
 494                 }
 495                 _ => {
 496                     while let Some((_, Ok(next_char))) = chars.peek() {
 497                         if next_char == &'{' {
 498                             break;
 499                         }
 500                         chars.next();
 501                     }
 502                 }
 503             };
 504         }
 505
 506         fn skip_char_and_emit<'a, I, F>(
 507             chars: &mut std::iter::Peekable<I>,
 508             emit: FormatSpecifier,
 509             callback: &mut F,
 510         ) where
 511             I: Iterator<Item = &'a (TextRange, Result<char, rustc_lexer::unescape::EscapeError>)>,
 512             F: FnMut(TextRange, FormatSpecifier),
 513         {
 514             let (range, _) = chars.next().unwrap();
 515             callback(*range, emit);
 516         }
 517
 518         fn read_integer<'a, I, F>(chars: &mut std::iter::Peekable<I>, callback: &mut F)
 519         where
 520             I: Iterator<Item = &'a (TextRange, Result<char, rustc_lexer::unescape::EscapeError>)>,
 521             F: FnMut(TextRange, FormatSpecifier),
 522         {
 523             let (mut range, c) = chars.next().unwrap();
 524             assert!(c.as_ref().unwrap().is_ascii_digit());
 525             while let Some((r, Ok(next_char))) = chars.peek() {
 526                 if next_char.is_ascii_digit() {
 527                     chars.next();
 528                     range = range.cover(*r);
 529                 } else {
 530                     break;
 531                 }
 532             }
 533             callback(range, FormatSpecifier::Integer);
 534         }
 535
 536         fn read_identifier<'a, I, F>(chars: &mut std::iter::Peekable<I>, callback: &mut F)
 537         where
 538             I: Iterator<Item = &'a (TextRange, Result<char, rustc_lexer::unescape::EscapeError>)>,
 539             F: FnMut(TextRange, FormatSpecifier),
 540         {
 541             let (mut range, c) = chars.next().unwrap();
 542             assert!(c.as_ref().unwrap().is_alphabetic() || *c.as_ref().unwrap() == '_');
 543             while let Some((r, Ok(next_char))) = chars.peek() {
 544                 if *next_char == '_' || next_char.is_ascii_digit() || next_char.is_alphabetic() {
 545                     chars.next();
 546                     range = range.cover(*r);
 547                 } else {
 548                     break;
 549                 }
 550             }
 551             callback(range, FormatSpecifier::Identifier);
 552         }
 553     }
 554 }
 555
 556 impl HasFormatSpecifier for ast::String {
 557     fn char_ranges(
 558         &self,
 559     ) -> Option<Vec<(TextRange, Result<char, rustc_lexer::unescape::EscapeError>)>> {
 560         let text = self.text();
 561         let text = &text[self.text_range_between_quotes()? - self.syntax().text_range().start()];
 562         let offset = self.text_range_between_quotes()?.start() - self.syntax().text_range().start();
 563
 564         let mut res = Vec::with_capacity(text.len());
 565         unescape_literal(text, Mode::Str, &mut |range, unescaped_char| {
 566             res.push((
 567                 TextRange::new(range.start.try_into().unwrap(), range.end.try_into().unwrap())
 568                     + offset,
 569                 unescaped_char,
 570             ))
 571         });
 572
 573         Some(res)
 574     }
 575 }
 576
 577 impl ast::IntNumber {
 578     pub fn radix(&self) -> Radix {
 579         match self.text().get(..2).unwrap_or_default() {
 580             "0b" => Radix::Binary,
 581             "0o" => Radix::Octal,
 582             "0x" => Radix::Hexadecimal,
 583             _ => Radix::Decimal,
 584         }
 585     }
 586
 587     pub fn value(&self) -> Option<u128> {
 588         let token = self.syntax();
 589
 590         let mut text = token.text();
 591         if let Some(suffix) = self.suffix() {
 592             text = &text[..text.len() - suffix.len()]
 593         }
 594
 595         let radix = self.radix();
 596         text = &text[radix.prefix_len()..];
 597
 598         let buf;
 599         if text.contains('_') {
 600             buf = text.replace('_', "");
 601             text = buf.as_str();
 602         };
 603
 604         let value = u128::from_str_radix(text, radix as u32).ok()?;
 605         Some(value)
 606     }
 607
 608     pub fn suffix(&self) -> Option<&str> {
 609         let text = self.text();
 610         let radix = self.radix();
 611         let mut indices = text.char_indices();
 612         if radix != Radix::Decimal {
 613             indices.next()?;
 614             indices.next()?;
 615         }
 616         let is_suffix_start: fn(&(usize, char)) -> bool = match radix {
 617             Radix::Hexadecimal => |(_, c)| matches!(c, 'g'..='z' | 'G'..='Z'),
 618             _ => |(_, c)| c.is_ascii_alphabetic(),
 619         };
 620         let (suffix_start, _) = indices.find(is_suffix_start)?;
