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 syntax::ast::{self, FunctionRetTy, Mutability};
  15 use syntax::source_map::{self, BytePos, Span};
  16 use syntax::symbol::keywords;
  17
  18 use crate::config::lists::*;
  19 use crate::config::{IndentStyle, TypeDensity};
  20 use crate::expr::{rewrite_assign_rhs, rewrite_tuple, rewrite_unary_prefix};
  21 use crate::lists::{definitive_tactic, itemize_list, write_list, ListFormatting, Separator};
  22 use crate::macros::{rewrite_macro, MacroPosition};
  23 use crate::overflow;
  24 use crate::pairs::{rewrite_pair, PairParts};
  25 use crate::rewrite::{Rewrite, RewriteContext};
  26 use crate::shape::Shape;
  27 use crate::source_map::SpanUtils;
  28 use crate::spanned::Spanned;
  29 use crate::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             ast::GenericArg::Const(..) => unreachable!(), // FIXME(#3336)
 156         }
 157     }
 158 }
 159
 160 impl<'a> Spanned for SegmentParam<'a> {
 161     fn span(&self) -> Span {
 162         match *self {
 163             SegmentParam::LifeTime(lt) => lt.ident.span,
 164             SegmentParam::Type(ty) => ty.span,
 165             SegmentParam::Binding(binding) => binding.span,
 166         }
 167     }
 168 }
 169
 170 impl<'a> Rewrite for SegmentParam<'a> {
 171     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 172         match *self {
 173             SegmentParam::LifeTime(lt) => lt.rewrite(context, shape),
 174             SegmentParam::Type(ty) => ty.rewrite(context, shape),
 175             SegmentParam::Binding(binding) => {
 176                 let mut result = match context.config.type_punctuation_density() {
 177                     TypeDensity::Wide => format!("{} = ", rewrite_ident(context, binding.ident)),
 178                     TypeDensity::Compressed => {
 179                         format!("{}=", rewrite_ident(context, binding.ident))
 180                     }
 181                 };
 182                 let budget = shape.width.checked_sub(result.len())?;
 183                 let rewrite = binding
 184                     .ty
 185                     .rewrite(context, Shape::legacy(budget, shape.indent + result.len()))?;
 186                 result.push_str(&rewrite);
 187                 Some(result)
 188             }
 189         }
 190     }
 191 }
 192
 193 // Formats a path segment. There are some hacks involved to correctly determine
 194 // the segment's associated span since it's not part of the AST.
 195 //
 196 // The span_lo is assumed to be greater than the end of any previous segment's
 197 // parameters and lesser or equal than the start of current segment.
 198 //
 199 // span_hi is assumed equal to the end of the entire path.
 200 //
 201 // When the segment contains a positive number of parameters, we update span_lo
 202 // so that invariants described above will hold for the next segment.
 203 fn rewrite_segment(
 204     path_context: PathContext,
 205     segment: &ast::PathSegment,
 206     span_lo: &mut BytePos,
 207     span_hi: BytePos,
 208     context: &RewriteContext<'_>,
 209     shape: Shape,
 210 ) -> Option<String> {
 211     let mut result = String::with_capacity(128);
 212     result.push_str(rewrite_ident(context, segment.ident));
 213
 214     let ident_len = result.len();
 215     let shape = if context.use_block_indent() {
 216         shape.offset_left(ident_len)?
 217     } else {
 218         shape.shrink_left(ident_len)?
 219     };
 220
 221     if let Some(ref args) = segment.args {
 222         match **args {
 223             ast::GenericArgs::AngleBracketed(ref data)
 224                 if !data.args.is_empty() || !data.bindings.is_empty() =>
 225             {
 226                 let param_list = data
 227                     .args
 228                     .iter()
 229                     .map(SegmentParam::from_generic_arg)
 230                     .chain(data.bindings.iter().map(|x| SegmentParam::Binding(&*x)))
 231                     .collect::<Vec<_>>();
 232
 233                 // HACK: squeeze out the span between the identifier and the parameters.
