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::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 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 separator = if path_context == PathContext::Expr {
 233                     "::"
 234                 } else {
 235                     ""
 236                 };
 237                 result.push_str(separator);
 238
 239                 let generics_str = overflow::rewrite_with_angle_brackets(
 240                     context,
 241                     "",
 242                     param_list.iter(),
 243                     shape,
 244                     mk_sp(*span_lo, span_hi),
 245                 )?;
 246
 247                 // Update position of last bracket.
 248                 *span_lo = context
 249                     .snippet_provider
 250                     .span_after(mk_sp(*span_lo, span_hi), "<");
 251
 252                 result.push_str(&generics_str)
 253             }
 254             ast::GenericArgs::Parenthesized(ref data) => {
 255                 let output = match data.output {
 256                     Some(ref ty) => FunctionRetTy::Ty(ty.clone()),
 257                     None => FunctionRetTy::Default(source_map::DUMMY_SP),
 258                 };
 259                 result.push_str(&format_function_type(
 260                     data.inputs.iter().map(|x| &**x),
 261                     &output,
 262                     false,
 263                     data.span,
 264                     context,
 265                     shape,
 266                 )?);
 267             }
 268             _ => (),
 269         }
 270     }
 271
 272     Some(result)
 273 }
 274
 275 fn format_function_type<'a, I>(
 276     inputs: I,
 277     output: &FunctionRetTy,
 278     variadic: bool,
 279     span: Span,
 280     context: &RewriteContext,
 281     shape: Shape,
 282 ) -> Option<String>
 283 where
 284     I: ExactSizeIterator,
 285     <I as Iterator>::Item: Deref,
 286     <I::Item as Deref>::Target: Rewrite + Spanned + 'a,
 287 {
 288     debug!("format_function_type {:#?}", shape);
 289
 290     // Code for handling variadics is somewhat duplicated for items, but they
 291     // are different enough to need some serious refactoring to share code.
 292     enum ArgumentKind<T>
 293     where
 294         T: Deref,
 295         <T as Deref>::Target: Rewrite + Spanned,
 296     {
 297         Regular(T),
 298         Variadic(BytePos),
 299     }
 300
 301     let variadic_arg = if variadic {
 302         let variadic_start = context.snippet_provider.span_before(span, "...");
 303         Some(ArgumentKind::Variadic(variadic_start))
 304     } else {
 305         None
 306     };
 307
 308     // 2 for ()
 309     let budget = shape.width.checked_sub(2)?;
 310     // 1 for (
 311     let offset = match context.config.indent_style() {
 312         IndentStyle::Block => {
 313             shape
 314                 .block()
 315                 .block_indent(context.config.tab_spaces())
 316                 .indent
 317         }
 318         IndentStyle::Visual => shape.indent + 1,
 319     };
 320     let list_shape = Shape::legacy(budget, offset);
 321     let list_lo = context.snippet_provider.span_after(span, "(");
 322     let items = itemize_list(
 323         context.snippet_provider,
 324         inputs.map(ArgumentKind::Regular).chain(variadic_arg),
 325         ")",
 326         ",",
 327         |arg| match *arg {
 328             ArgumentKind::Regular(ref ty) => ty.span().lo(),
 329             ArgumentKind::Variadic(start) => start,
 330         },
 331         |arg| match *arg {
 332             ArgumentKind::Regular(ref ty) => ty.span().hi(),
 333             ArgumentKind::Variadic(start) => start + BytePos(3),
 334         },
 335         |arg| match *arg {
 336             ArgumentKind::Regular(ref ty) => ty.rewrite(context, list_shape),
 337             ArgumentKind::Variadic(_) => Some("...".to_owned()),
 338         },
 339         list_lo,
 340         span.hi(),
 341         false,
 342     );
 343
 344     let item_vec: Vec<_> = items.collect();
 345
 346     let tactic = definitive_tactic(
 347         &*item_vec,
 348         ListTactic::HorizontalVertical,
 349         Separator::Comma,
 350         budget,
 351     );
 352     let trailing_separator = if !context.use_block_indent() || variadic {
 353         SeparatorTactic::Never
 354     } else {
 355         context.config.trailing_comma()
 356     };
 357
 358     let fmt = ListFormatting::new(list_shape, context.config)
 359         .tactic(tactic)
 360         .trailing_separator(trailing_separator)
 361         .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
 362         .preserve_newline(true);
 363     let list_str = write_list(&item_vec, &fmt)?;
 364
 365     let ty_shape = match context.config.indent_style() {
 366         // 4 = " -> "
 367         IndentStyle::Block => shape.offset_left(4)?,
 368         IndentStyle::Visual => shape.block_left(4)?,
