src/libsyntax/ext/format.rs

   1 // Copyright 2012 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 use self::ArgumentType::*;
  12 use self::Position::*;
  13
  14 use ast;
  15 use codemap::{Span, respan};
  16 use ext::base::*;
  17 use ext::base;
  18 use ext::build::AstBuilder;
  19 use fmt_macros as parse;
  20 use fold::Folder;
  21 use parse::token::special_idents;
  22 use parse::token;
  23 use ptr::P;
  24
  25 use std::collections::HashMap;
  26 use std::iter::repeat;
  27
  28 #[derive(PartialEq)]
  29 enum ArgumentType {
  30     Known(String),
  31     Unsigned
  32 }
  33
  34 enum Position {
  35     Exact(usize),
  36     Named(String),
  37 }
  38
  39 struct Context<'a, 'b:'a> {
  40     ecx: &'a mut ExtCtxt<'b>,
  41     /// The macro's call site. References to unstable formatting internals must
  42     /// use this span to pass the stability checker.
  43     macsp: Span,
  44     /// The span of the format string literal.
  45     fmtsp: Span,
  46
  47     /// Parsed argument expressions and the types that we've found so far for
  48     /// them.
  49     args: Vec<P<ast::Expr>>,
  50     arg_types: Vec<Option<ArgumentType>>,
  51     /// Parsed named expressions and the types that we've found for them so far.
  52     /// Note that we keep a side-array of the ordering of the named arguments
  53     /// found to be sure that we can translate them in the same order that they
  54     /// were declared in.
  55     names: HashMap<String, P<ast::Expr>>,
  56     name_types: HashMap<String, ArgumentType>,
  57     name_ordering: Vec<String>,
  58
  59     /// The latest consecutive literal strings, or empty if there weren't any.
  60     literal: String,
  61
  62     /// Collection of the compiled `rt::Argument` structures
  63     pieces: Vec<P<ast::Expr>>,
  64     /// Collection of string literals
  65     str_pieces: Vec<P<ast::Expr>>,
  66     /// Stays `true` if all formatting parameters are default (as in "{}{}").
  67     all_pieces_simple: bool,
  68
  69     name_positions: HashMap<String, usize>,
  70
  71     /// Updated as arguments are consumed or methods are entered
  72     nest_level: usize,
  73     next_arg: usize,
  74 }
  75
  76 /// Parses the arguments from the given list of tokens, returning None
  77 /// if there's a parse error so we can continue parsing other format!
  78 /// expressions.
  79 ///
  80 /// If parsing succeeds, the return value is:
  81 ///
  82 ///     Some((fmtstr, unnamed arguments, ordering of named arguments,
  83 ///           named arguments))
  84 fn parse_args(ecx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
  85               -> Option<(P<ast::Expr>, Vec<P<ast::Expr>>, Vec<String>,
  86                          HashMap<String, P<ast::Expr>>)> {
  87     let mut args = Vec::new();
  88     let mut names = HashMap::<String, P<ast::Expr>>::new();
  89     let mut order = Vec::new();
  90
  91     let mut p = ecx.new_parser_from_tts(tts);
  92
  93     if p.token == token::Eof {
  94         ecx.span_err(sp, "requires at least a format string argument");
  95         return None;
  96     }
  97     let fmtstr = p.parse_expr();
  98     let mut named = false;
  99     while p.token != token::Eof {
 100         if !panictry!(p.eat(&token::Comma)) {
 101             ecx.span_err(sp, "expected token: `,`");
 102             return None;
 103         }
 104         if p.token == token::Eof { break } // accept trailing commas
 105         if named || (p.token.is_ident() && p.look_ahead(1, |t| *t == token::Eq)) {
 106             named = true;
 107             let ident = match p.token {
 108                 token::Ident(i, _) => {
 109                     panictry!(p.bump());
 110                     i
 111                 }
 112                 _ if named => {
 113                     ecx.span_err(p.span,
 114                                  "expected ident, positional arguments \
 115                                  cannot follow named arguments");
 116                     return None;
 117                 }
 118                 _ => {
 119                     ecx.span_err(p.span,
 120                                  &format!("expected ident for named argument, found `{}`",
 121                                          p.this_token_to_string()));
 122                     return None;
 123                 }
 124             };
 125             let interned_name = token::get_ident(ident);
 126             let name = &interned_name[..];
 127
 128             panictry!(p.expect(&token::Eq));
 129             let e = p.parse_expr();
 130             match names.get(name) {
 131                 None => {}
 132                 Some(prev) => {
 133                     ecx.span_err(e.span,
 134                                  &format!("duplicate argument named `{}`",
 135                                          name));
 136                     ecx.parse_sess.span_diagnostic.span_note(prev.span, "previously here");
 137                     continue
 138                 }
 139             }
 140             order.push(name.to_string());
 141             names.insert(name.to_string(), e);
 142         } else {
 143             args.push(p.parse_expr());
 144         }
 145     }
 146     Some((fmtstr, args, order, names))
 147 }
 148
 149 impl<'a, 'b> Context<'a, 'b> {
 150     /// Verifies one piece of a parse string. All errors are not emitted as
 151     /// fatal so we can continue giving errors about this and possibly other
 152     /// format strings.