 234                 // The hack is requried so that we don't remove the separator inside macro calls.
 235                 // This does not work in the presence of comment, hoping that people are
 236                 // sane about where to put their comment.
 237                 let separator_snippet = context
 238                     .snippet(mk_sp(segment.ident.span.hi(), data.span.lo()))
 239                     .trim();
 240                 let force_separator = context.inside_macro() && separator_snippet.starts_with("::");
 241                 let separator = if path_context == PathContext::Expr || force_separator {
 242                     "::"
 243                 } else {
 244                     ""
 245                 };
 246                 result.push_str(separator);
 247
 248                 let generics_str = overflow::rewrite_with_angle_brackets(
 249                     context,
 250                     "",
 251                     param_list.iter(),
 252                     shape,
 253                     mk_sp(*span_lo, span_hi),
 254                 )?;
 255
 256                 // Update position of last bracket.
 257                 *span_lo = context
 258                     .snippet_provider
 259                     .span_after(mk_sp(*span_lo, span_hi), "<");
 260
 261                 result.push_str(&generics_str)
 262             }
 263             ast::GenericArgs::Parenthesized(ref data) => {
 264                 let output = match data.output {
 265                     Some(ref ty) => FunctionRetTy::Ty(ty.clone()),
 266                     None => FunctionRetTy::Default(source_map::DUMMY_SP),
 267                 };
 268                 result.push_str(&format_function_type(
 269                     data.inputs.iter().map(|x| &**x),
 270                     &output,
 271                     false,
 272                     data.span,
 273                     context,
 274                     shape,
 275                 )?);
 276             }
 277             _ => (),
 278         }
 279     }
 280
 281     Some(result)
 282 }
 283
 284 fn format_function_type<'a, I>(
 285     inputs: I,
 286     output: &FunctionRetTy,
 287     variadic: bool,
 288     span: Span,
 289     context: &RewriteContext<'_>,
 290     shape: Shape,
 291 ) -> Option<String>
 292 where
 293     I: ExactSizeIterator,
 294     <I as Iterator>::Item: Deref,
 295     <I::Item as Deref>::Target: Rewrite + Spanned + 'a,
 296 {
 297     debug!("format_function_type {:#?}", shape);
 298
 299     let ty_shape = match context.config.indent_style() {
 300         // 4 = " -> "
 301         IndentStyle::Block => shape.offset_left(4)?,
 302         IndentStyle::Visual => shape.block_left(4)?,
 303     };
 304     let output = match *output {
 305         FunctionRetTy::Ty(ref ty) => {
 306             let type_str = ty.rewrite(context, ty_shape)?;
 307             format!(" -> {}", type_str)
 308         }
 309         FunctionRetTy::Default(..) => String::new(),
 310     };
 311
 312     // Code for handling variadics is somewhat duplicated for items, but they
 313     // are different enough to need some serious refactoring to share code.
 314     enum ArgumentKind<T>
 315     where
 316         T: Deref,
 317         <T as Deref>::Target: Rewrite + Spanned,
 318     {
 319         Regular(T),
 320         Variadic(BytePos),
 321     }
 322
 323     let variadic_arg = if variadic {
 324         let variadic_start = context.snippet_provider.span_before(span, "...");
 325         Some(ArgumentKind::Variadic(variadic_start))
 326     } else {
 327         None
 328     };
 329
 330     let list_shape = if context.use_block_indent() {
 331         Shape::indented(
 332             shape.block().indent.block_indent(context.config),
 333             context.config,
 334         )
 335     } else {
 336         // 2 for ()
 337         let budget = shape.width.checked_sub(2)?;
 338         // 1 for (
 339         let offset = shape.indent + 1;
 340         Shape::legacy(budget, offset)
 341     };
 342     let list_lo = context.snippet_provider.span_after(span, "(");
 343     let items = itemize_list(
 344         context.snippet_provider,
 345         inputs.map(ArgumentKind::Regular).chain(variadic_arg),
 346         ")",
 347         ",",
 348         |arg| match *arg {
 349             ArgumentKind::Regular(ref ty) => ty.span().lo(),
 350             ArgumentKind::Variadic(start) => start,
 351         },
 352         |arg| match *arg {
 353             ArgumentKind::Regular(ref ty) => ty.span().hi(),
 354             ArgumentKind::Variadic(start) => start + BytePos(3),
 355         },
 356         |arg| match *arg {
 357             ArgumentKind::Regular(ref ty) => ty.rewrite(context, list_shape),
 358             ArgumentKind::Variadic(_) => Some("...".to_owned()),
 359         },
 360         list_lo,
 361         span.hi(),
 362         false,
 363     );
 364
 365     let item_vec: Vec<_> = items.collect();
 366
 367     // If the return type is multi-lined, then force to use multiple lines for
 368     // arguments as well.
