src/items.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // Formatting top-level items - functions, structs, enums, traits, impls.
  12
  13 use Indent;
  14 use utils::{CodeMapSpanUtils, format_mutability, format_visibility, contains_skip, end_typaram,
  15             wrap_str, last_line_width, semicolon_for_expr, format_unsafety, trim_newlines};
  16 use lists::{write_list, itemize_list, ListItem, ListFormatting, SeparatorTactic,
  17             DefinitiveListTactic, definitive_tactic, format_item_list};
  18 use expr::{is_empty_block, is_simple_block_stmt, rewrite_assign_rhs};
  19 use comment::{FindUncommented, contains_comment};
  20 use visitor::FmtVisitor;
  21 use rewrite::{Rewrite, RewriteContext};
  22 use config::{Config, BlockIndentStyle, Density, ReturnIndent, BraceStyle, FnArgLayoutStyle};
  23
  24 use syntax::{ast, abi, ptr, codemap};
  25 use syntax::codemap::{Span, BytePos, mk_sp};
  26 use syntax::parse::token;
  27 use syntax::ast::ImplItem;
  28
  29 // Statements of the form
  30 // let pat: ty = init;
  31 impl Rewrite for ast::Local {
  32     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
  33         let mut result = "let ".to_owned();
  34         let pattern_offset = offset + result.len();
  35         // 1 = ;
  36         let pattern_width = try_opt!(width.checked_sub(pattern_offset.width() + 1));
  37
  38         let pat_str = try_opt!(self.pat.rewrite(&context, pattern_width, pattern_offset));
  39         result.push_str(&pat_str);
  40
  41         // String that is placed within the assignment pattern and expression.
  42         let infix = {
  43             let mut infix = String::new();
  44
  45             if let Some(ref ty) = self.ty {
  46                 // 2 = ": ".len()
  47                 // 1 = ;
  48                 let indent = offset + last_line_width(&result) + 2;
  49                 let budget = try_opt!(width.checked_sub(indent.width() + 1));
  50                 let rewrite = try_opt!(ty.rewrite(context, budget, indent));
  51
  52                 infix.push_str(": ");
  53                 infix.push_str(&rewrite);
  54             }
  55
  56             if self.init.is_some() {
  57                 infix.push_str(" =");
  58             }
  59
  60             infix
  61         };
  62
  63         result.push_str(&infix);
  64
  65         if let Some(ref ex) = self.init {
  66             let budget = try_opt!(width.checked_sub(context.block_indent.width() + 1));
  67
  68             // 1 = trailing semicolon;
  69             result = try_opt!(rewrite_assign_rhs(&context,
  70                                                  result,
  71                                                  ex,
  72                                                  budget,
  73                                                  context.block_indent));
  74         }
  75
  76         result.push(';');
  77         Some(result)
  78     }
  79 }
  80
  81 impl<'a> FmtVisitor<'a> {
  82     pub fn format_foreign_mod(&mut self, fm: &ast::ForeignMod, span: Span) {
  83         self.buffer.push_str(&::utils::format_abi(fm.abi));
  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                                               None,
 122                                               generics,
 123                                               ast::Unsafety::Normal,
 124                                               ast::Constness::NotConst,
 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 mut_str = if is_mutable {
 145                     "mut "
 146                 } else {
 147                     ""
 148                 };
 149                 let prefix = format!("{}static {}{}: ",
 150                                      format_visibility(item.vis),
 151                                      mut_str,
 152                                      item.ident);
 153                 let offset = self.block_indent + prefix.len();
 154                 // 1 = ;
 155                 let width = self.config.max_width - offset.width() - 1;
 156                 let rewrite = ty.rewrite(&self.get_context(), width, offset);
 157
 158                 match rewrite {
 159                     Some(result) => {
 160                         self.buffer.push_str(&prefix);
 161                         self.buffer.push_str(&result);
 162                         self.buffer.push_str(";");
 163                     }
 164                     None => self.format_missing(item.span.hi),
 165                 }
 166             }
 167         }
 168
 169         self.last_pos = item.span.hi;
 170     }
 171
 172     pub fn rewrite_fn(&mut self,
 173                       indent: Indent,
 174                       ident: ast::Ident,
 175                       fd: &ast::FnDecl,
 176                       explicit_self: Option<&ast::ExplicitSelf>,
 177                       generics: &ast::Generics,
 178                       unsafety: ast::Unsafety,
 179                       constness: ast::Constness,
 180                       abi: abi::Abi,
 181                       vis: ast::Visibility,
 182                       span: Span,
 183                       block: &ast::Block)
 184                       -> Option<String> {
 185         let mut newline_brace = newline_for_brace(self.config, &generics.where_clause);
 186         let context = self.get_context();
 187
 188         let block_snippet = self.snippet(codemap::mk_sp(block.span.lo, block.span.hi));
 189         let has_body = !block_snippet[1..block_snippet.len() - 1].trim().is_empty() ||
 190                        !context.config.fn_empty_single_line;
 191
 192         let (mut result, force_newline_brace) = try_opt!(rewrite_fn_base(&context,
 193                                                                          indent,
 194                                                                          ident,
 195                                                                          fd,
 196                                                                          explicit_self,
 197                                                                          generics,
 198                                                                          unsafety,
 199                                                                          constness,
 200                                                                          abi,
 201                                                                          vis,
 202                                                                          span,
 203                                                                          newline_brace,
 204                                                                          has_body));
 205
 206         if self.config.fn_brace_style != BraceStyle::AlwaysNextLine && !result.contains('\n') {
 207             newline_brace = false;
 208         } else if force_newline_brace {
 209             newline_brace = true;
 210         }
 211
 212         // Prepare for the function body by possibly adding a newline and
 213         // indent.
 214         // FIXME we'll miss anything between the end of the signature and the
 215         // start of the body, but we need more spans from the compiler to solve
 216         // this.
 217         if newline_brace {
 218             result.push('\n');
 219             result.push_str(&indent.to_string(self.config));
 220         } else {
 221             result.push(' ');
 222         }
 223
 224         self.single_line_fn(&result, block).or_else(|| Some(result))
 225     }
 226
 227     pub fn rewrite_required_fn(&mut self,
 228                                indent: Indent,
 229                                ident: ast::Ident,
 230                                sig: &ast::MethodSig,
 231                                span: Span)
 232                                -> Option<String> {
 233         // Drop semicolon or it will be interpreted as comment.
