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