rustfmt-core/src/items.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // Formatting top-level items - functions, structs, enums, traits, impls.
  12
  13 use std::borrow::Cow;
  14 use std::cmp::min;
  15
  16 use config::lists::*;
  17 use syntax::{abi, ast, ptr, symbol};
  18 use syntax::ast::{CrateSugar, ImplItem};
  19 use syntax::codemap::{BytePos, Span};
  20 use syntax::visit;
  21
  22 use codemap::{LineRangeUtils, SpanUtils};
  23 use comment::{combine_strs_with_missing_comments, contains_comment, recover_comment_removed,
  24               recover_missing_comment_in_span, rewrite_missing_comment, FindUncommented};
  25 use config::{BraceStyle, Config, Density, IndentStyle};
  26 use expr::{format_expr, is_empty_block, is_simple_block_stmt, rewrite_assign_rhs,
  27            rewrite_call_inner, ExprType};
  28 use lists::{definitive_tactic, itemize_list, write_list, ListFormatting, ListItem, Separator};
  29 use rewrite::{Rewrite, RewriteContext};
  30 use shape::{Indent, Shape};
  31 use spanned::Spanned;
  32 use types::join_bounds;
  33 use utils::{colon_spaces, contains_skip, first_line_width, format_abi, format_constness,
  34             format_defaultness, format_mutability, format_unsafety, format_visibility,
  35             is_attributes_extendable, last_line_contains_single_line_comment,
  36             last_line_extendable, last_line_used_width, last_line_width, mk_sp,
  37             semicolon_for_expr, starts_with_newline, stmt_expr, trimmed_last_line_width};
  38 use vertical::rewrite_with_alignment;
  39 use visitor::FmtVisitor;
  40
  41 fn type_annotation_separator(config: &Config) -> &str {
  42     colon_spaces(config.space_before_colon(), config.space_after_colon())
  43 }
  44
  45 // Statements of the form
  46 // let pat: ty = init;
  47 impl Rewrite for ast::Local {
  48     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  49         debug!(
  50             "Local::rewrite {:?} {} {:?}",
  51             self, shape.width, shape.indent
  52         );
  53
  54         skip_out_of_file_lines_range!(context, self.span);
  55
  56         if contains_skip(&self.attrs) {
  57             return None;
  58         }
  59
  60         let attrs_str = self.attrs.rewrite(context, shape)?;
  61         let mut result = if attrs_str.is_empty() {
  62             "let ".to_owned()
  63         } else {
  64             combine_strs_with_missing_comments(
  65                 context,
  66                 &attrs_str,
  67                 "let ",
  68                 mk_sp(
  69                     self.attrs.last().map(|a| a.span.hi()).unwrap(),
  70                     self.span.lo(),
  71                 ),
  72                 shape,
  73                 false,
  74             )?
  75         };
  76
  77         // 4 = "let ".len()
  78         let pat_shape = shape.offset_left(4)?;
  79         // 1 = ;
  80         let pat_shape = pat_shape.sub_width(1)?;
  81         let pat_str = self.pat.rewrite(context, pat_shape)?;
  82         result.push_str(&pat_str);
  83
  84         // String that is placed within the assignment pattern and expression.
  85         let infix = {
  86             let mut infix = String::with_capacity(32);
  87
  88             if let Some(ref ty) = self.ty {
  89                 let separator = type_annotation_separator(context.config);
  90                 let indent = shape.indent + last_line_width(&result) + separator.len();
  91                 // 1 = ;
  92                 let budget = shape.width.checked_sub(indent.width() + 1)?;
  93                 let rewrite = ty.rewrite(context, Shape::legacy(budget, indent))?;
  94
  95                 infix.push_str(separator);
  96                 infix.push_str(&rewrite);
  97             }
  98
  99             if self.init.is_some() {
 100                 infix.push_str(" =");
 101             }
 102
 103             infix
 104         };
 105
 106         result.push_str(&infix);
 107
 108         if let Some(ref ex) = self.init {
 109             // 1 = trailing semicolon;
 110             let nested_shape = shape.sub_width(1)?;
 111
 112             result = rewrite_assign_rhs(context, result, &**ex, nested_shape)?;
 113         }
 114
 115         result.push(';');
 116         Some(result)
 117     }
 118 }
 119
 120 // TODO convert to using rewrite style rather than visitor
 121 // TODO format modules in this style
 122 #[allow(dead_code)]
 123 struct Item<'a> {
 124     keyword: &'static str,
 125     abi: Cow<'static, str>,
 126     vis: Option<&'a ast::Visibility>,
 127     body: Vec<BodyElement<'a>>,
 128     span: Span,
 129 }
 130
 131 impl<'a> Item<'a> {
 132     fn from_foreign_mod(fm: &'a ast::ForeignMod, span: Span, config: &Config) -> Item<'a> {
 133         Item {
 134             keyword: "",
 135             abi: format_abi(fm.abi, config.force_explicit_abi(), true),
 136             vis: None,
 137             body: fm.items
 138                 .iter()
 139                 .map(|i| BodyElement::ForeignItem(i))
 140                 .collect(),
 141             span,
 142         }
 143     }
 144 }
 145
 146 enum BodyElement<'a> {
 147     // Stmt(&'a ast::Stmt),
 148     // Field(&'a ast::Field),
 149     // Variant(&'a ast::Variant),
 150     // Item(&'a ast::Item),
 151     ForeignItem(&'a ast::ForeignItem),
 152 }
 153
 154 /// Represents a fn's signature.
 155 pub struct FnSig<'a> {
 156     decl: &'a ast::FnDecl,
 157     generics: &'a ast::Generics,
 158     abi: abi::Abi,
 159     constness: ast::Constness,
 160     defaultness: ast::Defaultness,
 161     unsafety: ast::Unsafety,
 162     visibility: ast::Visibility,
 163 }
 164
 165 impl<'a> FnSig<'a> {
 166     pub fn new(
 167         decl: &'a ast::FnDecl,
 168         generics: &'a ast::Generics,
 169         vis: ast::Visibility,
 170     ) -> FnSig<'a> {
 171         FnSig {
 172             decl,
 173             generics,
 174             abi: abi::Abi::Rust,
 175             constness: ast::Constness::NotConst,
 176             defaultness: ast::Defaultness::Final,
 177             unsafety: ast::Unsafety::Normal,
 178             visibility: vis,
 179         }
 180     }
 181
 182     pub fn from_method_sig(
 183         method_sig: &'a ast::MethodSig,
 184         generics: &'a ast::Generics,
 185     ) -> FnSig<'a> {
 186         FnSig {
 187             unsafety: method_sig.unsafety,
 188             constness: method_sig.constness.node,
 189             defaultness: ast::Defaultness::Final,
 190             abi: method_sig.abi,
 191             decl: &*method_sig.decl,
 192             generics,
 193             visibility: ast::Visibility::Inherited,
 194         }
 195     }
 196
 197     pub fn from_fn_kind(
 198         fn_kind: &'a visit::FnKind,
 199         generics: &'a ast::Generics,
 200         decl: &'a ast::FnDecl,
 201         defualtness: ast::Defaultness,
 202     ) -> FnSig<'a> {
 203         match *fn_kind {
 204             visit::FnKind::ItemFn(_, unsafety, constness, abi, visibility, _) => FnSig {
 205                 decl,
 206                 generics,
 207                 abi,
 208                 constness: constness.node,
 209                 defaultness: defualtness,
 210                 unsafety,
 211                 visibility: visibility.clone(),
 212             },
 213             visit::FnKind::Method(_, method_sig, vis, _) => {
 214                 let mut fn_sig = FnSig::from_method_sig(method_sig, generics);
 215                 fn_sig.defaultness = defualtness;
 216                 if let Some(vis) = vis {
 217                     fn_sig.visibility = vis.clone();
 218                 }
 219                 fn_sig
 220             }
 221             _ => unreachable!(),
 222         }
 223     }
 224
 225     fn to_str(&self, context: &RewriteContext) -> String {
 226         let mut result = String::with_capacity(128);
 227         // Vis defaultness constness unsafety abi.
 228         result.push_str(&*format_visibility(&self.visibility));
 229         result.push_str(format_defaultness(self.defaultness));
 230         result.push_str(format_constness(self.constness));
 231         result.push_str(format_unsafety(self.unsafety));
 232         result.push_str(&format_abi(
 233             self.abi,
 234             context.config.force_explicit_abi(),
 235             false,
 236         ));
 237         result
 238     }
 239 }
 240
 241 impl<'a> FmtVisitor<'a> {
 242     fn format_item(&mut self, item: &Item) {
 243         self.buffer.push_str(&item.abi);
 244
 245         let snippet = self.snippet(item.span);
 246         let brace_pos = snippet.find_uncommented("{").unwrap();
 247
 248         self.push_str("{");
 249         if !item.body.is_empty() || contains_comment(&snippet[brace_pos..]) {
 250             // FIXME: this skips comments between the extern keyword and the opening
 251             // brace.
 252             self.last_pos = item.span.lo() + BytePos(brace_pos as u32 + 1);
 253             self.block_indent = self.block_indent.block_indent(self.config);
 254
 255             if item.body.is_empty() {
 256                 self.format_missing_no_indent(item.span.hi() - BytePos(1));
 257                 self.block_indent = self.block_indent.block_unindent(self.config);
 258                 let indent_str = self.block_indent.to_string(self.config);
 259                 self.push_str(&indent_str);
 260             } else {
 261                 for item in &item.body {
 262                     self.format_body_element(item);
 263                 }
 264
 265                 self.block_indent = self.block_indent.block_unindent(self.config);
 266                 self.format_missing_with_indent(item.span.hi() - BytePos(1));
 267             }
 268         }
 269
 270         self.push_str("}");
 271         self.last_pos = item.span.hi();
 272     }
 273
 274     fn format_body_element(&mut self, element: &BodyElement) {
 275         match *element {
 276             BodyElement::ForeignItem(item) => self.format_foreign_item(item),
 277         }
 278     }
 279
 280     pub fn format_foreign_mod(&mut self, fm: &ast::ForeignMod, span: Span) {
 281         let item = Item::from_foreign_mod(fm, span, self.config);
 282         self.format_item(&item);
 283     }
 284
 285     fn format_foreign_item(&mut self, item: &ast::ForeignItem) {
 286         let rewrite = item.rewrite(&self.get_context(), self.shape());
 287         self.push_rewrite(item.span(), rewrite);
 288         self.last_pos = item.span.hi();
 289     }
 290
 291     pub fn rewrite_fn(
 292         &mut self,
 293         indent: Indent,
 294         ident: ast::Ident,
 295         fn_sig: &FnSig,
 296         span: Span,
 297         block: &ast::Block,
 298     ) -> Option<String> {
 299         let context = self.get_context();
 300
 301         let mut newline_brace = newline_for_brace(self.config, &fn_sig.generics.where_clause);
 302
 303         let (mut result, force_newline_brace) =
 304             rewrite_fn_base(&context, indent, ident, fn_sig, span, newline_brace, true)?;
 305
 306         // 2 = ` {`
 307         if self.config.brace_style() == BraceStyle::AlwaysNextLine || force_newline_brace
 308             || last_line_width(&result) + 2 > self.shape().width
 309         {
 310             newline_brace = true;
 311         } else if !result.contains('\n') {
 312             newline_brace = false;
 313         }
 314
 315         // Prepare for the function body by possibly adding a newline and
 316         // indent.
 317         // FIXME we'll miss anything between the end of the signature and the
 318         // start of the body, but we need more spans from the compiler to solve
 319         // this.
 320         if newline_brace {
 321             result.push_str(&indent.to_string_with_newline(self.config));
 322         } else {
 323             result.push(' ');
 324         }
 325
 326         self.single_line_fn(&result, block).or_else(|| Some(result))
 327     }
 328
 329     pub fn rewrite_required_fn(
 330         &mut self,
 331         indent: Indent,
 332         ident: ast::Ident,
 333         sig: &ast::MethodSig,
 334         generics: &ast::Generics,
 335         span: Span,
 336     ) -> Option<String> {
 337         // Drop semicolon or it will be interpreted as comment.