 234         let span = mk_sp(span.lo, span.hi - BytePos(1));
 235         let context = self.get_context();
 236
 237         let (mut result, _) = try_opt!(rewrite_fn_base(&context,
 238                                                        indent,
 239                                                        ident,
 240                                                        &sig.decl,
 241                                                        Some(&sig.explicit_self),
 242                                                        &sig.generics,
 243                                                        sig.unsafety,
 244                                                        sig.constness,
 245                                                        sig.abi,
 246                                                        ast::Visibility::Inherited,
 247                                                        span,
 248                                                        false,
 249                                                        false));
 250
 251         // Re-attach semicolon
 252         result.push(';');
 253
 254         Some(result)
 255     }
 256
 257     fn single_line_fn(&self, fn_str: &str, block: &ast::Block) -> Option<String> {
 258         if fn_str.contains('\n') {
 259             return None;
 260         }
 261
 262         let codemap = self.get_context().codemap;
 263
 264         if self.config.fn_empty_single_line && is_empty_block(block, codemap) &&
 265            self.block_indent.width() + fn_str.len() + 2 <= self.config.max_width {
 266             return Some(format!("{}{{}}", fn_str));
 267         }
 268
 269         if self.config.fn_single_line && is_simple_block_stmt(block, codemap) {
 270             let rewrite = {
 271                 if let Some(ref e) = block.expr {
 272                     let suffix = if semicolon_for_expr(e) {
 273                         ";"
 274                     } else {
 275                         ""
 276                     };
 277
 278                     e.rewrite(&self.get_context(),
 279                               self.config.max_width - self.block_indent.width(),
 280                               self.block_indent)
 281                      .map(|s| s + suffix)
 282                      .or_else(|| Some(self.snippet(e.span)))
 283                 } else if let Some(ref stmt) = block.stmts.first() {
 284                     stmt.rewrite(&self.get_context(),
 285                                  self.config.max_width - self.block_indent.width(),
 286                                  self.block_indent)
 287                 } else {
 288                     None
 289                 }
 290             };
 291
 292             if let Some(res) = rewrite {
 293                 let width = self.block_indent.width() + fn_str.len() + res.len() + 4;
 294                 if !res.contains('\n') && width <= self.config.max_width {
 295                     return Some(format!("{}{{ {} }}", fn_str, res));
 296                 }
 297             }
 298         }
 299
 300         None
 301     }
 302
 303     pub fn visit_enum(&mut self,
 304                       ident: ast::Ident,
 305                       vis: ast::Visibility,
 306                       enum_def: &ast::EnumDef,
 307                       generics: &ast::Generics,
 308                       span: Span) {
 309         let header_str = format_header("enum ", ident, vis);
 310         self.buffer.push_str(&header_str);
 311
 312         let enum_snippet = self.snippet(span);
 313         let body_start = span.lo + BytePos(enum_snippet.find_uncommented("{").unwrap() as u32 + 1);
 314         let generics_str = format_generics(&self.get_context(),
 315                                            generics,
 316                                            "{",
 317                                            "{",
 318                                            self.config.item_brace_style,
 319                                            enum_def.variants.is_empty(),
 320                                            self.block_indent,
 321                                            self.block_indent.block_indent(self.config),
 322                                            mk_sp(span.lo, body_start))
 323                                .unwrap();
 324         self.buffer.push_str(&generics_str);
 325
 326         self.last_pos = body_start;
 327
 328         self.block_indent = self.block_indent.block_indent(self.config);
 329         let variant_list = self.format_variant_list(enum_def, body_start, span.hi - BytePos(1));
 330         match variant_list {
 331             Some(ref body_str) => self.buffer.push_str(&body_str),
 332             None => self.format_missing(span.hi - BytePos(1)),
 333         }
 334         self.block_indent = self.block_indent.block_unindent(self.config);
 335
 336         if variant_list.is_some() {
 337             self.buffer.push_str(&self.block_indent.to_string(self.config));
 338         }
 339         self.buffer.push_str("}");
 340         self.last_pos = span.hi;
 341     }
 342
 343     // Format the body of an enum definition
 344     fn format_variant_list(&self,
 345                            enum_def: &ast::EnumDef,
 346                            body_lo: BytePos,
 347                            body_hi: BytePos)
 348                            -> Option<String> {
 349         if enum_def.variants.is_empty() {
 350             return None;
 351         }
 352         let mut result = String::with_capacity(1024);
 353         result.push('\n');
 354         let indentation = self.block_indent.to_string(self.config);
 355         result.push_str(&indentation);
 356
 357         let items = itemize_list(self.codemap,
 358                                  enum_def.variants.iter(),
 359                                  "}",
 360                                  |f| {
 361                                      if !f.node.attrs.is_empty() {
 362                                          f.node.attrs[0].span.lo
 363                                      } else {
 364                                          f.span.lo
 365                                      }
 366                                  },
 367                                  |f| f.span.hi,
 368                                  |f| self.format_variant(f),
 369                                  body_lo,
 370                                  body_hi);
 371
 372         let budget = self.config.max_width - self.block_indent.width() - 2;
 373         let fmt = ListFormatting {
 374             tactic: DefinitiveListTactic::Vertical,
 375             separator: ",",
 376             trailing_separator: SeparatorTactic::from_bool(self.config.enum_trailing_comma),
 377             indent: self.block_indent,
 378             width: budget,
 379             ends_with_newline: true,
 380             config: self.config,
 381         };
 382
 383         let list = try_opt!(write_list(items, &fmt));
 384         result.push_str(&list);
 385         result.push('\n');
 386         Some(result)
 387     }
 388
 389     // Variant of an enum.
 390     fn format_variant(&self, field: &ast::Variant) -> Option<String> {
 391         if contains_skip(&field.node.attrs) {
 392             let lo = field.node.attrs[0].span.lo;
 393             let span = mk_sp(lo, field.span.hi);
 394             return Some(self.snippet(span));
 395         }
 396
 397         let indent = self.block_indent;
 398         let mut result = try_opt!(field.node
 399                                        .attrs
 400                                        .rewrite(&self.get_context(),
 401                                                 self.config.max_width - indent.width(),
 402                                                 indent));
 403         if !result.is_empty() {
 404             result.push('\n');
 405             result.push_str(&indent.to_string(self.config));
 406         }
 407
 408         let context = self.get_context();
 409         let variant_body = match field.node.data {
 410             ast::VariantData::Tuple(..) |
 411             ast::VariantData::Struct(..) => {
 412                 // FIXME: Should limit the width, as we have a trailing comma
 413                 format_struct(&context,
 414                               "",
 415                               field.node.name,
 416                               ast::Visibility::Inherited,
 417                               &field.node.data,
 418                               None,
 419                               field.span,
 420                               indent)
 421             }
 422             ast::VariantData::Unit(..) => {
 423                 let tag = if let Some(ref expr) = field.node.disr_expr {
 424                     format!("{} = {}", field.node.name, self.snippet(expr.span))
 425                 } else {
 426                     field.node.name.to_string()
 427                 };
 428
 429                 wrap_str(tag,
 430                          self.config.max_width,
 431                          self.config.max_width - indent.width(),
 432                          indent)
 433             }
 434         };
 435
 436         if let Some(variant_str) = variant_body {
 437             result.push_str(&variant_str);
 438             Some(result)
 439         } else {
 440             None
 441         }
 442     }
 443 }
 444
 445 pub fn format_impl(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 446     if let ast::ItemKind::Impl(unsafety,
 447                                polarity,
 448                                ref generics,
 449                                ref trait_ref,
 450                                ref self_ty,
 451                                ref items) = item.node {
 452         let mut result = String::new();
 453         result.push_str(format_visibility(item.vis));
 454         result.push_str(format_unsafety(unsafety));
 455         result.push_str("impl");
 456
 457         let lo = context.codemap.span_after(item.span, "impl");
 458         let hi = match *trait_ref {
 459             Some(ref tr) => tr.path.span.lo,
 460             None => self_ty.span.lo,
 461         };
 462         let generics_str = try_opt!(rewrite_generics(context,
 463                                                      generics,
 464                                                      offset,
 465                                                      context.config.max_width,
 466                                                      offset + result.len(),
 467                                                      mk_sp(lo, hi)));
 468         result.push_str(&generics_str);
 469
 470         // FIXME might need to linebreak in the impl header, here would be a
 471         // good place.
