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::iter::ExactSizeIterator;
  12 use std::ops::Deref;
  13
  14 use config::lists::*;
  15 use syntax::ast::{self, FunctionRetTy, Mutability};
  16 use syntax::codemap::{self, BytePos, Span};
  17 use syntax::symbol::keywords;
  18
  19 use codemap::SpanUtils;
  20 use config::{IndentStyle, TypeDensity};
  21 use expr::{rewrite_assign_rhs, rewrite_tuple, rewrite_unary_prefix, ToExpr};
  22 use lists::{definitive_tactic, itemize_list, write_list, ListFormatting, Separator};
  23 use macros::{rewrite_macro, MacroPosition};
  24 use overflow;
  25 use pairs::{rewrite_pair, PairParts};
  26 use rewrite::{Rewrite, RewriteContext};
  27 use shape::Shape;
  28 use spanned::Spanned;
  29 use utils::{
  30     colon_spaces, extra_offset, first_line_width, format_abi, format_mutability,
  31     last_line_extendable, last_line_width, mk_sp, rewrite_ident,
  32 };
  33
  34 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  35 pub enum PathContext {
  36     Expr,
  37     Type,
  38     Import,
  39 }
  40
  41 // Does not wrap on simple segments.
  42 pub fn rewrite_path(
  43     context: &RewriteContext,
  44     path_context: PathContext,
  45     qself: Option<&ast::QSelf>,
  46     path: &ast::Path,
  47     shape: Shape,
  48 ) -> Option<String> {
  49     let skip_count = qself.map_or(0, |x| x.position);
  50
  51     let mut result = if path.is_global() && qself.is_none() && path_context != PathContext::Import {
  52         "::".to_owned()
  53     } else {
  54         String::new()
  55     };
  56
  57     let mut span_lo = path.span.lo();
  58
  59     if let Some(qself) = qself {
  60         result.push('<');
  61
  62         let fmt_ty = qself.ty.rewrite(context, shape)?;
  63         result.push_str(&fmt_ty);
  64
  65         if skip_count > 0 {
  66             result.push_str(" as ");
  67             if path.is_global() && path_context != PathContext::Import {
  68                 result.push_str("::");
  69             }
  70
  71             // 3 = ">::".len()
  72             let shape = shape.sub_width(3)?;
  73
  74             result = rewrite_path_segments(
  75                 PathContext::Type,
  76                 result,
  77                 path.segments.iter().take(skip_count),
  78                 span_lo,
  79                 path.span.hi(),
  80                 context,
  81                 shape,
  82             )?;
  83         }
  84
  85         result.push_str(">::");
  86         span_lo = qself.ty.span.hi() + BytePos(1);
  87     }
  88
  89     rewrite_path_segments(
  90         path_context,
  91         result,
  92         path.segments.iter().skip(skip_count),
  93         span_lo,
  94         path.span.hi(),
  95         context,
  96         shape,
  97     )
  98 }
  99
 100 fn rewrite_path_segments<'a, I>(
 101     path_context: PathContext,
 102     mut buffer: String,
 103     iter: I,
 104     mut span_lo: BytePos,
 105     span_hi: BytePos,
 106     context: &RewriteContext,
 107     shape: Shape,
 108 ) -> Option<String>
 109 where
 110     I: Iterator<Item = &'a ast::PathSegment>,
 111 {
 112     let mut first = true;
 113     let shape = shape.visual_indent(0);
 114
 115     for segment in iter {
 116         // Indicates a global path, shouldn't be rendered.
