src/types.rs

   1 // Copyright 2015 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 std::ops::Deref;
  12 use std::iter::ExactSizeIterator;
  13
  14 use syntax::ast::{self, Mutability, FunctionRetTy};
  15 use syntax::print::pprust;
  16 use syntax::codemap::{self, Span, BytePos};
  17 use syntax::abi;
  18
  19 use {Indent, Spanned};
  20 use codemap::SpanUtils;
  21 use lists::{format_item_list, itemize_list, format_fn_args};
  22 use rewrite::{Rewrite, RewriteContext};
  23 use utils::{extra_offset, format_mutability, wrap_str};
  24 use expr::{rewrite_unary_prefix, rewrite_pair, rewrite_tuple};
  25 use config::TypeDensity;
  26 use itertools::Itertools;
  27
  28 // Does not wrap on simple segments.
  29 pub fn rewrite_path(context: &RewriteContext,
  30                     expr_context: bool,
  31                     qself: Option<&ast::QSelf>,
  32                     path: &ast::Path,
  33                     width: usize,
  34                     offset: Indent)
  35                     -> Option<String> {
  36     let skip_count = qself.map_or(0, |x| x.position);
  37
  38     let mut result = if path.global && qself.is_none() {
  39         "::".to_owned()
  40     } else {
  41         String::new()
  42     };
  43
  44     let mut span_lo = path.span.lo;
  45
  46     if let Some(qself) = qself {
  47         result.push('<');
  48         let fmt_ty = try_opt!(qself.ty.rewrite(context, width, offset));
  49         result.push_str(&fmt_ty);
  50
  51         if skip_count > 0 {
  52             result.push_str(" as ");
  53             if path.global {
  54                 result.push_str("::");
  55             }
  56
  57             let extra_offset = extra_offset(&result, offset);
  58             // 3 = ">::".len()
  59             let budget = try_opt!(width.checked_sub(extra_offset + 3));
  60
  61             result = try_opt!(rewrite_path_segments(false,
  62                                                     result,
  63                                                     path.segments.iter().take(skip_count),
  64                                                     span_lo,
  65                                                     path.span.hi,
  66                                                     context,
  67                                                     budget,
  68                                                     offset + extra_offset));
  69         }
  70
  71         result.push_str(">::");
  72         span_lo = qself.ty.span.hi + BytePos(1);
  73     }
  74
  75     let extra_offset = extra_offset(&result, offset);
  76     let budget = try_opt!(width.checked_sub(extra_offset));
  77     rewrite_path_segments(expr_context,
  78                           result,
  79                           path.segments.iter().skip(skip_count),
  80                           span_lo,
  81                           path.span.hi,
  82                           context,
  83                           budget,
  84                           offset + extra_offset)
  85 }
  86
  87 fn rewrite_path_segments<'a, I>(expr_context: bool,
  88                                 mut buffer: String,
  89                                 iter: I,
  90                                 mut span_lo: BytePos,
  91                                 span_hi: BytePos,
  92                                 context: &RewriteContext,
  93                                 width: usize,
  94                                 offset: Indent)
  95                                 -> Option<String>
  96     where I: Iterator<Item = &'a ast::PathSegment>
  97 {
  98     let mut first = true;
  99
 100     for segment in iter {
 101         if first {
 102             first = false;
 103         } else {
 104             buffer.push_str("::");
 105         }
 106
 107         let extra_offset = extra_offset(&buffer, offset);
 108         let remaining_width = try_opt!(width.checked_sub(extra_offset));
 109         let new_offset = offset + extra_offset;
 110         let segment_string = try_opt!(rewrite_segment(expr_context,
 111                                                       segment,
 112                                                       &mut span_lo,
 113                                                       span_hi,
 114                                                       context,
 115                                                       remaining_width,
 116                                                       new_offset));
 117
 118         buffer.push_str(&segment_string);
 119     }
 120
 121     Some(buffer)
 122 }
 123
 124 #[derive(Debug)]
 125 enum SegmentParam<'a> {
 126     LifeTime(&'a ast::Lifetime),
 127     Type(&'a ast::Ty),
 128     Binding(&'a ast::TypeBinding),
 129 }
 130
 131 impl<'a> SegmentParam<'a> {
 132     fn get_span(&self) -> Span {
 133         match *self {
 134             SegmentParam::LifeTime(lt) => lt.span,
 135             SegmentParam::Type(ty) => ty.span,
 136             SegmentParam::Binding(binding) => binding.span,
 137         }
 138     }
 139 }
 140
 141 impl<'a> Rewrite for SegmentParam<'a> {
 142     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 143         match *self {
 144             SegmentParam::LifeTime(lt) => lt.rewrite(context, width, offset),
 145             SegmentParam::Type(ty) => ty.rewrite(context, width, offset),
 146             SegmentParam::Binding(binding) => {
 147                 let mut result = format!("{} = ", binding.ident);
 148                 let budget = try_opt!(width.checked_sub(result.len()));
 149                 let rewrite = try_opt!(binding.ty.rewrite(context, budget, offset + result.len()));
 150                 result.push_str(&rewrite);
 151                 Some(result)
 152             }
 153         }
 154     }
 155 }
 156
 157 // Formats a path segment. There are some hacks involved to correctly determine
 158 // the segment's associated span since it's not part of the AST.
