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::source_map::{self, BytePos, Span};
  17 use syntax::symbol::keywords;
  18
  19 use config::{IndentStyle, TypeDensity};
  20 use expr::{rewrite_assign_rhs, rewrite_tuple, rewrite_unary_prefix};
  21 use lists::{definitive_tactic, itemize_list, write_list, ListFormatting, Separator};
  22 use macros::{rewrite_macro, MacroPosition};
  23 use overflow;
  24 use pairs::{rewrite_pair, PairParts};
  25 use rewrite::{Rewrite, RewriteContext};
  26 use shape::Shape;
  27 use source_map::SpanUtils;
  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::PathRoot.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 pub 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> Rewrite for SegmentParam<'a> {
 170     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 171         match *self {
 172             SegmentParam::LifeTime(lt) => lt.rewrite(context, shape),
 173             SegmentParam::Type(ty) => ty.rewrite(context, shape),
 174             SegmentParam::Binding(binding) => {
 175                 let mut result = match context.config.type_punctuation_density() {
 176                     TypeDensity::Wide => format!("{} = ", rewrite_ident(context, binding.ident)),
 177                     TypeDensity::Compressed => {
 178                         format!("{}=", rewrite_ident(context, binding.ident))
 179                     }
 180                 };
 181                 let budget = shape.width.checked_sub(result.len())?;
 182                 let rewrite = binding
 183                     .ty
 184                     .rewrite(context, Shape::legacy(budget, shape.indent + result.len()))?;
 185                 result.push_str(&rewrite);
 186                 Some(result)
 187             }
 188         }
 189     }
 190 }
 191
 192 // Formats a path segment. There are some hacks involved to correctly determine
 193 // the segment's associated span since it's not part of the AST.
 194 //
 195 // The span_lo is assumed to be greater than the end of any previous segment's
 196 // parameters and lesser or equal than the start of current segment.
 197 //
 198 // span_hi is assumed equal to the end of the entire path.
 199 //
 200 // When the segment contains a positive number of parameters, we update span_lo
 201 // so that invariants described above will hold for the next segment.
 202 fn rewrite_segment(
 203     path_context: PathContext,
 204     segment: &ast::PathSegment,
 205     span_lo: &mut BytePos,
 206     span_hi: BytePos,
 207     context: &RewriteContext,
 208     shape: Shape,
 209 ) -> Option<String> {
 210     let mut result = String::with_capacity(128);
 211     result.push_str(rewrite_ident(context, segment.ident));
 212
 213     let ident_len = result.len();
 214     let shape = if context.use_block_indent() {
 215         shape.offset_left(ident_len)?
 216     } else {
 217         shape.shrink_left(ident_len)?
 218     };
 219
 220     if let Some(ref args) = segment.args {
 221         match **args {
 222             ast::GenericArgs::AngleBracketed(ref data)
 223                 if !data.args.is_empty() || !data.bindings.is_empty() =>
 224             {
 225                 let param_list = data
 226                     .args
 227                     .iter()
 228                     .map(SegmentParam::from_generic_arg)
 229                     .chain(data.bindings.iter().map(|x| SegmentParam::Binding(&*x)))
 230                     .collect::<Vec<_>>();
 231
 232                 let force_separator =
 233                     context.inside_macro() && context.snippet(data.span).starts_with("::");
 234                 let separator = if path_context == PathContext::Expr || force_separator {
 235                     "::"
 236                 } else {
 237                     ""
 238                 };
 239                 result.push_str(separator);
 240
 241                 let generics_str = overflow::rewrite_with_angle_brackets(
 242                     context,
 243                     "",
 244                     param_list.iter(),
 245                     shape,
 246                     mk_sp(*span_lo, span_hi),
 247                 )?;
 248
 249                 // Update position of last bracket.