 338         let span = mk_sp(span.lo(), span.hi() - BytePos(1));
 339         let context = self.get_context();
 340
 341         let (mut result, _) = rewrite_fn_base(
 342             &context,
 343             indent,
 344             ident,
 345             &FnSig::from_method_sig(sig, generics),
 346             span,
 347             false,
 348             false,
 349         )?;
 350
 351         // Re-attach semicolon
 352         result.push(';');
 353
 354         Some(result)
 355     }
 356
 357     fn single_line_fn(&self, fn_str: &str, block: &ast::Block) -> Option<String> {
 358         if fn_str.contains('\n') {
 359             return None;
 360         }
 361
 362         let codemap = self.get_context().codemap;
 363
 364         if self.config.empty_item_single_line() && is_empty_block(block, codemap)
 365             && self.block_indent.width() + fn_str.len() + 2 <= self.config.max_width()
 366         {
 367             return Some(format!("{}{{}}", fn_str));
 368         }
 369
 370         if self.config.fn_single_line() && is_simple_block_stmt(block, codemap) {
 371             let rewrite = {
 372                 if let Some(stmt) = block.stmts.first() {
 373                     match stmt_expr(stmt) {
 374                         Some(e) => {
 375                             let suffix = if semicolon_for_expr(&self.get_context(), e) {
 376                                 ";"
 377                             } else {
 378                                 ""
 379                             };
 380
 381                             format_expr(e, ExprType::Statement, &self.get_context(), self.shape())
 382                                 .map(|s| s + suffix)
 383                                 .or_else(|| Some(self.snippet(e.span).to_owned()))
 384                         }
 385                         None => stmt.rewrite(&self.get_context(), self.shape()),
 386                     }
 387                 } else {
 388                     None
 389                 }
 390             };
 391
 392             if let Some(res) = rewrite {
 393                 let width = self.block_indent.width() + fn_str.len() + res.len() + 4;
 394                 if !res.contains('\n') && width <= self.config.max_width() {
 395                     return Some(format!("{}{{ {} }}", fn_str, res));
 396                 }
 397             }
 398         }
 399
 400         None
 401     }
 402
 403     pub fn visit_static(&mut self, static_parts: &StaticParts) {
 404         let rewrite = rewrite_static(&self.get_context(), static_parts, self.block_indent);
 405         self.push_rewrite(static_parts.span, rewrite);
 406     }
 407
 408     pub fn visit_struct(&mut self, struct_parts: &StructParts) {
 409         let is_tuple = struct_parts.def.is_tuple();
 410         let rewrite = format_struct(&self.get_context(), struct_parts, self.block_indent, None)
 411             .map(|s| if is_tuple { s + ";" } else { s });
 412         self.push_rewrite(struct_parts.span, rewrite);
 413     }
 414
 415     pub fn visit_enum(
 416         &mut self,
 417         ident: ast::Ident,
 418         vis: &ast::Visibility,
 419         enum_def: &ast::EnumDef,
 420         generics: &ast::Generics,
 421         span: Span,
 422     ) {
 423         let enum_header = format_header("enum ", ident, vis);
 424         self.push_str(&enum_header);
 425
 426         let enum_snippet = self.snippet(span);
 427         let brace_pos = enum_snippet.find_uncommented("{").unwrap();
 428         let body_start = span.lo() + BytePos(brace_pos as u32 + 1);
 429         let generics_str = format_generics(
 430             &self.get_context(),
 431             generics,
 432             self.config.brace_style(),
 433             if enum_def.variants.is_empty() {
 434                 BracePos::ForceSameLine
 435             } else {
 436                 BracePos::Auto
 437             },
 438             self.block_indent,
 439             mk_sp(span.lo(), body_start),
 440             last_line_width(&enum_header),
 441         ).unwrap();
 442         self.push_str(&generics_str);
 443
 444         self.last_pos = body_start;
 445
 446         self.block_indent = self.block_indent.block_indent(self.config);
 447         let variant_list = self.format_variant_list(enum_def, body_start, span.hi() - BytePos(1));
 448         match variant_list {
 449             Some(ref body_str) => self.push_str(body_str),
 450             None => self.format_missing_no_indent(span.hi() - BytePos(1)),
 451         }
 452         self.block_indent = self.block_indent.block_unindent(self.config);
 453
 454         if variant_list.is_some() || contains_comment(&enum_snippet[brace_pos..]) {
 455             let indent_str = self.block_indent.to_string(self.config);
 456             self.push_str(&indent_str);
 457         }
 458         self.push_str("}");
 459         self.last_pos = span.hi();
 460     }
 461
 462     // Format the body of an enum definition
 463     fn format_variant_list(
 464         &self,
 465         enum_def: &ast::EnumDef,
 466         body_lo: BytePos,
 467         body_hi: BytePos,
 468     ) -> Option<String> {
 469         if enum_def.variants.is_empty() {
 470             return None;
 471         }
 472         let mut result = String::with_capacity(1024);
 473         let indentation = self.block_indent.to_string_with_newline(self.config);
 474         result.push_str(&indentation);
 475
 476         let itemize_list_with = |one_line_width: usize| {
 477             itemize_list(
 478                 self.snippet_provider,
 479                 enum_def.variants.iter(),
 480                 "}",
 481                 ",",
 482                 |f| {
 483                     if !f.node.attrs.is_empty() {
 484                         f.node.attrs[0].span.lo()
 485                     } else {
 486                         f.span.lo()
 487                     }
 488                 },
 489                 |f| f.span.hi(),
 490                 |f| self.format_variant(f, one_line_width),
 491                 body_lo,
 492                 body_hi,
 493                 false,
 494             ).collect()
 495         };
 496         let mut items: Vec<_> =
 497             itemize_list_with(self.config.width_heuristics().struct_variant_width);
 498         // If one of the variants use multiple lines, use multi-lined formatting for all variants.
 499         let has_multiline_variant = items.iter().any(|item| item.inner_as_ref().contains('\n'));
 500         let has_single_line_variant = items.iter().any(|item| !item.inner_as_ref().contains('\n'));
 501         if has_multiline_variant && has_single_line_variant {
 502             items = itemize_list_with(0);
 503         }
 504
 505         let shape = self.shape().sub_width(2)?;
 506         let fmt = ListFormatting {
 507             tactic: DefinitiveListTactic::Vertical,
 508             separator: ",",
 509             trailing_separator: self.config.trailing_comma(),
 510             separator_place: SeparatorPlace::Back,
 511             shape,
 512             ends_with_newline: true,
 513             preserve_newline: true,
 514             config: self.config,
 515         };
 516
 517         let list = write_list(&items, &fmt)?;
 518         result.push_str(&list);
 519         result.push('\n');
 520         Some(result)
 521     }
 522
 523     // Variant of an enum.
 524     fn format_variant(&self, field: &ast::Variant, one_line_width: usize) -> Option<String> {
 525         if contains_skip(&field.node.attrs) {
 526             let lo = field.node.attrs[0].span.lo();
 527             let span = mk_sp(lo, field.span.hi());
 528             return Some(self.snippet(span).to_owned());
 529         }
 530
 531         let context = self.get_context();
 532         // 1 = ','
 533         let shape = self.shape().sub_width(1)?;
 534         let attrs_str = field.node.attrs.rewrite(&context, shape)?;
 535         let lo = field
 536             .node
 537             .attrs
 538             .last()
 539             .map_or(field.span.lo(), |attr| attr.span.hi());
 540         let span = mk_sp(lo, field.span.lo());
 541
 542         let variant_body = match field.node.data {
 543             ast::VariantData::Tuple(..) | ast::VariantData::Struct(..) => format_struct(
 544                 &context,
 545                 &StructParts::from_variant(field),
 546                 self.block_indent,
 547                 Some(one_line_width),
 548             )?,
 549             ast::VariantData::Unit(..) => {
 550                 if let Some(ref expr) = field.node.disr_expr {
 551                     let lhs = format!("{} =", field.node.name);
 552                     rewrite_assign_rhs(&context, lhs, &**expr, shape)?
 553                 } else {
 554                     field.node.name.to_string()
 555                 }
 556             }
 557         };
 558
 559         combine_strs_with_missing_comments(&context, &attrs_str, &variant_body, span, shape, false)
 560     }
 561 }
 562
 563 pub fn format_impl(
 564     context: &RewriteContext,
 565     item: &ast::Item,
 566     offset: Indent,
 567     where_span_end: Option<BytePos>,
 568 ) -> Option<String> {
 569     if let ast::ItemKind::Impl(_, _, _, ref generics, _, ref self_ty, ref items) = item.node {
 570         let mut result = String::with_capacity(128);
 571         let ref_and_type = format_impl_ref_and_type(context, item, offset)?;
 572         let sep = offset.to_string_with_newline(context.config);
 573         result.push_str(&ref_and_type);
 574
 575         let where_budget = if result.contains('\n') {
 576             context.config.max_width()
 577         } else {
 578             context.budget(last_line_width(&result))
 579         };
 580         let option = WhereClauseOption::snuggled(&ref_and_type);
 581         let where_clause_str = rewrite_where_clause(
 582             context,
 583             &generics.where_clause,
 584             context.config.brace_style(),
 585             Shape::legacy(where_budget, offset.block_only()),
 586             Density::Vertical,
 587             "{",
 588             where_span_end,
 589             self_ty.span.hi(),
 590             option,
 591             false,
 592         )?;
 593
 594         // If there is no where clause, we may have missing comments between the trait name and
 595         // the opening brace.
 596         if generics.where_clause.predicates.is_empty() {
 597             if let Some(hi) = where_span_end {
 598                 match recover_missing_comment_in_span(
 599                     mk_sp(self_ty.span.hi(), hi),
 600                     Shape::indented(offset, context.config),
 601                     context,
 602                     last_line_width(&result),
 603                 ) {
 604                     Some(ref missing_comment) if !missing_comment.is_empty() => {
 605                         result.push_str(missing_comment);
 606                     }
 607                     _ => (),
 608                 }
 609             }
 610         }
 611
 612         if is_impl_single_line(context, items, &result, &where_clause_str, item)? {
 613             result.push_str(&where_clause_str);
 614             if where_clause_str.contains('\n') || last_line_contains_single_line_comment(&result) {
 615                 result.push_str(&format!("{}{{{}}}", &sep, &sep));
 616             } else {
 617                 result.push_str(" {}");
 618             }
 619             return Some(result);
 620         }
 621
 622         if !where_clause_str.is_empty() && !where_clause_str.contains('\n') {
 623             let width = offset.block_indent + context.config.tab_spaces() - 1;
 624             let where_indent = Indent::new(0, width);
 625             result.push_str(&where_indent.to_string_with_newline(context.config));
 626         }
 627         result.push_str(&where_clause_str);
 628
 629         let need_newline = !last_line_extendable(&result)
 630             && (last_line_contains_single_line_comment(&result) || result.contains('\n'));
 631         match context.config.brace_style() {
 632             _ if need_newline => result.push_str(&sep),
 633             BraceStyle::AlwaysNextLine => result.push_str(&sep),
 634             BraceStyle::PreferSameLine => result.push(' '),
 635             BraceStyle::SameLineWhere => {
 636                 if !where_clause_str.is_empty() {
 637                     result.push_str(&sep);
 638                 } else {
 639                     result.push(' ');
 640                 }
 641             }
 642         }
 643
 644         result.push('{');
 645
 646         let snippet = context.snippet(item.span);
 647         let open_pos = snippet.find_uncommented("{")? + 1;
 648
 649         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
 650             let mut visitor = FmtVisitor::from_context(context);
 651             visitor.block_indent = offset.block_only().block_indent(context.config);
 652             visitor.last_pos = item.span.lo() + BytePos(open_pos as u32);
 653
 654             visitor.visit_attrs(&item.attrs, ast::AttrStyle::Inner);
 655             for item in items {
 656                 visitor.visit_impl_item(item);
 657             }
 658
 659             visitor.format_missing(item.span.hi() - BytePos(1));
 660
 661             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
 662             let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
 663
 664             result.push_str(&inner_indent_str);
 665             result.push_str(visitor.buffer.to_string().trim());
 666             result.push_str(&outer_indent_str);
 667         }
 668
 669         if result.ends_with('{') {
 670             result.push_str(&sep);
 671         }
 672         result.push('}');
 673
 674         Some(result)
 675     } else {
 676         unreachable!();
 677     }
 678 }
 679
 680 fn is_impl_single_line(
 681     context: &RewriteContext,
 682     items: &[ImplItem],
 683     result: &str,
 684     where_clause_str: &str,
 685     item: &ast::Item,
 686 ) -> Option<bool> {
 687     let snippet = context.snippet(item.span);
 688     let open_pos = snippet.find_uncommented("{")? + 1;
 689
 690     Some(
 691         context.config.empty_item_single_line() && items.is_empty() && !result.contains('\n')
 692             && result.len() + where_clause_str.len() <= context.config.max_width()
 693             && !contains_comment(&snippet[open_pos..]),
 694     )
 695 }
 696
 697 fn format_impl_ref_and_type(
 698     context: &RewriteContext,
 699     item: &ast::Item,
 700     offset: Indent,
 701 ) -> Option<String> {
 702     if let ast::ItemKind::Impl(
 703         unsafety,
 704         polarity,
 705         defaultness,
 706         ref generics,
 707         ref trait_ref,
 708         ref self_ty,
 709         _,
 710     ) = item.node
 711     {
 712         let mut result = String::with_capacity(128);
 713
 714         result.push_str(&format_visibility(&item.vis));
 715         result.push_str(format_defaultness(defaultness));
 716         result.push_str(format_unsafety(unsafety));
 717         result.push_str("impl");
 718
 719         let lo = context.snippet_provider.span_after(item.span, "impl");
 720         let hi = match *trait_ref {
 721             Some(ref tr) => tr.path.span.lo(),
 722             None => self_ty.span.lo(),
 723         };
 724         let shape = generics_shape_from_config(
 725             context.config,
 726             Shape::indented(offset + last_line_width(&result), context.config),
 727             0,
 728         )?;
 729         let one_line_budget = shape.width.checked_sub(last_line_width(&result) + 2)?;
 730         let generics_str =
 731             rewrite_generics_inner(context, generics, shape, one_line_budget, mk_sp(lo, hi))?;
 732
 733         let polarity_str = if polarity == ast::ImplPolarity::Negative {
 734             "!"
