1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897
//! Traits for parsing the WebAssembly Text format //! //! This module contains the traits, abstractions, and utilities needed to //! define custom parsers for WebAssembly text format items. This module exposes //! a recursive descent parsing strategy and centers around the //! [`Parse`](crate::parser::Parse) trait for defining new fragments of //! WebAssembly text syntax. //! //! The top-level [`parse`](crate::parser::parse) function can be used to fully parse AST fragments: //! //! ``` //! use wast::Wat; //! use wast::parser::{self, ParseBuffer}; //! //! # fn foo() -> Result<(), wast::Error> { //! let wat = "(module (func))"; //! let buf = ParseBuffer::new(wat)?; //! let module = parser::parse::<Wat>(&buf)?; //! # Ok(()) //! # } //! ``` //! //! and you can also define your own new syntax with the //! [`Parse`](crate::parser::Parse) trait: //! //! ``` //! use wast::{kw, Import, Func}; //! use wast::parser::{Parser, Parse, Result}; //! //! // Fields of a WebAssembly which only allow imports and functions, and all //! // imports must come before all the functions //! struct OnlyImportsAndFunctions<'a> { //! imports: Vec<Import<'a>>, //! functions: Vec<Func<'a>>, //! } //! //! impl<'a> Parse<'a> for OnlyImportsAndFunctions<'a> { //! fn parse(parser: Parser<'a>) -> Result<Self> { //! // While the second token is `import` (the first is `(`, so we care //! // about the second) we parse an `ast::ModuleImport` inside of //! // parentheses. The `parens` function here ensures that what we //! // parse inside of it is surrounded by `(` and `)`. //! let mut imports = Vec::new(); //! while parser.peek2::<kw::import>() { //! let import = parser.parens(|p| p.parse())?; //! imports.push(import); //! } //! //! // Afterwards we assume everything else is a function. Note that //! // `parse` here is a generic function and type inference figures out //! // that we're parsing functions here and imports above. //! let mut functions = Vec::new(); //! while !parser.is_empty() { //! let func = parser.parens(|p| p.parse())?; //! functions.push(func); //! } //! //! Ok(OnlyImportsAndFunctions { imports, functions }) //! } //! } //! ``` //! //! This module is heavily inspired by [`syn`](https://docs.rs/syn) so you can //! likely also draw inspiration from the excellent examples in the `syn` crate. use crate::lexer::{Comment, Float, Integer, Lexer, Source, Token}; use crate::{Error, Span}; use std::cell::Cell; use std::fmt; /// A top-level convenience parseing function that parss a `T` from `buf` and /// requires that all tokens in `buf` are consume. /// /// This generic parsing function can be used to parse any `T` implementing the /// [`Parse`] trait. It is not used from [`Parse`] trait implementations. /// /// # Examples /// /// ``` /// use wast::Wat; /// use wast::parser::{self, ParseBuffer}; /// /// # fn foo() -> Result<(), wast::Error> { /// let wat = "(module (func))"; /// let buf = ParseBuffer::new(wat)?; /// let module = parser::parse::<Wat>(&buf)?; /// # Ok(()) /// # } /// ``` /// /// or parsing simply a fragment /// /// ``` /// use wast::parser::{self, ParseBuffer}; /// /// # fn foo() -> Result<(), wast::Error> { /// let wat = "12"; /// let buf = ParseBuffer::new(wat)?; /// let val = parser::parse::<u32>(&buf)?; /// assert_eq!(val, 12); /// # Ok(()) /// # } /// ``` pub fn parse<'a, T: Parse<'a>>(buf: &'a ParseBuffer<'a>) -> Result<T> { let parser = buf.parser(); let result = parser.parse()?; if parser.cursor().advance_token().is_none() { Ok(result) } else { Err(parser.error("extra tokens remaining after parse")) } } /// A trait for parsing a fragment of syntax in a recursive descent fashion. /// /// The [`Parse`] trait is main abstraction you'll be working with when defining /// custom parser or custom syntax for your WebAssembly text format (or when /// using the official format items). Almost all items in the /// [`ast`](crate::ast) module implement the [`Parse`] trait, and