 472         result.push(' ');
 473         if polarity == ast::ImplPolarity::Negative {
 474             result.push_str("!");
 475         }
 476         if let Some(ref trait_ref) = *trait_ref {
 477             let budget = try_opt!(context.config.max_width.checked_sub(result.len()));
 478             let indent = offset + result.len();
 479             result.push_str(&*try_opt!(trait_ref.rewrite(context, budget, indent)));
 480             result.push_str(" for ");
 481         }
 482
 483         let budget = try_opt!(context.config.max_width.checked_sub(result.len()));
 484         let indent = offset + result.len();
 485         result.push_str(&*try_opt!(self_ty.rewrite(context, budget, indent)));
 486
 487         let where_budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
 488         let where_clause_str = try_opt!(rewrite_where_clause(context,
 489                                                              &generics.where_clause,
 490                                                              context.config,
 491                                                              context.config.item_brace_style,
 492                                                              context.block_indent,
 493                                                              where_budget,
 494                                                              context.config.where_density,
 495                                                              "{",
 496                                                              true,
 497                                                              None));
 498
 499         if try_opt!(is_impl_single_line(context, &items, &result, &where_clause_str, &item)) {
 500             result.push_str(&where_clause_str);
 501             if where_clause_str.contains('\n') {
 502                 result.push_str("\n{\n}");
 503             } else {
 504                 result.push_str(" {}");
 505             }
 506             return Some(result);
 507         }
 508
 509         if !where_clause_str.is_empty() && !where_clause_str.contains('\n') {
 510             result.push('\n');
 511             let width = context.block_indent.width() + context.config.tab_spaces - 1;
 512             let where_indent = Indent::new(0, width);
 513             result.push_str(&where_indent.to_string(context.config));
 514         }
 515         result.push_str(&where_clause_str);
 516
 517         match context.config.item_brace_style {
 518             BraceStyle::AlwaysNextLine => result.push('\n'),
 519             BraceStyle::PreferSameLine => result.push(' '),
 520             BraceStyle::SameLineWhere => {
 521                 if !where_clause_str.is_empty() {
 522                     result.push('\n')
 523                 } else {
 524                     result.push(' ')
 525                 }
 526             }
 527         }
 528
 529         result.push('{');
 530
 531         let snippet = context.snippet(item.span);
 532         let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 533
 534         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
 535             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 536             visitor.block_indent = context.block_indent.block_indent(context.config);
 537             visitor.last_pos = item.span.lo + BytePos(open_pos as u32);
 538
 539             for item in items {
 540                 visitor.visit_impl_item(&item);
 541             }
 542
 543             visitor.format_missing(item.span.hi - BytePos(1));
 544
 545             let inner_indent_str = visitor.block_indent.to_string(context.config);
 546             let outer_indent_str = context.block_indent.to_string(context.config);
 547
 548             result.push('\n');
 549             result.push_str(&inner_indent_str);
 550             result.push_str(&trim_newlines(&visitor.buffer.to_string().trim()));
 551             result.push('\n');
 552             result.push_str(&outer_indent_str);
 553         }
 554
 555         if result.chars().last().unwrap() == '{' {
 556             result.push('\n');
 557         }
 558         result.push('}');
 559
 560         Some(result)
 561     } else {
 562         unreachable!();
 563     }
 564 }
 565
 566 fn is_impl_single_line(context: &RewriteContext,
 567                        items: &Vec<ImplItem>,
 568                        result: &str,
 569                        where_clause_str: &str,
 570                        item: &ast::Item)
 571                        -> Option<bool> {
 572     let snippet = context.snippet(item.span);
 573     let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 574
 575     Some(context.config.impl_empty_single_line && items.is_empty() &&
 576          result.len() + where_clause_str.len() <= context.config.max_width &&
 577          !contains_comment(&snippet[open_pos..]))
 578 }
 579
 580 pub fn format_struct(context: &RewriteContext,
 581                      item_name: &str,
 582                      ident: ast::Ident,
 583                      vis: ast::Visibility,
 584                      struct_def: &ast::VariantData,
 585                      generics: Option<&ast::Generics>,
 586                      span: Span,
 587                      offset: Indent)
 588                      -> Option<String> {
 589     match *struct_def {
 590         ast::VariantData::Unit(..) => format_unit_struct(item_name, ident, vis),
 591         ast::VariantData::Tuple(ref fields, _) => {
 592             format_tuple_struct(context,
 593                                 item_name,
 594                                 ident,
 595                                 vis,
 596                                 fields,
 597                                 generics,
 598                                 span,
 599                                 offset)
 600         }
 601         ast::VariantData::Struct(ref fields, _) => {
 602             format_struct_struct(context,
 603                                  item_name,
 604                                  ident,
 605                                  vis,
 606                                  fields,
 607                                  generics,
 608                                  span,
 609                                  offset)
 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 = if (context.config.where_density == Density::Compressed &&
 653                                 (!result.contains('\n') ||
 654                                  context.config.fn_args_layout == FnArgLayoutStyle::Block)) ||
 655                                (context.config.fn_args_layout == FnArgLayoutStyle::Block &&
 656                                 result.is_empty()) ||
 657                                (context.config.where_density == Density::CompressedIfEmpty &&
 658                                 !has_body &&
 659                                 !result.contains('\n')) {
 660             Density::Compressed
 661         } else {
 662             Density::Tall
 663         };
 664
 665         let where_budget = try_opt!(context.config
 666                                            .max_width
 667                                            .checked_sub(last_line_width(&result)));
 668         let where_clause_str = try_opt!(rewrite_where_clause(context,
 669                                                              &generics.where_clause,
 670                                                              context.config,
 671                                                              context.config.item_brace_style,
 672                                                              context.block_indent,
 673                                                              where_budget,
 674                                                              where_density,
 675                                                              "{",
 676                                                              has_body,
 677                                                              None));
 678         // If the where clause cannot fit on the same line,
 679         // put the where clause on a new line
 680         if !where_clause_str.contains('\n') &&
 681            last_line_width(&result) + where_clause_str.len() + offset.width() >
 682            context.config.ideal_width {
 683             result.push('\n');
 684             let width = context.block_indent.width() + context.config.tab_spaces - 1;
 685             let where_indent = Indent::new(0, width);
 686             result.push_str(&where_indent.to_string(context.config));
 687         }
 688         result.push_str(&where_clause_str);
 689
 690         match context.config.item_brace_style {
 691             BraceStyle::AlwaysNextLine => {
 692                 result.push('\n');
 693                 result.push_str(&offset.to_string(context.config));
 694             }
 695             BraceStyle::PreferSameLine => result.push(' '),
 696             BraceStyle::SameLineWhere => {
 697                 if !where_clause_str.is_empty() &&
 698                    (trait_items.len() > 0 || result.contains('\n')) {
 699                     result.push('\n');
 700                     result.push_str(&offset.to_string(context.config));
 701                 } else {
 702                     result.push(' ');
 703                 }
 704             }
 705         }
 706         result.push('{');
 707
 708         let snippet = context.snippet(item.span);
 709         let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 710
 711         if !trait_items.is_empty() || contains_comment(&snippet[open_pos..]) {
 712             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 713             visitor.block_indent = context.block_indent.block_indent(context.config);
 714             visitor.last_pos = item.span.lo + BytePos(open_pos as u32);
 715
 716             for item in trait_items {
 717                 visitor.visit_trait_item(&item);
 718             }
 719
 720             visitor.format_missing(item.span.hi - BytePos(1));
 721
 722             let inner_indent_str = visitor.block_indent.to_string(context.config);
 723             let outer_indent_str = context.block_indent.to_string(context.config);
 724
 725             result.push('\n');
 726             result.push_str(&inner_indent_str);
 727             result.push_str(&trim_newlines(&visitor.buffer.to_string().trim()));
 728             result.push('\n');
 729             result.push_str(&outer_indent_str);
 730         } else if result.contains('\n') {
 731             result.push('\n');
 732         }
 733
 734         result.push('}');
 735         Some(result)
 736     } else {
 737         unreachable!();
 738     }
 739 }
 740
 741 fn format_unit_struct(item_name: &str, ident: ast::Ident, vis: ast::Visibility) -> Option<String> {
 742     let mut result = String::with_capacity(1024);
 743
 744     let header_str = format_header(item_name, ident, vis);
 745     result.push_str(&header_str);
 746     result.push(';');
 747
 748     Some(result)
 749 }
 750
 751 fn format_struct_struct(context: &RewriteContext,
 752                         item_name: &str,
 753                         ident: ast::Ident,
 754                         vis: ast::Visibility,
 755                         fields: &[ast::StructField],
 756                         generics: Option<&ast::Generics>,
 757                         span: Span,
 758                         offset: Indent)
 759                         -> Option<String> {
 760     let mut result = String::with_capacity(1024);
 761
 762     let header_str = format_header(item_name, ident, vis);
 763     result.push_str(&header_str);
 764
 765     let body_lo = context.codemap.span_after(span, "{");
 766
 767     let generics_str = match generics {
 768         Some(g) => {
 769             try_opt!(format_generics(context,
 770                                      g,
 771                                      "{",
 772                                      "{",
 773                                      context.config.item_brace_style,
 774                                      fields.is_empty(),
 775                                      offset,
 776                                      offset + header_str.len(),
 777                                      mk_sp(span.lo, body_lo)))
 778         }
 779         None => {
 780             if context.config.item_brace_style == BraceStyle::AlwaysNextLine && !fields.is_empty() {
 781                 format!("\n{}{{", context.block_indent.to_string(context.config))
 782             } else {
 783                 " {".to_owned()
 784             }
 785         }
 786     };
 787     result.push_str(&generics_str);
 788
 789     // FIXME: properly format empty structs and their comments.