 250                 *span_lo = context
 251                     .snippet_provider
 252                     .span_after(mk_sp(*span_lo, span_hi), "<");
 253
 254                 result.push_str(&generics_str)
 255             }
 256             ast::GenericArgs::Parenthesized(ref data) => {
 257                 let output = match data.output {
 258                     Some(ref ty) => FunctionRetTy::Ty(ty.clone()),
 259                     None => FunctionRetTy::Default(source_map::DUMMY_SP),
 260                 };
 261                 result.push_str(&format_function_type(
 262                     data.inputs.iter().map(|x| &**x),
 263                     &output,
 264                     false,
 265                     data.span,
 266                     context,
 267                     shape,
 268                 )?);
 269             }
 270             _ => (),
 271         }
 272     }
 273
 274     Some(result)
 275 }
 276
 277 fn format_function_type<'a, I>(
 278     inputs: I,
 279     output: &FunctionRetTy,
 280     variadic: bool,
 281     span: Span,
 282     context: &RewriteContext,
 283     shape: Shape,
 284 ) -> Option<String>
 285 where
 286     I: ExactSizeIterator,
 287     <I as Iterator>::Item: Deref,
 288     <I::Item as Deref>::Target: Rewrite + Spanned + 'a,
 289 {
 290     debug!("format_function_type {:#?}", shape);
 291
 292     let ty_shape = match context.config.indent_style() {
 293         // 4 = " -> "
 294         IndentStyle::Block => shape.offset_left(4)?,
 295         IndentStyle::Visual => shape.block_left(4)?,
 296     };
 297     let output = match *output {
 298         FunctionRetTy::Ty(ref ty) => {
 299             let type_str = ty.rewrite(context, ty_shape)?;
 300             format!(" -> {}", type_str)
 301         }
 302         FunctionRetTy::Default(..) => String::new(),
 303     };
 304
 305     // Code for handling variadics is somewhat duplicated for items, but they
 306     // are different enough to need some serious refactoring to share code.
 307     enum ArgumentKind<T>
 308     where
 309         T: Deref,
 310         <T as Deref>::Target: Rewrite + Spanned,
 311     {
 312         Regular(T),
 313         Variadic(BytePos),
 314     }
 315
 316     let variadic_arg = if variadic {
 317         let variadic_start = context.snippet_provider.span_before(span, "...");
 318         Some(ArgumentKind::Variadic(variadic_start))
 319     } else {
 320         None
 321     };
 322
 323     let list_shape = if context.use_block_indent() {
 324         Shape::indented(
 325             shape.block().indent.block_indent(context.config),
 326             context.config,
 327         )
 328     } else {
 329         // 2 for ()
 330         let budget = shape.width.checked_sub(2)?;
 331         // 1 for (
 332         let offset = shape.indent + 1;
 333         Shape::legacy(budget, offset)
 334     };
 335     let list_lo = context.snippet_provider.span_after(span, "(");
 336     let items = itemize_list(
 337         context.snippet_provider,
 338         inputs.map(ArgumentKind::Regular).chain(variadic_arg),
 339         ")",
 340         ",",
 341         |arg| match *arg {
 342             ArgumentKind::Regular(ref ty) => ty.span().lo(),
 343             ArgumentKind::Variadic(start) => start,
 344         },
 345         |arg| match *arg {
 346             ArgumentKind::Regular(ref ty) => ty.span().hi(),
 347             ArgumentKind::Variadic(start) => start + BytePos(3),
 348         },
 349         |arg| match *arg {
 350             ArgumentKind::Regular(ref ty) => ty.rewrite(context, list_shape),
 351             ArgumentKind::Variadic(_) => Some("...".to_owned()),
 352         },
 353         list_lo,
 354         span.hi(),
 355         false,
 356     );
 357
 358     let item_vec: Vec<_> = items.collect();
 359
 360     // If the return type is multi-lined, then force to use multiple lines for
 361     // arguments as well.
