src/types.rs

   1 use std::iter::ExactSizeIterator;
   2 use std::ops::Deref;
   3
   4 use rustc_ast::ast::{self, FnRetTy, Mutability};
   5 use rustc_span::{symbol::kw, BytePos, Span};
   6
   7 use crate::config::lists::*;
   8 use crate::config::{IndentStyle, TypeDensity, Version};
   9 use crate::expr::{format_expr, rewrite_assign_rhs, rewrite_tuple, rewrite_unary_prefix, ExprType};
  10 use crate::lists::{
  11     definitive_tactic, itemize_list, write_list, ListFormatting, ListItem, Separator,
  12 };
  13 use crate::macros::{rewrite_macro, MacroPosition};
  14 use crate::overflow;
  15 use crate::pairs::{rewrite_pair, PairParts};
  16 use crate::rewrite::{Rewrite, RewriteContext};
  17 use crate::shape::Shape;
  18 use crate::source_map::SpanUtils;
  19 use crate::spanned::Spanned;
  20 use crate::utils::{
  21     colon_spaces, extra_offset, first_line_width, format_extern, format_mutability,
  22     last_line_extendable, last_line_width, mk_sp, rewrite_ident,
  23 };
  24
  25 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
  26 pub(crate) enum PathContext {
  27     Expr,
  28     Type,
  29     Import,
  30 }
  31
  32 // Does not wrap on simple segments.
  33 pub(crate) fn rewrite_path(
  34     context: &RewriteContext<'_>,
  35     path_context: PathContext,
  36     qself: Option<&ast::QSelf>,
  37     path: &ast::Path,
  38     shape: Shape,
  39 ) -> Option<String> {
  40     let skip_count = qself.map_or(0, |x| x.position);
  41
  42     let mut result = if path.is_global() && qself.is_none() && path_context != PathContext::Import {
  43         "::".to_owned()
  44     } else {
  45         String::new()
  46     };
  47
  48     let mut span_lo = path.span.lo();
  49
  50     if let Some(qself) = qself {
  51         result.push('<');
  52
  53         let fmt_ty = qself.ty.rewrite(context, shape)?;
  54         result.push_str(&fmt_ty);
  55
  56         if skip_count > 0 {
  57             result.push_str(" as ");
  58             if path.is_global() && path_context != PathContext::Import {
  59                 result.push_str("::");
  60             }
  61
  62             // 3 = ">::".len()
  63             let shape = shape.sub_width(3)?;
  64
  65             result = rewrite_path_segments(
  66                 PathContext::Type,
  67                 result,
  68                 path.segments.iter().take(skip_count),
  69                 span_lo,
  70                 path.span.hi(),
  71                 context,
  72                 shape,
  73             )?;
  74         }
  75
  76         result.push_str(">::");
  77         span_lo = qself.ty.span.hi() + BytePos(1);
  78     }
  79
  80     rewrite_path_segments(
  81         path_context,
  82         result,
  83         path.segments.iter().skip(skip_count),
  84         span_lo,
  85         path.span.hi(),
  86         context,
  87         shape,
  88     )
  89 }
  90
  91 fn rewrite_path_segments<'a, I>(
  92     path_context: PathContext,
  93     mut buffer: String,
  94     iter: I,
  95     mut span_lo: BytePos,
  96     span_hi: BytePos,
  97     context: &RewriteContext<'_>,
  98     shape: Shape,
  99 ) -> Option<String>
 100 where
 101     I: Iterator<Item = &'a ast::PathSegment>,
 102 {
 103     let mut first = true;
 104     let shape = shape.visual_indent(0);
 105
 106     for segment in iter {
 107         // Indicates a global path, shouldn't be rendered.