you'll /// commonly use this with: /// /// * The top-level [`parse`] function to parse an entire input. /// * The intermediate [`Parser::parse`] function to parse an item out of an /// input stream and then parse remaining items. /// /// Implementation of [`Parse`] take a [`Parser`] as input and will mutate the /// parser as they parse syntax. Once a token is consume it cannot be /// "un-consumed". Utilities such as [`Parser::peek`] and [`Parser::lookahead1`] /// can be used to determine what to parse next. /// /// ## When to parse `(` and `)`? /// /// Conventionally types are not responsible for parsing their own `(` and `)` /// tokens which surround the type. For example WebAssembly imports look like: /// /// ```text /// (import "foo" "bar" (func (type 0))) /// ``` /// /// but the [`Import`](crate::ast::Import) type parser looks like: /// /// ``` /// # use wast::kw; /// # use wast::parser::{Parser, Parse, Result}; /// # struct Import<'a>(&'a str); /// impl<'a> Parse<'a> for Import<'a> { /// fn parse(parser: Parser<'a>) -> Result<Self> { /// parser.parse::<kw::import>()?; /// // ... /// # panic!() /// } /// } /// ``` /// /// It is assumed here that the `(` and `)` tokens which surround an `import` /// statement in the WebAssembly text format are parsed by the parent item /// parsing `Import`. /// /// Note that this is just a a convention, so it's not necessarily required of /// all types. It's recommended that your types stick to this convention where /// possible to avoid nested calls to [`Parser::parens`] or accidentally trying /// to parse too many parenthesis. /// /// # Examples /// /// Let's say you want to define your own WebAssembly text format which only /// contains imports and functions. You also require all imports to be listed /// before all functions. An example [`Parse`] implementation might look like: /// /// ``` /// use wast::{Import, Func, kw}; /// use wast::parser::{Parser, Parse, Result}; /// /// // Fields of a WebAssembly which only allow imports and functions, and all /// // imports must come before all the functions /// struct OnlyImportsAndFunctions<'a> { /// imports: Vec<Import<'a>>, /// functions: Vec<Func<'a>>, /// } /// /// impl<'a> Parse<'a> for OnlyImportsAndFunctions<'a> { /// fn parse(parser: Parser<'a>) -> Result<Self> { /// // While the second token is `import` (the first is `(`, so we care /// // about the second) we parse an `ast::ModuleImport` inside of /// // parentheses. The `parens` function here ensures that what we /// // parse inside of it is surrounded by `(` and `)`. /// let mut imports = Vec::new(); /// while parser.peek2::<kw::import>() { /// let import = parser.parens(|p| p.parse())?; /// imports.push(import); /// } /// /// // Afterwards we assume everything else is a function. Note that /// // `parse` here is a generic function and type inference figures out /// // that we're parsing functions here and imports above. /// let mut functions = Vec::new(); /// while !parser.is_empty() { /// let func = parser.parens(|p| p.parse())?; /// functions.push(func); /// } /// /// Ok(OnlyImportsAndFunctions { imports, functions }) /// } /// } /// ``` pub trait Parse<'a>: Sized { /// Attempts to parse `Self` from `parser`, returning an error if it could /// not be parsed. /// /// This method will mutate the state of `parser` after attempting to parse /// an instance of `Self`. If an error happens then it is likely fatal and /// there is no guarantee of how many tokens have been consumed from /// `parser`. /// /// As recommended in the documentation of [`Parse`], implementations of /// this function should not start out by parsing `(` and `)` tokens, but /// rather parents calling recursive parsers should parse the `(` and `)` /// tokens for their child item that's being parsed. /// /// # Errors /// /// This function will return an error if `Self` could not be parsed. Note /// that creating an [`Error`] is not exactly a cheap operation, so /// [`Error`] is typically