 790     if fields.is_empty() {
 791         result.push_str(&context.snippet(mk_sp(body_lo, span.hi)));
 792         return Some(result);
 793     }
 794
 795     let item_indent = offset.block_indent(context.config);
 796     // 1 = ","
 797     let item_budget = try_opt!(context.config.max_width.checked_sub(item_indent.width() + 1));
 798
 799     let items = itemize_list(context.codemap,
 800                              fields.iter(),
 801                              "}",
 802                              |field| {
 803                                  // Include attributes and doc comments, if present
 804                                  if !field.node.attrs.is_empty() {
 805                                      field.node.attrs[0].span.lo
 806                                  } else {
 807                                      field.span.lo
 808                                  }
 809                              },
 810                              |field| field.node.ty.span.hi,
 811                              |field| field.rewrite(context, item_budget, item_indent),
 812                              context.codemap.span_after(span, "{"),
 813                              span.hi);
 814     // 1 = ,
 815     let budget = context.config.max_width - offset.width() + context.config.tab_spaces - 1;
 816     let fmt = ListFormatting {
 817         tactic: DefinitiveListTactic::Vertical,
 818         separator: ",",
 819         trailing_separator: context.config.struct_trailing_comma,
 820         indent: item_indent,
 821         width: budget,
 822         ends_with_newline: true,
 823         config: context.config,
 824     };
 825     Some(format!("{}\n{}{}\n{}}}",
 826                  result,
 827                  offset.block_indent(context.config).to_string(context.config),
 828                  try_opt!(write_list(items, &fmt)),
 829                  offset.to_string(context.config)))
 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     assert!(!fields.is_empty(), "Tuple struct with no fields?");
 842     let mut result = String::with_capacity(1024);
 843
 844     let header_str = format_header(item_name, ident, vis);
 845     result.push_str(&header_str);
 846
 847     let body_lo = fields[0].span.lo;
 848
 849     let where_clause_str = match generics {
 850         Some(ref generics) => {
 851             let generics_str = try_opt!(rewrite_generics(context,
 852                                                          generics,
 853                                                          offset,
 854                                                          context.config.max_width,
 855                                                          offset + header_str.len(),
 856                                                          mk_sp(span.lo, body_lo)));
 857             result.push_str(&generics_str);
 858
 859             let where_budget = try_opt!(context.config
 860                                                .max_width
 861                                                .checked_sub(last_line_width(&result)));
 862             try_opt!(rewrite_where_clause(context,
 863                                           &generics.where_clause,
 864                                           context.config,
 865                                           context.config.item_brace_style,
 866                                           context.block_indent,
 867                                           where_budget,
 868                                           Density::Compressed,
 869                                           ";",
 870                                           false,
 871                                           None))
 872         }
 873         None => "".to_owned(),
 874     };
 875     result.push('(');
 876
 877     let item_indent = context.block_indent + result.len();
 878     // 2 = ");"
 879     let item_budget = try_opt!(context.config.max_width.checked_sub(item_indent.width() + 2));
 880
 881     let items = itemize_list(context.codemap,
 882                              fields.iter(),
 883                              ")",
 884                              |field| {
 885                                  // Include attributes and doc comments, if present
 886                                  if !field.node.attrs.is_empty() {
 887                                      field.node.attrs[0].span.lo
 888                                  } else {
 889                                      field.span.lo
 890                                  }
 891                              },
 892                              |field| field.node.ty.span.hi,
 893                              |field| field.rewrite(context, item_budget, item_indent),
 894                              context.codemap.span_after(span, "("),
 895                              span.hi);
 896     let body = try_opt!(format_item_list(items, item_budget, item_indent, context.config));
 897     result.push_str(&body);
 898     result.push(')');
 899
 900     if !where_clause_str.is_empty() && !where_clause_str.contains('\n') &&
 901        (result.contains('\n') ||
 902         context.block_indent.width() + result.len() + where_clause_str.len() + 1 >
 903         context.config.max_width) {
 904         // We need to put the where clause on a new line, but we didn'to_string
 905         // know that earlier, so the where clause will not be indented properly.
 906         result.push('\n');
 907         result.push_str(&(context.block_indent + (context.config.tab_spaces - 1))
 908                              .to_string(context.config));
 909     }
 910     result.push_str(&where_clause_str);
 911
 912     Some(result)
 913 }
 914
 915 pub fn rewrite_type_alias(context: &RewriteContext,
 916                           indent: Indent,
 917                           ident: ast::Ident,
 918                           ty: &ast::Ty,
 919                           generics: &ast::Generics,
 920                           vis: ast::Visibility,
 921                           span: Span)
 922                           -> Option<String> {
 923     let mut result = String::new();
 924
 925     result.push_str(&format_visibility(vis));
 926     result.push_str("type ");
 927     result.push_str(&ident.to_string());
 928
 929     let generics_indent = indent + result.len();
 930     let generics_span = mk_sp(context.codemap.span_after(span, "type"), ty.span.lo);
 931     let generics_width = context.config.max_width - " =".len();
 932     let generics_str = try_opt!(rewrite_generics(context,
 933                                                  generics,
 934                                                  indent,
 935                                                  generics_width,
 936                                                  generics_indent,
 937                                                  generics_span));
 938
 939     result.push_str(&generics_str);
 940
 941     let where_budget = try_opt!(context.config
 942                                        .max_width
 943                                        .checked_sub(last_line_width(&result)));
 944     let where_clause_str = try_opt!(rewrite_where_clause(context,
 945                                                          &generics.where_clause,
 946                                                          context.config,
 947                                                          context.config.item_brace_style,
 948                                                          indent,
 949                                                          where_budget,
 950                                                          context.config.where_density,
 951                                                          "=",
 952                                                          false,
 953                                                          Some(span.hi)));
 954     result.push_str(&where_clause_str);
 955     result.push_str(" = ");
 956
 957     let line_width = last_line_width(&result);
 958     // This checked_sub may fail as the extra space after '=' is not taken into account
 959     // In that case the budget is set to 0 which will make ty.rewrite retry on a new line
 960     let budget = context.config
 961                         .max_width
 962                         .checked_sub(indent.width() + line_width + ";".len())
 963                         .unwrap_or(0);
 964     let type_indent = indent + line_width;
 965     // Try to fit the type on the same line
 966     let ty_str = try_opt!(ty.rewrite(context, budget, type_indent)
 967                             .or_else(|| {
 968                                 // The line was too short, try to put the type on the next line
 969
 970                                 // Remove the space after '='
 971                                 result.pop();
 972                                 let type_indent = indent.block_indent(context.config);
 973                                 result.push('\n');