 369     };
 370     let output = match *output {
 371         FunctionRetTy::Ty(ref ty) => {
 372             let type_str = ty.rewrite(context, ty_shape)?;
 373             format!(" -> {}", type_str)
 374         }
 375         FunctionRetTy::Default(..) => String::new(),
 376     };
 377
 378     let args = if (!list_str.contains('\n') || list_str.is_empty()) && !output.contains('\n')
 379         || !context.use_block_indent()
 380     {
 381         format!("({})", list_str)
 382     } else {
 383         format!(
 384             "({}{}{})",
 385             offset.to_string_with_newline(context.config),
 386             list_str,
 387             shape.block().indent.to_string_with_newline(context.config),
 388         )
 389     };
 390     if output.is_empty() || last_line_width(&args) + first_line_width(&output) <= shape.width {
 391         Some(format!("{}{}", args, output))
 392     } else {
 393         Some(format!(
 394             "{}\n{}{}",
 395             args,
 396             offset.to_string(context.config),
 397             output.trim_left()
 398         ))
 399     }
 400 }
 401
 402 fn type_bound_colon(context: &RewriteContext) -> &'static str {
 403     colon_spaces(
 404         context.config.space_before_colon(),
 405         context.config.space_after_colon(),
 406     )
 407 }
 408
 409 impl Rewrite for ast::WherePredicate {
 410     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 411         // FIXME: dead spans?
 412         let result = match *self {
 413             ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 414                 ref bound_generic_params,
 415                 ref bounded_ty,
 416                 ref bounds,
 417                 ..
 418             }) => {
 419                 let type_str = bounded_ty.rewrite(context, shape)?;
 420                 let colon = type_bound_colon(context).trim_right();
 421                 let lhs = if let Some(lifetime_str) =
 422                     rewrite_lifetime_param(context, shape, bound_generic_params)
 423                 {
 424                     format!("for<{}> {}{}", lifetime_str, type_str, colon)
 425                 } else {
 426                     format!("{}{}", type_str, colon)
 427                 };
 428
 429                 rewrite_assign_rhs(context, lhs, bounds, shape)?
 430             }
 431             ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
 432                 ref lifetime,
 433                 ref bounds,
 434                 ..
 435             }) => rewrite_bounded_lifetime(lifetime, bounds, context, shape)?,
 436             ast::WherePredicate::EqPredicate(ast::WhereEqPredicate {
 437                 ref lhs_ty,
 438                 ref rhs_ty,
 439                 ..
 440             }) => {
 441                 let lhs_ty_str = lhs_ty.rewrite(context, shape).map(|lhs| lhs + " =")?;
 442                 rewrite_assign_rhs(context, lhs_ty_str, &**rhs_ty, shape)?
 443             }
 444         };
 445
 446         Some(result)
 447     }
 448 }
 449
 450 impl Rewrite for ast::GenericArg {
 451     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 452         match *self {
 453             ast::GenericArg::Lifetime(ref lt) => lt.rewrite(context, shape),
 454             ast::GenericArg::Type(ref ty) => ty.rewrite(context, shape),
 455         }
 456     }
 457 }
 458
 459 fn rewrite_bounded_lifetime(
 460     lt: &ast::Lifetime,
 461     bounds: &[ast::GenericBound],
 462     context: &RewriteContext,
 463     shape: Shape,
 464 ) -> Option<String> {
 465     let result = lt.rewrite(context, shape)?;
 466
 467     if bounds.is_empty() {
 468         Some(result)
 469     } else {
 470         let colon = type_bound_colon(context);
 471         let overhead = last_line_width(&result) + colon.len();
 472         let result = format!(
 473             "{}{}{}",
 474             result,
 475             colon,
 476             join_bounds(context, shape.sub_width(overhead)?, bounds, true)?
 477         );
 478         Some(result)
 479     }
 480 }
 481
 482 impl Rewrite for ast::Lifetime {
 483     fn rewrite(&self, context: &RewriteContext, _: Shape) -> Option<String> {
 484         Some(rewrite_ident(context, self.ident).to_owned())
 485     }
 486 }
 487
 488 impl Rewrite for ast::GenericBound {
 489     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 490         match *self {
 491             ast::GenericBound::Trait(ref poly_trait_ref, trait_bound_modifier) => {
 492                 let snippet = context.snippet(self.span());
 493                 let has_paren = snippet.starts_with("(") && snippet.ends_with(")");
 494                 let rewrite = match trait_bound_modifier {
 495                     ast::TraitBoundModifier::None => poly_trait_ref.rewrite(context, shape),
 496                     ast::TraitBoundModifier::Maybe => poly_trait_ref
 497                         .rewrite(context, shape.offset_left(1)?)
