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 {Indent, Shape};
  14 use codemap::SpanUtils;
  15 use utils::{format_mutability, format_visibility, contains_skip, end_typaram, wrap_str,
  16             last_line_width, format_unsafety, trim_newlines, stmt_expr, semicolon_for_expr};
  17 use lists::{write_list, itemize_list, ListItem, ListFormatting, SeparatorTactic,
  18             DefinitiveListTactic, ListTactic, definitive_tactic, format_item_list};
  19 use expr::{is_empty_block, is_simple_block_stmt, rewrite_assign_rhs, type_annotation_separator};
  20 use comment::{FindUncommented, contains_comment};
  21 use visitor::FmtVisitor;
  22 use rewrite::{Rewrite, RewriteContext};
  23 use config::{Config, BlockIndentStyle, Density, ReturnIndent, BraceStyle, FnArgLayoutStyle};
  24 use itertools::Itertools;
  25
  26 use syntax::{ast, abi, codemap, ptr, symbol};
  27 use syntax::codemap::{Span, BytePos, mk_sp};
  28 use syntax::ast::ImplItem;
  29
  30 // Statements of the form
  31 // let pat: ty = init;
  32 impl Rewrite for ast::Local {
  33     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  34         debug!("Local::rewrite {:?} {} {:?}",
  35                self,
  36                shape.width,
  37                shape.indent);
  38         let mut result = "let ".to_owned();
  39         let pattern_offset = shape.indent + result.len();
  40         // 1 = ;
  41         let pattern_width = try_opt!(shape.width.checked_sub(pattern_offset.width() + 1));
  42
  43         let pat_str = try_opt!(self.pat
  44                                    .rewrite(&context,
  45                                             Shape::legacy(pattern_width, pattern_offset)));
  46         result.push_str(&pat_str);
  47
  48         // String that is placed within the assignment pattern and expression.
  49         let infix = {
  50             let mut infix = String::new();
  51
  52             if let Some(ref ty) = self.ty {
  53                 let separator = type_annotation_separator(context.config);
  54                 let indent = shape.indent + last_line_width(&result) + separator.len();
  55                 // 1 = ;
  56                 let budget = try_opt!(shape.width.checked_sub(indent.width() + 1));
  57                 let rewrite = try_opt!(ty.rewrite(context, Shape::legacy(budget, indent)));
  58
  59                 infix.push_str(separator);
  60                 infix.push_str(&rewrite);
  61             }
  62
  63             if self.init.is_some() {
  64                 infix.push_str(" =");
  65             }
  66
  67             infix
  68         };
  69
  70         result.push_str(&infix);
  71
  72         if let Some(ref ex) = self.init {
  73             // 1 = trailing semicolon;
  74             let budget = try_opt!(shape.width.checked_sub(shape.indent.block_only().width() + 1));
  75
  76             result = try_opt!(rewrite_assign_rhs(&context,
  77                                                  result,
  78                                                  ex,
  79                                                  Shape::legacy(budget, shape.indent.block_only())));
  80         }
  81
  82         result.push(';');
  83         Some(result)
  84     }
  85 }
  86
  87 // TODO convert to using rewrite style rather than visitor
  88 // TODO format modules in this style
  89 #[allow(dead_code)]
  90 struct Item<'a> {
  91     keyword: &'static str,
  92     abi: String,
  93     vis: Option<&'a ast::Visibility>,
  94     body: Vec<BodyElement<'a>>,
  95     span: Span,
  96 }
  97
  98 impl<'a> Item<'a> {
  99     fn from_foreign_mod(fm: &'a ast::ForeignMod, span: Span, config: &Config) -> Item<'a> {
 100         let abi = if fm.abi == abi::Abi::C && !config.force_explicit_abi {
 101             "extern".into()
 102         } else {
 103             format!("extern {}", fm.abi)
 104         };
 105         Item {
 106             keyword: "",
 107             abi: abi,
 108             vis: None,
 109             body: fm.items.iter().map(|i| BodyElement::ForeignItem(i)).collect(),
 110             span: span,
 111         }
 112     }
 113 }
 114
 115 enum BodyElement<'a> {
 116     // Stmt(&'a ast::Stmt),
 117     // Field(&'a ast::Field),
 118     // Variant(&'a ast::Variant),
 119     // Item(&'a ast::Item),
 120     ForeignItem(&'a ast::ForeignItem),
 121 }
 122
 123 impl<'a> FmtVisitor<'a> {
 124     fn format_item(&mut self, item: Item) {
 125         self.buffer.push_str(&item.abi);
 126         self.buffer.push_str(" ");
 127
 128         let snippet = self.snippet(item.span);
 129         let brace_pos = snippet.find_uncommented("{").unwrap();
 130
 131         self.buffer.push_str("{");
 132         if !item.body.is_empty() || contains_comment(&snippet[brace_pos..]) {
 133             // FIXME: this skips comments between the extern keyword and the opening
 134             // brace.
 135             self.last_pos = item.span.lo + BytePos(brace_pos as u32 + 1);
 136             self.block_indent = self.block_indent.block_indent(self.config);
 137
 138             if item.body.is_empty() {
 139                 self.format_missing_no_indent(item.span.hi - BytePos(1));
 140                 self.block_indent = self.block_indent.block_unindent(self.config);
 141
 142                 self.buffer.push_str(&self.block_indent.to_string(self.config));
 143             } else {
 144                 for item in &item.body {
 145                     self.format_body_element(item);
 146                 }
 147
 148                 self.block_indent = self.block_indent.block_unindent(self.config);
 149                 self.format_missing_with_indent(item.span.hi - BytePos(1));
 150             }
 151         }
 152
 153         self.buffer.push_str("}");
 154         self.last_pos = item.span.hi;
 155     }
 156
 157     fn format_body_element(&mut self, element: &BodyElement) {
 158         match *element {
 159             BodyElement::ForeignItem(ref item) => self.format_foreign_item(item),
 160         }
 161     }
 162
 163     pub fn format_foreign_mod(&mut self, fm: &ast::ForeignMod, span: Span) {
 164         let item = Item::from_foreign_mod(fm, span, self.config);
 165         self.format_item(item);
 166     }
 167
 168     fn format_foreign_item(&mut self, item: &ast::ForeignItem) {
 169         self.format_missing_with_indent(item.span.lo);
 170         // Drop semicolon or it will be interpreted as comment.
 171         // FIXME: this may be a faulty span from libsyntax.
 172         let span = mk_sp(item.span.lo, item.span.hi - BytePos(1));
 173
 174         match item.node {
 175             ast::ForeignItemKind::Fn(ref fn_decl, ref generics) => {
 176                 let indent = self.block_indent;
 177                 let rewrite = rewrite_fn_base(&self.get_context(),
 178                                               indent,
 179                                               item.ident,
 180                                               fn_decl,
 181                                               generics,
 182                                               ast::Unsafety::Normal,
 183                                               ast::Constness::NotConst,
 184                                               ast::Defaultness::Final,
 185                                               // These are not actually rust functions,
 186                                               // but we format them as such.
 187                                               abi::Abi::Rust,
 188                                               &item.vis,
 189                                               span,
 190                                               false,
 191                                               false);
 192
 193                 match rewrite {
 194                     Some((new_fn, _)) => {
 195                         self.buffer.push_str(&new_fn);
 196                         self.buffer.push_str(";");
 197                     }
 198                     None => self.format_missing(item.span.hi),
 199                 }
 200             }
 201             ast::ForeignItemKind::Static(ref ty, is_mutable) => {
 202                 // FIXME(#21): we're dropping potential comments in between the
 203                 // function keywords here.
 204                 let vis = format_visibility(&item.vis);
 205                 let mut_str = if is_mutable { "mut " } else { "" };
 206                 let prefix = format!("{}static {}{}: ", vis, mut_str, item.ident);
 207                 let offset = self.block_indent + prefix.len();
 208                 // 1 = ;
 209                 let width = self.config.max_width - offset.width() - 1;
 210                 let rewrite = ty.rewrite(&self.get_context(), Shape::legacy(width, offset));
 211
 212                 match rewrite {
 213                     Some(result) => {
 214                         self.buffer.push_str(&prefix);
 215                         self.buffer.push_str(&result);
 216                         self.buffer.push_str(";");
 217                     }
 218                     None => self.format_missing(item.span.hi),
 219                 }
 220             }
 221         }
 222
 223         self.last_pos = item.span.hi;
 224     }
 225
 226     pub fn rewrite_fn(&mut self,
 227                       indent: Indent,
 228                       ident: ast::Ident,
 229                       fd: &ast::FnDecl,
 230                       generics: &ast::Generics,
 231                       unsafety: ast::Unsafety,
 232                       constness: ast::Constness,
 233                       defaultness: ast::Defaultness,
 234                       abi: abi::Abi,
 235                       vis: &ast::Visibility,
 236                       span: Span,
 237                       block: &ast::Block)
 238                       -> Option<String> {
 239         let mut newline_brace = newline_for_brace(self.config, &generics.where_clause);
 240         let context = self.get_context();
 241
 242         let block_snippet = self.snippet(codemap::mk_sp(block.span.lo, block.span.hi));
 243         let has_body = !block_snippet[1..block_snippet.len() - 1].trim().is_empty() ||
 244                        !context.config.fn_empty_single_line;
 245
 246         let (mut result, force_newline_brace) = try_opt!(rewrite_fn_base(&context,
 247                                                                          indent,
 248                                                                          ident,
 249                                                                          fd,
 250                                                                          generics,
 251                                                                          unsafety,
 252                                                                          constness,
 253                                                                          defaultness,
 254                                                                          abi,
 255                                                                          vis,
 256                                                                          span,
 257                                                                          newline_brace,
 258                                                                          has_body));
 259
 260         if self.config.fn_brace_style != BraceStyle::AlwaysNextLine && !result.contains('\n') {
 261             newline_brace = false;
 262         } else if force_newline_brace {
 263             newline_brace = true;
 264         }
 265
 266         // Prepare for the function body by possibly adding a newline and
 267         // indent.