 108         if segment.ident.name == kw::PathRoot {
 109             continue;
 110         }
 111         if first {
 112             first = false;
 113         } else {
 114             buffer.push_str("::");
 115         }
 116
 117         let extra_offset = extra_offset(&buffer, shape);
 118         let new_shape = shape.shrink_left(extra_offset)?;
 119         let segment_string = rewrite_segment(
 120             path_context,
 121             segment,
 122             &mut span_lo,
 123             span_hi,
 124             context,
 125             new_shape,
 126         )?;
 127
 128         buffer.push_str(&segment_string);
 129     }
 130
 131     Some(buffer)
 132 }
 133
 134 #[derive(Debug)]
 135 pub(crate) enum SegmentParam<'a> {
 136     Const(&'a ast::AnonConst),
 137     LifeTime(&'a ast::Lifetime),
 138     Type(&'a ast::Ty),
 139     Binding(&'a ast::AssocTyConstraint),
 140 }
 141
 142 impl<'a> SegmentParam<'a> {
 143     fn from_generic_arg(arg: &ast::GenericArg) -> SegmentParam<'_> {
 144         match arg {
 145             ast::GenericArg::Lifetime(ref lt) => SegmentParam::LifeTime(lt),
 146             ast::GenericArg::Type(ref ty) => SegmentParam::Type(ty),
 147             ast::GenericArg::Const(const_) => SegmentParam::Const(const_),
 148         }
 149     }
 150 }
 151
 152 impl<'a> Spanned for SegmentParam<'a> {
 153     fn span(&self) -> Span {
 154         match *self {
 155             SegmentParam::Const(const_) => const_.value.span,
 156             SegmentParam::LifeTime(lt) => lt.ident.span,
 157             SegmentParam::Type(ty) => ty.span,
 158             SegmentParam::Binding(binding) => binding.span,
 159         }
 160     }
 161 }
 162
 163 impl<'a> Rewrite for SegmentParam<'a> {
 164     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 165         match *self {
 166             SegmentParam::Const(const_) => const_.rewrite(context, shape),
 167             SegmentParam::LifeTime(lt) => lt.rewrite(context, shape),
 168             SegmentParam::Type(ty) => ty.rewrite(context, shape),
 169             SegmentParam::Binding(assoc_ty_constraint) => {
 170                 let mut result = match assoc_ty_constraint.kind {
 171                     ast::AssocTyConstraintKind::Bound { .. } => {
 172                         format!("{}: ", rewrite_ident(context, assoc_ty_constraint.ident))
 173                     }
 174                     ast::AssocTyConstraintKind::Equality { .. } => {
 175                         match context.config.type_punctuation_density() {
 176                             TypeDensity::Wide => {
 177                                 format!("{} = ", rewrite_ident(context, assoc_ty_constraint.ident))
 178                             }
 179                             TypeDensity::Compressed => {
 180                                 format!("{}=", rewrite_ident(context, assoc_ty_constraint.ident))
 181                             }
 182                         }
 183                     }
 184                 };
 185
 186                 let budget = shape.width.checked_sub(result.len())?;
 187                 let rewrite = assoc_ty_constraint
 188                     .kind
 189                     .rewrite(context, Shape::legacy(budget, shape.indent + result.len()))?;
 190                 result.push_str(&rewrite);
 191                 Some(result)
 192             }
 193         }
 194     }
 195 }
 196
 197 impl Rewrite for ast::AssocTyConstraintKind {
 198     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 199         match self {
 200             ast::AssocTyConstraintKind::Equality { ty } => ty.rewrite(context, shape),
 201             ast::AssocTyConstraintKind::Bound { bounds } => bounds.rewrite(context, shape),
 202         }
 203     }
 204 }
 205
 206 // Formats a path segment. There are some hacks involved to correctly determine
 207 // the segment's associated span since it's not part of the AST.
 208 //
 209 // The span_lo is assumed to be greater than the end of any previous segment's
 210 // parameters and lesser or equal than the start of current segment.
 211 //
 212 // span_hi is assumed equal to the end of the entire path.
 213 //
 214 // When the segment contains a positive number of parameters, we update span_lo
 215 // so that invariants described above will hold for the next segment.
 216 fn rewrite_segment(
 217     path_context: PathContext,
 218     segment: &ast::PathSegment,
 219     span_lo: &mut BytePos,
 220     span_hi: BytePos,
 221     context: &RewriteContext<'_>,
 222     shape: Shape,
 223 ) -> Option<String> {
 224     let mut result = String::with_capacity(128);
 225     result.push_str(rewrite_ident(context, segment.ident));
 226
 227     let ident_len = result.len();
 228     let shape = if context.use_block_indent() {
 229         shape.offset_left(ident_len)?
 230     } else {
 231         shape.shrink_left(ident_len)?
