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