 117         if segment.ident.name == keywords::CrateRoot.name() {
 118             continue;
 119         }
 120         if first {
 121             first = false;
 122         } else {
 123             buffer.push_str("::");
 124         }
 125
 126         let extra_offset = extra_offset(&buffer, shape);
 127         let new_shape = shape.shrink_left(extra_offset)?;
 128         let segment_string = rewrite_segment(
 129             path_context,
 130             segment,
 131             &mut span_lo,
 132             span_hi,
 133             context,
 134             new_shape,
 135         )?;
 136
 137         buffer.push_str(&segment_string);
 138     }
 139
 140     Some(buffer)
 141 }
 142
 143 #[derive(Debug)]
 144 enum SegmentParam<'a> {
 145     LifeTime(&'a ast::Lifetime),
 146     Type(&'a ast::Ty),
 147     Binding(&'a ast::TypeBinding),
 148 }
 149
 150 impl<'a> SegmentParam<'a> {
 151     fn from_generic_arg(arg: &ast::GenericArg) -> SegmentParam {
 152         match arg {
 153             ast::GenericArg::Lifetime(ref lt) => SegmentParam::LifeTime(lt),
 154             ast::GenericArg::Type(ref ty) => SegmentParam::Type(ty),
 155         }
 156     }
 157 }
 158
 159 impl<'a> Spanned for SegmentParam<'a> {
 160     fn span(&self) -> Span {
 161         match *self {
 162             SegmentParam::LifeTime(lt) => lt.ident.span,
 163             SegmentParam::Type(ty) => ty.span,
 164             SegmentParam::Binding(binding) => binding.span,
 165         }
 166     }
 167 }
 168
 169 impl<'a> ToExpr for SegmentParam<'a> {
 170     fn to_expr(&self) -> Option<&ast::Expr> {
 171         None
 172     }
 173
 174     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
 175         match *self {
 176             SegmentParam::Type(ty) => ty.can_be_overflowed(context, len),
 177             _ => false,
 178         }
 179     }
 180 }
 181
 182 impl<'a> Rewrite for SegmentParam<'a> {
 183     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 184         match *self {
 185             SegmentParam::LifeTime(lt) => lt.rewrite(context, shape),
 186             SegmentParam::Type(ty) => ty.rewrite(context, shape),
 187             SegmentParam::Binding(binding) => {
 188                 let mut result = match context.config.type_punctuation_density() {
 189                     TypeDensity::Wide => format!("{} = ", rewrite_ident(context, binding.ident)),
 190                     TypeDensity::Compressed => {
 191                         format!("{}=", rewrite_ident(context, binding.ident))
 192                     }
 193                 };
 194                 let budget = shape.width.checked_sub(result.len())?;
 195                 let rewrite = binding
 196                     .ty
 197                     .rewrite(context, Shape::legacy(budget, shape.indent + result.len()))?;
 198                 result.push_str(&rewrite);
 199                 Some(result)
 200             }
 201         }
 202     }
 203 }
 204
 205 // Formats a path segment. There are some hacks involved to correctly determine
 206 // the segment's associated span since it's not part of the AST.
 207 //
 208 // The span_lo is assumed to be greater than the end of any previous segment's
 209 // parameters and lesser or equal than the start of current segment.
 210 //
 211 // span_hi is assumed equal to the end of the entire path.
 212 //
 213 // When the segment contains a positive number of parameters, we update span_lo
 214 // so that invariants described above will hold for the next segment.
 215 fn rewrite_segment(
 216     path_context: PathContext,
 217     segment: &ast::PathSegment,
 218     span_lo: &mut BytePos,
 219     span_hi: BytePos,
 220     context: &RewriteContext,
 221     shape: Shape,
 222 ) -> Option<String> {
 223     let mut result = String::with_capacity(128);
 224     result.push_str(rewrite_ident(context, segment.ident));
 225
 226     let ident_len = result.len();
 227     let shape = if context.use_block_indent() {
 228         shape.offset_left(ident_len)?
 229     } else {
 230         shape.shrink_left(ident_len)?
 231     };
 232
 233     if let Some(ref args) = segment.args {
 234         match **args {
 235             ast::GenericArgs::AngleBracketed(ref data)
 236                 if !data.args.is_empty() || !data.bindings.is_empty() =>
 237             {
 238                 let param_list = data
 239                     .args
 240                     .iter()
 241                     .map(SegmentParam::from_generic_arg)
 242                     .chain(data.bindings.iter().map(|x| SegmentParam::Binding(&*x)))
 243                     .collect::<Vec<_>>();
 244
 245                 let separator = if path_context == PathContext::Expr {
 246                     "::"
 247                 } else {
 248                     ""
 249                 };
 250                 result.push_str(separator);
 251
 252                 let generics_str = overflow::rewrite_with_angle_brackets(
 253                     context,
 254                     "",
 255                     &param_list.iter().map(|e| &*e).collect::<Vec<_>>(),
 256                     shape,
 257                     mk_sp(*span_lo, span_hi),
 258                 )?;
 259
 260                 // Update position of last bracket.