 974                                 result.push_str(&type_indent.to_string(context.config));
 975                                 let budget = try_opt!(context.config
 976                                                              .max_width
 977                                                              .checked_sub(type_indent.width() +
 978                                                                           ";".len()));
 979                                 ty.rewrite(context, budget, type_indent)
 980                             }));
 981     result.push_str(&ty_str);
 982     result.push_str(";");
 983     Some(result)
 984 }
 985
 986 impl Rewrite for ast::StructField {
 987     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 988         if contains_skip(&self.node.attrs) {
 989             let span = context.snippet(mk_sp(self.node.attrs[0].span.lo, self.span.hi));
 990             return wrap_str(span, context.config.max_width, width, offset);
 991         }
 992
 993         let name = match self.node.kind {
 994             ast::StructFieldKind::NamedField(ident, _) => Some(ident.to_string()),
 995             ast::StructFieldKind::UnnamedField(_) => None,
 996         };
 997         let vis = match self.node.kind {
 998             ast::StructFieldKind::NamedField(_, vis) |
 999             ast::StructFieldKind::UnnamedField(vis) => format_visibility(vis),
1000         };
1001         let mut attr_str = try_opt!(self.node
1002                                         .attrs
1003                                         .rewrite(context,
1004                                                  context.config.max_width - offset.width(),
1005                                                  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.node.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.as_slice();
1064         let bound_str = bounds.iter()
1065                               .filter_map(|ty_bound| {
1066                                   ty_bound.rewrite(context, context.config.max_width, indent)
1067                               })
1068                               .collect::<Vec<String>>()
1069                               .join(" + ");
1070         if bounds.len() > 0 {
1071             format!(": {}", bound_str)
1072         } else {
1073             String::new()
1074         }
1075     } else {
1076         String::new()
1077     };
1078
1079     if let Some(ty) = ty_opt {
1080         let ty_str = try_opt!(ty.rewrite(context,
1081                                          context.config.max_width - context.block_indent.width() -
1082                                          prefix.len() -
1083                                          2,
1084                                          context.block_indent));
1085         Some(format!("{} = {};", prefix, ty_str))
1086     } else {
1087         Some(format!("{}{};", prefix, type_bounds_str))
1088     }
1089 }
1090
1091 impl Rewrite for ast::FunctionRetTy {
1092     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
1093         match *self {
1094             ast::FunctionRetTy::Default(_) => Some(String::new()),
1095             ast::FunctionRetTy::None(_) => {
1096                 if width >= 4 {
1097                     Some("-> !".to_owned())
1098                 } else {
1099                     None
1100                 }
1101             }
1102             ast::FunctionRetTy::Ty(ref ty) => {
1103                 let inner_width = try_opt!(width.checked_sub(3));
1104                 ty.rewrite(context, inner_width, offset + 3).map(|r| format!("-> {}", r))
1105             }
1106         }
1107     }
1108 }
1109
1110 impl Rewrite for ast::Arg {
1111     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
1112         if is_named_arg(self) {
1113             let mut result = try_opt!(self.pat.rewrite(context, width, offset));
1114
1115             if self.ty.node != ast::TyKind::Infer {
1116                 result.push_str(": ");
1117                 let max_width = try_opt!(width.checked_sub(result.len()));
1118                 let ty_str = try_opt!(self.ty.rewrite(context, max_width, offset + result.len()));
1119                 result.push_str(&ty_str);
1120             }
1121
1122             Some(result)
1123         } else {
1124             self.ty.rewrite(context, width, offset)
1125         }
1126     }
1127 }
1128
1129 fn rewrite_explicit_self(explicit_self: &ast::ExplicitSelf,
1130                          args: &[ast::Arg],
1131                          context: &RewriteContext)
1132                          -> Option<String> {
1133     match explicit_self.node {
1134         ast::SelfKind::Region(lt, m, _) => {
1135             let mut_str = format_mutability(m);
1136             match lt {
1137                 Some(ref l) => {
1138                     let lifetime_str = try_opt!(l.rewrite(context,
1139                                                           usize::max_value(),
1140                                                           Indent::empty()));
1141                     Some(format!("&{} {}self", lifetime_str, mut_str))
1142                 }
1143                 None => Some(format!("&{}self", mut_str)),
1144             }
1145         }
1146         ast::SelfKind::Explicit(ref ty, _) => {
1147             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1148
1149             let mutability = explicit_self_mutability(&args[0]);
1150             let type_str = try_opt!(ty.rewrite(context, usize::max_value(), Indent::empty()));
1151
1152             Some(format!("{}self: {}", format_mutability(mutability), type_str))
1153         }
1154         ast::SelfKind::Value(_) => {
1155             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1156
1157             let mutability = explicit_self_mutability(&args[0]);
1158
1159             Some(format!("{}self", format_mutability(mutability)))
1160         }
1161         _ => None,
1162     }
1163 }
1164
1165 // Hacky solution caused by absence of `Mutability` in `SelfValue` and
1166 // `SelfExplicit` variants of `ast::ExplicitSelf_`.
1167 fn explicit_self_mutability(arg: &ast::Arg) -> ast::Mutability {
1168     if let ast::PatKind::Ident(ast::BindingMode::ByValue(mutability), _, _) = arg.pat.node {
1169         mutability
1170     } else {
1171         unreachable!()
1172     }
1173 }
1174
1175 pub fn span_lo_for_arg(arg: &ast::Arg) -> BytePos {
1176     if is_named_arg(arg) {
1177         arg.pat.span.lo
1178     } else {
1179         arg.ty.span.lo
1180     }
1181 }
1182
1183 pub fn span_hi_for_arg(arg: &ast::Arg) -> BytePos {
1184     match arg.ty.node {
1185         ast::TyKind::Infer if is_named_arg(arg) => arg.pat.span.hi,
1186         _ => arg.ty.span.hi,
1187     }
1188 }
1189
1190 pub fn is_named_arg(arg: &ast::Arg) -> bool {
1191     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
1192         ident.node != token::special_idents::invalid
1193     } else {
1194         true
1195     }
1196 }
1197
1198 fn span_for_return(ret: &ast::FunctionRetTy) -> Span {
1199     match *ret {
1200         ast::FunctionRetTy::None(ref span) |
1201         ast::FunctionRetTy::Default(ref span) => span.clone(),
1202         ast::FunctionRetTy::Ty(ref ty) => ty.span,
1203     }
1204 }
1205
1206 fn span_for_ty_param(ty: &ast::TyParam) -> Span {
1207     // Note that ty.span is the span for ty.ident, not the whole item.
1208     let lo = ty.span.lo;
1209     if let Some(ref def) = ty.default {
1210         return mk_sp(lo, def.span.hi);
1211     }
1212     if ty.bounds.is_empty() {
1213         return ty.span;
1214     }
1215     let hi = match ty.bounds[ty.bounds.len() - 1] {
1216         ast::TyParamBound::TraitTyParamBound(ref ptr, _) => ptr.span.hi,
1217         ast::TyParamBound::RegionTyParamBound(ref l) => l.span.hi,
1218     };
1219     mk_sp(lo, hi)
1220 }
1221
1222 fn span_for_where_pred(pred: &ast::WherePredicate) -> Span {
1223     match *pred {
1224         ast::WherePredicate::BoundPredicate(ref p) => p.span,
1225         ast::WherePredicate::RegionPredicate(ref p) => p.span,
1226         ast::WherePredicate::EqPredicate(ref p) => p.span,
1227     }
1228 }
1229
1230 // Return type is (result, force_new_line_for_brace)
1231 fn rewrite_fn_base(context: &RewriteContext,
1232                    indent: Indent,
1233                    ident: ast::Ident,
1234                    fd: &ast::FnDecl,
1235                    explicit_self: Option<&ast::ExplicitSelf>,
1236                    generics: &ast::Generics,
1237                    unsafety: ast::Unsafety,
1238                    constness: ast::Constness,
1239                    abi: abi::Abi,
1240                    vis: ast::Visibility,
1241                    span: Span,
1242                    newline_brace: bool,
1243                    has_body: bool)
1244                    -> Option<(String, bool)> {
1245     let mut force_new_line_for_brace = false;
1246     // FIXME we'll lose any comments in between parts of the function decl, but
1247     // anyone who comments there probably deserves what they get.