 153     fn verify_piece(&mut self, p: &parse::Piece) {
 154         match *p {
 155             parse::String(..) => {}
 156             parse::NextArgument(ref arg) => {
 157                 // width/precision first, if they have implicit positional
 158                 // parameters it makes more sense to consume them first.
 159                 self.verify_count(arg.format.width);
 160                 self.verify_count(arg.format.precision);
 161
 162                 // argument second, if it's an implicit positional parameter
 163                 // it's written second, so it should come after width/precision.
 164                 let pos = match arg.position {
 165                     parse::ArgumentNext => {
 166                         let i = self.next_arg;
 167                         if self.check_positional_ok() {
 168                             self.next_arg += 1;
 169                         }
 170                         Exact(i)
 171                     }
 172                     parse::ArgumentIs(i) => Exact(i),
 173                     parse::ArgumentNamed(s) => Named(s.to_string()),
 174                 };
 175
 176                 let ty = Known(arg.format.ty.to_string());
 177                 self.verify_arg_type(pos, ty);
 178             }
 179         }
 180     }
 181
 182     fn verify_count(&mut self, c: parse::Count) {
 183         match c {
 184             parse::CountImplied | parse::CountIs(..) => {}
 185             parse::CountIsParam(i) => {
 186                 self.verify_arg_type(Exact(i), Unsigned);
 187             }
 188             parse::CountIsName(s) => {
 189                 self.verify_arg_type(Named(s.to_string()), Unsigned);
 190             }
 191             parse::CountIsNextParam => {
 192                 if self.check_positional_ok() {
 193                     let next_arg = self.next_arg;
 194                     self.verify_arg_type(Exact(next_arg), Unsigned);
 195                     self.next_arg += 1;
 196                 }
 197             }
 198         }
 199     }
 200
 201     fn check_positional_ok(&mut self) -> bool {
 202         if self.nest_level != 0 {
 203             self.ecx.span_err(self.fmtsp, "cannot use implicit positional \
 204                                            arguments nested inside methods");
 205             false
 206         } else {
 207             true
 208         }
 209     }
 210
 211     fn describe_num_args(&self) -> String {
 212         match self.args.len() {
 213             0 => "no arguments given".to_string(),
 214             1 => "there is 1 argument".to_string(),
 215             x => format!("there are {} arguments", x),
 216         }
 217     }
 218
 219     fn verify_arg_type(&mut self, arg: Position, ty: ArgumentType) {
 220         match arg {
 221             Exact(arg) => {
 222                 if self.args.len() <= arg {
 223                     let msg = format!("invalid reference to argument `{}` ({})",
 224                                       arg, self.describe_num_args());
 225
 226                     self.ecx.span_err(self.fmtsp, &msg[..]);
 227                     return;
 228                 }
 229                 {
 230                     let arg_type = match self.arg_types[arg] {
 231                         None => None,
 232                         Some(ref x) => Some(x)
 233                     };
 234                     self.verify_same(self.args[arg].span, &ty, arg_type);
 235                 }
 236                 if self.arg_types[arg].is_none() {
 237                     self.arg_types[arg] = Some(ty);
 238                 }
 239             }
 240
 241             Named(name) => {
 242                 let span = match self.names.get(&name) {
 243                     Some(e) => e.span,
 244                     None => {
 245                         let msg = format!("there is no argument named `{}`", name);
 246                         self.ecx.span_err(self.fmtsp, &msg[..]);
 247                         return;
 248                     }
 249                 };
 250                 self.verify_same(span, &ty, self.name_types.get(&name));
 251                 if !self.name_types.contains_key(&name) {
 252                     self.name_types.insert(name.clone(), ty);
 253                 }
 254                 // Assign this named argument a slot in the arguments array if
 255                 // it hasn't already been assigned a slot.