 362     let tactic = if output.contains('\n') {
 363         DefinitiveListTactic::Vertical
 364     } else {
 365         definitive_tactic(
 366             &*item_vec,
 367             ListTactic::HorizontalVertical,
 368             Separator::Comma,
 369             shape.width.saturating_sub(2 + output.len()),
 370         )
 371     };
 372     let trailing_separator = if !context.use_block_indent() || variadic {
 373         SeparatorTactic::Never
 374     } else {
 375         context.config.trailing_comma()
 376     };
 377
 378     let fmt = ListFormatting::new(list_shape, context.config)
 379         .tactic(tactic)
 380         .trailing_separator(trailing_separator)
 381         .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
 382         .preserve_newline(true);
 383     let list_str = write_list(&item_vec, &fmt)?;
 384
 385     let args = if tactic == DefinitiveListTactic::Horizontal || !context.use_block_indent() {
 386         format!("({})", list_str)
 387     } else {
 388         format!(
 389             "({}{}{})",
 390             list_shape.indent.to_string_with_newline(context.config),
 391             list_str,
 392             shape.block().indent.to_string_with_newline(context.config),
 393         )
 394     };
 395     if output.is_empty() || last_line_width(&args) + first_line_width(&output) <= shape.width {
 396         Some(format!("{}{}", args, output))
 397     } else {
 398         Some(format!(
 399             "{}\n{}{}",
 400             args,
 401             list_shape.indent.to_string(context.config),
 402             output.trim_start()
 403         ))
 404     }
 405 }
 406
 407 fn type_bound_colon(context: &RewriteContext) -> &'static str {
 408     colon_spaces(
 409         context.config.space_before_colon(),
 410         context.config.space_after_colon(),
 411     )
 412 }
 413
 414 impl Rewrite for ast::WherePredicate {
 415     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 416         // FIXME: dead spans?
 417         let result = match *self {
 418             ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 419                 ref bound_generic_params,
 420                 ref bounded_ty,
 421                 ref bounds,
 422                 ..
 423             }) => {
 424                 let type_str = bounded_ty.rewrite(context, shape)?;
 425                 let colon = type_bound_colon(context).trim_end();
 426                 let lhs = if let Some(lifetime_str) =
 427                     rewrite_lifetime_param(context, shape, bound_generic_params)
 428                 {
 429                     format!("for<{}> {}{}", lifetime_str, type_str, colon)
 430                 } else {
 431                     format!("{}{}", type_str, colon)
 432                 };
 433
 434                 rewrite_assign_rhs(context, lhs, bounds, shape)?
 435             }
 436             ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
 437                 ref lifetime,
 438                 ref bounds,
 439                 ..
 440             }) => rewrite_bounded_lifetime(lifetime, bounds, context, shape)?,
 441             ast::WherePredicate::EqPredicate(ast::WhereEqPredicate {
 442                 ref lhs_ty,
 443                 ref rhs_ty,
 444                 ..
 445             }) => {
 446                 let lhs_ty_str = lhs_ty.rewrite(context, shape).map(|lhs| lhs + " =")?;
 447                 rewrite_assign_rhs(context, lhs_ty_str, &**rhs_ty, shape)?
 448             }
 449         };
 450
 451         Some(result)
 452     }
 453 }
 454
 455 impl Rewrite for ast::GenericArg {
 456     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 457         match *self {
 458             ast::GenericArg::Lifetime(ref lt) => lt.rewrite(context, shape),
 459             ast::GenericArg::Type(ref ty) => ty.rewrite(context, shape),
 460         }
 461     }
 462 }
 463
 464 fn rewrite_bounded_lifetime(
 465     lt: &ast::Lifetime,
 466     bounds: &[ast::GenericBound],
 467     context: &RewriteContext,
 468     shape: Shape,
 469 ) -> Option<String> {
 470     let result = lt.rewrite(context, shape)?;
 471
 472     if bounds.is_empty() {
 473         Some(result)
 474     } else {
 475         let colon = type_bound_colon(context);
 476         let overhead = last_line_width(&result) + colon.len();
 477         let result = format!(
 478             "{}{}{}",
 479             result,
 480             colon,
 481             join_bounds(context, shape.sub_width(overhead)?, bounds, true)?
