src/libfmt_macros/lib.rs

   1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Macro support for format strings
  12 //!
  13 //! These structures are used when parsing format strings for the compiler.
  14 //! Parsing does not happen at runtime: structures of `std::fmt::rt` are
  15 //! generated instead.
  16
  17 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
  18        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
  19        html_root_url = "https://doc.rust-lang.org/nightly/",
  20        html_playground_url = "https://play.rust-lang.org/",
  21        test(attr(deny(warnings))))]
  22
  23 #![cfg_attr(not(stage0), feature(nll))]
  24
  25 pub use self::Piece::*;
  26 pub use self::Position::*;
  27 pub use self::Alignment::*;
  28 pub use self::Flag::*;
  29 pub use self::Count::*;
  30
  31 use std::str;
  32 use std::string;
  33 use std::iter;
  34
  35 /// A piece is a portion of the format string which represents the next part
  36 /// to emit. These are emitted as a stream by the `Parser` class.
  37 #[derive(Copy, Clone, PartialEq)]
  38 pub enum Piece<'a> {
  39     /// A literal string which should directly be emitted
  40     String(&'a str),
  41     /// This describes that formatting should process the next argument (as
  42     /// specified inside) for emission.
  43     NextArgument(Argument<'a>),
  44 }
  45
  46 /// Representation of an argument specification.
  47 #[derive(Copy, Clone, PartialEq)]
  48 pub struct Argument<'a> {
  49     /// Where to find this argument
  50     pub position: Position<'a>,
  51     /// How to format the argument
  52     pub format: FormatSpec<'a>,
  53 }
  54
  55 /// Specification for the formatting of an argument in the format string.
  56 #[derive(Copy, Clone, PartialEq)]
  57 pub struct FormatSpec<'a> {
  58     /// Optionally specified character to fill alignment with
  59     pub fill: Option<char>,
  60     /// Optionally specified alignment
  61     pub align: Alignment,
  62     /// Packed version of various flags provided
  63     pub flags: u32,
  64     /// The integer precision to use
  65     pub precision: Count<'a>,
  66     /// The string width requested for the resulting format
  67     pub width: Count<'a>,
  68     /// The descriptor string representing the name of the format desired for
  69     /// this argument, this can be empty or any number of characters, although
  70     /// it is required to be one word.
  71     pub ty: &'a str,
  72 }
  73
  74 /// Enum describing where an argument for a format can be located.
  75 #[derive(Copy, Clone, PartialEq)]
  76 pub enum Position<'a> {
  77     /// The argument is implied to be located at an index
  78     ArgumentImplicitlyIs(usize),
  79     /// The argument is located at a specific index given in the format
  80     ArgumentIs(usize),
  81     /// The argument has a name.
  82     ArgumentNamed(&'a str),
  83 }
  84
  85 /// Enum of alignments which are supported.
  86 #[derive(Copy, Clone, PartialEq)]
  87 pub enum Alignment {
  88     /// The value will be aligned to the left.
  89     AlignLeft,
  90     /// The value will be aligned to the right.
  91     AlignRight,
  92     /// The value will be aligned in the center.
  93     AlignCenter,
  94     /// The value will take on a default alignment.
  95     AlignUnknown,
  96 }
  97
  98 /// Various flags which can be applied to format strings. The meaning of these
  99 /// flags is defined by the formatters themselves.
 100 #[derive(Copy, Clone, PartialEq)]
 101 pub enum Flag {
 102     /// A `+` will be used to denote positive numbers.
 103     FlagSignPlus,
 104     /// A `-` will be used to denote negative numbers. This is the default.
 105     FlagSignMinus,
 106     /// An alternate form will be used for the value. In the case of numbers,
 107     /// this means that the number will be prefixed with the supplied string.
 108     FlagAlternate,
 109     /// For numbers, this means that the number will be padded with zeroes,
 110     /// and the sign (`+` or `-`) will precede them.
 111     FlagSignAwareZeroPad,
 112     /// For Debug / `?`, format integers in lower-case hexadecimal.
 113     FlagDebugLowerHex,
 114     /// For Debug / `?`, format integers in upper-case hexadecimal.
 115     FlagDebugUpperHex,
 116 }
 117
 118 /// A count is used for the precision and width parameters of an integer, and
 119 /// can reference either an argument or a literal integer.
 120 #[derive(Copy, Clone, PartialEq)]
 121 pub enum Count<'a> {
 122     /// The count is specified explicitly.
