src/items.rs

   1 // Formatting top-level items - functions, structs, enums, traits, impls.
   2
   3 use std::borrow::Cow;
   4 use std::cmp::{max, min, Ordering};
   5
   6 use regex::Regex;
   7 use rustc_target::spec::abi;
   8 use syntax::source_map::{self, BytePos, Span};
   9 use syntax::visit;
  10 use syntax::{ast, ptr, symbol};
  11
  12 use crate::attr::filter_inline_attrs;
  13 use crate::comment::{
  14     combine_strs_with_missing_comments, contains_comment, is_last_comment_block,
  15     recover_comment_removed, recover_missing_comment_in_span, rewrite_missing_comment,
  16     FindUncommented,
  17 };
  18 use crate::config::lists::*;
  19 use crate::config::{BraceStyle, Config, IndentStyle, Version};
  20 use crate::expr::{
  21     is_empty_block, is_simple_block_stmt, rewrite_assign_rhs, rewrite_assign_rhs_with, RhsTactics,
  22 };
  23 use crate::lists::{definitive_tactic, itemize_list, write_list, ListFormatting, Separator};
  24 use crate::macros::{rewrite_macro, MacroPosition};
  25 use crate::overflow;
  26 use crate::rewrite::{Rewrite, RewriteContext};
  27 use crate::shape::{Indent, Shape};
  28 use crate::source_map::{LineRangeUtils, SpanUtils};
  29 use crate::spanned::Spanned;
  30 use crate::stmt::Stmt;
  31 use crate::utils::*;
  32 use crate::vertical::rewrite_with_alignment;
  33 use crate::visitor::FmtVisitor;
  34
  35 const DEFAULT_VISIBILITY: ast::Visibility = source_map::Spanned {
  36     node: ast::VisibilityKind::Inherited,
  37     span: source_map::DUMMY_SP,
  38 };
  39
  40 fn type_annotation_separator(config: &Config) -> &str {
  41     colon_spaces(config)
  42 }
  43
  44 // Statements of the form
  45 // let pat: ty = init;
  46 impl Rewrite for ast::Local {
  47     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
  48         debug!(
  49             "Local::rewrite {:?} {} {:?}",
  50             self, shape.width, shape.indent
  51         );
  52
  53         skip_out_of_file_lines_range!(context, self.span);
  54
  55         if contains_skip(&self.attrs) {
  56             return None;
  57         }
  58
  59         let attrs_str = self.attrs.rewrite(context, shape)?;
  60         let mut result = if attrs_str.is_empty() {
  61             "let ".to_owned()
  62         } else {
  63             combine_strs_with_missing_comments(
  64                 context,
  65                 &attrs_str,
  66                 "let ",
  67                 mk_sp(
  68                     self.attrs.last().map(|a| a.span.hi()).unwrap(),
  69                     self.span.lo(),
  70                 ),
  71                 shape,
  72                 false,
  73             )?
  74         };
  75
  76         // 4 = "let ".len()
  77         let pat_shape = shape.offset_left(4)?;
  78         // 1 = ;
  79         let pat_shape = pat_shape.sub_width(1)?;
  80         let pat_str = self.pat.rewrite(context, pat_shape)?;
  81         result.push_str(&pat_str);
  82
  83         // String that is placed within the assignment pattern and expression.
  84         let infix = {
  85             let mut infix = String::with_capacity(32);
  86
  87             if let Some(ref ty) = self.ty {
  88                 let separator = type_annotation_separator(context.config);
  89                 let ty_shape = if pat_str.contains('\n') {
  90                     shape.with_max_width(context.config)
  91                 } else {
  92                     shape
  93                 }
  94                 .offset_left(last_line_width(&result) + separator.len())?
  95                 // 2 = ` =`
  96                 .sub_width(2)?;
  97
  98                 let rewrite = ty.rewrite(context, ty_shape)?;
  99
 100                 infix.push_str(separator);
 101                 infix.push_str(&rewrite);
 102             }
 103
 104             if self.init.is_some() {
 105                 infix.push_str(" =");
 106             }
 107
 108             infix
 109         };
 110
 111         result.push_str(&infix);
 112
 113         if let Some(ref ex) = self.init {
 114             // 1 = trailing semicolon;
 115             let nested_shape = shape.sub_width(1)?;
 116
 117             result = rewrite_assign_rhs(context, result, &**ex, nested_shape)?;
 118         }
 119
 120         result.push(';');
 121         Some(result)
 122     }
 123 }
 124
 125 // FIXME convert to using rewrite style rather than visitor
 126 // FIXME format modules in this style
 127 #[allow(dead_code)]
 128 struct Item<'a> {
 129     keyword: &'static str,
 130     abi: Cow<'static, str>,
 131     vis: Option<&'a ast::Visibility>,
 132     body: Vec<BodyElement<'a>>,
 133     span: Span,
 134 }
 135
 136 impl<'a> Item<'a> {
 137     fn from_foreign_mod(fm: &'a ast::ForeignMod, span: Span, config: &Config) -> Item<'a> {
 138         Item {
 139             keyword: "",
 140             abi: format_abi(fm.abi, config.force_explicit_abi(), true),
 141             vis: None,
 142             body: fm
 143                 .items
 144                 .iter()
 145                 .map(|i| BodyElement::ForeignItem(i))
 146                 .collect(),
 147             span,
 148         }
 149     }
 150 }
 151
 152 enum BodyElement<'a> {
 153     // Stmt(&'a ast::Stmt),
 154     // Field(&'a ast::Field),
 155     // Variant(&'a ast::Variant),
 156     // Item(&'a ast::Item),
 157     ForeignItem(&'a ast::ForeignItem),
 158 }
 159
 160 /// Represents a fn's signature.
 161 pub(crate) struct FnSig<'a> {
 162     decl: &'a ast::FnDecl,
 163     generics: &'a ast::Generics,
 164     abi: abi::Abi,
 165     is_async: Cow<'a, ast::IsAsync>,
 166     constness: ast::Constness,
 167     defaultness: ast::Defaultness,
 168     unsafety: ast::Unsafety,
 169     visibility: ast::Visibility,
 170 }
 171
 172 impl<'a> FnSig<'a> {
 173     pub(crate) fn new(
 174         decl: &'a ast::FnDecl,
 175         generics: &'a ast::Generics,
 176         vis: ast::Visibility,
 177     ) -> FnSig<'a> {
 178         FnSig {
 179             decl,
 180             generics,
 181             abi: abi::Abi::Rust,
 182             is_async: Cow::Owned(ast::IsAsync::NotAsync),
 183             constness: ast::Constness::NotConst,
 184             defaultness: ast::Defaultness::Final,
 185             unsafety: ast::Unsafety::Normal,
 186             visibility: vis,
 187         }
 188     }
 189
 190     pub(crate) fn from_method_sig(
 191         method_sig: &'a ast::MethodSig,
 192         generics: &'a ast::Generics,
 193     ) -> FnSig<'a> {
 194         FnSig {
 195             unsafety: method_sig.header.unsafety,
 196             is_async: Cow::Borrowed(&method_sig.header.asyncness.node),
 197             constness: method_sig.header.constness.node,
 198             defaultness: ast::Defaultness::Final,
 199             abi: method_sig.header.abi,
 200             decl: &*method_sig.decl,
 201             generics,
 202             visibility: DEFAULT_VISIBILITY,
 203         }
 204     }
 205
 206     pub(crate) fn from_fn_kind(
 207         fn_kind: &'a visit::FnKind<'_>,
 208         generics: &'a ast::Generics,
 209         decl: &'a ast::FnDecl,
 210         defaultness: ast::Defaultness,
 211     ) -> FnSig<'a> {
 212         match *fn_kind {
 213             visit::FnKind::ItemFn(_, fn_header, visibility, _) => FnSig {
 214                 decl,
 215                 generics,
 216                 abi: fn_header.abi,
 217                 constness: fn_header.constness.node,
 218                 is_async: Cow::Borrowed(&fn_header.asyncness.node),
 219                 defaultness,
 220                 unsafety: fn_header.unsafety,
 221                 visibility: visibility.clone(),
 222             },
 223             visit::FnKind::Method(_, method_sig, vis, _) => {
 224                 let mut fn_sig = FnSig::from_method_sig(method_sig, generics);
 225                 fn_sig.defaultness = defaultness;
 226                 if let Some(vis) = vis {
 227                     fn_sig.visibility = vis.clone();
 228                 }
 229                 fn_sig
 230             }
 231             _ => unreachable!(),
 232         }
 233     }
 234
 235     fn to_str(&self, context: &RewriteContext<'_>) -> String {
 236         let mut result = String::with_capacity(128);
 237         // Vis defaultness constness unsafety abi.
 238         result.push_str(&*format_visibility(context, &self.visibility));
 239         result.push_str(format_defaultness(self.defaultness));
 240         result.push_str(format_constness(self.constness));
 241         result.push_str(format_async(&self.is_async));
 242         result.push_str(format_unsafety(self.unsafety));
 243         result.push_str(&format_abi(
 244             self.abi,
 245             context.config.force_explicit_abi(),
 246             false,
 247         ));
 248         result
 249     }
 250 }
 251
 252 impl<'a> FmtVisitor<'a> {
 253     fn format_item(&mut self, item: &Item<'_>) {
 254         self.buffer.push_str(&item.abi);
 255
 256         let snippet = self.snippet(item.span);
 257         let brace_pos = snippet.find_uncommented("{").unwrap();
 258
 259         self.push_str("{");
 260         if !item.body.is_empty() || contains_comment(&snippet[brace_pos..]) {
 261             // FIXME: this skips comments between the extern keyword and the opening
 262             // brace.
 263             self.last_pos = item.span.lo() + BytePos(brace_pos as u32 + 1);
 264             self.block_indent = self.block_indent.block_indent(self.config);
 265
 266             if item.body.is_empty() {
 267                 self.format_missing_no_indent(item.span.hi() - BytePos(1));
 268                 self.block_indent = self.block_indent.block_unindent(self.config);
 269                 let indent_str = self.block_indent.to_string(self.config);
 270                 self.push_str(&indent_str);
 271             } else {
 272                 for item in &item.body {
 273                     self.format_body_element(item);
 274                 }
 275
 276                 self.block_indent = self.block_indent.block_unindent(self.config);
 277                 self.format_missing_with_indent(item.span.hi() - BytePos(1));
 278             }
 279         }
 280
 281         self.push_str("}");
 282         self.last_pos = item.span.hi();
 283     }
 284
 285     fn format_body_element(&mut self, element: &BodyElement<'_>) {
 286         match *element {
 287             BodyElement::ForeignItem(item) => self.format_foreign_item(item),
 288         }
 289     }
 290
 291     pub(crate) fn format_foreign_mod(&mut self, fm: &ast::ForeignMod, span: Span) {
 292         let item = Item::from_foreign_mod(fm, span, self.config);
 293         self.format_item(&item);
 294     }
 295
 296     fn format_foreign_item(&mut self, item: &ast::ForeignItem) {
 297         let rewrite = item.rewrite(&self.get_context(), self.shape());
 298         self.push_rewrite(item.span(), rewrite);
 299         self.last_pos = item.span.hi();
 300     }
 301
 302     pub(crate) fn rewrite_fn_before_block(
 303         &mut self,
 304         indent: Indent,
 305         ident: ast::Ident,
 306         fn_sig: &FnSig<'_>,
 307         span: Span,
 308     ) -> Option<(String, FnBraceStyle)> {
 309         let context = self.get_context();
 310
 311         let mut fn_brace_style = newline_for_brace(self.config, &fn_sig.generics.where_clause);
 312         let (result, force_newline_brace) =
 313             rewrite_fn_base(&context, indent, ident, fn_sig, span, fn_brace_style)?;
 314
 315         // 2 = ` {`
 316         if self.config.brace_style() == BraceStyle::AlwaysNextLine
 317             || force_newline_brace
 318             || last_line_width(&result) + 2 > self.shape().width
 319         {
 320             fn_brace_style = FnBraceStyle::NextLine
 321         }
 322
 323         Some((result, fn_brace_style))
 324     }
 325
 326     pub(crate) fn rewrite_required_fn(
 327         &mut self,
 328         indent: Indent,
 329         ident: ast::Ident,
 330         sig: &ast::MethodSig,
 331         generics: &ast::Generics,
 332         span: Span,
 333     ) -> Option<String> {
 334         // Drop semicolon or it will be interpreted as comment.