 268         // FIXME we'll miss anything between the end of the signature and the
 269         // start of the body, but we need more spans from the compiler to solve
 270         // this.
 271         if newline_brace {
 272             result.push('\n');
 273             result.push_str(&indent.to_string(self.config));
 274         } else {
 275             result.push(' ');
 276         }
 277
 278         self.single_line_fn(&result, block).or_else(|| Some(result))
 279     }
 280
 281     pub fn rewrite_required_fn(&mut self,
 282                                indent: Indent,
 283                                ident: ast::Ident,
 284                                sig: &ast::MethodSig,
 285                                span: Span)
 286                                -> Option<String> {
 287         // Drop semicolon or it will be interpreted as comment.
 288         let span = mk_sp(span.lo, span.hi - BytePos(1));
 289         let context = self.get_context();
 290
 291         let (mut result, _) = try_opt!(rewrite_fn_base(&context,
 292                                                        indent,
 293                                                        ident,
 294                                                        &sig.decl,
 295                                                        &sig.generics,
 296                                                        sig.unsafety,
 297                                                        sig.constness.node,
 298                                                        ast::Defaultness::Final,
 299                                                        sig.abi,
 300                                                        &ast::Visibility::Inherited,
 301                                                        span,
 302                                                        false,
 303                                                        false));
 304
 305         // Re-attach semicolon
 306         result.push(';');
 307
 308         Some(result)
 309     }
 310
 311     fn single_line_fn(&self, fn_str: &str, block: &ast::Block) -> Option<String> {
 312         if fn_str.contains('\n') {
 313             return None;
 314         }
 315
 316         let codemap = self.get_context().codemap;
 317
 318         if self.config.fn_empty_single_line && is_empty_block(block, codemap) &&
 319            self.block_indent.width() + fn_str.len() + 2 <= self.config.max_width {
 320             return Some(format!("{}{{}}", fn_str));
 321         }
 322
 323         if self.config.fn_single_line && is_simple_block_stmt(block, codemap) {
 324             let rewrite = {
 325                 if let Some(ref stmt) = block.stmts.first() {
 326                     match stmt_expr(stmt) {
 327                         Some(e) => {
 328                             let suffix = if semicolon_for_expr(e) { ";" } else { "" };
 329
 330                             e.rewrite(&self.get_context(),
 331                                          Shape::legacy(self.config.max_width -
 332                                                        self.block_indent.width(),
 333                                                        self.block_indent))
 334                                 .map(|s| s + suffix)
 335                                 .or_else(|| Some(self.snippet(e.span)))
 336                         }
 337                         None => {
 338                             stmt.rewrite(&self.get_context(),
 339                                          Shape::legacy(self.config.max_width -
 340                                                        self.block_indent.width(),
 341                                                        self.block_indent))
 342                         }
 343                     }
 344                 } else {
 345                     None
 346                 }
 347             };
 348
 349             if let Some(res) = rewrite {
 350                 let width = self.block_indent.width() + fn_str.len() + res.len() + 4;
 351                 if !res.contains('\n') && width <= self.config.max_width {
 352                     return Some(format!("{}{{ {} }}", fn_str, res));
 353                 }
 354             }
 355         }
 356
 357         None
 358     }
 359
 360     pub fn visit_enum(&mut self,
 361                       ident: ast::Ident,
 362                       vis: &ast::Visibility,
 363                       enum_def: &ast::EnumDef,
 364                       generics: &ast::Generics,
 365                       span: Span) {
 366         self.buffer.push_str(&format_header("enum ", ident, vis));
 367
 368         let enum_snippet = self.snippet(span);
 369         let brace_pos = enum_snippet.find_uncommented("{").unwrap();
 370         let body_start = span.lo + BytePos(brace_pos as u32 + 1);
 371         let generics_str = format_generics(&self.get_context(),
 372                                            generics,
 373                                            "{",
 374                                            "{",
 375                                            self.config.item_brace_style,
 376                                            enum_def.variants.is_empty(),
 377                                            self.block_indent,
 378                                            self.block_indent.block_indent(self.config),
 379                                            mk_sp(span.lo, body_start))
 380                 .unwrap();
 381         self.buffer.push_str(&generics_str);
 382
 383         self.last_pos = body_start;
 384
 385         self.block_indent = self.block_indent.block_indent(self.config);
 386         let variant_list = self.format_variant_list(enum_def, body_start, span.hi - BytePos(1));
 387         match variant_list {
 388             Some(ref body_str) => self.buffer.push_str(body_str),
 389             None => {
 390                 if contains_comment(&enum_snippet[brace_pos..]) {
 391                     self.format_missing_no_indent(span.hi - BytePos(1))
 392                 } else {
 393                     self.format_missing(span.hi - BytePos(1))
 394                 }
 395             }
 396         }
 397         self.block_indent = self.block_indent.block_unindent(self.config);
 398
 399         if variant_list.is_some() || contains_comment(&enum_snippet[brace_pos..]) {
 400             self.buffer.push_str(&self.block_indent.to_string(self.config));
 401         }
 402         self.buffer.push_str("}");
 403         self.last_pos = span.hi;
 404     }
 405
 406     // Format the body of an enum definition
 407     fn format_variant_list(&self,
 408                            enum_def: &ast::EnumDef,
 409                            body_lo: BytePos,
 410                            body_hi: BytePos)
 411                            -> Option<String> {
 412         if enum_def.variants.is_empty() {
 413             return None;
 414         }
 415         let mut result = String::with_capacity(1024);
 416         result.push('\n');
 417         let indentation = self.block_indent.to_string(self.config);
 418         result.push_str(&indentation);
 419
 420         let items = itemize_list(self.codemap,
 421                                  enum_def.variants.iter(),
 422                                  "}",
 423                                  |f| if !f.node.attrs.is_empty() {
 424                                      f.node.attrs[0].span.lo
 425                                  } else {
 426                                      f.span.lo
 427                                  },
 428                                  |f| f.span.hi,
 429                                  |f| self.format_variant(f),
 430                                  body_lo,
 431                                  body_hi);
 432
 433         let budget = self.config.max_width - self.block_indent.width() - 2;
 434         let fmt = ListFormatting {
 435             tactic: DefinitiveListTactic::Vertical,
 436             separator: ",",
 437             trailing_separator: SeparatorTactic::from_bool(self.config.enum_trailing_comma),
 438             shape: Shape::legacy(budget, self.block_indent),
 439             ends_with_newline: true,
 440             config: self.config,
 441         };
 442
 443         let list = try_opt!(write_list(items, &fmt));
 444         result.push_str(&list);
 445         result.push('\n');
 446         Some(result)
 447     }
 448
 449     // Variant of an enum.
 450     fn format_variant(&self, field: &ast::Variant) -> Option<String> {
 451         if contains_skip(&field.node.attrs) {
 452             let lo = field.node.attrs[0].span.lo;
 453             let span = mk_sp(lo, field.span.hi);
 454             return Some(self.snippet(span));
 455         }
 456
 457         let indent = self.block_indent;
 458         let mut result = try_opt!(field.node
 459                                       .attrs
 460                                       .rewrite(&self.get_context(),
 461                                                Shape::legacy(self.config.max_width -
 462                                                              indent.width(),
 463                                                              indent)));
 464         if !result.is_empty() {
 465             result.push('\n');
 466             result.push_str(&indent.to_string(self.config));
 467         }
 468
 469         let context = self.get_context();
 470         let variant_body = match field.node.data {
 471             ast::VariantData::Tuple(..) |
 472             ast::VariantData::Struct(..) => {
 473                 // FIXME: Should limit the width, as we have a trailing comma
 474                 format_struct(&context,
 475                               "",
 476                               field.node.name,
 477                               &ast::Visibility::Inherited,
 478                               &field.node.data,
 479                               None,
 480                               field.span,
 481                               indent,
 482                               Some(self.config.struct_variant_width))
 483             }
 484             ast::VariantData::Unit(..) => {
 485                 let tag = if let Some(ref expr) = field.node.disr_expr {
 486                     format!("{} = {}", field.node.name, self.snippet(expr.span))
 487                 } else {
 488                     field.node.name.to_string()
 489                 };
 490
 491                 wrap_str(tag,
 492                          self.config.max_width,
 493                          Shape::legacy(self.config.max_width - indent.width(), indent))
 494             }
 495         };
 496
 497         if let Some(variant_str) = variant_body {
 498             result.push_str(&variant_str);
 499             Some(result)
 500         } else {
 501             None
 502         }
 503     }
 504 }
 505
 506 pub fn format_impl(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 507     if let ast::ItemKind::Impl(_, _, ref generics, ref trait_ref, _, ref items) = item.node {
 508         let mut result = String::new();
 509         // First try to format the ref and type without a split at the 'for'.
 510         let mut ref_and_type = try_opt!(format_impl_ref_and_type(context, item, offset, false));
 511
 512         // If there is a line break present in the first result format it again
 513         // with a split at the 'for'. Skip this if there is no trait ref and
 514         // therefore no 'for'.