 261                 *span_lo = context
 262                     .snippet_provider
 263                     .span_after(mk_sp(*span_lo, span_hi), "<");
 264
 265                 result.push_str(&generics_str)
 266             }
 267             ast::GenericArgs::Parenthesized(ref data) => {
 268                 let output = match data.output {
 269                     Some(ref ty) => FunctionRetTy::Ty(ty.clone()),
 270                     None => FunctionRetTy::Default(codemap::DUMMY_SP),
 271                 };
 272                 result.push_str(&format_function_type(
 273                     data.inputs.iter().map(|x| &**x),
 274                     &output,
 275                     false,
 276                     data.span,
 277                     context,
 278                     shape,
 279                 )?);
 280             }
 281             _ => (),
 282         }
 283     }
 284
 285     Some(result)
 286 }
 287
 288 fn format_function_type<'a, I>(
 289     inputs: I,
 290     output: &FunctionRetTy,
 291     variadic: bool,
 292     span: Span,
 293     context: &RewriteContext,
 294     shape: Shape,
 295 ) -> Option<String>
 296 where
 297     I: ExactSizeIterator,
 298     <I as Iterator>::Item: Deref,
 299     <I::Item as Deref>::Target: Rewrite + Spanned + 'a,
 300 {
 301     // Code for handling variadics is somewhat duplicated for items, but they
 302     // are different enough to need some serious refactoring to share code.
 303     enum ArgumentKind<T>
 304     where
 305         T: Deref,
 306         <T as Deref>::Target: Rewrite + Spanned,
 307     {
 308         Regular(T),
 309         Variadic(BytePos),
 310     }
 311
 312     let variadic_arg = if variadic {
 313         let variadic_start = context.snippet_provider.span_before(span, "...");
 314         Some(ArgumentKind::Variadic(variadic_start))
 315     } else {
 316         None
 317     };
 318
 319     // 2 for ()
 320     let budget = shape.width.checked_sub(2)?;
 321     // 1 for (
 322     let offset = match context.config.indent_style() {
 323         IndentStyle::Block => {
 324             shape
 325                 .block()
 326                 .block_indent(context.config.tab_spaces())
 327                 .indent
 328         }
 329         IndentStyle::Visual => shape.indent + 1,
 330     };
 331     let list_shape = Shape::legacy(budget, offset);
 332     let list_lo = context.snippet_provider.span_after(span, "(");
 333     let items = itemize_list(
 334         context.snippet_provider,
 335         inputs.map(ArgumentKind::Regular).chain(variadic_arg),
 336         ")",
 337         ",",
 338         |arg| match *arg {
 339             ArgumentKind::Regular(ref ty) => ty.span().lo(),
 340             ArgumentKind::Variadic(start) => start,
 341         },
 342         |arg| match *arg {
 343             ArgumentKind::Regular(ref ty) => ty.span().hi(),
 344             ArgumentKind::Variadic(start) => start + BytePos(3),
 345         },
 346         |arg| match *arg {
 347             ArgumentKind::Regular(ref ty) => ty.rewrite(context, list_shape),
 348             ArgumentKind::Variadic(_) => Some("...".to_owned()),
 349         },
 350         list_lo,
 351         span.hi(),
 352         false,
 353     );
 354
 355     let item_vec: Vec<_> = items.collect();
 356
 357     let tactic = definitive_tactic(
 358         &*item_vec,
 359         ListTactic::HorizontalVertical,
 360         Separator::Comma,
 361         budget,
 362     );
 363
 364     let fmt = ListFormatting {
 365         tactic,
 366         separator: ",",
 367         trailing_separator: if !context.use_block_indent() || variadic {
 368             SeparatorTactic::Never
 369         } else {
 370             context.config.trailing_comma()
 371         },
 372         separator_place: SeparatorPlace::Back,
 373         shape: list_shape,
 374         ends_with_newline: tactic.ends_with_newline(context.config.indent_style()),
 375         preserve_newline: true,
 376         nested: false,
 377         config: context.config,
 378     };
 379
 380     let list_str = write_list(&item_vec, &fmt)?;
 381
