compiler/rustc_parse_format/src/lib.rs

   1 //! Macro support for format strings
   2 //!
   3 //! These structures are used when parsing format strings for the compiler.
   4 //! Parsing does not happen at runtime: structures of `std::fmt::rt` are
   5 //! generated instead.
   6
   7 #![doc(
   8     html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
   9     html_playground_url = "https://play.rust-lang.org/",
  10     test(attr(deny(warnings)))
  11 )]
  12 #![feature(nll)]
  13 #![feature(or_patterns)]
  14 #![feature(bool_to_option)]
  15
  16 pub use Alignment::*;
  17 pub use Count::*;
  18 pub use Flag::*;
  19 pub use Piece::*;
  20 pub use Position::*;
  21
  22 use std::iter;
  23 use std::str;
  24 use std::string;
  25
  26 use rustc_span::{InnerSpan, Symbol};
  27
  28 /// The type of format string that we are parsing.
  29 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  30 pub enum ParseMode {
  31     /// A normal format string as per `format_args!`.
  32     Format,
  33     /// An inline assembly template string for `asm!`.
  34     InlineAsm,
  35 }
  36
  37 #[derive(Copy, Clone)]
  38 struct InnerOffset(usize);
  39
  40 impl InnerOffset {
  41     fn to(self, end: InnerOffset) -> InnerSpan {
  42         InnerSpan::new(self.0, end.0)
  43     }
  44 }
  45
  46 /// A piece is a portion of the format string which represents the next part
  47 /// to emit. These are emitted as a stream by the `Parser` class.
  48 #[derive(Copy, Clone, Debug, PartialEq)]
  49 pub enum Piece<'a> {
  50     /// A literal string which should directly be emitted
  51     String(&'a str),
  52     /// This describes that formatting should process the next argument (as
  53     /// specified inside) for emission.
  54     NextArgument(Argument<'a>),
  55 }
  56
  57 /// Representation of an argument specification.
  58 #[derive(Copy, Clone, Debug, PartialEq)]
  59 pub struct Argument<'a> {
  60     /// Where to find this argument
  61     pub position: Position,
  62     /// How to format the argument
  63     pub format: FormatSpec<'a>,
  64 }
  65
  66 /// Specification for the formatting of an argument in the format string.
  67 #[derive(Copy, Clone, Debug, PartialEq)]
  68 pub struct FormatSpec<'a> {
  69     /// Optionally specified character to fill alignment with.
  70     pub fill: Option<char>,
  71     /// Optionally specified alignment.
  72     pub align: Alignment,
  73     /// Packed version of various flags provided.
  74     pub flags: u32,
  75     /// The integer precision to use.
  76     pub precision: Count,
  77     /// The span of the precision formatting flag (for diagnostics).
  78     pub precision_span: Option<InnerSpan>,
  79     /// The string width requested for the resulting format.
  80     pub width: Count,
  81     /// The span of the width formatting flag (for diagnostics).
  82     pub width_span: Option<InnerSpan>,
  83     /// The descriptor string representing the name of the format desired for
  84     /// this argument, this can be empty or any number of characters, although
  85     /// it is required to be one word.
  86     pub ty: &'a str,
  87     /// The span of the descriptor string (for diagnostics).
  88     pub ty_span: Option<InnerSpan>,
  89 }
  90
  91 /// Enum describing where an argument for a format can be located.
  92 #[derive(Copy, Clone, Debug, PartialEq)]
  93 pub enum Position {
  94     /// The argument is implied to be located at an index
  95     ArgumentImplicitlyIs(usize),
  96     /// The argument is located at a specific index given in the format
  97     ArgumentIs(usize),
  98     /// The argument has a name.
  99     ArgumentNamed(Symbol),
 100 }
 101
 102 impl Position {
 103     pub fn index(&self) -> Option<usize> {
 104         match self {
 105             ArgumentIs(i) | ArgumentImplicitlyIs(i) => Some(*i),
 106             _ => None,
 107         }
 108     }
 109 }
 110
 111 /// Enum of alignments which are supported.
 112 #[derive(Copy, Clone, Debug, PartialEq)]
 113 pub enum Alignment {
 114     /// The value will be aligned to the left.
 115     AlignLeft,
 116     /// The value will be aligned to the right.
 117     AlignRight,
 118     /// The value will be aligned in the center.