 515         if ref_and_type.contains('\n') && trait_ref.is_some() {
 516             ref_and_type = try_opt!(format_impl_ref_and_type(context, item, offset, true));
 517         }
 518         result.push_str(&ref_and_type);
 519
 520         let where_budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
 521         let where_clause_str = try_opt!(rewrite_where_clause(context,
 522                                                              &generics.where_clause,
 523                                                              context.config,
 524                                                              context.config.item_brace_style,
 525                                                              Shape::legacy(where_budget,
 526                                                                            offset.block_only()),
 527                                                              context.config.where_density,
 528                                                              "{",
 529                                                              true,
 530                                                              None));
 531
 532         if try_opt!(is_impl_single_line(context, &items, &result, &where_clause_str, &item)) {
 533             result.push_str(&where_clause_str);
 534             if where_clause_str.contains('\n') {
 535                 let white_space = offset.to_string(context.config);
 536                 result.push_str(&format!("\n{}{{\n{}}}", &white_space, &white_space));
 537             } else {
 538                 result.push_str(" {}");
 539             }
 540             return Some(result);
 541         }
 542
 543         if !where_clause_str.is_empty() && !where_clause_str.contains('\n') {
 544             result.push('\n');
 545             let width = offset.block_indent + context.config.tab_spaces - 1;
 546             let where_indent = Indent::new(0, width);
 547             result.push_str(&where_indent.to_string(context.config));
 548         }
 549         result.push_str(&where_clause_str);
 550
 551         match context.config.item_brace_style {
 552             BraceStyle::AlwaysNextLine => {
 553                 result.push('\n');
 554                 result.push_str(&offset.to_string(context.config));
 555             }
 556             BraceStyle::PreferSameLine => result.push(' '),
 557             BraceStyle::SameLineWhere => {
 558                 if !where_clause_str.is_empty() {
 559                     result.push('\n');
 560                     result.push_str(&offset.to_string(context.config));
 561                 } else {
 562                     result.push(' ');
 563                 }
 564             }
 565         }
 566
 567         result.push('{');
 568
 569         let snippet = context.snippet(item.span);
 570         let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 571
 572         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
 573             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 574             visitor.block_indent = offset.block_only().block_indent(context.config);
 575             visitor.last_pos = item.span.lo + BytePos(open_pos as u32);
 576
 577             for item in items {
 578                 visitor.visit_impl_item(item);
 579             }
 580
 581             visitor.format_missing(item.span.hi - BytePos(1));
 582
 583             let inner_indent_str = visitor.block_indent.to_string(context.config);
 584             let outer_indent_str = offset.block_only().to_string(context.config);
 585
 586             result.push('\n');
 587             result.push_str(&inner_indent_str);
 588             result.push_str(trim_newlines(visitor.buffer.to_string().trim()));
 589             result.push('\n');
 590             result.push_str(&outer_indent_str);
 591         }
 592
 593         if result.chars().last().unwrap() == '{' {
 594             result.push('\n');
 595             result.push_str(&offset.to_string(context.config));
 596         }
 597         result.push('}');
 598
 599         Some(result)
 600     } else {
 601         unreachable!();
 602     }
 603 }
 604
 605 fn is_impl_single_line(context: &RewriteContext,
 606                        items: &[ImplItem],
 607                        result: &str,
 608                        where_clause_str: &str,
 609                        item: &ast::Item)
 610                        -> Option<bool> {
 611     let snippet = context.snippet(item.span);
 612     let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 613
 614     Some(context.config.impl_empty_single_line && items.is_empty() &&
 615          result.len() + where_clause_str.len() <= context.config.max_width &&
 616          !contains_comment(&snippet[open_pos..]))
 617 }
 618
 619 fn format_impl_ref_and_type(context: &RewriteContext,
 620                             item: &ast::Item,
 621                             offset: Indent,
 622                             split_at_for: bool)
 623                             -> Option<String> {
 624     if let ast::ItemKind::Impl(unsafety, polarity, ref generics, ref trait_ref, ref self_ty, _) =
 625         item.node {
 626         let mut result = String::new();
 627
 628         result.push_str(&*format_visibility(&item.vis));
 629         result.push_str(format_unsafety(unsafety));
 630         result.push_str("impl");
 631
 632         let lo = context.codemap.span_after(item.span, "impl");
 633         let hi = match *trait_ref {
 634             Some(ref tr) => tr.path.span.lo,
 635             None => self_ty.span.lo,
 636         };
 637         let generics_str = try_opt!(rewrite_generics(context,
 638                                                      generics,
 639                                                      Shape::legacy(context.config.max_width,
 640                                                                    offset),
 641                                                      offset + result.len(),
 642                                                      mk_sp(lo, hi)));
 643         result.push_str(&generics_str);
 644
 645         if polarity == ast::ImplPolarity::Negative {
 646             result.push_str(" !");
 647         }
 648         if let Some(ref trait_ref) = *trait_ref {
 649             if polarity != ast::ImplPolarity::Negative {
 650                 result.push_str(" ");
 651             }
 652             let budget = try_opt!(context.config.max_width.checked_sub(result.len()));
 653             let indent = offset + result.len();
 654             result.push_str(&*try_opt!(trait_ref.rewrite(context, Shape::legacy(budget, indent))));
 655
 656             if split_at_for {
 657                 result.push('\n');
 658
 659                 // Add indentation of one additional tab.
 660                 let width = offset.block_indent + context.config.tab_spaces;
 661                 let for_indent = Indent::new(0, width);
 662                 result.push_str(&for_indent.to_string(context.config));
 663
 664                 result.push_str("for");
 665             } else {
 666                 result.push_str(" for");
 667             }
 668         }
 669
 670         let mut used_space = last_line_width(&result);
 671         if generics.where_clause.predicates.is_empty() {
 672             // If there is no where clause adapt budget for type formatting to take space and curly
 673             // brace into account.
 674             match context.config.item_brace_style {
 675                 BraceStyle::AlwaysNextLine => {}
 676                 BraceStyle::PreferSameLine => used_space += 2,
 677                 BraceStyle::SameLineWhere => used_space += 2,
 678             }
 679         }
 680
 681         // 1 = space before the type.
 682         let budget = try_opt!(context.config.max_width.checked_sub(used_space + 1));
 683         let indent = offset + result.len() + 1;
 684         let self_ty_str = self_ty.rewrite(context, Shape::legacy(budget, indent));
 685         if let Some(self_ty_str) = self_ty_str {
 686             result.push_str(" ");
 687             result.push_str(&self_ty_str);
 688             return Some(result);
 689         }
 690
 691         // Can't fit the self type on what's left of the line, so start a new one.
 692         let indent = offset.block_indent(context.config);
 693         result.push_str(&format!("\n{}", indent.to_string(context.config)));
 694         let budget = try_opt!(context.config.max_width.checked_sub(indent.width()));
 695         result.push_str(&*try_opt!(self_ty.rewrite(context, Shape::legacy(budget, indent))));
 696         Some(result)
 697     } else {
 698         unreachable!();
 699     }
 700 }
 701
 702 pub fn format_struct(context: &RewriteContext,
 703                      item_name: &str,
 704                      ident: ast::Ident,
 705                      vis: &ast::Visibility,
 706                      struct_def: &ast::VariantData,
 707                      generics: Option<&ast::Generics>,
 708                      span: Span,
 709                      offset: Indent,
 710                      one_line_width: Option<usize>)
 711                      -> Option<String> {
 712     match *struct_def {
 713         ast::VariantData::Unit(..) => Some(format_unit_struct(item_name, ident, vis)),
 714         ast::VariantData::Tuple(ref fields, _) => {
 715             format_tuple_struct(context,
 716                                 item_name,
 717                                 ident,
 718                                 vis,
 719                                 fields,
 720                                 generics,
 721                                 span,
 722                                 offset)
 723         }
 724         ast::VariantData::Struct(ref fields, _) => {
 725             format_struct_struct(context,
 726                                  item_name,
 727                                  ident,
 728                                  vis,
 729                                  fields,
 730                                  generics,
 731                                  span,
 732                                  offset,
 733                                  one_line_width)
 734         }
 735     }
 736 }
 737
 738 pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 739     if let ast::ItemKind::Trait(unsafety, ref generics, ref type_param_bounds, ref trait_items) =
 740         item.node {
 741         let mut result = String::new();
 742         let header = format!("{}{}trait {}",
 743                              format_visibility(&item.vis),
 744                              format_unsafety(unsafety),
 745                              item.ident);
 746
 747         result.push_str(&header);
 748
 749         let body_lo = context.codemap.span_after(item.span, "{");
 750
 751         let generics_str = try_opt!(rewrite_generics(context,
 752                                                      generics,
 753                                                      Shape::legacy(context.config.max_width,
 754                                                                    offset),
 755                                                      offset + result.len(),
 756                                                      mk_sp(item.span.lo, body_lo)));
 757         result.push_str(&generics_str);
 758
 759         let trait_bound_str =
 760             try_opt!(rewrite_trait_bounds(context,
 761                                           type_param_bounds,
 762                                           Shape::legacy(context.config.max_width, offset)));
 763         // If the trait, generics, and trait bound cannot fit on the same line,
 764         // put the trait bounds on an indented new line
 765         if offset.width() + last_line_width(&result) + trait_bound_str.len() >
 766            context.config.ideal_width {
 767             result.push('\n');
 768             let trait_indent = offset.block_only().block_indent(context.config);
 769             result.push_str(&trait_indent.to_string(context.config));
 770         }
 771         result.push_str(&trait_bound_str);
 772
 773         let has_body = !trait_items.is_empty();
 774
 775         let where_density =
 776             if (context.config.where_density == Density::Compressed &&
 777                 (!result.contains('\n') ||
 778                  context.config.fn_args_layout == FnArgLayoutStyle::Block)) ||
 779                (context.config.fn_args_layout == FnArgLayoutStyle::Block && result.is_empty()) ||
 780                (context.config.where_density == Density::CompressedIfEmpty && !has_body &&