 369     let tactic = if output.contains('\n') {
 370         DefinitiveListTactic::Vertical
 371     } else {
 372         definitive_tactic(
 373             &*item_vec,
 374             ListTactic::HorizontalVertical,
 375             Separator::Comma,
 376             shape.width.saturating_sub(2 + output.len()),
 377         )
 378     };
 379     let trailing_separator = if !context.use_block_indent() || variadic {
 380         SeparatorTactic::Never
 381     } else {
 382         context.config.trailing_comma()
 383     };
 384
 385     let fmt = ListFormatting::new(list_shape, context.config)
 386         .tactic(tactic)
 387         .trailing_separator(trailing_separator)
 388         .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
 389         .preserve_newline(true);
 390     let list_str = write_list(&item_vec, &fmt)?;
 391
 392     let args = if tactic == DefinitiveListTactic::Horizontal || !context.use_block_indent() {
 393         format!("({})", list_str)
 394     } else {
 395         format!(
 396             "({}{}{})",
 397             list_shape.indent.to_string_with_newline(context.config),
 398             list_str,
 399             shape.block().indent.to_string_with_newline(context.config),
 400         )
 401     };
 402     if output.is_empty() || last_line_width(&args) + first_line_width(&output) <= shape.width {
 403         Some(format!("{}{}", args, output))
 404     } else {
 405         Some(format!(
 406             "{}\n{}{}",
 407             args,
 408             list_shape.indent.to_string(context.config),
 409             output.trim_start()
 410         ))
 411     }
 412 }
 413
 414 fn type_bound_colon(context: &RewriteContext<'_>) -> &'static str {
 415     colon_spaces(
 416         context.config.space_before_colon(),
 417         context.config.space_after_colon(),
 418     )
 419 }
 420
 421 impl Rewrite for ast::WherePredicate {
 422     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 423         // FIXME: dead spans?
 424         let result = match *self {
 425             ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 426                 ref bound_generic_params,
 427                 ref bounded_ty,
 428                 ref bounds,
 429                 ..
 430             }) => {
 431                 let type_str = bounded_ty.rewrite(context, shape)?;
 432                 let colon = type_bound_colon(context).trim_end();
 433                 let lhs = if let Some(lifetime_str) =
 434                     rewrite_lifetime_param(context, shape, bound_generic_params)
 435                 {
 436                     format!("for<{}> {}{}", lifetime_str, type_str, colon)
 437                 } else {
 438                     format!("{}{}", type_str, colon)
 439                 };
 440
 441                 rewrite_assign_rhs(context, lhs, bounds, shape)?
 442             }
 443             ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
 444                 ref lifetime,
 445                 ref bounds,
 446                 ..
 447             }) => rewrite_bounded_lifetime(lifetime, bounds, context, shape)?,
 448             ast::WherePredicate::EqPredicate(ast::WhereEqPredicate {
 449                 ref lhs_ty,
 450                 ref rhs_ty,
 451                 ..