 119     AlignCenter,
 120     /// The value will take on a default alignment.
 121     AlignUnknown,
 122 }
 123
 124 /// Various flags which can be applied to format strings. The meaning of these
 125 /// flags is defined by the formatters themselves.
 126 #[derive(Copy, Clone, Debug, PartialEq)]
 127 pub enum Flag {
 128     /// A `+` will be used to denote positive numbers.
 129     FlagSignPlus,
 130     /// A `-` will be used to denote negative numbers. This is the default.
 131     FlagSignMinus,
 132     /// An alternate form will be used for the value. In the case of numbers,
 133     /// this means that the number will be prefixed with the supplied string.
 134     FlagAlternate,
 135     /// For numbers, this means that the number will be padded with zeroes,
 136     /// and the sign (`+` or `-`) will precede them.
 137     FlagSignAwareZeroPad,
 138     /// For Debug / `?`, format integers in lower-case hexadecimal.
 139     FlagDebugLowerHex,
 140     /// For Debug / `?`, format integers in upper-case hexadecimal.
 141     FlagDebugUpperHex,
 142 }
 143
 144 /// A count is used for the precision and width parameters of an integer, and
 145 /// can reference either an argument or a literal integer.
 146 #[derive(Copy, Clone, Debug, PartialEq)]
 147 pub enum Count {
 148     /// The count is specified explicitly.
 149     CountIs(usize),
 150     /// The count is specified by the argument with the given name.
 151     CountIsName(Symbol),
 152     /// The count is specified by the argument at the given index.
 153     CountIsParam(usize),
 154     /// The count is implied and cannot be explicitly specified.
 155     CountImplied,
 156 }
 157
 158 pub struct ParseError {
 159     pub description: string::String,
 160     pub note: Option<string::String>,
 161     pub label: string::String,
 162     pub span: InnerSpan,
 163     pub secondary_label: Option<(string::String, InnerSpan)>,
 164 }
 165
 166 /// The parser structure for interpreting the input format string. This is
 167 /// modeled as an iterator over `Piece` structures to form a stream of tokens
 168 /// being output.
 169 ///
 170 /// This is a recursive-descent parser for the sake of simplicity, and if
 171 /// necessary there's probably lots of room for improvement performance-wise.
 172 pub struct Parser<'a> {
 173     mode: ParseMode,
 174     input: &'a str,
 175     cur: iter::Peekable<str::CharIndices<'a>>,
 176     /// Error messages accumulated during parsing
 177     pub errors: Vec<ParseError>,
 178     /// Current position of implicit positional argument pointer
 179     pub curarg: usize,
 180     /// `Some(raw count)` when the string is "raw", used to position spans correctly
 181     style: Option<usize>,
 182     /// Start and end byte offset of every successfully parsed argument
 183     pub arg_places: Vec<InnerSpan>,
 184     /// Characters that need to be shifted
 185     skips: Vec<usize>,
 186     /// Span of the last opening brace seen, used for error reporting
 187     last_opening_brace: Option<InnerSpan>,
 188     /// Whether the source string is comes from `println!` as opposed to `format!` or `print!`
 189     append_newline: bool,
 190     /// Whether this formatting string is a literal or it comes from a macro.
 191     pub is_literal: bool,
 192     /// Start position of the current line.
 193     cur_line_start: usize,
 194     /// Start and end byte offset of every line of the format string. Excludes
 195     /// newline characters and leading whitespace.