 781                 !result.contains('\n')) {
 782                 Density::Compressed
 783             } else {
 784                 Density::Tall
 785             };
 786
 787         let where_budget = try_opt!(context.config
 788                                         .max_width
 789                                         .checked_sub(last_line_width(&result)));
 790         let where_clause_str = try_opt!(rewrite_where_clause(context,
 791                                                              &generics.where_clause,
 792                                                              context.config,
 793                                                              context.config.item_brace_style,
 794                                                              Shape::legacy(where_budget,
 795                                                                            offset.block_only()),
 796                                                              where_density,
 797                                                              "{",
 798                                                              has_body,
 799                                                              None));
 800         // If the where clause cannot fit on the same line,
 801         // put the where clause on a new line
 802         if !where_clause_str.contains('\n') &&
 803            last_line_width(&result) + where_clause_str.len() + offset.width() >
 804            context.config.ideal_width {
 805             result.push('\n');
 806             let width = offset.block_indent + context.config.tab_spaces - 1;
 807             let where_indent = Indent::new(0, width);
 808             result.push_str(&where_indent.to_string(context.config));
 809         }
 810         result.push_str(&where_clause_str);
 811
 812         match context.config.item_brace_style {
 813             BraceStyle::AlwaysNextLine => {
 814                 result.push('\n');
 815                 result.push_str(&offset.to_string(context.config));
 816             }
 817             BraceStyle::PreferSameLine => result.push(' '),
 818             BraceStyle::SameLineWhere => {
 819                 if !where_clause_str.is_empty() &&
 820                    (!trait_items.is_empty() || result.contains('\n')) {
 821                     result.push('\n');
 822                     result.push_str(&offset.to_string(context.config));
 823                 } else {
 824                     result.push(' ');
 825                 }
 826             }
 827         }
 828         result.push('{');
 829
 830         let snippet = context.snippet(item.span);
 831         let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 832
 833         if !trait_items.is_empty() || contains_comment(&snippet[open_pos..]) {
 834             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 835             visitor.block_indent = offset.block_only().block_indent(context.config);
 836             visitor.last_pos = item.span.lo + BytePos(open_pos as u32);
 837
 838             for item in trait_items {
 839                 visitor.visit_trait_item(item);
 840             }
 841
 842             visitor.format_missing(item.span.hi - BytePos(1));
 843
 844             let inner_indent_str = visitor.block_indent.to_string(context.config);
 845             let outer_indent_str = offset.block_only().to_string(context.config);
 846
 847             result.push('\n');
 848             result.push_str(&inner_indent_str);
 849             result.push_str(trim_newlines(visitor.buffer.to_string().trim()));
 850             result.push('\n');
 851             result.push_str(&outer_indent_str);
 852         } else if result.contains('\n') {
 853             result.push('\n');
 854         }
 855
 856         result.push('}');
 857         Some(result)
 858     } else {
 859         unreachable!();
 860     }
 861 }
 862
 863 fn format_unit_struct(item_name: &str, ident: ast::Ident, vis: &ast::Visibility) -> String {
 864     format!("{};", format_header(item_name, ident, vis))
 865 }
 866
 867 fn format_struct_struct(context: &RewriteContext,
 868                         item_name: &str,
 869                         ident: ast::Ident,
 870                         vis: &ast::Visibility,
 871                         fields: &[ast::StructField],
 872                         generics: Option<&ast::Generics>,
 873                         span: Span,
 874                         offset: Indent,
 875                         one_line_width: Option<usize>)
 876                         -> Option<String> {
 877     let mut result = String::with_capacity(1024);
 878
 879     let header_str = format_header(item_name, ident, vis);
 880     result.push_str(&header_str);
 881
 882     let body_lo = context.codemap.span_after(span, "{");
 883
 884     let generics_str = match generics {
 885         Some(g) => {
 886             try_opt!(format_generics(context,
 887                                      g,
 888                                      "{",
 889                                      "{",
 890                                      context.config.item_brace_style,
 891                                      fields.is_empty(),
 892                                      offset,
 893                                      offset + header_str.len(),
 894                                      mk_sp(span.lo, body_lo)))
 895         }
 896         None => {
 897             if context.config.item_brace_style == BraceStyle::AlwaysNextLine && !fields.is_empty() {
 898                 format!("\n{}{{", offset.block_only().to_string(context.config))
 899             } else {
 900                 " {".to_owned()
 901             }
 902         }
 903     };
 904     result.push_str(&generics_str);
 905
 906     // FIXME(#919): properly format empty structs and their comments.
 907     if fields.is_empty() {
 908         let snippet = context.snippet(mk_sp(body_lo, span.hi - BytePos(1)));
 909         if snippet.trim().is_empty() {
 910             // `struct S {}`
 911         } else if snippet.trim_right_matches(&[' ', '\t'][..]).ends_with('\n') {
 912             // fix indent
 913             result.push_str(&snippet.trim_right());
 914             result.push('\n');
 915             result.push_str(&offset.to_string(context.config));
 916         } else {
 917             result.push_str(&snippet);
 918         }
 919         result.push('}');
 920         return Some(result);
 921     }
 922
 923     let item_indent = offset.block_indent(context.config);
 924     // 1 = ","
 925     let item_budget = try_opt!(context.config.max_width.checked_sub(item_indent.width() + 1));
 926
 927     let items =
 928         itemize_list(context.codemap,
 929                      fields.iter(),
 930                      "}",
 931                      |field| {
 932             // Include attributes and doc comments, if present
 933             if !field.attrs.is_empty() {
 934                 field.attrs[0].span.lo
 935             } else {
 936                 field.span.lo
 937             }
 938         },
 939                      |field| field.ty.span.hi,
 940                      |field| field.rewrite(context, Shape::legacy(item_budget, item_indent)),
 941                      context.codemap.span_after(span, "{"),
 942                      span.hi)
 943                 .collect::<Vec<_>>();
 944     // 1 = ,
 945     let budget = context.config.max_width - offset.width() + context.config.tab_spaces - 1;
 946
 947     let tactic = match one_line_width {
 948         Some(w) => definitive_tactic(&items, ListTactic::LimitedHorizontalVertical(w), budget),
 949         None => DefinitiveListTactic::Vertical,
 950     };
 951
 952     let fmt = ListFormatting {
 953         tactic: tactic,
 954         separator: ",",
 955         trailing_separator: context.config.struct_trailing_comma,
 956         shape: Shape::legacy(budget, item_indent),
 957         ends_with_newline: true,
 958         config: context.config,
 959     };
 960     let items_str = try_opt!(write_list(&items, &fmt));
 961     if one_line_width.is_some() && !items_str.contains('\n') {
 962         Some(format!("{} {} }}", result, items_str))
 963     } else {
 964         Some(format!("{}\n{}{}\n{}}}",
 965                      result,
 966                      offset.block_indent(context.config).to_string(context.config),
 967                      items_str,
 968                      offset.to_string(context.config)))
 969     }
 970 }
 971
 972 fn format_tuple_struct(context: &RewriteContext,
 973                        item_name: &str,
 974                        ident: ast::Ident,
 975                        vis: &ast::Visibility,
 976                        fields: &[ast::StructField],
 977                        generics: Option<&ast::Generics>,
 978                        span: Span,
 979                        offset: Indent)
 980                        -> Option<String> {
 981     let mut result = String::with_capacity(1024);
 982
 983     let header_str = format_header(item_name, ident, vis);
 984     result.push_str(&header_str);
 985
 986     // FIXME(#919): don't lose comments on empty tuple structs.
 987     let body_lo = if fields.is_empty() {
 988         span.hi
 989     } else {
 990         fields[0].span.lo
 991     };
 992
 993     let where_clause_str = match generics {
 994         Some(generics) => {
 995             let generics_str = try_opt!(rewrite_generics(context,
 996                                                          generics,
 997                                                          Shape::legacy(context.config.max_width,
 998                                                                        offset),
 999                                                          offset + header_str.len(),
1000                                                          mk_sp(span.lo, body_lo)));
1001             result.push_str(&generics_str);
1002
1003             let where_budget = try_opt!(context.config
1004                                             .max_width
1005                                             .checked_sub(last_line_width(&result)));
1006             try_opt!(rewrite_where_clause(context,
1007                                           &generics.where_clause,
1008                                           context.config,
1009                                           context.config.item_brace_style,
1010                                           Shape::legacy(where_budget, offset.block_only()),
1011                                           Density::Compressed,
1012                                           ";",
1013                                           false,
1014                                           None))
1015         }
1016         None => "".to_owned(),
1017     };
1018     result.push('(');
1019
1020     let item_indent = offset.block_only() + result.len();
1021     // 2 = ");"
1022     let item_budget = try_opt!(context.config.max_width.checked_sub(item_indent.width() + 2));
1023
1024     let items =
1025         itemize_list(context.codemap,
1026                      fields.iter(),
1027                      ")",
1028                      |field| {
1029             // Include attributes and doc comments, if present
1030             if !field.attrs.is_empty() {
1031                 field.attrs[0].span.lo
1032             } else {
1033                 field.span.lo
1034             }
1035         },
1036                      |field| field.ty.span.hi,
1037                      |field| field.rewrite(context, Shape::legacy(item_budget, item_indent)),
1038                      context.codemap.span_after(span, "("),
1039                      span.hi);
1040     let body = try_opt!(format_item_list(items,
1041                                          Shape::legacy(item_budget, item_indent),
1042                                          context.config));
1043
1044     if context.config.spaces_within_parens && body.len() > 0 {
1045         result.push(' ');
1046     }
1047
1048     result.push_str(&body);
1049
1050     if context.config.spaces_within_parens && body.len() > 0 {
1051         result.push(' ');
1052     }
1053
1054     result.push(')');
1055
1056     if !where_clause_str.is_empty() && !where_clause_str.contains('\n') &&
1057        (result.contains('\n') ||
1058         offset.block_indent + result.len() + where_clause_str.len() + 1 >
1059         context.config.max_width) {
1060         // We need to put the where clause on a new line, but we didn'to_string
1061         // know that earlier, so the where clause will not be indented properly.