 735         } else {
 736             ""
 737         };
 738
 739         if let Some(ref trait_ref) = *trait_ref {
 740             let result_len = result.len();
 741             if let Some(trait_ref_str) = rewrite_trait_ref(
 742                 context,
 743                 trait_ref,
 744                 offset,
 745                 &generics_str,
 746                 true,
 747                 polarity_str,
 748                 result_len,
 749             ) {
 750                 result.push_str(&trait_ref_str);
 751             } else {
 752                 let generics_str =
 753                     rewrite_generics_inner(context, generics, shape, 0, mk_sp(lo, hi))?;
 754                 result.push_str(&rewrite_trait_ref(
 755                     context,
 756                     trait_ref,
 757                     offset,
 758                     &generics_str,
 759                     false,
 760                     polarity_str,
 761                     result_len,
 762                 )?);
 763             }
 764         } else {
 765             result.push_str(&generics_str);
 766         }
 767
 768         // Try to put the self type in a single line.
 769         // ` for`
 770         let trait_ref_overhead = if trait_ref.is_some() { 4 } else { 0 };
 771         let curly_brace_overhead = if generics.where_clause.predicates.is_empty() {
 772             // If there is no where clause adapt budget for type formatting to take space and curly
 773             // brace into account.
 774             match context.config.brace_style() {
 775                 BraceStyle::AlwaysNextLine => 0,
 776                 _ => 2,
 777             }
 778         } else {
 779             0
 780         };
 781         let used_space = last_line_width(&result) + trait_ref_overhead + curly_brace_overhead;
 782         // 1 = space before the type.
 783         let budget = context.budget(used_space + 1);
 784         if let Some(self_ty_str) = self_ty.rewrite(context, Shape::legacy(budget, offset)) {
 785             if !self_ty_str.contains('\n') {
 786                 if trait_ref.is_some() {
 787                     result.push_str(" for ");
 788                 } else {
 789                     result.push(' ');
 790                 }
 791                 result.push_str(&self_ty_str);
 792                 return Some(result);
 793             }
 794         }
 795
 796         // Couldn't fit the self type on a single line, put it on a new line.
 797         result.push('\n');
 798         // Add indentation of one additional tab.
 799         let new_line_offset = offset.block_indent(context.config);
 800         result.push_str(&new_line_offset.to_string(context.config));
 801         if trait_ref.is_some() {
 802             result.push_str("for ");
 803         }
 804         let budget = context.budget(last_line_width(&result));
 805         let type_offset = match context.config.indent_style() {
 806             IndentStyle::Visual => new_line_offset + trait_ref_overhead,
 807             IndentStyle::Block => new_line_offset,
 808         };
 809         result.push_str(&*self_ty.rewrite(context, Shape::legacy(budget, type_offset))?);
 810         Some(result)
 811     } else {
 812         unreachable!();
 813     }
 814 }
 815
 816 fn rewrite_trait_ref(
 817     context: &RewriteContext,
 818     trait_ref: &ast::TraitRef,
 819     offset: Indent,
 820     generics_str: &str,
 821     retry: bool,
 822     polarity_str: &str,
 823     result_len: usize,
 824 ) -> Option<String> {
 825     // 1 = space between generics and trait_ref
 826     let used_space = 1 + polarity_str.len() + last_line_used_width(generics_str, result_len);
 827     let shape = Shape::indented(offset + used_space, context.config);
 828     if let Some(trait_ref_str) = trait_ref.rewrite(context, shape) {
 829         if !(retry && trait_ref_str.contains('\n')) {
 830             return Some(format!(
 831                 "{} {}{}",
 832                 generics_str, polarity_str, &trait_ref_str
 833             ));
 834         }
 835     }
 836     // We could not make enough space for trait_ref, so put it on new line.
 837     if !retry {
 838         let offset = offset.block_indent(context.config);
 839         let shape = Shape::indented(offset, context.config);
 840         let trait_ref_str = trait_ref.rewrite(context, shape)?;
 841         Some(format!(
 842             "{}\n{}{}{}",
 843             generics_str,
 844             &offset.to_string(context.config),
 845             polarity_str,
 846             &trait_ref_str
 847         ))
 848     } else {
 849         None
 850     }
 851 }
 852
 853 pub struct StructParts<'a> {
 854     prefix: &'a str,
 855     ident: ast::Ident,
 856     vis: &'a ast::Visibility,
 857     def: &'a ast::VariantData,
 858     generics: Option<&'a ast::Generics>,
 859     span: Span,
 860 }
 861
 862 impl<'a> StructParts<'a> {
 863     fn format_header(&self) -> String {
 864         format_header(self.prefix, self.ident, self.vis)
 865     }
 866
 867     fn from_variant(variant: &'a ast::Variant) -> Self {
 868         StructParts {
 869             prefix: "",
 870             ident: variant.node.name,
 871             vis: &ast::Visibility::Inherited,
 872             def: &variant.node.data,
 873             generics: None,
 874             span: variant.span,
 875         }
 876     }
 877
 878     pub fn from_item(item: &'a ast::Item) -> Self {
 879         let (prefix, def, generics) = match item.node {
 880             ast::ItemKind::Struct(ref def, ref generics) => ("struct ", def, generics),
 881             ast::ItemKind::Union(ref def, ref generics) => ("union ", def, generics),
 882             _ => unreachable!(),
 883         };
 884         StructParts {
 885             prefix,
 886             ident: item.ident,
 887             vis: &item.vis,
 888             def,
 889             generics: Some(generics),
 890             span: item.span,
 891         }
 892     }
 893 }
 894
 895 fn format_struct(
 896     context: &RewriteContext,
 897     struct_parts: &StructParts,
 898     offset: Indent,
 899     one_line_width: Option<usize>,
 900 ) -> Option<String> {
 901     match *struct_parts.def {
 902         ast::VariantData::Unit(..) => format_unit_struct(context, struct_parts, offset),
 903         ast::VariantData::Tuple(ref fields, _) => {
 904             format_tuple_struct(context, struct_parts, fields, offset)
 905         }
 906         ast::VariantData::Struct(ref fields, _) => {
 907             format_struct_struct(context, struct_parts, fields, offset, one_line_width)
 908         }
 909     }
 910 }
 911
 912 pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 913     if let ast::ItemKind::Trait(_, unsafety, ref generics, ref type_param_bounds, ref trait_items) =
 914         item.node
 915     {
 916         let mut result = String::with_capacity(128);
 917         let header = format!(
 918             "{}{}trait {}",
 919             format_visibility(&item.vis),
 920             format_unsafety(unsafety),
 921             item.ident
 922         );
 923
 924         result.push_str(&header);
 925
 926         let body_lo = context.snippet_provider.span_after(item.span, "{");
 927
 928         let shape = Shape::indented(offset, context.config).offset_left(result.len())?;
 929         let generics_str =
 930             rewrite_generics(context, generics, shape, mk_sp(item.span.lo(), body_lo))?;
 931         result.push_str(&generics_str);
 932
 933         // FIXME(#2055): rustfmt fails to format when there are comments between trait bounds.
 934         if !type_param_bounds.is_empty() {
 935             let ident_hi = context
 936                 .snippet_provider
 937                 .span_after(item.span, &format!("{}", item.ident));
 938             let bound_hi = type_param_bounds.last().unwrap().span().hi();
 939             let snippet = context.snippet(mk_sp(ident_hi, bound_hi));
 940             if contains_comment(snippet) {
 941                 return None;
 942             }
 943         }
 944         let trait_bound_str = rewrite_trait_bounds(
 945             context,
 946             type_param_bounds,
 947             Shape::indented(offset, context.config),
 948         )?;
 949         // If the trait, generics, and trait bound cannot fit on the same line,
 950         // put the trait bounds on an indented new line
 951         if offset.width() + last_line_width(&result) + trait_bound_str.len()
 952             > context.config.comment_width()
 953         {
 954             let trait_indent = offset.block_only().block_indent(context.config);
 955             result.push_str(&trait_indent.to_string_with_newline(context.config));
 956         }
 957         result.push_str(&trait_bound_str);
 958
 959         let where_density =
 960             if context.config.indent_style() == IndentStyle::Block && result.is_empty() {
 961                 Density::Compressed
 962             } else {
 963                 Density::Tall
 964             };
 965
 966         let where_budget = context.budget(last_line_width(&result));
 967         let pos_before_where = if type_param_bounds.is_empty() {
 968             generics.where_clause.span.lo()
 969         } else {
 970             type_param_bounds[type_param_bounds.len() - 1].span().hi()
 971         };
 972         let option = WhereClauseOption::snuggled(&generics_str);
 973         let where_clause_str = rewrite_where_clause(
 974             context,
 975             &generics.where_clause,
 976             context.config.brace_style(),
 977             Shape::legacy(where_budget, offset.block_only()),
 978             where_density,
 979             "{",
 980             None,
 981             pos_before_where,
 982             option,
 983             false,
 984         )?;
 985         // If the where clause cannot fit on the same line,
 986         // put the where clause on a new line
 987         if !where_clause_str.contains('\n')
 988             && last_line_width(&result) + where_clause_str.len() + offset.width()
 989                 > context.config.comment_width()
 990         {
 991             let width = offset.block_indent + context.config.tab_spaces() - 1;
 992             let where_indent = Indent::new(0, width);
 993             result.push_str(&where_indent.to_string_with_newline(context.config));
 994         }
 995         result.push_str(&where_clause_str);
 996
 997         if generics.where_clause.predicates.is_empty() {
 998             let item_snippet = context.snippet(item.span);
 999             if let Some(lo) = item_snippet.chars().position(|c| c == '/') {
1000                 // 1 = `{`
1001                 let comment_hi = body_lo - BytePos(1);
1002                 let comment_lo = item.span.lo() + BytePos(lo as u32);
1003                 if comment_lo < comment_hi {
1004                     match recover_missing_comment_in_span(
1005                         mk_sp(comment_lo, comment_hi),
1006                         Shape::indented(offset, context.config),
1007                         context,
1008                         last_line_width(&result),
1009                     ) {
1010                         Some(ref missing_comment) if !missing_comment.is_empty() => {
1011                             result.push_str(missing_comment);
1012                         }
1013                         _ => (),
1014                     }
1015                 }
1016             }
1017         }
1018
1019         match context.config.brace_style() {
1020             _ if last_line_contains_single_line_comment(&result) => {
1021                 result.push_str(&offset.to_string_with_newline(context.config));
1022             }
1023             BraceStyle::AlwaysNextLine => {
1024                 result.push_str(&offset.to_string_with_newline(context.config));
1025             }
1026             BraceStyle::PreferSameLine => result.push(' '),
1027             BraceStyle::SameLineWhere => {
1028                 if !where_clause_str.is_empty()
1029                     && (!trait_items.is_empty() || result.contains('\n'))
1030                 {
1031                     result.push_str(&offset.to_string_with_newline(context.config));
1032                 } else {
1033                     result.push(' ');
1034                 }
1035             }
1036         }
1037         result.push('{');
1038
1039         let snippet = context.snippet(item.span);
1040         let open_pos = snippet.find_uncommented("{")? + 1;
1041
1042         if !trait_items.is_empty() || contains_comment(&snippet[open_pos..]) {
1043             let mut visitor = FmtVisitor::from_context(context);
1044             visitor.block_indent = offset.block_only().block_indent(context.config);
1045             visitor.last_pos = item.span.lo() + BytePos(open_pos as u32);
1046
1047             for item in trait_items {
1048                 visitor.visit_trait_item(item);
1049             }
1050
1051             visitor.format_missing(item.span.hi() - BytePos(1));
1052
1053             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
1054             let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
1055
1056             result.push_str(&inner_indent_str);
1057             result.push_str(visitor.buffer.to_string().trim());
1058             result.push_str(&outer_indent_str);
1059         } else if result.contains('\n') {
1060             result.push('\n');
1061         }
1062
1063         result.push('}');
1064         Some(result)
1065     } else {
1066         unreachable!();
1067     }
1068 }
1069
1070 pub fn format_trait_alias(
1071     context: &RewriteContext,
1072     ident: ast::Ident,
1073     generics: &ast::Generics,
1074     ty_param_bounds: &ast::TyParamBounds,
1075     shape: Shape,
1076 ) -> Option<String> {
1077     let alias = ident.name.as_str();
1078     // 6 = "trait ", 2 = " ="
1079     let g_shape = shape.offset_left(6 + alias.len())?.sub_width(2)?;
1080     let generics_str = rewrite_generics(context, generics, g_shape, generics.span)?;
1081     let lhs = format!("trait {}{} =", alias, generics_str);
1082     // 1 = ";"
1083     rewrite_assign_rhs(context, lhs, ty_param_bounds, shape.sub_width(1)?).map(|s| s + ";")
1084 }
1085
1086 fn format_unit_struct(context: &RewriteContext, p: &StructParts, offset: Indent) -> Option<String> {
1087     let header_str = format_header(p.prefix, p.ident, p.vis);
1088     let generics_str = if let Some(generics) = p.generics {
1089         let hi = if generics.where_clause.predicates.is_empty() {
1090             generics.span.hi()
1091         } else {
1092             generics.where_clause.span.hi()
1093         };
1094         format_generics(
1095             context,
1096             generics,
1097             context.config.brace_style(),
1098             BracePos::None,
1099             offset,
1100             mk_sp(generics.span.lo(), hi),
1101             last_line_width(&header_str),
1102         )?