 335         let span = mk_sp(span.lo(), span.hi() - BytePos(1));
 336         let context = self.get_context();
 337
 338         let (mut result, _) = rewrite_fn_base(
 339             &context,
 340             indent,
 341             ident,
 342             &FnSig::from_method_sig(sig, generics),
 343             span,
 344             FnBraceStyle::None,
 345         )?;
 346
 347         // Re-attach semicolon
 348         result.push(';');
 349
 350         Some(result)
 351     }
 352
 353     pub(crate) fn single_line_fn(
 354         &self,
 355         fn_str: &str,
 356         block: &ast::Block,
 357         inner_attrs: Option<&[ast::Attribute]>,
 358     ) -> Option<String> {
 359         if fn_str.contains('\n') || inner_attrs.map_or(false, |a| !a.is_empty()) {
 360             return None;
 361         }
 362
 363         let source_map = self.get_context().source_map;
 364
 365         if self.config.empty_item_single_line()
 366             && is_empty_block(block, None, source_map)
 367             && self.block_indent.width() + fn_str.len() + 3 <= self.config.max_width()
 368             && !last_line_contains_single_line_comment(fn_str)
 369         {
 370             return Some(format!("{} {{}}", fn_str));
 371         }
 372
 373         if !self.config.fn_single_line() || !is_simple_block_stmt(block, None, source_map) {
 374             return None;
 375         }
 376
 377         let res = Stmt::from_ast_node(block.stmts.first()?, true)
 378             .rewrite(&self.get_context(), self.shape())?;
 379
 380         let width = self.block_indent.width() + fn_str.len() + res.len() + 5;
 381         if !res.contains('\n') && width <= self.config.max_width() {
 382             Some(format!("{} {{ {} }}", fn_str, res))
 383         } else {
 384             None
 385         }
 386     }
 387
 388     pub(crate) fn visit_static(&mut self, static_parts: &StaticParts<'_>) {
 389         let rewrite = rewrite_static(&self.get_context(), static_parts, self.block_indent);
 390         self.push_rewrite(static_parts.span, rewrite);
 391     }
 392
 393     pub(crate) fn visit_struct(&mut self, struct_parts: &StructParts<'_>) {
 394         let is_tuple = match struct_parts.def {
 395             ast::VariantData::Tuple(..) => true,
 396             _ => false,
 397         };
 398         let rewrite = format_struct(&self.get_context(), struct_parts, self.block_indent, None)
 399             .map(|s| if is_tuple { s + ";" } else { s });
 400         self.push_rewrite(struct_parts.span, rewrite);
 401     }
 402
 403     pub(crate) fn visit_enum(
 404         &mut self,
 405         ident: ast::Ident,
 406         vis: &ast::Visibility,
 407         enum_def: &ast::EnumDef,
 408         generics: &ast::Generics,
 409         span: Span,
 410     ) {
 411         let enum_header = format_header(&self.get_context(), "enum ", ident, vis);
 412         self.push_str(&enum_header);
 413
 414         let enum_snippet = self.snippet(span);
 415         let brace_pos = enum_snippet.find_uncommented("{").unwrap();
 416         let body_start = span.lo() + BytePos(brace_pos as u32 + 1);
 417         let generics_str = format_generics(
 418             &self.get_context(),
 419             generics,
 420             self.config.brace_style(),
 421             if enum_def.variants.is_empty() {
 422                 BracePos::ForceSameLine
 423             } else {
 424                 BracePos::Auto
 425             },
 426             self.block_indent,
 427             // make a span that starts right after `enum Foo`
 428             mk_sp(ident.span.hi(), body_start),
 429             last_line_width(&enum_header),
 430         )
 431         .unwrap();
 432         self.push_str(&generics_str);
 433
 434         self.last_pos = body_start;
 435
 436         match self.format_variant_list(enum_def, body_start, span.hi()) {
 437             Some(ref s) if enum_def.variants.is_empty() => self.push_str(s),
 438             rw => {
 439                 self.push_rewrite(mk_sp(body_start, span.hi()), rw);
 440                 self.block_indent = self.block_indent.block_unindent(self.config);
 441             }
 442         }
 443     }
 444
 445     // Format the body of an enum definition
 446     fn format_variant_list(
 447         &mut self,
 448         enum_def: &ast::EnumDef,
 449         body_lo: BytePos,
 450         body_hi: BytePos,
 451     ) -> Option<String> {
 452         if enum_def.variants.is_empty() {
 453             let mut buffer = String::with_capacity(128);
 454             // 1 = "}"
 455             let span = mk_sp(body_lo, body_hi - BytePos(1));
 456             format_empty_struct_or_tuple(
 457                 &self.get_context(),
 458                 span,
 459                 self.block_indent,
 460                 &mut buffer,
 461                 "",
 462                 "}",
 463             );
 464             return Some(buffer);
 465         }
 466         let mut result = String::with_capacity(1024);
 467         let original_offset = self.block_indent;
 468         self.block_indent = self.block_indent.block_indent(self.config);
 469
 470         // If enum variants have discriminants, try to vertically align those,
 471         // provided the discrims are not shifted too much  to the right
 472         let align_threshold: usize = self.config.enum_discrim_align_threshold();
 473         let discr_ident_lens: Vec<usize> = enum_def
 474             .variants
 475             .iter()
 476             .filter(|var| var.disr_expr.is_some())
 477             .map(|var| rewrite_ident(&self.get_context(), var.ident).len())
 478             .collect();
 479         // cut the list at the point of longest discrim shorter than the threshold
 480         // All of the discrims under the threshold will get padded, and all above - left as is.
 481         let pad_discrim_ident_to = *discr_ident_lens
 482             .iter()
 483             .filter(|&l| *l <= align_threshold)
 484             .max()
 485             .unwrap_or(&0);
 486
 487         let itemize_list_with = |one_line_width: usize| {
 488             itemize_list(
 489                 self.snippet_provider,
 490                 enum_def.variants.iter(),
 491                 "}",
 492                 ",",
 493                 |f| {
 494                     if !f.attrs.is_empty() {
 495                         f.attrs[0].span.lo()
 496                     } else {
 497                         f.span.lo()
 498                     }
 499                 },
 500                 |f| f.span.hi(),
 501                 |f| self.format_variant(f, one_line_width, pad_discrim_ident_to),
 502                 body_lo,
 503                 body_hi,
 504                 false,
 505             )
 506             .collect()
 507         };
 508         let mut items: Vec<_> =
 509             itemize_list_with(self.config.width_heuristics().struct_variant_width);
 510         // If one of the variants use multiple lines, use multi-lined formatting for all variants.
 511         let has_multiline_variant = items.iter().any(|item| item.inner_as_ref().contains('\n'));
 512         let has_single_line_variant = items.iter().any(|item| !item.inner_as_ref().contains('\n'));
 513         if has_multiline_variant && has_single_line_variant {
 514             items = itemize_list_with(0);
 515         }
 516
 517         let shape = self.shape().sub_width(2)?;
 518         let fmt = ListFormatting::new(shape, self.config)
 519             .trailing_separator(self.config.trailing_comma())
 520             .preserve_newline(true);
 521
 522         let list = write_list(&items, &fmt)?;
 523         result.push_str(&list);
 524         result.push_str(&original_offset.to_string_with_newline(self.config));
 525         result.push('}');
 526         Some(result)
 527     }
 528
 529     // Variant of an enum.
 530     fn format_variant(
 531         &self,
 532         field: &ast::Variant,
 533         one_line_width: usize,
 534         pad_discrim_ident_to: usize,
 535     ) -> Option<String> {
 536         if contains_skip(&field.attrs) {
 537             let lo = field.attrs[0].span.lo();
 538             let span = mk_sp(lo, field.span.hi());
 539             return Some(self.snippet(span).to_owned());
 540         }
 541
 542         let context = self.get_context();
 543         // 1 = ','
 544         let shape = self.shape().sub_width(1)?;
 545         let attrs_str = field.attrs.rewrite(&context, shape)?;
 546         let lo = field
 547             .attrs
 548             .last()
 549             .map_or(field.span.lo(), |attr| attr.span.hi());
 550         let span = mk_sp(lo, field.span.lo());
 551
 552         let variant_body = match field.data {
 553             ast::VariantData::Tuple(..) | ast::VariantData::Struct(..) => format_struct(
 554                 &context,
 555                 &StructParts::from_variant(field),
 556                 self.block_indent,
 557                 Some(one_line_width),
 558             )?,
 559             ast::VariantData::Unit(..) => rewrite_ident(&context, field.ident).to_owned(),
 560         };
 561
 562         let variant_body = if let Some(ref expr) = field.disr_expr {
 563             let lhs = format!("{:1$} =", variant_body, pad_discrim_ident_to);
 564             rewrite_assign_rhs_with(
 565                 &context,
 566                 lhs,
 567                 &*expr.value,
 568                 shape,
 569                 RhsTactics::AllowOverflow,
 570             )?
 571         } else {
 572             variant_body
 573         };
 574
 575         combine_strs_with_missing_comments(&context, &attrs_str, &variant_body, span, shape, false)
 576     }
 577
 578     fn visit_impl_items(&mut self, items: &[ast::ImplItem]) {
 579         if self.get_context().config.reorder_impl_items() {
 580             // Create visitor for each items, then reorder them.
 581             let mut buffer = vec![];
 582             for item in items {
 583                 self.visit_impl_item(item);
 584                 buffer.push((self.buffer.clone(), item.clone()));
 585                 self.buffer.clear();
 586             }
 587             // type -> opaque -> const -> macro -> method
 588             use crate::ast::ImplItemKind::*;
 589             fn need_empty_line(a: &ast::ImplItemKind, b: &ast::ImplItemKind) -> bool {
 590                 match (a, b) {
 591                     (TyAlias(..), TyAlias(..))
 592                     | (Const(..), Const(..))
 593                     | (OpaqueTy(..), OpaqueTy(..)) => false,
 594                     _ => true,
 595                 }
 596             }
 597
 598             buffer.sort_by(|(_, a), (_, b)| match (&a.kind, &b.kind) {
 599                 (TyAlias(..), TyAlias(..))
 600                 | (Const(..), Const(..))
 601                 | (Macro(..), Macro(..))
 602                 | (OpaqueTy(..), OpaqueTy(..)) => a.ident.as_str().cmp(&b.ident.as_str()),
 603                 (Method(..), Method(..)) => a.span.lo().cmp(&b.span.lo()),
 604                 (TyAlias(..), _) => Ordering::Less,
 605                 (_, TyAlias(..)) => Ordering::Greater,
 606                 (OpaqueTy(..), _) => Ordering::Less,
 607                 (_, OpaqueTy(..)) => Ordering::Greater,
 608                 (Const(..), _) => Ordering::Less,
 609                 (_, Const(..)) => Ordering::Greater,
 610                 (Macro(..), _) => Ordering::Less,
 611                 (_, Macro(..)) => Ordering::Greater,
 612             });
 613             let mut prev_kind = None;
 614             for (buf, item) in buffer {
 615                 // Make sure that there are at least a single empty line between
 616                 // different impl items.
 617                 if prev_kind
 618                     .as_ref()
 619                     .map_or(false, |prev_kind| need_empty_line(prev_kind, &item.kind))
 620                 {
 621                     self.push_str("\n");
 622                 }
 623                 let indent_str = self.block_indent.to_string_with_newline(self.config);
 624                 self.push_str(&indent_str);
 625                 self.push_str(buf.trim());
 626                 prev_kind = Some(item.kind.clone());
 627             }
 628         } else {
 629             for item in items {
 630                 self.visit_impl_item(item);
 631             }
 632         }
 633     }
 634 }
 635
 636 pub(crate) fn format_impl(
 637     context: &RewriteContext<'_>,
 638     item: &ast::Item,
 639     offset: Indent,
 640 ) -> Option<String> {
 641     if let ast::ItemKind::Impl(_, _, _, ref generics, _, ref self_ty, ref items) = item.kind {
 642         let mut result = String::with_capacity(128);
 643         let ref_and_type = format_impl_ref_and_type(context, item, offset)?;
 644         let sep = offset.to_string_with_newline(context.config);
 645         result.push_str(&ref_and_type);
 646
 647         let where_budget = if result.contains('\n') {
 648             context.config.max_width()
 649         } else {
 650             context.budget(last_line_width(&result))
 651         };
 652
 653         let mut option = WhereClauseOption::snuggled(&ref_and_type);
 654         let snippet = context.snippet(item.span);
 655         let open_pos = snippet.find_uncommented("{")? + 1;
 656         if !contains_comment(&snippet[open_pos..])
 657             && items.is_empty()
 658             && generics.where_clause.predicates.len() == 1
 659             && !result.contains('\n')
 660         {
 661             option.suppress_comma();
 662             option.snuggle();
 663             option.allow_single_line();
 664         }
 665
 666         let missing_span = mk_sp(self_ty.span.hi(), item.span.hi());
 667         let where_span_end = context.snippet_provider.opt_span_before(missing_span, "{");
 668         let where_clause_str = rewrite_where_clause(
 669             context,
 670             &generics.where_clause,
 671             context.config.brace_style(),
 672             Shape::legacy(where_budget, offset.block_only()),
 673             false,
 674             "{",
 675             where_span_end,
 676             self_ty.span.hi(),
 677             option,
 678         )?;
 679
 680         // If there is no where-clause, we may have missing comments between the trait name and
 681         // the opening brace.
 682         if generics.where_clause.predicates.is_empty() {
 683             if let Some(hi) = where_span_end {
 684                 match recover_missing_comment_in_span(
 685                     mk_sp(self_ty.span.hi(), hi),
 686                     Shape::indented(offset, context.config),
 687                     context,
 688                     last_line_width(&result),
 689                 ) {
 690                     Some(ref missing_comment) if !missing_comment.is_empty() => {
 691                         result.push_str(missing_comment);
 692                     }
 693                     _ => (),
 694                 }
 695             }
 696         }
 697
 698         if is_impl_single_line(context, items, &result, &where_clause_str, item)? {
 699             result.push_str(&where_clause_str);
 700             if where_clause_str.contains('\n') || last_line_contains_single_line_comment(&result) {
 701                 // if the where_clause contains extra comments AND
 702                 // there is only one where-clause predicate
 703                 // recover the suppressed comma in single line where_clause formatting
 704                 if generics.where_clause.predicates.len() == 1 {
 705                     result.push_str(",");
 706                 }
 707                 result.push_str(&format!("{}{{{}}}", sep, sep));
 708             } else {
 709                 result.push_str(" {}");
 710             }
 711             return Some(result);
 712         }
 713
 714         result.push_str(&where_clause_str);
 715
 716         let need_newline = last_line_contains_single_line_comment(&result) || result.contains('\n');
 717         match context.config.brace_style() {
 718             _ if need_newline => result.push_str(&sep),
 719             BraceStyle::AlwaysNextLine => result.push_str(&sep),
 720             BraceStyle::PreferSameLine => result.push(' '),
 721             BraceStyle::SameLineWhere => {
 722                 if !where_clause_str.is_empty() {
 723                     result.push_str(&sep);
 724                 } else {
 725                     result.push(' ');
 726                 }
 727             }
 728         }
 729
 730         result.push('{');
 731         // this is an impl body snippet(impl SampleImpl { /* here */ })
 732         let lo = max(self_ty.span.hi(), generics.where_clause.span.hi());
 733         let snippet = context.snippet(mk_sp(lo, item.span.hi()));
 734         let open_pos = snippet.find_uncommented("{")? + 1;
 735
 736         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
 737             let mut visitor = FmtVisitor::from_context(context);
 738             let item_indent = offset.block_only().block_indent(context.config);
 739             visitor.block_indent = item_indent;
 740             visitor.last_pos = lo + BytePos(open_pos as u32);
 741
 742             visitor.visit_attrs(&item.attrs, ast::AttrStyle::Inner);
 743             visitor.visit_impl_items(items);
 744
 745             visitor.format_missing(item.span.hi() - BytePos(1));
 746
 747             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
 748             let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
 749
 750             result.push_str(&inner_indent_str);
 751             result.push_str(visitor.buffer.trim());
 752             result.push_str(&outer_indent_str);
 753         } else if need_newline || !context.config.empty_item_single_line() {
 754             result.push_str(&sep);
 755         }
 756
 757         result.push('}');
 758
 759         Some(result)
 760     } else {
 761         unreachable!();
 762     }
 763 }
 764
 765 fn is_impl_single_line(
 766     context: &RewriteContext<'_>,
 767     items: &[ast::ImplItem],
 768     result: &str,
 769     where_clause_str: &str,
 770     item: &ast::Item,
 771 ) -> Option<bool> {
 772     let snippet = context.snippet(item.span);
 773     let open_pos = snippet.find_uncommented("{")? + 1;
 774
 775     Some(
 776         context.config.empty_item_single_line()
 777             && items.is_empty()
 778             && !result.contains('\n')
 779             && result.len() + where_clause_str.len() <= context.config.max_width()
 780             && !contains_comment(&snippet[open_pos..]),
 781     )
 782 }
 783
 784 fn format_impl_ref_and_type(
 785     context: &RewriteContext<'_>,
 786     item: &ast::Item,
 787     offset: Indent,
 788 ) -> Option<String> {
 789     if let ast::ItemKind::Impl(
 790         unsafety,
 791         polarity,
 792         defaultness,
 793         ref generics,
 794         ref trait_ref,
 795         ref self_ty,
 796         _,
 797     ) = item.kind
 798     {
 799         let mut result = String::with_capacity(128);
 800
 801         result.push_str(&format_visibility(context, &item.vis));
 802         result.push_str(format_defaultness(defaultness));
 803         result.push_str(format_unsafety(unsafety));
 804
 805         let shape = if context.config.version() == Version::Two {
 806             Shape::indented(offset + last_line_width(&result), context.config)
 807         } else {
 808             generics_shape_from_config(
 809                 context.config,
 810                 Shape::indented(offset + last_line_width(&result), context.config),
 811                 0,
 812             )?