1062         result.push('\n');
1063         result.push_str(&(offset.block_only() + (context.config.tab_spaces - 1))
1064                              .to_string(context.config));
1065     }
1066     result.push_str(&where_clause_str);
1067
1068     Some(result)
1069 }
1070
1071 pub fn rewrite_type_alias(context: &RewriteContext,
1072                           indent: Indent,
1073                           ident: ast::Ident,
1074                           ty: &ast::Ty,
1075                           generics: &ast::Generics,
1076                           vis: &ast::Visibility,
1077                           span: Span)
1078                           -> Option<String> {
1079     let mut result = String::new();
1080
1081     result.push_str(&format_visibility(vis));
1082     result.push_str("type ");
1083     result.push_str(&ident.to_string());
1084
1085     let generics_indent = indent + result.len();
1086     let generics_span = mk_sp(context.codemap.span_after(span, "type"), ty.span.lo);
1087     let generics_width = context.config.max_width - " =".len();
1088     let generics_str = try_opt!(rewrite_generics(context,
1089                                                  generics,
1090                                                  Shape::legacy(generics_width, indent),
1091                                                  generics_indent,
1092                                                  generics_span));
1093
1094     result.push_str(&generics_str);
1095
1096     let where_budget = try_opt!(context.config
1097                                     .max_width
1098                                     .checked_sub(last_line_width(&result)));
1099     let where_clause_str = try_opt!(rewrite_where_clause(context,
1100                                                          &generics.where_clause,
1101                                                          context.config,
1102                                                          context.config.item_brace_style,
1103                                                          Shape::legacy(where_budget, indent),
1104                                                          context.config.where_density,
1105                                                          "=",
1106                                                          false,
1107                                                          Some(span.hi)));
1108     result.push_str(&where_clause_str);
1109     result.push_str(" = ");
1110
1111     let line_width = last_line_width(&result);
1112     // This checked_sub may fail as the extra space after '=' is not taken into account
1113     // In that case the budget is set to 0 which will make ty.rewrite retry on a new line
1114     let budget = context.config
1115         .max_width
1116         .checked_sub(indent.width() + line_width + ";".len())
1117         .unwrap_or(0);
1118     let type_indent = indent + line_width;
1119     // Try to fit the type on the same line
1120     let ty_str = try_opt!(ty.rewrite(context, Shape::legacy(budget, type_indent))
1121                               .or_else(|| {
1122         // The line was too short, try to put the type on the next line
1123
1124         // Remove the space after '='
1125         result.pop();
1126         let type_indent = indent.block_indent(context.config);
1127         result.push('\n');
1128         result.push_str(&type_indent.to_string(context.config));
1129         let budget = try_opt!(context.config
1130                                   .max_width
1131                                   .checked_sub(type_indent.width() + ";".len()));
1132         ty.rewrite(context, Shape::legacy(budget, type_indent))
1133     }));
1134     result.push_str(&ty_str);
1135     result.push_str(";");
1136     Some(result)
1137 }
1138
1139 fn type_annotation_spacing(config: &Config) -> (&str, &str) {
1140     (if config.space_before_type_annotation {
1141          " "
1142      } else {
1143          ""
1144      },
1145      if config.space_after_type_annotation_colon {
1146          " "
1147      } else {
1148          ""
1149      })
1150 }
1151
1152 impl Rewrite for ast::StructField {
1153     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1154         if contains_skip(&self.attrs) {
1155             let span = context.snippet(mk_sp(self.attrs[0].span.lo, self.span.hi));
1156             return wrap_str(span, context.config.max_width, shape);
1157         }
1158
1159         let name = self.ident;
1160         let vis = format_visibility(&self.vis);
1161         let mut attr_str = try_opt!(self.attrs
1162                                         .rewrite(context,
1163                                                  Shape::legacy(context.config.max_width -
1164                                                                shape.indent.width(),
1165                                                                shape.indent)));
1166         if !attr_str.is_empty() {
1167             attr_str.push('\n');
1168             attr_str.push_str(&shape.indent.to_string(context.config));
1169         }
1170
1171         let type_annotation_spacing = type_annotation_spacing(context.config);
1172         let result = match name {
1173             Some(name) => {
1174                 format!("{}{}{}{}:{}",
1175                         attr_str,
1176                         vis,
1177                         name,
1178                         type_annotation_spacing.0,
1179                         type_annotation_spacing.1)
1180             }
1181             None => format!("{}{}", attr_str, vis),
1182         };
1183
1184         let last_line_width = last_line_width(&result);
1185         let budget = try_opt!(shape.width.checked_sub(last_line_width));
1186         let rewrite = try_opt!(self.ty.rewrite(context,
1187                                                Shape::legacy(budget,
1188                                                              shape.indent + last_line_width)));
1189         Some(result + &rewrite)
1190     }
1191 }
1192
1193 pub fn rewrite_static(prefix: &str,
1194                       vis: &ast::Visibility,
1195                       ident: ast::Ident,
1196                       ty: &ast::Ty,
1197                       mutability: ast::Mutability,
1198                       expr_opt: Option<&ptr::P<ast::Expr>>,
1199                       offset: Indent,
1200                       context: &RewriteContext)
1201                       -> Option<String> {
1202     let type_annotation_spacing = type_annotation_spacing(context.config);
1203     let prefix = format!("{}{} {}{}{}:{}",
1204                          format_visibility(vis),
1205                          prefix,
1206                          format_mutability(mutability),
1207                          ident,
1208                          type_annotation_spacing.0,
1209                          type_annotation_spacing.1);
1210     // 2 = " =".len()
1211     let ty_str = try_opt!(ty.rewrite(context,
1212                                      Shape::legacy(context.config.max_width - offset.block_indent -
1213                                                    prefix.len() -
1214                                                    2,
1215                                                    offset.block_only())));
1216
1217     if let Some(expr) = expr_opt {
1218         let lhs = format!("{}{} =", prefix, ty_str);
1219         // 1 = ;
1220         let remaining_width = context.config.max_width - offset.block_indent - 1;
1221         rewrite_assign_rhs(context,
1222                            lhs,
1223                            expr,
1224                            Shape::legacy(remaining_width, offset.block_only()))
1225                 .map(|s| s + ";")
1226     } else {
1227         let lhs = format!("{}{};", prefix, ty_str);
1228         Some(lhs)
1229     }
1230 }
1231
1232 pub fn rewrite_associated_type(ident: ast::Ident,
1233                                ty_opt: Option<&ptr::P<ast::Ty>>,
1234                                ty_param_bounds_opt: Option<&ast::TyParamBounds>,
1235                                context: &RewriteContext,
1236                                indent: Indent)
1237                                -> Option<String> {
1238     let prefix = format!("type {}", ident);
1239
1240     let type_bounds_str = if let Some(ty_param_bounds) = ty_param_bounds_opt {
1241         let bounds: &[_] = ty_param_bounds;
1242         let bound_str = try_opt!(bounds.iter()
1243                                      .map(|ty_bound| {
1244             ty_bound.rewrite(context, Shape::legacy(context.config.max_width, indent))
1245         })
1246                                      .intersperse(Some(" + ".to_string()))
1247                                      .collect::<Option<String>>());
1248         if bounds.len() > 0 {
1249             format!(": {}", bound_str)
1250         } else {
1251             String::new()
1252         }
1253     } else {
1254         String::new()
1255     };
1256
1257     if let Some(ty) = ty_opt {
1258         let ty_str = try_opt!(ty.rewrite(context,
1259                                          Shape::legacy(context.config.max_width -
1260                                                        indent.block_indent -
1261                                                        prefix.len() -
1262                                                        2,
1263                                                        indent.block_only())));
1264         Some(format!("{} = {};", prefix, ty_str))
1265     } else {
1266         Some(format!("{}{};", prefix, type_bounds_str))
1267     }
1268 }
1269
1270 impl Rewrite for ast::FunctionRetTy {
1271     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1272         match *self {
1273             ast::FunctionRetTy::Default(_) => Some(String::new()),
1274             ast::FunctionRetTy::Ty(ref ty) => {
1275                 let inner_width = try_opt!(shape.width.checked_sub(3));
1276                 ty.rewrite(context, Shape::legacy(inner_width, shape.indent + 3))
1277                     .map(|r| format!("-> {}", r))
1278             }
1279         }
1280     }
1281 }
1282
1283 impl Rewrite for ast::Arg {
1284     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1285         if is_named_arg(self) {
1286             let mut result = try_opt!(self.pat
1287                                           .rewrite(context,
1288                                                    Shape::legacy(shape.width, shape.indent)));
1289
1290             if self.ty.node != ast::TyKind::Infer {
1291                 if context.config.space_before_type_annotation {
1292                     result.push_str(" ");
1293                 }
1294                 result.push_str(":");
1295                 if context.config.space_after_type_annotation_colon {
1296                     result.push_str(" ");
1297                 }
1298                 let max_width = try_opt!(shape.width.checked_sub(result.len()));
1299                 let ty_str = try_opt!(self.ty.rewrite(context,
1300                                                       Shape::legacy(max_width,
1301                                                                     shape.indent + result.len())));
1302                 result.push_str(&ty_str);
1303             }
1304
1305             Some(result)
1306         } else {
1307             self.ty.rewrite(context, shape)
1308         }
1309     }
1310 }
1311
1312 fn rewrite_explicit_self(explicit_self: &ast::ExplicitSelf,
1313                          args: &[ast::Arg],
1314                          context: &RewriteContext)
1315                          -> Option<String> {
1316     match explicit_self.node {
1317         ast::SelfKind::Region(lt, m) => {
1318             let mut_str = format_mutability(m);
1319             match lt {
1320                 Some(ref l) => {
1321                     let lifetime_str =
1322                         try_opt!(l.rewrite(context,
1323                                            Shape::legacy(usize::max_value(), Indent::empty())));
1324                     Some(format!("&{} {}self", lifetime_str, mut_str))
1325                 }
1326                 None => Some(format!("&{}self", mut_str)),
1327             }
1328         }
1329         ast::SelfKind::Explicit(ref ty, _) => {
1330             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1331
1332             let mutability = explicit_self_mutability(&args[0]);
1333             let type_str = try_opt!(ty.rewrite(context,
1334                                                Shape::legacy(usize::max_value(), Indent::empty())));
1335
1336             Some(format!("{}self: {}", format_mutability(mutability), type_str))
1337         }
1338         ast::SelfKind::Value(_) => {
1339             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1340
1341             let mutability = explicit_self_mutability(&args[0]);
1342
1343             Some(format!("{}self", format_mutability(mutability)))
1344         }
1345     }
1346 }
1347
1348 // Hacky solution caused by absence of `Mutability` in `SelfValue` and
1349 // `SelfExplicit` variants of `ast::ExplicitSelf_`.