1103     } else {
1104         String::new()
1105     };
1106     Some(format!("{}{};", header_str, generics_str))
1107 }
1108
1109 pub fn format_struct_struct(
1110     context: &RewriteContext,
1111     struct_parts: &StructParts,
1112     fields: &[ast::StructField],
1113     offset: Indent,
1114     one_line_width: Option<usize>,
1115 ) -> Option<String> {
1116     let mut result = String::with_capacity(1024);
1117     let span = struct_parts.span;
1118
1119     let header_str = struct_parts.format_header();
1120     result.push_str(&header_str);
1121
1122     let header_hi = span.lo() + BytePos(header_str.len() as u32);
1123     let body_lo = context.snippet_provider.span_after(span, "{");
1124
1125     let generics_str = match struct_parts.generics {
1126         Some(g) => format_generics(
1127             context,
1128             g,
1129             context.config.brace_style(),
1130             if fields.is_empty() {
1131                 BracePos::ForceSameLine
1132             } else {
1133                 BracePos::Auto
1134             },
1135             offset,
1136             mk_sp(header_hi, body_lo),
1137             last_line_width(&result),
1138         )?,
1139         None => {
1140             // 3 = ` {}`, 2 = ` {`.
1141             let overhead = if fields.is_empty() { 3 } else { 2 };
1142             if (context.config.brace_style() == BraceStyle::AlwaysNextLine && !fields.is_empty())
1143                 || context.config.max_width() < overhead + result.len()
1144             {
1145                 format!("\n{}{{", offset.block_only().to_string(context.config))
1146             } else {
1147                 " {".to_owned()
1148             }
1149         }
1150     };
1151     // 1 = `}`
1152     let overhead = if fields.is_empty() { 1 } else { 0 };
1153     let total_width = result.len() + generics_str.len() + overhead;
1154     if !generics_str.is_empty() && !generics_str.contains('\n')
1155         && total_width > context.config.max_width()
1156     {
1157         result.push('\n');
1158         result.push_str(&offset.to_string(context.config));
1159         result.push_str(generics_str.trim_left());
1160     } else {
1161         result.push_str(&generics_str);
1162     }
1163
1164     if fields.is_empty() {
1165         let snippet = context.snippet(mk_sp(body_lo, span.hi() - BytePos(1)));
1166         if snippet.trim().is_empty() {
1167             // `struct S {}`
1168         } else if snippet.trim_right_matches(&[' ', '\t'][..]).ends_with('\n') {
1169             // fix indent
1170             result.push_str(snippet.trim_right());
1171             result.push('\n');
1172             result.push_str(&offset.to_string(context.config));
1173         } else {
1174             result.push_str(snippet);
1175         }
1176         result.push('}');
1177         return Some(result);
1178     }
1179
1180     // 3 = ` ` and ` }`
1181     let one_line_budget = context.budget(result.len() + 3 + offset.width());
1182     let one_line_budget =
1183         one_line_width.map_or(0, |one_line_width| min(one_line_width, one_line_budget));
1184
1185     let items_str = rewrite_with_alignment(
1186         fields,
1187         context,
1188         Shape::indented(offset, context.config).sub_width(1)?,
1189         mk_sp(body_lo, span.hi()),
1190         one_line_budget,
1191     )?;
1192
1193     if !items_str.contains('\n') && !result.contains('\n') && items_str.len() <= one_line_budget
1194         && !last_line_contains_single_line_comment(&items_str)
1195     {
1196         Some(format!("{} {} }}", result, items_str))
1197     } else {
1198         Some(format!(
1199             "{}\n{}{}\n{}}}",
1200             result,
1201             offset
1202                 .block_indent(context.config)
1203                 .to_string(context.config),
1204             items_str,
1205             offset.to_string(context.config)
1206         ))
1207     }
1208 }
1209
1210 /// Returns a bytepos that is after that of `(` in `pub(..)`. If the given visibility does not
1211 /// contain `pub(..)`, then return the `lo` of the `defualt_span`. Yeah, but for what? Well, we need
1212 /// to bypass the `(` in the visibility when creating a span of tuple's body or fn's args.
1213 fn get_bytepos_after_visibility(
1214     context: &RewriteContext,
1215     vis: &ast::Visibility,
1216     default_span: Span,
1217     terminator: &str,
1218 ) -> BytePos {
1219     match *vis {
1220         ast::Visibility::Crate(s, CrateSugar::PubCrate) => context
1221             .snippet_provider
1222             .span_after(mk_sp(s.hi(), default_span.hi()), terminator),
1223         ast::Visibility::Crate(s, CrateSugar::JustCrate) => s.hi(),
1224         ast::Visibility::Restricted { ref path, .. } => path.span.hi(),
1225         _ => default_span.lo(),
1226     }
1227 }
1228
1229 fn format_tuple_struct(
1230     context: &RewriteContext,
1231     struct_parts: &StructParts,
1232     fields: &[ast::StructField],
1233     offset: Indent,
1234 ) -> Option<String> {
1235     let mut result = String::with_capacity(1024);
1236     let span = struct_parts.span;
1237
1238     let header_str = struct_parts.format_header();
1239     result.push_str(&header_str);
1240
1241     let body_lo = if fields.is_empty() {
1242         let lo = get_bytepos_after_visibility(context, struct_parts.vis, span, ")");
1243         context
1244             .snippet_provider
1245             .span_after(mk_sp(lo, span.hi()), "(")
1246     } else {
1247         fields[0].span.lo()
1248     };
1249     let body_hi = if fields.is_empty() {
1250         context
1251             .snippet_provider
1252             .span_after(mk_sp(body_lo, span.hi()), ")")
1253     } else {
1254         // This is a dirty hack to work around a missing `)` from the span of the last field.
1255         let last_arg_span = fields[fields.len() - 1].span;
1256         if context.snippet(last_arg_span).ends_with(')') {
1257             last_arg_span.hi()
1258         } else {
1259             context
1260                 .snippet_provider
1261                 .span_after(mk_sp(last_arg_span.hi(), span.hi()), ")")
1262         }
1263     };
1264
1265     let where_clause_str = match struct_parts.generics {
1266         Some(generics) => {
1267             let budget = context.budget(last_line_width(&header_str));
1268             let shape = Shape::legacy(budget, offset);
1269             let g_span = mk_sp(span.lo(), body_lo);
1270             let generics_str = rewrite_generics(context, generics, shape, g_span)?;
1271             result.push_str(&generics_str);
1272
1273             let where_budget = context.budget(last_line_width(&result));
1274             let option = WhereClauseOption::new(true, false);
1275             rewrite_where_clause(
1276                 context,
1277                 &generics.where_clause,
1278                 context.config.brace_style(),
1279                 Shape::legacy(where_budget, offset.block_only()),
1280                 Density::Compressed,
1281                 ";",
1282                 None,
1283                 body_hi,
1284                 option,
1285                 false,
1286             )?
1287         }
1288         None => "".to_owned(),
1289     };
1290
1291     if fields.is_empty() {
1292         // 3 = `();`
1293         let used_width = last_line_used_width(&result, offset.width()) + 3;
1294         if used_width > context.config.max_width() {
1295             result.push('\n');
1296             result.push_str(&offset
1297                 .block_indent(context.config)
1298                 .to_string(context.config))
1299         }
1300         result.push('(');
1301         let snippet = context.snippet(mk_sp(
1302             body_lo,
1303             context
1304                 .snippet_provider
1305                 .span_before(mk_sp(body_lo, span.hi()), ")"),
1306         ));
1307         if snippet.is_empty() {
1308             // `struct S ()`
1309         } else if snippet.trim_right_matches(&[' ', '\t'][..]).ends_with('\n') {
1310             result.push_str(snippet.trim_right());
1311             result.push('\n');
1312             result.push_str(&offset.to_string(context.config));
1313         } else {
1314             result.push_str(snippet);
1315         }
1316         result.push(')');
1317     } else {
1318         let shape = Shape::indented(offset, context.config).sub_width(1)?;
1319         let fields = &fields.iter().collect::<Vec<_>>()[..];
1320         let one_line_width = context.config.width_heuristics().fn_call_width;
1321         result = rewrite_call_inner(context, &result, fields, span, shape, one_line_width, false)?;
1322     }
1323
1324     if !where_clause_str.is_empty() && !where_clause_str.contains('\n')
1325         && (result.contains('\n')
1326             || offset.block_indent + result.len() + where_clause_str.len() + 1
1327                 > context.config.max_width())
1328     {
1329         // We need to put the where clause on a new line, but we didn't
1330         // know that earlier, so the where clause will not be indented properly.
1331         result.push('\n');
1332         result
1333             .push_str(&(offset.block_only() + (context.config.tab_spaces() - 1))
1334                 .to_string(context.config));
1335     }
1336     result.push_str(&where_clause_str);
1337
1338     Some(result)
1339 }
1340
1341 pub fn rewrite_type_alias(
1342     context: &RewriteContext,
1343     indent: Indent,
1344     ident: ast::Ident,
1345     ty: &ast::Ty,
1346     generics: &ast::Generics,
1347     vis: &ast::Visibility,
1348     span: Span,
1349 ) -> Option<String> {
1350     let mut result = String::with_capacity(128);
1351
1352     result.push_str(&format_visibility(vis));
1353     result.push_str("type ");
1354     result.push_str(&ident.to_string());
1355
1356     // 2 = `= `
1357     let g_shape = Shape::indented(indent, context.config)
1358         .offset_left(result.len())?
1359         .sub_width(2)?;
1360     let g_span = mk_sp(
1361         context.snippet_provider.span_after(span, "type"),
1362         ty.span.lo(),
1363     );
1364     let generics_str = rewrite_generics(context, generics, g_shape, g_span)?;
1365     result.push_str(&generics_str);
1366
1367     let where_budget = context.budget(last_line_width(&result));
1368     let option = WhereClauseOption::snuggled(&result);
1369     let where_clause_str = rewrite_where_clause(
1370         context,
1371         &generics.where_clause,
1372         context.config.brace_style(),
1373         Shape::legacy(where_budget, indent),
1374         Density::Vertical,
1375         "=",
1376         Some(span.hi()),
1377         generics.span.hi(),
1378         option,
1379         false,
1380     )?;
1381     result.push_str(&where_clause_str);
1382     if where_clause_str.is_empty() {
1383         result.push_str(" =");
1384     } else {
1385         result.push_str(&format!(
1386             "{}=",
1387             indent.to_string_with_newline(context.config)
1388         ));
1389     }
1390
1391     // 1 = ";"
1392     let ty_shape = Shape::indented(indent, context.config).sub_width(1)?;
1393     rewrite_assign_rhs(context, result, ty, ty_shape).map(|s| s + ";")
1394 }
1395
1396 fn type_annotation_spacing(config: &Config) -> (&str, &str) {
1397     (
1398         if config.space_before_colon() { " " } else { "" },
1399         if config.space_after_colon() { " " } else { "" },
1400     )
1401 }
1402
1403 pub fn rewrite_struct_field_prefix(
1404     context: &RewriteContext,
1405     field: &ast::StructField,
1406 ) -> Option<String> {
1407     let vis = format_visibility(&field.vis);
1408     let type_annotation_spacing = type_annotation_spacing(context.config);
1409     Some(match field.ident {
1410         Some(name) => format!("{}{}{}:", vis, name, type_annotation_spacing.0),
1411         None => format!("{}", vis),
1412     })
1413 }
1414
1415 impl Rewrite for ast::StructField {
1416     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1417         rewrite_struct_field(context, self, shape, 0)
1418     }
1419 }
1420
1421 pub fn rewrite_struct_field(
1422     context: &RewriteContext,
1423     field: &ast::StructField,
1424     shape: Shape,
1425     lhs_max_width: usize,
1426 ) -> Option<String> {
1427     if contains_skip(&field.attrs) {
1428         return Some(context.snippet(field.span()).to_owned());
1429     }
1430
1431     let type_annotation_spacing = type_annotation_spacing(context.config);
1432     let prefix = rewrite_struct_field_prefix(context, field)?;
1433
1434     let attrs_str = field.attrs.rewrite(context, shape)?;
1435     let attrs_extendable = field.ident.is_none() && is_attributes_extendable(&attrs_str);
1436     let missing_span = if field.attrs.is_empty() {
1437         mk_sp(field.span.lo(), field.span.lo())
1438     } else {
1439         mk_sp(field.attrs.last().unwrap().span.hi(), field.span.lo())
1440     };
1441     let mut spacing = String::from(if field.ident.is_some() {
1442         type_annotation_spacing.1
1443     } else {
1444         ""
1445     });
1446     // Try to put everything on a single line.