 256                 if !self.name_positions.contains_key(&name) {
 257                     let slot = self.name_positions.len();
 258                     self.name_positions.insert(name, slot);
 259                 }
 260             }
 261         }
 262     }
 263
 264     /// When we're keeping track of the types that are declared for certain
 265     /// arguments, we assume that `None` means we haven't seen this argument
 266     /// yet, `Some(None)` means that we've seen the argument, but no format was
 267     /// specified, and `Some(Some(x))` means that the argument was declared to
 268     /// have type `x`.
 269     ///
 270     /// Obviously `Some(Some(x)) != Some(Some(y))`, but we consider it true
 271     /// that: `Some(None) == Some(Some(x))`
 272     fn verify_same(&self,
 273                    sp: Span,
 274                    ty: &ArgumentType,
 275                    before: Option<&ArgumentType>) {
 276         let cur = match before {
 277             None => return,
 278             Some(t) => t,
 279         };
 280         if *ty == *cur {
 281             return
 282         }
 283         match (cur, ty) {
 284             (&Known(ref cur), &Known(ref ty)) => {
 285                 self.ecx.span_err(sp,
 286                                   &format!("argument redeclared with type `{}` when \
 287                                            it was previously `{}`",
 288                                           *ty,
 289                                           *cur));
 290             }
 291             (&Known(ref cur), _) => {
 292                 self.ecx.span_err(sp,
 293                                   &format!("argument used to format with `{}` was \
 294                                            attempted to not be used for formatting",
 295                                            *cur));
 296             }
 297             (_, &Known(ref ty)) => {
 298                 self.ecx.span_err(sp,
 299                                   &format!("argument previously used as a format \
 300                                            argument attempted to be used as `{}`",
 301                                            *ty));
 302             }
 303             (_, _) => {
 304                 self.ecx.span_err(sp, "argument declared with multiple formats");
 305             }
 306         }
 307     }
 308
 309     fn rtpath(ecx: &ExtCtxt, s: &str) -> Vec<ast::Ident> {
 310         vec![ecx.ident_of_std("core"), ecx.ident_of("fmt"), ecx.ident_of("rt"),
 311              ecx.ident_of("v1"), ecx.ident_of(s)]
 312     }
 313
 314     fn trans_count(&self, c: parse::Count) -> P<ast::Expr> {
 315         let sp = self.macsp;
 316         let count = |c, arg| {
 317             let mut path = Context::rtpath(self.ecx, "Count");
 318             path.push(self.ecx.ident_of(c));
 319             match arg {
 320                 Some(arg) => self.ecx.expr_call_global(sp, path, vec![arg]),
 321                 None => self.ecx.expr_path(self.ecx.path_global(sp, path)),
 322             }
 323         };
 324         match c {
 325             parse::CountIs(i) => count("Is", Some(self.ecx.expr_usize(sp, i))),
 326             parse::CountIsParam(i) => {
 327                 count("Param", Some(self.ecx.expr_usize(sp, i)))
 328             }
 329             parse::CountImplied => count("Implied", None),
 330             parse::CountIsNextParam => count("NextParam", None),
 331             parse::CountIsName(n) => {
 332                 let i = match self.name_positions.get(n) {
 333                     Some(&i) => i,
 334                     None => 0, // error already emitted elsewhere
 335                 };
 336                 let i = i + self.args.len();
 337                 count("Param", Some(self.ecx.expr_usize(sp, i)))
 338             }
 339         }
 340     }
 341
 342     /// Translate the accumulated string literals to a literal expression
 343     fn trans_literal_string(&mut self) -> P<ast::Expr> {
 344         let sp = self.fmtsp;
 345         let s = token::intern_and_get_ident(&self.literal);
 346         self.literal.clear();
 347         self.ecx.expr_str(sp, s)
 348     }
 349
 350     /// Translate a `parse::Piece` to a static `rt::Argument` or append
 351     /// to the `literal` string.