 382     let ty_shape = match context.config.indent_style() {
 383         // 4 = " -> "
 384         IndentStyle::Block => shape.offset_left(4)?,
 385         IndentStyle::Visual => shape.block_left(4)?,
 386     };
 387     let output = match *output {
 388         FunctionRetTy::Ty(ref ty) => {
 389             let type_str = ty.rewrite(context, ty_shape)?;
 390             format!(" -> {}", type_str)
 391         }
 392         FunctionRetTy::Default(..) => String::new(),
 393     };
 394
 395     let args = if (!list_str.contains('\n') || list_str.is_empty()) && !output.contains('\n')
 396         || !context.use_block_indent()
 397     {
 398         format!("({})", list_str)
 399     } else {
 400         format!(
 401             "({}{}{})",
 402             offset.to_string_with_newline(context.config),
 403             list_str,
 404             shape.block().indent.to_string_with_newline(context.config),
 405         )
 406     };
 407     if last_line_width(&args) + first_line_width(&output) <= shape.width {
 408         Some(format!("{}{}", args, output))
 409     } else {
 410         Some(format!(
 411             "{}\n{}{}",
 412             args,
 413             offset.to_string(context.config),
 414             output.trim_left()
 415         ))
 416     }
 417 }
 418
 419 fn type_bound_colon(context: &RewriteContext) -> &'static str {
 420     colon_spaces(
 421         context.config.space_before_colon(),
 422         context.config.space_after_colon(),
 423     )
 424 }
 425
 426 impl Rewrite for ast::WherePredicate {
 427     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 428         // FIXME: dead spans?
 429         let result = match *self {
 430             ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 431                 ref bound_generic_params,
 432                 ref bounded_ty,
 433                 ref bounds,
 434                 ..
 435             }) => {
 436                 let type_str = bounded_ty.rewrite(context, shape)?;
 437                 let colon = type_bound_colon(context).trim_right();
 438                 let lhs = if let Some(lifetime_str) =
 439                     rewrite_lifetime_param(context, shape, bound_generic_params)
 440                 {
 441                     format!("for<{}> {}{}", lifetime_str, type_str, colon)
 442                 } else {
 443                     format!("{}{}", type_str, colon)
 444                 };
 445
 446                 rewrite_assign_rhs(context, lhs, bounds, shape)?
 447             }
 448             ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
 449                 ref lifetime,
 450                 ref bounds,
 451                 ..
 452             }) => rewrite_bounded_lifetime(lifetime, bounds, context, shape)?,
 453             ast::WherePredicate::EqPredicate(ast::WhereEqPredicate {
 454                 ref lhs_ty,
 455                 ref rhs_ty,
 456                 ..
 457             }) => {
 458                 let lhs_ty_str = lhs_ty.rewrite(context, shape).map(|lhs| lhs + " =")?;
 459                 rewrite_assign_rhs(context, lhs_ty_str, &**rhs_ty, shape)?
 460             }
 461         };
 462
 463         Some(result)
 464     }
 465 }
 466
 467 impl Rewrite for ast::GenericArg {
 468     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 469         match *self {
 470             ast::GenericArg::Lifetime(ref lt) => lt.rewrite(context, shape),
 471             ast::GenericArg::Type(ref ty) => ty.rewrite(context, shape),
 472         }
 473     }
 474 }
 475
 476 fn rewrite_bounded_lifetime(
 477     lt: &ast::Lifetime,
 478     bounds: &[ast::GenericBound],
 479     context: &RewriteContext,
 480     shape: Shape,
 481 ) -> Option<String> {
 482     let result = lt.rewrite(context, shape)?;
 483
 484     if bounds.is_empty() {
 485         Some(result)
 486     } else {
 487         let colon = type_bound_colon(context);
 488         let overhead = last_line_width(&result) + colon.len();
 489         let result = format!(
 490             "{}{}{}",
 491             result,
 492             colon,
 493             join_bounds(context, shape.sub_width(overhead)?, bounds, true)?