1447     let attr_prefix = combine_strs_with_missing_comments(
1448         context,
1449         &attrs_str,
1450         &prefix,
1451         missing_span,
1452         shape,
1453         attrs_extendable,
1454     )?;
1455     let overhead = last_line_width(&attr_prefix);
1456     let lhs_offset = lhs_max_width.checked_sub(overhead).unwrap_or(0);
1457     for _ in 0..lhs_offset {
1458         spacing.push(' ');
1459     }
1460     // In this extreme case we will be missing a space betweeen an attribute and a field.
1461     if prefix.is_empty() && !attrs_str.is_empty() && attrs_extendable && spacing.is_empty() {
1462         spacing.push(' ');
1463     }
1464     let orig_ty = shape
1465         .offset_left(overhead + spacing.len())
1466         .and_then(|ty_shape| field.ty.rewrite(context, ty_shape));
1467     if let Some(ref ty) = orig_ty {
1468         if !ty.contains('\n') {
1469             return Some(attr_prefix + &spacing + ty);
1470         }
1471     }
1472
1473     let is_prefix_empty = prefix.is_empty();
1474     // We must use multiline. We are going to put attributes and a field on different lines.
1475     let field_str = rewrite_assign_rhs(context, prefix, &*field.ty, shape)?;
1476     // Remove a leading white-space from `rewrite_assign_rhs()` when rewriting a tuple struct.
1477     let field_str = if is_prefix_empty {
1478         field_str.trim_left()
1479     } else {
1480         &field_str
1481     };
1482     combine_strs_with_missing_comments(context, &attrs_str, field_str, missing_span, shape, false)
1483 }
1484
1485 pub struct StaticParts<'a> {
1486     prefix: &'a str,
1487     vis: &'a ast::Visibility,
1488     ident: ast::Ident,
1489     ty: &'a ast::Ty,
1490     mutability: ast::Mutability,
1491     expr_opt: Option<&'a ptr::P<ast::Expr>>,
1492     defaultness: Option<ast::Defaultness>,
1493     span: Span,
1494 }
1495
1496 impl<'a> StaticParts<'a> {
1497     pub fn from_item(item: &'a ast::Item) -> Self {
1498         let (prefix, ty, mutability, expr) = match item.node {
1499             ast::ItemKind::Static(ref ty, mutability, ref expr) => ("static", ty, mutability, expr),
1500             ast::ItemKind::Const(ref ty, ref expr) => {
1501                 ("const", ty, ast::Mutability::Immutable, expr)
1502             }
1503             _ => unreachable!(),
1504         };
1505         StaticParts {
1506             prefix,
1507             vis: &item.vis,
1508             ident: item.ident,
1509             ty,
1510             mutability,
1511             expr_opt: Some(expr),
1512             defaultness: None,
1513             span: item.span,
1514         }
1515     }
1516
1517     pub fn from_trait_item(ti: &'a ast::TraitItem) -> Self {
1518         let (ty, expr_opt) = match ti.node {
1519             ast::TraitItemKind::Const(ref ty, ref expr_opt) => (ty, expr_opt),
1520             _ => unreachable!(),
1521         };
1522         StaticParts {
1523             prefix: "const",
1524             vis: &ast::Visibility::Inherited,
1525             ident: ti.ident,
1526             ty,
1527             mutability: ast::Mutability::Immutable,
1528             expr_opt: expr_opt.as_ref(),
1529             defaultness: None,
1530             span: ti.span,
1531         }
1532     }
1533
1534     pub fn from_impl_item(ii: &'a ast::ImplItem) -> Self {
1535         let (ty, expr) = match ii.node {
1536             ast::ImplItemKind::Const(ref ty, ref expr) => (ty, expr),
1537             _ => unreachable!(),
1538         };
1539         StaticParts {
1540             prefix: "const",
1541             vis: &ii.vis,
1542             ident: ii.ident,
1543             ty,
1544             mutability: ast::Mutability::Immutable,
1545             expr_opt: Some(expr),
1546             defaultness: Some(ii.defaultness),
1547             span: ii.span,
1548         }
1549     }
1550 }
1551
1552 fn rewrite_static(
1553     context: &RewriteContext,
1554     static_parts: &StaticParts,
1555     offset: Indent,
1556 ) -> Option<String> {
1557     let colon = colon_spaces(
1558         context.config.space_before_colon(),
1559         context.config.space_after_colon(),
1560     );
1561     let mut prefix = format!(
1562         "{}{}{} {}{}{}",
1563         format_visibility(static_parts.vis),
1564         static_parts.defaultness.map_or("", format_defaultness),
1565         static_parts.prefix,
1566         format_mutability(static_parts.mutability),
1567         static_parts.ident,
1568         colon,
1569     );
1570     // 2 = " =".len()
1571     let ty_shape =
1572         Shape::indented(offset.block_only(), context.config).offset_left(prefix.len() + 2)?;
1573     let ty_str = match static_parts.ty.rewrite(context, ty_shape) {
1574         Some(ty_str) => ty_str,
1575         None => {
1576             if prefix.ends_with(' ') {
1577                 prefix.pop();
1578             }
1579             let nested_indent = offset.block_indent(context.config);
1580             let nested_shape = Shape::indented(nested_indent, context.config);
1581             let ty_str = static_parts.ty.rewrite(context, nested_shape)?;
1582             format!(
1583                 "{}{}",
1584                 nested_indent.to_string_with_newline(context.config),
1585                 ty_str
1586             )
1587         }
1588     };
1589
1590     if let Some(expr) = static_parts.expr_opt {
1591         let lhs = format!("{}{} =", prefix, ty_str);
1592         // 1 = ;
1593         let remaining_width = context.budget(offset.block_indent + 1);
1594         rewrite_assign_rhs(
1595             context,
1596             lhs,
1597             &**expr,
1598             Shape::legacy(remaining_width, offset.block_only()),
1599         ).and_then(|res| recover_comment_removed(res, static_parts.span, context))
1600             .map(|s| if s.ends_with(';') { s } else { s + ";" })
1601     } else {
1602         Some(format!("{}{};", prefix, ty_str))
1603     }
1604 }
1605
1606 pub fn rewrite_associated_type(
1607     ident: ast::Ident,
1608     ty_opt: Option<&ptr::P<ast::Ty>>,
1609     ty_param_bounds_opt: Option<&ast::TyParamBounds>,
1610     context: &RewriteContext,
1611     indent: Indent,
1612 ) -> Option<String> {
1613     let prefix = format!("type {}", ident);
1614
1615     let type_bounds_str = if let Some(bounds) = ty_param_bounds_opt {
1616         // 2 = ": ".len()
1617         let shape = Shape::indented(indent, context.config).offset_left(prefix.len() + 2)?;
1618         let bound_str = bounds
1619             .iter()
1620             .map(|ty_bound| ty_bound.rewrite(context, shape))
1621             .collect::<Option<Vec<_>>>()?;
1622         if !bounds.is_empty() {
1623             format!(": {}", join_bounds(context, shape, &bound_str))
1624         } else {
1625             String::new()
1626         }
1627     } else {
1628         String::new()
1629     };
1630
1631     if let Some(ty) = ty_opt {
1632         // 1 = `;`
1633         let shape = Shape::indented(indent, context.config).sub_width(1)?;
1634         let lhs = format!("{}{} =", prefix, type_bounds_str);
1635         rewrite_assign_rhs(context, lhs, &**ty, shape).map(|s| s + ";")
1636     } else {
1637         Some(format!("{}{};", prefix, type_bounds_str))
1638     }
1639 }
1640
1641 pub fn rewrite_associated_impl_type(
1642     ident: ast::Ident,
1643     defaultness: ast::Defaultness,
1644     ty_opt: Option<&ptr::P<ast::Ty>>,
1645     ty_param_bounds_opt: Option<&ast::TyParamBounds>,
1646     context: &RewriteContext,
1647     indent: Indent,
1648 ) -> Option<String> {
1649     let result = rewrite_associated_type(ident, ty_opt, ty_param_bounds_opt, context, indent)?;
1650
1651     match defaultness {
1652         ast::Defaultness::Default => Some(format!("default {}", result)),
1653         _ => Some(result),
1654     }
1655 }
1656
1657 impl Rewrite for ast::FunctionRetTy {
1658     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1659         match *self {
1660             ast::FunctionRetTy::Default(_) => Some(String::new()),
1661             ast::FunctionRetTy::Ty(ref ty) => {
1662                 let inner_width = shape.width.checked_sub(3)?;
1663                 ty.rewrite(context, Shape::legacy(inner_width, shape.indent + 3))
1664                     .map(|r| format!("-> {}", r))
1665             }
1666         }
1667     }
1668 }
1669
1670 fn is_empty_infer(context: &RewriteContext, ty: &ast::Ty) -> bool {
1671     match ty.node {
1672         ast::TyKind::Infer => {
1673             let original = context.snippet(ty.span);
1674             original != "_"
1675         }
1676         _ => false,
1677     }
1678 }
1679
1680 impl Rewrite for ast::Arg {
1681     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1682         if is_named_arg(self) {
1683             let mut result = self.pat
1684                 .rewrite(context, Shape::legacy(shape.width, shape.indent))?;
1685
1686             if !is_empty_infer(context, &*self.ty) {
1687                 if context.config.space_before_colon() {
1688                     result.push_str(" ");
1689                 }
1690                 result.push_str(":");
1691                 if context.config.space_after_colon() {
1692                     result.push_str(" ");
1693                 }
1694                 let overhead = last_line_width(&result);
1695                 let max_width = shape.width.checked_sub(overhead)?;
1696                 let ty_str = self.ty
1697                     .rewrite(context, Shape::legacy(max_width, shape.indent))?;
1698                 result.push_str(&ty_str);
1699             }
1700
1701             Some(result)
1702         } else {
1703             self.ty.rewrite(context, shape)
1704         }
1705     }
1706 }
1707
1708 fn rewrite_explicit_self(
1709     explicit_self: &ast::ExplicitSelf,
1710     args: &[ast::Arg],
1711     context: &RewriteContext,
1712 ) -> Option<String> {
1713     match explicit_self.node {
1714         ast::SelfKind::Region(lt, m) => {
1715             let mut_str = format_mutability(m);
1716             match lt {
1717                 Some(ref l) => {
1718                     let lifetime_str = l.rewrite(
1719                         context,
1720                         Shape::legacy(context.config.max_width(), Indent::empty()),
1721                     )?;
1722                     Some(format!("&{} {}self", lifetime_str, mut_str))
1723                 }
1724                 None => Some(format!("&{}self", mut_str)),
1725             }
1726         }
1727         ast::SelfKind::Explicit(ref ty, _) => {
1728             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1729
1730             let mutability = explicit_self_mutability(&args[0]);
1731             let type_str = ty.rewrite(
1732                 context,
1733                 Shape::legacy(context.config.max_width(), Indent::empty()),
1734             )?;
1735
1736             Some(format!(
1737                 "{}self: {}",
1738                 format_mutability(mutability),
1739                 type_str
1740             ))
1741         }
1742         ast::SelfKind::Value(_) => {
1743             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1744
1745             let mutability = explicit_self_mutability(&args[0]);
1746
1747             Some(format!("{}self", format_mutability(mutability)))
1748         }
1749     }
1750 }
1751
1752 // Hacky solution caused by absence of `Mutability` in `SelfValue` and
1753 // `SelfExplicit` variants of `ast::ExplicitSelf_`.
1754 fn explicit_self_mutability(arg: &ast::Arg) -> ast::Mutability {
1755     if let ast::PatKind::Ident(ast::BindingMode::ByValue(mutability), _, _) = arg.pat.node {
1756         mutability
1757     } else {
1758         unreachable!()
1759     }
1760 }
1761
1762 pub fn span_lo_for_arg(arg: &ast::Arg) -> BytePos {
1763     if is_named_arg(arg) {
1764         arg.pat.span.lo()
1765     } else {
1766         arg.ty.span.lo()
1767     }
1768 }
1769
1770 pub fn span_hi_for_arg(context: &RewriteContext, arg: &ast::Arg) -> BytePos {
1771     match arg.ty.node {
1772         ast::TyKind::Infer if context.snippet(arg.ty.span) == "_" => arg.ty.span.hi(),
1773         ast::TyKind::Infer if is_named_arg(arg) => arg.pat.span.hi(),
1774         _ => arg.ty.span.hi(),
1775     }
1776 }
1777
1778 pub fn is_named_arg(arg: &ast::Arg) -> bool {
1779     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
1780         ident.node != symbol::keywords::Invalid.ident()
1781     } else {
1782         true
1783     }
1784 }
1785
1786 // Return type is (result, force_new_line_for_brace)
1787 fn rewrite_fn_base(
1788     context: &RewriteContext,
1789     indent: Indent,
1790     ident: ast::Ident,
1791     fn_sig: &FnSig,
1792     span: Span,
1793     newline_brace: bool,
1794     has_body: bool,
1795 ) -> Option<(String, bool)> {
1796     let mut force_new_line_for_brace = false;
1797
1798     let where_clause = &fn_sig.generics.where_clause;
1799
1800     let mut result = String::with_capacity(1024);
1801     result.push_str(&fn_sig.to_str(context));
1802
1803     // fn foo
1804     result.push_str("fn ");
1805     result.push_str(&ident.to_string());
1806
1807     // Generics.