1248
1249     let where_clause = &generics.where_clause;
1250
1251     let mut result = String::with_capacity(1024);
1252     // Vis unsafety abi.
1253     result.push_str(format_visibility(vis));
1254
1255     if let ast::Constness::Const = constness {
1256         result.push_str("const ");
1257     }
1258
1259     result.push_str(::utils::format_unsafety(unsafety));
1260
1261     if abi != abi::Abi::Rust {
1262         result.push_str(&::utils::format_abi(abi));
1263     }
1264
1265     // fn foo
1266     result.push_str("fn ");
1267     result.push_str(&ident.to_string());
1268
1269     // Generics.
1270     let generics_indent = indent + result.len();
1271     let generics_span = mk_sp(span.lo, span_for_return(&fd.output).lo);
1272     let generics_str = try_opt!(rewrite_generics(context,
1273                                                  generics,
1274                                                  indent,
1275                                                  context.config.max_width,
1276                                                  generics_indent,
1277                                                  generics_span));
1278     result.push_str(&generics_str);
1279
1280     // Note that if the width and indent really matter, we'll re-layout the
1281     // return type later anyway.
1282     let ret_str = try_opt!(fd.output
1283                              .rewrite(&context, context.config.max_width - indent.width(), indent));
1284
1285     let multi_line_ret_str = ret_str.contains('\n');
1286     let ret_str_len = if multi_line_ret_str {
1287         0
1288     } else {
1289         ret_str.len()
1290     };
1291
1292     // Args.
1293     let (mut one_line_budget, mut multi_line_budget, mut arg_indent) =
1294         compute_budgets_for_args(context, &result, indent, ret_str_len, newline_brace);
1295
1296     if context.config.fn_args_layout == FnArgLayoutStyle::Block ||
1297        context.config.fn_args_layout == FnArgLayoutStyle::BlockAlways {
1298         arg_indent = indent.block_indent(context.config);
1299         multi_line_budget = context.config.max_width - arg_indent.width();
1300     }
1301
1302     debug!("rewrite_fn: one_line_budget: {}, multi_line_budget: {}, arg_indent: {:?}",
1303            one_line_budget,
1304            multi_line_budget,
1305            arg_indent);
1306
1307     // Check if vertical layout was forced by compute_budget_for_args.
1308     if one_line_budget == 0 {
1309         if context.config.fn_args_paren_newline {
1310             result.push('\n');
1311             result.push_str(&arg_indent.to_string(context.config));
1312             arg_indent = arg_indent + 1; // extra space for `(`
1313             result.push('(');
1314         } else {
1315             result.push_str("(\n");
1316             result.push_str(&arg_indent.to_string(context.config));
1317         }
1318     } else {
1319         result.push('(');
1320     }
1321
1322     if multi_line_ret_str {
1323         one_line_budget = 0;
1324     }
1325
1326     // A conservative estimation, to goal is to be over all parens in generics
1327     let args_start = generics.ty_params
1328                              .last()
1329                              .map_or(span.lo, |tp| end_typaram(tp));
1330     let args_span = mk_sp(context.codemap.span_after(mk_sp(args_start, span.hi), "("),
1331                           span_for_return(&fd.output).lo);
1332     let arg_str = try_opt!(rewrite_args(context,
1333                                         &fd.inputs,
1334                                         explicit_self,
1335                                         one_line_budget,
1336                                         multi_line_budget,
1337                                         indent,
1338                                         arg_indent,
1339                                         args_span,
1340                                         fd.variadic));
1341
1342     let multi_line_arg_str = arg_str.contains('\n');
1343
1344     let put_args_in_block = match context.config.fn_args_layout {
1345         FnArgLayoutStyle::Block => multi_line_arg_str,
1346         FnArgLayoutStyle::BlockAlways => true,
1347         _ => false,
1348     } && fd.inputs.len() > 0;
1349
1350     if put_args_in_block {
1351         arg_indent = indent.block_indent(context.config);
1352         result.push('\n');
1353         result.push_str(&arg_indent.to_string(context.config));
1354         result.push_str(&arg_str);
1355         result.push('\n');
1356         result.push_str(&indent.to_string(context.config));
1357         result.push(')');
1358     } else {
1359         result.push_str(&arg_str);
1360         result.push(')');
1361     }
1362
1363     // Return type.
1364     if !ret_str.is_empty() {
1365         let ret_should_indent = match context.config.fn_args_layout {
1366             // If our args are block layout then we surely must have space.
1367             FnArgLayoutStyle::Block if put_args_in_block => false,
1368             FnArgLayoutStyle::BlockAlways => false,
1369             _ => {
1370                 // If we've already gone multi-line, or the return type would push
1371                 // over the max width, then put the return type on a new line.
1372                 result.contains("\n") || multi_line_ret_str ||
1373                 result.len() + indent.width() + ret_str_len > context.config.max_width
1374             }
1375         };
1376         let ret_indent = if ret_should_indent {
1377             let indent = match context.config.fn_return_indent {
1378                 ReturnIndent::WithWhereClause => indent + 4,
1379                 // Aligning with non-existent args looks silly.
1380                 _ if arg_str.is_empty() => {
1381                     force_new_line_for_brace = true;
1382                     indent + 4
1383                 }
1384                 // FIXME: we might want to check that using the arg indent
1385                 // doesn't blow our budget, and if it does, then fallback to
1386                 // the where clause indent.
1387                 _ => arg_indent,
1388             };
1389
1390             result.push('\n');
1391             result.push_str(&indent.to_string(context.config));
1392             indent
1393         } else {
1394             result.push(' ');
1395             Indent::new(indent.width(), result.len())
1396         };
1397
1398         if multi_line_ret_str {
1399             // Now that we know the proper indent and width, we need to
1400             // re-layout the return type.
1401
1402             let budget = try_opt!(context.config.max_width.checked_sub(ret_indent.width()));
1403             let ret_str = try_opt!(fd.output
1404                                      .rewrite(context, budget, ret_indent));
1405             result.push_str(&ret_str);
1406         } else {
1407             result.push_str(&ret_str);
1408         }
1409
1410         // Comment between return type and the end of the decl.
1411         let snippet_lo = fd.output.span().hi;
1412         if where_clause.predicates.is_empty() {
1413             let snippet_hi = span.hi;
1414             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
1415             let snippet = snippet.trim();
1416             if !snippet.is_empty() {
1417                 result.push(' ');
1418                 result.push_str(snippet);
1419             }
1420         } else {
1421             // FIXME it would be nice to catch comments between the return type
1422             // and the where clause, but we don't have a span for the where
1423             // clause.
1424         }
1425     }
1426
1427     let should_compress_where = match context.config.where_density {
1428         Density::Compressed => !result.contains('\n') || put_args_in_block,
1429         Density::CompressedIfEmpty => !has_body && !result.contains('\n'),
1430         _ => false,
1431     } || (put_args_in_block && ret_str.is_empty());
1432
1433     let where_density = if should_compress_where {
1434         Density::Compressed
1435     } else {
1436         Density::Tall
1437     };
1438
1439     // Where clause.