 482         );
 483         Some(result)
 484     }
 485 }
 486
 487 impl Rewrite for ast::Lifetime {
 488     fn rewrite(&self, context: &RewriteContext, _: Shape) -> Option<String> {
 489         Some(rewrite_ident(context, self.ident).to_owned())
 490     }
 491 }
 492
 493 impl Rewrite for ast::GenericBound {
 494     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 495         match *self {
 496             ast::GenericBound::Trait(ref poly_trait_ref, trait_bound_modifier) => {
 497                 let snippet = context.snippet(self.span());
 498                 let has_paren = snippet.starts_with('(') && snippet.ends_with(')');
 499                 let rewrite = match trait_bound_modifier {
 500                     ast::TraitBoundModifier::None => poly_trait_ref.rewrite(context, shape),
 501                     ast::TraitBoundModifier::Maybe => poly_trait_ref
 502                         .rewrite(context, shape.offset_left(1)?)
 503                         .map(|s| format!("?{}", s)),
 504                 };
 505                 rewrite.map(|s| if has_paren { format!("({})", s) } else { s })
 506             }
 507             ast::GenericBound::Outlives(ref lifetime) => lifetime.rewrite(context, shape),
 508         }
 509     }
 510 }
 511
 512 impl Rewrite for ast::GenericBounds {
 513     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 514         if self.is_empty() {
 515             return Some(String::new());
 516         }
 517
 518         join_bounds(context, shape, self, true)
 519     }
 520 }
 521
 522 impl Rewrite for ast::GenericParam {
 523     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 524         let mut result = String::with_capacity(128);
 525         // FIXME: If there are more than one attributes, this will force multiline.
 526         match self.attrs.rewrite(context, shape) {
 527             Some(ref rw) if !rw.is_empty() => result.push_str(&format!("{} ", rw)),
 528             _ => (),
 529         }
 530         result.push_str(rewrite_ident(context, self.ident));
 531         if !self.bounds.is_empty() {
 532             result.push_str(type_bound_colon(context));
 533             result.push_str(&self.bounds.rewrite(context, shape)?)
 534         }
 535         if let ast::GenericParamKind::Type {
 536             default: Some(ref def),
 537         } = self.kind
 538         {
 539             let eq_str = match context.config.type_punctuation_density() {
 540                 TypeDensity::Compressed => "=",
 541                 TypeDensity::Wide => " = ",
 542             };
 543             result.push_str(eq_str);
 544             let budget = shape.width.checked_sub(result.len())?;
 545             let rewrite =
 546                 def.rewrite(context, Shape::legacy(budget, shape.indent + result.len()))?;
 547             result.push_str(&rewrite);
 548         }
 549
 550         Some(result)
 551     }
 552 }
 553
 554 impl Rewrite for ast::PolyTraitRef {
 555     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 556         if let Some(lifetime_str) =
 557             rewrite_lifetime_param(context, shape, &self.bound_generic_params)
 558         {
 559             // 6 is "for<> ".len()
 560             let extra_offset = lifetime_str.len() + 6;
 561             let path_str = self
 562                 .trait_ref
 563                 .rewrite(context, shape.offset_left(extra_offset)?)?;
 564
 565             Some(format!("for<{}> {}", lifetime_str, path_str))
 566         } else {
 567             self.trait_ref.rewrite(context, shape)
 568         }
 569     }
 570 }
 571
 572 impl Rewrite for ast::TraitRef {
 573     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 574         rewrite_path(context, PathContext::Type, None, &self.path, shape)
 575     }
 576 }
 577
 578 impl Rewrite for ast::Ty {
 579     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 580         match self.node {
 581             ast::TyKind::TraitObject(ref bounds, tobj_syntax) => {
 582                 // we have to consider 'dyn' keyword is used or not!!!