fatal and propagated all the way back to the top /// parse call site. fn parse(parser: Parser<'a>) -> Result<Self>; } /// A trait for types which be used to "peek" to see if they're the next token /// in an input stream of [`Parser`]. /// /// Often when implementing [`Parse`] you'll need to query what the next token /// in the stream is to figure out what to parse next. This [`Peek`] trait /// defines the set of types that can be tested whether they're the next token /// in the input stream. /// /// Implementations of [`Peek`] should only be present on types that consume /// exactly one token (not zero, not more, exactly one). Types implementing /// [`Peek`] should also typically implement [`Parse`] should also typically /// implement [`Parse`]. /// /// See the documentation of [`Parser::peek`] for example usage. pub trait Peek { /// Tests to see whether this token is the first token within the [`Cursor`] /// specified. /// /// Returns `true` if [`Parse`] for this type is highly likely to succeed /// failing no other error conditions happening (like an integer literal /// being too big). fn peek(cursor: Cursor<'_>) -> bool; /// Returns a human-readable name of this token to display when generating /// errors about this token missing. fn display() -> &'static str; } /// A convenience type definition for `Result` where the error is hardwired to /// [`Error`]. pub type Result<T> = std::result::Result<T, Error>; /// A low-level buffer of tokens which represents a completely lexed file. /// /// A `ParseBuffer` will immediately lex an entire file and then store all /// tokens internally. A `ParseBuffer` only used to pass to the top-level /// [`parse`] function. pub struct ParseBuffer<'a> { // list of tokens from the tokenized source (including whitespace and // comments), and the second element is the index of the next `Token` token, // if any. tokens: Box<[(Source<'a>, Option<usize>)]>, input: &'a str, cur: Cell<usize>, } /// An in-progress parser for the tokens of a WebAssembly text file. /// /// A `Parser` is argument to the [`Parse`] trait and is now the input stream is /// interacted with to parse new items. Cloning [`Parser`] or copying a parser /// refers to the same stream of tokens to parse, you cannot clone a [`Parser`] /// and clone two items. /// /// For more information about a [`Parser`] see its methods. #[derive(Copy, Clone)] pub struct Parser<'a> { buf: &'a ParseBuffer<'a>, } /// A helpful structure to perform a lookahead of one token to determine what to /// parse. /// /// For more information see the [`Parser::lookahead1`] method. pub struct Lookahead1<'a> { parser: Parser<'a>, attempts: Vec<&'static str>, } /// An immutable cursor into a list of tokens. /// /// This cursor cannot be mutated but can be used to parse more tokens in a list /// of tokens. Cursors are created from the [`Parser::step`] method. This is a /// very low-level parsing structure and you likely won't use it much. #[derive(Copy, Clone)] pub struct Cursor<'a> { parser: Parser<'a>, cur: usize, } impl ParseBuffer<'_> { /// Creates a new [`ParseBuffer`] by lexing the given `input` completely. /// /// # Errors /// /// Returns an error if `input` fails to lex. pub fn new(input: &str) -> Result<ParseBuffer<'_>> { let mut tokens = Vec::new(); for token in Lexer::new(input) { tokens.push((token?, None)); } // Calculate the "next token" for each token in the list. This'll allow // us to advance quickly inside of `advance_token` below instead of // having to skip over all comments/whitespace, perhaps repeatedly. // // To calculate this we go back-to-front, and just keep track of where // the last token was seen and fill that in for all the `next_token` // blanks. let mut last_token = None; for (i, (token, next_token)) in tokens.iter_mut().enumerate().rev() { *next_token = last_token; if let Source::Token(_) = token { last_token = Some(i); } } Ok(ParseBuffer { tokens: tokens.into_boxed_slice(), cur: Cell::new(0), input, }) } fn