1440     let where_budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
1441     let where_clause_str = try_opt!(rewrite_where_clause(context,
1442                                                          where_clause,
1443                                                          context.config,
1444                                                          context.config.fn_brace_style,
1445                                                          indent,
1446                                                          where_budget,
1447                                                          where_density,
1448                                                          "{",
1449                                                          has_body,
1450                                                          Some(span.hi)));
1451
1452     if last_line_width(&result) + where_clause_str.len() > context.config.max_width &&
1453        !where_clause_str.contains('\n') {
1454         result.push('\n');
1455     }
1456
1457     result.push_str(&where_clause_str);
1458
1459     Some((result, force_new_line_for_brace))
1460 }
1461
1462 fn rewrite_args(context: &RewriteContext,
1463                 args: &[ast::Arg],
1464                 explicit_self: Option<&ast::ExplicitSelf>,
1465                 one_line_budget: usize,
1466                 multi_line_budget: usize,
1467                 indent: Indent,
1468                 arg_indent: Indent,
1469                 span: Span,
1470                 variadic: bool)
1471                 -> Option<String> {
1472     let mut arg_item_strs = try_opt!(args.iter()
1473                                          .map(|arg| {
1474                                              arg.rewrite(&context, multi_line_budget, arg_indent)
1475                                          })
1476                                          .collect::<Option<Vec<_>>>());
1477
1478     // Account for sugary self.
1479     // FIXME: the comment for the self argument is dropped. This is blocked
1480     // on rust issue #27522.
1481     let min_args = explicit_self.and_then(|explicit_self| {
1482                                     rewrite_explicit_self(explicit_self, args, context)
1483                                 })
1484                                 .map_or(1, |self_str| {
1485                                     arg_item_strs[0] = self_str;
1486                                     2
1487                                 });
1488
1489     // Comments between args.
1490     let mut arg_items = Vec::new();
1491     if min_args == 2 {
1492         arg_items.push(ListItem::from_str(""));
1493     }
1494
1495     // FIXME(#21): if there are no args, there might still be a comment, but
1496     // without spans for the comment or parens, there is no chance of
1497     // getting it right. You also don't get to put a comment on self, unless
1498     // it is explicit.
1499     if args.len() >= min_args || variadic {
1500         let comment_span_start = if min_args == 2 {
1501             let second_arg_start = if arg_has_pattern(&args[1]) {
1502                 args[1].pat.span.lo
1503             } else {
1504                 args[1].ty.span.lo
1505             };
1506             let reduced_span = mk_sp(span.lo, second_arg_start);
1507
1508             context.codemap.span_after_last(reduced_span, ",")
1509         } else {
1510             span.lo
1511         };
1512
1513         enum ArgumentKind<'a> {
1514             Regular(&'a ast::Arg),
1515             Variadic(BytePos),
1516         }
1517
1518         let variadic_arg = if variadic {
1519             let variadic_span = mk_sp(args.last().unwrap().ty.span.hi, span.hi);
1520             let variadic_start = context.codemap.span_after(variadic_span, "...") - BytePos(3);
1521             Some(ArgumentKind::Variadic(variadic_start))
1522         } else {
1523             None
1524         };
1525
1526         let more_items = itemize_list(context.codemap,
1527                                       args[min_args - 1..]
1528                                           .iter()
1529                                           .map(ArgumentKind::Regular)
1530                                           .chain(variadic_arg),
1531                                       ")",
1532                                       |arg| {
1533                                           match *arg {
1534                                               ArgumentKind::Regular(arg) => span_lo_for_arg(arg),
1535                                               ArgumentKind::Variadic(start) => start,
1536                                           }
1537                                       },
1538                                       |arg| {
1539                                           match *arg {
1540                                               ArgumentKind::Regular(arg) => arg.ty.span.hi,
1541                                               ArgumentKind::Variadic(start) => start + BytePos(3),
1542                                           }
1543                                       },
1544                                       |arg| {
1545                                           match *arg {
1546                                               ArgumentKind::Regular(..) => None,
1547                                               ArgumentKind::Variadic(..) => Some("...".to_owned()),
1548                                           }
1549                                       },
1550                                       comment_span_start,
1551                                       span.hi);
1552
1553         arg_items.extend(more_items);
1554     }
1555
1556     for (item, arg) in arg_items.iter_mut().zip(arg_item_strs) {
1557         item.item = Some(arg);
1558     }
1559
1560     let indent = match context.config.fn_arg_indent {
1561         BlockIndentStyle::Inherit => indent,
1562         BlockIndentStyle::Tabbed => indent.block_indent(context.config),
1563         BlockIndentStyle::Visual => arg_indent,
1564     };
1565
1566     let tactic = definitive_tactic(&arg_items,
1567                                    context.config.fn_args_density.to_list_tactic(),
1568                                    one_line_budget);
1569     let budget = match tactic {
1570         DefinitiveListTactic::Horizontal => one_line_budget,
1571         _ => multi_line_budget,
1572     };
1573
1574     debug!("rewrite_args: budget: {}, tactic: {:?}", budget, tactic);
1575
1576     let end_with_newline = match context.config.fn_args_layout {
1577         FnArgLayoutStyle::Block | FnArgLayoutStyle::BlockAlways => true,
1578         _ => false,
1579     };
1580
1581     let fmt = ListFormatting {
1582         tactic: tactic,
1583         separator: ",",
1584         trailing_separator: SeparatorTactic::Never,
1585         indent: indent,
1586         width: budget,
1587         ends_with_newline: end_with_newline,
1588         config: context.config,
1589     };
1590
1591     write_list(&arg_items, &fmt)
1592 }
1593
1594 fn arg_has_pattern(arg: &ast::Arg) -> bool {
1595     if let ast::PatKind::Ident(_,
1596                                codemap::Spanned {
1597                                    node: ast::Ident { name: ast::Name(0u32), .. },
1598                                    ..
1599                                },
1600                                _) = arg.pat.node {
1601         false
1602     } else {
1603         true
1604     }
1605 }
1606
1607 fn compute_budgets_for_args(context: &RewriteContext,
1608                             result: &str,
1609                             indent: Indent,
1610                             ret_str_len: usize,
1611                             newline_brace: bool)
1612                             -> (usize, usize, Indent) {
1613     // Try keeping everything on the same line.
1614     if !result.contains("\n") {
1615         // 3 = `() `, space is before ret_string.
1616         let mut used_space = indent.width() + result.len() + ret_str_len + 3;
1617         if !newline_brace {
1618             used_space += 2;
1619         }
1620         let one_line_budget = context.config.max_width.checked_sub(used_space).unwrap_or(0);
1621
1622         if one_line_budget > 0 {
1623             let multi_line_budget = context.config.max_width -
1624                                     (indent.width() + result.len() + "()".len());
1625
1626             return (one_line_budget, multi_line_budget, indent + result.len() + 1);
1627         }
1628     }
1629
1630     // Didn't work. we must force vertical layout and put args on a newline.
1631     let new_indent = indent.block_indent(context.config);
1632     let used_space = new_indent.width() + 2; // account for `(` and `)`
1633     let max_space = context.config.max_width;
1634     if used_space <= max_space {
1635         (0, max_space - used_space, new_indent)
1636     } else {
1637         // Whoops! bankrupt.
1638         // FIXME: take evasive action, perhaps kill the indent or something.
1639         panic!("in compute_budgets_for_args");
1640     }
1641 }
1642
1643 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause) -> bool {
1644     match config.fn_brace_style {
1645         BraceStyle::AlwaysNextLine => true,
1646         BraceStyle::SameLineWhere if !where_clause.predicates.is_empty() => true,
1647         _ => false,
1648     }
1649 }
1650
1651 fn rewrite_generics(context: &RewriteContext,
1652                     generics: &ast::Generics,
1653                     offset: Indent,
1654                     width: usize,
1655                     generics_offset: Indent,
1656                     span: Span)
1657                     -> Option<String> {
1658     // FIXME: convert bounds to where clauses where they get too big or if
1659     // there is a where clause at all.
1660     let lifetimes: &[_] = &generics.lifetimes;
1661     let tys: &[_] = &generics.ty_params;
1662     if lifetimes.is_empty() && tys.is_empty() {
1663         return Some(String::new());
1664     }
1665
1666     let offset = match context.config.generics_indent {
1667         BlockIndentStyle::Inherit => offset,
1668         BlockIndentStyle::Tabbed => offset.block_indent(context.config),
1669         // 1 = <
1670         BlockIndentStyle::Visual => generics_offset + 1,
1671     };
1672
1673     let h_budget = try_opt!(width.checked_sub(generics_offset.width() + 2));
1674     // FIXME: might need to insert a newline if the generics are really long.