 196     pub line_spans: Vec<InnerSpan>,
 197 }
 198
 199 impl<'a> Iterator for Parser<'a> {
 200     type Item = Piece<'a>;
 201
 202     fn next(&mut self) -> Option<Piece<'a>> {
 203         if let Some(&(pos, c)) = self.cur.peek() {
 204             match c {
 205                 '{' => {
 206                     let curr_last_brace = self.last_opening_brace;
 207                     let byte_pos = self.to_span_index(pos);
 208                     self.last_opening_brace = Some(byte_pos.to(InnerOffset(byte_pos.0 + 1)));
 209                     self.cur.next();
 210                     if self.consume('{') {
 211                         self.last_opening_brace = curr_last_brace;
 212
 213                         Some(String(self.string(pos + 1)))
 214                     } else {
 215                         let arg = self.argument();
 216                         if let Some(end) = self.must_consume('}') {
 217                             let start = self.to_span_index(pos);
 218                             let end = self.to_span_index(end + 1);
 219                             if self.is_literal {
 220                                 self.arg_places.push(start.to(end));
 221                             }
 222                         }
 223                         Some(NextArgument(arg))
 224                     }
 225                 }
 226                 '}' => {
 227                     self.cur.next();
 228                     if self.consume('}') {
 229                         Some(String(self.string(pos + 1)))
 230                     } else {
 231                         let err_pos = self.to_span_index(pos);
 232                         self.err_with_note(
 233                             "unmatched `}` found",
 234                             "unmatched `}`",
 235                             "if you intended to print `}`, you can escape it using `}}`",
 236                             err_pos.to(err_pos),
 237                         );
 238                         None
 239                     }
 240                 }
 241                 _ => Some(String(self.string(pos))),
 242             }
 243         } else {
 244             if self.is_literal {
 245                 let start = self.to_span_index(self.cur_line_start);
 246                 let end = self.to_span_index(self.input.len());
 247                 let span = start.to(end);
 248                 if self.line_spans.last() != Some(&span) {
 249                     self.line_spans.push(span);
 250                 }
 251             }
 252             None
 253         }
 254     }
 255 }
 256
 257 impl<'a> Parser<'a> {
 258     /// Creates a new parser for the given format string
 259     pub fn new(
 260         s: &'a str,
 261         style: Option<usize>,
 262         snippet: Option<string::String>,
 263         append_newline: bool,
 264         mode: ParseMode,
 265     ) -> Parser<'a> {
 266         let (skips, is_literal) = find_skips_from_snippet(snippet, style);
 267         Parser {
 268             mode,
 269             input: s,
 270             cur: s.char_indices().peekable(),
 271             errors: vec![],
 272             curarg: 0,
 273             style,
 274             arg_places: vec![],
 275             skips,
 276             last_opening_brace: None,
 277             append_newline,
 278             is_literal,
 279             cur_line_start: 0,
 280             line_spans: vec![],
 281         }
 282     }
 283
 284     /// Notifies of an error. The message doesn't actually need to be of type
 285     /// String, but I think it does when this eventually uses conditions so it
 286     /// might as well start using it now.
 287     fn err<S1: Into<string::String>, S2: Into<string::String>>(
 288         &mut self,
 289         description: S1,
 290         label: S2,
 291         span: InnerSpan,
 292     ) {
 293         self.errors.push(ParseError {
 294             description: description.into(),
 295             note: None,
 296             label: label.into(),
 297             span,
 298             secondary_label: None,
 299         });
 300     }
 301
 302     /// Notifies of an error. The message doesn't actually need to be of type
 303     /// String, but I think it does when this eventually uses conditions so it
 304     /// might as well start using it now.
 305     fn err_with_note<
 306         S1: Into<string::String>,
 307         S2: Into<string::String>,
 308         S3: Into<string::String>,
 309     >(
 310         &mut self,
 311         description: S1,
 312         label: S2,
 313         note: S3,
 314         span: InnerSpan,
 315     ) {
 316         self.errors.push(ParseError {
 317             description: description.into(),
 318             note: Some(note.into()),
 319             label: label.into(),
 320             span,
 321             secondary_label: None,
 322         });
 323     }
 324
 325     /// Optionally consumes the specified character. If the character is not at
 326     /// the current position, then the current iterator isn't moved and `false` is
 327     /// returned, otherwise the character is consumed and `true` is returned.
 328     fn consume(&mut self, c: char) -> bool {
 329         self.consume_pos(c).is_some()
 330     }
 331
 332     /// Optionally consumes the specified character. If the character is not at
 333     /// the current position, then the current iterator isn't moved and `None` is
 334     /// returned, otherwise the character is consumed and the current position is
 335     /// returned.
 336     fn consume_pos(&mut self, c: char) -> Option<usize> {
 337         if let Some(&(pos, maybe)) = self.cur.peek() {
 338             if c == maybe {
 339                 self.cur.next();
 340                 return Some(pos);
 341             }
 342         }
 343         None
 344     }
 345
 346     fn to_span_index(&self, pos: usize) -> InnerOffset {
 347         let mut pos = pos;
 348         // This handles the raw string case, the raw argument is the number of #
 349         // in r###"..."### (we need to add one because of the `r`).