 232     };
 233
 234     if let Some(ref args) = segment.args {
 235         match **args {
 236             ast::GenericArgs::AngleBracketed(ref data) if !data.args.is_empty() => {
 237                 let param_list = data
 238                     .args
 239                     .iter()
 240                     .map(|x| match x {
 241                         ast::AngleBracketedArg::Arg(generic_arg) => {
 242                             SegmentParam::from_generic_arg(generic_arg)
 243                         }
 244                         ast::AngleBracketedArg::Constraint(constraint) => {
 245                             SegmentParam::Binding(constraint)
 246                         }
 247                     })
 248                     .collect::<Vec<_>>();
 249
 250                 // HACK: squeeze out the span between the identifier and the parameters.
 251                 // The hack is requried so that we don't remove the separator inside macro calls.
 252                 // This does not work in the presence of comment, hoping that people are
 253                 // sane about where to put their comment.
 254                 let separator_snippet = context
 255                     .snippet(mk_sp(segment.ident.span.hi(), data.span.lo()))
 256                     .trim();
 257                 let force_separator = context.inside_macro() && separator_snippet.starts_with("::");
 258                 let separator = if path_context == PathContext::Expr || force_separator {
 259                     "::"
 260                 } else {
 261                     ""
 262                 };
 263                 result.push_str(separator);
 264
 265                 let generics_str = overflow::rewrite_with_angle_brackets(
 266                     context,
 267                     "",
 268                     param_list.iter(),
 269                     shape,
 270                     mk_sp(*span_lo, span_hi),
 271                 )?;
 272
 273                 // Update position of last bracket.
 274                 *span_lo = context
 275                     .snippet_provider
 276                     .span_after(mk_sp(*span_lo, span_hi), "<");
 277
 278                 result.push_str(&generics_str)
 279             }
 280             ast::GenericArgs::Parenthesized(ref data) => {
 281                 result.push_str(&format_function_type(
 282                     data.inputs.iter().map(|x| &**x),
 283                     &data.output,
 284                     false,
 285                     data.span,
 286                     context,
 287                     shape,
 288                 )?);
 289             }
 290             _ => (),
 291         }
 292     }
 293
 294     Some(result)
 295 }
 296
 297 fn format_function_type<'a, I>(
 298     inputs: I,
 299     output: &FnRetTy,
 300     variadic: bool,
 301     span: Span,
 302     context: &RewriteContext<'_>,
 303     shape: Shape,
 304 ) -> Option<String>
 305 where
 306     I: ExactSizeIterator,
 307     <I as Iterator>::Item: Deref,
 308     <I::Item as Deref>::Target: Rewrite + Spanned + 'a,
 309 {
 310     debug!("format_function_type {:#?}", shape);
 311
 312     let ty_shape = match context.config.indent_style() {
 313         // 4 = " -> "
 314         IndentStyle::Block => shape.offset_left(4)?,
 315         IndentStyle::Visual => shape.block_left(4)?,
 316     };
 317     let output = match *output {
 318         FnRetTy::Ty(ref ty) => {
 319             let type_str = ty.rewrite(context, ty_shape)?;
 320             format!(" -> {}", type_str)
 321         }
 322         FnRetTy::Default(..) => String::new(),
 323     };
 324
 325     let list_shape = if context.use_block_indent() {
 326         Shape::indented(
 327             shape.block().indent.block_indent(context.config),
 328             context.config,
 329         )
 330     } else {
 331         // 2 for ()
 332         let budget = shape.width.checked_sub(2)?;
 333         // 1 for (
 334         let offset = shape.indent + 1;
 335         Shape::legacy(budget, offset)
 336     };
 337
 338     let is_inputs_empty = inputs.len() == 0;
 339     let list_lo = context.snippet_provider.span_after(span, "(");
 340     let (list_str, tactic) = if is_inputs_empty {
 341         let tactic = get_tactics(&[], &output, shape);
 342         let list_hi = context.snippet_provider.span_before(span, ")");
 343         let comment = context
 344             .snippet_provider
 345             .span_to_snippet(mk_sp(list_lo, list_hi))?