 498                         .map(|s| format!("?{}", s)),
 499                 };
 500                 rewrite.map(|s| if has_paren { format!("({})", s) } else { s })
 501             }
 502             ast::GenericBound::Outlives(ref lifetime) => lifetime.rewrite(context, shape),
 503         }
 504     }
 505 }
 506
 507 impl Rewrite for ast::GenericBounds {
 508     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 509         if self.is_empty() {
 510             return Some(String::new());
 511         }
 512
 513         join_bounds(context, shape, self, true)
 514     }
 515 }
 516
 517 impl Rewrite for ast::GenericParam {
 518     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 519         let mut result = String::with_capacity(128);
 520         // FIXME: If there are more than one attributes, this will force multiline.
 521         match self.attrs.rewrite(context, shape) {
 522             Some(ref rw) if !rw.is_empty() => result.push_str(&format!("{} ", rw)),
 523             _ => (),
 524         }
 525         result.push_str(rewrite_ident(context, self.ident));
 526         if !self.bounds.is_empty() {
 527             result.push_str(type_bound_colon(context));
 528             result.push_str(&self.bounds.rewrite(context, shape)?)
 529         }
 530         if let ast::GenericParamKind::Type {
 531             default: Some(ref def),
 532         } = self.kind
 533         {
 534             let eq_str = match context.config.type_punctuation_density() {
 535                 TypeDensity::Compressed => "=",
 536                 TypeDensity::Wide => " = ",
 537             };
 538             result.push_str(eq_str);
 539             let budget = shape.width.checked_sub(result.len())?;
 540             let rewrite =
 541                 def.rewrite(context, Shape::legacy(budget, shape.indent + result.len()))?;
 542             result.push_str(&rewrite);
 543         }
 544
 545         Some(result)
 546     }
 547 }
 548
 549 impl Rewrite for ast::PolyTraitRef {
 550     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 551         if let Some(lifetime_str) =
 552             rewrite_lifetime_param(context, shape, &self.bound_generic_params)
 553         {
 554             // 6 is "for<> ".len()
 555             let extra_offset = lifetime_str.len() + 6;
 556             let path_str = self
 557                 .trait_ref
 558                 .rewrite(context, shape.offset_left(extra_offset)?)?;
 559
 560             Some(format!("for<{}> {}", lifetime_str, path_str))
 561         } else {
 562             self.trait_ref.rewrite(context, shape)
 563         }
 564     }
 565 }
 566
 567 impl Rewrite for ast::TraitRef {
 568     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 569         rewrite_path(context, PathContext::Type, None, &self.path, shape)
 570     }
 571 }
 572
 573 impl Rewrite for ast::Ty {
 574     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 575         match self.node {
 576             ast::TyKind::TraitObject(ref bounds, tobj_syntax) => {
 577                 // we have to consider 'dyn' keyword is used or not!!!
 578                 let is_dyn = tobj_syntax == ast::TraitObjectSyntax::Dyn;
 579                 // 4 is length of 'dyn '
 580                 let shape = if is_dyn { shape.offset_left(4)? } else { shape };
 581                 let res = bounds.rewrite(context, shape)?;
 582                 if is_dyn {
 583                     Some(format!("dyn {}", res))
 584                 } else {
 585                     Some(res)
 586                 }
 587             }
 588             ast::TyKind::Ptr(ref mt) => {
 589                 let prefix = match mt.mutbl {
 590                     Mutability::Mutable => "*mut ",
 591                     Mutability::Immutable => "*const ",
 592                 };
 593
 594                 rewrite_unary_prefix(context, prefix, &*mt.ty, shape)
 595             }
 596             ast::TyKind::Rptr(ref lifetime, ref mt) => {
 597                 let mut_str = format_mutability(mt.mutbl);
 598                 let mut_len = mut_str.len();
 599                 Some(match *lifetime {
 600                     Some(ref lifetime) => {
 601                         let lt_budget = shape.width.checked_sub(2 + mut_len)?;
 602                         let lt_str = lifetime.rewrite(
 603                             context,
 604                             Shape::legacy(lt_budget, shape.indent + 2 + mut_len),
 605                         )?;
 606                         let lt_len = lt_str.len();
 607                         let budget = shape.width.checked_sub(2 + mut_len + lt_len)?;
 608                         format!(
 609                             "&{} {}{}",
 610                             lt_str,
 611                             mut_str,
 612                             mt.ty.rewrite(
 613                                 context,
 614                                 Shape::legacy(budget, shape.indent + 2 + mut_len + lt_len)
 615                             )?