parser(&self) -> Parser<'_> { Parser { buf: self } } } impl<'a> Parser<'a> { /// Returns whether there are no more `Token` tokens to parse from this /// [`Parser`]. /// /// This indicates that either we've reached the end of the input, or we're /// a sub-[`Parser`] inside of a parenthesized expression and we've hit the /// `)` token. /// /// Note that if `false` is returned there *may* be more comments. Comments /// and whitespace are not considered for whether this parser is empty. pub fn is_empty(self) -> bool { match self.cursor().advance_token() { Some(Token::RParen(_)) | None => true, Some(_) => false, // more tokens to parse! } } /// Parses a `T` from this [`Parser`]. /// /// This method has a trivial definition (it simply calls /// [`T::parse`](Parse::parse)) but is here for syntactic purposes. This is /// what you'll call 99% of the time in a [`Parse`] implementation in order /// to parse sub-items. /// /// Typically you always want to use `?` with the result of this method, you /// should not handle errors and decide what else to parse. To handle /// branches in parsing, ue [`Parser::peek`]. /// /// # Examples /// /// A good example of using `parse` is to see how the [`TableType`] type is /// parsed in this crate. A [`TableType`] is defined in the official /// specification as [`tabletype`][spec] and is defined as: /// /// [spec]: https://webassembly.github.io/spec/core/text/types.html#table-types /// /// ```text /// tabletype ::= lim:limits et:elemtype /// ``` /// /// so to parse a [`TableType`] we recursively need to parse a [`Limits`] /// and a [`TableElemType`] /// /// ``` /// # use wast::*; /// # use wast::parser::*; /// struct TableType { /// limits: Limits, /// elem: TableElemType, /// } /// /// impl<'a> Parse<'a> for TableType { /// fn parse(parser: Parser<'a>) -> Result<Self> { /// // parse the `lim` then `et` in sequence /// Ok(TableType { /// limits: parser.parse()?, /// elem: parser.parse()?, /// }) /// } /// } /// ``` /// /// [`Limits`]: crate::ast::Limits /// [`TableType`]: crate::ast::TableType /// [`TableElemType`]: crate::ast::TableElemType pub fn parse<T: Parse<'a>>(self) -> Result<T> { T::parse(self) } /// Performs a cheap test to see whether the current token in this stream is /// `T`. /// /// This method can be used to efficiently determine what next to parse. The /// [`Peek`] trait is defined for types which can be used to test if they're /// the next item in the input stream. /// /// Nothing is actually parsed in this method, nor does this mutate the /// state of this [`Parser`]. Instead, this simply performs a check. /// /// This method is frequently combined with the [`Parser::lookahead1`] /// method to automatically produce nice error messages if some tokens /// aren't found. /// /// # Examples /// /// For an example of using the `peek` method let's take a look at parsing /// the [`Limits`] type. This is [defined in the official spec][spec] as: /// /// ```text /// limits ::= n:u32 /// | n:u32 m:u32 /// ``` /// /// which means that it's either one `u32` token or two, so we need to know /// whether to consume two tokens or one: /// /// ``` /// # use wast::parser::*; /// struct Limits { /// min: u32, /// max: Option<u32>, /// } /// /// impl<'a> Parse<'a> for Limits { /// fn parse(parser: Parser<'a>) -> Result<Self> { /// // Always parse the first number... /// let min = parser.parse()?; /// /// // ... and then test if there's a second number before parsing /// let max = if parser.peek::<u32>() { /// Some(parser.parse()?) /// } else { /// None /// }; /// /// Ok(Limits { min, max }) /// } /// } /// ``` /// /// [spec]: https://webassembly.github.io/spec/core/text/types.html#limits /// [`Limits`]: crate::ast::Limits pub fn peek<T: Peek>(self) -> bool { T::peek(self.cursor()) } /// Same as the [`Parser::peek`] method, except checks the next token, not /// the current token. pub fn peek2<T: Peek>(self) -> bool { let mut cursor = self.cursor(); if cursor.advance_token().is_some() { T::peek(cursor) } else { false } } /// A helper structure to perform a sequence of `peek` operations and if /// they all fail produce a nice error message. /// /// This method purely exists for conveniently producing error messages and /// provides no functionality that [`Parser::peek`] doesn't already give. /// The [`Lookahead1`] structure has one main method [`Lookahead1::peek`], /// which is the same method as [`Parser::peek`]. The difference is that the /// [`Lookahead1::error`] method needs no arguments. /// /// # Examples /// /// Let's look at the parsing of [`Index`]. This type is either a `u32` or /// an [`Id`] and is used in name resolution primarily. The [official /// grammar for an index][spec] is: /// /// ```text /// idx ::= x:u32 /// | v:id /// ``` /// /// Which is to say that an index is either a `u32` or an [`Id`]. When /// parsing an [`Index`] we can do: /// /// ``` /// # use wast::*; /// # use wast::parser::*; /// enum Index<'a> { /// Num(u32), /// Id(Id<'a>), /// } /// /// impl<'a> Parse<'a> for Index<'a> { /// fn parse(parser: Parser<'a>) -> Result<Self> { /// let mut l = parser.lookahead1(); /// if l.peek::<Id>() { /// Ok(Index::Id(parser.parse()?)) /// } else if l.peek::<u32>() { /// Ok(Index::Num(parser.parse()?)) /// } else { /// // produces error message of `expected identifier or u32` /// Err(l.error()) /// } /// } /// } /// ``` /// /// [spec]: https://webassembly.github.io/spec/core/text/modules.html#indices /// [`Index`]: crate::ast::Index /// [`Id`]: crate::ast::Id pub fn lookahead1(self) -> Lookahead1<'a> { Lookahead1 { attempts: Vec::new(), parser: self, } } /// Parsea an item surrounded by parentheses. /// /// WebAssembly's text format is all based on s-expressions, so naturally /// you're going to want to parse a lot of parenthesized things! As noted in /// the documentation of [`Parse`] you typically don't parse your own /// surrounding `(` and `)` tokens, but the parser above you parsed them for /// you. This is method method the parser above you uses. /// /// This method will parse a `(` token, and then call `f` on a sub-parser /// which when finished asserts that a `)` token is the next token. This /// requires that `f` consumes all tokens leading up to the paired `)`. /// /// Usage will often simply be `parser.parens(|p| p.parse())?` to /// automatically parse a type within parentheses, but you can, as always, /// go crazy and do whatever you'd like too. /// /// # Examples /// /// A good example of this is to see how a `Module` is parsed. This isn't /// the exact definition, but it's close enough! /// /// ``` /// # use wast::*; /// # use wast::parser::*; /// struct Module<'a> { /// fields: Vec<ModuleField<'a>>, /// } /// /// impl<'a> Parse<'a> for Module<'a> { /// fn parse(parser: Parser<'a>) -> Result<Self> { /// // Modules start out with a `module` keyword /// parser.parse::<kw::module>()?; /// /// // And then everything else is `(field ...)`, so while we've got /// // items left we continuously parse parenthesized items. /// let mut fields = Vec::new(); /// while !parser.is_empty() { /// fields.push(parser.parens(|p| p.parse())?); /// } /// Ok(Module { fields }) /// } /// } /// ``` pub fn parens<T>(self, f: impl FnOnce(Parser<'a>) -> Result<T>) -> Result<T> { let before = self.buf.cur.get(); let res = self.step(|cursor| { let mut cursor = match cursor.lparen() { Some(rest) => rest, None => return Err(cursor.error("expected `(`")), }; cursor.parser.buf.cur.set(cursor.cur); let result = f(cursor.parser)?; cursor.cur = cursor.parser.buf.cur.get(); match cursor.rparen() { Some(rest) => Ok((result, rest)), None => Err(cursor.error("expected `)`")), } }); if res.is_err() { self.buf.cur.set(before); } return res; } fn cursor(self) -> Cursor<'a> { Cursor { parser: self, cur: self.buf.cur.get(), } } /// A low-level parsing method you probably won't use. /// /// This is used to implement parsing of the most primitive types in the /// [`ast`](crate::ast) module. You probably don't want to