 813         };
 814         let generics_str = rewrite_generics(context, "impl", generics, shape)?;
 815         result.push_str(&generics_str);
 816
 817         let polarity_str = if polarity == ast::ImplPolarity::Negative {
 818             "!"
 819         } else {
 820             ""
 821         };
 822
 823         if let Some(ref trait_ref) = *trait_ref {
 824             let result_len = last_line_width(&result);
 825             result.push_str(&rewrite_trait_ref(
 826                 context,
 827                 trait_ref,
 828                 offset,
 829                 polarity_str,
 830                 result_len,
 831             )?);
 832         }
 833
 834         // Try to put the self type in a single line.
 835         // ` for`
 836         let trait_ref_overhead = if trait_ref.is_some() { 4 } else { 0 };
 837         let curly_brace_overhead = if generics.where_clause.predicates.is_empty() {
 838             // If there is no where-clause adapt budget for type formatting to take space and curly
 839             // brace into account.
 840             match context.config.brace_style() {
 841                 BraceStyle::AlwaysNextLine => 0,
 842                 _ => 2,
 843             }
 844         } else {
 845             0
 846         };
 847         let used_space = last_line_width(&result) + trait_ref_overhead + curly_brace_overhead;
 848         // 1 = space before the type.
 849         let budget = context.budget(used_space + 1);
 850         if let Some(self_ty_str) = self_ty.rewrite(context, Shape::legacy(budget, offset)) {
 851             if !self_ty_str.contains('\n') {
 852                 if trait_ref.is_some() {
 853                     result.push_str(" for ");
 854                 } else {
 855                     result.push(' ');
 856                 }
 857                 result.push_str(&self_ty_str);
 858                 return Some(result);
 859             }
 860         }
 861
 862         // Couldn't fit the self type on a single line, put it on a new line.
 863         result.push('\n');
 864         // Add indentation of one additional tab.
 865         let new_line_offset = offset.block_indent(context.config);
 866         result.push_str(&new_line_offset.to_string(context.config));
 867         if trait_ref.is_some() {
 868             result.push_str("for ");
 869         }
 870         let budget = context.budget(last_line_width(&result));
 871         let type_offset = match context.config.indent_style() {
 872             IndentStyle::Visual => new_line_offset + trait_ref_overhead,
 873             IndentStyle::Block => new_line_offset,
 874         };
 875         result.push_str(&*self_ty.rewrite(context, Shape::legacy(budget, type_offset))?);
 876         Some(result)
 877     } else {
 878         unreachable!();
 879     }
 880 }
 881
 882 fn rewrite_trait_ref(
 883     context: &RewriteContext<'_>,
 884     trait_ref: &ast::TraitRef,
 885     offset: Indent,
 886     polarity_str: &str,
 887     result_len: usize,
 888 ) -> Option<String> {
 889     // 1 = space between generics and trait_ref
 890     let used_space = 1 + polarity_str.len() + result_len;
 891     let shape = Shape::indented(offset + used_space, context.config);
 892     if let Some(trait_ref_str) = trait_ref.rewrite(context, shape) {
 893         if !trait_ref_str.contains('\n') {
 894             return Some(format!(" {}{}", polarity_str, trait_ref_str));
 895         }
 896     }
 897     // We could not make enough space for trait_ref, so put it on new line.
 898     let offset = offset.block_indent(context.config);
 899     let shape = Shape::indented(offset, context.config);
 900     let trait_ref_str = trait_ref.rewrite(context, shape)?;
 901     Some(format!(
 902         "{}{}{}",
 903         offset.to_string_with_newline(context.config),
 904         polarity_str,
 905         trait_ref_str
 906     ))
 907 }
 908
 909 pub(crate) struct StructParts<'a> {
 910     prefix: &'a str,
 911     ident: ast::Ident,
 912     vis: &'a ast::Visibility,
 913     def: &'a ast::VariantData,
 914     generics: Option<&'a ast::Generics>,
 915     span: Span,
 916 }
 917
 918 impl<'a> StructParts<'a> {
 919     fn format_header(&self, context: &RewriteContext<'_>) -> String {
 920         format_header(context, self.prefix, self.ident, self.vis)
 921     }
 922
 923     fn from_variant(variant: &'a ast::Variant) -> Self {
 924         StructParts {
 925             prefix: "",
 926             ident: variant.ident,
 927             vis: &DEFAULT_VISIBILITY,
 928             def: &variant.data,
 929             generics: None,
 930             span: variant.span,
 931         }
 932     }
 933
 934     pub(crate) fn from_item(item: &'a ast::Item) -> Self {
 935         let (prefix, def, generics) = match item.kind {
 936             ast::ItemKind::Struct(ref def, ref generics) => ("struct ", def, generics),
 937             ast::ItemKind::Union(ref def, ref generics) => ("union ", def, generics),
 938             _ => unreachable!(),
 939         };
 940         StructParts {
 941             prefix,
 942             ident: item.ident,
 943             vis: &item.vis,
 944             def,
 945             generics: Some(generics),
 946             span: item.span,
 947         }
 948     }
 949 }
 950
 951 fn format_struct(
 952     context: &RewriteContext<'_>,
 953     struct_parts: &StructParts<'_>,
 954     offset: Indent,
 955     one_line_width: Option<usize>,
 956 ) -> Option<String> {
 957     match *struct_parts.def {
 958         ast::VariantData::Unit(..) => format_unit_struct(context, struct_parts, offset),
 959         ast::VariantData::Tuple(ref fields, _) => {
 960             format_tuple_struct(context, struct_parts, fields, offset)
 961         }
 962         ast::VariantData::Struct(ref fields, _) => {
 963             format_struct_struct(context, struct_parts, fields, offset, one_line_width)
 964         }
 965     }
 966 }
 967
 968 pub(crate) fn format_trait(
 969     context: &RewriteContext<'_>,
 970     item: &ast::Item,
 971     offset: Indent,
 972 ) -> Option<String> {
 973     if let ast::ItemKind::Trait(
 974         is_auto,
 975         unsafety,
 976         ref generics,
 977         ref generic_bounds,
 978         ref trait_items,
 979     ) = item.kind
 980     {
 981         let mut result = String::with_capacity(128);
 982         let header = format!(
 983             "{}{}{}trait ",
 984             format_visibility(context, &item.vis),
 985             format_unsafety(unsafety),
 986             format_auto(is_auto),
 987         );
 988         result.push_str(&header);
 989
 990         let body_lo = context.snippet_provider.span_after(item.span, "{");
 991
 992         let shape = Shape::indented(offset, context.config).offset_left(result.len())?;
 993         let generics_str =
 994             rewrite_generics(context, rewrite_ident(context, item.ident), generics, shape)?;
 995         result.push_str(&generics_str);
 996
 997         // FIXME(#2055): rustfmt fails to format when there are comments between trait bounds.
 998         if !generic_bounds.is_empty() {
 999             let ident_hi = context
1000                 .snippet_provider
1001                 .span_after(item.span, &item.ident.as_str());
1002             let bound_hi = generic_bounds.last().unwrap().span().hi();
1003             let snippet = context.snippet(mk_sp(ident_hi, bound_hi));
1004             if contains_comment(snippet) {
1005                 return None;
1006             }
1007
1008             result = rewrite_assign_rhs_with(
1009                 context,
1010                 result + ":",
1011                 generic_bounds,
1012                 shape,
1013                 RhsTactics::ForceNextLineWithoutIndent,
1014             )?;
1015         }
1016
1017         // Rewrite where-clause.
1018         if !generics.where_clause.predicates.is_empty() {
1019             let where_on_new_line = context.config.indent_style() != IndentStyle::Block;
1020
1021             let where_budget = context.budget(last_line_width(&result));
1022             let pos_before_where = if generic_bounds.is_empty() {
1023                 generics.where_clause.span.lo()
1024             } else {
1025                 generic_bounds[generic_bounds.len() - 1].span().hi()
1026             };
1027             let option = WhereClauseOption::snuggled(&generics_str);
1028             let where_clause_str = rewrite_where_clause(
1029                 context,
1030                 &generics.where_clause,
1031                 context.config.brace_style(),
1032                 Shape::legacy(where_budget, offset.block_only()),
1033                 where_on_new_line,
1034                 "{",
1035                 None,
1036                 pos_before_where,
1037                 option,
1038             )?;
1039             // If the where-clause cannot fit on the same line,
1040             // put the where-clause on a new line
1041             if !where_clause_str.contains('\n')
1042                 && last_line_width(&result) + where_clause_str.len() + offset.width()
1043                     > context.config.comment_width()
1044             {
1045                 let width = offset.block_indent + context.config.tab_spaces() - 1;
1046                 let where_indent = Indent::new(0, width);
1047                 result.push_str(&where_indent.to_string_with_newline(context.config));
1048             }
1049             result.push_str(&where_clause_str);
1050         } else {
1051             let item_snippet = context.snippet(item.span);
1052             if let Some(lo) = item_snippet.find('/') {
1053                 // 1 = `{`
1054                 let comment_hi = body_lo - BytePos(1);
1055                 let comment_lo = item.span.lo() + BytePos(lo as u32);
1056                 if comment_lo < comment_hi {
1057                     match recover_missing_comment_in_span(
1058                         mk_sp(comment_lo, comment_hi),
1059                         Shape::indented(offset, context.config),
1060                         context,
1061                         last_line_width(&result),
1062                     ) {
1063                         Some(ref missing_comment) if !missing_comment.is_empty() => {
1064                             result.push_str(missing_comment);
1065                         }
1066                         _ => (),
1067                     }
1068                 }
1069             }
1070         }
1071
1072         match context.config.brace_style() {
1073             _ if last_line_contains_single_line_comment(&result)
1074                 || last_line_width(&result) + 2 > context.budget(offset.width()) =>
1075             {
1076                 result.push_str(&offset.to_string_with_newline(context.config));
1077             }
1078             BraceStyle::AlwaysNextLine => {
1079                 result.push_str(&offset.to_string_with_newline(context.config));
1080             }
1081             BraceStyle::PreferSameLine => result.push(' '),
1082             BraceStyle::SameLineWhere => {
1083                 if result.contains('\n')
1084                     || (!generics.where_clause.predicates.is_empty() && !trait_items.is_empty())
1085                 {
1086                     result.push_str(&offset.to_string_with_newline(context.config));
1087                 } else {
1088                     result.push(' ');
1089                 }
1090             }
1091         }
1092         result.push('{');
1093
1094         let snippet = context.snippet(item.span);
1095         let open_pos = snippet.find_uncommented("{")? + 1;
1096         let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
1097
1098         if !trait_items.is_empty() || contains_comment(&snippet[open_pos..]) {
1099             let mut visitor = FmtVisitor::from_context(context);
1100             visitor.block_indent = offset.block_only().block_indent(context.config);
1101             visitor.last_pos = item.span.lo() + BytePos(open_pos as u32);
1102
1103             for item in trait_items {
1104                 visitor.visit_trait_item(item);
1105             }
1106
1107             visitor.format_missing(item.span.hi() - BytePos(1));
1108
1109             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
1110
1111             result.push_str(&inner_indent_str);
1112             result.push_str(visitor.buffer.trim());
1113             result.push_str(&outer_indent_str);
1114         } else if result.contains('\n') {
1115             result.push_str(&outer_indent_str);
1116         }
1117
1118         result.push('}');
1119         Some(result)
1120     } else {
1121         unreachable!();
1122     }
1123 }
1124
1125 struct OpaqueTypeBounds<'a> {
1126     generic_bounds: &'a ast::GenericBounds,
1127 }
1128
1129 impl<'a> Rewrite for OpaqueTypeBounds<'a> {
1130     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1131         self.generic_bounds
1132             .rewrite(context, shape)
1133             .map(|s| format!("impl {}", s))
1134     }
1135 }
1136
1137 pub(crate) struct TraitAliasBounds<'a> {
1138     generic_bounds: &'a ast::GenericBounds,
1139     generics: &'a ast::Generics,
1140 }
1141
1142 impl<'a> Rewrite for TraitAliasBounds<'a> {
1143     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1144         let generic_bounds_str = self.generic_bounds.rewrite(context, shape)?;
1145
1146         let mut option = WhereClauseOption::new(true, WhereClauseSpace::None);
1147         option.allow_single_line();
1148
1149         let where_str = rewrite_where_clause(
1150             context,
1151             &self.generics.where_clause,
1152             context.config.brace_style(),
1153             shape,
1154             false,
1155             ";",
1156             None,
1157             self.generics.where_clause.span.lo(),
1158             option,
1159         )?;
1160
1161         let fits_single_line = !generic_bounds_str.contains('\n')
1162             && !where_str.contains('\n')
1163             && generic_bounds_str.len() + where_str.len() + 1 <= shape.width;
1164         let space = if generic_bounds_str.is_empty() || where_str.is_empty() {
1165             Cow::from("")
1166         } else if fits_single_line {
1167             Cow::from(" ")
1168         } else {
1169             shape.indent.to_string_with_newline(&context.config)
1170         };
1171
1172         Some(format!("{}{}{}", generic_bounds_str, space, where_str))
1173     }
1174 }
1175
1176 pub(crate) fn format_trait_alias(
1177     context: &RewriteContext<'_>,
1178     ident: ast::Ident,
1179     vis: &ast::Visibility,
1180     generics: &ast::Generics,
1181     generic_bounds: &ast::GenericBounds,
1182     shape: Shape,
1183 ) -> Option<String> {
1184     let alias = rewrite_ident(context, ident);
1185     // 6 = "trait ", 2 = " ="
1186     let g_shape = shape.offset_left(6)?.sub_width(2)?;
1187     let generics_str = rewrite_generics(context, &alias, generics, g_shape)?;
1188     let vis_str = format_visibility(context, vis);
1189     let lhs = format!("{}trait {} =", vis_str, generics_str);
1190     // 1 = ";"
1191     let trait_alias_bounds = TraitAliasBounds {
1192         generics,
1193         generic_bounds,
1194     };
1195     rewrite_assign_rhs(context, lhs, &trait_alias_bounds, shape.sub_width(1)?).map(|s| s + ";")
1196 }
1197
1198 fn format_unit_struct(
1199     context: &RewriteContext<'_>,
1200     p: &StructParts<'_>,
1201     offset: Indent,
1202 ) -> Option<String> {
1203     let header_str = format_header(context, p.prefix, p.ident, p.vis);
1204     let generics_str = if let Some(generics) = p.generics {
1205         let hi = context.snippet_provider.span_before(p.span, ";");
1206         format_generics(
1207             context,
1208             generics,
1209             context.config.brace_style(),
1210             BracePos::None,
1211             offset,
1212             // make a span that starts right after `struct Foo`
1213             mk_sp(p.ident.span.hi(), hi),
1214             last_line_width(&header_str),
1215         )?