 352     fn trans_piece(&mut self, piece: &parse::Piece) -> Option<P<ast::Expr>> {
 353         let sp = self.macsp;
 354         match *piece {
 355             parse::String(s) => {
 356                 self.literal.push_str(s);
 357                 None
 358             }
 359             parse::NextArgument(ref arg) => {
 360                 // Translate the position
 361                 let pos = {
 362                     let pos = |c, arg| {
 363                         let mut path = Context::rtpath(self.ecx, "Position");
 364                         path.push(self.ecx.ident_of(c));
 365                         match arg {
 366                             Some(i) => {
 367                                 let arg = self.ecx.expr_usize(sp, i);
 368                                 self.ecx.expr_call_global(sp, path, vec![arg])
 369                             }
 370                             None => {
 371                                 self.ecx.expr_path(self.ecx.path_global(sp, path))
 372                             }
 373                         }
 374                     };
 375                     match arg.position {
 376                         // These two have a direct mapping
 377                         parse::ArgumentNext => pos("Next", None),
 378                         parse::ArgumentIs(i) => pos("At", Some(i)),
 379
 380                         // Named arguments are converted to positional arguments
 381                         // at the end of the list of arguments
 382                         parse::ArgumentNamed(n) => {
 383                             let i = match self.name_positions.get(n) {
 384                                 Some(&i) => i,
 385                                 None => 0, // error already emitted elsewhere
 386                             };
 387                             let i = i + self.args.len();
 388                             pos("At", Some(i))
 389                         }
 390                     }
 391                 };
 392
 393                 let simple_arg = parse::Argument {
 394                     position: parse::ArgumentNext,
 395                     format: parse::FormatSpec {
 396                         fill: arg.format.fill,
 397                         align: parse::AlignUnknown,
 398                         flags: 0,
 399                         precision: parse::CountImplied,
 400                         width: parse::CountImplied,
 401                         ty: arg.format.ty
 402                     }
 403                 };
 404
 405                 let fill = match arg.format.fill { Some(c) => c, None => ' ' };
 406
 407                 if *arg != simple_arg || fill != ' ' {
 408                     self.all_pieces_simple = false;
 409                 }
 410
 411                 // Translate the format
 412                 let fill = self.ecx.expr_lit(sp, ast::LitChar(fill));
 413                 let align = |name| {
 414                     let mut p = Context::rtpath(self.ecx, "Alignment");
 415                     p.push(self.ecx.ident_of(name));
 416                     self.ecx.path_global(sp, p)
 417                 };
 418                 let align = match arg.format.align {
 419                     parse::AlignLeft => align("Left"),
 420                     parse::AlignRight => align("Right"),
 421                     parse::AlignCenter => align("Center"),
 422                     parse::AlignUnknown => align("Unknown"),
 423                 };
 424                 let align = self.ecx.expr_path(align);
 425                 let flags = self.ecx.expr_u32(sp, arg.format.flags);
 426                 let prec = self.trans_count(arg.format.precision);
 427                 let width = self.trans_count(arg.format.width);
 428                 let path = self.ecx.path_global(sp, Context::rtpath(self.ecx, "FormatSpec"));
 429                 let fmt = self.ecx.expr_struct(sp, path, vec!(
 430                     self.ecx.field_imm(sp, self.ecx.ident_of("fill"), fill),
 431                     self.ecx.field_imm(sp, self.ecx.ident_of("align"), align),
 432                     self.ecx.field_imm(sp, self.ecx.ident_of("flags"), flags),
 433                     self.ecx.field_imm(sp, self.ecx.ident_of("precision"), prec),
 434                     self.ecx.field_imm(sp, self.ecx.ident_of("width"), width)));
 435
 436                 let path = self.ecx.path_global(sp, Context::rtpath(self.ecx, "Argument"));
 437                 Some(self.ecx.expr_struct(sp, path, vec!(
 438                     self.ecx.field_imm(sp, self.ecx.ident_of("position"), pos),
 439                     self.ecx.field_imm(sp, self.ecx.ident_of("format"), fmt))))
 440             }
 441         }
 442     }
 443
 444     fn static_array(ecx: &mut ExtCtxt,
 445                     name: &str,
 446                     piece_ty: P<ast::Ty>,
 447                     pieces: Vec<P<ast::Expr>>)
 448                     -> P<ast::Expr> {
 449         let sp = piece_ty.span;
 450         let ty = ecx.ty_rptr(sp,
 451             ecx.ty(sp, ast::TyVec(piece_ty)),
 452             Some(ecx.lifetime(sp, special_idents::static_lifetime.name)),
 453             ast::MutImmutable);
 454         let slice = ecx.expr_vec_slice(sp, pieces);
 455         // static instead of const to speed up codegen by not requiring this to be inlined
 456         let st = ast::ItemStatic(ty, ast::MutImmutable, slice);
 457
 458         let name = ecx.ident_of(name);
 459         let item = ecx.item(sp, name, vec![], st);
 460         let decl = respan(sp, ast::DeclItem(item));
 461
 462         // Wrap the declaration in a block so that it forms a single expression.