 583                 let is_dyn = tobj_syntax == ast::TraitObjectSyntax::Dyn;
 584                 // 4 is length of 'dyn '
 585                 let shape = if is_dyn { shape.offset_left(4)? } else { shape };
 586                 let mut res = bounds.rewrite(context, shape)?;
 587                 // We may have falsely removed a trailing `+` inside macro call.
 588                 if context.inside_macro() && bounds.len() == 1 {
 589                     if context.snippet(self.span).ends_with('+') && !res.ends_with('+') {
 590                         res.push('+');
 591                     }
 592                 }
 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) => {
 655                 rewrite_tuple(context, items.iter(), self.span, shape, items.len() == 1)
 656             }
 657             ast::TyKind::Path(ref q_self, ref path) => {
 658                 rewrite_path(context, PathContext::Type, q_self.as_ref(), path, shape)
 659             }
 660             ast::TyKind::Array(ref ty, ref repeats) => rewrite_pair(
 661                 &**ty,
 662                 &*repeats.value,
 663                 PairParts::new("[", "; ", "]"),
 664                 context,
 665                 shape,
 666                 SeparatorPlace::Back,
 667             ),
 668             ast::TyKind::Infer => {
 669                 if shape.width >= 1 {
 670                     Some("_".to_owned())
 671                 } else {
 672                     None
 673                 }
 674             }
 675             ast::TyKind::BareFn(ref bare_fn) => rewrite_bare_fn(bare_fn, self.span, context, shape),
 676             ast::TyKind::Never => Some(String::from("!")),
 677             ast::TyKind::Mac(ref mac) => {
 678                 rewrite_macro(mac, None, context, shape, MacroPosition::Expression)
 679             }
 680             ast::TyKind::ImplicitSelf => Some(String::from("")),
 681             ast::TyKind::ImplTrait(_, ref it) => it
 682                 .rewrite(context, shape)
 683                 .map(|it_str| format!("impl {}", it_str)),
 684             ast::TyKind::Err | ast::TyKind::Typeof(..) => unreachable!(),
 685         }
 686     }
 687 }
 688
 689 fn rewrite_bare_fn(
 690     bare_fn: &ast::BareFnTy,
 691     span: Span,
 692     context: &RewriteContext,
 693     shape: Shape,
 694 ) -> Option<String> {
 695     debug!("rewrite_bare_fn {:#?}", shape);
 696
 697     let mut result = String::with_capacity(128);
 698
 699     if let Some(ref lifetime_str) = rewrite_lifetime_param(context, shape, &bare_fn.generic_params)
 700     {
 701         result.push_str("for<");
 702         // 6 = "for<> ".len(), 4 = "for<".
 703         // This doesn't work out so nicely for multiline situation with lots of
 704         // rightward drift. If that is a problem, we could use the list stuff.
 705         result.push_str(lifetime_str);
 706         result.push_str("> ");
 707     }
 708
 709     result.push_str(::utils::format_unsafety(bare_fn.unsafety));
 710
 711     result.push_str(&format_abi(
 712         bare_fn.abi,
 713         context.config.force_explicit_abi(),
 714         false,
 715     ));
 716
 717     result.push_str("fn");
 718
 719     let func_ty_shape = if context.use_block_indent() {
 720         shape.offset_left(result.len())?
 721     } else {
 722         shape.visual_indent(result.len()).sub_width(result.len())?