 123     CountIs(usize),
 124     /// The count is specified by the argument with the given name.
 125     CountIsName(&'a str),
 126     /// The count is specified by the argument at the given index.
 127     CountIsParam(usize),
 128     /// The count is implied and cannot be explicitly specified.
 129     CountImplied,
 130 }
 131
 132 pub struct ParseError {
 133     pub description: string::String,
 134     pub note: Option<string::String>,
 135     pub label: string::String,
 136     pub start: usize,
 137     pub end: usize,
 138 }
 139
 140 /// The parser structure for interpreting the input format string. This is
 141 /// modeled as an iterator over `Piece` structures to form a stream of tokens
 142 /// being output.
 143 ///
 144 /// This is a recursive-descent parser for the sake of simplicity, and if
 145 /// necessary there's probably lots of room for improvement performance-wise.
 146 pub struct Parser<'a> {
 147     input: &'a str,
 148     cur: iter::Peekable<str::CharIndices<'a>>,
 149     /// Error messages accumulated during parsing
 150     pub errors: Vec<ParseError>,
 151     /// Current position of implicit positional argument pointer
 152     curarg: usize,
 153     /// `Some(raw count)` when the string is "raw", used to position spans correctly
 154     style: Option<usize>,
 155     /// How many newlines have been seen in the string so far, to adjust the error spans
 156     seen_newlines: usize,
 157     /// Start and end byte offset of every successfully parsed argument
 158     pub arg_places: Vec<(usize, usize)>,
 159 }
 160
 161 impl<'a> Iterator for Parser<'a> {
 162     type Item = Piece<'a>;
 163
 164     fn next(&mut self) -> Option<Piece<'a>> {
 165         let raw = self.style.map(|raw| raw + self.seen_newlines).unwrap_or(0);
 166         if let Some(&(pos, c)) = self.cur.peek() {
 167             match c {
 168                 '{' => {
 169                     self.cur.next();
 170                     if self.consume('{') {
 171                         Some(String(self.string(pos + 1)))
 172                     } else {
 173                         let arg = self.argument();
 174                         if let Some(arg_pos) = self.must_consume('}').map(|end| {
 175                             (pos + raw + 1, end + raw + 2)
 176                         }) {
 177                             self.arg_places.push(arg_pos);
 178                         }
 179                         Some(NextArgument(arg))
 180                     }
 181                 }
 182                 '}' => {
 183                     self.cur.next();
 184                     if self.consume('}') {
 185                         Some(String(self.string(pos + 1)))
 186                     } else {
 187                         let err_pos = pos + raw + 1;
 188                         self.err_with_note(
 189                             "unmatched `}` found",
 190                             "unmatched `}`",
 191                             "if you intended to print `}`, you can escape it using `}}`",
 192                             err_pos,
 193                             err_pos,
 194                         );
 195                         None
 196                     }
 197                 }
 198                 '\n' => {
 199                     self.seen_newlines += 1;
 200                     Some(String(self.string(pos)))
 201                 }
 202                 _ => Some(String(self.string(pos))),
 203             }
 204         } else {
 205             None
 206         }
 207     }
 208 }
 209
 210 impl<'a> Parser<'a> {
 211     /// Creates a new parser for the given format string
 212     pub fn new(s: &'a str, style: Option<usize>) -> Parser<'a> {
 213         Parser {
 214             input: s,
 215             cur: s.char_indices().peekable(),
 216             errors: vec![],
 217             curarg: 0,
 218             style,
 219             seen_newlines: 0,
 220             arg_places: vec![],
 221         }
 222     }
 223
 224     /// Notifies of an error. The message doesn't actually need to be of type
 225     /// String, but I think it does when this eventually uses conditions so it
 226     /// might as well start using it now.
 227     fn err<S1: Into<string::String>, S2: Into<string::String>>(
 228         &mut self,
 229         description: S1,
 230         label: S2,
 231         start: usize,
 232         end: usize,
 233     ) {
 234         self.errors.push(ParseError {
 235             description: description.into(),
 236             note: None,
 237             label: label.into(),
 238             start,
 239             end,
 240         });
 241     }
 242
 243     /// Notifies of an error. The message doesn't actually need to be of type
 244     /// String, but I think it does when this eventually uses conditions so it
 245     /// might as well start using it now.