 463         ecx.expr_block(ecx.block(sp,
 464             vec![P(respan(sp, ast::StmtDecl(P(decl), ast::DUMMY_NODE_ID)))],
 465             Some(ecx.expr_ident(sp, name))))
 466     }
 467
 468     /// Actually builds the expression which the iformat! block will be expanded
 469     /// to
 470     fn into_expr(mut self) -> P<ast::Expr> {
 471         let mut locals = Vec::new();
 472         let mut names: Vec<_> = repeat(None).take(self.name_positions.len()).collect();
 473         let mut pats = Vec::new();
 474         let mut heads = Vec::new();
 475
 476         // First, build up the static array which will become our precompiled
 477         // format "string"
 478         let static_lifetime = self.ecx.lifetime(self.fmtsp, special_idents::static_lifetime.name);
 479         let piece_ty = self.ecx.ty_rptr(
 480                 self.fmtsp,
 481                 self.ecx.ty_ident(self.fmtsp, self.ecx.ident_of("str")),
 482                 Some(static_lifetime),
 483                 ast::MutImmutable);
 484         let pieces = Context::static_array(self.ecx,
 485                                            "__STATIC_FMTSTR",
 486                                            piece_ty,
 487                                            self.str_pieces);
 488
 489
 490         // Right now there is a bug such that for the expression:
 491         //      foo(bar(&1))
 492         // the lifetime of `1` doesn't outlast the call to `bar`, so it's not
 493         // valid for the call to `foo`. To work around this all arguments to the
 494         // format! string are shoved into locals. Furthermore, we shove the address
 495         // of each variable because we don't want to move out of the arguments
 496         // passed to this function.
 497         for (i, e) in self.args.into_iter().enumerate() {
 498             let arg_ty = match self.arg_types[i].as_ref() {
 499                 Some(ty) => ty,
 500                 None => continue // error already generated
 501             };
 502
 503             let name = self.ecx.ident_of(&format!("__arg{}", i));
 504             pats.push(self.ecx.pat_ident(e.span, name));
 505             locals.push(Context::format_arg(self.ecx, self.macsp, e.span, arg_ty,
 506                                             self.ecx.expr_ident(e.span, name)));
 507             heads.push(self.ecx.expr_addr_of(e.span, e));
 508         }
 509         for name in &self.name_ordering {
 510             let e = match self.names.remove(name) {
 511                 Some(e) => e,
 512                 None => continue
 513             };
 514             let arg_ty = match self.name_types.get(name) {
 515                 Some(ty) => ty,
 516                 None => continue
 517             };
 518
 519             let lname = self.ecx.ident_of(&format!("__arg{}",
 520                                                   *name));
 521             pats.push(self.ecx.pat_ident(e.span, lname));
 522             names[*self.name_positions.get(name).unwrap()] =
 523                 Some(Context::format_arg(self.ecx, self.macsp, e.span, arg_ty,
 524                                          self.ecx.expr_ident(e.span, lname)));
 525             heads.push(self.ecx.expr_addr_of(e.span, e));
 526         }
 527
 528         // Now create a vector containing all the arguments
 529         let args = locals.into_iter().chain(names.into_iter().map(|a| a.unwrap()));
 530
 531         let args_array = self.ecx.expr_vec(self.fmtsp, args.collect());
 532
 533         // Constructs an AST equivalent to:
 534         //
 535         //      match (&arg0, &arg1) {
 536         //          (tmp0, tmp1) => args_array
 537         //      }
 538         //
 539         // It was:
 540         //
 541         //      let tmp0 = &arg0;
 542         //      let tmp1 = &arg1;
 543         //      args_array
 544         //
 545         // Because of #11585 the new temporary lifetime rule, the enclosing
 546         // statements for these temporaries become the let's themselves.