 494         );
 495         Some(result)
 496     }
 497 }
 498
 499 impl Rewrite for ast::Lifetime {
 500     fn rewrite(&self, context: &RewriteContext, _: Shape) -> Option<String> {
 501         Some(rewrite_ident(context, self.ident).to_owned())
 502     }
 503 }
 504
 505 impl Rewrite for ast::GenericBound {
 506     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 507         match *self {
 508             ast::GenericBound::Trait(ref poly_trait_ref, trait_bound_modifier) => {
 509                 match trait_bound_modifier {
 510                     ast::TraitBoundModifier::None => poly_trait_ref.rewrite(context, shape),
 511                     ast::TraitBoundModifier::Maybe => {
 512                         let rw = poly_trait_ref.rewrite(context, shape.offset_left(1)?)?;
 513                         Some(format!("?{}", rw))
 514                     }
 515                 }
 516             }
 517             ast::GenericBound::Outlives(ref lifetime) => lifetime.rewrite(context, shape),
 518         }
 519     }
 520 }
 521
 522 impl Rewrite for ast::GenericBounds {
 523     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 524         join_bounds(context, shape, self, true)
 525     }
 526 }
 527
 528 impl Rewrite for ast::GenericParam {
 529     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 530         let mut result = String::with_capacity(128);
 531         // FIXME: If there are more than one attributes, this will force multiline.
 532         match self.attrs.rewrite(context, shape) {
 533             Some(ref rw) if !rw.is_empty() => result.push_str(&format!("{} ", rw)),
 534             _ => (),
 535         }
 536         result.push_str(rewrite_ident(context, self.ident));
 537         if !self.bounds.is_empty() {
 538             result.push_str(type_bound_colon(context));
 539             result.push_str(&self.bounds.rewrite(context, shape)?)
 540         }
 541         if let ast::GenericParamKind::Type {
 542             default: Some(ref def),
 543         } = self.kind
 544         {
 545             let eq_str = match context.config.type_punctuation_density() {
 546                 TypeDensity::Compressed => "=",
 547                 TypeDensity::Wide => " = ",
 548             };
 549             result.push_str(eq_str);
 550             let budget = shape.width.checked_sub(result.len())?;
 551             let rewrite =
 552                 def.rewrite(context, Shape::legacy(budget, shape.indent + result.len()))?;
 553             result.push_str(&rewrite);
 554         }
 555
 556         Some(result)
 557     }
 558 }
 559
 560 impl Rewrite for ast::PolyTraitRef {
 561     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 562         if let Some(lifetime_str) =
 563             rewrite_lifetime_param(context, shape, &self.bound_generic_params)
 564         {
 565             // 6 is "for<> ".len()
 566             let extra_offset = lifetime_str.len() + 6;
 567             let path_str = self
 568                 .trait_ref
 569                 .rewrite(context, shape.offset_left(extra_offset)?)?;
 570
 571             Some(format!("for<{}> {}", lifetime_str, path_str))
 572         } else {
 573             self.trait_ref.rewrite(context, shape)
 574         }
 575     }
 576 }
 577
 578 impl Rewrite for ast::TraitRef {
 579     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 580         rewrite_path(context, PathContext::Type, None, &self.path, shape)
 581     }
 582 }
 583
 584 impl Rewrite for ast::Ty {
 585     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 586         match self.node {
 587             ast::TyKind::TraitObject(ref bounds, tobj_syntax) => {
 588                 // we have to consider 'dyn' keyword is used or not!!!
 589                 let is_dyn = tobj_syntax == ast::TraitObjectSyntax::Dyn;
 590                 // 4 is length of 'dyn '
 591                 let shape = if is_dyn { shape.offset_left(4)? } else { shape };
 592                 let res = bounds.rewrite(context, shape)?;
 593                 if is_dyn {
 594                     Some(format!("dyn {}", res))
 595                 } else {
 596                     Some(res)
 597                 }
 598             }
 599             ast::TyKind::Ptr(ref mt) => {
 600                 let prefix = match mt.mutbl {
 601                     Mutability::Mutable => "*mut ",
 602                     Mutability::Immutable => "*const ",
 603                 };
 604
 605                 rewrite_unary_prefix(context, prefix, &*mt.ty, shape)
 606             }
 607             ast::TyKind::Rptr(ref lifetime, ref mt) => {
 608                 let mut_str = format_mutability(mt.mutbl);
 609                 let mut_len = mut_str.len();
 610                 Some(match *lifetime {
 611                     Some(ref lifetime) => {
 612                         let lt_budget = shape.width.checked_sub(2 + mut_len)?;
 613                         let lt_str = lifetime.rewrite(
 614                             context,
 615                             Shape::legacy(lt_budget, shape.indent + 2 + mut_len),
 616                         )?;
 617                         let lt_len = lt_str.len();
 618                         let budget = shape.width.checked_sub(2 + mut_len + lt_len)?;
 619                         format!(
 620                             "&{} {}{}",
 621                             lt_str,
 622                             mut_str,
 623                             mt.ty.rewrite(
 624                                 context,
 625                                 Shape::legacy(budget, shape.indent + 2 + mut_len + lt_len)
 626                             )?