 159 //
 160 // The span_lo is assumed to be greater than the end of any previous segment's
 161 // parameters and lesser or equal than the start of current segment.
 162 //
 163 // span_hi is assumed equal to the end of the entire path.
 164 //
 165 // When the segment contains a positive number of parameters, we update span_lo
 166 // so that invariants described above will hold for the next segment.
 167 fn rewrite_segment(expr_context: bool,
 168                    segment: &ast::PathSegment,
 169                    span_lo: &mut BytePos,
 170                    span_hi: BytePos,
 171                    context: &RewriteContext,
 172                    width: usize,
 173                    offset: Indent)
 174                    -> Option<String> {
 175     let ident_len = segment.identifier.to_string().len();
 176     let width = try_opt!(width.checked_sub(ident_len));
 177     let offset = offset + ident_len;
 178
 179     let params = match segment.parameters {
 180         ast::PathParameters::AngleBracketed(ref data) if !data.lifetimes.is_empty() ||
 181                                                          !data.types.is_empty() ||
 182                                                          !data.bindings.is_empty() => {
 183             let param_list = data.lifetimes
 184                 .iter()
 185                 .map(SegmentParam::LifeTime)
 186                 .chain(data.types.iter().map(|x| SegmentParam::Type(&*x)))
 187                 .chain(data.bindings.iter().map(|x| SegmentParam::Binding(&*x)))
 188                 .collect::<Vec<_>>();
 189
 190             let next_span_lo = param_list.last().unwrap().get_span().hi + BytePos(1);
 191             let list_lo = context.codemap.span_after(codemap::mk_sp(*span_lo, span_hi), "<");
 192             let separator = if expr_context { "::" } else { "" };
 193
 194             // 1 for <
 195             let extra_offset = 1 + separator.len();
 196             // 1 for >
 197             let list_width = try_opt!(width.checked_sub(extra_offset + 1));
 198
 199             let items = itemize_list(context.codemap,
 200                                      param_list.into_iter(),
 201                                      ">",
 202                                      |param| param.get_span().lo,
 203                                      |param| param.get_span().hi,
 204                                      |seg| seg.rewrite(context, list_width, offset + extra_offset),
 205                                      list_lo,
 206                                      span_hi);
 207             let list_str = try_opt!(format_item_list(items,
 208                                                      list_width,
 209                                                      offset + extra_offset,
 210                                                      context.config));
 211
 212             // Update position of last bracket.
 213             *span_lo = next_span_lo;
 214
 215             format!("{}<{}>", separator, list_str)
 216         }
 217         ast::PathParameters::Parenthesized(ref data) => {
 218             let output = match data.output {
 219                 Some(ref ty) => FunctionRetTy::Ty(ty.clone()),
 220                 None => FunctionRetTy::Default(codemap::DUMMY_SP),
 221             };
 222             try_opt!(format_function_type(data.inputs.iter().map(|x| &**x),
 223                                           &output,
 224                                           false,
 225                                           data.span,
 226                                           context,
 227                                           width,
 228                                           offset))
 229         }
 230         _ => String::new(),
 231     };
 232
 233     Some(format!("{}{}", segment.identifier, params))
 234 }
 235
 236 fn format_function_type<'a, I>(inputs: I,
 237                                output: &FunctionRetTy,
 238                                variadic: bool,
 239                                span: Span,
 240                                context: &RewriteContext,
 241                                width: usize,
 242                                offset: Indent)
 243                                -> Option<String>
 244     where I: ExactSizeIterator,
 245           <I as Iterator>::Item: Deref,
 246           <I::Item as Deref>::Target: Rewrite + Spanned + 'a
 247 {
 248     // Code for handling variadics is somewhat duplicated for items, but they
 249     // are different enough to need some serious refactoring to share code.