 547         // If one or more of them are RefCell's, RefCell borrow() will also
 548         // end there; they don't last long enough for args_array to use them.
 549         // The match expression solves the scope problem.
 550         //
 551         // Note, it may also very well be transformed to:
 552         //
 553         //      match arg0 {
 554         //          ref tmp0 => {
 555         //              match arg1 => {
 556         //                  ref tmp1 => args_array } } }
 557         //
 558         // But the nested match expression is proved to perform not as well
 559         // as series of let's; the first approach does.
 560         let pat = self.ecx.pat_tuple(self.fmtsp, pats);
 561         let arm = self.ecx.arm(self.fmtsp, vec!(pat), args_array);
 562         let head = self.ecx.expr(self.fmtsp, ast::ExprTup(heads));
 563         let result = self.ecx.expr_match(self.fmtsp, head, vec!(arm));
 564
 565         let args_slice = self.ecx.expr_addr_of(self.fmtsp, result);
 566
 567         // Now create the fmt::Arguments struct with all our locals we created.
 568         let (fn_name, fn_args) = if self.all_pieces_simple {
 569             ("new_v1", vec![pieces, args_slice])
 570         } else {
 571             // Build up the static array which will store our precompiled
 572             // nonstandard placeholders, if there are any.
 573             let piece_ty = self.ecx.ty_path(self.ecx.path_global(
 574                     self.macsp,
 575                     Context::rtpath(self.ecx, "Argument")));
 576             let fmt = Context::static_array(self.ecx,
 577                                             "__STATIC_FMTARGS",
 578                                             piece_ty,
 579                                             self.pieces);
 580
 581             ("new_v1_formatted", vec![pieces, args_slice, fmt])
 582         };
 583
 584         self.ecx.expr_call_global(self.macsp, vec!(
 585                 self.ecx.ident_of_std("core"),
 586                 self.ecx.ident_of("fmt"),
 587                 self.ecx.ident_of("Arguments"),
 588                 self.ecx.ident_of(fn_name)), fn_args)
 589     }
 590
 591     fn format_arg(ecx: &ExtCtxt, macsp: Span, sp: Span,
 592                   ty: &ArgumentType, arg: P<ast::Expr>)
 593                   -> P<ast::Expr> {
 594         let trait_ = match *ty {
 595             Known(ref tyname) => {
 596                 match &tyname[..] {
 597                     ""  => "Display",
 598                     "?" => "Debug",
 599                     "e" => "LowerExp",
 600                     "E" => "UpperExp",
 601                     "o" => "Octal",
 602                     "p" => "Pointer",
 603                     "b" => "Binary",
 604                     "x" => "LowerHex",
 605                     "X" => "UpperHex",
 606                     _ => {
 607                         ecx.span_err(sp,
 608                                      &format!("unknown format trait `{}`",
 609                                              *tyname));
 610                         "Dummy"
 611                     }
 612                 }
 613             }
 614             Unsigned => {
 615                 return ecx.expr_call_global(macsp, vec![
 616                         ecx.ident_of_std("core"),
 617                         ecx.ident_of("fmt"),
 618                         ecx.ident_of("ArgumentV1"),
 619                         ecx.ident_of("from_usize")], vec![arg])
 620             }
 621         };
 622
 623         let format_fn = ecx.path_global(sp, vec![
 624                 ecx.ident_of_std("core"),
 625                 ecx.ident_of("fmt"),
 626                 ecx.ident_of(trait_),
 627                 ecx.ident_of("fmt")]);
 628         ecx.expr_call_global(macsp, vec![
 629                 ecx.ident_of_std("core"),
 630                 ecx.ident_of("fmt"),
 631                 ecx.ident_of("ArgumentV1"),
 632                 ecx.ident_of("new")], vec![arg, ecx.expr_path(format_fn)])
 633     }
 634 }
 635
 636 pub fn expand_format_args<'cx>(ecx: &'cx mut ExtCtxt, sp: Span,
 637                                tts: &[ast::TokenTree])
 638                                -> Box<base::MacResult+'cx> {
 639
 640     match parse_args(ecx, sp, tts) {
 641         Some((efmt, args, order, names)) => {
 642             MacEager::expr(expand_preparsed_format_args(ecx, sp, efmt,
 643                                                       args, order, names))
 644         }
 645         None => DummyResult::expr(sp)
 646     }
 647 }
 648
 649 /// Take the various parts of `format_args!(efmt, args..., name=names...)`
 650 /// and construct the appropriate formatting expression.
