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