 621         Some(&text[suffix_start..])
 622     }
 623 }
 624
 625 impl ast::FloatNumber {
 626     pub fn suffix(&self) -> Option<&str> {
 627         let text = self.text();
 628         let mut indices = text.char_indices();
 629         let (mut suffix_start, c) = indices.by_ref().find(|(_, c)| c.is_ascii_alphabetic())?;
 630         if c == 'e' || c == 'E' {
 631             suffix_start = indices.find(|(_, c)| c.is_ascii_alphabetic())?.0;
 632         }
 633         Some(&text[suffix_start..])
 634     }
 635 }
 636
 637 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
 638 pub enum Radix {
 639     Binary = 2,
 640     Octal = 8,
 641     Decimal = 10,
 642     Hexadecimal = 16,
 643 }
 644
 645 impl Radix {
 646     pub const ALL: &'static [Radix] =
 647         &[Radix::Binary, Radix::Octal, Radix::Decimal, Radix::Hexadecimal];
 648
 649     const fn prefix_len(&self) -> usize {
 650         match self {
 651             Self::Decimal => 0,
 652             _ => 2,
 653         }
 654     }
 655 }
 656
 657 #[cfg(test)]
 658 mod tests {
 659     use crate::ast::{self, make, FloatNumber, IntNumber};
 660
 661     fn check_float_suffix<'a>(lit: &str, expected: impl Into<Option<&'a str>>) {
 662         assert_eq!(FloatNumber { syntax: make::tokens::literal(lit) }.suffix(), expected.into());
 663     }
 664
 665     fn check_int_suffix<'a>(lit: &str, expected: impl Into<Option<&'a str>>) {
 666         assert_eq!(IntNumber { syntax: make::tokens::literal(lit) }.suffix(), expected.into());
 667     }
 668
 669     #[test]
 670     fn test_float_number_suffix() {
 671         check_float_suffix("123.0", None);
 672         check_float_suffix("123f32", "f32");
 673         check_float_suffix("123.0e", None);
 674         check_float_suffix("123.0e4", None);
 675         check_float_suffix("123.0ef32", "f32");
 676         check_float_suffix("123.0E4f32", "f32");
 677         check_float_suffix("1_2_3.0_f32", "f32");
 678     }
 679
 680     #[test]
 681     fn test_int_number_suffix() {
 682         check_int_suffix("123", None);
 683         check_int_suffix("123i32", "i32");
 684         check_int_suffix("1_0_1_l_o_l", "l_o_l");
 685         check_int_suffix("0b11", None);
 686         check_int_suffix("0o11", None);
 687         check_int_suffix("0xff", None);
 688         check_int_suffix("0b11u32", "u32");
 689         check_int_suffix("0o11u32", "u32");
 690         check_int_suffix("0xffu32", "u32");
 691     }
 692
 693     fn check_string_value<'a>(lit: &str, expected: impl Into<Option<&'a str>>) {
 694         assert_eq!(
 695             ast::String { syntax: make::tokens::literal(&format!("\"{}\"", lit)) }
 696                 .value()
 697                 .as_deref(),
 698             expected.into()
 699         );
 700     }
 701
 702     #[test]
 703     fn test_string_escape() {
 704         check_string_value(r"foobar", "foobar");
 705         check_string_value(r"\foobar", None);
 706         check_string_value(r"\nfoobar", "\nfoobar");
 707         check_string_value(r"C:\\Windows\\System32\\", "C:\\Windows\\System32\\");
 708     }
 709 }