1675
1676     // Strings for the generics.
1677     let lt_strs = lifetimes.iter().map(|lt| lt.rewrite(&context, h_budget, offset));
1678     let ty_strs = tys.iter().map(|ty_param| ty_param.rewrite(&context, h_budget, offset));
1679
1680     // Extract comments between generics.
1681     let lt_spans = lifetimes.iter().map(|l| {
1682         let hi = if l.bounds.is_empty() {
1683             l.lifetime.span.hi
1684         } else {
1685             l.bounds[l.bounds.len() - 1].span.hi
1686         };
1687         mk_sp(l.lifetime.span.lo, hi)
1688     });
1689     let ty_spans = tys.iter().map(span_for_ty_param);
1690
1691     let items = itemize_list(context.codemap,
1692                              lt_spans.chain(ty_spans).zip(lt_strs.chain(ty_strs)),
1693                              ">",
1694                              |&(sp, _)| sp.lo,
1695                              |&(sp, _)| sp.hi,
1696                              // FIXME: don't clone
1697                              |&(_, ref str)| str.clone(),
1698                              context.codemap.span_after(span, "<"),
1699                              span.hi);
1700     let list_str = try_opt!(format_item_list(items, h_budget, offset, context.config));
1701
1702     Some(format!("<{}>", list_str))
1703 }
1704
1705 fn rewrite_trait_bounds(context: &RewriteContext,
1706                         type_param_bounds: &ast::TyParamBounds,
1707                         indent: Indent,
1708                         width: usize)
1709                         -> Option<String> {
1710     let bounds: &[_] = &type_param_bounds.as_slice();
1711
1712     if bounds.is_empty() {
1713         return Some(String::new());
1714     }
1715
1716     let bound_str = bounds.iter()
1717                           .filter_map(|ty_bound| ty_bound.rewrite(&context, width, indent))
1718                           .collect::<Vec<String>>()
1719                           .join(" + ");
1720
1721     let mut result = String::new();
1722     result.push_str(": ");
1723     result.push_str(&bound_str);
1724     Some(result)
1725 }
1726
1727 fn rewrite_where_clause(context: &RewriteContext,
1728                         where_clause: &ast::WhereClause,
1729                         config: &Config,
1730                         brace_style: BraceStyle,
1731                         indent: Indent,
1732                         width: usize,
1733                         density: Density,
1734                         terminator: &str,
1735                         allow_trailing_comma: bool,
1736                         span_end: Option<BytePos>)
1737                         -> Option<String> {
1738     if where_clause.predicates.is_empty() {
1739         return Some(String::new());
1740     }
1741
1742     let extra_indent = match context.config.where_indent {
1743         BlockIndentStyle::Inherit => Indent::empty(),
1744         BlockIndentStyle::Tabbed | BlockIndentStyle::Visual => Indent::new(config.tab_spaces, 0),
1745     };
1746
1747     let offset = match context.config.where_pred_indent {
1748         BlockIndentStyle::Inherit => indent + extra_indent,
1749         BlockIndentStyle::Tabbed => indent + extra_indent.block_indent(config),
1750         // 6 = "where ".len()
1751         BlockIndentStyle::Visual => indent + extra_indent + 6,
1752     };
1753     // FIXME: if where_pred_indent != Visual, then the budgets below might
1754     // be out by a char or two.
1755
1756     let budget = context.config.max_width - offset.width();
1757     let span_start = span_for_where_pred(&where_clause.predicates[0]).lo;
1758     // If we don't have the start of the next span, then use the end of the
1759     // predicates, but that means we miss comments.
1760     let len = where_clause.predicates.len();
1761     let end_of_preds = span_for_where_pred(&where_clause.predicates[len - 1]).hi;
1762     let span_end = span_end.unwrap_or(end_of_preds);
1763     let items = itemize_list(context.codemap,
1764                              where_clause.predicates.iter(),
1765                              terminator,
1766                              |pred| span_for_where_pred(pred).lo,
1767                              |pred| span_for_where_pred(pred).hi,
1768                              |pred| pred.rewrite(&context, budget, offset),
1769                              span_start,
1770                              span_end);
1771     let item_vec = items.collect::<Vec<_>>();
1772     // FIXME: we don't need to collect here if the where_layout isn't
1773     // HorizontalVertical.
1774     let tactic = definitive_tactic(&item_vec, context.config.where_layout, budget);
1775     let use_trailing_comma = allow_trailing_comma && context.config.where_trailing_comma;
1776
1777     let fmt = ListFormatting {
1778         tactic: tactic,
1779         separator: ",",
1780         trailing_separator: SeparatorTactic::from_bool(use_trailing_comma),
1781         indent: offset,
1782         width: budget,
1783         ends_with_newline: true,
1784         config: context.config,
1785     };
1786     let preds_str = try_opt!(write_list(&item_vec, &fmt));
1787
1788     let end_length = if terminator == "{" {
1789         // If the brace is on the next line we don't need to count it otherwise it needs two
1790         // characters " {"
1791         match brace_style {
1792             BraceStyle::AlwaysNextLine => 0,
1793             BraceStyle::PreferSameLine => 2,
1794             BraceStyle::SameLineWhere => 0,
1795         }
1796     } else if terminator == "=" {
1797         2
1798     } else {
1799         terminator.len()
1800     };
1801     if density == Density::Tall || preds_str.contains('\n') ||
1802        indent.width() + " where ".len() + preds_str.len() + end_length > width {
1803         Some(format!("\n{}where {}",
1804                      (indent + extra_indent).to_string(context.config),
1805                      preds_str))
1806     } else {
1807         Some(format!(" where {}", preds_str))
1808     }
1809 }
1810
1811 fn format_header(item_name: &str, ident: ast::Ident, vis: ast::Visibility) -> String {
1812     format!("{}{}{}", format_visibility(vis), item_name, ident)
1813 }
1814
1815 fn format_generics(context: &RewriteContext,
1816                    generics: &ast::Generics,
1817                    opener: &str,
1818                    terminator: &str,
1819                    brace_style: BraceStyle,
1820                    force_same_line_brace: bool,
1821                    offset: Indent,
1822                    generics_offset: Indent,
1823                    span: Span)
1824                    -> Option<String> {
1825     let mut result = try_opt!(rewrite_generics(context,
1826                                                generics,
1827                                                offset,
1828                                                context.config.max_width,
1829                                                generics_offset,
1830                                                span));
1831
1832     if !generics.where_clause.predicates.is_empty() || result.contains('\n') {
1833         let budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
1834         let where_clause_str = try_opt!(rewrite_where_clause(context,
1835                                                              &generics.where_clause,
1836                                                              context.config,
1837                                                              brace_style,
1838                                                              context.block_indent,
1839                                                              budget,
1840                                                              Density::Tall,
1841                                                              terminator,
1842                                                              true,
1843                                                              Some(span.hi)));
1844         result.push_str(&where_clause_str);
1845         if !force_same_line_brace &&
1846            (brace_style == BraceStyle::SameLineWhere || brace_style == BraceStyle::AlwaysNextLine) {
1847             result.push('\n');
1848             result.push_str(&context.block_indent.to_string(context.config));
1849         } else {
1850             result.push(' ');
1851         }
1852         result.push_str(opener);
1853     } else {
1854         if !force_same_line_brace && brace_style == BraceStyle::AlwaysNextLine {
1855             result.push('\n');
1856             result.push_str(&context.block_indent.to_string(context.config));
1857         } else {
1858             result.push(' ');
1859         }
1860         result.push_str(opener);
1861     }
1862
1863     Some(result)
1864 }