 250     enum ArgumentKind<T>
 251         where T: Deref,
 252               <T as Deref>::Target: Rewrite + Spanned
 253     {
 254         Regular(Box<T>),
 255         Variadic(BytePos),
 256     }
 257
 258     let variadic_arg = if variadic {
 259         let variadic_start = context.codemap.span_before(span, "...");
 260         Some(ArgumentKind::Variadic(variadic_start))
 261     } else {
 262         None
 263     };
 264
 265     // 2 for ()
 266     let budget = try_opt!(width.checked_sub(2));
 267     // 1 for (
 268     let offset = offset + 1;
 269     let list_lo = context.codemap.span_after(span, "(");
 270     let items = itemize_list(context.codemap,
 271                              // FIXME Would be nice to avoid this allocation,
 272                              // but I couldn't get the types to work out.
 273                              inputs.map(|i| ArgumentKind::Regular(Box::new(i)))
 274                                  .chain(variadic_arg),
 275                              ")",
 276                              |arg| {
 277                                  match *arg {
 278                                      ArgumentKind::Regular(ref ty) => ty.span().lo,
 279                                      ArgumentKind::Variadic(start) => start,
 280                                  }
 281                              },
 282                              |arg| {
 283                                  match *arg {
 284                                      ArgumentKind::Regular(ref ty) => ty.span().hi,
 285                                      ArgumentKind::Variadic(start) => start + BytePos(3),
 286                                  }
 287                              },
 288                              |arg| {
 289         match *arg {
 290             ArgumentKind::Regular(ref ty) => ty.rewrite(context, budget, offset),
 291             ArgumentKind::Variadic(_) => Some("...".to_owned()),
 292         }
 293     },
 294                              list_lo,
 295                              span.hi);
 296
 297     let list_str = try_opt!(format_fn_args(items, budget, offset, context.config));
 298
 299     let output = match *output {
 300         FunctionRetTy::Ty(ref ty) => {
 301             let budget = try_opt!(width.checked_sub(4));
 302             let type_str = try_opt!(ty.rewrite(context, budget, offset + 4));
 303             format!(" -> {}", type_str)
 304         }
 305         FunctionRetTy::Default(..) => String::new(),
 306     };
 307
 308     let infix = if !output.is_empty() && output.len() + list_str.len() > width {
 309         format!("\n{}", (offset - 1).to_string(context.config))
 310     } else {
 311         String::new()
 312     };
 313
 314     Some(format!("({}){}{}", list_str, infix, output))
 315 }
 316
 317 impl Rewrite for ast::WherePredicate {
 318     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 319         // TODO: dead spans?