1808     let overhead = if has_body && !newline_brace {
1809         // 4 = `() {`
1810         4
1811     } else {
1812         // 2 = `()`
1813         2
1814     };
1815     let used_width = last_line_used_width(&result, indent.width());
1816     let one_line_budget = context.budget(used_width + overhead);
1817     let shape = Shape {
1818         width: one_line_budget,
1819         indent,
1820         offset: used_width,
1821     };
1822     let fd = fn_sig.decl;
1823     let g_span = mk_sp(span.lo(), fd.output.span().lo());
1824     let generics_str = rewrite_generics(context, fn_sig.generics, shape, g_span)?;
1825     result.push_str(&generics_str);
1826
1827     let snuggle_angle_bracket = generics_str
1828         .lines()
1829         .last()
1830         .map_or(false, |l| l.trim_left().len() == 1);
1831
1832     // Note that the width and indent don't really matter, we'll re-layout the
1833     // return type later anyway.
1834     let ret_str = fd.output
1835         .rewrite(context, Shape::indented(indent, context.config))?;
1836
1837     let multi_line_ret_str = ret_str.contains('\n');
1838     let ret_str_len = if multi_line_ret_str { 0 } else { ret_str.len() };
1839
1840     // Args.
1841     let (one_line_budget, multi_line_budget, mut arg_indent) = compute_budgets_for_args(
1842         context,
1843         &result,
1844         indent,
1845         ret_str_len,
1846         newline_brace,
1847         has_body,
1848         multi_line_ret_str,
1849     )?;
1850
1851     debug!(
1852         "rewrite_fn_base: one_line_budget: {}, multi_line_budget: {}, arg_indent: {:?}",
1853         one_line_budget, multi_line_budget, arg_indent
1854     );
1855
1856     // Check if vertical layout was forced.
1857     if one_line_budget == 0 {
1858         if snuggle_angle_bracket {
1859             result.push('(');
1860         } else {
1861             result.push_str("(");
1862             if context.config.indent_style() == IndentStyle::Visual {
1863                 result.push_str(&arg_indent.to_string_with_newline(context.config));
1864             }
1865         }
1866     } else {
1867         result.push('(');
1868     }
1869     if context.config.spaces_within_parens_and_brackets() && !fd.inputs.is_empty()
1870         && result.ends_with('(')
1871     {
1872         result.push(' ')
1873     }
1874
1875     // Skip `pub(crate)`.
1876     let lo_after_visibility = get_bytepos_after_visibility(context, &fn_sig.visibility, span, ")");
1877     // A conservative estimation, to goal is to be over all parens in generics
1878     let args_start = fn_sig
1879         .generics
1880         .params
1881         .iter()
1882         .last()
1883         .map_or(lo_after_visibility, |param| param.span().hi());
1884     let args_end = if fd.inputs.is_empty() {
1885         context
1886             .snippet_provider
1887             .span_after(mk_sp(args_start, span.hi()), ")")
1888     } else {
1889         let last_span = mk_sp(fd.inputs[fd.inputs.len() - 1].span().hi(), span.hi());
1890         context.snippet_provider.span_after(last_span, ")")
1891     };
1892     let args_span = mk_sp(
1893         context
1894             .snippet_provider
1895             .span_after(mk_sp(args_start, span.hi()), "("),
1896         args_end,
1897     );
1898     let arg_str = rewrite_args(
1899         context,
1900         &fd.inputs,
1901         fd.get_self().as_ref(),
1902         one_line_budget,
1903         multi_line_budget,
1904         indent,
1905         arg_indent,
1906         args_span,
1907         fd.variadic,
1908         generics_str.contains('\n'),
1909     )?;
1910
1911     let put_args_in_block = match context.config.indent_style() {
1912         IndentStyle::Block => arg_str.contains('\n') || arg_str.len() > one_line_budget,
1913         _ => false,
1914     } && !fd.inputs.is_empty();
1915
1916     let mut args_last_line_contains_comment = false;
1917     if put_args_in_block {
1918         arg_indent = indent.block_indent(context.config);
1919         result.push_str(&arg_indent.to_string_with_newline(context.config));
1920         result.push_str(&arg_str);
1921         result.push_str(&indent.to_string_with_newline(context.config));
1922         result.push(')');
1923     } else {
1924         result.push_str(&arg_str);
1925         let used_width = last_line_used_width(&result, indent.width()) + first_line_width(&ret_str);
1926         // Put the closing brace on the next line if it overflows the max width.
1927         // 1 = `)`
1928         if fd.inputs.is_empty() && used_width + 1 > context.config.max_width() {
1929             result.push('\n');
1930         }
1931         if context.config.spaces_within_parens_and_brackets() && !fd.inputs.is_empty() {
1932             result.push(' ')
1933         }
1934         // If the last line of args contains comment, we cannot put the closing paren
1935         // on the same line.
1936         if arg_str
1937             .lines()
1938             .last()
1939             .map_or(false, |last_line| last_line.contains("//"))
1940         {
1941             args_last_line_contains_comment = true;
1942             result.push_str(&arg_indent.to_string_with_newline(context.config));
1943         }
1944         result.push(')');
1945     }
1946
1947     // Return type.
1948     if let ast::FunctionRetTy::Ty(..) = fd.output {
1949         let ret_should_indent = match context.config.indent_style() {
1950             // If our args are block layout then we surely must have space.
1951             IndentStyle::Block if put_args_in_block || fd.inputs.is_empty() => false,
1952             _ if args_last_line_contains_comment => false,
1953             _ if result.contains('\n') || multi_line_ret_str => true,
1954             _ => {
1955                 // If the return type would push over the max width, then put the return type on
1956                 // a new line. With the +1 for the signature length an additional space between
1957                 // the closing parenthesis of the argument and the arrow '->' is considered.
1958                 let mut sig_length = result.len() + indent.width() + ret_str_len + 1;
1959
1960                 // If there is no where clause, take into account the space after the return type
1961                 // and the brace.
1962                 if where_clause.predicates.is_empty() {
1963                     sig_length += 2;
1964                 }
1965
1966                 sig_length > context.config.max_width()
1967             }
1968         };
1969         let ret_indent = if ret_should_indent {
1970             let indent = if arg_str.is_empty() {
1971                 // Aligning with non-existent args looks silly.
1972                 force_new_line_for_brace = true;
1973                 indent + 4
1974             } else {
1975                 // FIXME: we might want to check that using the arg indent
1976                 // doesn't blow our budget, and if it does, then fallback to
1977                 // the where clause indent.
1978                 arg_indent
1979             };
1980
1981             result.push_str(&indent.to_string_with_newline(context.config));
1982             indent
1983         } else {
1984             result.push(' ');
1985             Indent::new(indent.block_indent, last_line_width(&result))
1986         };
1987
1988         if multi_line_ret_str || ret_should_indent {
1989             // Now that we know the proper indent and width, we need to
1990             // re-layout the return type.
1991             let ret_str = fd.output
1992                 .rewrite(context, Shape::indented(ret_indent, context.config))?;
1993             result.push_str(&ret_str);
1994         } else {
1995             result.push_str(&ret_str);
1996         }
1997
1998         // Comment between return type and the end of the decl.
1999         let snippet_lo = fd.output.span().hi();
2000         if where_clause.predicates.is_empty() {
2001             let snippet_hi = span.hi();
2002             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
2003             // Try to preserve the layout of the original snippet.
2004             let original_starts_with_newline = snippet
2005                 .find(|c| c != ' ')
2006                 .map_or(false, |i| starts_with_newline(&snippet[i..]));
2007             let original_ends_with_newline = snippet
2008                 .rfind(|c| c != ' ')
2009                 .map_or(false, |i| snippet[i..].ends_with('\n'));
2010             let snippet = snippet.trim();
2011             if !snippet.is_empty() {
2012                 result.push(if original_starts_with_newline {
2013                     '\n'
2014                 } else {
2015                     ' '
2016                 });
2017                 result.push_str(snippet);
2018                 if original_ends_with_newline {
2019                     force_new_line_for_brace = true;
2020                 }
2021             }
2022         }
2023     }
2024
2025     let pos_before_where = match fd.output {
2026         ast::FunctionRetTy::Default(..) => args_span.hi(),
2027         ast::FunctionRetTy::Ty(ref ty) => ty.span.hi(),
2028     };
2029
2030     let is_args_multi_lined = arg_str.contains('\n');
2031
2032     let option = WhereClauseOption::new(!has_body, put_args_in_block && ret_str.is_empty());
2033     let where_clause_str = rewrite_where_clause(
2034         context,
2035         where_clause,
2036         context.config.brace_style(),
2037         Shape::indented(indent, context.config),
2038         Density::Tall,
2039         "{",
2040         Some(span.hi()),
2041         pos_before_where,
2042         option,
2043         is_args_multi_lined,
2044     )?;
2045     // If there are neither where clause nor return type, we may be missing comments between
2046     // args and `{`.
2047     if where_clause_str.is_empty() {
2048         if let ast::FunctionRetTy::Default(ret_span) = fd.output {
2049             match recover_missing_comment_in_span(
2050                 mk_sp(args_span.hi(), ret_span.hi()),
2051                 shape,
2052                 context,
2053                 last_line_width(&result),
2054             ) {
2055                 Some(ref missing_comment) if !missing_comment.is_empty() => {
2056                     result.push_str(missing_comment);
2057                     force_new_line_for_brace = true;
2058                 }
2059                 _ => (),
2060             }
2061         }
2062     }
2063
2064     result.push_str(&where_clause_str);
2065
2066     force_new_line_for_brace |= last_line_contains_single_line_comment(&result);
2067     force_new_line_for_brace |= is_args_multi_lined && context.config.where_single_line();
2068     Some((result, force_new_line_for_brace))
2069 }
2070
2071 #[derive(Copy, Clone)]
2072 struct WhereClauseOption {
2073     suppress_comma: bool, // Force no trailing comma
2074     snuggle: bool,        // Do not insert newline before `where`
2075     compress_where: bool, // Try single line where clause instead of vertical layout
2076 }
2077
2078 impl WhereClauseOption {
2079     pub fn new(suppress_comma: bool, snuggle: bool) -> WhereClauseOption {
2080         WhereClauseOption {
2081             suppress_comma,
2082             snuggle,
2083             compress_where: false,
2084         }
2085     }
2086
2087     pub fn snuggled(current: &str) -> WhereClauseOption {
2088         WhereClauseOption {
2089             suppress_comma: false,
2090             snuggle: trimmed_last_line_width(current) == 1,
2091             compress_where: false,
2092         }
2093     }
2094 }
2095
2096 fn rewrite_args(
2097     context: &RewriteContext,
2098     args: &[ast::Arg],
2099     explicit_self: Option<&ast::ExplicitSelf>,
2100     one_line_budget: usize,
2101     multi_line_budget: usize,
2102     indent: Indent,
2103     arg_indent: Indent,
2104     span: Span,
2105     variadic: bool,
2106     generics_str_contains_newline: bool,
2107 ) -> Option<String> {
2108     let mut arg_item_strs = args.iter()
2109         .map(|arg| arg.rewrite(context, Shape::legacy(multi_line_budget, arg_indent)))
2110         .collect::<Option<Vec<_>>>()?;
2111
2112     // Account for sugary self.
2113     // FIXME: the comment for the self argument is dropped. This is blocked
2114     // on rust issue #27522.
2115     let min_args = explicit_self
2116         .and_then(|explicit_self| rewrite_explicit_self(explicit_self, args, context))
2117         .map_or(1, |self_str| {
2118             arg_item_strs[0] = self_str;
2119             2
2120         });
2121
2122     // Comments between args.
2123     let mut arg_items = Vec::new();
2124     if min_args == 2 {
2125         arg_items.push(ListItem::from_str(""));
2126     }
2127
2128     // FIXME(#21): if there are no args, there might still be a comment, but
2129     // without spans for the comment or parens, there is no chance of
2130     // getting it right. You also don't get to put a comment on self, unless
2131     // it is explicit.