 246     fn err_with_note<S1: Into<string::String>, S2: Into<string::String>, S3: Into<string::String>>(
 247         &mut self,
 248         description: S1,
 249         label: S2,
 250         note: S3,
 251         start: usize,
 252         end: usize,
 253     ) {
 254         self.errors.push(ParseError {
 255             description: description.into(),
 256             note: Some(note.into()),
 257             label: label.into(),
 258             start,
 259             end,
 260         });
 261     }
 262
 263     /// Optionally consumes the specified character. If the character is not at
 264     /// the current position, then the current iterator isn't moved and false is
 265     /// returned, otherwise the character is consumed and true is returned.
 266     fn consume(&mut self, c: char) -> bool {
 267         if let Some(&(_, maybe)) = self.cur.peek() {
 268             if c == maybe {
 269                 self.cur.next();
 270                 true
 271             } else {
 272                 false
 273             }
 274         } else {
 275             false
 276         }
 277     }
 278
 279     /// Forces consumption of the specified character. If the character is not
 280     /// found, an error is emitted.
 281     fn must_consume(&mut self, c: char) -> Option<usize> {
 282         self.ws();
 283         let raw = self.style.unwrap_or(0);
 284
 285         let padding = raw + self.seen_newlines;
 286         if let Some(&(pos, maybe)) = self.cur.peek() {
 287             if c == maybe {
 288                 self.cur.next();
 289                 Some(pos)
 290             } else {
 291                 let pos = pos + padding + 1;
 292                 self.err(format!("expected `{:?}`, found `{:?}`", c, maybe),
 293                          format!("expected `{}`", c),
 294                          pos,
 295                          pos);
 296                 None
 297             }
 298         } else {
 299             let msg = format!("expected `{:?}` but string was terminated", c);
 300             // point at closing `"`, unless the last char is `\n` to account for `println`
 301             let pos = match self.input.chars().last() {
 302                 Some('\n') => self.input.len(),
 303                 _ => self.input.len() + 1,
 304             };
 305             if c == '}' {
 306                 self.err_with_note(msg,
 307                                    format!("expected `{:?}`", c),
 308                                    "if you intended to print `{`, you can escape it using `{{`",
 309                                    pos + padding,
 310                                    pos + padding);
 311             } else {
 312                 self.err(msg, format!("expected `{:?}`", c), pos, pos);
 313             }
 314             None
 315         }
 316     }
 317
 318     /// Consumes all whitespace characters until the first non-whitespace
 319     /// character
 320     fn ws(&mut self) {
 321         while let Some(&(_, c)) = self.cur.peek() {
 322             if c.is_whitespace() {
 323                 self.cur.next();
 324             } else {
 325                 break;
 326             }
 327         }
 328     }
 329
 330     /// Parses all of a string which is to be considered a "raw literal" in a
 331     /// format string. This is everything outside of the braces.
 332     fn string(&mut self, start: usize) -> &'a str {
 333         // we may not consume the character, peek the iterator
 334         while let Some(&(pos, c)) = self.cur.peek() {
 335             match c {
 336                 '{' | '}' => {
 337                     return &self.input[start..pos];
 338                 }
 339                 _ => {
 340                     self.cur.next();
 341                 }
 342             }
 343         }
 344         &self.input[start..self.input.len()]
 345     }
 346
 347     /// Parses an Argument structure, or what's contained within braces inside
 348     /// the format string
 349     fn argument(&mut self) -> Argument<'a> {
 350         let pos = self.position();
 351         let format = self.format();
 352
 353         // Resolve position after parsing format spec.
 354         let pos = match pos {
 355             Some(position) => position,
 356             None => {
 357                 let i = self.curarg;
 358                 self.curarg += 1;
 359                 ArgumentImplicitlyIs(i)
 360             }
 361         };
 362
 363         Argument {
 364             position: pos,
 365             format,
 366         }
 367     }
 368
 369     /// Parses a positional argument for a format. This could either be an
 370     /// integer index of an argument, a named argument, or a blank string.
 371     /// Returns `Some(parsed_position)` if the position is not implicitly
 372     /// consuming a macro argument, `None` if it's the case.
 373     fn position(&mut self) -> Option<Position<'a>> {
 374         if let Some(i) = self.integer() {
 375             Some(ArgumentIs(i))
 376         } else {
 377             match self.cur.peek() {
 378                 Some(&(_, c)) if c.is_alphabetic() => Some(ArgumentNamed(self.word())),
 379                 Some(&(pos, c)) if c == '_' => {
 380                     let invalid_name = self.string(pos);
 381                     self.err_with_note(format!("invalid argument name `{}`", invalid_name),
 382                                        "invalid argument name",
 383                                        "argument names cannot start with an underscore",
 384                                        pos + 1, // add 1 to account for leading `{`
 385                                        pos + 1 + invalid_name.len());
 386                     Some(ArgumentNamed(invalid_name))
 387                 },
 388
 389                 // This is an `ArgumentNext`.