 627                         )
 628                     }
 629                     None => {
 630                         let budget = shape.width.checked_sub(1 + mut_len)?;
 631                         format!(
 632                             "&{}{}",
 633                             mut_str,
 634                             mt.ty.rewrite(
 635                                 context,
 636                                 Shape::legacy(budget, shape.indent + 1 + mut_len)
 637                             )?
 638                         )
 639                     }
 640                 })
 641             }
 642             // FIXME: we drop any comments here, even though it's a silly place to put
 643             // comments.
 644             ast::TyKind::Paren(ref ty) => {
 645                 let budget = shape.width.checked_sub(2)?;
 646                 ty.rewrite(context, Shape::legacy(budget, shape.indent + 1))
 647                     .map(|ty_str| format!("({})", ty_str))
 648             }
 649             ast::TyKind::Slice(ref ty) => {
 650                 let budget = shape.width.checked_sub(4)?;
 651                 ty.rewrite(context, Shape::legacy(budget, shape.indent + 1))
 652                     .map(|ty_str| format!("[{}]", ty_str))
 653             }
 654             ast::TyKind::Tup(ref items) => rewrite_tuple(
 655                 context,
 656                 &::utils::ptr_vec_to_ref_vec(items),
 657                 self.span,
 658                 shape,
 659             ),
 660             ast::TyKind::Path(ref q_self, ref path) => {
 661                 rewrite_path(context, PathContext::Type, q_self.as_ref(), path, shape)
 662             }
 663             ast::TyKind::Array(ref ty, ref repeats) => rewrite_pair(
 664                 &**ty,
 665                 &*repeats.value,
 666                 PairParts::new("[", "; ", "]"),
 667                 context,
 668                 shape,
 669                 SeparatorPlace::Back,
 670             ),
 671             ast::TyKind::Infer => {
 672                 if shape.width >= 1 {
 673                     Some("_".to_owned())
 674                 } else {
 675                     None
 676                 }
 677             }
 678             ast::TyKind::BareFn(ref bare_fn) => rewrite_bare_fn(bare_fn, self.span, context, shape),
 679             ast::TyKind::Never => Some(String::from("!")),
 680             ast::TyKind::Mac(ref mac) => {
 681                 rewrite_macro(mac, None, context, shape, MacroPosition::Expression)
 682             }
 683             ast::TyKind::ImplicitSelf => Some(String::from("")),
 684             ast::TyKind::ImplTrait(_, ref it) => it
 685                 .rewrite(context, shape)
 686                 .map(|it_str| format!("impl {}", it_str)),
 687             ast::TyKind::Err | ast::TyKind::Typeof(..) => unreachable!(),
 688         }
 689     }
 690 }
 691
 692 fn rewrite_bare_fn(
 693     bare_fn: &ast::BareFnTy,
 694     span: Span,
 695     context: &RewriteContext,
 696     shape: Shape,
 697 ) -> Option<String> {
 698     let mut result = String::with_capacity(128);
 699
 700     if let Some(ref lifetime_str) = rewrite_lifetime_param(context, shape, &bare_fn.generic_params)
 701     {
 702         result.push_str("for<");
 703         // 6 = "for<> ".len(), 4 = "for<".
 704         // This doesn't work out so nicely for multiline situation with lots of
 705         // rightward drift. If that is a problem, we could use the list stuff.