 346             .trim();
 347         let comment = if comment.starts_with("//") {
 348             format!(
 349                 "{}{}{}",
 350                 &list_shape.indent.to_string_with_newline(context.config),
 351                 comment,
 352                 &shape.block().indent.to_string_with_newline(context.config)
 353             )
 354         } else {
 355             comment.to_string()
 356         };
 357         (comment, tactic)
 358     } else {
 359         let items = itemize_list(
 360             context.snippet_provider,
 361             inputs,
 362             ")",
 363             ",",
 364             |arg| arg.span().lo(),
 365             |arg| arg.span().hi(),
 366             |arg| arg.rewrite(context, list_shape),
 367             list_lo,
 368             span.hi(),
 369             false,
 370         );
 371
 372         let item_vec: Vec<_> = items.collect();
 373         let tactic = get_tactics(&item_vec, &output, shape);
 374         let trailing_separator = if !context.use_block_indent() || variadic {
 375             SeparatorTactic::Never
 376         } else {
 377             context.config.trailing_comma()
 378         };
 379
 380         let fmt = ListFormatting::new(list_shape, context.config)
 381             .tactic(tactic)
 382             .trailing_separator(trailing_separator)
 383             .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
 384             .preserve_newline(true);
 385         (write_list(&item_vec, &fmt)?, tactic)
 386     };
 387
 388     let args = if tactic == DefinitiveListTactic::Horizontal
 389         || !context.use_block_indent()
 390         || is_inputs_empty
 391     {
 392         format!("({})", list_str)
 393     } else {
 394         format!(
 395             "({}{}{})",
 396             list_shape.indent.to_string_with_newline(context.config),
 397             list_str,
 398             shape.block().indent.to_string_with_newline(context.config),
 399         )
 400     };
 401     if output.is_empty() || last_line_width(&args) + first_line_width(&output) <= shape.width {
 402         Some(format!("{}{}", args, output))
 403     } else {
 404         Some(format!(
 405             "{}\n{}{}",
 406             args,
 407             list_shape.indent.to_string(context.config),
 408             output.trim_start()
 409         ))
 410     }
 411 }
 412
 413 fn type_bound_colon(context: &RewriteContext<'_>) -> &'static str {
 414     colon_spaces(context.config)
 415 }
 416
 417 // If the return type is multi-lined, then force to use multiple lines for
 418 // arguments as well.
 419 fn get_tactics(item_vec: &[ListItem], output: &str, shape: Shape) -> DefinitiveListTactic {
 420     if output.contains('\n') {
 421         DefinitiveListTactic::Vertical
 422     } else {
 423         definitive_tactic(
 424             item_vec,
 425             ListTactic::HorizontalVertical,
 426             Separator::Comma,
 427             // 2 is for the case of ',\n'
 428             shape.width.saturating_sub(2 + output.len()),
 429         )
 430     }
 431 }
 432
 433 impl Rewrite for ast::WherePredicate {
 434     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 435         // FIXME: dead spans?
 436         let result = match *self {
 437             ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 438                 ref bound_generic_params,
 439                 ref bounded_ty,
 440                 ref bounds,
 441                 ..
 442             }) => {
 443                 let type_str = bounded_ty.rewrite(context, shape)?;
 444                 let colon = type_bound_colon(context).trim_end();
 445                 let lhs = if let Some(lifetime_str) =
 446                     rewrite_lifetime_param(context, shape, bound_generic_params)
 447                 {
 448                     format!("for<{}> {}{}", lifetime_str, type_str, colon)
 449                 } else {
 450                     format!("{}{}", type_str, colon)
 451                 };
 452
 453                 rewrite_assign_rhs(context, lhs, bounds, shape)?
 454             }
 455             ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
 456                 ref lifetime,
 457                 ref bounds,
 458                 ..
 459             }) => rewrite_bounded_lifetime(lifetime, bounds, context, shape)?,
 460             ast::WherePredicate::EqPredicate(ast::WhereEqPredicate {
 461                 ref lhs_ty,
 462                 ref rhs_ty,
 463                 ..
 464             }) => {
 465                 let lhs_ty_str = lhs_ty.rewrite(context, shape).map(|lhs| lhs + " =")?;
 466                 rewrite_assign_rhs(context, lhs_ty_str, &**rhs_ty, shape)?