use this, but /// probably want to use something like [`Parser::parse`] or /// [`Parser::parens`]. pub fn step<F, T>(self, f: F) -> Result<T> where F: FnOnce(Cursor<'a>) -> Result<(T, Cursor<'a>)>, { let (result, cursor) = f(self.cursor())?; self.buf.cur.set(cursor.cur); Ok(result) } /// Creates an error whose line/column information is pointing at the /// current token. /// /// This is used to produce human-readable error messages which point to the /// right location in the input stream, and the `msg` here is arbitrary text /// used to associate with the error and indicate why it was generated. pub fn error(self, msg: impl fmt::Display) -> Error { self.error_at(self.cursor().cur_span(), &msg) } fn error_at(self, span: Span, msg: &dyn fmt::Display) -> Error { Error::parse(span, self.buf.input, msg.to_string()) } fn input_pos(self, src: &'a str) -> usize { src.as_ptr() as usize - self.buf.input.as_ptr() as usize } /// Returns the span of the current token pub fn cur_span(&self) -> Span { self.cursor().cur_span() } } impl<'a> Cursor<'a> { /// Returns the span of the next `Token` token. /// /// Does not take into account whitespace or comments. pub fn cur_span(&self) -> Span { let offset = match self.clone().advance_token() { Some(t) => self.parser.input_pos(t.src()), None => self.parser.buf.input.len(), }; Span { offset } } /// Same as [`Parser::error`], but works with the current token in this /// [`Cursor`] instead. pub fn error(&self, msg: impl fmt::Display) -> Error { self.parser.error_at(self.cur_span(), &msg) } /// Attempts to advance this cursor if the current token is a `(`. /// /// If the current token is `(`, returns a new [`Cursor`] pointing at the /// rest of the tokens in the stream. Otherwise returns `None`. /// /// This function will automatically skip over any comment or whitespace /// tokens. pub fn lparen(mut self) -> Option<Self> { match self.advance_token()? { Token::LParen(_) => Some(self), _ => None, } } /// Attempts to advance this cursor if the current token is a `)`. /// /// If the current token is `)`, returns a new [`Cursor`] pointing at the /// rest of the tokens in the stream. Otherwise returns `None`. /// /// This function will automatically skip over any comment or whitespace /// tokens. pub fn rparen(mut self) -> Option<Self> { match self.advance_token()? { Token::RParen(_) => Some(self), _ => None, } } /// Attempts to advance this cursor if the current token is a /// [`Token::Id`](crate::lexer::Token) /// /// If the current token is `Id`, returns the identifier minus the leading /// `$` character as well as a new [`Cursor`] pointing at the rest of the /// tokens in the stream. Otherwise returns `None`. /// /// This function will automatically skip over any comment or whitespace /// tokens. pub fn id(mut self) -> Option<(&'a str, Self)> { match self.advance_token()? { Token::Id(id) => Some((&id[1..], self)), _ => None, } } /// Attempts to advance this cursor if the current token is a /// [`Token::Keyword`](crate::lexer::Token) /// /// If the current token is `Keyword`, returns the keyword as well as a new /// [`Cursor`] pointing at the rest of the tokens in the stream. Otherwise /// returns `None`. /// /// This function will automatically skip over any comment or whitespace /// tokens. pub fn keyword(mut self) -> Option<(&'a str, Self)> { match self.advance_token()? { Token::Keyword(id) => Some((id, self)), _ => None, } } /// Attempts to advance this cursor if the current token is a /// [`Token::Reserved`](crate::lexer::Token) /// /// If the current token is `Reserved`, returns the reserved token as well /// as a new [`Cursor`] pointing at the rest of the tokens in the stream. /// Otherwise returns `None`. /// /// This function will automatically skip over any comment or whitespace /// tokens. pub fn reserved(mut self) -> Option<(&'a str, Self)> { match self.advance_token()? { Token::Reserved(id) => Some((id, self)), _ => None, } } /// Attempts to advance this cursor if the