1350 fn explicit_self_mutability(arg: &ast::Arg) -> ast::Mutability {
1351     if let ast::PatKind::Ident(ast::BindingMode::ByValue(mutability), _, _) = arg.pat.node {
1352         mutability
1353     } else {
1354         unreachable!()
1355     }
1356 }
1357
1358 pub fn span_lo_for_arg(arg: &ast::Arg) -> BytePos {
1359     if is_named_arg(arg) {
1360         arg.pat.span.lo
1361     } else {
1362         arg.ty.span.lo
1363     }
1364 }
1365
1366 pub fn span_hi_for_arg(arg: &ast::Arg) -> BytePos {
1367     match arg.ty.node {
1368         ast::TyKind::Infer if is_named_arg(arg) => arg.pat.span.hi,
1369         _ => arg.ty.span.hi,
1370     }
1371 }
1372
1373 pub fn is_named_arg(arg: &ast::Arg) -> bool {
1374     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
1375         ident.node != symbol::keywords::Invalid.ident()
1376     } else {
1377         true
1378     }
1379 }
1380
1381 fn span_for_return(ret: &ast::FunctionRetTy) -> Span {
1382     match *ret {
1383         ast::FunctionRetTy::Default(ref span) => span.clone(),
1384         ast::FunctionRetTy::Ty(ref ty) => ty.span,
1385     }
1386 }
1387
1388 fn span_for_ty_param(ty: &ast::TyParam) -> Span {
1389     // Note that ty.span is the span for ty.ident, not the whole item.
1390     let lo = ty.span.lo;
1391     if let Some(ref def) = ty.default {
1392         return mk_sp(lo, def.span.hi);
1393     }
1394     if ty.bounds.is_empty() {
1395         return ty.span;
1396     }
1397     let hi = match ty.bounds[ty.bounds.len() - 1] {
1398         ast::TyParamBound::TraitTyParamBound(ref ptr, _) => ptr.span.hi,
1399         ast::TyParamBound::RegionTyParamBound(ref l) => l.span.hi,
1400     };
1401     mk_sp(lo, hi)
1402 }
1403
1404 fn span_for_where_pred(pred: &ast::WherePredicate) -> Span {
1405     match *pred {
1406         ast::WherePredicate::BoundPredicate(ref p) => p.span,
1407         ast::WherePredicate::RegionPredicate(ref p) => p.span,
1408         ast::WherePredicate::EqPredicate(ref p) => p.span,
1409     }
1410 }
1411
1412 // Return type is (result, force_new_line_for_brace)
1413 fn rewrite_fn_base(context: &RewriteContext,
1414                    indent: Indent,
1415                    ident: ast::Ident,
1416                    fd: &ast::FnDecl,
1417                    generics: &ast::Generics,
1418                    unsafety: ast::Unsafety,
1419                    constness: ast::Constness,
1420                    defaultness: ast::Defaultness,
1421                    abi: abi::Abi,
1422                    vis: &ast::Visibility,
1423                    span: Span,
1424                    newline_brace: bool,
1425                    has_body: bool)
1426                    -> Option<(String, bool)> {
1427     let mut force_new_line_for_brace = false;
1428
1429     let where_clause = &generics.where_clause;
1430
1431     let mut result = String::with_capacity(1024);
1432     // Vis unsafety abi.
1433     result.push_str(&*format_visibility(vis));
1434
1435     if let ast::Defaultness::Default = defaultness {
1436         result.push_str("default ");
1437     }
1438
1439     if let ast::Constness::Const = constness {
1440         result.push_str("const ");
1441     }
1442
1443     result.push_str(::utils::format_unsafety(unsafety));
1444
1445     if abi != abi::Abi::Rust {
1446         result.push_str(&::utils::format_abi(abi, context.config.force_explicit_abi));
1447     }
1448
1449     // fn foo
1450     result.push_str("fn ");
1451     result.push_str(&ident.to_string());
1452
1453     // Generics.
1454     let generics_indent = indent + result.len();
1455     let generics_span = mk_sp(span.lo, span_for_return(&fd.output).lo);
1456     let generics_str = try_opt!(rewrite_generics(context,
1457                                                  generics,
1458                                                  Shape::legacy(context.config.max_width, indent),
1459                                                  generics_indent,
1460                                                  generics_span));
1461     result.push_str(&generics_str);
1462
1463     // Note that if the width and indent really matter, we'll re-layout the
1464     // return type later anyway.
1465     let ret_str = try_opt!(fd.output
1466                                .rewrite(&context,
1467                                         Shape::legacy(context.config.max_width -
1468                                                       indent.width(),
1469                                                       indent)));
1470
1471     let multi_line_ret_str = ret_str.contains('\n');
1472     let ret_str_len = if multi_line_ret_str { 0 } else { ret_str.len() };
1473
1474     // Args.
1475     let (mut one_line_budget, mut multi_line_budget, mut arg_indent) =
1476         try_opt!(compute_budgets_for_args(context, &result, indent, ret_str_len, newline_brace));
1477
1478     if context.config.fn_args_layout == FnArgLayoutStyle::Block ||
1479        context.config.fn_args_layout == FnArgLayoutStyle::BlockAlways {
1480         arg_indent = indent.block_indent(context.config);
1481         multi_line_budget = context.config.max_width - arg_indent.width();
1482     }
1483
1484     debug!("rewrite_fn_base: one_line_budget: {}, multi_line_budget: {}, arg_indent: {:?}",
1485            one_line_budget,
1486            multi_line_budget,
1487            arg_indent);
1488
1489     // Check if vertical layout was forced.
1490     if one_line_budget == 0 {
1491         if context.config.fn_args_paren_newline {
1492             result.push('\n');
1493             result.push_str(&arg_indent.to_string(context.config));
1494             arg_indent = arg_indent + 1; // extra space for `(`
1495             result.push('(');
1496             if context.config.spaces_within_parens && fd.inputs.len() > 0 {
1497                 result.push(' ')
1498             }
1499         } else {
1500             result.push_str("(\n");
1501             result.push_str(&arg_indent.to_string(context.config));
1502         }
1503     } else {
1504         result.push('(');
1505         if context.config.spaces_within_parens && fd.inputs.len() > 0 {
1506             result.push(' ')
1507         }
1508     }
1509
1510     if multi_line_ret_str {
1511         one_line_budget = 0;
1512     }
1513
1514     // A conservative estimation, to goal is to be over all parens in generics
1515     let args_start = generics.ty_params
1516         .last()
1517         .map_or(span.lo, |tp| end_typaram(tp));
1518     let args_span = mk_sp(context.codemap.span_after(mk_sp(args_start, span.hi), "("),
1519                           span_for_return(&fd.output).lo);
1520     let arg_str = try_opt!(rewrite_args(context,
1521                                         &fd.inputs,
1522                                         fd.get_self().as_ref(),
1523                                         one_line_budget,
1524                                         multi_line_budget,
1525                                         indent,
1526                                         arg_indent,
1527                                         args_span,
1528                                         fd.variadic));
1529
1530     let multi_line_arg_str = arg_str.contains('\n');
1531
1532     let put_args_in_block = match context.config.fn_args_layout {
1533         FnArgLayoutStyle::Block => multi_line_arg_str,
1534         FnArgLayoutStyle::BlockAlways => true,
1535         _ => false,
1536     } && !fd.inputs.is_empty();
1537
1538     if put_args_in_block {
1539         arg_indent = indent.block_indent(context.config);
1540         result.push('\n');
1541         result.push_str(&arg_indent.to_string(context.config));
1542         result.push_str(&arg_str);
1543         result.push('\n');
1544         result.push_str(&indent.to_string(context.config));
1545         result.push(')');
1546     } else {
1547         result.push_str(&arg_str);
1548         if context.config.spaces_within_parens && fd.inputs.len() > 0 {
1549             result.push(' ')
1550         }
1551         result.push(')');
1552     }
1553
1554     // Return type.
1555     if !ret_str.is_empty() {
1556         let ret_should_indent = match context.config.fn_args_layout {
1557             // If our args are block layout then we surely must have space.