 651 pub fn expand_preparsed_format_args(ecx: &mut ExtCtxt, sp: Span,
 652                                     efmt: P<ast::Expr>,
 653                                     args: Vec<P<ast::Expr>>,
 654                                     name_ordering: Vec<String>,
 655                                     names: HashMap<String, P<ast::Expr>>)
 656                                     -> P<ast::Expr> {
 657     let arg_types: Vec<_> = (0..args.len()).map(|_| None).collect();
 658     let macsp = ecx.call_site();
 659     // Expand the format literal so that efmt.span will have a backtrace. This
 660     // is essential for locating a bug when the format literal is generated in
 661     // a macro. (e.g. println!("{}"), which uses concat!($fmt, "\n")).
 662     let efmt = ecx.expander().fold_expr(efmt);
 663     let mut cx = Context {
 664         ecx: ecx,
 665         args: args,
 666         arg_types: arg_types,
 667         names: names,
 668         name_positions: HashMap::new(),
 669         name_types: HashMap::new(),
 670         name_ordering: name_ordering,
 671         nest_level: 0,
 672         next_arg: 0,
 673         literal: String::new(),
 674         pieces: Vec::new(),
 675         str_pieces: Vec::new(),
 676         all_pieces_simple: true,
 677         macsp: macsp,
 678         fmtsp: efmt.span,
 679     };
 680     let fmt = match expr_to_string(cx.ecx,
 681                                    efmt,
 682                                    "format argument must be a string literal.") {
 683         Some((fmt, _)) => fmt,
 684         None => return DummyResult::raw_expr(sp)
 685     };
 686
 687     let mut parser = parse::Parser::new(&fmt);
 688
 689     loop {
 690         match parser.next() {
 691             Some(piece) => {
 692                 if !parser.errors.is_empty() { break }
 693                 cx.verify_piece(&piece);
 694                 match cx.trans_piece(&piece) {
 695                     Some(piece) => {
 696                         let s = cx.trans_literal_string();
 697                         cx.str_pieces.push(s);
 698                         cx.pieces.push(piece);
 699                     }
 700                     None => {}
 701                 }
 702             }
 703             None => break
 704         }
 705     }
 706     if !parser.errors.is_empty() {
 707         cx.ecx.span_err(cx.fmtsp, &format!("invalid format string: {}",
 708                                           parser.errors.remove(0)));
 709         return DummyResult::raw_expr(sp);
 710     }
 711     if !cx.literal.is_empty() {
 712         let s = cx.trans_literal_string();
 713         cx.str_pieces.push(s);
 714     }
 715
 716     // Make sure that all arguments were used and all arguments have types.
 717     for (i, ty) in cx.arg_types.iter().enumerate() {
 718         if ty.is_none() {
 719             cx.ecx.span_err(cx.args[i].span, "argument never used");
 720         }
 721     }
 722     for (name, e) in &cx.names {
 723         if !cx.name_types.contains_key(name) {
 724             cx.ecx.span_err(e.span, "named argument never used");
 725         }
 726     }
 727
 728     cx.into_expr()
 729 }