 467             }
 468         };
 469
 470         Some(result)
 471     }
 472 }
 473
 474 impl Rewrite for ast::GenericArg {
 475     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 476         match *self {
 477             ast::GenericArg::Lifetime(ref lt) => lt.rewrite(context, shape),
 478             ast::GenericArg::Type(ref ty) => ty.rewrite(context, shape),
 479             ast::GenericArg::Const(ref const_) => const_.rewrite(context, shape),
 480         }
 481     }
 482 }
 483
 484 fn rewrite_bounded_lifetime(
 485     lt: &ast::Lifetime,
 486     bounds: &[ast::GenericBound],
 487     context: &RewriteContext<'_>,
 488     shape: Shape,
 489 ) -> Option<String> {
 490     let result = lt.rewrite(context, shape)?;
 491
 492     if bounds.is_empty() {
 493         Some(result)
 494     } else {
 495         let colon = type_bound_colon(context);
 496         let overhead = last_line_width(&result) + colon.len();
 497         let result = format!(
 498             "{}{}{}",
 499             result,
 500             colon,
 501             join_bounds(context, shape.sub_width(overhead)?, bounds, true)?
 502         );
 503         Some(result)
 504     }
 505 }
 506
 507 impl Rewrite for ast::AnonConst {
 508     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 509         format_expr(&self.value, ExprType::SubExpression, context, shape)
 510     }
 511 }
 512
 513 impl Rewrite for ast::Lifetime {
 514     fn rewrite(&self, context: &RewriteContext<'_>, _: Shape) -> Option<String> {
 515         Some(rewrite_ident(context, self.ident).to_owned())
 516     }
 517 }
 518
 519 impl Rewrite for ast::GenericBound {
 520     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 521         match *self {
 522             ast::GenericBound::Trait(ref poly_trait_ref, trait_bound_modifier) => {
 523                 let snippet = context.snippet(self.span());
 524                 let has_paren = snippet.starts_with('(') && snippet.ends_with(')');
 525                 let rewrite = match trait_bound_modifier {
 526                     ast::TraitBoundModifier::None => poly_trait_ref.rewrite(context, shape),
 527                     ast::TraitBoundModifier::Maybe => poly_trait_ref
 528                         .rewrite(context, shape.offset_left(1)?)
 529                         .map(|s| format!("?{}", s)),
 530                     ast::TraitBoundModifier::MaybeConst => poly_trait_ref
 531                         .rewrite(context, shape.offset_left(7)?)
 532                         .map(|s| format!("?const {}", s)),
 533                     ast::TraitBoundModifier::MaybeConstMaybe => poly_trait_ref
 534                         .rewrite(context, shape.offset_left(8)?)
 535                         .map(|s| format!("?const ?{}", s)),
 536                 };
 537                 rewrite.map(|s| if has_paren { format!("({})", s) } else { s })
 538             }
 539             ast::GenericBound::Outlives(ref lifetime) => lifetime.rewrite(context, shape),
 540         }
 541     }
 542 }
 543
 544 impl Rewrite for ast::GenericBounds {
 545     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 546         if self.is_empty() {
 547             return Some(String::new());
 548         }
 549
 550         join_bounds(context, shape, self, true)
 551     }
 552 }
 553
 554 impl Rewrite for ast::GenericParam {
 555     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 556         let mut result = String::with_capacity(128);
 557         // FIXME: If there are more than one attributes, this will force multiline.
 558         match self.attrs.rewrite(context, shape) {
 559             Some(ref rw) if !rw.is_empty() => result.push_str(&format!("{} ", rw)),
 560             _ => (),
 561         }
 562
 563         if let rustc_ast::ast::GenericParamKind::Const { ref ty } = &self.kind {
 564             result.push_str("const ");
 565             result.push_str(rewrite_ident(context, self.ident));
 566             result.push_str(": ");
 567             result.push_str(&ty.rewrite(context, shape)?);
 568         } else {
 569             result.push_str(rewrite_ident(context, self.ident));
 570         }
 571
 572         if !self.bounds.is_empty() {
 573             result.push_str(type_bound_colon(context));
 574             result.push_str(&self.bounds.rewrite(context, shape)?)