current token is a /// [`Token::Integer`](crate::lexer::Token) /// /// If the current token is `Integer`, returns the integer as well as a new /// [`Cursor`] pointing at the rest of the tokens in the stream. Otherwise /// returns `None`. /// /// This function will automatically skip over any comment or whitespace /// tokens. pub fn integer(mut self) -> Option<(&'a Integer<'a>, Self)> { match self.advance_token()? { Token::Integer(i) => Some((i, self)), _ => None, } } /// Attempts to advance this cursor if the current token is a /// [`Token::Float`](crate::lexer::Token) /// /// If the current token is `Float`, returns the float as well as a new /// [`Cursor`] pointing at the rest of the tokens in the stream. Otherwise /// returns `None`. /// /// This function will automatically skip over any comment or whitespace /// tokens. pub fn float(mut self) -> Option<(&'a Float<'a>, Self)> { match self.advance_token()? { Token::Float(f) => Some((f, self)), _ => None, } } /// Attempts to advance this cursor if the current token is a /// [`Token::String`](crate::lexer::Token) /// /// If the current token is `String`, returns the byte value of the string /// as well as a new [`Cursor`] pointing at the rest of the tokens in the /// stream. Otherwise returns `None`. /// /// This function will automatically skip over any comment or whitespace /// tokens. pub fn string(mut self) -> Option<(&'a [u8], Self)> { match self.advance_token()? { Token::String { val, .. } => Some((&**val, self)), _ => None, } } /// Attempts to advance this cursor if the current token is a /// [`Source::Comment`](crate::lexer::Comment) /// /// This function will skip any whitespace tokens, but it will not skip any /// other tokens. pub fn comment(mut self) -> Option<(&'a Comment<'a>, Self)> { let comment = loop { match &self.parser.buf.tokens.get(self.cur)?.0 { Source::Token(_) => return None, Source::Comment(c) => { self.cur += 1; break c; } Source::Whitespace(_) => { self.cur += 1; } } }; Some((comment, self)) } fn advance_token(&mut self) -> Option<&'a Token<'a>> { let (token, next) = self.parser.buf.tokens.get(self.cur)?; match token { // If the current token is a `Token`, then only advance ourselves // one token further. That way if after this `Token` you want // comments, we can find the comments! Source::Token(t) => { self.cur += 1; Some(t) } // Otherwise this is a comment or whitespace token. In that case // `next` points to the next `Token` token if `next` was listed. _ => { let next = (*next)?; let (token, _) = &self.parser.buf.tokens[next]; match token { Source::Token(t) => { self.cur = next + 1; Some(t) } _ => unreachable!(), } } } } } impl Lookahead1<'_> { /// Attempts to see if `T` is the next token in the [`Parser`] this /// [`Lookahead1`] references. /// /// For more information see [`Parser::lookahead1`] and [`Parser::peek`] pub fn peek<T: Peek>(&mut self) -> bool { if self.parser.peek::<T>() { true } else { self.attempts.push(T::display()); false } } /// Generates an error message saying that one of the tokens passed to /// [`Lookahead1::peek`] method was expected. /// /// Before calling this method you should call [`Lookahead1::peek`] for all /// possible tokens you'd like to parse. pub fn error(self) -> Error { match self.attempts.len() { 0 => { if self.parser.is_empty() { self.parser.error("unexpected end of input") } else { self.parser.error("unexpected token") } } 1 => { let message = format!("unexpected token, expected {}", self.attempts[0]); self.parser.error(&message) } 2 => { let message = format!( "unexpected token, expected {} or {}", self.attempts[0], self.attempts[1] ); self.parser.error(&message) } _ => { let join = self.attempts.join(", "); let message = format!("unexpected token, expected one of: {}", join); self.parser.error(&message) } } } } impl<'a, T: Peek + Parse<'a>> Parse<'a> for Option<T> { fn parse(parser: Parser<'a>) -> Result<Option<T>> { if parser.peek::<T>() { Ok(Some(parser.parse()?)) } else { Ok(None) } } }