 452             }) => {
 453                 let lhs_ty_str = lhs_ty.rewrite(context, shape).map(|lhs| lhs + " =")?;
 454                 rewrite_assign_rhs(context, lhs_ty_str, &**rhs_ty, shape)?
 455             }
 456         };
 457
 458         Some(result)
 459     }
 460 }
 461
 462 impl Rewrite for ast::GenericArg {
 463     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 464         match *self {
 465             ast::GenericArg::Lifetime(ref lt) => lt.rewrite(context, shape),
 466             ast::GenericArg::Type(ref ty) => ty.rewrite(context, shape),
 467             ast::GenericArg::Const(..) => unreachable!(), // FIXME(#3336)
 468         }
 469     }
 470 }
 471
 472 fn rewrite_bounded_lifetime(
 473     lt: &ast::Lifetime,
 474     bounds: &[ast::GenericBound],
 475     context: &RewriteContext<'_>,
 476     shape: Shape,
 477 ) -> Option<String> {
 478     let result = lt.rewrite(context, shape)?;
 479
 480     if bounds.is_empty() {
 481         Some(result)
 482     } else {
 483         let colon = type_bound_colon(context);
 484         let overhead = last_line_width(&result) + colon.len();
 485         let result = format!(
 486             "{}{}{}",
 487             result,
 488             colon,
 489             join_bounds(context, shape.sub_width(overhead)?, bounds, true)?
 490         );
 491         Some(result)
 492     }
 493 }
 494
 495 impl Rewrite for ast::Lifetime {
 496     fn rewrite(&self, context: &RewriteContext<'_>, _: Shape) -> Option<String> {
 497         Some(rewrite_ident(context, self.ident).to_owned())
 498     }
 499 }
 500
 501 impl Rewrite for ast::GenericBound {
 502     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 503         match *self {
 504             ast::GenericBound::Trait(ref poly_trait_ref, trait_bound_modifier) => {
 505                 let snippet = context.snippet(self.span());
 506                 let has_paren = snippet.starts_with('(') && snippet.ends_with(')');
 507                 let rewrite = match trait_bound_modifier {
 508                     ast::TraitBoundModifier::None => poly_trait_ref.rewrite(context, shape),
 509                     ast::TraitBoundModifier::Maybe => poly_trait_ref
 510                         .rewrite(context, shape.offset_left(1)?)
 511                         .map(|s| format!("?{}", s)),
 512                 };
 513                 rewrite.map(|s| if has_paren { format!("({})", s) } else { s })
 514             }
 515             ast::GenericBound::Outlives(ref lifetime) => lifetime.rewrite(context, shape),
 516         }
 517     }
 518 }
 519
 520 impl Rewrite for ast::GenericBounds {
 521     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 522         if self.is_empty() {
 523             return Some(String::new());
 524         }
 525
 526         join_bounds(context, shape, self, true)
 527     }
 528 }
 529
 530 impl Rewrite for ast::GenericParam {
 531     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 532         let mut result = String::with_capacity(128);
 533         // FIXME: If there are more than one attributes, this will force multiline.
 534         match self.attrs.rewrite(context, shape) {
 535             Some(ref rw) if !rw.is_empty() => result.push_str(&format!("{} ", rw)),
 536             _ => (),
 537         }
 538         result.push_str(rewrite_ident(context, self.ident));
 539         if !self.bounds.is_empty() {
 540             result.push_str(type_bound_colon(context));
 541             result.push_str(&self.bounds.rewrite(context, shape)?)