 575         }
 576         if let ast::GenericParamKind::Type {
 577             default: Some(ref def),
 578         } = self.kind
 579         {
 580             let eq_str = match context.config.type_punctuation_density() {
 581                 TypeDensity::Compressed => "=",
 582                 TypeDensity::Wide => " = ",
 583             };
 584             result.push_str(eq_str);
 585             let budget = shape.width.checked_sub(result.len())?;
 586             let rewrite =
 587                 def.rewrite(context, Shape::legacy(budget, shape.indent + result.len()))?;
 588             result.push_str(&rewrite);
 589         }
 590
 591         Some(result)
 592     }
 593 }
 594
 595 impl Rewrite for ast::PolyTraitRef {
 596     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 597         if let Some(lifetime_str) =
 598             rewrite_lifetime_param(context, shape, &self.bound_generic_params)
 599         {
 600             // 6 is "for<> ".len()
 601             let extra_offset = lifetime_str.len() + 6;
 602             let path_str = self
 603                 .trait_ref
 604                 .rewrite(context, shape.offset_left(extra_offset)?)?;
 605
 606             Some(format!("for<{}> {}", lifetime_str, path_str))
 607         } else {
 608             self.trait_ref.rewrite(context, shape)
 609         }
 610     }
 611 }
 612
 613 impl Rewrite for ast::TraitRef {
 614     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 615         rewrite_path(context, PathContext::Type, None, &self.path, shape)
 616     }
 617 }
 618
 619 impl Rewrite for ast::Ty {
 620     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 621         match self.kind {
 622             ast::TyKind::TraitObject(ref bounds, tobj_syntax) => {
 623                 // we have to consider 'dyn' keyword is used or not!!!
 624                 let is_dyn = tobj_syntax == ast::TraitObjectSyntax::Dyn;
 625                 // 4 is length of 'dyn '
 626                 let shape = if is_dyn { shape.offset_left(4)? } else { shape };
 627                 let mut res = bounds.rewrite(context, shape)?;
 628                 // We may have falsely removed a trailing `+` inside macro call.
 629                 if context.inside_macro() && bounds.len() == 1 {
 630                     if context.snippet(self.span).ends_with('+') && !res.ends_with('+') {
 631                         res.push('+');
 632                     }
 633                 }
 634                 if is_dyn {
 635                     Some(format!("dyn {}", res))
 636                 } else {
 637                     Some(res)
 638                 }
 639             }
 640             ast::TyKind::Ptr(ref mt) => {
 641                 let prefix = match mt.mutbl {
 642                     Mutability::Mut => "*mut ",
 643                     Mutability::Not => "*const ",
 644                 };
 645
 646                 rewrite_unary_prefix(context, prefix, &*mt.ty, shape)
 647             }
 648             ast::TyKind::Rptr(ref lifetime, ref mt) => {
 649                 let mut_str = format_mutability(mt.mutbl);
 650                 let mut_len = mut_str.len();
 651                 Some(match *lifetime {
 652                     Some(ref lifetime) => {
 653                         let lt_budget = shape.width.checked_sub(2 + mut_len)?;
 654                         let lt_str = lifetime.rewrite(
 655                             context,
 656                             Shape::legacy(lt_budget, shape.indent + 2 + mut_len),
 657                         )?;
 658                         let lt_len = lt_str.len();
 659                         let budget = shape.width.checked_sub(2 + mut_len + lt_len)?;
 660                         format!(
 661                             "&{} {}{}",
 662                             lt_str,
 663                             mut_str,
 664                             mt.ty.rewrite(
 665                                 context,
 666                                 Shape::legacy(budget, shape.indent + 2 + mut_len + lt_len)
 667                             )?
 668                         )
 669                     }
 670                     None => {
 671                         let budget = shape.width.checked_sub(1 + mut_len)?;
 672                         format!(
 673                             "&{}{}",
 674                             mut_str,
 675                             mt.ty.rewrite(
 676                                 context,
 677                                 Shape::legacy(budget, shape.indent + 1 + mut_len)
 678                             )?
 679                         )
 680                     }
 681                 })
 682             }
 683             // FIXME: we drop any comments here, even though it's a silly place to put
 684             // comments.