1558             FnArgLayoutStyle::Block if put_args_in_block => false,
1559             FnArgLayoutStyle::BlockAlways => false,
1560             _ => {
1561                 // If we've already gone multi-line, or the return type would push over the max
1562                 // width, then put the return type on a new line. With the +1 for the signature
1563                 // length an additional space between the closing parenthesis of the argument and
1564                 // the arrow '->' is considered.
1565                 let mut sig_length = result.len() + indent.width() + ret_str_len + 1;
1566
1567                 // If there is no where clause, take into account the space after the return type
1568                 // and the brace.
1569                 if where_clause.predicates.is_empty() {
1570                     sig_length += 2;
1571                 }
1572
1573                 let overlong_sig = sig_length > context.config.max_width;
1574
1575                 result.contains('\n') || multi_line_ret_str || overlong_sig
1576             }
1577         };
1578         let ret_indent = if ret_should_indent {
1579             let indent = match context.config.fn_return_indent {
1580                 ReturnIndent::WithWhereClause => indent + 4,
1581                 // Aligning with non-existent args looks silly.
1582                 _ if arg_str.is_empty() => {
1583                     force_new_line_for_brace = true;
1584                     indent + 4
1585                 }
1586                 // FIXME: we might want to check that using the arg indent
1587                 // doesn't blow our budget, and if it does, then fallback to
1588                 // the where clause indent.
1589                 _ => arg_indent,
1590             };
1591
1592             result.push('\n');
1593             result.push_str(&indent.to_string(context.config));
1594             indent
1595         } else {
1596             result.push(' ');
1597             Indent::new(indent.width(), result.len())
1598         };
1599
1600         if multi_line_ret_str {
1601             // Now that we know the proper indent and width, we need to
1602             // re-layout the return type.
1603             let budget = try_opt!(context.config.max_width.checked_sub(ret_indent.width()));
1604             let ret_str = try_opt!(fd.output.rewrite(context, Shape::legacy(budget, ret_indent)));
1605             result.push_str(&ret_str);
1606         } else {
1607             result.push_str(&ret_str);
1608         }
1609
1610         // Comment between return type and the end of the decl.
1611         let snippet_lo = fd.output.span().hi;
1612         if where_clause.predicates.is_empty() {
1613             let snippet_hi = span.hi;
1614             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
1615             let snippet = snippet.trim();
1616             if !snippet.is_empty() {
1617                 result.push(' ');
1618                 result.push_str(snippet);
1619             }
1620         } else {
1621             // FIXME it would be nice to catch comments between the return type
1622             // and the where clause, but we don't have a span for the where
1623             // clause.
1624         }
1625     }
1626
1627     let should_compress_where = match context.config.where_density {
1628         Density::Compressed => !result.contains('\n') || put_args_in_block,
1629         Density::CompressedIfEmpty => !has_body && !result.contains('\n'),
1630         _ => false,
1631     } || (put_args_in_block && ret_str.is_empty());
1632
1633     let where_density = if should_compress_where {
1634         Density::Compressed
1635     } else {
1636         Density::Tall
1637     };
1638
1639     // Where clause.
1640     let where_budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
1641     let where_clause_str = try_opt!(rewrite_where_clause(context,
1642                                                          where_clause,
1643                                                          context.config,
1644                                                          context.config.fn_brace_style,
1645                                                          Shape::legacy(where_budget, indent),
1646                                                          where_density,
1647                                                          "{",
1648                                                          has_body,
1649                                                          Some(span.hi)));
1650
1651     if last_line_width(&result) + where_clause_str.len() > context.config.max_width &&
1652        !where_clause_str.contains('\n') {
1653         result.push('\n');
1654     }
1655
1656     result.push_str(&where_clause_str);
1657
1658     Some((result, force_new_line_for_brace))
1659 }
1660
1661 fn rewrite_args(context: &RewriteContext,
1662                 args: &[ast::Arg],
1663                 explicit_self: Option<&ast::ExplicitSelf>,
1664                 one_line_budget: usize,
1665                 multi_line_budget: usize,
1666                 indent: Indent,
1667                 arg_indent: Indent,
1668                 span: Span,
1669                 variadic: bool)
1670                 -> Option<String> {
1671     let mut arg_item_strs = try_opt!(args.iter()
1672                                          .map(|arg| {
1673         arg.rewrite(&context, Shape::legacy(multi_line_budget, arg_indent))
1674     })
1675                                          .collect::<Option<Vec<_>>>());
1676
1677     // Account for sugary self.
1678     // FIXME: the comment for the self argument is dropped. This is blocked
1679     // on rust issue #27522.
1680     let min_args = explicit_self.and_then(|explicit_self| {
1681             rewrite_explicit_self(explicit_self, args, context)
1682         })
1683         .map_or(1, |self_str| {
1684             arg_item_strs[0] = self_str;
1685             2
1686         });
1687
1688     // Comments between args.
1689     let mut arg_items = Vec::new();
1690     if min_args == 2 {
1691         arg_items.push(ListItem::from_str(""));
1692     }
1693
1694     // FIXME(#21): if there are no args, there might still be a comment, but
1695     // without spans for the comment or parens, there is no chance of
1696     // getting it right. You also don't get to put a comment on self, unless
1697     // it is explicit.
1698     if args.len() >= min_args || variadic {
1699         let comment_span_start = if min_args == 2 {
1700             let second_arg_start = if arg_has_pattern(&args[1]) {
1701                 args[1].pat.span.lo
1702             } else {
1703                 args[1].ty.span.lo
1704             };
1705             let reduced_span = mk_sp(span.lo, second_arg_start);
1706
1707             context.codemap.span_after_last(reduced_span, ",")
1708         } else {
1709             span.lo
1710         };
1711
1712         enum ArgumentKind<'a> {
1713             Regular(&'a ast::Arg),
1714             Variadic(BytePos),
1715         }
1716
1717         let variadic_arg = if variadic {
1718             let variadic_span = mk_sp(args.last().unwrap().ty.span.hi, span.hi);
1719             let variadic_start = context.codemap.span_after(variadic_span, "...") - BytePos(3);
1720             Some(ArgumentKind::Variadic(variadic_start))
1721         } else {
1722             None
1723         };
1724
1725         let more_items = itemize_list(context.codemap,
1726                                       args[min_args - 1..]
1727                                           .iter()
1728                                           .map(ArgumentKind::Regular)
1729                                           .chain(variadic_arg),
1730                                       ")",
1731                                       |arg| match *arg {
1732                                           ArgumentKind::Regular(arg) => span_lo_for_arg(arg),
1733                                           ArgumentKind::Variadic(start) => start,
1734                                       },
1735                                       |arg| match *arg {
1736                                           ArgumentKind::Regular(arg) => arg.ty.span.hi,
1737                                           ArgumentKind::Variadic(start) => start + BytePos(3),
1738                                       },
1739                                       |arg| match *arg {
1740                                           ArgumentKind::Regular(..) => None,
1741                                           ArgumentKind::Variadic(..) => Some("...".to_owned()),
1742                                       },
1743                                       comment_span_start,
1744                                       span.hi);
1745
1746         arg_items.extend(more_items);
1747     }
1748
1749     for (item, arg) in arg_items.iter_mut().zip(arg_item_strs) {
1750         item.item = Some(arg);
1751     }
1752
1753     let indent = match context.config.fn_arg_indent {
1754         BlockIndentStyle::Inherit => indent,
1755         BlockIndentStyle::Tabbed => indent.block_indent(context.config),
1756         BlockIndentStyle::Visual => arg_indent,
1757     };
1758
1759     let tactic = definitive_tactic(&arg_items,
1760                                    context.config.fn_args_density.to_list_tactic(),
1761                                    one_line_budget);
1762     let budget = match tactic {
1763         DefinitiveListTactic::Horizontal => one_line_budget,
1764         _ => multi_line_budget,
1765     };
1766
1767     debug!("rewrite_args: budget: {}, tactic: {:?}", budget, tactic);
1768
1769     let end_with_newline = match context.config.fn_args_layout {
1770         FnArgLayoutStyle::Block |
1771         FnArgLayoutStyle::BlockAlways => true,
1772         _ => false,
1773     };
1774
1775     let fmt = ListFormatting {
1776         tactic: tactic,
1777         separator: ",",
1778         trailing_separator: SeparatorTactic::Never,
1779         shape: Shape::legacy(budget, indent),
1780         ends_with_newline: end_with_newline,
1781         config: context.config,
1782     };
1783
1784     write_list(&arg_items, &fmt)
1785 }
1786
1787 fn arg_has_pattern(arg: &ast::Arg) -> bool {
1788     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
1789         ident.node != symbol::keywords::Invalid.ident()
1790     } else {
1791         true
1792     }
1793 }
1794
1795 fn compute_budgets_for_args(context: &RewriteContext,
1796                             result: &str,
1797                             indent: Indent,
1798                             ret_str_len: usize,
1799                             newline_brace: bool)
1800                             -> Option<((usize, usize, Indent))> {
1801     debug!("compute_budgets_for_args {} {:?}, {}, {}",
1802            result.len(),
1803            indent,
1804            ret_str_len,
1805            newline_brace);
1806     // Try keeping everything on the same line.
1807     if !result.contains('\n') {
1808         // 3 = `() `, space is before ret_string.
1809         let mut used_space = indent.width() + result.len() + ret_str_len + 3;
1810         if !newline_brace {
1811             used_space += 2;
1812         }
1813         let one_line_budget = context.config.max_width.checked_sub(used_space).unwrap_or(0);
1814
1815         if one_line_budget > 0 {
1816             // 4 = "() {".len()
1817             let multi_line_budget =
1818                 try_opt!(context.config.max_width.checked_sub(indent.width() + result.len() + 4));
1819
1820             return Some((one_line_budget, multi_line_budget, indent + result.len() + 1));
1821         }
1822     }
1823
1824     // Didn't work. we must force vertical layout and put args on a newline.