 723     };
 724
 725     let rewrite = format_function_type(
 726         bare_fn.decl.inputs.iter(),
 727         &bare_fn.decl.output,
 728         bare_fn.decl.variadic,
 729         span,
 730         context,
 731         func_ty_shape,
 732     )?;
 733
 734     result.push_str(&rewrite);
 735
 736     Some(result)
 737 }
 738
 739 fn is_generic_bounds_in_order(generic_bounds: &[ast::GenericBound]) -> bool {
 740     let is_trait = |b: &ast::GenericBound| match b {
 741         ast::GenericBound::Outlives(..) => false,
 742         ast::GenericBound::Trait(..) => true,
 743     };
 744     let is_lifetime = |b: &ast::GenericBound| !is_trait(b);
 745     let last_trait_index = generic_bounds.iter().rposition(is_trait);
 746     let first_lifetime_index = generic_bounds.iter().position(is_lifetime);
 747     match (last_trait_index, first_lifetime_index) {
 748         (Some(last_trait_index), Some(first_lifetime_index)) => {
 749             last_trait_index < first_lifetime_index
 750         }
 751         _ => true,
 752     }
 753 }
 754
 755 fn join_bounds(
 756     context: &RewriteContext,
 757     shape: Shape,
 758     items: &[ast::GenericBound],
 759     need_indent: bool,
 760 ) -> Option<String> {
 761     debug_assert!(!items.is_empty());
 762
 763     // Try to join types in a single line
 764     let joiner = match context.config.type_punctuation_density() {
 765         TypeDensity::Compressed => "+",
 766         TypeDensity::Wide => " + ",
 767     };
 768     let type_strs = items
 769         .iter()
 770         .map(|item| item.rewrite(context, shape))
 771         .collect::<Option<Vec<_>>>()?;
 772     let result = type_strs.join(joiner);
 773     if items.len() <= 1 || (!result.contains('\n') && result.len() <= shape.width) {
 774         return Some(result);
 775     }
 776
 777     // We need to use multiple lines.
 778     let (type_strs, offset) = if need_indent {
 779         // Rewrite with additional indentation.
 780         let nested_shape = shape.block_indent(context.config.tab_spaces());
 781         let type_strs = items
 782             .iter()
 783             .map(|item| item.rewrite(context, nested_shape))
 784             .collect::<Option<Vec<_>>>()?;
 785         (type_strs, nested_shape.indent)
 786     } else {
 787         (type_strs, shape.indent)
 788     };
 789
 790     let is_bound_extendable = |s: &str, b: &ast::GenericBound| match b {
 791         ast::GenericBound::Outlives(..) => true,
 792         ast::GenericBound::Trait(..) => last_line_extendable(s),
 793     };
 794     let mut result = String::with_capacity(128);
 795     result.push_str(&type_strs[0]);
 796     let mut can_be_put_on_the_same_line = is_bound_extendable(&result, &items[0]);
 797     let generic_bounds_in_order = is_generic_bounds_in_order(items);
 798     for (bound, bound_str) in items[1..].iter().zip(type_strs[1..].iter()) {
 799         if generic_bounds_in_order && can_be_put_on_the_same_line {
 800             result.push_str(joiner);
 801         } else {
 802             result.push_str(&offset.to_string_with_newline(context.config));
 803             result.push_str("+ ");
 804         }
 805         result.push_str(bound_str);
 806         can_be_put_on_the_same_line = is_bound_extendable(bound_str, bound);
 807     }
 808
 809     Some(result)
 810 }
 811
 812 pub fn can_be_overflowed_type(context: &RewriteContext, ty: &ast::Ty, len: usize) -> bool {
 813     match ty.node {
 814         ast::TyKind::Tup(..) => context.use_block_indent() && len == 1,
 815         ast::TyKind::Rptr(_, ref mutty) | ast::TyKind::Ptr(ref mutty) => {
 816             can_be_overflowed_type(context, &*mutty.ty, len)
 817         }
 818         _ => false,
 819     }
 820 }
 821
 822 /// Returns `None` if there is no `LifetimeDef` in the given generic parameters.
 823 fn rewrite_lifetime_param(
 824     context: &RewriteContext,
 825     shape: Shape,
 826     generic_params: &[ast::GenericParam],
 827 ) -> Option<String> {
 828     let result = generic_params
 829         .iter()
 830         .filter(|p| match p.kind {
 831             ast::GenericParamKind::Lifetime => true,
 832             _ => false,
 833         })
 834         .map(|lt| lt.rewrite(context, shape))
 835         .collect::<Option<Vec<_>>>()?
 836         .join(", ");
 837     if result.is_empty() {
 838         None
 839     } else {
 840         Some(result)
 841     }
 842 }