2132     if args.len() >= min_args || variadic {
2133         let comment_span_start = if min_args == 2 {
2134             let second_arg_start = if arg_has_pattern(&args[1]) {
2135                 args[1].pat.span.lo()
2136             } else {
2137                 args[1].ty.span.lo()
2138             };
2139             let reduced_span = mk_sp(span.lo(), second_arg_start);
2140
2141             context.snippet_provider.span_after_last(reduced_span, ",")
2142         } else {
2143             span.lo()
2144         };
2145
2146         enum ArgumentKind<'a> {
2147             Regular(&'a ast::Arg),
2148             Variadic(BytePos),
2149         }
2150
2151         let variadic_arg = if variadic {
2152             let variadic_span = mk_sp(args.last().unwrap().ty.span.hi(), span.hi());
2153             let variadic_start =
2154                 context.snippet_provider.span_after(variadic_span, "...") - BytePos(3);
2155             Some(ArgumentKind::Variadic(variadic_start))
2156         } else {
2157             None
2158         };
2159
2160         let more_items = itemize_list(
2161             context.snippet_provider,
2162             args[min_args - 1..]
2163                 .iter()
2164                 .map(ArgumentKind::Regular)
2165                 .chain(variadic_arg),
2166             ")",
2167             ",",
2168             |arg| match *arg {
2169                 ArgumentKind::Regular(arg) => span_lo_for_arg(arg),
2170                 ArgumentKind::Variadic(start) => start,
2171             },
2172             |arg| match *arg {
2173                 ArgumentKind::Regular(arg) => arg.ty.span.hi(),
2174                 ArgumentKind::Variadic(start) => start + BytePos(3),
2175             },
2176             |arg| match *arg {
2177                 ArgumentKind::Regular(..) => None,
2178                 ArgumentKind::Variadic(..) => Some("...".to_owned()),
2179             },
2180             comment_span_start,
2181             span.hi(),
2182             false,
2183         );
2184
2185         arg_items.extend(more_items);
2186     }
2187
2188     let fits_in_one_line = !generics_str_contains_newline
2189         && (arg_items.is_empty()
2190             || arg_items.len() == 1 && arg_item_strs[0].len() <= one_line_budget);
2191
2192     for (item, arg) in arg_items.iter_mut().zip(arg_item_strs) {
2193         item.item = Some(arg);
2194     }
2195
2196     let last_line_ends_with_comment = arg_items
2197         .iter()
2198         .last()
2199         .and_then(|item| item.post_comment.as_ref())
2200         .map_or(false, |s| s.trim().starts_with("//"));
2201
2202     let (indent, trailing_comma) = match context.config.indent_style() {
2203         IndentStyle::Block if fits_in_one_line => {
2204             (indent.block_indent(context.config), SeparatorTactic::Never)
2205         }
2206         IndentStyle::Block => (
2207             indent.block_indent(context.config),
2208             context.config.trailing_comma(),
2209         ),
2210         IndentStyle::Visual if last_line_ends_with_comment => {
2211             (arg_indent, context.config.trailing_comma())
2212         }
2213         IndentStyle::Visual => (arg_indent, SeparatorTactic::Never),
2214     };
2215
2216     let tactic = definitive_tactic(
2217         &arg_items,
2218         context.config.fn_args_density().to_list_tactic(),
2219         Separator::Comma,
2220         one_line_budget,
2221     );
2222     let budget = match tactic {
2223         DefinitiveListTactic::Horizontal => one_line_budget,
2224         _ => multi_line_budget,
2225     };
2226
2227     debug!("rewrite_args: budget: {}, tactic: {:?}", budget, tactic);
2228
2229     let fmt = ListFormatting {
2230         tactic,
2231         separator: ",",
2232         trailing_separator: if variadic {
2233             SeparatorTactic::Never
2234         } else {
2235             trailing_comma
2236         },
2237         separator_place: SeparatorPlace::Back,
2238         shape: Shape::legacy(budget, indent),
2239         ends_with_newline: tactic.ends_with_newline(context.config.indent_style()),
2240         preserve_newline: true,
2241         config: context.config,
2242     };
2243
2244     write_list(&arg_items, &fmt)
2245 }
2246
2247 fn arg_has_pattern(arg: &ast::Arg) -> bool {
2248     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
2249         ident.node != symbol::keywords::Invalid.ident()
2250     } else {
2251         true
2252     }
2253 }
2254
2255 fn compute_budgets_for_args(
2256     context: &RewriteContext,
2257     result: &str,
2258     indent: Indent,
2259     ret_str_len: usize,
2260     newline_brace: bool,
2261     has_braces: bool,
2262     force_vertical_layout: bool,
2263 ) -> Option<((usize, usize, Indent))> {
2264     debug!(
2265         "compute_budgets_for_args {} {:?}, {}, {}",
2266         result.len(),
2267         indent,
2268         ret_str_len,
2269         newline_brace
2270     );
2271     // Try keeping everything on the same line.
2272     if !result.contains('\n') && !force_vertical_layout {
2273         // 2 = `()`, 3 = `() `, space is before ret_string.
2274         let overhead = if ret_str_len == 0 { 2 } else { 3 };
2275         let mut used_space = indent.width() + result.len() + ret_str_len + overhead;
2276         if has_braces {
2277             if !newline_brace {
2278                 // 2 = `{}`
2279                 used_space += 2;
2280             }
2281         } else {
2282             // 1 = `;`
2283             used_space += 1;
2284         }
2285         let one_line_budget = context.budget(used_space);
2286
2287         if one_line_budget > 0 {
2288             // 4 = "() {".len()
2289             let (indent, multi_line_budget) = match context.config.indent_style() {
2290                 IndentStyle::Block => {
2291                     let indent = indent.block_indent(context.config);
2292                     (indent, context.budget(indent.width() + 1))
2293                 }
2294                 IndentStyle::Visual => {
2295                     let indent = indent + result.len() + 1;
2296                     let multi_line_overhead = indent.width() + if newline_brace { 2 } else { 4 };
2297                     (indent, context.budget(multi_line_overhead))
2298                 }
2299             };
2300
2301             return Some((one_line_budget, multi_line_budget, indent));
2302         }
2303     }
2304
2305     // Didn't work. we must force vertical layout and put args on a newline.
2306     let new_indent = indent.block_indent(context.config);
2307     let used_space = match context.config.indent_style() {
2308         // 1 = `,`
2309         IndentStyle::Block => new_indent.width() + 1,
2310         // Account for `)` and possibly ` {`.
2311         IndentStyle::Visual => new_indent.width() + if ret_str_len == 0 { 1 } else { 3 },
2312     };
2313     Some((0, context.budget(used_space), new_indent))
2314 }
2315
2316 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause) -> bool {
2317     let predicate_count = where_clause.predicates.len();
2318
2319     if config.where_single_line() && predicate_count == 1 {
2320         return false;
2321     }
2322     let brace_style = config.brace_style();
2323
2324     brace_style == BraceStyle::AlwaysNextLine
2325         || (brace_style == BraceStyle::SameLineWhere && predicate_count > 0)
2326 }
2327
2328 fn rewrite_generics(
2329     context: &RewriteContext,
2330     generics: &ast::Generics,
2331     shape: Shape,
2332     span: Span,
2333 ) -> Option<String> {
2334     let g_shape = generics_shape_from_config(context.config, shape, 0)?;
2335     let one_line_width = shape.width.checked_sub(2).unwrap_or(0);
2336     rewrite_generics_inner(context, generics, g_shape, one_line_width, span)
2337         .or_else(|| rewrite_generics_inner(context, generics, g_shape, 0, span))
2338 }
2339
2340 fn rewrite_generics_inner(
2341     context: &RewriteContext,
2342     generics: &ast::Generics,
2343     shape: Shape,
2344     one_line_width: usize,
2345     span: Span,
2346 ) -> Option<String> {
2347     // FIXME: convert bounds to where clauses where they get too big or if
2348     // there is a where clause at all.
2349
2350     if generics.params.is_empty() {
2351         return Some(String::new());
2352     }
2353
2354     let items = itemize_list(
2355         context.snippet_provider,
2356         generics.params.iter(),
2357         ">",
2358         ",",
2359         |arg| arg.span().lo(),
2360         |arg| arg.span().hi(),
2361         |arg| arg.rewrite(context, shape),
2362         context.snippet_provider.span_after(span, "<"),
2363         span.hi(),
2364         false,
2365     );
2366     format_generics_item_list(context, items, shape, one_line_width)
2367 }
2368
2369 pub fn generics_shape_from_config(config: &Config, shape: Shape, offset: usize) -> Option<Shape> {
2370     match config.indent_style() {
2371         IndentStyle::Visual => shape.visual_indent(1 + offset).sub_width(offset + 2),
2372         IndentStyle::Block => {
2373             // 1 = ","
2374             shape
2375                 .block()
2376                 .block_indent(config.tab_spaces())
2377                 .with_max_width(config)
2378                 .sub_width(1)
2379         }
2380     }
2381 }
2382
2383 pub fn format_generics_item_list<I>(
2384     context: &RewriteContext,
2385     items: I,
2386     shape: Shape,
2387     one_line_budget: usize,
2388 ) -> Option<String>
2389 where
2390     I: Iterator<Item = ListItem>,
2391 {
2392     let item_vec = items.collect::<Vec<_>>();
2393
2394     let tactic = definitive_tactic(
2395         &item_vec,
2396         ListTactic::HorizontalVertical,
2397         Separator::Comma,
2398         one_line_budget,
2399     );
2400     let fmt = ListFormatting {
2401         tactic,
2402         separator: ",",
2403         trailing_separator: if context.config.indent_style() == IndentStyle::Visual {
2404             SeparatorTactic::Never
2405         } else {
2406             context.config.trailing_comma()
2407         },
2408         separator_place: SeparatorPlace::Back,
2409         shape,
2410         ends_with_newline: tactic.ends_with_newline(context.config.indent_style()),
2411         preserve_newline: true,
2412         config: context.config,
2413     };
2414
2415     let list_str = write_list(&item_vec, &fmt)?;
2416
2417     Some(wrap_generics_with_angle_brackets(
2418         context,
2419         &list_str,
2420         shape.indent,
2421     ))
2422 }
2423
2424 pub fn wrap_generics_with_angle_brackets(
2425     context: &RewriteContext,
2426     list_str: &str,
2427     list_offset: Indent,
2428 ) -> String {
2429     if context.config.indent_style() == IndentStyle::Block
2430         && (list_str.contains('\n') || list_str.ends_with(','))
2431     {
2432         format!(
2433             "<\n{}{}\n{}>",
2434             list_offset.to_string(context.config),
2435             list_str,
2436             list_offset
2437                 .block_unindent(context.config)
2438                 .to_string(context.config)
2439         )
2440     } else if context.config.spaces_within_parens_and_brackets() {
2441         format!("< {} >", list_str)
2442     } else {
2443         format!("<{}>", list_str)
2444     }
2445 }
2446
2447 fn rewrite_trait_bounds(
2448     context: &RewriteContext,
2449     bounds: &[ast::TyParamBound],
2450     shape: Shape,
2451 ) -> Option<String> {
2452     if bounds.is_empty() {
2453         return Some(String::new());
2454     }
2455     let bound_str = bounds
2456         .iter()
2457         .map(|ty_bound| ty_bound.rewrite(context, shape))
2458         .collect::<Option<Vec<_>>>()?;
2459     Some(format!(": {}", join_bounds(context, shape, &bound_str)))
2460 }
2461
2462 fn rewrite_where_clause_rfc_style(
2463     context: &RewriteContext,
2464     where_clause: &ast::WhereClause,
2465     shape: Shape,
2466     terminator: &str,
2467     span_end: Option<BytePos>,
2468     span_end_before_where: BytePos,
2469     where_clause_option: WhereClauseOption,
2470     is_args_multi_line: bool,
2471 ) -> Option<String> {
2472     let block_shape = shape.block().with_max_width(context.config);
2473
2474     let (span_before, span_after) =
2475         missing_span_before_after_where(span_end_before_where, where_clause);
2476     let (comment_before, comment_after) =
2477         rewrite_comments_before_after_where(context, span_before, span_after, shape)?;
2478
2479     let starting_newline = if where_clause_option.snuggle && comment_before.is_empty() {
2480         Cow::from(" ")
2481     } else {
2482         block_shape.indent.to_string_with_newline(context.config)
2483     };
2484
2485     let clause_shape = block_shape.block_left(context.config.tab_spaces())?;
2486     // 1 = `,`
2487     let clause_shape = clause_shape.sub_width(1)?;
2488     // each clause on one line, trailing comma (except if suppress_comma)
2489     let span_start = where_clause.predicates[0].span().lo();
2490     // If we don't have the start of the next span, then use the end of the
2491     // predicates, but that means we miss comments.