 320         let result = match *self {
 321             ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate { ref bound_lifetimes,
 322                                                                            ref bounded_ty,
 323                                                                            ref bounds,
 324                                                                            .. }) => {
 325                 let type_str = try_opt!(bounded_ty.rewrite(context, width, offset));
 326
 327                 if !bound_lifetimes.is_empty() {
 328                     let lifetime_str: String = try_opt!(bound_lifetimes.iter()
 329                                                                .map(|lt| {
 330                                                                    lt.rewrite(context,
 331                                                                               width,
 332                                                                               offset)
 333                                                                })
 334                                                                .intersperse(Some(", ".to_string()))
 335                                                                .collect());
 336
 337                     // 8 = "for<> : ".len()
 338                     let used_width = lifetime_str.len() + type_str.len() + 8;
 339                     let budget = try_opt!(width.checked_sub(used_width));
 340                     let bounds_str: String = try_opt!(bounds.iter()
 341                                                     .map(|ty_bound| {
 342                                                         ty_bound.rewrite(context,
 343                                                                          budget,
 344                                                                          offset + used_width)
 345                                                     })
 346                                                     .intersperse(Some(" + ".to_string()))
 347                                                     .collect());
 348
 349                     format!("for<{}> {}: {}", lifetime_str, type_str, bounds_str)
 350                 } else {
 351                     // 2 = ": ".len()
 352                     let used_width = type_str.len() + 2;
 353                     let budget = try_opt!(width.checked_sub(used_width));
 354                     let bounds_str: String = try_opt!(bounds.iter()
 355                                                     .map(|ty_bound| {
 356                                                         ty_bound.rewrite(context,
 357                                                                          budget,
 358                                                                          offset + used_width)
 359                                                     })
 360                                                     .intersperse(Some(" + ".to_string()))
 361                                                     .collect());
 362
 363                     format!("{}: {}", type_str, bounds_str)
 364                 }
 365             }
 366             ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate { ref lifetime,
 367                                                                              ref bounds,
 368                                                                              .. }) => {
 369                 try_opt!(rewrite_bounded_lifetime(lifetime, bounds.iter(), context, width, offset))
 370             }
 371             ast::WherePredicate::EqPredicate(ast::WhereEqPredicate { ref path, ref ty, .. }) => {
 372                 let ty_str = try_opt!(ty.rewrite(context, width, offset));
 373                 // 3 = " = ".len()
 374                 let used_width = 3 + ty_str.len();
 375                 let budget = try_opt!(width.checked_sub(used_width));
 376                 let path_str =
 377                     try_opt!(rewrite_path(context, false, None, path, budget, offset + used_width));
 378                 format!("{} = {}", path_str, ty_str)
 379             }
 380         };
 381
 382         wrap_str(result, context.config.max_width, width, offset)
 383     }
 384 }
 385
 386 impl Rewrite for ast::LifetimeDef {
 387     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 388         rewrite_bounded_lifetime(&self.lifetime, self.bounds.iter(), context, width, offset)
 389     }
 390 }
 391
 392 fn rewrite_bounded_lifetime<'b, I>(lt: &ast::Lifetime,
 393                                    bounds: I,
 394                                    context: &RewriteContext,
 395                                    width: usize,
 396                                    offset: Indent)
 397                                    -> Option<String>
 398     where I: ExactSizeIterator<Item = &'b ast::Lifetime>
 399 {
 400     let result = try_opt!(lt.rewrite(context, width, offset));
 401
 402     if bounds.len() == 0 {
 403         Some(result)
 404     } else {
 405         let appendix: Vec<_> = try_opt!(bounds.into_iter()
 406             .map(|b| b.rewrite(context, width, offset))
 407             .collect());
 408         let bound_spacing_before = if context.config.space_before_bound {
 409             " "
 410         } else {
 411             ""
 412         };
 413         let bound_spacing_after = if context.config.space_after_bound_colon {
 414             " "
 415         } else {
 416             ""
 417         };
 418         let result = format!("{}{}:{}{}",
 419                              result,
 420                              bound_spacing_before,
 421                              bound_spacing_after,
 422                              appendix.join(" + "));
 423         wrap_str(result, context.config.max_width, width, offset)
 424     }
 425 }
 426
 427 impl Rewrite for ast::TyParamBound {
 428     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 429         match *self {
 430             ast::TyParamBound::TraitTyParamBound(ref tref, ast::TraitBoundModifier::None) => {
 431                 tref.rewrite(context, width, offset)
 432             }
 433             ast::TyParamBound::TraitTyParamBound(ref tref, ast::TraitBoundModifier::Maybe) => {