1825     let new_indent = indent.block_indent(context.config);
1826     let used_space = new_indent.width() + 4; // Account for `(` and `)` and possibly ` {`.
1827     let max_space = context.config.max_width;
1828     if used_space <= max_space {
1829         Some((0, max_space - used_space, new_indent))
1830     } else {
1831         // Whoops! bankrupt.
1832         None
1833     }
1834 }
1835
1836 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause) -> bool {
1837     match config.fn_brace_style {
1838         BraceStyle::AlwaysNextLine => true,
1839         BraceStyle::SameLineWhere if !where_clause.predicates.is_empty() => true,
1840         _ => false,
1841     }
1842 }
1843
1844 fn rewrite_generics(context: &RewriteContext,
1845                     generics: &ast::Generics,
1846                     shape: Shape,
1847                     // TODO shouldn't need this
1848                     generics_offset: Indent,
1849                     span: Span)
1850                     -> Option<String> {
1851     // FIXME: convert bounds to where clauses where they get too big or if
1852     // there is a where clause at all.
1853     let lifetimes: &[_] = &generics.lifetimes;
1854     let tys: &[_] = &generics.ty_params;
1855     if lifetimes.is_empty() && tys.is_empty() {
1856         return Some(String::new());
1857     }
1858
1859     let offset = match context.config.generics_indent {
1860         BlockIndentStyle::Inherit => shape.indent,
1861         BlockIndentStyle::Tabbed => shape.indent.block_indent(context.config),
1862         // 1 = <
1863         BlockIndentStyle::Visual => generics_offset + 1,
1864     };
1865
1866     let h_budget = try_opt!(shape.width.checked_sub(generics_offset.width() + 2));
1867     // FIXME: might need to insert a newline if the generics are really long.
1868
1869     // Strings for the generics.
1870     let lt_strs = lifetimes.iter().map(|lt| lt.rewrite(context, Shape::legacy(h_budget, offset)));
1871     let ty_strs = tys.iter()
1872         .map(|ty_param| ty_param.rewrite(context, Shape::legacy(h_budget, offset)));
1873
1874     // Extract comments between generics.
1875     let lt_spans = lifetimes.iter().map(|l| {
1876         let hi = if l.bounds.is_empty() {
1877             l.lifetime.span.hi
1878         } else {
1879             l.bounds[l.bounds.len() - 1].span.hi
1880         };
1881         mk_sp(l.lifetime.span.lo, hi)
1882     });
1883     let ty_spans = tys.iter().map(span_for_ty_param);
1884
1885     let items = itemize_list(context.codemap,
1886                              lt_spans.chain(ty_spans).zip(lt_strs.chain(ty_strs)),
1887                              ">",
1888                              |&(sp, _)| sp.lo,
1889                              |&(sp, _)| sp.hi,
1890                              // FIXME: don't clone
1891                              |&(_, ref str)| str.clone(),
1892                              context.codemap.span_after(span, "<"),
1893                              span.hi);
1894     let list_str =
1895         try_opt!(format_item_list(items, Shape::legacy(h_budget, offset), context.config));
1896
1897     Some(if context.config.spaces_within_angle_brackets {
1898              format!("< {} >", list_str)
1899          } else {
1900              format!("<{}>", list_str)
1901          })
1902 }
1903
1904 fn rewrite_trait_bounds(context: &RewriteContext,
1905                         type_param_bounds: &ast::TyParamBounds,
1906                         shape: Shape)
1907                         -> Option<String> {
1908     let bounds: &[_] = type_param_bounds;
1909
1910     if bounds.is_empty() {
1911         return Some(String::new());
1912     }
1913
1914     let bound_str = try_opt!(bounds.iter()
1915                                  .map(|ty_bound| ty_bound.rewrite(&context, shape))
1916                                  .intersperse(Some(" + ".to_string()))
1917                                  .collect::<Option<String>>());
1918
1919     let mut result = String::new();
1920     result.push_str(": ");
1921     result.push_str(&bound_str);
1922     Some(result)
1923 }
1924
1925 fn rewrite_where_clause(context: &RewriteContext,
1926                         where_clause: &ast::WhereClause,
1927                         config: &Config,
1928                         brace_style: BraceStyle,
1929                         shape: Shape,
1930                         density: Density,
1931                         terminator: &str,
1932                         allow_trailing_comma: bool,
1933                         span_end: Option<BytePos>)
1934                         -> Option<String> {
1935     if where_clause.predicates.is_empty() {
1936         return Some(String::new());
1937     }
1938
1939     let extra_indent = match context.config.where_indent {
1940         BlockIndentStyle::Inherit => Indent::empty(),
1941         BlockIndentStyle::Tabbed | BlockIndentStyle::Visual => Indent::new(config.tab_spaces, 0),
1942     };
1943
1944     let offset = match context.config.where_pred_indent {
1945         BlockIndentStyle::Inherit => shape.indent + extra_indent,
1946         BlockIndentStyle::Tabbed => shape.indent + extra_indent.block_indent(config),
1947         // 6 = "where ".len()
1948         BlockIndentStyle::Visual => shape.indent + extra_indent + 6,
1949     };
1950     // FIXME: if where_pred_indent != Visual, then the budgets below might
1951     // be out by a char or two.
1952
1953     let budget = context.config.max_width - offset.width();
1954     let span_start = span_for_where_pred(&where_clause.predicates[0]).lo;
1955     // If we don't have the start of the next span, then use the end of the
1956     // predicates, but that means we miss comments.
1957     let len = where_clause.predicates.len();
1958     let end_of_preds = span_for_where_pred(&where_clause.predicates[len - 1]).hi;
1959     let span_end = span_end.unwrap_or(end_of_preds);
1960     let items = itemize_list(context.codemap,
1961                              where_clause.predicates.iter(),
1962                              terminator,
1963                              |pred| span_for_where_pred(pred).lo,
1964                              |pred| span_for_where_pred(pred).hi,
1965                              |pred| pred.rewrite(context, Shape::legacy(budget, offset)),
1966                              span_start,
1967                              span_end);
1968     let item_vec = items.collect::<Vec<_>>();
1969     // FIXME: we don't need to collect here if the where_layout isn't
1970     // HorizontalVertical.
1971     let tactic = definitive_tactic(&item_vec, context.config.where_layout, budget);
1972     let use_trailing_comma = allow_trailing_comma && context.config.where_trailing_comma;
1973
1974     let fmt = ListFormatting {
1975         tactic: tactic,
1976         separator: ",",
1977         trailing_separator: SeparatorTactic::from_bool(use_trailing_comma),
1978         shape: Shape::legacy(budget, offset),
1979         ends_with_newline: true,
1980         config: context.config,
1981     };
1982     let preds_str = try_opt!(write_list(&item_vec, &fmt));
1983
1984     let end_length = if terminator == "{" {
1985         // If the brace is on the next line we don't need to count it otherwise it needs two
1986         // characters " {"
1987         match brace_style {
1988             BraceStyle::AlwaysNextLine |
1989             BraceStyle::SameLineWhere => 0,
1990             BraceStyle::PreferSameLine => 2,
1991         }
1992     } else if terminator == "=" {
1993         2
1994     } else {
1995         terminator.len()
1996     };
1997     if density == Density::Tall || preds_str.contains('\n') ||
1998        shape.indent.width() + " where ".len() + preds_str.len() + end_length > shape.width {
1999         Some(format!("\n{}where {}",
2000                      (shape.indent + extra_indent).to_string(context.config),
2001                      preds_str))
2002     } else {
2003         Some(format!(" where {}", preds_str))
2004     }
2005 }
2006
2007 fn format_header(item_name: &str, ident: ast::Ident, vis: &ast::Visibility) -> String {
2008     format!("{}{}{}", format_visibility(vis), item_name, ident)
2009 }
2010
2011 fn format_generics(context: &RewriteContext,
2012                    generics: &ast::Generics,
2013                    opener: &str,
2014                    terminator: &str,
2015                    brace_style: BraceStyle,
2016                    force_same_line_brace: bool,
2017                    offset: Indent,
2018                    generics_offset: Indent,
2019                    span: Span)
2020                    -> Option<String> {
2021     let mut result = try_opt!(rewrite_generics(context,
2022                                                generics,
2023                                                Shape::legacy(context.config.max_width, offset),
2024                                                generics_offset,
2025                                                span));
2026
2027     if !generics.where_clause.predicates.is_empty() || result.contains('\n') {
2028         let budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
2029         let where_clause_str = try_opt!(rewrite_where_clause(context,
2030                                                              &generics.where_clause,
2031                                                              context.config,
2032                                                              brace_style,
2033                                                              Shape::legacy(budget,
2034                                                                            offset.block_only()),
2035                                                              Density::Tall,
2036                                                              terminator,
2037                                                              true,
2038                                                              Some(span.hi)));
2039         result.push_str(&where_clause_str);
2040         if !force_same_line_brace &&
2041            (brace_style == BraceStyle::SameLineWhere || brace_style == BraceStyle::AlwaysNextLine) {
2042             result.push('\n');
2043             result.push_str(&offset.block_only().to_string(context.config));
2044         } else {
2045             result.push(' ');
2046         }
2047         result.push_str(opener);
2048     } else {
2049         if !force_same_line_brace && brace_style == BraceStyle::AlwaysNextLine {
2050             result.push('\n');
2051             result.push_str(&offset.block_only().to_string(context.config));
2052         } else {
2053             result.push(' ');
2054         }
2055         result.push_str(opener);
2056     }
2057
2058     Some(result)
2059 }