2492     let len = where_clause.predicates.len();
2493     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2494     let span_end = span_end.unwrap_or(end_of_preds);
2495     let items = itemize_list(
2496         context.snippet_provider,
2497         where_clause.predicates.iter(),
2498         terminator,
2499         ",",
2500         |pred| pred.span().lo(),
2501         |pred| pred.span().hi(),
2502         |pred| pred.rewrite(context, clause_shape),
2503         span_start,
2504         span_end,
2505         false,
2506     );
2507     let where_single_line = context.config.where_single_line() && len == 1 && !is_args_multi_line;
2508     let comma_tactic = if where_clause_option.suppress_comma || where_single_line {
2509         SeparatorTactic::Never
2510     } else {
2511         context.config.trailing_comma()
2512     };
2513
2514     // shape should be vertical only and only if we have `where_single_line` option enabled
2515     // and the number of items of the where clause is equal to 1
2516     let shape_tactic = if where_single_line {
2517         DefinitiveListTactic::Horizontal
2518     } else {
2519         DefinitiveListTactic::Vertical
2520     };
2521
2522     let fmt = ListFormatting {
2523         tactic: shape_tactic,
2524         separator: ",",
2525         trailing_separator: comma_tactic,
2526         separator_place: SeparatorPlace::Back,
2527         shape: clause_shape,
2528         ends_with_newline: true,
2529         preserve_newline: true,
2530         config: context.config,
2531     };
2532     let preds_str = write_list(&items.collect::<Vec<_>>(), &fmt)?;
2533
2534     let comment_separator = |comment: &str, shape: Shape| {
2535         if comment.is_empty() {
2536             Cow::from("")
2537         } else {
2538             shape.indent.to_string_with_newline(context.config)
2539         }
2540     };
2541     let newline_before_where = comment_separator(&comment_before, shape);
2542     let newline_after_where = comment_separator(&comment_after, clause_shape);
2543
2544     // 6 = `where `
2545     let clause_sep = if where_clause_option.compress_where && comment_before.is_empty()
2546         && comment_after.is_empty() && !preds_str.contains('\n')
2547         && 6 + preds_str.len() <= shape.width || where_single_line
2548     {
2549         Cow::from(" ")
2550     } else {
2551         clause_shape.indent.to_string_with_newline(context.config)
2552     };
2553     Some(format!(
2554         "{}{}{}where{}{}{}{}",
2555         starting_newline,
2556         comment_before,
2557         newline_before_where,
2558         newline_after_where,
2559         comment_after,
2560         clause_sep,
2561         preds_str
2562     ))
2563 }
2564
2565 fn rewrite_where_clause(
2566     context: &RewriteContext,
2567     where_clause: &ast::WhereClause,
2568     brace_style: BraceStyle,
2569     shape: Shape,
2570     density: Density,
2571     terminator: &str,
2572     span_end: Option<BytePos>,
2573     span_end_before_where: BytePos,
2574     where_clause_option: WhereClauseOption,
2575     is_args_multi_line: bool,
2576 ) -> Option<String> {
2577     if where_clause.predicates.is_empty() {
2578         return Some(String::new());
2579     }
2580
2581     if context.config.indent_style() == IndentStyle::Block {
2582         return rewrite_where_clause_rfc_style(
2583             context,
2584             where_clause,
2585             shape,
2586             terminator,
2587             span_end,
2588             span_end_before_where,
2589             where_clause_option,
2590             is_args_multi_line,
2591         );
2592     }
2593
2594     let extra_indent = Indent::new(context.config.tab_spaces(), 0);
2595
2596     let offset = match context.config.indent_style() {
2597         IndentStyle::Block => shape.indent + extra_indent.block_indent(context.config),
2598         // 6 = "where ".len()
2599         IndentStyle::Visual => shape.indent + extra_indent + 6,
2600     };
2601     // FIXME: if indent_style != Visual, then the budgets below might
2602     // be out by a char or two.
2603
2604     let budget = context.config.max_width() - offset.width();
2605     let span_start = where_clause.predicates[0].span().lo();
2606     // If we don't have the start of the next span, then use the end of the
2607     // predicates, but that means we miss comments.
2608     let len = where_clause.predicates.len();
2609     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2610     let span_end = span_end.unwrap_or(end_of_preds);
2611     let items = itemize_list(
2612         context.snippet_provider,
2613         where_clause.predicates.iter(),
2614         terminator,
2615         ",",
2616         |pred| pred.span().lo(),
2617         |pred| pred.span().hi(),
2618         |pred| pred.rewrite(context, Shape::legacy(budget, offset)),
2619         span_start,
2620         span_end,
2621         false,
2622     );
2623     let item_vec = items.collect::<Vec<_>>();
2624     // FIXME: we don't need to collect here
2625     let tactic = definitive_tactic(&item_vec, ListTactic::Vertical, Separator::Comma, budget);
2626
2627     let mut comma_tactic = context.config.trailing_comma();
2628     // Kind of a hack because we don't usually have trailing commas in where clauses.
2629     if comma_tactic == SeparatorTactic::Vertical || where_clause_option.suppress_comma {
2630         comma_tactic = SeparatorTactic::Never;
2631     }
2632
2633     let fmt = ListFormatting {
2634         tactic,
2635         separator: ",",
2636         trailing_separator: comma_tactic,
2637         separator_place: SeparatorPlace::Back,
2638         shape: Shape::legacy(budget, offset),
2639         ends_with_newline: tactic.ends_with_newline(context.config.indent_style()),
2640         preserve_newline: true,
2641         config: context.config,
2642     };
2643     let preds_str = write_list(&item_vec, &fmt)?;
2644
2645     let end_length = if terminator == "{" {
2646         // If the brace is on the next line we don't need to count it otherwise it needs two
2647         // characters " {"
2648         match brace_style {
2649             BraceStyle::AlwaysNextLine | BraceStyle::SameLineWhere => 0,
2650             BraceStyle::PreferSameLine => 2,
2651         }
2652     } else if terminator == "=" {
2653         2
2654     } else {
2655         terminator.len()
2656     };
2657     if density == Density::Tall || preds_str.contains('\n')
2658         || shape.indent.width() + " where ".len() + preds_str.len() + end_length > shape.width
2659     {
2660         Some(format!(
2661             "\n{}where {}",
2662             (shape.indent + extra_indent).to_string(context.config),
2663             preds_str
2664         ))
2665     } else {
2666         Some(format!(" where {}", preds_str))
2667     }
2668 }
2669
2670 fn missing_span_before_after_where(
2671     before_item_span_end: BytePos,
2672     where_clause: &ast::WhereClause,
2673 ) -> (Span, Span) {
2674     let missing_span_before = mk_sp(before_item_span_end, where_clause.span.lo());
2675     // 5 = `where`
2676     let pos_after_where = where_clause.span.lo() + BytePos(5);
2677     let missing_span_after = mk_sp(pos_after_where, where_clause.predicates[0].span().lo());
2678     (missing_span_before, missing_span_after)
2679 }
2680
2681 fn rewrite_comments_before_after_where(
2682     context: &RewriteContext,
2683     span_before_where: Span,
2684     span_after_where: Span,
2685     shape: Shape,
2686 ) -> Option<(String, String)> {
2687     let before_comment = rewrite_missing_comment(span_before_where, shape, context)?;
2688     let after_comment = rewrite_missing_comment(
2689         span_after_where,
2690         shape.block_indent(context.config.tab_spaces()),
2691         context,
2692     )?;
2693     Some((before_comment, after_comment))
2694 }
2695
2696 fn format_header(item_name: &str, ident: ast::Ident, vis: &ast::Visibility) -> String {
2697     format!("{}{}{}", format_visibility(vis), item_name, ident)
2698 }
2699
2700 #[derive(PartialEq, Eq, Clone, Copy)]
2701 enum BracePos {
2702     None,
2703     Auto,
2704     ForceSameLine,
2705 }
2706
2707 fn format_generics(
2708     context: &RewriteContext,
2709     generics: &ast::Generics,
2710     brace_style: BraceStyle,
2711     brace_pos: BracePos,
2712     offset: Indent,
2713     span: Span,
2714     used_width: usize,
2715 ) -> Option<String> {
2716     let shape = Shape::legacy(context.budget(used_width + offset.width()), offset);
2717     let mut result = rewrite_generics(context, generics, shape, span)?;
2718
2719     let same_line_brace = if !generics.where_clause.predicates.is_empty() || result.contains('\n') {
2720         let budget = context.budget(last_line_used_width(&result, offset.width()));
2721         let mut option = WhereClauseOption::snuggled(&result);
2722         if brace_pos == BracePos::None {
2723             option.suppress_comma = true;
2724         }
2725         // If the generics are not parameterized then generics.span.hi() == 0,
2726         // so we use span.lo(), which is the position after `struct Foo`.
2727         let span_end_before_where = if generics.is_parameterized() {
2728             generics.span.hi()
2729         } else {
2730             span.lo()
2731         };
2732         let where_clause_str = rewrite_where_clause(
2733             context,
2734             &generics.where_clause,
2735             brace_style,
2736             Shape::legacy(budget, offset.block_only()),
2737             Density::Tall,
2738             "{",
2739             Some(span.hi()),
2740             span_end_before_where,
2741             option,
2742             false,
2743         )?;
2744         result.push_str(&where_clause_str);
2745         brace_pos == BracePos::ForceSameLine || brace_style == BraceStyle::PreferSameLine
2746             || (generics.where_clause.predicates.is_empty()
2747                 && trimmed_last_line_width(&result) == 1)
2748     } else {
2749         brace_pos == BracePos::ForceSameLine || trimmed_last_line_width(&result) == 1
2750             || brace_style != BraceStyle::AlwaysNextLine
2751     };
2752     if brace_pos == BracePos::None {
2753         return Some(result);
2754     }
2755     let total_used_width = last_line_used_width(&result, used_width);
2756     let remaining_budget = context.budget(total_used_width);
2757     // If the same line brace if forced, it indicates that we are rewriting an item with empty body,
2758     // and hence we take the closer into account as well for one line budget.
2759     // We assume that the closer has the same length as the opener.
2760     let overhead = if brace_pos == BracePos::ForceSameLine {
2761         // 3 = ` {}`
2762         3
2763     } else {
2764         // 2 = ` {`
2765         2
2766     };
2767     let forbid_same_line_brace = overhead > remaining_budget;
2768     if !forbid_same_line_brace && same_line_brace {
2769         result.push(' ');
2770     } else {
2771         result.push('\n');
2772         result.push_str(&offset.block_only().to_string(context.config));
2773     }
2774     result.push('{');
2775
2776     Some(result)
2777 }
2778
2779 impl Rewrite for ast::ForeignItem {
2780     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
2781         let attrs_str = self.attrs.rewrite(context, shape)?;
2782         // Drop semicolon or it will be interpreted as comment.
2783         // FIXME: this may be a faulty span from libsyntax.
2784         let span = mk_sp(self.span.lo(), self.span.hi() - BytePos(1));
2785
2786         let item_str = match self.node {
2787             ast::ForeignItemKind::Fn(ref fn_decl, ref generics) => {
2788                 rewrite_fn_base(
2789                     context,
2790                     shape.indent,
2791                     self.ident,
2792                     &FnSig::new(fn_decl, generics, self.vis.clone()),
2793                     span,
2794                     false,
2795                     false,
2796                 ).map(|(s, _)| format!("{};", s))
2797             }
2798             ast::ForeignItemKind::Static(ref ty, is_mutable) => {
2799                 // FIXME(#21): we're dropping potential comments in between the
2800                 // function keywords here.
2801                 let vis = format_visibility(&self.vis);
2802                 let mut_str = if is_mutable { "mut " } else { "" };
2803                 let prefix = format!("{}static {}{}:", vis, mut_str, self.ident);
2804                 // 1 = ;
2805                 let shape = shape.sub_width(1)?;
2806                 ty.rewrite(context, shape).map(|ty_str| {
2807                     // 1 = space between prefix and type.
2808                     let sep = if prefix.len() + ty_str.len() + 1 <= shape.width {
2809                         Cow::from(" ")
2810                     } else {
2811                         let nested_indent = shape.indent.block_indent(context.config);
2812                         nested_indent.to_string_with_newline(context.config)
2813                     };
2814                     format!("{}{}{};", prefix, sep, ty_str)
2815                 })
2816             }
2817             ast::ForeignItemKind::Ty => {
2818                 let vis = format_visibility(&self.vis);
2819                 Some(format!("{}type {};", vis, self.ident))
2820             }
2821         }?;
2822
2823         let missing_span = if self.attrs.is_empty() {
2824             mk_sp(self.span.lo(), self.span.lo())
2825         } else {
2826             mk_sp(self.attrs[self.attrs.len() - 1].span.hi(), self.span.lo())
2827         };
2828         combine_strs_with_missing_comments(
2829             context,
2830             &attrs_str,
2831             &item_str,
2832             missing_span,
2833             shape,
2834             false,
2835         )
2836     }
2837 }
2838
2839 impl Rewrite for ast::GenericParam {
2840     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
2841         match *self {
2842             ast::GenericParam::Lifetime(ref lifetime_def) => lifetime_def.rewrite(context, shape),
2843             ast::GenericParam::Type(ref ty) => ty.rewrite(context, shape),
2844         }
2845     }
2846 }
2847
2848 /// Rewrite an inline mod.
2849 pub fn rewrite_mod(item: &ast::Item) -> String {
2850     let mut result = String::with_capacity(32);
2851     result.push_str(&*format_visibility(&item.vis));
2852     result.push_str("mod ");
2853     result.push_str(&item.ident.to_string());
2854     result.push(';');
2855     result
2856 }