1216     } else {
1217         String::new()
1218     };
1219     Some(format!("{}{};", header_str, generics_str))
1220 }
1221
1222 pub(crate) fn format_struct_struct(
1223     context: &RewriteContext<'_>,
1224     struct_parts: &StructParts<'_>,
1225     fields: &[ast::StructField],
1226     offset: Indent,
1227     one_line_width: Option<usize>,
1228 ) -> Option<String> {
1229     let mut result = String::with_capacity(1024);
1230     let span = struct_parts.span;
1231
1232     let header_str = struct_parts.format_header(context);
1233     result.push_str(&header_str);
1234
1235     let header_hi = struct_parts.ident.span.hi();
1236     let body_lo = context.snippet_provider.span_after(span, "{");
1237
1238     let generics_str = match struct_parts.generics {
1239         Some(g) => format_generics(
1240             context,
1241             g,
1242             context.config.brace_style(),
1243             if fields.is_empty() {
1244                 BracePos::ForceSameLine
1245             } else {
1246                 BracePos::Auto
1247             },
1248             offset,
1249             // make a span that starts right after `struct Foo`
1250             mk_sp(header_hi, body_lo),
1251             last_line_width(&result),
1252         )?,
1253         None => {
1254             // 3 = ` {}`, 2 = ` {`.
1255             let overhead = if fields.is_empty() { 3 } else { 2 };
1256             if (context.config.brace_style() == BraceStyle::AlwaysNextLine && !fields.is_empty())
1257                 || context.config.max_width() < overhead + result.len()
1258             {
1259                 format!("\n{}{{", offset.block_only().to_string(context.config))
1260             } else {
1261                 " {".to_owned()
1262             }
1263         }
1264     };
1265     // 1 = `}`
1266     let overhead = if fields.is_empty() { 1 } else { 0 };
1267     let total_width = result.len() + generics_str.len() + overhead;
1268     if !generics_str.is_empty()
1269         && !generics_str.contains('\n')
1270         && total_width > context.config.max_width()
1271     {
1272         result.push('\n');
1273         result.push_str(&offset.to_string(context.config));
1274         result.push_str(generics_str.trim_start());
1275     } else {
1276         result.push_str(&generics_str);
1277     }
1278
1279     if fields.is_empty() {
1280         let inner_span = mk_sp(body_lo, span.hi() - BytePos(1));
1281         format_empty_struct_or_tuple(context, inner_span, offset, &mut result, "", "}");
1282         return Some(result);
1283     }
1284
1285     // 3 = ` ` and ` }`
1286     let one_line_budget = context.budget(result.len() + 3 + offset.width());
1287     let one_line_budget =
1288         one_line_width.map_or(0, |one_line_width| min(one_line_width, one_line_budget));
1289
1290     let items_str = rewrite_with_alignment(
1291         fields,
1292         context,
1293         Shape::indented(offset.block_indent(context.config), context.config).sub_width(1)?,
1294         mk_sp(body_lo, span.hi()),
1295         one_line_budget,
1296     )?;
1297
1298     if !items_str.contains('\n')
1299         && !result.contains('\n')
1300         && items_str.len() <= one_line_budget
1301         && !last_line_contains_single_line_comment(&items_str)
1302     {
1303         Some(format!("{} {} }}", result, items_str))
1304     } else {
1305         Some(format!(
1306             "{}\n{}{}\n{}}}",
1307             result,
1308             offset
1309                 .block_indent(context.config)
1310                 .to_string(context.config),
1311             items_str,
1312             offset.to_string(context.config)
1313         ))
1314     }
1315 }
1316
1317 fn get_bytepos_after_visibility(vis: &ast::Visibility, default_span: Span) -> BytePos {
1318     match vis.node {
1319         ast::VisibilityKind::Crate(..) | ast::VisibilityKind::Restricted { .. } => vis.span.hi(),
1320         _ => default_span.lo(),
1321     }
1322 }
1323
1324 // Format tuple or struct without any fields. We need to make sure that the comments
1325 // inside the delimiters are preserved.
1326 fn format_empty_struct_or_tuple(
1327     context: &RewriteContext<'_>,
1328     span: Span,
1329     offset: Indent,
1330     result: &mut String,
1331     opener: &str,
1332     closer: &str,
1333 ) {
1334     // 3 = " {}" or "();"
1335     let used_width = last_line_used_width(&result, offset.width()) + 3;
1336     if used_width > context.config.max_width() {
1337         result.push_str(&offset.to_string_with_newline(context.config))
1338     }
1339     result.push_str(opener);
1340     match rewrite_missing_comment(span, Shape::indented(offset, context.config), context) {
1341         Some(ref s) if s.is_empty() => (),
1342         Some(ref s) => {
1343             if !is_single_line(s) || first_line_contains_single_line_comment(s) {
1344                 let nested_indent_str = offset
1345                     .block_indent(context.config)
1346                     .to_string_with_newline(context.config);
1347                 result.push_str(&nested_indent_str);
1348             }
1349             result.push_str(s);
1350             if last_line_contains_single_line_comment(s) {
1351                 result.push_str(&offset.to_string_with_newline(context.config));
1352             }
1353         }
1354         None => result.push_str(context.snippet(span)),
1355     }
1356     result.push_str(closer);
1357 }
1358
1359 fn format_tuple_struct(
1360     context: &RewriteContext<'_>,
1361     struct_parts: &StructParts<'_>,
1362     fields: &[ast::StructField],
1363     offset: Indent,
1364 ) -> Option<String> {
1365     let mut result = String::with_capacity(1024);
1366     let span = struct_parts.span;
1367
1368     let header_str = struct_parts.format_header(context);
1369     result.push_str(&header_str);
1370
1371     let body_lo = if fields.is_empty() {
1372         let lo = get_bytepos_after_visibility(struct_parts.vis, span);
1373         context
1374             .snippet_provider
1375             .span_after(mk_sp(lo, span.hi()), "(")
1376     } else {
1377         fields[0].span.lo()
1378     };
1379     let body_hi = if fields.is_empty() {
1380         context
1381             .snippet_provider
1382             .span_after(mk_sp(body_lo, span.hi()), ")")
1383     } else {
1384         // This is a dirty hack to work around a missing `)` from the span of the last field.
1385         let last_arg_span = fields[fields.len() - 1].span;
1386         context
1387             .snippet_provider
1388             .opt_span_after(mk_sp(last_arg_span.hi(), span.hi()), ")")
1389             .unwrap_or_else(|| last_arg_span.hi())
1390     };
1391
1392     let where_clause_str = match struct_parts.generics {
1393         Some(generics) => {
1394             let budget = context.budget(last_line_width(&header_str));
1395             let shape = Shape::legacy(budget, offset);
1396             let generics_str = rewrite_generics(context, "", generics, shape)?;
1397             result.push_str(&generics_str);
1398
1399             let where_budget = context.budget(last_line_width(&result));
1400             let option = WhereClauseOption::new(true, WhereClauseSpace::Newline);
1401             rewrite_where_clause(
1402                 context,
1403                 &generics.where_clause,
1404                 context.config.brace_style(),
1405                 Shape::legacy(where_budget, offset.block_only()),
1406                 false,
1407                 ";",
1408                 None,
1409                 body_hi,
1410                 option,
1411             )?
1412         }
1413         None => "".to_owned(),
1414     };
1415
1416     if fields.is_empty() {
1417         let body_hi = context
1418             .snippet_provider
1419             .span_before(mk_sp(body_lo, span.hi()), ")");
1420         let inner_span = mk_sp(body_lo, body_hi);
1421         format_empty_struct_or_tuple(context, inner_span, offset, &mut result, "(", ")");
1422     } else {
1423         let shape = Shape::indented(offset, context.config).sub_width(1)?;
1424         result = overflow::rewrite_with_parens(
1425             context,
1426             &result,
1427             fields.iter(),
1428             shape,
1429             span,
1430             context.config.width_heuristics().fn_call_width,
1431             None,
1432         )?;
1433     }
1434
1435     if !where_clause_str.is_empty()
1436         && !where_clause_str.contains('\n')
1437         && (result.contains('\n')
1438             || offset.block_indent + result.len() + where_clause_str.len() + 1
1439                 > context.config.max_width())
1440     {
1441         // We need to put the where-clause on a new line, but we didn't
1442         // know that earlier, so the where-clause will not be indented properly.
1443         result.push('\n');
1444         result.push_str(
1445             &(offset.block_only() + (context.config.tab_spaces() - 1)).to_string(context.config),
1446         );
1447     }
1448     result.push_str(&where_clause_str);
1449
1450     Some(result)
1451 }
1452
1453 fn rewrite_type_prefix(
1454     context: &RewriteContext<'_>,
1455     indent: Indent,
1456     prefix: &str,
1457     ident: ast::Ident,
1458     generics: &ast::Generics,
1459 ) -> Option<String> {
1460     let mut result = String::with_capacity(128);
1461     result.push_str(prefix);
1462     let ident_str = rewrite_ident(context, ident);
1463
1464     // 2 = `= `
1465     if generics.params.is_empty() {
1466         result.push_str(ident_str)
1467     } else {
1468         let g_shape = Shape::indented(indent, context.config)
1469             .offset_left(result.len())?
1470             .sub_width(2)?;
1471         let generics_str = rewrite_generics(context, ident_str, generics, g_shape)?;
1472         result.push_str(&generics_str);
1473     }
1474
1475     let where_budget = context.budget(last_line_width(&result));
1476     let option = WhereClauseOption::snuggled(&result);
1477     let where_clause_str = rewrite_where_clause(
1478         context,
1479         &generics.where_clause,
1480         context.config.brace_style(),
1481         Shape::legacy(where_budget, indent),
1482         false,
1483         "=",
1484         None,
1485         generics.span.hi(),
1486         option,
1487     )?;
1488     result.push_str(&where_clause_str);
1489
1490     Some(result)
1491 }
1492
1493 fn rewrite_type_item<R: Rewrite>(
1494     context: &RewriteContext<'_>,
1495     indent: Indent,
1496     prefix: &str,
1497     suffix: &str,
1498     ident: ast::Ident,
1499     rhs: &R,
1500     generics: &ast::Generics,
1501     vis: &ast::Visibility,
1502 ) -> Option<String> {
1503     let mut result = String::with_capacity(128);
1504     result.push_str(&rewrite_type_prefix(
1505         context,
1506         indent,
1507         &format!("{}{} ", format_visibility(context, vis), prefix),
1508         ident,
1509         generics,
1510     )?);
1511
1512     if generics.where_clause.predicates.is_empty() {
1513         result.push_str(suffix);
1514     } else {
1515         result.push_str(&indent.to_string_with_newline(context.config));
1516         result.push_str(suffix.trim_start());
1517     }
1518
1519     // 1 = ";"
1520     let rhs_shape = Shape::indented(indent, context.config).sub_width(1)?;
1521     rewrite_assign_rhs(context, result, rhs, rhs_shape).map(|s| s + ";")
1522 }
1523
1524 pub(crate) fn rewrite_type_alias(
1525     context: &RewriteContext<'_>,
1526     indent: Indent,
1527     ident: ast::Ident,
1528     ty: &ast::Ty,
1529     generics: &ast::Generics,
1530     vis: &ast::Visibility,
1531 ) -> Option<String> {
1532     rewrite_type_item(context, indent, "type", " =", ident, ty, generics, vis)
1533 }
1534
1535 pub(crate) fn rewrite_opaque_type(
1536     context: &RewriteContext<'_>,
1537     indent: Indent,
1538     ident: ast::Ident,
1539     generic_bounds: &ast::GenericBounds,
1540     generics: &ast::Generics,
1541     vis: &ast::Visibility,
1542 ) -> Option<String> {
1543     let opaque_type_bounds = OpaqueTypeBounds { generic_bounds };
1544     rewrite_type_item(
1545         context,
1546         indent,
1547         "type",
1548         " =",
1549         ident,
1550         &opaque_type_bounds,
1551         generics,
1552         vis,
1553     )
1554 }
1555
1556 fn type_annotation_spacing(config: &Config) -> (&str, &str) {
1557     (
1558         if config.space_before_colon() { " " } else { "" },
1559         if config.space_after_colon() { " " } else { "" },
1560     )
1561 }
1562
1563 pub(crate) fn rewrite_struct_field_prefix(
1564     context: &RewriteContext<'_>,
1565     field: &ast::StructField,
1566 ) -> Option<String> {
1567     let vis = format_visibility(context, &field.vis);
1568     let type_annotation_spacing = type_annotation_spacing(context.config);
1569     Some(match field.ident {
1570         Some(name) => format!(
1571             "{}{}{}:",
1572             vis,
1573             rewrite_ident(context, name),
1574             type_annotation_spacing.0
1575         ),
1576         None => vis.to_string(),
1577     })
1578 }
1579
1580 impl Rewrite for ast::StructField {
1581     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1582         rewrite_struct_field(context, self, shape, 0)
1583     }
1584 }
1585
1586 pub(crate) fn rewrite_struct_field(
1587     context: &RewriteContext<'_>,
1588     field: &ast::StructField,
1589     shape: Shape,
1590     lhs_max_width: usize,
1591 ) -> Option<String> {
1592     if contains_skip(&field.attrs) {
1593         return Some(context.snippet(field.span()).to_owned());
1594     }
1595
1596     let type_annotation_spacing = type_annotation_spacing(context.config);
1597     let prefix = rewrite_struct_field_prefix(context, field)?;
1598
1599     let attrs_str = field.attrs.rewrite(context, shape)?;
1600     let attrs_extendable = field.ident.is_none() && is_attributes_extendable(&attrs_str);
1601     let missing_span = if field.attrs.is_empty() {
1602         mk_sp(field.span.lo(), field.span.lo())
1603     } else {
1604         mk_sp(field.attrs.last().unwrap().span.hi(), field.span.lo())
1605     };
1606     let mut spacing = String::from(if field.ident.is_some() {
1607         type_annotation_spacing.1
1608     } else {
1609         ""
1610     });
1611     // Try to put everything on a single line.