 350         let raw = self.style.map(|raw| raw + 1).unwrap_or(0);
 351         for skip in &self.skips {
 352             if pos > *skip {
 353                 pos += 1;
 354             } else if pos == *skip && raw == 0 {
 355                 pos += 1;
 356             } else {
 357                 break;
 358             }
 359         }
 360         InnerOffset(raw + pos + 1)
 361     }
 362
 363     /// Forces consumption of the specified character. If the character is not
 364     /// found, an error is emitted.
 365     fn must_consume(&mut self, c: char) -> Option<usize> {
 366         self.ws();
 367
 368         if let Some(&(pos, maybe)) = self.cur.peek() {
 369             if c == maybe {
 370                 self.cur.next();
 371                 Some(pos)
 372             } else {
 373                 let pos = self.to_span_index(pos);
 374                 let description = format!("expected `'}}'`, found `{:?}`", maybe);
 375                 let label = "expected `}`".to_owned();
 376                 let (note, secondary_label) = if c == '}' {
 377                     (
 378                         Some(
 379                             "if you intended to print `{`, you can escape it using `{{`".to_owned(),
 380                         ),
 381                         self.last_opening_brace
 382                             .map(|sp| ("because of this opening brace".to_owned(), sp)),
 383                     )
 384                 } else {
 385                     (None, None)
 386                 };
 387                 self.errors.push(ParseError {
 388                     description,
 389                     note,
 390                     label,
 391                     span: pos.to(pos),
 392                     secondary_label,
 393                 });
 394                 None
 395             }
 396         } else {
 397             let description = format!("expected `{:?}` but string was terminated", c);
 398             // point at closing `"`
 399             let pos = self.input.len() - if self.append_newline { 1 } else { 0 };
 400             let pos = self.to_span_index(pos);
 401             if c == '}' {
 402                 let label = format!("expected `{:?}`", c);
 403                 let (note, secondary_label) = if c == '}' {
 404                     (
 405                         Some(
 406                             "if you intended to print `{`, you can escape it using `{{`".to_owned(),
 407                         ),
 408                         self.last_opening_brace
 409                             .map(|sp| ("because of this opening brace".to_owned(), sp)),
 410                     )
 411                 } else {
 412                     (None, None)
 413                 };
 414                 self.errors.push(ParseError {
 415                     description,
 416                     note,
 417                     label,
 418                     span: pos.to(pos),
 419                     secondary_label,
 420                 });
 421             } else {
 422                 self.err(description, format!("expected `{:?}`", c), pos.to(pos));
 423             }
 424             None
 425         }
 426     }
 427
 428     /// Consumes all whitespace characters until the first non-whitespace character
 429     fn ws(&mut self) {
 430         while let Some(&(_, c)) = self.cur.peek() {
 431             if c.is_whitespace() {
 432                 self.cur.next();
 433             } else {
 434                 break;
 435             }
 436         }
 437     }
 438
 439     /// Parses all of a string which is to be considered a "raw literal" in a
 440     /// format string. This is everything outside of the braces.
 441     fn string(&mut self, start: usize) -> &'a str {
 442         // we may not consume the character, peek the iterator
 443         while let Some(&(pos, c)) = self.cur.peek() {
 444             match c {
 445                 '{' | '}' => {
 446                     return &self.input[start..pos];
 447                 }
 448                 '\n' if self.is_literal => {
 449                     let start = self.to_span_index(self.cur_line_start);
 450                     let end = self.to_span_index(pos);
 451                     self.line_spans.push(start.to(end));
 452                     self.cur_line_start = pos + 1;
 453                     self.cur.next();
 454                 }
 455                 _ => {
 456                     if self.is_literal && pos == self.cur_line_start && c.is_whitespace() {
 457                         self.cur_line_start = pos + c.len_utf8();
 458                     }
 459                     self.cur.next();
 460                 }
 461             }
 462         }
 463         &self.input[start..self.input.len()]
 464     }
 465
 466     /// Parses an `Argument` structure, or what's contained within braces inside the format string.
 467     fn argument(&mut self) -> Argument<'a> {
 468         let pos = self.position();
 469         let format = match self.mode {
 470             ParseMode::Format => self.format(),
 471             ParseMode::InlineAsm => self.inline_asm(),
 472         };
 473
 474         // Resolve position after parsing format spec.