 434                 let budget = try_opt!(width.checked_sub(1));
 435                 Some(format!("?{}", try_opt!(tref.rewrite(context, budget, offset + 1))))
 436             }
 437             ast::TyParamBound::RegionTyParamBound(ref l) => l.rewrite(context, width, offset),
 438         }
 439     }
 440 }
 441
 442 impl Rewrite for ast::Lifetime {
 443     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 444         wrap_str(pprust::lifetime_to_string(self),
 445                  context.config.max_width,
 446                  width,
 447                  offset)
 448     }
 449 }
 450
 451 impl Rewrite for ast::TyParamBounds {
 452     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 453         let strs: Vec<_> = try_opt!(self.iter()
 454             .map(|b| b.rewrite(context, width, offset))
 455             .collect());
 456         wrap_str(strs.join(" + "), context.config.max_width, width, offset)
 457     }
 458 }
 459
 460 impl Rewrite for ast::TyParam {
 461     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 462         let mut result = String::with_capacity(128);
 463         result.push_str(&self.ident.to_string());
 464         if !self.bounds.is_empty() {
 465             if context.config.space_before_bound {
 466                 result.push_str(" ");
 467             }
 468             result.push_str(":");
 469             if context.config.space_after_bound_colon {
 470                 result.push_str(" ");
 471             }
 472
 473             let bounds: String = try_opt!(self.bounds
 474                 .iter()
 475                 .map(|ty_bound| ty_bound.rewrite(context, width, offset))
 476                 .intersperse(Some(" + ".to_string()))
 477                 .collect());
 478
 479             result.push_str(&bounds);
 480         }
 481         if let Some(ref def) = self.default {
 482
 483             let eq_str = match context.config.type_punctuation_density {
 484                 TypeDensity::Compressed => "=",
 485                 TypeDensity::Wide => " = ",
 486             };
 487             result.push_str(eq_str);
 488             let budget = try_opt!(width.checked_sub(result.len()));
 489             let rewrite = try_opt!(def.rewrite(context, budget, offset + result.len()));
 490             result.push_str(&rewrite);
 491         }
 492
 493         wrap_str(result, context.config.max_width, width, offset)
 494     }
 495 }
 496
 497 impl Rewrite for ast::PolyTraitRef {
 498     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 499         if !self.bound_lifetimes.is_empty() {
 500             let lifetime_str: String = try_opt!(self.bound_lifetimes
 501                 .iter()
 502                 .map(|lt| lt.rewrite(context, width, offset))
 503                 .intersperse(Some(", ".to_string()))
 504                 .collect());
 505
 506             // 6 is "for<> ".len()
 507             let extra_offset = lifetime_str.len() + 6;
 508             let max_path_width = try_opt!(width.checked_sub(extra_offset));
 509             let path_str = try_opt!(self.trait_ref
 510                 .rewrite(context, max_path_width, offset + extra_offset));
 511
 512             Some(format!("for<{}> {}", lifetime_str, path_str))
 513         } else {
 514             self.trait_ref.rewrite(context, width, offset)
 515         }
 516     }
 517 }
 518
 519 impl Rewrite for ast::TraitRef {
 520     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 521         rewrite_path(context, false, None, &self.path, width, offset)
 522     }
 523 }
 524
 525 impl Rewrite for ast::Ty {
 526     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 527         match self.node {
 528             ast::TyKind::ObjectSum(ref ty, ref bounds) => {
 529                 let ty_str = try_opt!(ty.rewrite(context, width, offset));
 530                 let overhead = ty_str.len() + 3;
 531                 let plus_str = match context.config.type_punctuation_density {
 532                     TypeDensity::Compressed => "+",
 533                     TypeDensity::Wide => " + ",
 534                 };
 535                 Some(format!("{}{}{}",
 536                              ty_str,
 537                              plus_str,
 538                              try_opt!(bounds.rewrite(context,
 539                                                      try_opt!(width.checked_sub(overhead)),
 540                                                      offset + overhead))))
 541             }
 542             ast::TyKind::Ptr(ref mt) => {
 543                 let prefix = match mt.mutbl {
 544                     Mutability::Mutable => "*mut ",
 545                     Mutability::Immutable => "*const ",
 546                 };
 547
 548                 rewrite_unary_prefix(context, prefix, &*mt.ty, width, offset)
 549             }
 550             ast::TyKind::Rptr(ref lifetime, ref mt) => {
 551                 let mut_str = format_mutability(mt.mutbl);
 552                 let mut_len = mut_str.len();
 553                 Some(match *lifetime {
 554                     Some(ref lifetime) => {
 555                         let lt_budget = try_opt!(width.checked_sub(2 + mut_len));
 556                         let lt_str =
 557                             try_opt!(lifetime.rewrite(context, lt_budget, offset + 2 + mut_len));
 558                         let lt_len = lt_str.len();
 559                         let budget = try_opt!(width.checked_sub(2 + mut_len + lt_len));
 560                         format!("&{} {}{}",
 561                                 lt_str,
 562                                 mut_str,
 563                                 try_opt!(mt.ty
 564                                     .rewrite(context, budget, offset + 2 + mut_len + lt_len)))
 565                     }
 566                     None => {
 567                         let budget = try_opt!(width.checked_sub(1 + mut_len));
 568                         format!("&{}{}",
 569                                 mut_str,
 570                                 try_opt!(mt.ty.rewrite(context, budget, offset + 1 + mut_len)))
 571                     }
 572                 })
 573             }
 574             // FIXME: we drop any comments here, even though it's a silly place to put
 575             // comments.