 390                 // Record the fact and do the resolution after parsing the
 391                 // format spec, to make things like `{:.*}` work.
 392                 _ => None,
 393             }
 394         }
 395     }
 396
 397     /// Parses a format specifier at the current position, returning all of the
 398     /// relevant information in the FormatSpec struct.
 399     fn format(&mut self) -> FormatSpec<'a> {
 400         let mut spec = FormatSpec {
 401             fill: None,
 402             align: AlignUnknown,
 403             flags: 0,
 404             precision: CountImplied,
 405             width: CountImplied,
 406             ty: &self.input[..0],
 407         };
 408         if !self.consume(':') {
 409             return spec;
 410         }
 411
 412         // fill character
 413         if let Some(&(_, c)) = self.cur.peek() {
 414             match self.cur.clone().nth(1) {
 415                 Some((_, '>')) | Some((_, '<')) | Some((_, '^')) => {
 416                     spec.fill = Some(c);
 417                     self.cur.next();
 418                 }
 419                 _ => {}
 420             }
 421         }
 422         // Alignment
 423         if self.consume('<') {
 424             spec.align = AlignLeft;
 425         } else if self.consume('>') {
 426             spec.align = AlignRight;
 427         } else if self.consume('^') {
 428             spec.align = AlignCenter;
 429         }
 430         // Sign flags
 431         if self.consume('+') {
 432             spec.flags |= 1 << (FlagSignPlus as u32);
 433         } else if self.consume('-') {
 434             spec.flags |= 1 << (FlagSignMinus as u32);
 435         }
 436         // Alternate marker
 437         if self.consume('#') {
 438             spec.flags |= 1 << (FlagAlternate as u32);
 439         }
 440         // Width and precision
 441         let mut havewidth = false;
 442         if self.consume('0') {
 443             // small ambiguity with '0$' as a format string. In theory this is a
 444             // '0' flag and then an ill-formatted format string with just a '$'
 445             // and no count, but this is better if we instead interpret this as
 446             // no '0' flag and '0$' as the width instead.
 447             if self.consume('$') {
 448                 spec.width = CountIsParam(0);
 449                 havewidth = true;
 450             } else {
 451                 spec.flags |= 1 << (FlagSignAwareZeroPad as u32);
 452             }
 453         }
 454         if !havewidth {
 455             spec.width = self.count();
 456         }
 457         if self.consume('.') {
 458             if self.consume('*') {
 459                 // Resolve `CountIsNextParam`.
 460                 // We can do this immediately as `position` is resolved later.
 461                 let i = self.curarg;
 462                 self.curarg += 1;
 463                 spec.precision = CountIsParam(i);
 464             } else {
 465                 spec.precision = self.count();
 466             }
 467         }
 468         // Optional radix followed by the actual format specifier
 469         if self.consume('x') {
 470             if self.consume('?') {
 471                 spec.flags |= 1 << (FlagDebugLowerHex as u32);
 472                 spec.ty = "?";
 473             } else {
 474                 spec.ty = "x";
 475             }
 476         } else if self.consume('X') {
 477             if self.consume('?') {
 478                 spec.flags |= 1 << (FlagDebugUpperHex as u32);
 479                 spec.ty = "?";
 480             } else {
 481                 spec.ty = "X";
 482             }
 483         } else if self.consume('?') {
 484             spec.ty = "?";
 485         } else {
 486             spec.ty = self.word();
 487         }
 488         spec
 489     }
 490
 491     /// Parses a Count parameter at the current position. This does not check
 492     /// for 'CountIsNextParam' because that is only used in precision, not
 493     /// width.
 494     fn count(&mut self) -> Count<'a> {
 495         if let Some(i) = self.integer() {
 496             if self.consume('$') {
 497                 CountIsParam(i)
 498             } else {
 499                 CountIs(i)
 500             }
 501         } else {
 502             let tmp = self.cur.clone();
 503             let word = self.word();
 504             if word.is_empty() {
 505                 self.cur = tmp;
 506                 CountImplied
 507             } else if self.consume('$') {
 508                 CountIsName(word)
 509             } else {
 510                 self.cur = tmp;
 511                 CountImplied
 512             }
 513         }
 514     }
 515
 516     /// Parses a word starting at the current position. A word is considered to
 517     /// be an alphabetic character followed by any number of alphanumeric
 518     /// characters.