 475         let pos = match pos {
 476             Some(position) => position,
 477             None => {
 478                 let i = self.curarg;
 479                 self.curarg += 1;
 480                 ArgumentImplicitlyIs(i)
 481             }
 482         };
 483
 484         Argument { position: pos, format }
 485     }
 486
 487     /// Parses a positional argument for a format. This could either be an
 488     /// integer index of an argument, a named argument, or a blank string.
 489     /// Returns `Some(parsed_position)` if the position is not implicitly
 490     /// consuming a macro argument, `None` if it's the case.
 491     fn position(&mut self) -> Option<Position> {
 492         if let Some(i) = self.integer() {
 493             Some(ArgumentIs(i))
 494         } else {
 495             match self.cur.peek() {
 496                 Some(&(_, c)) if rustc_lexer::is_id_start(c) => {
 497                     Some(ArgumentNamed(Symbol::intern(self.word())))
 498                 }
 499
 500                 // This is an `ArgumentNext`.
 501                 // Record the fact and do the resolution after parsing the
 502                 // format spec, to make things like `{:.*}` work.
 503                 _ => None,
 504             }
 505         }
 506     }
 507
 508     /// Parses a format specifier at the current position, returning all of the
 509     /// relevant information in the `FormatSpec` struct.
 510     fn format(&mut self) -> FormatSpec<'a> {
 511         let mut spec = FormatSpec {
 512             fill: None,
 513             align: AlignUnknown,
 514             flags: 0,
 515             precision: CountImplied,
 516             precision_span: None,
 517             width: CountImplied,
 518             width_span: None,
 519             ty: &self.input[..0],
 520             ty_span: None,
 521         };
 522         if !self.consume(':') {
 523             return spec;
 524         }
 525
 526         // fill character
 527         if let Some(&(_, c)) = self.cur.peek() {
 528             if let Some((_, '>' | '<' | '^')) = self.cur.clone().nth(1) {
 529                 spec.fill = Some(c);
 530                 self.cur.next();
 531             }
 532         }
 533         // Alignment
 534         if self.consume('<') {
 535             spec.align = AlignLeft;
 536         } else if self.consume('>') {
 537             spec.align = AlignRight;
 538         } else if self.consume('^') {
 539             spec.align = AlignCenter;
 540         }
 541         // Sign flags
 542         if self.consume('+') {
 543             spec.flags |= 1 << (FlagSignPlus as u32);
 544         } else if self.consume('-') {
 545             spec.flags |= 1 << (FlagSignMinus as u32);
 546         }
 547         // Alternate marker
 548         if self.consume('#') {
 549             spec.flags |= 1 << (FlagAlternate as u32);
 550         }
 551         // Width and precision
 552         let mut havewidth = false;
 553
 554         if self.consume('0') {
 555             // small ambiguity with '0$' as a format string. In theory this is a
 556             // '0' flag and then an ill-formatted format string with just a '$'
 557             // and no count, but this is better if we instead interpret this as
 558             // no '0' flag and '0$' as the width instead.
 559             if self.consume('$') {
 560                 spec.width = CountIsParam(0);
 561                 havewidth = true;
 562             } else {
 563                 spec.flags |= 1 << (FlagSignAwareZeroPad as u32);
 564             }
 565         }
 566         if !havewidth {
 567             let width_span_start = if let Some((pos, _)) = self.cur.peek() { *pos } else { 0 };
 568             let (w, sp) = self.count(width_span_start);
 569             spec.width = w;
 570             spec.width_span = sp;
 571         }
 572         if let Some(start) = self.consume_pos('.') {
 573             if let Some(end) = self.consume_pos('*') {
 574                 // Resolve `CountIsNextParam`.
 575                 // We can do this immediately as `position` is resolved later.