 576             ast::TyKind::Paren(ref ty) => {
 577                 let budget = try_opt!(width.checked_sub(2));
 578                 ty.rewrite(context, budget, offset + 1).map(|ty_str| format!("({})", ty_str))
 579             }
 580             ast::TyKind::Vec(ref ty) => {
 581                 let budget = try_opt!(width.checked_sub(2));
 582                 ty.rewrite(context, budget, offset + 1).map(|ty_str| format!("[{}]", ty_str))
 583             }
 584             ast::TyKind::Tup(ref items) => {
 585                 rewrite_tuple(context,
 586                               items.iter().map(|x| &**x),
 587                               self.span,
 588                               width,
 589                               offset)
 590             }
 591             ast::TyKind::PolyTraitRef(ref trait_ref) => trait_ref.rewrite(context, width, offset),
 592             ast::TyKind::Path(ref q_self, ref path) => {
 593                 rewrite_path(context, false, q_self.as_ref(), path, width, offset)
 594             }
 595             ast::TyKind::FixedLengthVec(ref ty, ref repeats) => {
 596                 rewrite_pair(&**ty, &**repeats, "[", "; ", "]", context, width, offset)
 597             }
 598             ast::TyKind::Infer => {
 599                 if width >= 1 {
 600                     Some("_".to_owned())
 601                 } else {
 602                     None
 603                 }
 604             }
 605             ast::TyKind::BareFn(ref bare_fn) => {
 606                 rewrite_bare_fn(bare_fn, self.span, context, width, offset)
 607             }
 608             ast::TyKind::Never => Some(String::from("!")),
 609             ast::TyKind::Mac(..) |
 610             ast::TyKind::Typeof(..) => unreachable!(),
 611             ast::TyKind::ImplicitSelf => Some(String::from("")),
 612             ast::TyKind::ImplTrait(..) => {
 613                 // FIXME(#1154) Implement impl Trait
 614                 Some(String::from("impl TODO"))
 615             }
 616         }
 617     }
 618 }
 619
 620 fn rewrite_bare_fn(bare_fn: &ast::BareFnTy,
 621                    span: Span,
 622                    context: &RewriteContext,
 623                    width: usize,
 624                    offset: Indent)
 625                    -> Option<String> {
 626     let mut result = String::with_capacity(128);
 627
 628     if !bare_fn.lifetimes.is_empty() {
 629         result.push_str("for<");
 630         // 6 = "for<> ".len(), 4 = "for<".
 631         // This doesn't work out so nicely for mutliline situation with lots of
 632         // rightward drift. If that is a problem, we could use the list stuff.
 633         result.push_str(&try_opt!(bare_fn.lifetimes
 634             .iter()
 635             .map(|l| l.rewrite(context, try_opt!(width.checked_sub(6)), offset + 4))
 636             .intersperse(Some(", ".to_string()))
 637             .collect::<Option<String>>()));
 638         result.push_str("> ");
 639     }
 640
 641     result.push_str(::utils::format_unsafety(bare_fn.unsafety));
 642
 643     if bare_fn.abi != abi::Abi::Rust {
 644         result.push_str(&::utils::format_abi(bare_fn.abi, context.config.force_explicit_abi));
 645     }
 646
 647     result.push_str("fn");
 648
 649     let budget = try_opt!(width.checked_sub(result.len()));
 650     let indent = offset + result.len();
 651
 652     let rewrite = try_opt!(format_function_type(bare_fn.decl.inputs.iter(),
 653                                                 &bare_fn.decl.output,
 654                                                 bare_fn.decl.variadic,
 655                                                 span,
 656                                                 context,
 657                                                 budget,
 658                                                 indent));
 659
 660     result.push_str(&rewrite);
 661
 662     Some(result)
 663 }