 519     fn word(&mut self) -> &'a str {
 520         let start = match self.cur.peek() {
 521             Some(&(pos, c)) if c.is_xid_start() => {
 522                 self.cur.next();
 523                 pos
 524             }
 525             _ => {
 526                 return &self.input[..0];
 527             }
 528         };
 529         while let Some(&(pos, c)) = self.cur.peek() {
 530             if c.is_xid_continue() {
 531                 self.cur.next();
 532             } else {
 533                 return &self.input[start..pos];
 534             }
 535         }
 536         &self.input[start..self.input.len()]
 537     }
 538
 539     /// Optionally parses an integer at the current position. This doesn't deal
 540     /// with overflow at all, it's just accumulating digits.
 541     fn integer(&mut self) -> Option<usize> {
 542         let mut cur = 0;
 543         let mut found = false;
 544         while let Some(&(_, c)) = self.cur.peek() {
 545             if let Some(i) = c.to_digit(10) {
 546                 cur = cur * 10 + i as usize;
 547                 found = true;
 548                 self.cur.next();
 549             } else {
 550                 break;
 551             }
 552         }
 553         if found {
 554             Some(cur)
 555         } else {
 556             None
 557         }
 558     }
 559 }
 560
 561 #[cfg(test)]
 562 mod tests {
 563     use super::*;
 564
 565     fn same(fmt: &'static str, p: &[Piece<'static>]) {
 566         let parser = Parser::new(fmt, None);
 567         assert!(parser.collect::<Vec<Piece<'static>>>() == p);
 568     }
 569
 570     fn fmtdflt() -> FormatSpec<'static> {
 571         return FormatSpec {
 572             fill: None,
 573             align: AlignUnknown,
 574             flags: 0,
 575             precision: CountImplied,
 576             width: CountImplied,
 577             ty: "",
 578         };
 579     }
 580
 581     fn musterr(s: &str) {
 582         let mut p = Parser::new(s, None);
 583         p.next();
 584         assert!(!p.errors.is_empty());
 585     }
 586
 587     #[test]
 588     fn simple() {
 589         same("asdf", &[String("asdf")]);
 590         same("a{{b", &[String("a"), String("{b")]);
 591         same("a}}b", &[String("a"), String("}b")]);
 592         same("a}}", &[String("a"), String("}")]);
 593         same("}}", &[String("}")]);
 594         same("\\}}", &[String("\\"), String("}")]);
 595     }
 596
 597     #[test]
 598     fn invalid01() {
 599         musterr("{")
 600     }
 601     #[test]
 602     fn invalid02() {
 603         musterr("}")
 604     }
 605     #[test]
 606     fn invalid04() {
 607         musterr("{3a}")
 608     }
 609     #[test]
 610     fn invalid05() {
 611         musterr("{:|}")
 612     }
 613     #[test]
 614     fn invalid06() {
 615         musterr("{:>>>}")
 616     }
 617
 618     #[test]
 619     fn format_nothing() {
 620         same("{}",
 621              &[NextArgument(Argument {
 622                    position: ArgumentImplicitlyIs(0),
 623                    format: fmtdflt(),
 624                })]);
 625     }
 626     #[test]
 627     fn format_position() {
 628         same("{3}",
 629              &[NextArgument(Argument {
 630                    position: ArgumentIs(3),
 631                    format: fmtdflt(),
 632                })]);
 633     }
 634     #[test]
 635     fn format_position_nothing_else() {
 636         same("{3:}",
 637              &[NextArgument(Argument {
 638                    position: ArgumentIs(3),
 639                    format: fmtdflt(),
 640                })]);
 641     }
 642     #[test]
 643     fn format_type() {
 644         same("{3:a}",
 645              &[NextArgument(Argument {
 646                    position: ArgumentIs(3),
 647                    format: FormatSpec {
 648                        fill: None,
 649                        align: AlignUnknown,
 650                        flags: 0,
 651                        precision: CountImplied,
 652                        width: CountImplied,
 653                        ty: "a",
 654                    },
 655                })]);
 656     }
 657     #[test]
 658     fn format_align_fill() {
 659         same("{3:>}",
 660              &[NextArgument(Argument {
 661                    position: ArgumentIs(3),
 662                    format: FormatSpec {
 663                        fill: None,
 664                        align: AlignRight,
 665                        flags: 0,
 666                        precision: CountImplied,
 667                        width: CountImplied,
 668                        ty: "",
 669                    },
 670                })]);
 671         same("{3:0<}",
 672              &[NextArgument(Argument {
 673                    position: ArgumentIs(3),
 674                    format: FormatSpec {
 675                        fill: Some('0'),
 676                        align: AlignLeft,
 677                        flags: 0,