1612     let attr_prefix = combine_strs_with_missing_comments(
1613         context,
1614         &attrs_str,
1615         &prefix,
1616         missing_span,
1617         shape,
1618         attrs_extendable,
1619     )?;
1620     let overhead = last_line_width(&attr_prefix);
1621     let lhs_offset = lhs_max_width.saturating_sub(overhead);
1622     for _ in 0..lhs_offset {
1623         spacing.push(' ');
1624     }
1625     // In this extreme case we will be missing a space between an attribute and a field.
1626     if prefix.is_empty() && !attrs_str.is_empty() && attrs_extendable && spacing.is_empty() {
1627         spacing.push(' ');
1628     }
1629     let orig_ty = shape
1630         .offset_left(overhead + spacing.len())
1631         .and_then(|ty_shape| field.ty.rewrite(context, ty_shape));
1632     if let Some(ref ty) = orig_ty {
1633         if !ty.contains('\n') {
1634             return Some(attr_prefix + &spacing + ty);
1635         }
1636     }
1637
1638     let is_prefix_empty = prefix.is_empty();
1639     // We must use multiline. We are going to put attributes and a field on different lines.
1640     let field_str = rewrite_assign_rhs(context, prefix, &*field.ty, shape)?;
1641     // Remove a leading white-space from `rewrite_assign_rhs()` when rewriting a tuple struct.
1642     let field_str = if is_prefix_empty {
1643         field_str.trim_start()
1644     } else {
1645         &field_str
1646     };
1647     combine_strs_with_missing_comments(context, &attrs_str, field_str, missing_span, shape, false)
1648 }
1649
1650 pub(crate) struct StaticParts<'a> {
1651     prefix: &'a str,
1652     vis: &'a ast::Visibility,
1653     ident: ast::Ident,
1654     ty: &'a ast::Ty,
1655     mutability: ast::Mutability,
1656     expr_opt: Option<&'a ptr::P<ast::Expr>>,
1657     defaultness: Option<ast::Defaultness>,
1658     span: Span,
1659 }
1660
1661 impl<'a> StaticParts<'a> {
1662     pub(crate) fn from_item(item: &'a ast::Item) -> Self {
1663         let (prefix, ty, mutability, expr) = match item.kind {
1664             ast::ItemKind::Static(ref ty, mutability, ref expr) => ("static", ty, mutability, expr),
1665             ast::ItemKind::Const(ref ty, ref expr) => {
1666                 ("const", ty, ast::Mutability::Immutable, expr)
1667             }
1668             _ => unreachable!(),
1669         };
1670         StaticParts {
1671             prefix,
1672             vis: &item.vis,
1673             ident: item.ident,
1674             ty,
1675             mutability,
1676             expr_opt: Some(expr),
1677             defaultness: None,
1678             span: item.span,
1679         }
1680     }
1681
1682     pub(crate) fn from_trait_item(ti: &'a ast::TraitItem) -> Self {
1683         let (ty, expr_opt) = match ti.kind {
1684             ast::TraitItemKind::Const(ref ty, ref expr_opt) => (ty, expr_opt),
1685             _ => unreachable!(),
1686         };
1687         StaticParts {
1688             prefix: "const",
1689             vis: &DEFAULT_VISIBILITY,
1690             ident: ti.ident,
1691             ty,
1692             mutability: ast::Mutability::Immutable,
1693             expr_opt: expr_opt.as_ref(),
1694             defaultness: None,
1695             span: ti.span,
1696         }
1697     }
1698
1699     pub(crate) fn from_impl_item(ii: &'a ast::ImplItem) -> Self {
1700         let (ty, expr) = match ii.kind {
1701             ast::ImplItemKind::Const(ref ty, ref expr) => (ty, expr),
1702             _ => unreachable!(),
1703         };
1704         StaticParts {
1705             prefix: "const",
1706             vis: &ii.vis,
1707             ident: ii.ident,
1708             ty,
1709             mutability: ast::Mutability::Immutable,
1710             expr_opt: Some(expr),
1711             defaultness: Some(ii.defaultness),
1712             span: ii.span,
1713         }
1714     }
1715 }
1716
1717 fn rewrite_static(
1718     context: &RewriteContext<'_>,
1719     static_parts: &StaticParts<'_>,
1720     offset: Indent,
1721 ) -> Option<String> {
1722     let colon = colon_spaces(context.config);
1723     let mut prefix = format!(
1724         "{}{}{} {}{}{}",
1725         format_visibility(context, static_parts.vis),
1726         static_parts.defaultness.map_or("", format_defaultness),
1727         static_parts.prefix,
1728         format_mutability(static_parts.mutability),
1729         rewrite_ident(context, static_parts.ident),
1730         colon,
1731     );
1732     // 2 = " =".len()
1733     let ty_shape =
1734         Shape::indented(offset.block_only(), context.config).offset_left(prefix.len() + 2)?;
1735     let ty_str = match static_parts.ty.rewrite(context, ty_shape) {
1736         Some(ty_str) => ty_str,
1737         None => {
1738             if prefix.ends_with(' ') {
1739                 prefix.pop();
1740             }
1741             let nested_indent = offset.block_indent(context.config);
1742             let nested_shape = Shape::indented(nested_indent, context.config);
1743             let ty_str = static_parts.ty.rewrite(context, nested_shape)?;
1744             format!(
1745                 "{}{}",
1746                 nested_indent.to_string_with_newline(context.config),
1747                 ty_str
1748             )
1749         }
1750     };
1751
1752     if let Some(expr) = static_parts.expr_opt {
1753         let lhs = format!("{}{} =", prefix, ty_str);
1754         // 1 = ;
1755         let remaining_width = context.budget(offset.block_indent + 1);
1756         rewrite_assign_rhs(
1757             context,
1758             lhs,
1759             &**expr,
1760             Shape::legacy(remaining_width, offset.block_only()),
1761         )
1762         .and_then(|res| recover_comment_removed(res, static_parts.span, context))
1763         .map(|s| if s.ends_with(';') { s } else { s + ";" })
1764     } else {
1765         Some(format!("{}{};", prefix, ty_str))
1766     }
1767 }
1768
1769 pub(crate) fn rewrite_associated_type(
1770     ident: ast::Ident,
1771     ty_opt: Option<&ptr::P<ast::Ty>>,
1772     generics: &ast::Generics,
1773     generic_bounds_opt: Option<&ast::GenericBounds>,
1774     context: &RewriteContext<'_>,
1775     indent: Indent,
1776 ) -> Option<String> {
1777     let ident_str = rewrite_ident(context, ident);
1778     // 5 = "type "
1779     let generics_shape = Shape::indented(indent, context.config).offset_left(5)?;
1780     let generics_str = rewrite_generics(context, ident_str, generics, generics_shape)?;
1781     let prefix = format!("type {}", generics_str);
1782
1783     let type_bounds_str = if let Some(bounds) = generic_bounds_opt {
1784         if bounds.is_empty() {
1785             String::new()
1786         } else {
1787             // 2 = ": ".len()
1788             let shape = Shape::indented(indent, context.config).offset_left(prefix.len() + 2)?;
1789             bounds.rewrite(context, shape).map(|s| format!(": {}", s))?
1790         }
1791     } else {
1792         String::new()
1793     };
1794
1795     if let Some(ty) = ty_opt {
1796         // 1 = `;`
1797         let shape = Shape::indented(indent, context.config).sub_width(1)?;
1798         let lhs = format!("{}{} =", prefix, type_bounds_str);
1799         rewrite_assign_rhs(context, lhs, &**ty, shape).map(|s| s + ";")
1800     } else {
1801         Some(format!("{}{};", prefix, type_bounds_str))
1802     }
1803 }
1804
1805 struct OpaqueType<'a> {
1806     bounds: &'a ast::GenericBounds,
1807 }
1808
1809 impl<'a> Rewrite for OpaqueType<'a> {
1810     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1811         let shape = shape.offset_left(5)?; // `impl `
1812         self.bounds
1813             .rewrite(context, shape)
1814             .map(|s| format!("impl {}", s))
1815     }
1816 }
1817
1818 pub(crate) fn rewrite_opaque_impl_type(
1819     context: &RewriteContext<'_>,
1820     ident: ast::Ident,
1821     generics: &ast::Generics,
1822     generic_bounds: &ast::GenericBounds,
1823     indent: Indent,
1824 ) -> Option<String> {
1825     let ident_str = rewrite_ident(context, ident);
1826     // 5 = "type "
1827     let generics_shape = Shape::indented(indent, context.config).offset_left(5)?;
1828     let generics_str = rewrite_generics(context, ident_str, generics, generics_shape)?;
1829     let prefix = format!("type {} =", generics_str);
1830     let rhs = OpaqueType {
1831         bounds: generic_bounds,
1832     };
1833
1834     rewrite_assign_rhs(
1835         context,
1836         &prefix,
1837         &rhs,
1838         Shape::indented(indent, context.config).sub_width(1)?,
1839     )
1840     .map(|s| s + ";")
1841 }
1842
1843 pub(crate) fn rewrite_associated_impl_type(
1844     ident: ast::Ident,
1845     defaultness: ast::Defaultness,
1846     ty_opt: Option<&ptr::P<ast::Ty>>,
1847     generics: &ast::Generics,
1848     context: &RewriteContext<'_>,
1849     indent: Indent,
1850 ) -> Option<String> {
1851     let result = rewrite_associated_type(ident, ty_opt, generics, None, context, indent)?;
1852
1853     match defaultness {
1854         ast::Defaultness::Default => Some(format!("default {}", result)),
1855         _ => Some(result),
1856     }
1857 }
1858
1859 impl Rewrite for ast::FunctionRetTy {
1860     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1861         match *self {
1862             ast::FunctionRetTy::Default(_) => Some(String::new()),
1863             ast::FunctionRetTy::Ty(ref ty) => {
1864                 if context.config.version() == Version::One
1865                     || context.config.indent_style() == IndentStyle::Visual
1866                 {
1867                     let inner_width = shape.width.checked_sub(3)?;
1868                     return ty
1869                         .rewrite(context, Shape::legacy(inner_width, shape.indent + 3))
1870                         .map(|r| format!("-> {}", r));
1871                 }
1872
1873                 ty.rewrite(context, shape.offset_left(3)?)
1874                     .map(|s| format!("-> {}", s))
1875             }
1876         }
1877     }
1878 }
1879
1880 fn is_empty_infer(ty: &ast::Ty, pat_span: Span) -> bool {
1881     match ty.kind {
1882         ast::TyKind::Infer => ty.span.hi() == pat_span.hi(),
1883         _ => false,
1884     }
1885 }
1886
1887 /// Recover any missing comments between the param and the type.
1888 ///
1889 /// # Returns
1890 ///
1891 /// A 2-len tuple with the comment before the colon in first position, and the comment after the
1892 /// colon in second position.
1893 fn get_missing_param_comments(
1894     context: &RewriteContext<'_>,
1895     pat_span: Span,
1896     ty_span: Span,
1897     shape: Shape,
1898 ) -> (String, String) {
1899     let missing_comment_span = mk_sp(pat_span.hi(), ty_span.lo());
1900
1901     let span_before_colon = {
1902         let missing_comment_span_hi = context
1903             .snippet_provider
1904             .span_before(missing_comment_span, ":");
1905         mk_sp(pat_span.hi(), missing_comment_span_hi)
1906     };
1907     let span_after_colon = {
1908         let missing_comment_span_lo = context
1909             .snippet_provider
1910             .span_after(missing_comment_span, ":");
1911         mk_sp(missing_comment_span_lo, ty_span.lo())
1912     };
1913
1914     let comment_before_colon = rewrite_missing_comment(span_before_colon, shape, context)
1915         .filter(|comment| !comment.is_empty())
1916         .map_or(String::new(), |comment| format!(" {}", comment));
1917     let comment_after_colon = rewrite_missing_comment(span_after_colon, shape, context)
1918         .filter(|comment| !comment.is_empty())
1919         .map_or(String::new(), |comment| format!("{} ", comment));
1920     (comment_before_colon, comment_after_colon)
1921 }
1922
1923 impl Rewrite for ast::Param {
1924     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1925         let param_attrs_result = self
1926             .attrs
1927             .rewrite(context, Shape::legacy(shape.width, shape.indent))?;
1928         let (span, has_multiple_attr_lines) = if !self.attrs.is_empty() {
1929             let num_attrs = self.attrs.len();
1930             (
1931                 mk_sp(self.attrs[num_attrs - 1].span.hi(), self.pat.span.lo()),
1932                 param_attrs_result.contains("\n"),
1933             )
1934         } else {
1935             (mk_sp(self.span.lo(), self.span.lo()), false)
1936         };
1937
1938         if let Some(ref explicit_self) = self.to_self() {
1939             rewrite_explicit_self(
1940                 context,
1941                 explicit_self,
1942                 &param_attrs_result,
1943                 span,
1944                 shape,
1945                 has_multiple_attr_lines,
1946             )
1947         } else if is_named_param(self) {
1948             let mut result = combine_strs_with_missing_comments(
1949                 context,
1950                 &param_attrs_result,
1951                 &self
1952                     .pat
1953                     .rewrite(context, Shape::legacy(shape.width, shape.indent))?,
1954                 span,
1955                 shape,
1956                 !has_multiple_attr_lines,
1957             )?;
1958
1959             if !is_empty_infer(&*self.ty, self.pat.span) {
1960                 let (before_comment, after_comment) =
1961                     get_missing_param_comments(context, self.pat.span, self.ty.span, shape);
1962                 result.push_str(&before_comment);
1963                 result.push_str(colon_spaces(context.config));
1964                 result.push_str(&after_comment);
1965                 let overhead = last_line_width(&result);
1966                 let max_width = shape.width.checked_sub(overhead)?;
1967                 let ty_str = self
1968                     .ty
1969                     .rewrite(context, Shape::legacy(max_width, shape.indent))?;
1970                 result.push_str(&ty_str);
1971             }
1972
1973             Some(result)
1974         } else {
1975             self.ty.rewrite(context, shape)
1976         }
1977     }
1978 }
1979
1980 fn rewrite_explicit_self(
1981     context: &RewriteContext<'_>,
1982     explicit_self: &ast::ExplicitSelf,
1983     param_attrs: &str,
1984     span: Span,
1985     shape: Shape,
1986     has_multiple_attr_lines: bool,
1987 ) -> Option<String> {
1988     match explicit_self.node {
1989         ast::SelfKind::Region(lt, m) => {
1990             let mut_str = format_mutability(m);
1991             match lt {
1992                 Some(ref l) => {
1993                     let lifetime_str = l.rewrite(
1994                         context,
1995                         Shape::legacy(context.config.max_width(), Indent::empty()),
1996                     )?;
1997                     Some(combine_strs_with_missing_comments(
1998                         context,
1999                         &param_attrs,
2000                         &format!("&{} {}self", lifetime_str, mut_str),
2001                         span,
2002                         shape,
2003                         !has_multiple_attr_lines,
2004                     )?)