 685             ast::TyKind::Paren(ref ty) => {
 686                 if context.config.version() == Version::One
 687                     || context.config.indent_style() == IndentStyle::Visual
 688                 {
 689                     let budget = shape.width.checked_sub(2)?;
 690                     return ty
 691                         .rewrite(context, Shape::legacy(budget, shape.indent + 1))
 692                         .map(|ty_str| format!("({})", ty_str));
 693                 }
 694
 695                 // 2 = ()
 696                 if let Some(sh) = shape.sub_width(2) {
 697                     if let Some(ref s) = ty.rewrite(context, sh) {
 698                         if !s.contains('\n') {
 699                             return Some(format!("({})", s));
 700                         }
 701                     }
 702                 }
 703
 704                 let indent_str = shape.indent.to_string_with_newline(context.config);
 705                 let shape = shape
 706                     .block_indent(context.config.tab_spaces())
 707                     .with_max_width(context.config);
 708                 let rw = ty.rewrite(context, shape)?;
 709                 Some(format!(
 710                     "({}{}{})",
 711                     shape.to_string_with_newline(context.config),
 712                     rw,
 713                     indent_str
 714                 ))
 715             }
 716             ast::TyKind::Slice(ref ty) => {
 717                 let budget = shape.width.checked_sub(4)?;
 718                 ty.rewrite(context, Shape::legacy(budget, shape.indent + 1))
 719                     .map(|ty_str| format!("[{}]", ty_str))
 720             }
 721             ast::TyKind::Tup(ref items) => {
 722                 rewrite_tuple(context, items.iter(), self.span, shape, items.len() == 1)
 723             }
 724             ast::TyKind::Path(ref q_self, ref path) => {
 725                 rewrite_path(context, PathContext::Type, q_self.as_ref(), path, shape)
 726             }
 727             ast::TyKind::Array(ref ty, ref repeats) => rewrite_pair(
 728                 &**ty,
 729                 &*repeats.value,
 730                 PairParts::new("[", "; ", "]"),
 731                 context,
 732                 shape,
 733                 SeparatorPlace::Back,
 734             ),
 735             ast::TyKind::Infer => {
 736                 if shape.width >= 1 {
 737                     Some("_".to_owned())
 738                 } else {
 739                     None
 740                 }
 741             }
 742             ast::TyKind::BareFn(ref bare_fn) => rewrite_bare_fn(bare_fn, self.span, context, shape),
 743             ast::TyKind::Never => Some(String::from("!")),
 744             ast::TyKind::MacCall(ref mac) => {
 745                 rewrite_macro(mac, None, context, shape, MacroPosition::Expression)
 746             }
 747             ast::TyKind::ImplicitSelf => Some(String::from("")),
 748             ast::TyKind::ImplTrait(_, ref it) => {
 749                 // Empty trait is not a parser error.
 750                 if it.is_empty() {
 751                     return Some("impl".to_owned());
 752                 }
 753                 let rw = if context.config.version() == Version::One {
 754                     it.rewrite(context, shape)
 755                 } else {
 756                     join_bounds(context, shape, it, false)
 757                 };
 758                 rw.map(|it_str| {
 759                     let space = if it_str.is_empty() { "" } else { " " };
 760                     format!("impl{}{}", space, it_str)
 761                 })
 762             }
 763             ast::TyKind::CVarArgs => Some("...".to_owned()),
 764             ast::TyKind::Err | ast::TyKind::Typeof(..) => unreachable!(),
 765         }
 766     }
 767 }
 768
 769 fn rewrite_bare_fn(
 770     bare_fn: &ast::BareFnTy,
 771     span: Span,
 772     context: &RewriteContext<'_>,
 773     shape: Shape,
 774 ) -> Option<String> {
 775     debug!("rewrite_bare_fn {:#?}", shape);
 776
 777     let mut result = String::with_capacity(128);
 778
 779     if let Some(ref lifetime_str) = rewrite_lifetime_param(context, shape, &bare_fn.generic_params)
 780     {
 781         result.push_str("for<");
 782         // 6 = "for<> ".len(), 4 = "for<".
 783         // This doesn't work out so nicely for multiline situation with lots of
 784         // rightward drift. If that is a problem, we could use the list stuff.
 785         result.push_str(lifetime_str);
 786         result.push_str("> ");
 787     }
 788
 789     result.push_str(crate::utils::format_unsafety(bare_fn.unsafety));
 790
 791     result.push_str(&format_extern(
 792         bare_fn.ext,
 793         context.config.force_explicit_abi(),
 794         false,
 795     ));
 796
 797     result.push_str("fn");
 798
 799     let func_ty_shape = if context.use_block_indent() {
 800         shape.offset_left(result.len())?
 801     } else {
 802         shape.visual_indent(result.len()).sub_width(result.len())?