 678                        precision: CountImplied,
 679                        width: CountImplied,
 680                        ty: "",
 681                    },
 682                })]);
 683         same("{3:*<abcd}",
 684              &[NextArgument(Argument {
 685                    position: ArgumentIs(3),
 686                    format: FormatSpec {
 687                        fill: Some('*'),
 688                        align: AlignLeft,
 689                        flags: 0,
 690                        precision: CountImplied,
 691                        width: CountImplied,
 692                        ty: "abcd",
 693                    },
 694                })]);
 695     }
 696     #[test]
 697     fn format_counts() {
 698         same("{:10s}",
 699              &[NextArgument(Argument {
 700                    position: ArgumentImplicitlyIs(0),
 701                    format: FormatSpec {
 702                        fill: None,
 703                        align: AlignUnknown,
 704                        flags: 0,
 705                        precision: CountImplied,
 706                        width: CountIs(10),
 707                        ty: "s",
 708                    },
 709                })]);
 710         same("{:10$.10s}",
 711              &[NextArgument(Argument {
 712                    position: ArgumentImplicitlyIs(0),
 713                    format: FormatSpec {
 714                        fill: None,
 715                        align: AlignUnknown,
 716                        flags: 0,
 717                        precision: CountIs(10),
 718                        width: CountIsParam(10),
 719                        ty: "s",
 720                    },
 721                })]);
 722         same("{:.*s}",
 723              &[NextArgument(Argument {
 724                    position: ArgumentImplicitlyIs(1),
 725                    format: FormatSpec {
 726                        fill: None,
 727                        align: AlignUnknown,
 728                        flags: 0,
 729                        precision: CountIsParam(0),
 730                        width: CountImplied,
 731                        ty: "s",
 732                    },
 733                })]);
 734         same("{:.10$s}",
 735              &[NextArgument(Argument {
 736                    position: ArgumentImplicitlyIs(0),
 737                    format: FormatSpec {
 738                        fill: None,
 739                        align: AlignUnknown,
 740                        flags: 0,
 741                        precision: CountIsParam(10),
 742                        width: CountImplied,
 743                        ty: "s",
 744                    },
 745                })]);
 746         same("{:a$.b$s}",
 747              &[NextArgument(Argument {
 748                    position: ArgumentImplicitlyIs(0),
 749                    format: FormatSpec {
 750                        fill: None,
 751                        align: AlignUnknown,
 752                        flags: 0,
 753                        precision: CountIsName("b"),
 754                        width: CountIsName("a"),
 755                        ty: "s",
 756                    },
 757                })]);
 758     }
 759     #[test]
 760     fn format_flags() {
 761         same("{:-}",
 762              &[NextArgument(Argument {
 763                    position: ArgumentImplicitlyIs(0),
 764                    format: FormatSpec {
 765                        fill: None,
 766                        align: AlignUnknown,
 767                        flags: (1 << FlagSignMinus as u32),
 768                        precision: CountImplied,
 769                        width: CountImplied,
 770                        ty: "",
 771                    },
 772                })]);
 773         same("{:+#}",
 774              &[NextArgument(Argument {
 775                    position: ArgumentImplicitlyIs(0),
 776                    format: FormatSpec {
 777                        fill: None,
 778                        align: AlignUnknown,
 779                        flags: (1 << FlagSignPlus as u32) | (1 << FlagAlternate as u32),
 780                        precision: CountImplied,
 781                        width: CountImplied,
 782                        ty: "",
 783                    },
 784                })]);
 785     }
 786     #[test]
 787     fn format_mixture() {
 788         same("abcd {3:a} efg",
 789              &[String("abcd "),
 790                NextArgument(Argument {
 791                    position: ArgumentIs(3),
 792                    format: FormatSpec {
 793                        fill: None,
 794                        align: AlignUnknown,
 795                        flags: 0,
 796                        precision: CountImplied,
 797                        width: CountImplied,
 798                        ty: "a",
 799                    },
 800                }),
 801                String(" efg")]);
 802     }
 803 }