2005                 }
2006                 None => Some(combine_strs_with_missing_comments(
2007                     context,
2008                     &param_attrs,
2009                     &format!("&{}self", mut_str),
2010                     span,
2011                     shape,
2012                     !has_multiple_attr_lines,
2013                 )?),
2014             }
2015         }
2016         ast::SelfKind::Explicit(ref ty, mutability) => {
2017             let type_str = ty.rewrite(
2018                 context,
2019                 Shape::legacy(context.config.max_width(), Indent::empty()),
2020             )?;
2021
2022             Some(combine_strs_with_missing_comments(
2023                 context,
2024                 &param_attrs,
2025                 &format!("{}self: {}", format_mutability(mutability), type_str),
2026                 span,
2027                 shape,
2028                 !has_multiple_attr_lines,
2029             )?)
2030         }
2031         ast::SelfKind::Value(mutability) => Some(combine_strs_with_missing_comments(
2032             context,
2033             &param_attrs,
2034             &format!("{}self", format_mutability(mutability)),
2035             span,
2036             shape,
2037             !has_multiple_attr_lines,
2038         )?),
2039     }
2040 }
2041
2042 pub(crate) fn span_lo_for_param(param: &ast::Param) -> BytePos {
2043     if param.attrs.is_empty() {
2044         if is_named_param(param) {
2045             param.pat.span.lo()
2046         } else {
2047             param.ty.span.lo()
2048         }
2049     } else {
2050         param.attrs[0].span.lo()
2051     }
2052 }
2053
2054 pub(crate) fn span_hi_for_param(context: &RewriteContext<'_>, param: &ast::Param) -> BytePos {
2055     match param.ty.kind {
2056         ast::TyKind::Infer if context.snippet(param.ty.span) == "_" => param.ty.span.hi(),
2057         ast::TyKind::Infer if is_named_param(param) => param.pat.span.hi(),
2058         _ => param.ty.span.hi(),
2059     }
2060 }
2061
2062 pub(crate) fn is_named_param(param: &ast::Param) -> bool {
2063     if let ast::PatKind::Ident(_, ident, _) = param.pat.kind {
2064         ident.name != symbol::kw::Invalid
2065     } else {
2066         true
2067     }
2068 }
2069
2070 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
2071 pub(crate) enum FnBraceStyle {
2072     SameLine,
2073     NextLine,
2074     None,
2075 }
2076
2077 // Return type is (result, force_new_line_for_brace)
2078 fn rewrite_fn_base(
2079     context: &RewriteContext<'_>,
2080     indent: Indent,
2081     ident: ast::Ident,
2082     fn_sig: &FnSig<'_>,
2083     span: Span,
2084     fn_brace_style: FnBraceStyle,
2085 ) -> Option<(String, bool)> {
2086     let mut force_new_line_for_brace = false;
2087
2088     let where_clause = &fn_sig.generics.where_clause;
2089
2090     let mut result = String::with_capacity(1024);
2091     result.push_str(&fn_sig.to_str(context));
2092
2093     // fn foo
2094     result.push_str("fn ");
2095
2096     // Generics.
2097     let overhead = if let FnBraceStyle::SameLine = fn_brace_style {
2098         // 4 = `() {`
2099         4
2100     } else {
2101         // 2 = `()`
2102         2
2103     };
2104     let used_width = last_line_used_width(&result, indent.width());
2105     let one_line_budget = context.budget(used_width + overhead);
2106     let shape = Shape {
2107         width: one_line_budget,
2108         indent,
2109         offset: used_width,
2110     };
2111     let fd = fn_sig.decl;
2112     let generics_str = rewrite_generics(
2113         context,
2114         rewrite_ident(context, ident),
2115         fn_sig.generics,
2116         shape,
2117     )?;
2118     result.push_str(&generics_str);
2119
2120     let snuggle_angle_bracket = generics_str
2121         .lines()
2122         .last()
2123         .map_or(false, |l| l.trim_start().len() == 1);
2124
2125     // Note that the width and indent don't really matter, we'll re-layout the
2126     // return type later anyway.
2127     let ret_str = fd
2128         .output
2129         .rewrite(context, Shape::indented(indent, context.config))?;
2130
2131     let multi_line_ret_str = ret_str.contains('\n');
2132     let ret_str_len = if multi_line_ret_str { 0 } else { ret_str.len() };
2133
2134     // Params.
2135     let (one_line_budget, multi_line_budget, mut param_indent) = compute_budgets_for_params(
2136         context,
2137         &result,
2138         indent,
2139         ret_str_len,
2140         fn_brace_style,
2141         multi_line_ret_str,
2142     )?;
2143
2144     debug!(
2145         "rewrite_fn_base: one_line_budget: {}, multi_line_budget: {}, param_indent: {:?}",
2146         one_line_budget, multi_line_budget, param_indent
2147     );
2148
2149     result.push('(');
2150     // Check if vertical layout was forced.
2151     if one_line_budget == 0
2152         && !snuggle_angle_bracket
2153         && context.config.indent_style() == IndentStyle::Visual
2154     {
2155         result.push_str(&param_indent.to_string_with_newline(context.config));
2156     }
2157
2158     // Skip `pub(crate)`.
2159     let lo_after_visibility = get_bytepos_after_visibility(&fn_sig.visibility, span);
2160     // A conservative estimation, to goal is to be over all parens in generics
2161     let params_start = fn_sig
2162         .generics
2163         .params
2164         .iter()
2165         .last()
2166         .map_or(lo_after_visibility, |param| param.span().hi());
2167     let params_end = if fd.inputs.is_empty() {
2168         context
2169             .snippet_provider
2170             .span_after(mk_sp(params_start, span.hi()), ")")
2171     } else {
2172         let last_span = mk_sp(fd.inputs[fd.inputs.len() - 1].span().hi(), span.hi());
2173         context.snippet_provider.span_after(last_span, ")")
2174     };
2175     let params_span = mk_sp(
2176         context
2177             .snippet_provider
2178             .span_after(mk_sp(params_start, span.hi()), "("),
2179         params_end,
2180     );
2181     let param_str = rewrite_params(
2182         context,
2183         &fd.inputs,
2184         one_line_budget,
2185         multi_line_budget,
2186         indent,
2187         param_indent,
2188         params_span,
2189         fd.c_variadic(),
2190     )?;
2191
2192     let put_params_in_block = match context.config.indent_style() {
2193         IndentStyle::Block => param_str.contains('\n') || param_str.len() > one_line_budget,
2194         _ => false,
2195     } && !fd.inputs.is_empty();
2196
2197     let mut params_last_line_contains_comment = false;
2198     let mut no_params_and_over_max_width = false;
2199
2200     if put_params_in_block {
2201         param_indent = indent.block_indent(context.config);
2202         result.push_str(&param_indent.to_string_with_newline(context.config));
2203         result.push_str(&param_str);
2204         result.push_str(&indent.to_string_with_newline(context.config));
2205         result.push(')');
2206     } else {
2207         result.push_str(&param_str);
2208         let used_width = last_line_used_width(&result, indent.width()) + first_line_width(&ret_str);
2209         // Put the closing brace on the next line if it overflows the max width.
2210         // 1 = `)`
2211         let closing_paren_overflow_max_width =
2212             fd.inputs.is_empty() && used_width + 1 > context.config.max_width();
2213         // If the last line of params contains comment, we cannot put the closing paren
2214         // on the same line.
2215         params_last_line_contains_comment = param_str
2216             .lines()
2217             .last()
2218             .map_or(false, |last_line| last_line.contains("//"));
2219
2220         if context.config.version() == Version::Two {
2221             result.push(')');
2222             if closing_paren_overflow_max_width || params_last_line_contains_comment {
2223                 result.push_str(&indent.to_string_with_newline(context.config));
2224                 no_params_and_over_max_width = true;
2225             }
2226         } else {
2227             if closing_paren_overflow_max_width || params_last_line_contains_comment {
2228                 result.push_str(&indent.to_string_with_newline(context.config));
2229             }
2230             result.push(')');
2231         }
2232     }
2233
2234     // Return type.
2235     if let ast::FunctionRetTy::Ty(..) = fd.output {
2236         let ret_should_indent = match context.config.indent_style() {
2237             // If our params are block layout then we surely must have space.
2238             IndentStyle::Block if put_params_in_block || fd.inputs.is_empty() => false,
2239             _ if params_last_line_contains_comment => false,
2240             _ if result.contains('\n') || multi_line_ret_str => true,
2241             _ => {
2242                 // If the return type would push over the max width, then put the return type on
2243                 // a new line. With the +1 for the signature length an additional space between
2244                 // the closing parenthesis of the param and the arrow '->' is considered.
2245                 let mut sig_length = result.len() + indent.width() + ret_str_len + 1;
2246
2247                 // If there is no where-clause, take into account the space after the return type
2248                 // and the brace.
2249                 if where_clause.predicates.is_empty() {
2250                     sig_length += 2;
2251                 }
2252
2253                 sig_length > context.config.max_width()
2254             }
2255         };
2256         let ret_shape = if ret_should_indent {
2257             if context.config.version() == Version::One
2258                 || context.config.indent_style() == IndentStyle::Visual
2259             {
2260                 let indent = if param_str.is_empty() {
2261                     // Aligning with non-existent params looks silly.
2262                     force_new_line_for_brace = true;
2263                     indent + 4
2264                 } else {
2265                     // FIXME: we might want to check that using the param indent
2266                     // doesn't blow our budget, and if it does, then fallback to
2267                     // the where-clause indent.
2268                     param_indent
2269                 };
2270
2271                 result.push_str(&indent.to_string_with_newline(context.config));
2272                 Shape::indented(indent, context.config)
2273             } else {
2274                 let mut ret_shape = Shape::indented(indent, context.config);
2275                 if param_str.is_empty() {
2276                     // Aligning with non-existent params looks silly.
2277                     force_new_line_for_brace = true;
2278                     ret_shape = if context.use_block_indent() {
2279                         ret_shape.offset_left(4).unwrap_or(ret_shape)
2280                     } else {
2281                         ret_shape.indent = ret_shape.indent + 4;
2282                         ret_shape
2283                     };
2284                 }
2285
2286                 result.push_str(&ret_shape.indent.to_string_with_newline(context.config));
2287                 ret_shape
2288             }
2289         } else {
2290             if context.config.version() == Version::Two {
2291                 if !param_str.is_empty() || !no_params_and_over_max_width {
2292                     result.push(' ');
2293                 }
2294             } else {
2295                 result.push(' ');
2296             }
2297
2298             let ret_shape = Shape::indented(indent, context.config);
2299             ret_shape
2300                 .offset_left(last_line_width(&result))
2301                 .unwrap_or(ret_shape)
2302         };
2303
2304         if multi_line_ret_str || ret_should_indent {
2305             // Now that we know the proper indent and width, we need to
2306             // re-layout the return type.
2307             let ret_str = fd.output.rewrite(context, ret_shape)?;
2308             result.push_str(&ret_str);
2309         } else {
2310             result.push_str(&ret_str);
2311         }
2312
2313         // Comment between return type and the end of the decl.
2314         let snippet_lo = fd.output.span().hi();
2315         if where_clause.predicates.is_empty() {
2316             let snippet_hi = span.hi();
2317             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
2318             // Try to preserve the layout of the original snippet.
2319             let original_starts_with_newline = snippet
2320                 .find(|c| c != ' ')
2321                 .map_or(false, |i| starts_with_newline(&snippet[i..]));
2322             let original_ends_with_newline = snippet
2323                 .rfind(|c| c != ' ')
2324                 .map_or(false, |i| snippet[i..].ends_with('\n'));
2325             let snippet = snippet.trim();
2326             if !snippet.is_empty() {
2327                 result.push(if original_starts_with_newline {
2328                     '\n'
2329                 } else {
2330                     ' '
2331                 });
2332                 result.push_str(snippet);
2333                 if original_ends_with_newline {
2334                     force_new_line_for_brace = true;
2335                 }
2336             }
2337         }
2338     }
2339
2340     let pos_before_where = match fd.output {
2341         ast::FunctionRetTy::Default(..) => params_span.hi(),
2342         ast::FunctionRetTy::Ty(ref ty) => ty.span.hi(),
2343     };
2344
2345     let is_params_multi_lined = param_str.contains('\n');
2346
2347     let space = if put_params_in_block && ret_str.is_empty() {
2348         WhereClauseSpace::Space
2349     } else {
2350         WhereClauseSpace::Newline
2351     };
2352     let mut option = WhereClauseOption::new(fn_brace_style == FnBraceStyle::None, space);
2353     if is_params_multi_lined {
2354         option.veto_single_line();
2355     }
2356     let where_clause_str = rewrite_where_clause(
2357         context,
2358         where_clause,
2359         context.config.brace_style(),
2360         Shape::indented(indent, context.config),
2361         true,
2362         "{",
2363         Some(span.hi()),
2364         pos_before_where,
2365         option,
2366     )?;
2367     // If there are neither where-clause nor return type, we may be missing comments between
2368     // params and `{`.