 706         result.push_str(lifetime_str);
 707         result.push_str("> ");
 708     }
 709
 710     result.push_str(::utils::format_unsafety(bare_fn.unsafety));
 711
 712     result.push_str(&format_abi(
 713         bare_fn.abi,
 714         context.config.force_explicit_abi(),
 715         false,
 716     ));
 717
 718     result.push_str("fn");
 719
 720     let func_ty_shape = shape.offset_left(result.len())?;
 721
 722     let rewrite = format_function_type(
 723         bare_fn.decl.inputs.iter(),
 724         &bare_fn.decl.output,
 725         bare_fn.decl.variadic,
 726         span,
 727         context,
 728         func_ty_shape,
 729     )?;
 730
 731     result.push_str(&rewrite);
 732
 733     Some(result)
 734 }
 735
 736 fn is_generic_bounds_in_order(generic_bounds: &[ast::GenericBound]) -> bool {
 737     let is_trait = |b: &ast::GenericBound| match b {
 738         ast::GenericBound::Outlives(..) => false,
 739         ast::GenericBound::Trait(..) => true,
 740     };
 741     let is_lifetime = |b: &ast::GenericBound| !is_trait(b);
 742     let last_trait_index = generic_bounds.iter().rposition(is_trait);
 743     let first_lifetime_index = generic_bounds.iter().position(is_lifetime);
 744     match (last_trait_index, first_lifetime_index) {
 745         (Some(last_trait_index), Some(first_lifetime_index)) => {
 746             last_trait_index < first_lifetime_index
 747         }
 748         _ => true,
 749     }
 750 }
 751
 752 fn join_bounds(
 753     context: &RewriteContext,
 754     shape: Shape,
 755     items: &[ast::GenericBound],
 756     need_indent: bool,
 757 ) -> Option<String> {
 758     // Try to join types in a single line
 759     let joiner = match context.config.type_punctuation_density() {
 760         TypeDensity::Compressed => "+",
 761         TypeDensity::Wide => " + ",
 762     };
 763     let type_strs = items
 764         .iter()
 765         .map(|item| item.rewrite(context, shape))
 766         .collect::<Option<Vec<_>>>()?;
 767     let result = type_strs.join(joiner);
 768     if items.len() <= 1 || (!result.contains('\n') && result.len() <= shape.width) {
 769         return Some(result);
 770     }
 771
 772     // We need to use multiple lines.
 773     let (type_strs, offset) = if need_indent {
 774         // Rewrite with additional indentation.
 775         let nested_shape = shape.block_indent(context.config.tab_spaces());
 776         let type_strs = items
 777             .iter()
 778             .map(|item| item.rewrite(context, nested_shape))
 779             .collect::<Option<Vec<_>>>()?;
 780         (type_strs, nested_shape.indent)
 781     } else {
 782         (type_strs, shape.indent)
 783     };
 784
 785     let is_bound_extendable = |s: &str, b: &ast::GenericBound| match b {
 786         ast::GenericBound::Outlives(..) => true,
 787         ast::GenericBound::Trait(..) => last_line_extendable(s),
 788     };
 789     let mut result = String::with_capacity(128);
 790     result.push_str(&type_strs[0]);
 791     let mut can_be_put_on_the_same_line = is_bound_extendable(&result, &items[0]);
 792     let generic_bounds_in_order = is_generic_bounds_in_order(items);
 793     for (bound, bound_str) in items[1..].iter().zip(type_strs[1..].iter()) {
 794         if generic_bounds_in_order && can_be_put_on_the_same_line {
 795             result.push_str(joiner);
 796         } else {
 797             result.push_str(&offset.to_string_with_newline(context.config));
 798             result.push_str("+ ");
 799         }
 800         result.push_str(bound_str);
 801         can_be_put_on_the_same_line = is_bound_extendable(bound_str, bound);
 802     }
 803
 804     Some(result)
 805 }
 806
 807 pub fn can_be_overflowed_type(context: &RewriteContext, ty: &ast::Ty, len: usize) -> bool {
 808     match ty.node {
 809         ast::TyKind::Tup(..) => context.use_block_indent() && len == 1,
 810         ast::TyKind::Rptr(_, ref mutty) | ast::TyKind::Ptr(ref mutty) => {
 811             can_be_overflowed_type(context, &*mutty.ty, len)
 812         }
 813         _ => false,
 814     }
 815 }
 816
 817 /// Returns `None` if there is no `LifetimeDef` in the given generic parameters.
 818 fn rewrite_lifetime_param(
 819     context: &RewriteContext,
 820     shape: Shape,
 821     generic_params: &[ast::GenericParam],
 822 ) -> Option<String> {
 823     let result = generic_params
 824         .iter()
 825         .filter(|p| match p.kind {
 826             ast::GenericParamKind::Lifetime => true,
 827             _ => false,
 828         }).map(|lt| lt.rewrite(context, shape))
 829         .collect::<Option<Vec<_>>>()?
 830         .join(", ");
 831     if result.is_empty() {
 832         None
 833     } else {
 834         Some(result)
 835     }
 836 }