 616                         )
 617                     }
 618                     None => {
 619                         let budget = shape.width.checked_sub(1 + mut_len)?;
 620                         format!(
 621                             "&{}{}",
 622                             mut_str,
 623                             mt.ty.rewrite(
 624                                 context,
 625                                 Shape::legacy(budget, shape.indent + 1 + mut_len)
 626                             )?
 627                         )
 628                     }
 629                 })
 630             }
 631             // FIXME: we drop any comments here, even though it's a silly place to put
 632             // comments.
 633             ast::TyKind::Paren(ref ty) => {
 634                 let budget = shape.width.checked_sub(2)?;
 635                 ty.rewrite(context, Shape::legacy(budget, shape.indent + 1))
 636                     .map(|ty_str| format!("({})", ty_str))
 637             }
 638             ast::TyKind::Slice(ref ty) => {
 639                 let budget = shape.width.checked_sub(4)?;
 640                 ty.rewrite(context, Shape::legacy(budget, shape.indent + 1))
 641                     .map(|ty_str| format!("[{}]", ty_str))
 642             }
 643             ast::TyKind::Tup(ref items) => {
 644                 rewrite_tuple(context, items.iter(), self.span, shape, items.len() == 1)
 645             }
 646             ast::TyKind::Path(ref q_self, ref path) => {
 647                 rewrite_path(context, PathContext::Type, q_self.as_ref(), path, shape)
 648             }
 649             ast::TyKind::Array(ref ty, ref repeats) => rewrite_pair(
 650                 &**ty,
 651                 &*repeats.value,
 652                 PairParts::new("[", "; ", "]"),
 653                 context,
 654                 shape,
 655                 SeparatorPlace::Back,
 656             ),
 657             ast::TyKind::Infer => {
 658                 if shape.width >= 1 {
 659                     Some("_".to_owned())
 660                 } else {
 661                     None
 662                 }
 663             }
 664             ast::TyKind::BareFn(ref bare_fn) => rewrite_bare_fn(bare_fn, self.span, context, shape),
 665             ast::TyKind::Never => Some(String::from("!")),
 666             ast::TyKind::Mac(ref mac) => {
 667                 rewrite_macro(mac, None, context, shape, MacroPosition::Expression)
 668             }
 669             ast::TyKind::ImplicitSelf => Some(String::from("")),
 670             ast::TyKind::ImplTrait(_, ref it) => it
 671                 .rewrite(context, shape)
 672                 .map(|it_str| format!("impl {}", it_str)),
 673             ast::TyKind::Err | ast::TyKind::Typeof(..) => unreachable!(),
 674         }
 675     }
 676 }
 677
 678 fn rewrite_bare_fn(
 679     bare_fn: &ast::BareFnTy,
 680     span: Span,
 681     context: &RewriteContext,
 682     shape: Shape,
 683 ) -> Option<String> {
 684     debug!("rewrite_bare_fn {:#?}", shape);
 685
 686     let mut result = String::with_capacity(128);
 687
 688     if let Some(ref lifetime_str) = rewrite_lifetime_param(context, shape, &bare_fn.generic_params)
 689     {
 690         result.push_str("for<");
 691         // 6 = "for<> ".len(), 4 = "for<".
 692         // This doesn't work out so nicely for multiline situation with lots of
 693         // rightward drift. If that is a problem, we could use the list stuff.
 694         result.push_str(lifetime_str);
 695         result.push_str("> ");
 696     }
 697
 698     result.push_str(::utils::format_unsafety(bare_fn.unsafety));
 699
 700     result.push_str(&format_abi(
 701         bare_fn.abi,
 702         context.config.force_explicit_abi(),
 703         false,
 704     ));
 705
 706     result.push_str("fn");
 707
 708     let func_ty_shape = if context.use_block_indent() {
 709         shape.offset_left(result.len())?
 710     } else {
 711         shape.visual_indent(result.len()).sub_width(result.len())?