 542         }
 543         if let ast::GenericParamKind::Type {
 544             default: Some(ref def),
 545         } = self.kind
 546         {
 547             let eq_str = match context.config.type_punctuation_density() {
 548                 TypeDensity::Compressed => "=",
 549                 TypeDensity::Wide => " = ",
 550             };
 551             result.push_str(eq_str);
 552             let budget = shape.width.checked_sub(result.len())?;
 553             let rewrite =
 554                 def.rewrite(context, Shape::legacy(budget, shape.indent + result.len()))?;
 555             result.push_str(&rewrite);
 556         }
 557
 558         Some(result)
 559     }
 560 }
 561
 562 impl Rewrite for ast::PolyTraitRef {
 563     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 564         if let Some(lifetime_str) =
 565             rewrite_lifetime_param(context, shape, &self.bound_generic_params)
 566         {
 567             // 6 is "for<> ".len()
 568             let extra_offset = lifetime_str.len() + 6;
 569             let path_str = self
 570                 .trait_ref
 571                 .rewrite(context, shape.offset_left(extra_offset)?)?;
 572
 573             Some(format!("for<{}> {}", lifetime_str, path_str))
 574         } else {
 575             self.trait_ref.rewrite(context, shape)
 576         }
 577     }
 578 }
 579
 580 impl Rewrite for ast::TraitRef {
 581     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 582         rewrite_path(context, PathContext::Type, None, &self.path, shape)
 583     }
 584 }
 585
 586 impl Rewrite for ast::Ty {
 587     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 588         match self.node {
 589             ast::TyKind::TraitObject(ref bounds, tobj_syntax) => {
 590                 // we have to consider 'dyn' keyword is used or not!!!
 591                 let is_dyn = tobj_syntax == ast::TraitObjectSyntax::Dyn;
 592                 // 4 is length of 'dyn '
 593                 let shape = if is_dyn { shape.offset_left(4)? } else { shape };
 594                 let mut res = bounds.rewrite(context, shape)?;
 595                 // We may have falsely removed a trailing `+` inside macro call.
 596                 if context.inside_macro() && bounds.len() == 1 {
 597                     if context.snippet(self.span).ends_with('+') && !res.ends_with('+') {
 598                         res.push('+');
 599                     }
 600                 }
 601                 if is_dyn {
 602                     Some(format!("dyn {}", res))
 603                 } else {
 604                     Some(res)
 605                 }
 606             }
 607             ast::TyKind::Ptr(ref mt) => {
 608                 let prefix = match mt.mutbl {
 609                     Mutability::Mutable => "*mut ",
 610                     Mutability::Immutable => "*const ",
 611                 };
 612
 613                 rewrite_unary_prefix(context, prefix, &*mt.ty, shape)
 614             }
 615             ast::TyKind::Rptr(ref lifetime, ref mt) => {
 616                 let mut_str = format_mutability(mt.mutbl);
 617                 let mut_len = mut_str.len();
 618                 Some(match *lifetime {
 619                     Some(ref lifetime) => {
 620                         let lt_budget = shape.width.checked_sub(2 + mut_len)?;
 621                         let lt_str = lifetime.rewrite(
 622                             context,
 623                             Shape::legacy(lt_budget, shape.indent + 2 + mut_len),
 624                         )?;
 625                         let lt_len = lt_str.len();
 626                         let budget = shape.width.checked_sub(2 + mut_len + lt_len)?;
 627                         format!(
 628                             "&{} {}{}",
 629                             lt_str,
 630                             mut_str,
 631                             mt.ty.rewrite(
 632                                 context,
 633                                 Shape::legacy(budget, shape.indent + 2 + mut_len + lt_len)
 634                             )?
 635                         )
 636                     }
 637                     None => {
 638                         let budget = shape.width.checked_sub(1 + mut_len)?;
 639                         format!(
 640                             "&{}{}",
 641                             mut_str,
 642                             mt.ty.rewrite(
 643                                 context,
 644                                 Shape::legacy(budget, shape.indent + 1 + mut_len)
 645                             )?
 646                         )
 647                     }
 648                 })
 649             }
 650             // FIXME: we drop any comments here, even though it's a silly place to put
 651             // comments.