 803     };
 804
 805     let rewrite = format_function_type(
 806         bare_fn.decl.inputs.iter(),
 807         &bare_fn.decl.output,
 808         bare_fn.decl.c_variadic(),
 809         span,
 810         context,
 811         func_ty_shape,
 812     )?;
 813
 814     result.push_str(&rewrite);
 815
 816     Some(result)
 817 }
 818
 819 fn is_generic_bounds_in_order(generic_bounds: &[ast::GenericBound]) -> bool {
 820     let is_trait = |b: &ast::GenericBound| match b {
 821         ast::GenericBound::Outlives(..) => false,
 822         ast::GenericBound::Trait(..) => true,
 823     };
 824     let is_lifetime = |b: &ast::GenericBound| !is_trait(b);
 825     let last_trait_index = generic_bounds.iter().rposition(is_trait);
 826     let first_lifetime_index = generic_bounds.iter().position(is_lifetime);
 827     match (last_trait_index, first_lifetime_index) {
 828         (Some(last_trait_index), Some(first_lifetime_index)) => {
 829             last_trait_index < first_lifetime_index
 830         }
 831         _ => true,
 832     }
 833 }
 834
 835 fn join_bounds(
 836     context: &RewriteContext<'_>,
 837     shape: Shape,
 838     items: &[ast::GenericBound],
 839     need_indent: bool,
 840 ) -> Option<String> {
 841     debug_assert!(!items.is_empty());
 842
 843     // Try to join types in a single line
 844     let joiner = match context.config.type_punctuation_density() {
 845         TypeDensity::Compressed => "+",
 846         TypeDensity::Wide => " + ",
 847     };
 848     let type_strs = items
 849         .iter()
 850         .map(|item| item.rewrite(context, shape))
 851         .collect::<Option<Vec<_>>>()?;
 852     let result = type_strs.join(joiner);
 853     if items.len() <= 1 || (!result.contains('\n') && result.len() <= shape.width) {
 854         return Some(result);
 855     }
 856
 857     // We need to use multiple lines.
 858     let (type_strs, offset) = if need_indent {
 859         // Rewrite with additional indentation.
 860         let nested_shape = shape
 861             .block_indent(context.config.tab_spaces())
 862             .with_max_width(context.config);
 863         let type_strs = items
 864             .iter()
 865             .map(|item| item.rewrite(context, nested_shape))
 866             .collect::<Option<Vec<_>>>()?;
 867         (type_strs, nested_shape.indent)
 868     } else {
 869         (type_strs, shape.indent)
 870     };
 871
 872     let is_bound_extendable = |s: &str, b: &ast::GenericBound| match b {
 873         ast::GenericBound::Outlives(..) => true,
 874         ast::GenericBound::Trait(..) => last_line_extendable(s),
 875     };
 876     let mut result = String::with_capacity(128);
 877     result.push_str(&type_strs[0]);
 878     let mut can_be_put_on_the_same_line = is_bound_extendable(&result, &items[0]);
 879     let generic_bounds_in_order = is_generic_bounds_in_order(items);
 880     for (bound, bound_str) in items[1..].iter().zip(type_strs[1..].iter()) {
 881         if generic_bounds_in_order && can_be_put_on_the_same_line {
 882             result.push_str(joiner);
 883         } else {
 884             result.push_str(&offset.to_string_with_newline(context.config));
 885             result.push_str("+ ");
 886         }
 887         result.push_str(bound_str);
 888         can_be_put_on_the_same_line = is_bound_extendable(bound_str, bound);
 889     }
 890
 891     Some(result)
 892 }
 893
 894 pub(crate) fn can_be_overflowed_type(
 895     context: &RewriteContext<'_>,
 896     ty: &ast::Ty,
 897     len: usize,
 898 ) -> bool {
 899     match ty.kind {
 900         ast::TyKind::Tup(..) => context.use_block_indent() && len == 1,
 901         ast::TyKind::Rptr(_, ref mutty) | ast::TyKind::Ptr(ref mutty) => {
 902             can_be_overflowed_type(context, &*mutty.ty, len)
 903         }
 904         _ => false,
 905     }
 906 }
 907
 908 /// Returns `None` if there is no `LifetimeDef` in the given generic parameters.
 909 fn rewrite_lifetime_param(
 910     context: &RewriteContext<'_>,
 911     shape: Shape,
 912     generic_params: &[ast::GenericParam],
 913 ) -> Option<String> {
 914     let result = generic_params
 915         .iter()
 916         .filter(|p| match p.kind {
 917             ast::GenericParamKind::Lifetime => true,
 918             _ => false,
 919         })
 920         .map(|lt| lt.rewrite(context, shape))
 921         .collect::<Option<Vec<_>>>()?
 922         .join(", ");
 923     if result.is_empty() {
 924         None
 925     } else {
 926         Some(result)
 927     }
 928 }