 576                 let i = self.curarg;
 577                 self.curarg += 1;
 578                 spec.precision = CountIsParam(i);
 579                 spec.precision_span =
 580                     Some(self.to_span_index(start).to(self.to_span_index(end + 1)));
 581             } else {
 582                 let (p, sp) = self.count(start);
 583                 spec.precision = p;
 584                 spec.precision_span = sp;
 585             }
 586         }
 587         let ty_span_start = self.cur.peek().map(|(pos, _)| *pos);
 588         // Optional radix followed by the actual format specifier
 589         if self.consume('x') {
 590             if self.consume('?') {
 591                 spec.flags |= 1 << (FlagDebugLowerHex as u32);
 592                 spec.ty = "?";
 593             } else {
 594                 spec.ty = "x";
 595             }
 596         } else if self.consume('X') {
 597             if self.consume('?') {
 598                 spec.flags |= 1 << (FlagDebugUpperHex as u32);
 599                 spec.ty = "?";
 600             } else {
 601                 spec.ty = "X";
 602             }
 603         } else if self.consume('?') {
 604             spec.ty = "?";
 605         } else {
 606             spec.ty = self.word();
 607             let ty_span_end = self.cur.peek().map(|(pos, _)| *pos);
 608             if !spec.ty.is_empty() {
 609                 spec.ty_span = ty_span_start
 610                     .and_then(|s| ty_span_end.map(|e| (s, e)))
 611                     .map(|(start, end)| self.to_span_index(start).to(self.to_span_index(end)));
 612             }
 613         }
 614         spec
 615     }
 616
 617     /// Parses an inline assembly template modifier at the current position, returning the modifier
 618     /// in the `ty` field of the `FormatSpec` struct.
 619     fn inline_asm(&mut self) -> FormatSpec<'a> {
 620         let mut spec = FormatSpec {
 621             fill: None,
 622             align: AlignUnknown,
 623             flags: 0,
 624             precision: CountImplied,
 625             precision_span: None,
 626             width: CountImplied,
 627             width_span: None,
 628             ty: &self.input[..0],
 629             ty_span: None,
 630         };
 631         if !self.consume(':') {
 632             return spec;
 633         }
 634
 635         let ty_span_start = self.cur.peek().map(|(pos, _)| *pos);
 636         spec.ty = self.word();
 637         let ty_span_end = self.cur.peek().map(|(pos, _)| *pos);
 638         if !spec.ty.is_empty() {
 639             spec.ty_span = ty_span_start
 640                 .and_then(|s| ty_span_end.map(|e| (s, e)))
 641                 .map(|(start, end)| self.to_span_index(start).to(self.to_span_index(end)));
 642         }
 643
 644         spec
 645     }
 646
 647     /// Parses a `Count` parameter at the current position. This does not check
 648     /// for 'CountIsNextParam' because that is only used in precision, not
 649     /// width.
 650     fn count(&mut self, start: usize) -> (Count, Option<InnerSpan>) {
 651         if let Some(i) = self.integer() {
 652             if let Some(end) = self.consume_pos('$') {
 653                 let span = self.to_span_index(start).to(self.to_span_index(end + 1));
 654                 (CountIsParam(i), Some(span))
 655             } else {
 656                 (CountIs(i), None)
 657             }
 658         } else {
 659             let tmp = self.cur.clone();
 660             let word = self.word();
 661             if word.is_empty() {
 662                 self.cur = tmp;
 663                 (CountImplied, None)
 664             } else if self.consume('$') {
 665                 (CountIsName(Symbol::intern(word)), None)
 666             } else {
 667                 self.cur = tmp;
 668                 (CountImplied, None)
 669             }
 670         }
 671     }
 672
 673     /// Parses a word starting at the current position. A word is the same as
 674     /// Rust identifier, except that it can't start with `_` character.
 675     fn word(&mut self) -> &'a str {
 676         let start = match self.cur.peek() {
 677             Some(&(pos, c)) if rustc_lexer::is_id_start(c) => {
 678                 self.cur.next();
 679                 pos
 680             }
 681             _ => {
 682                 return "";
 683             }
 684         };
 685         let mut end = None;
 686         while let Some(&(pos, c)) = self.cur.peek() {
 687             if rustc_lexer::is_id_continue(c) {
 688                 self.cur.next();
 689             } else {
 690                 end = Some(pos);
 691                 break;
 692             }
 693         }
 694         let end = end.unwrap_or(self.input.len());
 695         let word = &self.input[start..end];
 696         if word == "_" {
 697             self.err_with_note(
 698                 "invalid argument name `_`",
 699                 "invalid argument name",
 700                 "argument name cannot be a single underscore",
 701                 self.to_span_index(start).to(self.to_span_index(end)),
 702             );
 703         }
 704         word
 705     }
 706
 707     /// Optionally parses an integer at the current position. This doesn't deal
 708     /// with overflow at all, it's just accumulating digits.