 712     };
 713
 714     let rewrite = format_function_type(
 715         bare_fn.decl.inputs.iter(),
 716         &bare_fn.decl.output,
 717         bare_fn.decl.variadic,
 718         span,
 719         context,
 720         func_ty_shape,
 721     )?;
 722
 723     result.push_str(&rewrite);
 724
 725     Some(result)
 726 }
 727
 728 fn is_generic_bounds_in_order(generic_bounds: &[ast::GenericBound]) -> bool {
 729     let is_trait = |b: &ast::GenericBound| match b {
 730         ast::GenericBound::Outlives(..) => false,
 731         ast::GenericBound::Trait(..) => true,
 732     };
 733     let is_lifetime = |b: &ast::GenericBound| !is_trait(b);
 734     let last_trait_index = generic_bounds.iter().rposition(is_trait);
 735     let first_lifetime_index = generic_bounds.iter().position(is_lifetime);
 736     match (last_trait_index, first_lifetime_index) {
 737         (Some(last_trait_index), Some(first_lifetime_index)) => {
 738             last_trait_index < first_lifetime_index
 739         }
 740         _ => true,
 741     }
 742 }
 743
 744 fn join_bounds(
 745     context: &RewriteContext,
 746     shape: Shape,
 747     items: &[ast::GenericBound],
 748     need_indent: bool,
 749 ) -> Option<String> {
 750     debug_assert!(!items.is_empty());
 751
 752     // Try to join types in a single line
 753     let joiner = match context.config.type_punctuation_density() {
 754         TypeDensity::Compressed => "+",
 755         TypeDensity::Wide => " + ",
 756     };
 757     let type_strs = items
 758         .iter()
 759         .map(|item| item.rewrite(context, shape))
 760         .collect::<Option<Vec<_>>>()?;
 761     let result = type_strs.join(joiner);
 762     if items.len() <= 1 || (!result.contains('\n') && result.len() <= shape.width) {
 763         return Some(result);
 764     }
 765
 766     // We need to use multiple lines.
 767     let (type_strs, offset) = if need_indent {
 768         // Rewrite with additional indentation.
 769         let nested_shape = shape.block_indent(context.config.tab_spaces());
 770         let type_strs = items
 771             .iter()
 772             .map(|item| item.rewrite(context, nested_shape))
 773             .collect::<Option<Vec<_>>>()?;
 774         (type_strs, nested_shape.indent)
 775     } else {
 776         (type_strs, shape.indent)
 777     };
 778
 779     let is_bound_extendable = |s: &str, b: &ast::GenericBound| match b {
 780         ast::GenericBound::Outlives(..) => true,
 781         ast::GenericBound::Trait(..) => last_line_extendable(s),
 782     };
 783     let mut result = String::with_capacity(128);
 784     result.push_str(&type_strs[0]);
 785     let mut can_be_put_on_the_same_line = is_bound_extendable(&result, &items[0]);
 786     let generic_bounds_in_order = is_generic_bounds_in_order(items);
 787     for (bound, bound_str) in items[1..].iter().zip(type_strs[1..].iter()) {
 788         if generic_bounds_in_order && can_be_put_on_the_same_line {
 789             result.push_str(joiner);
 790         } else {
 791             result.push_str(&offset.to_string_with_newline(context.config));
 792             result.push_str("+ ");
 793         }
 794         result.push_str(bound_str);
 795         can_be_put_on_the_same_line = is_bound_extendable(bound_str, bound);
 796     }
 797
 798     Some(result)
 799 }
 800
 801 pub fn can_be_overflowed_type(context: &RewriteContext, ty: &ast::Ty, len: usize) -> bool {
 802     match ty.node {
 803         ast::TyKind::Tup(..) => context.use_block_indent() && len == 1,
 804         ast::TyKind::Rptr(_, ref mutty) | ast::TyKind::Ptr(ref mutty) => {
 805             can_be_overflowed_type(context, &*mutty.ty, len)
 806         }
 807         _ => false,
 808     }
 809 }
 810
 811 /// Returns `None` if there is no `LifetimeDef` in the given generic parameters.
 812 fn rewrite_lifetime_param(
 813     context: &RewriteContext,
 814     shape: Shape,
 815     generic_params: &[ast::GenericParam],
 816 ) -> Option<String> {
 817     let result = generic_params
 818         .iter()
 819         .filter(|p| match p.kind {
 820             ast::GenericParamKind::Lifetime => true,
 821             _ => false,
 822         })
 823         .map(|lt| lt.rewrite(context, shape))
 824         .collect::<Option<Vec<_>>>()?
 825         .join(", ");
 826     if result.is_empty() {
 827         None
 828     } else {
 829         Some(result)
 830     }
 831 }