 652             ast::TyKind::Paren(ref ty) => {
 653                 let budget = shape.width.checked_sub(2)?;
 654                 ty.rewrite(context, Shape::legacy(budget, shape.indent + 1))
 655                     .map(|ty_str| format!("({})", ty_str))
 656             }
 657             ast::TyKind::Slice(ref ty) => {
 658                 let budget = shape.width.checked_sub(4)?;
 659                 ty.rewrite(context, Shape::legacy(budget, shape.indent + 1))
 660                     .map(|ty_str| format!("[{}]", ty_str))
 661             }
 662             ast::TyKind::Tup(ref items) => {
 663                 rewrite_tuple(context, items.iter(), self.span, shape, items.len() == 1)
 664             }
 665             ast::TyKind::Path(ref q_self, ref path) => {
 666                 rewrite_path(context, PathContext::Type, q_self.as_ref(), path, shape)
 667             }
 668             ast::TyKind::Array(ref ty, ref repeats) => rewrite_pair(
 669                 &**ty,
 670                 &*repeats.value,
 671                 PairParts::new("[", "; ", "]"),
 672                 context,
 673                 shape,
 674                 SeparatorPlace::Back,
 675             ),
 676             ast::TyKind::Infer => {
 677                 if shape.width >= 1 {
 678                     Some("_".to_owned())
 679                 } else {
 680                     None
 681                 }
 682             }
 683             ast::TyKind::BareFn(ref bare_fn) => rewrite_bare_fn(bare_fn, self.span, context, shape),
 684             ast::TyKind::Never => Some(String::from("!")),
 685             ast::TyKind::Mac(ref mac) => {
 686                 rewrite_macro(mac, None, context, shape, MacroPosition::Expression)
 687             }
 688             ast::TyKind::ImplicitSelf => Some(String::from("")),
 689             ast::TyKind::ImplTrait(_, ref it) => it
 690                 .rewrite(context, shape)
 691                 .map(|it_str| format!("impl {}", it_str)),
 692             ast::TyKind::Err | ast::TyKind::Typeof(..) => unreachable!(),
 693         }
 694     }
 695 }
 696
 697 fn rewrite_bare_fn(
 698     bare_fn: &ast::BareFnTy,
 699     span: Span,
 700     context: &RewriteContext<'_>,
 701     shape: Shape,
 702 ) -> Option<String> {
 703     debug!("rewrite_bare_fn {:#?}", shape);
 704
 705     let mut result = String::with_capacity(128);
 706
 707     if let Some(ref lifetime_str) = rewrite_lifetime_param(context, shape, &bare_fn.generic_params)
 708     {
 709         result.push_str("for<");
 710         // 6 = "for<> ".len(), 4 = "for<".
 711         // This doesn't work out so nicely for multiline situation with lots of
 712         // rightward drift. If that is a problem, we could use the list stuff.
 713         result.push_str(lifetime_str);
 714         result.push_str("> ");
 715     }
 716
 717     result.push_str(crate::utils::format_unsafety(bare_fn.unsafety));
 718
 719     result.push_str(&format_abi(
 720         bare_fn.abi,
 721         context.config.force_explicit_abi(),
 722         false,
 723     ));
 724
 725     result.push_str("fn");
 726
 727     let func_ty_shape = if context.use_block_indent() {
 728         shape.offset_left(result.len())?
 729     } else {
 730         shape.visual_indent(result.len()).sub_width(result.len())?
