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