2369     if where_clause_str.is_empty() {
2370         if let ast::FunctionRetTy::Default(ret_span) = fd.output {
2371             match recover_missing_comment_in_span(
2372                 mk_sp(params_span.hi(), ret_span.hi()),
2373                 shape,
2374                 context,
2375                 last_line_width(&result),
2376             ) {
2377                 Some(ref missing_comment) if !missing_comment.is_empty() => {
2378                     result.push_str(missing_comment);
2379                     force_new_line_for_brace = true;
2380                 }
2381                 _ => (),
2382             }
2383         }
2384     }
2385
2386     result.push_str(&where_clause_str);
2387
2388     force_new_line_for_brace |= last_line_contains_single_line_comment(&result);
2389     force_new_line_for_brace |= is_params_multi_lined && context.config.where_single_line();
2390     Some((result, force_new_line_for_brace))
2391 }
2392
2393 /// Kind of spaces to put before `where`.
2394 #[derive(Copy, Clone)]
2395 enum WhereClauseSpace {
2396     /// A single space.
2397     Space,
2398     /// A new line.
2399     Newline,
2400     /// Nothing.
2401     None,
2402 }
2403
2404 #[derive(Copy, Clone)]
2405 struct WhereClauseOption {
2406     suppress_comma: bool, // Force no trailing comma
2407     snuggle: WhereClauseSpace,
2408     allow_single_line: bool, // Try single line where-clause instead of vertical layout
2409     veto_single_line: bool,  // Disallow a single-line where-clause.
2410 }
2411
2412 impl WhereClauseOption {
2413     fn new(suppress_comma: bool, snuggle: WhereClauseSpace) -> WhereClauseOption {
2414         WhereClauseOption {
2415             suppress_comma,
2416             snuggle,
2417             allow_single_line: false,
2418             veto_single_line: false,
2419         }
2420     }
2421
2422     fn snuggled(current: &str) -> WhereClauseOption {
2423         WhereClauseOption {
2424             suppress_comma: false,
2425             snuggle: if last_line_width(current) == 1 {
2426                 WhereClauseSpace::Space
2427             } else {
2428                 WhereClauseSpace::Newline
2429             },
2430             allow_single_line: false,
2431             veto_single_line: false,
2432         }
2433     }
2434
2435     fn suppress_comma(&mut self) {
2436         self.suppress_comma = true
2437     }
2438
2439     fn allow_single_line(&mut self) {
2440         self.allow_single_line = true
2441     }
2442
2443     fn snuggle(&mut self) {
2444         self.snuggle = WhereClauseSpace::Space
2445     }
2446
2447     fn veto_single_line(&mut self) {
2448         self.veto_single_line = true;
2449     }
2450 }
2451
2452 fn rewrite_params(
2453     context: &RewriteContext<'_>,
2454     params: &[ast::Param],
2455     one_line_budget: usize,
2456     multi_line_budget: usize,
2457     indent: Indent,
2458     param_indent: Indent,
2459     span: Span,
2460     variadic: bool,
2461 ) -> Option<String> {
2462     if params.is_empty() {
2463         let comment = context
2464             .snippet(mk_sp(
2465                 span.lo(),
2466                 // to remove ')'
2467                 span.hi() - BytePos(1),
2468             ))
2469             .trim();
2470         return Some(comment.to_owned());
2471     }
2472     let param_items: Vec<_> = itemize_list(
2473         context.snippet_provider,
2474         params.iter(),
2475         ")",
2476         ",",
2477         |param| span_lo_for_param(param),
2478         |param| param.ty.span.hi(),
2479         |param| {
2480             param
2481                 .rewrite(context, Shape::legacy(multi_line_budget, param_indent))
2482                 .or_else(|| Some(context.snippet(param.span()).to_owned()))
2483         },
2484         span.lo(),
2485         span.hi(),
2486         false,
2487     )
2488     .collect();
2489
2490     let tactic = definitive_tactic(
2491         &param_items,
2492         context
2493             .config
2494             .fn_args_layout()
2495             .to_list_tactic(param_items.len()),
2496         Separator::Comma,
2497         one_line_budget,
2498     );
2499     let budget = match tactic {
2500         DefinitiveListTactic::Horizontal => one_line_budget,
2501         _ => multi_line_budget,
2502     };
2503     let indent = match context.config.indent_style() {
2504         IndentStyle::Block => indent.block_indent(context.config),
2505         IndentStyle::Visual => param_indent,
2506     };
2507     let trailing_separator = if variadic {
2508         SeparatorTactic::Never
2509     } else {
2510         match context.config.indent_style() {
2511             IndentStyle::Block => context.config.trailing_comma(),
2512             IndentStyle::Visual => SeparatorTactic::Never,
2513         }
2514     };
2515     let fmt = ListFormatting::new(Shape::legacy(budget, indent), context.config)
2516         .tactic(tactic)
2517         .trailing_separator(trailing_separator)
2518         .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
2519         .preserve_newline(true);
2520     write_list(&param_items, &fmt)
2521 }
2522
2523 fn compute_budgets_for_params(
2524     context: &RewriteContext<'_>,
2525     result: &str,
2526     indent: Indent,
2527     ret_str_len: usize,
2528     fn_brace_style: FnBraceStyle,
2529     force_vertical_layout: bool,
2530 ) -> Option<((usize, usize, Indent))> {
2531     debug!(
2532         "compute_budgets_for_params {} {:?}, {}, {:?}",
2533         result.len(),
2534         indent,
2535         ret_str_len,
2536         fn_brace_style,
2537     );
2538     // Try keeping everything on the same line.
2539     if !result.contains('\n') && !force_vertical_layout {
2540         // 2 = `()`, 3 = `() `, space is before ret_string.
2541         let overhead = if ret_str_len == 0 { 2 } else { 3 };
2542         let mut used_space = indent.width() + result.len() + ret_str_len + overhead;
2543         match fn_brace_style {
2544             FnBraceStyle::None => used_space += 1,     // 1 = `;`
2545             FnBraceStyle::SameLine => used_space += 2, // 2 = `{}`
2546             FnBraceStyle::NextLine => (),
2547         }
2548         let one_line_budget = context.budget(used_space);
2549
2550         if one_line_budget > 0 {
2551             // 4 = "() {".len()
2552             let (indent, multi_line_budget) = match context.config.indent_style() {
2553                 IndentStyle::Block => {
2554                     let indent = indent.block_indent(context.config);
2555                     (indent, context.budget(indent.width() + 1))
2556                 }
2557                 IndentStyle::Visual => {
2558                     let indent = indent + result.len() + 1;
2559                     let multi_line_overhead = match fn_brace_style {
2560                         FnBraceStyle::SameLine => 4,
2561                         _ => 2,
2562                     } + indent.width();
2563                     (indent, context.budget(multi_line_overhead))
2564                 }
2565             };
2566
2567             return Some((one_line_budget, multi_line_budget, indent));
2568         }
2569     }
2570
2571     // Didn't work. we must force vertical layout and put params on a newline.
2572     let new_indent = indent.block_indent(context.config);
2573     let used_space = match context.config.indent_style() {
2574         // 1 = `,`
2575         IndentStyle::Block => new_indent.width() + 1,
2576         // Account for `)` and possibly ` {`.
2577         IndentStyle::Visual => new_indent.width() + if ret_str_len == 0 { 1 } else { 3 },
2578     };
2579     Some((0, context.budget(used_space), new_indent))
2580 }
2581
2582 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause) -> FnBraceStyle {
2583     let predicate_count = where_clause.predicates.len();
2584
2585     if config.where_single_line() && predicate_count == 1 {
2586         return FnBraceStyle::SameLine;
2587     }
2588     let brace_style = config.brace_style();
2589
2590     let use_next_line = brace_style == BraceStyle::AlwaysNextLine
2591         || (brace_style == BraceStyle::SameLineWhere && predicate_count > 0);
2592     if use_next_line {
2593         FnBraceStyle::NextLine
2594     } else {
2595         FnBraceStyle::SameLine
2596     }
2597 }
2598
2599 fn rewrite_generics(
2600     context: &RewriteContext<'_>,
2601     ident: &str,
2602     generics: &ast::Generics,
2603     shape: Shape,
2604 ) -> Option<String> {
2605     // FIXME: convert bounds to where-clauses where they get too big or if
2606     // there is a where-clause at all.
2607
2608     if generics.params.is_empty() {
2609         return Some(ident.to_owned());
2610     }
2611
2612     let params = generics.params.iter();
2613     overflow::rewrite_with_angle_brackets(context, ident, params, shape, generics.span)
2614 }
2615
2616 fn generics_shape_from_config(config: &Config, shape: Shape, offset: usize) -> Option<Shape> {
2617     match config.indent_style() {
2618         IndentStyle::Visual => shape.visual_indent(1 + offset).sub_width(offset + 2),
2619         IndentStyle::Block => {
2620             // 1 = ","
2621             shape
2622                 .block()
2623                 .block_indent(config.tab_spaces())
2624                 .with_max_width(config)
2625                 .sub_width(1)
2626         }
2627     }
2628 }
2629
2630 fn rewrite_where_clause_rfc_style(
2631     context: &RewriteContext<'_>,
2632     where_clause: &ast::WhereClause,
2633     shape: Shape,
2634     terminator: &str,
2635     span_end: Option<BytePos>,
2636     span_end_before_where: BytePos,
2637     where_clause_option: WhereClauseOption,
2638 ) -> Option<String> {
2639     let (where_keyword, allow_single_line) = rewrite_where_keyword(
2640         context,
2641         where_clause,
2642         shape,
2643         span_end_before_where,
2644         where_clause_option,
2645     )?;
2646
2647     // 1 = `,`
2648     let clause_shape = shape
2649         .block()
2650         .with_max_width(context.config)
2651         .block_left(context.config.tab_spaces())?
2652         .sub_width(1)?;
2653     let force_single_line = context.config.where_single_line()
2654         && where_clause.predicates.len() == 1
2655         && !where_clause_option.veto_single_line;
2656
2657     let preds_str = rewrite_bounds_on_where_clause(
2658         context,
2659         where_clause,
2660         clause_shape,
2661         terminator,
2662         span_end,
2663         where_clause_option,
2664         force_single_line,
2665     )?;
2666
2667     // 6 = `where `
2668     let clause_sep =
2669         if allow_single_line && !preds_str.contains('\n') && 6 + preds_str.len() <= shape.width
2670             || force_single_line
2671         {
2672             Cow::from(" ")
2673         } else {
2674             clause_shape.indent.to_string_with_newline(context.config)
2675         };
2676
2677     Some(format!("{}{}{}", where_keyword, clause_sep, preds_str))
2678 }
2679
2680 /// Rewrite `where` and comment around it.
2681 fn rewrite_where_keyword(
2682     context: &RewriteContext<'_>,
2683     where_clause: &ast::WhereClause,
2684     shape: Shape,
2685     span_end_before_where: BytePos,
2686     where_clause_option: WhereClauseOption,
2687 ) -> Option<(String, bool)> {
2688     let block_shape = shape.block().with_max_width(context.config);
2689     // 1 = `,`
2690     let clause_shape = block_shape
2691         .block_left(context.config.tab_spaces())?
2692         .sub_width(1)?;
2693
2694     let comment_separator = |comment: &str, shape: Shape| {
2695         if comment.is_empty() {
2696             Cow::from("")
2697         } else {
2698             shape.indent.to_string_with_newline(context.config)
2699         }
2700     };
2701
2702     let (span_before, span_after) =
2703         missing_span_before_after_where(span_end_before_where, where_clause);
2704     let (comment_before, comment_after) =
2705         rewrite_comments_before_after_where(context, span_before, span_after, shape)?;
2706
2707     let starting_newline = match where_clause_option.snuggle {
2708         WhereClauseSpace::Space if comment_before.is_empty() => Cow::from(" "),
2709         WhereClauseSpace::None => Cow::from(""),
2710         _ => block_shape.indent.to_string_with_newline(context.config),
2711     };
2712
2713     let newline_before_where = comment_separator(&comment_before, shape);
2714     let newline_after_where = comment_separator(&comment_after, clause_shape);
2715     let result = format!(
2716         "{}{}{}where{}{}",
2717         starting_newline, comment_before, newline_before_where, newline_after_where, comment_after
2718     );
2719     let allow_single_line = where_clause_option.allow_single_line
2720         && comment_before.is_empty()
2721         && comment_after.is_empty();
2722
2723     Some((result, allow_single_line))
2724 }
2725
2726 /// Rewrite bounds on a where clause.
2727 fn rewrite_bounds_on_where_clause(
2728     context: &RewriteContext<'_>,
2729     where_clause: &ast::WhereClause,
2730     shape: Shape,
2731     terminator: &str,
2732     span_end: Option<BytePos>,
2733     where_clause_option: WhereClauseOption,
2734     force_single_line: bool,
2735 ) -> Option<String> {
2736     let span_start = where_clause.predicates[0].span().lo();
2737     // If we don't have the start of the next span, then use the end of the
2738     // predicates, but that means we miss comments.