 731     };
 732
 733     let rewrite = format_function_type(
 734         bare_fn.decl.inputs.iter(),
 735         &bare_fn.decl.output,
 736         bare_fn.decl.variadic,
 737         span,
 738         context,
 739         func_ty_shape,
 740     )?;
 741
 742     result.push_str(&rewrite);
 743
 744     Some(result)
 745 }
 746
 747 fn is_generic_bounds_in_order(generic_bounds: &[ast::GenericBound]) -> bool {
 748     let is_trait = |b: &ast::GenericBound| match b {
 749         ast::GenericBound::Outlives(..) => false,
 750         ast::GenericBound::Trait(..) => true,
 751     };
 752     let is_lifetime = |b: &ast::GenericBound| !is_trait(b);
 753     let last_trait_index = generic_bounds.iter().rposition(is_trait);
 754     let first_lifetime_index = generic_bounds.iter().position(is_lifetime);
 755     match (last_trait_index, first_lifetime_index) {
 756         (Some(last_trait_index), Some(first_lifetime_index)) => {
 757             last_trait_index < first_lifetime_index
 758         }
 759         _ => true,
 760     }
 761 }
 762
 763 fn join_bounds(
 764     context: &RewriteContext<'_>,
 765     shape: Shape,
 766     items: &[ast::GenericBound],
 767     need_indent: bool,
 768 ) -> Option<String> {
 769     debug_assert!(!items.is_empty());
 770
 771     // Try to join types in a single line
 772     let joiner = match context.config.type_punctuation_density() {
 773         TypeDensity::Compressed => "+",
 774         TypeDensity::Wide => " + ",
 775     };
 776     let type_strs = items
 777         .iter()
 778         .map(|item| item.rewrite(context, shape))
 779         .collect::<Option<Vec<_>>>()?;
 780     let result = type_strs.join(joiner);
 781     if items.len() <= 1 || (!result.contains('\n') && result.len() <= shape.width) {
 782         return Some(result);
 783     }
 784
 785     // We need to use multiple lines.
 786     let (type_strs, offset) = if need_indent {
 787         // Rewrite with additional indentation.
 788         let nested_shape = shape.block_indent(context.config.tab_spaces());
 789         let type_strs = items
 790             .iter()
 791             .map(|item| item.rewrite(context, nested_shape))
 792             .collect::<Option<Vec<_>>>()?;
 793         (type_strs, nested_shape.indent)
 794     } else {
 795         (type_strs, shape.indent)
 796     };
 797
 798     let is_bound_extendable = |s: &str, b: &ast::GenericBound| match b {
 799         ast::GenericBound::Outlives(..) => true,
 800         ast::GenericBound::Trait(..) => last_line_extendable(s),
 801     };
 802     let mut result = String::with_capacity(128);
 803     result.push_str(&type_strs[0]);
 804     let mut can_be_put_on_the_same_line = is_bound_extendable(&result, &items[0]);
 805     let generic_bounds_in_order = is_generic_bounds_in_order(items);
 806     for (bound, bound_str) in items[1..].iter().zip(type_strs[1..].iter()) {
 807         if generic_bounds_in_order && can_be_put_on_the_same_line {
 808             result.push_str(joiner);
 809         } else {
 810             result.push_str(&offset.to_string_with_newline(context.config));
 811             result.push_str("+ ");
 812         }
 813         result.push_str(bound_str);
 814         can_be_put_on_the_same_line = is_bound_extendable(bound_str, bound);
 815     }
 816
 817     Some(result)
 818 }
 819
 820 pub fn can_be_overflowed_type(context: &RewriteContext<'_>, ty: &ast::Ty, len: usize) -> bool {
 821     match ty.node {
 822         ast::TyKind::Tup(..) => context.use_block_indent() && len == 1,
 823         ast::TyKind::Rptr(_, ref mutty) | ast::TyKind::Ptr(ref mutty) => {
 824             can_be_overflowed_type(context, &*mutty.ty, len)
 825         }
 826         _ => false,
 827     }
 828 }
 829
 830 /// Returns `None` if there is no `LifetimeDef` in the given generic parameters.
 831 fn rewrite_lifetime_param(
 832     context: &RewriteContext<'_>,
 833     shape: Shape,
 834     generic_params: &[ast::GenericParam],
 835 ) -> Option<String> {
 836     let result = generic_params
 837         .iter()
 838         .filter(|p| match p.kind {
 839             ast::GenericParamKind::Lifetime => true,
 840             _ => false,
 841         })
 842         .map(|lt| lt.rewrite(context, shape))
 843         .collect::<Option<Vec<_>>>()?
 844         .join(", ");
 845     if result.is_empty() {
 846         None
 847     } else {
 848         Some(result)
 849     }
 850 }