 709     fn integer(&mut self) -> Option<usize> {
 710         let mut cur = 0;
 711         let mut found = false;
 712         while let Some(&(_, c)) = self.cur.peek() {
 713             if let Some(i) = c.to_digit(10) {
 714                 cur = cur * 10 + i as usize;
 715                 found = true;
 716                 self.cur.next();
 717             } else {
 718                 break;
 719             }
 720         }
 721         found.then_some(cur)
 722     }
 723 }
 724
 725 /// Finds the indices of all characters that have been processed and differ between the actual
 726 /// written code (code snippet) and the `InternedString` that gets processed in the `Parser`
 727 /// in order to properly synthethise the intra-string `Span`s for error diagnostics.
 728 fn find_skips_from_snippet(
 729     snippet: Option<string::String>,
 730     str_style: Option<usize>,
 731 ) -> (Vec<usize>, bool) {
 732     let snippet = match snippet {
 733         Some(ref s) if s.starts_with('"') || s.starts_with("r#") => s,
 734         _ => return (vec![], false),
 735     };
 736
 737     fn find_skips(snippet: &str, is_raw: bool) -> Vec<usize> {
 738         let mut eat_ws = false;
 739         let mut s = snippet.chars().enumerate().peekable();
 740         let mut skips = vec![];
 741         while let Some((pos, c)) = s.next() {
 742             match (c, s.peek()) {
 743                 // skip whitespace and empty lines ending in '\\'
 744                 ('\\', Some((next_pos, '\n'))) if !is_raw => {
 745                     eat_ws = true;
 746                     skips.push(pos);
 747                     skips.push(*next_pos);
 748                     let _ = s.next();
 749                 }
 750                 ('\\', Some((next_pos, '\n' | 'n' | 't'))) if eat_ws => {
 751                     skips.push(pos);
 752                     skips.push(*next_pos);
 753                     let _ = s.next();
 754                 }
 755                 (' ' | '\n' | '\t', _) if eat_ws => {
 756                     skips.push(pos);
 757                 }
 758                 ('\\', Some((next_pos, 'n' | 't' | 'r' | '0' | '\\' | '\'' | '\"'))) => {
 759                     skips.push(*next_pos);
 760                     let _ = s.next();
 761                 }
 762                 ('\\', Some((_, 'x'))) if !is_raw => {
 763                     for _ in 0..3 {
 764                         // consume `\xAB` literal
 765                         if let Some((pos, _)) = s.next() {
 766                             skips.push(pos);
 767                         } else {
 768                             break;
 769                         }
 770                     }
 771                 }
 772                 ('\\', Some((_, 'u'))) if !is_raw => {
 773                     if let Some((pos, _)) = s.next() {
 774                         skips.push(pos);
 775                     }
 776                     if let Some((next_pos, next_c)) = s.next() {
 777                         if next_c == '{' {
 778                             skips.push(next_pos);
 779                             let mut i = 0; // consume up to 6 hexanumeric chars + closing `}`
 780                             while let (Some((next_pos, c)), true) = (s.next(), i < 7) {
 781                                 if c.is_digit(16) {
 782                                     skips.push(next_pos);
 783                                 } else if c == '}' {
 784                                     skips.push(next_pos);
 785                                     break;
 786                                 } else {
 787                                     break;
 788                                 }
 789                                 i += 1;
 790                             }
 791                         } else if next_c.is_digit(16) {
 792                             skips.push(next_pos);
 793                             // We suggest adding `{` and `}` when appropriate, accept it here as if
 794                             // it were correct
 795                             let mut i = 0; // consume up to 6 hexanumeric chars
 796                             while let (Some((next_pos, c)), _) = (s.next(), i < 6) {
 797                                 if c.is_digit(16) {
 798                                     skips.push(next_pos);
 799                                 } else {
 800                                     break;
 801                                 }
 802                                 i += 1;
 803                             }
 804                         }
 805                     }
 806                 }
 807                 _ if eat_ws => {
 808                     // `take_while(|c| c.is_whitespace())`
 809                     eat_ws = false;
 810                 }
 811                 _ => {}
 812             }
 813         }
 814         skips
 815     }
 816
 817     let r_start = str_style.map(|r| r + 1).unwrap_or(0);
 818     let r_end = str_style.unwrap_or(0);
 819     let s = &snippet[r_start + 1..snippet.len() - r_end - 1];
 820     (find_skips(s, str_style.is_some()), true)
 821 }
 822
 823 #[cfg(test)]
 824 mod tests;