2739     let len = where_clause.predicates.len();
2740     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2741     let span_end = span_end.unwrap_or(end_of_preds);
2742     let items = itemize_list(
2743         context.snippet_provider,
2744         where_clause.predicates.iter(),
2745         terminator,
2746         ",",
2747         |pred| pred.span().lo(),
2748         |pred| pred.span().hi(),
2749         |pred| pred.rewrite(context, shape),
2750         span_start,
2751         span_end,
2752         false,
2753     );
2754     let comma_tactic = if where_clause_option.suppress_comma || force_single_line {
2755         SeparatorTactic::Never
2756     } else {
2757         context.config.trailing_comma()
2758     };
2759
2760     // shape should be vertical only and only if we have `force_single_line` option enabled
2761     // and the number of items of the where-clause is equal to 1
2762     let shape_tactic = if force_single_line {
2763         DefinitiveListTactic::Horizontal
2764     } else {
2765         DefinitiveListTactic::Vertical
2766     };
2767
2768     let fmt = ListFormatting::new(shape, context.config)
2769         .tactic(shape_tactic)
2770         .trailing_separator(comma_tactic)
2771         .preserve_newline(true);
2772     write_list(&items.collect::<Vec<_>>(), &fmt)
2773 }
2774
2775 fn rewrite_where_clause(
2776     context: &RewriteContext<'_>,
2777     where_clause: &ast::WhereClause,
2778     brace_style: BraceStyle,
2779     shape: Shape,
2780     on_new_line: bool,
2781     terminator: &str,
2782     span_end: Option<BytePos>,
2783     span_end_before_where: BytePos,
2784     where_clause_option: WhereClauseOption,
2785 ) -> Option<String> {
2786     if where_clause.predicates.is_empty() {
2787         return Some(String::new());
2788     }
2789
2790     if context.config.indent_style() == IndentStyle::Block {
2791         return rewrite_where_clause_rfc_style(
2792             context,
2793             where_clause,
2794             shape,
2795             terminator,
2796             span_end,
2797             span_end_before_where,
2798             where_clause_option,
2799         );
2800     }
2801
2802     let extra_indent = Indent::new(context.config.tab_spaces(), 0);
2803
2804     let offset = match context.config.indent_style() {
2805         IndentStyle::Block => shape.indent + extra_indent.block_indent(context.config),
2806         // 6 = "where ".len()
2807         IndentStyle::Visual => shape.indent + extra_indent + 6,
2808     };
2809     // FIXME: if indent_style != Visual, then the budgets below might
2810     // be out by a char or two.
2811
2812     let budget = context.config.max_width() - offset.width();
2813     let span_start = where_clause.predicates[0].span().lo();
2814     // If we don't have the start of the next span, then use the end of the
2815     // predicates, but that means we miss comments.
2816     let len = where_clause.predicates.len();
2817     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2818     let span_end = span_end.unwrap_or(end_of_preds);
2819     let items = itemize_list(
2820         context.snippet_provider,
2821         where_clause.predicates.iter(),
2822         terminator,
2823         ",",
2824         |pred| pred.span().lo(),
2825         |pred| pred.span().hi(),
2826         |pred| pred.rewrite(context, Shape::legacy(budget, offset)),
2827         span_start,
2828         span_end,
2829         false,
2830     );
2831     let item_vec = items.collect::<Vec<_>>();
2832     // FIXME: we don't need to collect here
2833     let tactic = definitive_tactic(&item_vec, ListTactic::Vertical, Separator::Comma, budget);
2834
2835     let mut comma_tactic = context.config.trailing_comma();
2836     // Kind of a hack because we don't usually have trailing commas in where-clauses.
2837     if comma_tactic == SeparatorTactic::Vertical || where_clause_option.suppress_comma {
2838         comma_tactic = SeparatorTactic::Never;
2839     }
2840
2841     let fmt = ListFormatting::new(Shape::legacy(budget, offset), context.config)
2842         .tactic(tactic)
2843         .trailing_separator(comma_tactic)
2844         .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
2845         .preserve_newline(true);
2846     let preds_str = write_list(&item_vec, &fmt)?;
2847
2848     let end_length = if terminator == "{" {
2849         // If the brace is on the next line we don't need to count it otherwise it needs two
2850         // characters " {"
2851         match brace_style {
2852             BraceStyle::AlwaysNextLine | BraceStyle::SameLineWhere => 0,
2853             BraceStyle::PreferSameLine => 2,
2854         }
2855     } else if terminator == "=" {
2856         2
2857     } else {
2858         terminator.len()
2859     };
2860     if on_new_line
2861         || preds_str.contains('\n')
2862         || shape.indent.width() + " where ".len() + preds_str.len() + end_length > shape.width
2863     {
2864         Some(format!(
2865             "\n{}where {}",
2866             (shape.indent + extra_indent).to_string(context.config),
2867             preds_str
2868         ))
2869     } else {
2870         Some(format!(" where {}", preds_str))
2871     }
2872 }
2873
2874 fn missing_span_before_after_where(
2875     before_item_span_end: BytePos,
2876     where_clause: &ast::WhereClause,
2877 ) -> (Span, Span) {
2878     let missing_span_before = mk_sp(before_item_span_end, where_clause.span.lo());
2879     // 5 = `where`
2880     let pos_after_where = where_clause.span.lo() + BytePos(5);
2881     let missing_span_after = mk_sp(pos_after_where, where_clause.predicates[0].span().lo());
2882     (missing_span_before, missing_span_after)
2883 }
2884
2885 fn rewrite_comments_before_after_where(
2886     context: &RewriteContext<'_>,
2887     span_before_where: Span,
2888     span_after_where: Span,
2889     shape: Shape,
2890 ) -> Option<(String, String)> {
2891     let before_comment = rewrite_missing_comment(span_before_where, shape, context)?;
2892     let after_comment = rewrite_missing_comment(
2893         span_after_where,
2894         shape.block_indent(context.config.tab_spaces()),
2895         context,
2896     )?;
2897     Some((before_comment, after_comment))
2898 }
2899
2900 fn format_header(
2901     context: &RewriteContext<'_>,
2902     item_name: &str,
2903     ident: ast::Ident,
2904     vis: &ast::Visibility,
2905 ) -> String {
2906     format!(
2907         "{}{}{}",
2908         format_visibility(context, vis),
2909         item_name,
2910         rewrite_ident(context, ident)
2911     )
2912 }
2913
2914 #[derive(PartialEq, Eq, Clone, Copy)]
2915 enum BracePos {
2916     None,
2917     Auto,
2918     ForceSameLine,
2919 }
2920
2921 fn format_generics(
2922     context: &RewriteContext<'_>,
2923     generics: &ast::Generics,
2924     brace_style: BraceStyle,
2925     brace_pos: BracePos,
2926     offset: Indent,
2927     span: Span,
2928     used_width: usize,
2929 ) -> Option<String> {
2930     let shape = Shape::legacy(context.budget(used_width + offset.width()), offset);
2931     let mut result = rewrite_generics(context, "", generics, shape)?;
2932
2933     // If the generics are not parameterized then generics.span.hi() == 0,
2934     // so we use span.lo(), which is the position after `struct Foo`.
2935     let span_end_before_where = if !generics.params.is_empty() {
2936         generics.span.hi()
2937     } else {
2938         span.lo()
2939     };
2940     let (same_line_brace, missed_comments) = if !generics.where_clause.predicates.is_empty() {
2941         let budget = context.budget(last_line_used_width(&result, offset.width()));
2942         let mut option = WhereClauseOption::snuggled(&result);
2943         if brace_pos == BracePos::None {
2944             option.suppress_comma = true;
2945         }
2946         let where_clause_str = rewrite_where_clause(
2947             context,
2948             &generics.where_clause,
2949             brace_style,
2950             Shape::legacy(budget, offset.block_only()),
2951             true,
2952             "{",
2953             Some(span.hi()),
2954             span_end_before_where,
2955             option,
2956         )?;
2957         result.push_str(&where_clause_str);
2958         (
2959             brace_pos == BracePos::ForceSameLine || brace_style == BraceStyle::PreferSameLine,
2960             // missed comments are taken care of in #rewrite_where_clause
2961             None,
2962         )
2963     } else {
2964         (
2965             brace_pos == BracePos::ForceSameLine
2966                 || (result.contains('\n') && brace_style == BraceStyle::PreferSameLine
2967                     || brace_style != BraceStyle::AlwaysNextLine)
2968                 || trimmed_last_line_width(&result) == 1,
2969             rewrite_missing_comment(
2970                 mk_sp(
2971                     span_end_before_where,
2972                     if brace_pos == BracePos::None {
2973                         span.hi()
2974                     } else {
2975                         context.snippet_provider.span_before(span, "{")
2976                     },
2977                 ),
2978                 shape,
2979                 context,
2980             ),
2981         )
2982     };
2983     // add missing comments
2984     let missed_line_comments = missed_comments
2985         .filter(|missed_comments| !missed_comments.is_empty())
2986         .map_or(false, |missed_comments| {
2987             let is_block = is_last_comment_block(&missed_comments);
2988             let sep = if is_block { " " } else { "\n" };
2989             result.push_str(sep);
2990             result.push_str(&missed_comments);
2991             !is_block
2992         });
2993     if brace_pos == BracePos::None {
2994         return Some(result);
2995     }
2996     let total_used_width = last_line_used_width(&result, used_width);
2997     let remaining_budget = context.budget(total_used_width);
2998     // If the same line brace if forced, it indicates that we are rewriting an item with empty body,
2999     // and hence we take the closer into account as well for one line budget.
3000     // We assume that the closer has the same length as the opener.
3001     let overhead = if brace_pos == BracePos::ForceSameLine {
3002         // 3 = ` {}`
3003         3
3004     } else {
3005         // 2 = ` {`
3006         2
3007     };
3008     let forbid_same_line_brace = missed_line_comments || overhead > remaining_budget;
3009     if !forbid_same_line_brace && same_line_brace {
3010         result.push(' ');
3011     } else {
3012         result.push('\n');
3013         result.push_str(&offset.block_only().to_string(context.config));
3014     }
3015     result.push('{');
3016
3017     Some(result)
3018 }
3019
3020 impl Rewrite for ast::ForeignItem {
3021     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
3022         let attrs_str = self.attrs.rewrite(context, shape)?;
3023         // Drop semicolon or it will be interpreted as comment.
3024         // FIXME: this may be a faulty span from libsyntax.
3025         let span = mk_sp(self.span.lo(), self.span.hi() - BytePos(1));
3026
3027         let item_str = match self.kind {
3028             ast::ForeignItemKind::Fn(ref fn_decl, ref generics) => rewrite_fn_base(
3029                 context,
3030                 shape.indent,
3031                 self.ident,
3032                 &FnSig::new(fn_decl, generics, self.vis.clone()),
3033                 span,
3034                 FnBraceStyle::None,
3035             )
3036             .map(|(s, _)| format!("{};", s)),
3037             ast::ForeignItemKind::Static(ref ty, mutability) => {
3038                 // FIXME(#21): we're dropping potential comments in between the
3039                 // function kw here.
3040                 let vis = format_visibility(context, &self.vis);
3041                 let mut_str = format_mutability(mutability);
3042                 let prefix = format!(
3043                     "{}static {}{}:",
3044                     vis,
3045                     mut_str,
3046                     rewrite_ident(context, self.ident)
3047                 );
3048                 // 1 = ;
3049                 rewrite_assign_rhs(context, prefix, &**ty, shape.sub_width(1)?).map(|s| s + ";")
3050             }
3051             ast::ForeignItemKind::Ty => {
3052                 let vis = format_visibility(context, &self.vis);
3053                 Some(format!(
3054                     "{}type {};",
3055                     vis,
3056                     rewrite_ident(context, self.ident)
3057                 ))
3058             }
3059             ast::ForeignItemKind::Macro(ref mac) => {
3060                 rewrite_macro(mac, None, context, shape, MacroPosition::Item)
3061             }
3062         }?;
3063
3064         let missing_span = if self.attrs.is_empty() {
3065             mk_sp(self.span.lo(), self.span.lo())
3066         } else {
3067             mk_sp(self.attrs[self.attrs.len() - 1].span.hi(), self.span.lo())
3068         };
3069         combine_strs_with_missing_comments(
3070             context,
3071             &attrs_str,
3072             &item_str,
3073             missing_span,
3074             shape,
3075             false,
3076         )
3077     }
3078 }
3079
3080 /// Rewrite the attributes of an item.
3081 fn rewrite_attrs(
3082     context: &RewriteContext<'_>,
3083     item: &ast::Item,
3084     item_str: &str,
3085     shape: Shape,
3086 ) -> Option<String> {
3087     let attrs = filter_inline_attrs(&item.attrs, item.span());
3088     let attrs_str = attrs.rewrite(context, shape)?;
3089
3090     let missed_span = if attrs.is_empty() {
3091         mk_sp(item.span.lo(), item.span.lo())
3092     } else {
3093         mk_sp(attrs[attrs.len() - 1].span.hi(), item.span.lo())
3094     };
3095
3096     let allow_extend = if attrs.len() == 1 {
3097         let line_len = attrs_str.len() + 1 + item_str.len();
3098         !attrs.first().unwrap().is_sugared_doc
3099             && context.config.inline_attribute_width() >= line_len
3100     } else {
3101         false
3102     };
3103
3104     combine_strs_with_missing_comments(
3105         context,
3106         &attrs_str,
3107         &item_str,
3108         missed_span,
3109         shape,
3110         allow_extend,
3111     )
3112 }
3113
3114 /// Rewrite an inline mod.
3115 /// The given shape is used to format the mod's attributes.
3116 pub(crate) fn rewrite_mod(
3117     context: &RewriteContext<'_>,
3118     item: &ast::Item,
3119     attrs_shape: Shape,
3120 ) -> Option<String> {
3121     let mut result = String::with_capacity(32);
3122     result.push_str(&*format_visibility(context, &item.vis));
3123     result.push_str("mod ");
3124     result.push_str(rewrite_ident(context, item.ident));
3125     result.push(';');
3126     rewrite_attrs(context, item, &result, attrs_shape)
3127 }
3128
3129 /// Rewrite `extern crate foo;`.
3130 /// The given shape is used to format the extern crate's attributes.
3131 pub(crate) fn rewrite_extern_crate(
3132     context: &RewriteContext<'_>,
3133     item: &ast::Item,
3134     attrs_shape: Shape,
3135 ) -> Option<String> {
3136     assert!(is_extern_crate(item));
3137     let new_str = context.snippet(item.span);
3138     let item_str = if contains_comment(new_str) {
3139         new_str.to_owned()
3140     } else {
3141         let no_whitespace = &new_str.split_whitespace().collect::<Vec<&str>>().join(" ");
3142         String::from(&*Regex::new(r"\s;").unwrap().replace(no_whitespace, ";"))
3143     };
3144     rewrite_attrs(context, item, &item_str, attrs_shape)
3145 }
3146
3147 /// Returns `true` for `mod foo;`, false for `mod foo { .. }`.
3148 pub(crate) fn is_mod_decl(item: &ast::Item) -> bool {
3149     match item.kind {
3150         ast::ItemKind::Mod(ref m) => m.inner.hi() != item.span.hi(),
3151         _ => false,
3152     }
3153 }
3154
3155 pub(crate) fn is_use_item(item: &ast::Item) -> bool {
3156     match item.kind {
3157         ast::ItemKind::Use(_) => true,
3158         _ => false,
3159     }
3160 }
3161
3162 pub(crate) fn is_extern_crate(item: &ast::Item) -> bool {
3163     match item.kind {
3164         ast::ItemKind::ExternCrate(..) => true,
3165         _ => false,
3166     }
3167 }